Brown, Courtney - Biology 831F Manuscript Final Draft

Brown, Courtney BIOL 831E Spring 2014 2 May 2014 1

Influence of High Volume Human Populations on the Common Starfish, Asterias rubens

Courtney N. Brown, Department of Biology, University of Nebraska at Kearney, Kearney, NE 68849


ABSTRACT 1

The goal of this study was to examine the influence of high volume human populations 2

on the near-shore populations of the starfish species Asterias rubens, or the Common Starfish. 3

Specifically, the purpose of this study was to examine the relationship of human populations and 4

the arm damage that A. rubens incurs from these human populations. For two separate beaches 5

with similar conditions aside from human population, sixty-five A. rubens starfish were collected 6

from thirteen random, different feeding spots of pre-designated criteria. Five A. rubens 7

specimens were collected from each of these spots, including ones that had missing or damaged 8

arms. Arm lengths were measured from the center of the starfish to the outermost point of each 9

arm. These lengths were averaged for each A. rubens measured, and an overall average was 10

calculated. When compared statistically, the overall average arm length of the A. rubens at the 11

beach with the smaller human population was found to be significantly different than the overall 12

average arm length for the beach with the larger human population. These results suggest that 13

high volume human populations do influence the size of Asterias rubens in a beach setting. 14

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Key Words: Asterias rubens, arm damage, habitat, human interference, conservation 16

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INTRODUCTION 1

Disruption of a habitat by humans can cause lasting effect (Sano et al., 1987). Over time, 2

the more humans disturb a habitat, including that of starfish such as Asterias rubens, the less 3

food a species within that habitat will be able to obtain (Sano et al., 1987). As in all species, 4

when food supply is low many changes will occur (Vevers, 1949). Some of these changes may 5

be irreversible (Whilde, 1985). When the food supply diminishes, individual starfish size trends 6

smaller through time. (Menge, 1972). In addition, high levels of human impact cause physical 7

damage to the bodies of starfish, causing them to have to regenerate limbs (Ramsay et al., 2001). 8

While regeneration is one of the defining traits of starfish, continued regeneration will require 9

energy from the starfish that would be used differently if a specimen did not have to deal with so 10

much damage (Ramsay et al., 2001). Energy that would have gone toward reproduction or 11

hunting larger prey would have to go toward arm regeneration (Barker and Nichols, 1983). 12

Starfish that regenerate limbs multiple times due to constant damage can lose up to 40% of their 13

lipids and 85% of the amount of kilojoules in their pyloric caeca (Lawrence and Larrain, 1994). 14

While large, this loss of lipids and energy is not necessarily lethal for starfish (Lawrence et al., 15

1999). However, starfish with arms that are lost multiple times will have a lowered ability to feed 16

(Ramsay et al., 2001). Furthermore, a continuously damaged habitat on top of arm loss will 17

result in decreased size of the starfish, including misshapen or shorter limbs (Marrs et al., 2000). 18

Starfish arm regeneration is not a cost-free attribute for any starfish species (Bingham and 19

Burr, 2000). While this regenerative ability is helpful and allows starfish to escape many 20

potentially life-threatening situations (Ramsay et al., 2000), the starfish does trade a lot of energy 21

to regenerate a lost appendage (Bingham and Burr, 2000). This energy used for regeneration will 22

lower the ability of the starfish to reproduce (Bingham and Burr, 2000). Also, when starfish has 23


to regenerate arms more than normal, and it does not have enough energy to do this since it 1

cannot catch prey as well, the arms can come back shorter and not quite equal to the other arms 2

(Ramsay et al., 2001). However, starfish having a normal, pentameral symmetry is advantageous 3

to the organism (Wu et al., 2012). A starfish that has all five of its arms is best at autotomy, or 4

self-amputation, which gives it a better chance of escaping a deadly situation in comparison to 5

starfish that do not have that pentameral shape (Wu et al., 2012). In combination with autotomy, 6

starfish with five arms have an advantage in detection, turning over, and adherence versus those 7

with a different number of arms (Wu et al., 2012). 8

Humans influence the environment of starfish in more ways than one. For example, the 9

starfish caught by towed, bottom fishing gears are adversely affected as well as areas that were 10

subjected to different levels of fishing intensity (Ramsay et al., 2001). This does not only result 11

in arm loss that will result in regeneration as a means of repair (Ramsay et al., 2001). In an even 12

worse scenario, starfish will not lose the arm, but will have its ambularal ossicles damaged 13

