BLUE CRAB RESIDENCY AND MIGRATION IN THE MOBILE BAY ESTUARY: A STABLE ISOTOPE

STUDY INVESTIGATING CONNECTIVITY

by

ANTHONY JAMES VEDRAL

BEHZAD MORTAZAVI, COMMITTEE CHAIR ROBERT H. FINDLAY JOHN F. VALENTINE

A THESIS

Submitted in partial fulfillment of the requirements for the degree of Master of Science

in the Department of Biological Sciences in the Graduate School of The University of Alabama

TUSCALOOSA, ALABAMA

2012

Copyright Anthony James Vedral 2012 ALL RIGHTS RESERVED

ii

ABSTRACT

The blue crab (Callinectes sapidus) is an important commercial species throughout Gulf

of Mexico. We used carbon and nitrogen stable isotopes from fast and slow turnover tissues to

investigate residency and migration of blue crabs in Mobile Bay. A laboratory diet switch

experiment was conducted to estimate tissue turnover. By day 83 of the experiment,

hepatopancreas tissue turnover averaged 94%, while muscle turnover averaged 43%. Results

confirmed that hepatopancreas and muscle tissues are indicators of recent and past diets,

respectively. Therefore, these two tissue types were sampled from individual crabs from the

Delta, mid-bay (Fowl River), and coastal sites to investigate residency. Average divergence in

δ13C values between the two tissues from crabs in the delta (-0.41‰) and Fowl River (-0.31‰)

was small, while for crabs in the coastal sites such as Fort Morgan featured a large average

divergence (2.39‰). The convergence of hepatopancreas and muscle tissues to similar δ13C

values are indicative of residency, while a large divergence between the tissues is characteristic

of migratory crabs. Additionally, we found that the Fowl River site is a hot spot for female crabs

that delay their spawning migration to coastal waters. Blue crabs and other migratory species

link the food webs in the delta and Gulf of Mexico. A greater understanding the role of

migratory species as agents of connectivity is critical for fisheries management in response to

climate and human induced changes.

iii

LIST OF ABBREVIATIONS AND SYMBOLS

12C carbon isotope with an atomic mass of 12

13C carbon isotope with an atomic mass of 13

14N nitrogen isotope with an atomic mass of 14

15N nitrogen isotope with an atomic mass of 15

C3 vegetation using the C3 photosynthetic pathway

C4 vegetation using the C4 photosynthetic pathway

cm centimeters

c:n carbon to nitrogen ratio

°C degrees Celsius

δ The “delta” or isotopic value of the ratios of each isotope concentration in a

sample compared to the standard

DISL Dauphin Island Sea Lab

= equal to

g grams

h-m hepatopancreas minus muscle

km kilometers

< less than

L liters

m meters

iv

mg milligrams

mL milliliters

mm millimeters

n sample size

p probability of an outcome under the null hypothesis as or more extreme than

the observed value

% percent

‰ per mil: unit delta values are reported in

rpm revolutions per minute

s seconds

SD standard deviation

psu practical salinity units

v

ACKNOWLEDGMENTS

This work was made possible through the excellent advice and insights from my advisor,

Dr. Behzad Mortazavi, as well as my committee members Dr. Robert Findlay and Dr. John

Valentine. Assistance with statistical analysis was generously provided by Dr. Christina

Staudhammer. I would like to thank Rebecca Bernard and Agota Horel for their assistance in

maintaining crabs during the feeding experiment as well as processing of samples. Additionally,

thank you to the Valentine lab, Eric Sparks, and Marshall Johnson for their help in the field, as

well as Tech Support at the Dauphin Island Sea Lab for their relentless work to help manage

water conditions in my mesocosms. Finally, I would like to thank the University of Alabama, the

Dauphin Island Sea Lab, and the Northern Gulf Institute.

vi

CONTENTS

ABSTRACT...................................................................................................... ii

LIST OF ABBREVIATIONS AND SYMBOLS....................................................... iii

ACKNOWLEDGMENTS................................................................................... v

LIST OF FIGURES............................................................................................ vii

1. INTRODUCTION......................................................................................... 1

2. MATERIALS AND METHODS...................................................................... 9

3. RESULTS..................................................................................................... 13

4. DISCUSSION............................................................................................... 18

REFERENCES.................................................................................................. 35

APPENDIX...................................................................................................... 51

vii

LIST OF FIGURES

Figure 1. Study sites………………………………………………….............................................. 41

Figure 2. Lipid extraction………………………………………………………………………................. 42

Figure 3. Diet switch δ15N and δ13C values………………………………………...................... 43

Figure 4. Diet switch turnover…………………………………………………………….................... 44

Figure 5. Diet switch hepatopancreas-muscle (h-m) divergence….………………………. 45

Figure 6. Crab carapace length…………………………………………………………..................... 46

Figure 7. Site average δ15N and δ13C values………………………………………..................... 47

Figure 8. δ13C hepatopancreas-muscle (h-m) divergence...…………………................... 48

Figure 9. δ15N hepatopancreas-muscle (h-m) divergence ……….……......................... 50

1

INTRODUCTION

The complexity of a deltaic food web results from nutritional inputs from in-situ

production, marine, and terrestrial sources (Peterson et al. 1985, Deegan & Garritt 1997,

Goecker et al. 2009). Terrestrial detritus, phytoplankton, and benthic algae are all key

contributors to production within estuarine food webs (Peterson & Howarth 1987, Chanton &

Lewis 2002). The proximity of a region within an estuary to terrestrial sources as well as marsh

estuary exchange rates can influence the reliance of the food web on terrestrially derived

material. During times of high river flow, a greater proportion of terrestrial material will enter

the estuary (Abrantes & Sheaves 2010). As river flow decreases, marine waters will infiltrate

further into the estuary. As a result, seasonal variation in river flow can alter the influx of

terrestrial or marine based organic matter within such environments (Cifuentes 1991, Chanton

& Lewis 2002). Additionally, migratory organisms can transport organic matter from the deltaic

to the marine food web, or vice versa, throughout their life histories. These inputs can aid in

fueling the food web in the case of prey species, or act as a predatory force if the migrating

species are of a relatively higher trophic level. Such migrating organisms provide connectivity

between food webs that are spatially and physically separated (Beger 2010).

The life histories of many fish and invertebrate species encompass both the estuarine

and marine environments. For many crustaceans, marshes and seagrass beds of upper

estuaries act as a crucial nursery area for larval and juvenile development (Heck et al. 2001).

2

Shelter from predation and increased food availability creates an optimal environment for

growth. Upon maturation, many of these animals migrate to offshore spawning areas where

they aggregate in large numbers. Specific temperature and salinity ranges such as those found

in certain coastal and offshore waters have been demonstrated to increase egg and larval

survival (Holt et al. 1981) for estuarine species. Recruitment of larval stages back into the

upper estuary completes the typical life history of estuarine species.

The concept of connectivity asserts that almost all habitats (even those that seem

isolated) are linked with other food webs through a multitude of abiotic vectors such as wind

and water, as well as biotic vectors of mobile organisms feeding in one environment and

moving into another (Polis et al. 1997). Connectivity occurs throughout a multitude of habitats,

vectors, and scales, creating an intricate system of continuity among food webs (Sheaves 2009).

Connectivity between aquatic habitats occurs abiotically through upwelling, sinking of organic

material, currents, tides, and eddy-diffusion, while water and land habitats are connected

through terrestrial runoff, allochthonous detritus, and localized flooding (Polis et al. 1997). On

land, connectivity occurs through vectors such as wind and detritus transport through melted

water and precipitation (Polis et al. 1997). Additionally, mobile organisms provide vectors of

connectivity throughout each of these interfaces. The degree of connectivity between food

webs varies through exchange rates, the ratio of interface perimeter to the area of total habitat

(Polis & Hurd 1996), and mobility of organisms (Polis et al. 1997).

Migrations play a key role in the life histories of many animals, with the most well-

known including aquatic organisms such as salmon, whales, and waterfowl. Migrations can

3

occur over ranges of thousands of kilometers in the case of some birds (Henningsson &

Alerstam 2005), whereas the daily migration of smaller creatures such as zooplankton can occur

on the scale of meters (Zaret & Suffern 1976). Motives for migration vary among organisms.

Food availability and weather are considered vital reasons for whale and many bird migrations

(Boyle & Conway 2007). Fishes such as salmon return to the freshwater streams of which they

were born to spawn (Miller et al. 2009), whereas many aquatic estuarine species move to

marine waters for spawning purposes. Daily vertical zooplankton migrations occur as a

mechanism for predator evasion (Zaret & Suffern 1976).

Recruitment of juveniles or migration of mature organisms into an ecosystem can shift

populations within the local food web (Hansson et al. 2007). Inputs of prey species provide an

abundance of food for higher trophic levels, and alter food web structure on a temporal scale.

Contrarily, movement of predators can create additional pressures within a food web in the

form of competition.

A common method for studying animal migration is tagging of individuals. Mark and

recapture methods involve placing a tag on an individual, and either actively attempting to

recapture that organism at a later day or in some cases, relying on fishing reports of the catch

of a marked individual (Cappo et al, 2000). Satellite tags using global positioning systems (gps)

as well as acoustic monitoring have become increasingly common as it removes the need for

recapture in many studies. Additional methods using genetics (Refseth et al. 1998) can be used

to connect certain populations to one another, and otolith chemistry serves as a way to gain

insight into an organism’s early nursery habitat (Rooker et al. 2001). An increasingly powerful

4

method of investigating the past locations of animals uses stable isotopes. This method uses

the isotopic ratios of elements such as carbon and nitrogen in an organism’s tissues to identify

its food sources and relative location (DeNiro & Epstein 1978), and is especially useful when

dealing with organisms where tagging methods are impractical.

Blue Crab Ecology

The blue crab (Callinectes sapidus, Rathbun 1896) is an economically valuable aquatic

crustacean. Total U.S. hard blue crab landings in 2010 were 83.4 million kg, with 18.6 million kg

caught from the Gulf of Mexico (NMFS 2010). They are widely distributed throughout eastern

and Gulf coastal waters of the United States with a range extending from Nova Scotia to

Argentina (Williams 1974, Hines 1987).

Blue crabs are an ecologically important species that occupy multiple trophic positions

within an ecosystem. Juvenile blue crabs are preyed upon by many fish including drum

(Sciaenidae), as well as avian predators (Perry & McIlwain 1986). Adult blue crabs act as

predators on fish, crustaceans, mollusks and other blue crabs, while additionally often acting as

benthic detritivores.

