Donald M. BaltzDenise L. BreitburgLouis E. BurnettJohn F. CaddyEdward J. ChesneyDaniel J. ConleyJ. Kevin CraigLarry B CrowderMary Beth DeckerRobert J. DiazQuay DortchJohn W. FleegerWilliam M. Graham Charlotte D. GrayJames G. HanifenDonald E. Harper, Jr.Tyrrell A. HenwoodAlf B. JosefsonDubravko JustićWalter R. Keithly, Jr.Sarah E. Kolesar

Carrie J. McDanielNancy H. MarcusJames N. NanceLeif PihlEmil PlatonSean P. PowersJennifer PurcellNaureen Azia QureshiNancy N. RabalaisKevin A. RaskoffRutger RosenbergBarun K. Sen GuptaJoseph W. SmithLorene E. SmithWilliam B. StickleR. Eugene TurnerJohn M. WardMarkus A. WetzelMarsh J. YoungbluthRoger J. Zimmerman

2001

SYNTHESIS

1. Increased nutrient loading results in increased incidence or size of hypoxia2. Behavioral and physiological responses to hypoxia by individual organisms

a) nektonb) zooplanktonc) epibenthosd) benthic organisms

3. Benthic community response to hypoxia4. Commercial fisheries species response to hypoxia

a) menhadenb) shrimpc) other large nekton

5. Sea turtle and marine mammal responses to hypoxia6. Food web responses to hypoxia or to causes of hypoxia

a) by primary producer communityb) by secondary producer or higherc) jellyfish

7. Officer and Ryther's [1980] prediction supported (regarding Si:N loading ratio)8. Evidence for rapid decline in resource after period of gain (a catastrophic decline)9. Societal recognition of the effects of hypoxia on fisheries

a) recognize possible effectsb) implemented management to reduce nutrient loading

Shifts from Heavily Silicified Diatoms

To LighltySilicified Diatoms

& Non-Silicified, Flagellates

Evidence of Increased Diatom production, as N ↑Evidence of Silica Limitation, as Si↓ & Si:N of 1:1

(Turner & Rabalais 1994;Turner et al. 1998;Dortch et al. 2001)

Si:N>1+1

<1

PhytoplanktonSinking Diatoms

Non-sinking DiatomsNon-DiatomsNon-Diatoms

Non-sinking Diatoms

ConsequencesPersistent HypoxiaSeasonal Hypoxia

Sporadic Harmful Algal BloomsFrequent Harmful Algal Blooms

Algal Blooms

0

25

50

75

100

0

25

50

75

100

0

25

50

75

100

0

25

50

75

100

Surf.

6 m

14 m

Bott.

Mar

Apr

May Jun

Jul

Aug Se

p

Others

Meroplankton

Chaetognaths

Larvaceans

Cop Nauplii

Copepods

(Qureshi & Rabalais 2001)

MarAprMayJun Jul AugSep Surf.6m

14mBott.0

100200300400500600

MarAprMayJun Jul AugSep Surf.6m

14mBott.0

50100150

200

250

Copepods

CopepodNauplii

Month*Depth

Num

ber/L

iter

Num

ber/L

iter

Month* Depth*

(Qureshi and Rabalais 2001)

RF2 C

8

D2A

-2 D21

C6B

4

C6B

5 C9

D2A

3 D6 C7

C6B

1

C11

B D'3 E2

Surf.Abv-PycnBlw-Pycn

Bott.

0

200

400

600

800

1000

1200

1400

Num

ber/L

iter

Copepod Nauplii

0.05-0.7mg/L

1.8-2.3mg/L

2.9-3.5mg/L

(Qureshi and Rabalais 2001)

Aurelia moon jelly 1995

1987

Jellyfish abundance:

an indicator of altered food

webs

Source: M. Graham, DISL

Jellyfish abundance: an indicator of altered

food webs

0 1 2 3 4 50.0

0.2

0.4

0.6

0.8

1.0

0 1 2 3 4 50.0

0.2

0.4

0.6

0.8

1.0

0 1 2 3 4 50.0

0.2

0.4

0.6

0.8

1.0

Bottom Water Dissolved Oxygen (mg/l)

Prop

orti o

nal D

ensi

ty

i n B

ott o

m L

ayer

Copepods Chrysaora

Mnemiopsis

(Purcell et al. 2001)

TABLE 1. Behavioral and physiological responses of different organisms to hypoxia.