(Ramsay et al., 2001). These little plates that cover the arm of starfish, when damaged, can cause 14

misshapen arms that do not heal (Ramsay et al., 2001). This type of damage can result in reduced 15

fitness and reduced ability to capture prey, which can result in reduced size and reduced arm 16

length (Ramsay et al., 2001). The continued, potentially severe damage often has more severe 17

repercussions than simply not being able to capture prey and reduced size. The starfish with 18

missing or damaged arms showed a 44 – 69% decrease in egg production seven months after arm 19

loss (Bingham and Burr, 2001). Even 19 months after the arm damage or arm loss occurred, 20

lowered egg reproduction was still evident (Bingham and Burr, 2001). It is estimated that even 21

normal arm damage, such as partial arm loss from a predator, can reduce the ability of a starfish 22

to reproduce by 7 – 10% (Bingham and Burr, 2001). 23


There are quite a few factors regarding starfish feeding and the specific prey starfish will 1

pursue (Menge, 1972). Some of these factors include the caloric content of the potential prey, 2

how easy the prey is to capture, and the size of the prey (Menge and Menge, 1974). While 3

starfish are typically food generalists, the type of prey they tend to search for is usually 4

influenced by the environment that they live in (Menge, 1983; Gallagher et al., 2008). If human 5

interactions with the environment of Asterias rubens has altered the environment or cause 6

excessive arm damage or arm removal at, then this species of starfish will have a difficulty 7

catching prey (Marrs et al., 2000). This includes being able to pry open bivalves (Marrs et al., 8

2000). In addition, starfish that are disfigured or constantly missing an arm will not be able to go 9

after the normal size of prey they have been known to seek (Marrs et al., 2000). 10

The major goal of this study is to determine if a beach with more human traffic 11

negatively impacts the size of starfish in a beach setting in comparison to a beach with much less 12

human traffic. Specifically, this study will examine the average arm length of the Common 13

starfish, Asterias reubens. A second goal is to examine conservation methods of near-shore 14

habitats of the Asterias reubens in regards to human interference. 15

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MATERIALS AND METHODS 17

Animals 18

All specimens used in this study are invertebrates of one starfish species, Asterias rubens. 19

Even though neither the Guide for the Use and Care of Laboratory Animals (NAS, 2011) nor a 20

review board will be needed for this study, it is a goal of this study not to damage any animals or 21

disturb their habitat. Sixty-five specimens of A. rubens will be obtained by hand from shallow 22

feeding spots less than a meter deep on both beach study sites. Feeding spots are defined as the 23


shallow, rocky tide pool areas found near the shores of both beaches. The species of starfish 1

being examined usually eats bivalves, but will eat small crustaceans and other echinoderms if 2

necessary in order to survive (Tuya and Duarte, 2012). All of these organisms exist in the 3

feeding spots along with A. rubens. To randomize the selection of the feeding spots, twenty-five 4

spots will be located and numbered before the study is conducted. The names of the spots will be 5

entered in Excel and, using the random function, thirteen spots will be chosen. Five specimens 6

will be carefully removed from each feeding area. Each specimen obtained will then have its 7

arms measured with a standard ruler. Natural rubber gloves will be worn to decrease contact with 8

the A. rubens. This will help to prevent any mishandling or dropping of the specimen due to 9

spines that can be irritating to touch. Specimens of A. rubens that do not have all of their legs 10

intact will still be measured so that results will not be incorrect or skewed. 11

No A. rubens will be permanently removed, sacrificed, or modified during the duration of 12

the study. Each specimen will be removed from its habitat, have its arms measured, and returned 13

to its original location. All arm measurements and weather conditions will be logged on custom 14

logbook sheets. 15

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Arm Length Average 17

Arms on each A. rubens will be measured and noted. The arm lengths will then be 18

averaged for each starfish. The arm of each starfish will be measured from the center of the 19

specimen to the tip of each arm. These averages will then be used for statistical analysis. 20

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Weather Conditions and Feeding Location Marking 22