Salinity gradients play an important role in the life cycle of blue crabs. Blue crabs

tolerate wide ranges of salinity, allowing them to survive in both the low salinity waters of an

upper estuary and the more marine lower estuary. Juvenile crabs use the marshes and

grassbeds located in the upper estuary as a nursery ground (Heck et al. 2001). Immature

females mate in the soft shell state prior to their terminal molt (Dickinson et al. 2006). After

molting, female crabs migrate to higher salinity waters before spawning, while males remain

5

behind in fresher waters (Aguilar 2005). Female blue crabs mate only once and store excess

sperm for future spawning (Hines et al. 2003).

Blue crab zoea require high salinity waters to survive their early molt stages. Fatality

rates are typically high in salinities of less than 20 psu (Costlow & Bookhout 1959). As blue

crabs reach the megalopae stage, they are transported by tides and currents to estuarine

waters (Moksnes & Heck, 2006). Recruitment of juveniles to upper estuarine waters concludes

the developmental migration.

The movement of female blue crabs after mating occurs in two phases. Following

mating, female crabs move from the low salinity waters of the upper estuary to higher salinity

waters near the mouth of the estuary (Tankersley et al. 1998). As they near spawning, females

migrate to the lower estuary, with some traveling out into coastal waters (Tankersley et al.

1998).

Migration throughout estuarine waters typically occurs at night. Crabs undergo a daily

vertical migration and exploit currents and tides in order to travel (Tankersley et al. 1998).

During this movement, crabs typically are passively transported and do not rely on active

swimming (Tankersley et al. 1998). Following spawning, crabs may ride tidal currents back into

the lower estuary (Forward et al. 2003) or remain in coastal waters outside of the estuary

(Aguilar et al. 2005).

Blue crabs are a valuable species due to their commercial and ecological roles. Their

migration patterns have the potential to make crab populations vulnerable to adverse

conditions such as climate change, oil spills, or fishing pressures. Therefore, it is necessary to

6

obtain a better understanding of the movement and residency of this commercially important

species.

Stable Isotopes

Stable isotopes, particularly those of carbon and nitrogen, are used as a means for

describing trophic interactions within and between ecosystems (Stapp et al. 1999). The isotopic

value (δ value) of an element within an organism’s tissues is a reflection of the environment in

which it feeds (DeNiro & Epstein 1978). Isotopic values are calculated as a ratio of the heavy to

light isotopes of an element relative to a known standard. For carbon, the standard is the

13C/12C ratio in Vienna Peedee belemnite limestone (Hoefs 2009), while for nitrogen the

standard is the 15N/14N ratio in air (Hoefs 2009). All isotopic ratios (R) values are reported on a

per mil (‰) basis according to the following equation:

(equation 1)

where x is 13C or 15N, and R is 13C/12C or 15N/14N of the sample and standards (Peterson &

Howarth 1987).

δ13C values can be used to indicate the origin of an organism’s diet. Consumers will

typically display a similar δ 13C ratio to their basal food source. Basal food sources such as

plankton normally have a δ13C value of -20‰. Terrestrial C3 plants display a δ13C value of

approximately -27‰, whereas C4 vegetation is normally near -13‰ (Peterson & Howarth

1987).

7

δ15N ratios act as an indicator of trophic position within a food web. δ15N typically is

enriched by 3-5‰ through each trophic level within a food web (Stapp et al. 1999). However

basal food sources have varying δ15N values. Terrestrial plants have δ15N values of

approximately 0‰ and phytoplankton range from 6-10‰ (Peterson & Howarth 1987).

As organisms move from one habitat to another, a diet shift will cause a change in the

isotopic content of their tissues (Herzka 2005). Fast turnover tissues, such as hepatopancreas,

reflect a change in diet quickly and act as a marker of recent diet shifts (Fry et al. 2003). Tissues

with slower turnover rates, such as muscle, indicate long term past diet (Fry et al. 2003). For

brown shrimp, for example, hepatopancreas tissue was found to have a half-life of 2 days, while

muscle tissue half-life was approximately 8 days (Parker et al. 1991).

Once an organism migrates to a new location and its diet changes, the stable isotope δ

values of fast turnover tissues begin to move in the direction of the new food source. As a

result, the deviation in isotopic value between the fast and slow turnover tissue ratios

increases. Once an organism settles in this environment for a period of time, the slow turnover

tissue equilibrates with the new food source value, causing the disparity between tissues to

vanish. This pattern allows stable isotope analysis of multiple tissues to function as a tool for

identifying movement and residency of organisms.

Fry et al. (2003), for example, used the fast turnover hepatopancreas tissue and slow

turnover muscle tissue of Louisiana brown shrimp (Farfantepenaeus aztecus) to develop a

method of analyzing the divergence between the isotopic values of multiple tissues within an

organism to indicate residency or movement. Shrimp with both tissues having isotopic values

8

close to the site average isotopic values were considered residents. Shrimp with

hepatopancreas tissue with near site average values, but muscle tissue not yet equilibrated to

the food source at the site were categorized as recently migratory (Fry et al. 2003). We used

their work on juvenile brown shrimp to form the basis of our study investigating the migration

of female adult blue crabs.

This study was conducted to demonstrate the cross habitat linkage provided throughout

estuaries by migratory species such as blue crabs. We chose to investigate the migratory

behavior of blue crabs through stable isotope analysis of multiple tissues and use that

information to characterize migratory and resident crab populations acting as vectors of

connectivity throughout the estuary. Blue crab migration occurs over a spatial scale involving

distinct basal food sources, allowing for stable isotopes to be an appropriate method to

investigate their movements.

9

MATERIALS AND METHODS

Study Site

Mobile Bay (Fig. 1) is located in the southwestern region of the state of Alabama in the

northern Gulf of Mexico. Mobile Bay watershed is the 6th largest in the nation and has an

average freshwater input of 1750 m3s-1, the 4th highest in North America (MBNEP 2010). The

bay stretches 50 km north to south, is 37 km at its widest point, and has an average water

depth of 3m (MBNEP 2010). Dauphin Island and the Fort Morgan Peninsula form the southern

boundary of the bay with the Gulf of Mexico. The mouth of the bay is approximately 5 km wide

and 4 m deep (Morgan et al. 1996).

The Alabama coastline is populated by approximately 12.1 km2 of submerged aquatic

vegetation and 20.2 km2 of marshland, two prime habitats for blue crabs (Morgan et al. 1996).

In the northern reaches of the estuary, water is of low salinity during the spring and early

summer months (Valentine & Sklenar 2008). An increase in salinity occurs during late summer

and fall as river discharge decreases with salinity levels approaching 15 psu in the upper estuary

(Valentine & Sklenar 2008).

Three study areas were selected throughout Mobile Bay (Fig. 1). The Delta site was

selected in an area of Mobile Bay just north of the causeway known as Chocolatta Bay. An area

north of the mouth of Fowl River was selected as a mid-bay site. The coastal sites were located

10

on Dauphin Island, Sand Island, and the Fort Morgan Peninsula. These sites were chosen in an

effort to collect crabs at specific stages of their migration, including a site where they are long

term residents (Delta), undergoing migration (Fowl River), and entering spawning grounds (DISL

Dock, Fort Morgan, and Sand Island).

Diet Switch

A diet switch experiment was conducted with blue crabs captured from the Delta site.

Crabs were collected with trawls, crab pots, box traps, and dip nets in September 2010. Once

captured, crabs were placed in a live well with their claws restrained by rubber bands to

prevent cannibalism. Before being placed in mesocosms, specimen were weighed and

measured for total carapace length. A swimming leg from each individual was clipped and

saved for isotopic analysis as an initial muscle sample to compare to muscle samples from

future days in the experiment. Rubber bands were removed and crabs were placed in

individual 37.5 L enclosures. Salinity was maintained at 10 psu, with temperature ranging from

20-22° C throughout the experiment. The entire system was composed of approximately 1200

L of water. Water quality was maintained by biological and mechanical filtration through a

fluidized bed in addition to a protein skimmer and ozone generator. Water changes were

conducted as necessary. Crabs were fed offshore caught Atlantic bumper (Chloroscombrus

chrysurus) of a known δ13C ratio daily for a period of 83 days. Excess food was removed from

the enclosure if not consumed within 15 minutes. Specimen (n = 4 to 10) were killed after 2, 5,

10, 20, 40 and 83 days from the start of the experiment. A final weight and total carapace

11

length was recorded from each crab before processing. A total of 35 crabs were used during

the feeding experiment.

Field Study

The field portion of this study included crabs captured from all five study sites. Blue

crabs were collected by trawls, crab pots, box traps, and dip nets. Sampling began in August

and concluded in November 2010. Crabs were immediately rinsed with deionized water and

placed in individual Ziploc bags on ice during transport. Upon arrival at the Dauphin Island Sea

Lab, samples were stored in a -20°C freezer until dissection. In total, 86 crabs were collected

for this portion of the study.

Lab Processing

Muscle was removed from blue crab chelipeds and swimming legs (for organisms used

in the feeding experiment). Hepatopancreas samples were collected and carefully removed

from connective tissue and ovaries (in mature females). All tissues were rinsed with deionized

water and were frozen at -20°C.

Prior to being freeze dried, vials were placed in a -80°C freezer for at least one hour,

followed by a 48 hour lyophilization period. Dried samples were ground to a fine powder by

mortar and pestle. Between 0.4-0.5 mg of tissue was weighed out and packed into 4x6 mm tin

capsules. Samples were analyzed at the Washington State University stable isotope facility.

Hepatopancreas samples underwent a lipid removal process according to a modified

version of the method presented by Folch et al. (1957). Subsamples (0.2 g) of hepatopancreas

12

material were placed in 15 mL centrifuge vials and treated with a 2:1 chloroform-methanol

solution of 20 times the sample volume. The contents were vortexed for 10 seconds to

suspend the material in solution, followed by 20 minutes of constant resuspension on a shaker

table. Contents were centrifuged for 5 minutes at 3000 rpm and the supernatant was

decanted. The process was repeated 4 times with deionized water replacing the chloroform-

methanol solution during the final repetition. Subsequently, samples were dried at 60°C for 48

hours.

13

RESULTS

Lipid Extraction

A subset of 15 crab hepatopancreas tissue samples that underwent lipid removal had

lower and less variable C:N ratios (3.49 ± 0.21, mean +/- 1 SD, n = 15) than samples that did not

undergo the extraction (8.82 ± 3.08, n = 15) (Fig. 2a). In addition, the extracted samples also

had more enriched average δ13C values (-21.64‰ ± 3.00, n = 15) than their lipid containing

counterparts (-24.80‰ ± 3.58, n = 15). Samples with higher original C:N ratios generally show

greater δ13C enrichment after removal (Fig. 2b) of lipids. Crab muscle tissue consistently

contained C:N ratios in the range of lipid free samples (mean 3.09 ± 0.09, n = 15). For all

subsequent samples, all hepatopancreas tissues underwent lipid extraction.