Weather conditions will be monitored closely, recorded, and should be similar and close 23


to optimal conditions for the study on both beaches. Optimal conditions, in this study, would 1

mean no rain, an average humidity of 75% to 80%, an average wind velocity of 24.14 to 32.19 2

kph, and an average temperature of 23.85° to 25.85° Celsius for both beaches. Weather will be 3

recorded for both beaches each day the study is conducted. Specifically, temperature, humidity, 4

wind velocity, tide height, and tide speed will be measured in regards to weather. The study will 5

not be conducted in inclement weather, including thunderstorms of any severity. For records, 6

each A. rubens feeding spot will be noted in terms of latitude and longitude with a GPS receiver 7

– a Bushnell 360310BG Backtrack D-Tour. 8

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Statistical Analysis 10

The data will be tested for normality using the Shapiro-Wilks test. Provided that the data 11

collected is normal, it will be analyzed using the Student’s t-test. The level of significance will 12

be α = 0.05. This means that if the calculated p-value for average arm length is less than the 13

significance level, or p < 0.05, the null hypothesis of the average arm length of the starfish on the 14

two beaches no different will be rejected in favor of the alternative hypothesis. However, if the 15

data is shown to be non-normal, then the Wilcoxon rank-sum test can be used as an alternative to 16

a Student’s t-test. 17

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RESULTS 19

The data sets collected from both Wrightsville Beach, NC and Myrtle Beach, SC were 20

shown to be normal and have equal variances, allowing a Student’s t-test to be used to examine 21

the data. The overall average arm length of the Asterias rubens specimens that were collected 22

and measured from Wrightsville Beach, NC were significantly different (p=0.001) in comparison 23


to the overall average arm length of the Asterias rubens specimens that were collected and 1

measured from Myrtle Beach, SC (Wrightsville 8.77 + 1.28; Myrtle 8.09 + 1.06. The five 2

individual averaged arm lengths were larger for the Asterias rubens data set collected from 3

Wrightsville Beach, NC. 4

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DISCUSSION 6

The interference by humans on starfish habitats has been known to lead to increased 7

instances of arm damage and an overall reduction in size of starfish species over time 8

(Barthelemy, 1992). Anywhere up to 80 – 85% of the kilojoules of energy that Asterias rubens 9

stores can be used to regenerate lost limbs (Fan et al., 2005; Franco et al., 2012). If this energy 10

expenditure can lead to an overall reduction in size, normal prey such as the mussel Mytilus 11

edulis or other smaller species of starfish may become harder to catch by Asterias rubens (Allen, 12

1983; Dolmer, 1998). In addition, if arm damage occurs often and in multiple arms, prying 13

mussels open can become increasingly difficult for Asterias rubens (Anger et al., 1977; Jackson 14

et al., 2008). The observation of significant differences in overall Asterias rubens arm length on 15

the shores of Wrightsville Beach, NC and Myrtle Beach, SC suggests that interference from high 16

volume human populations does influence these arm length differences when other conditions 17

are similar. The beach with the larger human population, Myrtle Beach, had the smaller overall 18

arm length as well as smaller individual average arm lengths. This is consistent with the 19

observation that increased human interference, physical, mechanical, or otherwise, on starfish 20

populations correlates with increased damage to members of these populations (Kaiser, 1996; 21

Joly-Turquin et al., 2009). The larger the volume of a human population, the more damaged 22

limbs Asterias rubens seem to have. In addition, the observation in this study is consistent with 23


the observation that continued injuries to members of a starfish population will lead to an overall 1

decrease in size to cut back on the energy used to regenerate limbs. If Asterias rubens have limbs 2

that are smaller in general, less energy will be spent to regenerate those limbs after damage or 3

loss has occurred. 4

The ways high volume human populations influence arm lengths can upset the balance of 5

the ecosystem that exists in near-shore feeding spots as well. Since Asterias rubens cannot pry 6

open mussels or successfully prey on other starfish species if they are missing or have damaged 7

arms, this can lead to a number of problems involving the population control of other species 8