Diet Switch

A diet switch experiment was conducted over 83 days. Average initial muscle values for

blue crab δ13C was -23.7 ± 1.75‰ (n = 40). The food source (Atlantic bumper) had a δ13C and

δ15N value of -16.9 ± 0.12‰ (n = 3) and δ15N value of 14.45 ± 0.60‰ (n = 3). Muscle and

hepatopancreas δ13C and δ15N values became more enriched throughout the experiment,

reflective of the new food source. A total of 6 crabs molted during the study, resulting in

greater weight gain for those individuals than crabs that did not molt. Muscle values were

14

corrected to account for only metabolic turnover as opposed to new growth according to:

(equation 2)

where is the new isotopic value due to only metabolic turnover, is the final raw value,

the initial value and the value of the new food source. and are the initial and final

weights of the crabs, respectively.

At the conclusion of the experiment, crabs from day 83 had average raw muscle δ13C

values of -17.94 ± 0.66‰, (n = 4), while their growth corrected δ13C values were -20.84 ±

1.12‰, (n = 4). Hepatopancreas values were not corrected for growth, as turnover occurred

much more rapidly than muscle, and a mathematical correction would grossly underestimate

metabolic turnover. At day 83, average hepatopancreas δ13C values were -17.36 ± 0.50‰, (n =

4). Raw hepatopancreas and muscle values displayed a trend towards the value of the food

source when plotted over time (Fig. 3a and b). However, in some instances, final δ13C values

remained more depleted for later days than previous ones.

Percent tissue turnover was calculated by the equation:

(equation 3)

where is the final raw value (for muscle it is the final value due to metabolic turnover),

the initial value and the value of the new food source. The percentage of tissue turnover

after 83 days for hepatopancreas averaged 94.16 ± 8.71% (n = 4). In contrast, muscle had an

average turnover of 42.58 ± 14.68% (n = 4) (Fig. 4a and b). Average δ13C divergence between

15

hepatopancreas and muscle (corrected for growth) at days 40 and 83 was 3.40 ± 1.51‰ (n = 4) and

3.48 ± 1.56‰ (n = 4), respectively (Fig. 5).

Initial muscle samples were collected from a swimming leg immediately prior to the

feeding experiment. Final muscle tissue was collected from crab cheliped. We used initial

muscle δ13C to estimate for initial hepatopancreas δ13C values. Crabs collected in the delta and

immediately killed displayed nearly identical δ13C values for swimming leg and cheliped muscle

tissues (mean difference 0.03 ± 0.18‰, n = 3). Hepatopancreas and initial muscle tissues had

slightly more variable δ13C values, possibly because of recent variations in diet (mean difference

0.30 ± 1.01‰, n = 3). To further assess this larger variance, we compared the muscle and

hepatopancreas δ13C values of the 15 crabs captured from the Delta site during the field

portion of this study. The δ13C values of their tissues displayed a similar pattern with slightly

less variation (mean difference 0.41 ± 0.68‰, n = 15) and were not significantly different (p =

0.422 t-test). Therefore we used initial muscle δ13C values as an estimate for initial

hepatopancreas δ13C values during the feeding experiment.

Field Study

In total, 86 blue crabs were processed for the field portion of this study. Fifteen crabs

(13 male, 2 immature female) were collected from the delta, 29 (10 male, 19 mature female)

from Fowl River, 13 (1 male, 12 mature female) from DISL Dock, 19 (all mature female) from

Fort Morgan, and 10 (all mature female) from Sand Island. These numbers do not reflect actual

catch ratios as we released unnecessary specimen. For instance, we were interested in females

from Fowl River, but caught a much higher percentage of males. Additionally, we chose to keep

16

the two immature female crabs from the delta to verify those crabs fit the same pattern as

others at the site. Average total carapace length by site of crabs used in the study (Fig. 6) were

not significantly different from one another (p = 0.121 one way ANOVA). Average sizes were

14.28 ± 2.35 cm (n = 15, Delta), 15.56 ± 1.65 cm (n = 29, Fowl River), 15.19 ± 1.26 cm (n = 13,

DISL), 15.16 ± 1.15 cm (n = 19, Fort Morgan), and 15.73 ± 1.01 cm (n = 10, Sand Island).

Hepatopancreas and muscle δ13C ratios varied by site, both followed the same general

pattern (Fig. 7a and b). A shift occurred from depleted δ13C values for crabs in the delta to

more enriched values at the coastal sites. Crabs with the most depleted δ13C values

(hepatopancreas -25.12 ± 1.25‰, muscle-24.71 ± 1.49‰, n = 10) were located in the Delta site,

with Fowl River showing slightly more enriched values than the delta. The coastal sites showed

much more enriched δ13C values, with crabs at the DISL Dock site the most enriched in δ13C

(hepatopancreas -18.83 ± 1.19‰, muscle -19.05 ± 1.80‰, n = 13). δ15N did not show a

consistent directional pattern, displaying similar values at all sites, with the exception of slightly

more enriched δ15N values at the DISL dock site (Fig. 7a and b).

Individual crab differences (Fig. 8) of δ13C between hepatopancreas and muscle (δ13Ch-m)

values showed minor variability in the delta (-0.41 ± 0.68‰, n = 15) and Fowl River (-0.31 ±

0.71‰, n = 29) sites. The maximum divergence in δ13C for an individual crab at the Delta site

was 1.45‰. At the Fort Morgan (2.39 ± 1.8‰, n = 19) and Sand Island (1.31 ± 1.06‰, n = 10)

sites, crabs with little variance between δ13C values for muscle and hepatopancreas made up a

portion of samples. However, a number of crabs showed a large divergence between muscle

and hepatopancreas δ13C values. At Fort Morgan, twelve crabs had a divergence in δ13C of at

17

least 1.45‰, while at Sand Island three crabs showed this trend. Typically, for crabs with a

large divergence, hepatopancreas tissues closely reflected the site average δ13C value, while

muscle tissues were reflective of a more depleted δ13C source. Additionally, at the Sand Island

site, two crabs displayed both muscle and hepatopancreas δ13C values that were more than

2.5‰ away from the site average values. Crabs from the DISL Dock site had an average δ13Ch-m

of -0.21 ± 1.15‰ (n = 13). At this site, the divergence between hepatopancreas and muscle

tissue δ13C values exhibited a multidirectional pattern compared to a more unidirectional

pattern at the other sites (Fig. 8e).

To analyze the difference in divergence of muscle and hepatopancreas δ13C ratios

between study sites, a Mann-Whitney Rank Sum Test was performed comparing each site to

the Delta site (Fig. 8). This test was conducted on the difference of individual crab muscle from

hepatopancreas δ13Ch-m values for all crabs collected at each site. δ13Ch-m values of crabs from

the Fowl River site were not significantly different (p = 0.766) from ones at the Delta site.

Additionally, δ13Ch-m values of crabs at the DISL dock site were also not significantly different (p

= 0.117) from the Delta site. δ13Ch-m values of crabs from the Fort Morgan (p < 0.001) and Sand

Island (p < 0.001) sites were statistically different than crabs at the Delta site. For δ15Nh-m, crabs

collected at the DISL Dock site and Fort Morgan site were significantly different than both the

Delta and Fowl River sites (p < 0.005; one way ANOVA: all pair wise multiple comparison (Holm-

Sidak method)) (Fig. 9).

18

DISCUSSION

Hepatopancreas tissue samples contained high lipid content, as determined by sample

C:N ratios. Lipids, biologically processed differently than proteins, are typically more depleted

in δ13C than protein (DeNiro & Epstein 1978). It was originally our intention to correct for the

effect of variable lipid concentrations on δ13C values in hepatopancreas samples by with a

mathematical model based on the sample’s C:N ratio (Post et al 2007). In some cases, however,

hepatopancreas C:N ratios exceeded the upper limit for a mathematical correction. In these

high lipid content samples, extrapolation using the Post et al. (2007) model could result in

inaccurate estimates (Sweeting et al. 2006, Post et al. 2007). Therefore, we chose to perform a

lipid extraction on all hepatopancreas samples. Crab muscle tissue consistently contained C:N

ratios in the range of lipid free samples, and therefore were not subjected to lipid extraction.

Following extraction, we were able to compare the isotopic values of the remaining protein

within hepatopancreas and muscle tissues.

This project involved a lab and field aspect in order to assess blue crab movement. The

lab portion of the study provided evidence of a difference in turnover rates for δ13C values

between muscle and hepatopancreas tissues. We were able to use this diversion to assess the

crab populations in our field sites to determine whether crabs in these locations were resident

or migratory. This demonstrated the application of stable isotopes as a tool to assess

connectivity within an estuary by migrating organisms such as blue crabs.

19

Diet Switch

The purpose of the lab feeding experiment was to simulate the change in diet of adult

female blue crabs migrating from the low salinity deltaic regions to marine coastal waters

where spawning occurs. By feeding the organisms a diet reflective of marine food sources, we

simulated the shift from a deltaic food source to one of marine origins, as the crabs moved into

their new environment. Crabs were sampled at multiple time intervals over an 83 day period in

order to compare the turnover rates of hepatopancreas and muscle tissues. Previous studies

have demonstrated the use of feeding experiments to compare turnover of multiple tissues

within organisms (Fry et al. 2003, Church et al. 2009, Buchheister & Latour 2010). Studies such

as these provide evidence for variation between turnover rates of different tissues and provide

a framework for using such variation to investigate changes in diet of organisms.

The hepatopancreas is a digestive organ involved in the production of enzymes and

absorption of food. Due to its nature, this organ rapidly undergoes loss and replacement of

tissues through the release of enzymes and storage of new materials absorbed through food.

Muscle tissue, in contrast, is often built up and maintained for longer time periods. Although

muscle undergoes turnover and replacement as well, this typically occurs at a much slower

rate. The diversion of δ13C values between these two tissues can therefore be used to estimate

changes in diet.

We used a mathematical correction for muscle turnover to remove the variability

associated with the incorporation of new tissue through growth during the experiment. The

addition of new tissue during growth comes from materials derived from the new food source

20

and would lead to a bias in the estimate of tissue turnover as the crabs grow at different rates.

Therefore, we removed that aspect and looked at isotopic changes due to only metabolic

turnover. We calculated this isotopic δ13C ratio according to a modified version of the

equation:

(equation 4)

provided by Hesslein et al (1993), which was used to calculate the isotopic value due to growth

alone, where is the new isotopic value due to growth only, the initial isotopic value and

the value of the new food source. and are the initial and final weights of the

organism, respectively. This equation provided an isotopic ratio for the tissue based only on

growth, whereas we were interested in the isotopic value based only on metabolic turnover.

By modifying the equation to equation 3, we were able to calculate the δ13C value based only

on metabolic turnover.

As expected, hepatopancreas tissues had rapid turnover rates with a half-life of

approximately 13.4 days according to the regression fit to fig. 4a by the exponential rise to

maximum 2 parameter equation:

(equation 5)

where y is % tissue turnover and x is days since start of experiment. Muscle turnover, however,

was much slower and highly variable. As a result, estimating half-life for muscle tissue, and

using that to estimate times of residency and migration (as we originally intended to) was not

feasible.

21

We estimate that crabs with a δ13C divergence between hepatopancreas and muscle

similar to those measured by day 40 of the feeding experiment (Fig. 5) are crabs that have been

feeding on a new food source for a comparable period of time. However, because crabs in the

field study were not subjected to food of a constant isotopic value the divergence in δ13C values

between muscle and hepatopancreas tissues were more variable than observed during the

feeding experiment.

The concept of using hepatopancreas and muscle tissues to reflect recent and past

diets, as demonstrated by Fry et al. (2003), was successfully incorporated into our study.

Similarly to the work on brown shrimp by Fry et al. (2003), a comparison of final turnover for

blue crabs during the feeding experiment indicated turnover is occurring at a higher rate in

hepatopancreas than in muscle (t-test p < 0.001), with percentage of tissue turnover after 83

days for hepatopancreas averaging 94.16% turnover, and muscle 42.58%. Llewellyn & La Peyre

(2011) conducted a similar feeding experiment on blue crabs. Their findings suggest a half-life

for hepatopancreas tissue δ13C of 10 days, a result similar to our estimate. They suggest muscle

δ13C half-life to be 39 days. They did not observe significant growth or correct for it, as their

feeding experiment encompassed only 20 days compared to the 83 day duration of our study.

By day 83 of our experiment, crab δ13C values (corrected for growth) were just approaching

50% turnover. Other studies have also conducted feeding experiments to investigate migration

of organisms through the use of multiple tissue stable isotopes. Rodgers & Wing (2008) used

multiple tissue isotope analysis on movement of blue cod (Parapercis colias), and Nelson et al.

(2011) investigated gag (Mycteroperca microlepis). Similarly to our results, feeding experiments

22

from these studies did not include a time frame long enough for all tissues to fully equilibrate to

a new food source.

As noted in the results, in some cases final raw δ13C values from earlier days during the

experiment more closely resembled the new food source than later days (Fig. 7). This is

exemplified by days 2 and 10 for muscle, where values at day 2 were more reflective of the new

diet than those from day 10. This can be explained as a result of natural variation based on

random selection, as crabs at this later day had more depleted initial values than ones from the

other group.

We chose to use swimming leg muscle for an initial muscle sample in order to avoid

removing a claw, possibly interfering with feeding. Hepatopancreas samples could not be taken

prior to the experiment without damaging the organisms, which led to the use of initial muscle

to estimate initial hepatopancreas δ13C, which was not found to be significantly different from

hepatopancreas for crabs at the Delta site. We acknowledge two potential pitfalls with the

structure of this feeding experiment. Removal of an appendage to collect an initial muscle

sample potentially may have led to slightly shifted turnover rates due to energy being spent for

regeneration. However, this practice was applied to all crabs used for the feeding experiment

so consistent comparisons could be made.

Secondly, due to the migratory nature of adult female crabs, we were unable to capture

mature females in our Delta site. In order to compare the turnover of the hepatopancreas and

muscle tissues, it was appropriate to use crabs that were initially resident and had been feeding

on a constant food source. For this reason, we chose to use mostly male crabs (with 4

23

immature females) during this part of the study. We acknowledge the possibility that adult

female crabs may have slightly altered turnover rates compared to males due to ovary and egg

production.

Field Study

Fast turnover hepatopancreas tissue and slow turnover muscle tissue were used to

indicate residency and movement of blue crabs. The divergence between the δ13C values of a

fast turnover and slow turnover tissue has been used to indicate residency or migration for

species such as brown shrimp (Fry et al. 2003) and blue cod (Parapercis colias) (Rodgers & Wing

2008). To assess migration, we utilized the maximum divergence between muscle and

hepatopancreas tissue δ13C from crabs at the delta (Fig. 7a) as a cutoff to categorize migrants.

Crabs with tissues having a smaller divergence in δ13C were considered residents, while those

with a greater divergence were categorized as migrants. Crabs reach the waters of the delta as

megalopae and juveniles where they use the shallow waters and vast beds of submerged

aquatic vegetation as a nursery habitat (Heck et al. 2001). Adult crabs found in this region have

likely experienced multiple molts over a period of at least 12 months. During this time, they

have undergone rapid growth while feeding on food resources dominated by a terrestrial signal

(Goecker et al. 2009). As a result, the two tissues consistently display similar δ13C values.

All of the adult crabs we captured at the Delta site were males, with the only females

captured being immature. Female crabs mate with a male crab upon undergoing their molt to

maturation. Following mating, female crabs move toward marine waters in order to spawn

24

(Aguilar 2005). Such movement is explanatory of the absence of adult females in our

collections within the delta.

Blue crabs at the Fowl River site displayed unexpected but explainable characteristics.

In this region we captured both male and female crabs (Fig. 8b). Male crabs displayed entirely

resident characteristics, with both tissues having similar δ13C values. Based on the life history

of blue crabs, we expected to find female crabs in this region to be migrating down through this

site after mating. However, stable isotope analysis of tissues showed these crabs had small

divergence in their δ13C values, which is characteristic of resident crabs.

We propose two explanations for the lack of divergence of δ13C between

hepatopancreas and muscle tissues for female crabs at the Fowl River site. Female blue crabs

at this site may have actually been residents, as it has been documented that female crabs may

delay their offshore migration for months following mating (Turner et al. 2003). The slightly

more enriched δ13C average δ13C values for crabs the Fowl River site compared to the delta (t-

test p = 0.002), without any excessive deviation between the tissues, suggest that these crabs

have been in this region for a period of time long enough for both tissues to converge to the

similar δ13C ratios. If female crabs had just recently migrated into this region, we would expect

to have found a noticeable difference between muscle and hepatopancreas tissues to account

for the slightly more enriched δ13C diet. Therefore, lack of variation between tissues may

potentially be explained by the idea that crabs are using this region as a “hot spot” and may

have been resident at least for a period long enough for both of their tissues to reach

equilibrium with the new diet. If this is the case, the Fowl River site is likely a major site of

25

recruitment similar to the delta site, with the one exception being adult females were absent

from the delta, yet were present at Fowl River. The presence of adult females at Fowl River and

not at the delta supports the idea of this region being a “hot spot” for adult crabs delaying their

migration.

Alternatively, female crabs that are moving through this site are still feeding on a similar

diet to what was available in the Delta site, resulting in only a small change in the δ13C values of

their hepatopancreas and muscle tissues. Therefore, even if crabs are recent migrants into this

site, the lack of a large discrepancy between the diets limits isotopic methods from

characterizing such movement. A further study investigating the food sources available at the

Fowl River site would allow for a better understanding of the nature of crabs at this location. In

summary, it is possible that female crabs at the Fowl River site consisted of both crabs which

had moved down from the delta following mating as well as crabs that developed, matured,

and mated in this region.

Female blue crabs at the Fort Morgan and Sand Island sites shared similar patterns of

δ13C divergence between the two tissues (Fig. 8c and d). Both resident (small divergence) and

migrant (divergence larger than 1.45‰) were present at these locations (Fig. 7c and d). In

addition, we found two crabs at Sand Island that could be categorized as a very recent migrant

due to both tissues having a small divergence and δ13C values similar to those found in the delta

and depleted compared to the site average hepatopancreas δ13C (data not shown). Crabs

displaying resident characteristics are likely to have been females that migrated to these

regions to spawn in previous years. Because females are able to store sperm for future

26

spawning events (Hines et al. 2003), they remain in these coastal areas to overwinter. Migrant

crabs had likely moved down into these regions within the recent past. Based on the turnover

of hepatopancreas tissues in the lab feeding experiment, we can estimate that the crabs

characterized as an extremely recent migrant had likely moved into this area within a time

frame of less than a month, as its hepatopancreas tissues were still not close to equilibrium

with more enriched average δ13C values of other crabs at the site likely feeding on δ13C

enriched marine based food sources.

The DISL Dock site was expected to be similar to the other two coastal sites, with a mix

of resident and migratory crabs. Because this site was slightly further north and near the

mouth of the bay, we were initially expecting to catch crabs that were just completing their

migration to marine waters. These crabs would have had δ13C values mostly characteristic of a

terrestrial food web in their tissues, with hepatopancreas tissues showing a diversion towards a

new, more marine signature. Crabs at this site, however, did not display the drastic divergence

between tissues as seen in the Sand Island and Fort Morgan sites (Fig. 8e) and did not show

values consistent with a terrestrially based diet. In fact, crabs at this location displayed the

most enriched marine δ13C values of any of our sites.

The DISL dock site is an area where research and recreational vessels launch from and

sort catch on a daily basis. Most of this catch is offshore fish, especially red snapper (Lutjanus

campechanus). Fish carcasses are often discarded at this site by fishermen, and become a

presumably common food source for blue crabs residing nearby. It is safe to assume that crabs

27

in this region were likely crabs that had migrated down in previous years, overwintered, and

remained in this resource rich location.

Crabs at the DISL dock site, however, did show more variation between tissues than

Delta and Fowl River sites. Unlike the majority of crabs at the other coastal sites, the variation

between tissues was multidirectional, with some crabs having hepatopancreas δ13C values

more enriched than their muscle, while others had more depleted δ13C values of

hepatopancreas compared to muscle. This is potentially a result of inconsistent amounts of

offshore fish being discarded here. Some crabs may have potentially fed on an abundance of

fish carcasses in the recent weeks, giving them a more enriched hepatopancreas value. While

others may have been feeding on locally more depleted natural sources within the area.

For all sites, δ15N values did not show a directional pattern such as with δ13C (Fig. 7).