(Kamermans et al., 2009). Asterias rubens typically preys on and are most successful with 9

averaged sized mussels, not under or over sized ones (Norberg and Tedengren, 1995). If Asterias 10

rubens are not able to prey on mussels, such as Mytilus edulis, it can lead to that particular size 11

or species of mussel overcrowding a habitat and not allowing other, smaller species of mussels to 12

coexist with them (Yamada et al., 1992; Kulakovskii and Lezin, 1999; Reimer et al., 1999). Also, 13

if Asterias rubens cannot hunt smaller starfish or outcompete other starfish species in their 14

habitat, problems can still occur (Zeidler, 1992; Saier, 2001). Either situation would allow 15

another species of starfish to overpopulate a habitat and upset the balance of that habitat (Penney 16

and Griffiths, 1984). Asterias rubens can also be reduced in size enough or damaged enough to 17

become easier prey to more species (Aldrich, 1976). Other species in a habitat that are not 18

normally predators may become predators if Asterias rubens are reduced in size or are 19

continuously damaged (Arrontes and Underwood, 1991). Regardless of the main cause for 20

Asterias rubens not being able to obtain prey, mortality rates of this species if they are deprived 21

of a food source or have a harder time obtaining it (Paine, 1976; Bergmann and Moore, 2001). 22

The loss of the ability to prey on mussels is the biggest, since Asterias rubens need sterols to 23


function and mussels are a major source of them (Voogt and Rheenen, 1976). 1

It is important to try and limit the amount of damage dealt to Asterias rubens populations 2

by human interference. Asterias rubens can already face difficulty thriving by other 3

environmental changes, and human interference can only add to these problems (Guillou et al., 4

2012). Changes such as ocean acidification can suppress the immune system of Asterias rubens 5

(Hernroth et al., 2011). In addition, increased salinity can lead to decreased adhesive tenacity as 6

well as slowed or improper development in Asterias rubens (Saranchova and Kulakovskii, 1982; 7

Berger and Naumov, 1996). Environmental changes alone can lead to abnormal behavior in 8

Asterias rubens, such as retreating to deeper waters, since this species of starfish does not 9

tolerate environmental changes as well as other competitive starfish species (Smith, 1940; 10

Shulgina, 2006). Even sediment changes can lead to a change in the vertical distribution of 11

starfish (Kurihara, 1999). These environmental changes, coupled with human interference in 12

high levels, can lead to Asterias rubens that are very easy to damage or easily lose their limbs 13

(Rogers et al., 2001; Hotchkiss, 2008). At minimum, if this human interference is lowered, 14

Asterias rubens could face less amounts of damage or lost limbs. 15

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ACKNOWLEDGEMENTS 17

Thanks to Dr. Marc Albrecht for assistance with editing suggestions for this manuscript 18

and guidance throughout the entire research project it is based around and to the UNK 19

Department of Biology for technical assistance and the chance to design and carry out this 20

research project21


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Table 1. Averages for individual and overall arm length of collected Asterias rubens specimens from Wrightsville Beach, NC and Myrtle Beach, SC. _____________________________________________________________________________________ Arm 1 Arm 2 Arm 3 Arm 4 Arm 5 Overall Average Wrightsville (n=65) 8.75 + 1.49 8.79 + 1.40 8.77 + 1.50 8.82 + 1.46 8.74 + 1.56 8.77 + 1.28* Myrtle (n=65) 8.16 + 1.41 8.06 + 1.45 7.93 + 1.54 8.08 + 1.55 8.26 + 1.17 8.09 + 1.06* _____________________________________________________________________________________ Values in Table 1 are means + standard deviations. Arm lengths expressed in centimeters (cm). Starfish were measured from center to the tip of each arm, even if the arm had been damaged or removed. Starfish from each location were taken from randomly selected feeding spots of pre-determined criteria. Weather conditions for collection days were of pre-determined criteria and were similar for both beach collection sites. *When the overall average arm lengths are compared in a two-tailed t-test, the p-value = 0.001, which is less than the alpha level of α = 0.05.


Figure 1. Legend


Figure 1. Average arm length of individual arms of Asterias rubens collected from Myrtle Beach, SC and

Wrightsville Beach, NC. Arm lengths are measured in centimeters to the nearest tenth. Error bars are with

the standard deviation of each averaged arm length. n = 65 for each group and includes damaged or

missing arms.

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Brown, Courtney - Biology 831F Manuscript Final Draft