There was no consistent trend towards a more enriched δ15N food source at our coastal study

sites, with the exception of the DISL Dock site, which was influenced by the availability of

offshore caught fish of a relatively high trophic level. Instead, however, blue crabs displayed

divergent δ15N values for hepatopancreas and muscle (h-m) at our Delta and Fowl river sites

(Fig. 9a and b). δ13C values at these sites were consistently similar for both tissues, whereas for

δ15N, hepatopancreas tissues were typically more depleted than muscle tissues. This disparity

could be explained by a seasonal or trophic shift in diet. If the cause was a trophic shift, we

would expect the hepatopancreas (recent diet) tissue to yield higher δ15N values than muscle

(long term diet) as the organism moves up to a higher trophic level. However, because δ15N

was typically more depleted, assessment of a trophic shift becomes more complicated. The

28

change may still be linked to a trophic shift to a new food derived from a different basal source

naturally more depleted in δ15N. Alternatively, more depleted δ15N values in hepatopancreas

tissue compared to muscle may be linked to a seasonal shift in the food web due to changes in

river flow or other vectors of connectivity. We do not have the necessary data to support this

idea; however future studies incorporating compound specific stable isotopes could reveal the

cause of this disparity. Compound specific studies involving δ15N use look specifically at amino

acids that are enriched based on trophic level (glutamic acid), as well as amino acids that are

generally conserved (phenylalanine, glycine) (Olson et al. 2010). A comparison of the two

types of amino acids within samples can generate a much better understanding of whether

δ15N values are being altered by trophic shifts or changes in basal food resource.

Connectivity and Ecological Consequences

The primary goal of this study was to use stable isotopes to demonstrate the cross

habitat linkage between the spatially separated terrestrial based deltaic and marine based gulf

food webs. We wanted to present migratory organisms as a vector of connectivity between

these regions and chose the blue crab for the following reasons. This crustacean is of high

commercial importance within the region, has well documented migration patterns, and

occupies multiple roles within the food web throughout its life history.

Multiple stable isotope studies have been conducted to investigate the contributions of

marine and terrestrial food sources within an estuary (Peterson & Howarth 1987, Chanton &

Lewis 2002, Goecker et al. 2009). In addition stable isotopes have been used to explore multi-

tissue turnover and migratory patterns of organisms (Fry et al. 2003, Church et al. 2009). This

29

study used a combination of the two to draw emphasis to the importance of migratory

organisms connecting food webs within estuaries.

Results of this study exemplify the habitat connectivity provided by blue crabs as well as

other migratory organisms within the region. As blue crabs enter the marine food web, their

tissues contain organic matter assimilated in the delta. We can visually observe this connection

based on the muscle tissue of many of the migrant crabs still displaying a depleted δ13C

signature (Fig. 8c and d), which is reflective of a diet based on terrestrially derived carbon

sources found in the delta (Fig. 7). As predators feed on these migratory crabs in marine

waters, they are consuming organic matter originating from the deltaic food web.

Alternatively, these formerly deltaic crabs are now acting as a predator and detritivore in the

marine food web, as referenced by the turnover of hepatopancreas and eventually muscle

tissues to more enriched, marine based isotopic δ13C values. Spawning, an aspect not detailed

in this study completes the cycle of the blue crab derived linkage between the two food webs.

As new crabs are spawned offshore and travel into deltaic waters, they act as carrier of organic

matter derived from marine sources into the deltaic food web.

The use of nursery grounds within estuaries by marine species is essential to the life

cycles of many species whose adult stages live well offshore. The sustainability of fisheries

related to such species is critically connected to such vital nursery habitats. The degree of

which certain habitats contribute to the reproductive success of organisms varies between

species, with some spending days in nursery grounds compared to others which remain for

years. The pathways in which transient species move from juvenile to adult habitats are

30

potentially vital links relating to future survival of populations. An improved understanding of

which specific habitats are most essential to individual species success will aide in conservation

efforts as changes in anthropogenic interactions and climate occur (Gillanders et al 2003). Gag

grouper (Myctereoperca microlepis), a marine species, have been shown to derive a major

portion of their diet from seagrass derived organic matter during their spawning season. Nelson

et al. (2011) hypothesized that this connectivity is occurring through the movement of both

seagrass dwelling fish to nearshore waters and movement of grouper to intercept such

migrations. It is likely that these vectors of connectivity occur between many additional

estuarine and marine species throughout their life histories.

Crabs, fish, and other mobile organisms use estuaries in a multitude of manners.

Transient species include those whose life history requires use of the estuary, facultative users,

and stray organisms which are there by chance (Able 2005). Estuarine dependence by

facultative users may fluctuate based on geographic, cohort-specific, and annual variability

(Able 2005), therefore shifting the degree of connectivity between the marine and terrestrial

food webs provided by such species. Such fluctuations may also contribute to a change in

mortality rates of species as they are exposed to adverse or favorable conditions for survival

(Ray 2005).

Changes in river flow can alter the level of connectivity between habitats within an

estuary. During times of low river flow, distinct food webs with less diversity can occur within

estuaries (Vinagre et al. 2011), resulting in decreased connectivity throughout the overall range

of the estuary. Smaller food webs result in a reduced chance for organisms capable of surviving

31

climate changes to be present (McCann 2000), which in turn increases the potential for a

collapse of the food web. Conversely, when river flow is higher and a large, diverse, connected

food web exists, the ecosystem is better suited to deal with disturbances such as climate

change.

Pulses of food from inundation of floodplains provide subsidies for aquatic food webs.

Many fishes are adapted to take advantage of such local pulses (Jardine et al. 2012). As a result

these surges of nutrients are rapidly infused into the estuarine food web, from both the

exchange of terrestrial matter being deposited into the aquatic food web and from

opportunistic aquatic organisms moving into the flooded region to feed on available prey items

that have become submerged. Additionally, during periods of inundation, smaller prey species

may enter the shelter of the floodplains as an escape mechanism from predators. As

floodwaters recede, these smaller prey species are forced to return to their original habitats

resulting in another shift in the local food web. Such inundations are highly variable in

magnitude and duration, creating continuous shifts in the food web and increasing diversity

(Jardine et al. 2012).

Barriers to connectivity occur both naturally and through anthropogenic activity.

Natural isolations such as tide pools occur throughout many marshes and floodplains.

Anthropogenic developments also create permanent and temporary barriers to connectivity.

The construction of dams create alterations to river flow affecting nutrient availability,

movement of transient organisms, and can create physical barriers as a result of less water

discharge. Similarly, anthropogenic modifications, specifically such as the construction of the

32

causeway in Mobile Bay, Alabama (Goecker et al. 2009), may impact consistent salinity

gradients throughout the estuary. Additionally, the establishment of bulkheads on waterfront

property to prevent erosion eliminates the land water interface and exchange of materials that

typically occurs at such sites. The structures are intended to preserve the economic value of

the land they are protecting; however, they can destroy the biological value naturally provided

by natural structures existing prior to construction (Gabriel & Terich 2005). These interfaces

serve as important links between terrestrial and aquatic habitats. The economic value of

marshlands has been well documented. And bulkheads, while being a short term solution to

erosion, may create a long term environmental and economical loss.

An advanced understanding of habitat connectivity is critical to managing fisheries in

nature. Blue crabs are one of many migrating organisms that link spatially separated food webs

in the gulf and the delta. With this knowledge, we must recognize the potential for alterations

in one region to have significant impacts in areas outside of the immediate vicinity. For

instance, anthropogenic influences resulting in eutrophication in deltaic waters could create

anoxic conditions impacting survival of migratory organisms. Lower numbers of these

organisms traveling to marine waters could cause a shortage of food for their predators,

creating a shift in food web structure. Additionally, disturbances in the marine environment

could have long lasting effects on areas spatially separated from these disturbances. For

example, offshore disasters such as the 2010 Deepwater Horizon oil spill could indirectly impact

areas far from those directly exposed to oil through interactions between food webs. Such

impacts from this specific event are still being investigated, with long term consequences yet to

be determined. Fishing pressure of adult populations of organisms must also be considered

33

when studying sustainability of the population of migratory organisms, as the spawning success

of an adult population will directly influence the recruitment of new classes.

On a species specific level, the connectivity between food webs mediated by blue crabs

is critical for the commercial importance of the species. Blue crabs are a valuable commercial

food source for the gulf region as well as the country as a whole. Salinity gradients are known

to affect the distribution of blue crabs throughout estuaries. Alterations to river flow caused by

climate change resulting in changes in salinity gradients within estuaries could negatively

impact the life history of species such as blue crabs. Low river flow may be associated with

increased predation by marine species on juvenile crabs (Wilber 1994) and prey limitation

leading to cannibalism (Lipcius & Van Engel 1990), both limiting crab population size. Loss or

damage of essential habitat within nursery grounds or spawning grounds could potentially

interfere with the life history of the species and deplete population numbers, creating a

tremendous loss of commercial capital and food supplies. Damage to sensitive nursery grounds

in the delta may not cause an immediate noticeable impact on commercially harvested blue

crabs further south in the bay, however, higher juvenile mortality rates may cause a dramatic

population decrease in subsequent years, leading to great economic loss. The nursery habitats

of the Mobile-Tensaw delta are vital to the juvenile stages of many other estuarine species such

as the southern flounder (Paralichthys lethostigma) with evidence showing this species spends

much of its early life in the some of the most oligohaline reaches of the bay before moving out

to more marine waters as an adult (Lowe et al. 2011). Such observations must lead us to

broaden the scope of habitats we deem important for the survival of many species. This idea is

applicable for other commercially valuable organisms within the gulf as well, such as shrimp

34

(Panaeidae), trout (Salmonidae), menhaden (Clupeidae), anchovies (Engrulidae), and drum

(Sciaenidae), all of which utilize the delta and gulf throughout their life histories.

35

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41

FIGURES

Figure 1. Study sites: The five study sites chosen throughout Mobile Bay for the field study.

42

Figure 2. Lipid extraction: (a) δ13C‰ vs. C:N ratios for a subset of fifteen samples of

hepatopancreas tissue. Closed circles are samples which underwent a lipid extraction. Open

circles represent tissues from the same set of samples prior to lipid removal. (b) Change in

δ13C‰ after lipid extraction vs. original C:N ratio before extraction. The line represents lipid

corrections based on the mathematical model provided by Post et al. (2007). Closed circles are

samples that underwent lipid extraction.

43

Figure 3. Diet switch δ15N and δ13C values: Day specific values of δ15N and δ13C of

hepatopancreas (a) and muscle (raw values) (b) tissue from blue crabs in the diet switch

experiment. The average δ value of all crabs killed at day 2 (closed circle), day 5 (open square),

day 10 (closed square), day 20 (open triangle) day 40 (closed triangle), day 83 (open diamond)

and the food source (closed diamond).

44

Figure 4. Diet switch turnover: Percent tissue turnover of hepatopancreas (a) and muscle (b) by

day for each individual crab from the diet switch experiment. The regression for each figure is

the exponential 2 parameter rise to maximum equation fit to the dataset.

45

Figure 5. Diet switch hepatopancreas-muscle (h-m) divergence: Average δ13Ch-m for crabs killed

at each time point of the feeding experiment. Error bars indicate standard error.

46

Figure 6. Crab carapace length: Total carapace length (cm) of blue crabs for each site of the

field study. No sites were significantly different (p = 0.121; one way ANOVA) from one another.

47

Figure 7. Site average δ15N and δ13C values: Average crab hepatopancreas (a) and muscle (b)

δ15N and δ13C values at the Delta (diamond), DISL dock (square), Fort Morgan (triangle) Fowl

River (x) and Sand Island (circle) sites. Error bars represent standard error.

48

49

Figure 8. δ13C hepatopancreas-muscle (h-m) divergence: Individual crab hepatopancreas-

muscle δ13C values for each study site. Blue crabs are ranked from most negative to positive

divergence. The Sand Island and Fort Morgan Sites were significantly different when compared

to the resident Delta site (p < 0.001; Mann Whitney Rank Sum Test). The dotted line is the

maximum divergence found at the delta. This cutoff was used to categorize resident and

migratory crabs at the remaining sites.

50

Figure 9: δ15N hepatopancreas-muscle (h-m) divergence: Individual crab hepatopancreas-

muscle δ15N values for each study site. Blue crabs are ranked from most negative to positive

divergence. Sites not containing the same letter (y or z) are significantly different from one

another (p < 0.001; one way ANOVA all pair wise multiple comparison (Holm-Sidak method)).

51

APPENDIX

Blue Crab Lipid Removal

Before Lipid Removal

After Lipid Removal

Tissue δ13C(‰) C% δ15N(‰) N% C:N δ13C(‰) C% δ15N(‰) N% C:N

Hepatopancreas -20.25 46.78 9.17 6.24 7.49 -16.96 35.58 9.40 10.38 3.43

Hepatopancreas -20.41 40.58 11.69 9.69 4.19 -20.22 38.67 12.26 12.63 3.06

Hepatopancreas -20.17 45.71 11.35 7.31 6.26 -18.30 35.74 11.60 10.83 3.30

Hepatopancreas -20.87 32.85 10.43 6.17 5.32 -17.05 22.50 10.29 6.69 3.36

Hepatopancreas -27.22 47.44 10.21 5.08 9.34 -24.54 27.71 10.40 7.92 3.50

Hepatopancreas -28.66 49.52 9.75 4.90 10.10 -24.41 30.69 10.28 8.29 3.70

Hepatopancreas -28.84 47.60 10.38 3.46 13.75 -23.55 23.33 10.60 6.88 3.39

Hepatopancreas -26.23 41.08 10.35 4.76 8.63 -23.45 22.60 10.41 6.50 3.47

Hepatopancreas -29.85 50.33 9.23 6.63 7.60 -25.83 26.48 8.64 7.26 3.65

Hepatopancreas -28.62 37.62 8.62 6.52 5.77 -24.48 17.38 7.97 5.13 3.39

Hepatopancreas -25.51 47.05 11.40 5.17 9.09 -22.83 19.38 10.84 5.59 3.47

Hepatopancreas -23.62 35.67 11.80 4.90 7.28 -22.84 16.50 11.10 4.82 3.42

Hepatopancreas -21.82 44.44 13.44 3.54 12.54 -19.54 14.81 12.50 3.90 3.79

Hepatopancreas -22.46 60.95 14.42 4.10 14.86 -17.97 47.61 14.90 12.21 3.90

Hepatopancreas -27.46 50.95 8.75 5.05 10.08 -22.25 24.97 8.96 6.95 3.59

Muscle -24.78 42.79 10.06 13.77 3.11 Muscle -24.42 42.38 10.28 13.62 3.11 Muscle -23.13 40.00 10.15 12.98 3.08 Muscle -22.52 39.15 9.10 13.29 2.95 Muscle -26.51 44.88 11.58 14.62 3.07 Muscle -24.78 41.23 11.08 13.44 3.07 Muscle -24.76 43.27 11.13 13.90 3.11

52

Muscle -27.15 39.18 11.24 12.22 3.21 Muscle -27.07 43.31 12.98 14.17 3.06 Muscle -24.92 45.27 9.78 14.55 3.11 Muscle -25.76 41.80 10.39 12.82 3.26 Muscle -23.61 43.94 10.90 14.27 3.08 Muscle -25.22 40.72 9.92 13.69 2.98 Muscle -22.34 44.34 10.92 13.91 3.19 Muscle -23.78 43.76 10.19 14.86 2.94

53

Diet Switch Sample

ID Organism Tissue Sex Length (Initial)

Weight (Initial)

Length (Final)

Weight (Final) Molted

δ13C (‰)

δ15N (‰)

Time 2 DS2 Blue Crab initial muscle M 11.8 97.8 11.8 111.3

-22.72 13.14

final muscle

-22.1 13.34

hepatopancreas

-22.97 10.28

DS8 Blue Crab initial muscle M 11.6 96.5 11.6 102.1

-23.4 11.93

final muscle

-22.4 11.94

hepatopancreas

-23.46 10.77

DS27 Blue Crab initial muscle F 11.4 68.8 11.4 75.8

-21.63 9.62

final muscle

-21.26 10.87

hepatopancreas

-21.64 12.03

DS30 Blue Crab initial muscle M 11.5 91.0 11.4 91.0

-22.82 11.52

final muscle

-22.26 12.62

hepatopancreas

-22.9 11.18

Time 5 DS 11 Blue Crab initial muscle M 10.0 76.4 10.0 76.4

-22.36 12.41

final muscle

-20.88 12.76

hepatopancreas

-20.1 11.07

DS14 Blue Crab initial muscle F 10.6 68.0 10.6 72.3

-22.17 12.12

final muscle

-19.84 12.66

hepatopancreas

-20.29 11.94

54

DS18 Blue Crab initial muscle M 13.4 139.5 13.4 139.5

-23.08 11.82

final muscle

-20.54 12.98

hepatopancreas

-20.69 11.37

DS21 Blue Crab initial muscle M 15.4 202.1 15.4 202.1

-27.76 12.66

final muscle

-26.84 12.33

hepatopancreas

-22.84 11.1

DS49 Blue Crab initial muscle M 16.7 275.0 16.6 275.0

-26.16 10.5

final muscle

-25.53 10.92

hepatopancreas

-25.54 10.53

DS50 Blue Crab initial muscle M 14.9 184.7 14.7 186.6

-24.45 10.47

final muscle

-24.31 10.9

hepatopancreas

-24.53 7.74

DS51 Blue Crab initial muscle M 12.7 131.4 12.7 131.4

-23.96 11.33

final muscle

-23.78 12.2

hepatopancreas

-23.68 9.1

DS52 Blue Crab initial muscle M 14.5 211.6 14.5 211.6

-26.07 11.28

final muscle

-25.69 10.78

hepatopancreas

-25.11 9.57

DS53 Blue Crab initial muscle M 17.2 287.4 17.2 287.4

-24.84 10.5

final muscle

-24.82 10.33

hepatopancreas

-23.65 9.11

55

DS55 Blue Crab initial muscle M 15.6 240.3 15.6 240.3

-25.47 11.24

final muscle

-25.41 11.71

hepatopancreas

-26.37 9.82

Time 10

DS7 Blue Crab initial muscle M 15.0 214.3 15.0 217.1

-25.54 10.73

final muscle

-23.9 11.53

hepatopancreas

-20.64 11.94

DS6 Blue Crab initial muscle M 16.5 243.1 16.5 265.4

-25.85 11.11

final muscle

-24.44 12.15

hepatopancreas

-21.02 12.62

DS15 Blue Crab initial muscle M 15.0 191.3 15.0 200.1

-22.61 11.11

final muscle

-21.32 13.1

hepatopancreas

-20.2 11.37

DS17 Blue Crab initial muscle M 15.0 220.9 15.0 220.9

-26.14 11.21

final muscle

-25.04 11.93

hepatopancreas

-21.52 11.99

DS16 Blue Crab initial muscle M 12.9 119.9 12.9 167.1

-23.58 11.41

final muscle

-22.6 12.02

hepatopancreas

-20.86 12.25

DS9 Blue Crab initial muscle M 11.1 93.0 11.1 98.5

-21.38 11.4

56

final muscle

-20.18 13.67

hepatopancreas

-18.33 12.6

DS22 Blue Crab initial muscle F 13.5 94.9 13.5 101.3

-21.24 9.11

final muscle

-19.98 10.56

hepatopancreas

-19.08 11.84

DS20 Blue Crab initial muscle F 12.1 91.5 12.1 98.8

-23.16 13.26

final muscle

-20.6 12.79

hepatopancreas

-19.09 12.38

Time 20

DS 31 Blue Crab initial muscle M 15.2 221.7 15.2 225.2

-25.19 10.65

final muscle

-23.63 11.17

hepatopancreas

-20.53 11.58

DS38 Blue Crab initial muscle M 12.2 120.6 12.2 120.6

-22.19 11.51

final muscle

-19.43 13.12

hepatopancreas

-18.5 12.58

DS39 Blue Crab initial muscle M 11.2 98.6 14.4 165.9 yes -22.87 13.09

final muscle

-19.43 13.91

hepatopancreas

-20.47 13.51

DS46 Blue Crab initial muscle M 11.7 91.7 11.7 96.4

-22.36 13.03

final muscle

-18.7 14.48

hepatopancreas

-18.02 11.37

57

DS33 Blue Crab initial muscle M 14.6 207.6 14.6 213.0

-24.15 11.82

final muscle

-23.6 12.37

hepatopancreas

-20.7 12.53

Time 40

DS35 Blue Crab initial muscle M 15.2 207.9 15.2 212.1

-25.41 11.15

final muscle

-23.17 12

hepatopancreas

-18.27 12.72

DS36 Blue Crab initial muscle M 15.7 233.8 15.7 234.9

-25.56 11.52

final muscle

-23.52 11.88

hepatopancreas

-19.54 12.5

DS32 Blue Crab initial muscle M 15.0 232.0 15.0 233.5

-22.72 13.79

final muscle

-21.19 13.75

hepatopancreas

-18.22 13.68

DS47 Blue Crab initial muscle M 10.8 80.9 11.6 94.6 yes -22.25 11.76

final muscle

-18.26 13.6

hepatopancreas

-17.5 12.21

Time 83

DS 34 Blue Crab initial muscle M 15.7 211.1 18.7 344.3 yes -24.71 11.19

final muscle

-18.51 14.21

hepatopancreas

-17.56 14.04

58

DS40 Blue Crab initial muscle M 14.2 126.8 15.9 213.4 yes -22.64 10.72

final muscle

-16.97 14.7

hepatopancreas

-17.97 14.9

DS44 Blue Crab initial muscle M 11.8 116.8 14.5 191.5 yes -23.94 9.51

final muscle

-18.13 13.31

hepatopancreas

-17.13 14.58

DS48 Blue Crab initial muscle M 9.8 61.0 12.7 144.0 yes -23.31 10.64

final muscle

-18.15 14.18

hepatopancreas

-16.8 14.31

59

Diet Switch

Sample

ID

Organism Final Muscle δ13C

(‰)(Metabolic

Turnover Only)

Muscle Raw %

Turnover

Muscle % Tissue Turnover

(Metabolic Turnover Only)

Hepatopancreas %

Turnover

Time 2

DS2 Blue Crab -22.79 10.83 -1.30 -4.37

DS8 Blue Crab -22.75 15.62 10.13 -0.94

DS27 Blue Crab -21.69 7.99 -1.25 -0.22

DS30 Blue Crab -22.26 9.62 9.62 -1.37

Time 5

DS 11 Blue Crab -20.88 27.59 27.59 42.14

DS14 Blue Crab -20.15 45.04 39.09 36.34

DS18 Blue Crab -20.54 41.75 41.75 39.29

DS21 Blue Crab -26.84 8.55 8.55 45.71

DS49 Blue Crab -25.53 6.88 6.88 6.77

DS50 Blue Crab -24.39 1.88 0.86 -1.07

DS51 Blue Crab -23.78 2.58 2.58 4.02

60

DS52 Blue Crab -25.69 4.19 4.19 10.58

DS53 Blue Crab -24.82 0.25 0.25 15.17

DS55 Blue Crab -25.41 0.71 0.71 -10.62

Time 10

DS7 Blue Crab -24.01 19.20 17.91 57.35

DS6 Blue Crab -25.18 15.93 7.52 54.56

DS15 Blue Crab -21.57 22.98 18.58 42.93

DS17 Blue Crab -25.04 12.03 12.03 50.53

DS16 Blue Crab -24.46 14.89 -13.36 41.32

DS9 Blue Crab -20.42 27.38 21.79 69.58

DS22 Blue Crab -20.25 29.69 23.38 50.90

DS20 Blue Crab -21.06 41.54 34.15 66.04

Time 20

DS 31 Blue Crab -23.76 19.04 17.49 56.88

DS38 Blue Crab -19.43 53.15 53.15 71.05

DS39 Blue Crab -21.81 58.57 18.00 40.86

DS46 Blue Crab -18.96 68.24 63.37 80.92

61

DS33 Blue Crab -23.78 7.69 5.15 48.23

Time 40

DS35 Blue Crab -23.34 26.62 24.64 84.87

DS36 Blue Crab -23.56 23.82 23.35 70.30

DS32 Blue Crab -21.23 26.73 26.09 78.63

DS47 Blue Crab -19.02 75.95 61.47 90.42

Time 83

DS 34 Blue Crab -21.49 80.38 41.69 92.70

DS40 Blue Crab -19.26 100.47 59.89 82.75

DS44 Blue Crab -20.84 83.68 44.67 98.08

DS48 Blue Crab -21.79 81.73 24.09 103.12

62

Diet Switch

Food

Organism δ13C (‰) δ15N (‰)

Atlantic Bumper -16.89 13.78

Atlantic Bumper -16.97 14.63

Atlantic Bumper -17.13 14.93

63

Field Study

Sample ID Organism Tissue Date Location Carapace Length

(cm)

Weight (g) Sex δ13C

(‰)

δ15N

(‰)

BC173 Blue Crab Muscle 11/11/2010 Delta 16.9 266.9 M -24.78 10.06

BC174 Blue Crab Hepatopancreas 11/11/2010 Delta -25.83 8.64

BC175 Blue Crab Muscle 11/11/2010 Delta 12.9 118.7 M -24.42 10.28

BC176 Blue Crab Hepatopancreas 11/11/2010 Delta -24.48 7.97

BC177 Blue Crab Muscle 11/11/2010 Delta 13.6 129.8 M -23.13 10.15

BC178 Blue Crab Hepatopancreas 11/11/2010 Delta -24.04 9.08

BC179 Blue Crab Muscle 11/11/2010 Delta 14.1 104.4 M -22.52 9.1

BC180 Blue Crab Hepatopancreas 11/11/2010 Delta -23.97 9.57

BC181 Blue Crab Muscle 11/11/2010 Delta 14.8 214.4 M -26.51 11.58

BC182 Blue Crab Hepatopancreas 11/11/2010 Delta -26.75 9.8

BC183 Blue Crab Muscle 11/11/2010 Delta 16.1 237.8 M -24.78 11.08

BC184 Blue Crab Hepatopancreas 11/11/2010 Delta -25.63 10.2

BC185 Blue Crab Muscle 11/11/2010 Delta 14 206.9 M -24.76 11.13

64

BC186 Blue Crab Hepatopancreas 11/11/2010 Delta -25.66 10.3

BC187 Blue Crab Muscle 11/11/2010 Delta 20.1 286.6 M -27.15 11.24

BC188 Blue Crab Hepatopancreas 11/11/2010 Delta -26.72 10.41

BC189 Blue Crab Muscle 9/2/2010 Delta 13.1 140.3 M -27.07 12.98

BC190 Blue Crab Hepatopancreas 9/2/2010 Delta -27.19 10.77

BC191 Blue Crab Muscle 9/2/2010 Delta 12.8 147 M -24.92 9.78

BC192 Blue Crab Hepatopancreas 9/2/2010 Delta -25.8 7.15

BC193 Blue Crab Muscle 9/2/2010 Delta 15.6 198.9 M -25.76 10.39

BC194 Blue Crab Hepatopancreas 9/2/2010 Delta -24.58 9.84

BC195 Blue Crab Muscle 9/2/2010 Delta 14.2 234.2 M -23.61 10.9

BC196 Blue Crab Hepatopancreas 9/2/2010 Delta -23.53 9.59

BC197 Blue Crab Muscle 9/2/2010 Delta 14.5 163.1 M -25.22 9.92

BC198 Blue Crab Hepatopancreas 9/2/2010 Delta -25.2 8.9

BC209 Blue Crab Muscle 9/24/2010 Delta 10 56 F -22.34 10.92

BC210 Blue Crab Hepatopancreas 9/24/2010 Delta -22.83 10.84

BC211 Blue Crab Muscle 9/24/2010 Delta 11.6 88.9 F -23.78 10.19

BC212 Blue Crab Hepatopancreas 9/24/2010 Delta -24.7 6.78

65

BC83 Blue Crab Muscle 10/10/2010 DISL Dock 16.1 243.7 M -17.29 14.15

BC84 Blue Crab Hepatopancreas 10/10/2010 DISL Dock -19.12 14.09

BC85 Blue Crab Muscle 10/10/2010 DISL Dock 15.9 201.1 F -19.71 12.16

BC86 Blue Crab Hepatopancreas 10/10/2010 DISL Dock -18.59 11.68

BC87 Blue Crab Muscle 10/10/2010 DISL Dock 14.2 120.4 F -17.36 12.72

BC88 Blue Crab Hepatopancreas 10/10/2010 DISL Dock -17.94 12.62

BC89 Blue Crab Muscle 10/10/2010 DISL Dock 14.5 183.1 F -16.79 11.09

BC90 Blue Crab Hepatopancreas 10/10/2010 DISL Dock -17.62 12.69

BC91 Blue Crab Muscle 10/10/2010 DISL Dock 15.6 179.4 F -18.37 9.79

BC92 Blue Crab Hepatopancreas 10/10/2010 DISL Dock -17.77 11.56

BC93 Blue Crab Muscle 10/10/2010 DISL Dock 16.6 162.8 F -21.98 12.57

BC94 Blue Crab Hepatopancreas 10/10/2010 DISL Dock -20.31 11.22

BC95 Blue Crab Muscle 10/10/2010 DISL Dock 13.7 111.6 F -22.76 12.28

BC96 Blue Crab Hepatopancreas 10/10/2010 DISL Dock -21.05 12.38

BC97 Blue Crab Muscle 10/19/2010 DISL Dock 14.7 155.6 F -18.25 12.94

BC98 Blue Crab Hepatopancreas 10/15/2010 DISL Dock -17.37 12.35

BC99 Blue Crab Muscle 10/15/2010 DISL Dock 17.9 198.5 F -17.69 14.36

66

BC100 Blue Crab Hepatopancreas 10/15/2010 DISL Dock -18.45 13.42

BC101 Blue Crab Muscle 10/15/2010 DISL Dock 14 127.2 F -20.17 9.28

BC102 Blue Crab Hepatopancreas 10/15/2010 DISL Dock -20.38 7.87

BC103 Blue Crab Muscle 10/15/2010 DISL Dock 14.9 160.1 F -19.08 11.4

BC104 Blue Crab Hepatopancreas 10/15/2010 DISL Dock -17.7 10.64

BC105 Blue Crab Muscle 10/15/2010 DISL Dock 15.8 209.4 F -19.76 11.95

BC106 Blue Crab Hepatopancreas 10/15/2010 DISL Dock -19.04 13.26

BC107 Blue Crab Muscle 10/18/2010 DISL Dock 13.6 131.4 F -18.45 10.62

BC108 Blue Crab Hepatopancreas 10/18/2010 DISL Dock -19.52 9.96

BC7 Blue Crab Muscle 9/17/2010 Fort

Morgan

16.3 178.4 F -22.27 11.16

BC8 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-20.14 10.35

BC9 Blue Crab Muscle 9/17/2010 Fort

Morgan

16.9 221.7 F -20.38 10.65

BC10 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-19.37 10.58

BC11 Blue Crab Muscle 9/17/2010 Fort

Morgan

15.7 151.4 F -19.83 10.68

67

BC12 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-17.33 10.11

BC13 Blue Crab Muscle 9/17/2010 Fort

Morgan

15.8 143 F -23.39 11.75

BC14 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-18.65 11.07

BC15 Blue Crab Muscle 9/17/2010 Fort

Morgan

15.4 161.1 F -18.71 11.68

BC16 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-19.48 11.08

BC17 Blue Crab Muscle 9/17/2010 Fort

Morgan

13.6 104 F -19.24 9.52

BC18 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-17.6 10.25

BC19 Blue Crab Muscle 9/17/2010 Fort

Morgan

15 170 F -20.51 11.5

BC20 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-18.48 11.05

BC21 Blue Crab Muscle 9/17/2010 Fort

Morgan

14.6 150.1 F -23.09 9.03

68

BC22 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-19.81 9.95

BC23 Blue Crab Muscle 9/17/2010 Fort

Morgan

13.8 113.2 F -18.02 9.09

BC24 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-16.96 9.4

BC25 Blue Crab Muscle 9/17/2010 Fort

Morgan

15 215.8 F -24.91 11.46

BC26 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-20.22 12.26

BC31 Blue Crab Muscle 9/17/2010 Fort

Morgan

13.1 92.2 F -23.41 11.84

BC32 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-18.54 12.8

BC33 Blue Crab Muscle 9/17/2010 Fort

Morgan

16.1 174.3 F -20.52 11.23

BC34 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-18.68 11.6

BC35 Blue Crab Muscle 9/17/2010 Fort

Morgan

14.9 127.3 F -23.7 11.84

69

BC38 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-18.3 11.6

BC39 Blue Crab Muscle 9/17/2010 Fort

Morgan

17 245.5 F -19.98 9.62

BC40 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-18.91 9.92

BC41 Blue Crab Muscle 9/17/2010 Fort

Morgan

16.4 184 F -17.44 11.69

BC42 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-17.25 10.84

BC43 Blue Crab Muscle 9/17/2010 Fort

Morgan

15.6 160.1 F -22.57 11.73

BC44 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-18.59 10.12

BC45 Blue Crab Muscle 9/17/2010 Fort

Morgan

13.6 111.9 F -17.57 11.76

BC46 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-17.18 9.86

BC47 Blue Crab Muscle 9/17/2010 Fort

Morgan

14.9 113.3 F -21.52 9.24

70

BC48 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-20.23 9.66

BC49 Blue Crab Muscle 9/17/2010 Fort

Morgan

15.4 140.3 F -23.66 11.03

BC50 Blue Crab Hepatopancreas 9/17/2010 Fort

Morgan

-19.53 10.78

BC111 Blue Crab Muscle 10/8/2010 Fowl River 15.2 234 M -23.08 11.36

BC112 Blue Crab Hepatopancreas 10/8/2010 Fowl River -22.36 9.53

BC113 Blue Crab Muscle 10/8/2010 Fowl River 13.7 197.2 M -23.66 11.36

BC114 Blue Crab Hepatopancreas 10/8/2010 Fowl River -23.72 10.36

BC115 Blue Crab Muscle 10/8/2010 Fowl River 19.8 311.8 M -24.65 12.33

BC116 Blue Crab Hepatopancreas 10/8/2010 Fowl River -24.24 10.52

BC117 Blue Crab Muscle 10/8/2010 Fowl River 17.6 319.8 M -23.91 11.48

BC118 Blue Crab Hepatopancreas 10/8/2010 Fowl River -24.54 10.4

BC119 Blue Crab Muscle 10/8/2010 Fowl River 13.5 186.1 M -24.91 11.9

BC120 Blue Crab Hepatopancreas 10/8/2010 Fowl River -25.13 10.94

BC121 Blue Crab Muscle 10/8/2010 Fowl River 15.5 249.4 M -23.85 11.53

BC122 Blue Crab Hepatopancreas 10/8/2010 Fowl River -24.37 10.8

71

BC123 Blue Crab Muscle 10/8/2010 Fowl River 14.4 196.7 M -22.92 11.73

BC124 Blue Crab Hepatopancreas 10/8/2010 Fowl River -23.57 10.96

BC125 Blue Crab Muscle 10/8/2010 Fowl River 12.8 153.7 M -24.44 11.1

BC126 Blue Crab Hepatopancreas 10/8/2010 Fowl River -25.37 9.07

BC127 Blue Crab Muscle 10/8/2010 Fowl River 13.6 137.2 M -23.03 12.34

BC128 Blue Crab Hepatopancreas 10/8/2010 Fowl River -24.27 9.84

BC129 Blue Crab Muscle 10/8/2010 Fowl River 16.9 239.6 M -23.32 11.49

BC130 Blue Crab Hepatopancreas 10/8/2010 Fowl River -22.72 9.21

BC131 Blue Crab Muscle 10/8/2010 Fowl River 16.5 256.4 F -23.38 11.6

BC132 Blue Crab Hepatopancreas 10/8/2010 Fowl River -24.41 10.28

BC133 Blue Crab Muscle 10/8/2010 Fowl River 16.8 235.7 F -23.16 11.26

BC134 Blue Crab Hepatopancreas 10/8/2010 Fowl River -23.48 10.22

BC135 Blue Crab Muscle 10/8/2010 Fowl River 15.2 170.1 F -21.54 12.94

BC136 Blue Crab Hepatopancreas 10/8/2010 Fowl River -22.97 12.74

BC137 Blue Crab Muscle 10/8/2010 Fowl River 15.4 161.5 F -23.04 12.36

BC138 Blue Crab Hepatopancreas 10/8/2010 Fowl River -23.73 11.31

BC139 Blue Crab Muscle 10/22/2010 Fowl River 14.8 162.2 F -23.67 11.49

72

BC140 Blue Crab Hepatopancreas 10/22/2010 Fowl River -24.8 9.68

BC143 Blue Crab Muscle 10/22/2010 Fowl River 16.1 159.8 F -26.42 11.56

BC144 Blue Crab Hepatopancreas 10/22/2010 Fowl River -26.54 10.58

BC145 Blue Crab Muscle 10/22/2010 Fowl River 17.1 193.7 F -23.8 10.7

BC146 Blue Crab Hepatopancreas 10/22/2010 Fowl River -24.98 10.34

BC147 Blue Crab Muscle 10/22/2010 Fowl River 16.2 237.8 F -23.9 11.52

BC148 Blue Crab Hepatopancreas 10/22/2010 Fowl River -24.76 9.6

BC149 Blue Crab Muscle 10/22/2010 Fowl River 16.9 199.4 F -23.81 11.46

BC150 Blue Crab Hepatopancreas 10/22/2010 Fowl River -24.23 10

BC151 Blue Crab Muscle 10/22/2010 Fowl River 17.1 192.5 F -24.72 11.75

BC152 Blue Crab Hepatopancreas 10/22/2010 Fowl River -24.76 10.1

BC155 Blue Crab Muscle 10/18/2010 Fowl River 15 174.9 F -23.2 11.63

BC156 Blue Crab Hepatopancreas 10/18/2010 Fowl River -23.81 10.24

BC157 Blue Crab Muscle 10/18/2010 Fowl River 14.2 169.9 F -23.38 10.88

BC158 Blue Crab Hepatopancreas 10/18/2010 Fowl River -22.95 9.99

BC159 Blue Crab Muscle 10/18/2010 Fowl River 17 224.7 F -22.14 9.58

BC160 Blue Crab Hepatopancreas 10/18/2010 Fowl River -23.12 10.07

73

BC161 Blue Crab Muscle 10/18/2010 Fowl River 15.9 217.7 F -22.2 12.76

BC162 Blue Crab Hepatopancreas 10/18/2010 Fowl River -22.82 11.49

BC163 Blue Crab Muscle 10/18/2010 Fowl River 12.8 105.9 F -23.91 10.71

BC164 Blue Crab Hepatopancreas 10/18/2010 Fowl River -23.99 9.65

BC165 Blue Crab Muscle 10/18/2010 Fowl River 13.1 119.4 F -23.24 12.36

BC166 Blue Crab Hepatopancreas 10/18/2010 Fowl River -23.55 10.6

BC167 Blue Crab Muscle 10/18/2010 Fowl River 15.8 232.1 F -23.51 12.08

BC168 Blue Crab Hepatopancreas 10/18/2010 Fowl River -22.96 10.34

BC169 Blue Crab Muscle 10/18/2010 Fowl River 15.1 208.8 F -23.54 12.48

BC170 Blue Crab Hepatopancreas 10/18/2010 Fowl River -23.02 11.68

BC171 Blue Crab Muscle 10/18/2010 Fowl River 17.5 265.4 F -25.12 12.25

BC172 Blue Crab Hepatopancreas 10/18/2010 Fowl River -23.45 10.41

BC53 Blue Crab Muscle 9/8/2010 Sand Island 15.6 156.3 F -22.84 9.77

BC54 Blue Crab Hepatopancreas 9/8/2010 Sand Island -21.21 10.45

BC55 Blue Crab Muscle 9/8/2010 Sand Island 16.2 171.7 F -19.22 11.85

BC56 Blue Crab Hepatopancreas 9/8/2010 Sand Island -18.46 9.94

BC57 Blue Crab Muscle 9/8/2010 Sand Island 16.7 153.4 F -20.96 10.06

74

BC58 Blue Crab Hepatopancreas 9/8/2010 Sand Island -19.79 10.06

BC59 Blue Crab Muscle 9/8/2010 Sand Island 13.7 108.1 F -18.05 9.6

BC60 Blue Crab Hepatopancreas 9/8/2010 Sand Island -17.05 10.29

BC61 Blue Crab Muscle 9/11/2010 Sand Island 15.1 189.2 F -19.54 10.99

BC62 Blue Crab Hepatopancreas 9/11/2010 Sand Island -18.71 10.52

BC63 Blue Crab Muscle 9/11/2010 Sand Island 16.1 198.7 F -25.12 11.34

BC64 Blue Crab Hepatopancreas 9/11/2010 Sand Island -21.06 9.05

BC65 Blue Crab Muscle 9/11/2010 Sand Island 14.6 166 F -25.06 11.25

BC66 Blue Crab Hepatopancreas 9/11/2010 Sand Island -23.49 10.35

BC67 Blue Crab Muscle 9/11/2010 Sand Island 16.6 209.7 F -18.94 12.06

BC68 Blue Crab Hepatopancreas 9/11/2010 Sand Island -18.64 11.15

BC69 Blue Crab Muscle 9/11/2010 Sand Island 16.9 176.6 F -22.66 11.07

BC70 Blue Crab Hepatopancreas 9/11/2010 Sand Island -21.24 9.95

BC71 Blue Crab Muscle 9/18/2010 Sand Island 15.8 199.8 F -23.16 11.5

BC72 Blue Crab Hepatopancreas 9/18/2010 Sand Island -22.74 9.01