Organism

Response to Hypoxia

Reference

Shrimp Penaeus aztecus Penaeus setiferus Penaeus monodon

detect and avoid detect and avoid decrease hemocyte

phagocytosis

Renaud, 1986 Renaud, 1986 Direkbusarakom & Danayadol, 1998

Penaeus stylirostris

decrease total hemocyte count increased mortality induced

by Vibrio alginolyticus

Le Moullac et al., 1998 Le Moullac et al., 1998

Crabs Callinectes sapidus

detect and avoid decrease feeding reduce growth rate Acute Hypoxia increase ventilation rate increase heart rate slight increase in cardiac output Chronic Hypoxia decrease oxygen consumption no change in ventilation no change in heart rate increase hemocyanin O2

affinity and concentration

Das & Stickle, 1994 Das & Stickle, 1993 Das & Stickle, 1993 Batterton & Cameron, 1978 deFur & Pease, 1988 deFur & Pease, 1988 Das & Stickle, 1993 deFur & Pease, 1988 deFur & Pease, 1988 deFur et al., 1990

Callinectes similis

detect and avoid increase oxygen consumption decrease feeding

Das & Stickle, 1994 Das & Stickle, 1993 Das & Stickle, 1993

Gastropod Molluscs Stramonita haemastoma

reduce growth rate large reduction in metabolism decrease oxygen consumption

Das & Stickle, 1993 Liu et al., 1990 Das & Stickle, 1993

Bivalved Molluscs Crassostrea virginica

switch to anaerobic metabolism small reduction in metabolism decrease production of

reactive oxygen species

Stickle et al., 1989 Stickle et al., 1989 Boyd & Burnett, 1999 (Burnett and Stickle 2001)

NektonDemersalinverte-brates

Epibenthicinverte-brates

Larger infauna

Macro-infauna

2.0

1.5

1.0

0.5

0.20.05

Most present

Absent

Most present

Few mantis & penaeid

shrimp

Absent

Present Present & burrowed

Stressed(starfish,

brittle stars)

Present & burrowed

Dead Stressed(anemones, gastropods)

Dead

Bacterial mats

Anoxic sediment, H2S in sediment and water

2.0

1.5

1.0

0.5

(mg

O2

l-1)

(fish kills)Dead

0.20.05

(mg

O2

l-1)

Moribund polychaetes

(Rabalais, Harper & Turner, 2001)

(Rabalais et al., 2001)

Severe Hypoxia 1990, C6A

02468

6 7 8 9 10

D.O

. mg/

L

Month

Mean No. of Individuals/m2

109 8 7 6 5 4 0

2000

4000

6000

8000

10000

12000

Mediomastus ambisetaParaprionospio pinnataAmpharete sp. A Magelona sp. HOwenia fusiformisAspidosiphon sp.Clymenella torquata

4 6 7 8 9 100

50

Number of Species

Polychaeta

100

150

NemerteaBivalviaGastropodaCrustaceaOphiuroideaSipunculaOther

Characteristics of Louisiana Shelf Benthos Subjected to Seasonally

Severe Hypoxia• Reduced species richness• Severely reduced abundances (but never azoic)• Low biomass• Limited taxa (none with direct development)• Characteristic resistant infauna (e.g., a few

polychaetes and sipunculans)• Limited recovery following abatement of oxygen

stress

(Rabalais et al., 2001b)

Severe hypoxia Normoxic Order/Genus Settlement Traps Sediment Settlement Traps Sediment Enoplida Dolicholaimus • — — — Halalaimus • — — • Nemanema — — — • Oncholaimus • — — — Viscosia • — — — Chromadorida Cyartonema • — — • Leptolaimus — — — • Microlaimus • — — — Neochromadora • — — — Paracanthonchus • — — • Prochromadorella • — — — Pselionema • — — — Sabatieria — — — • Spirinia • — — — Synonchiella • — — — Monhysterida Ascolaimus — — — • Cobbia • — — — Daptonema • •a — • Metadesmolaimus • — — — Odontophora • — — • Sphaerolaimus • — — — Terschelingia • — — • Parodontophora • — — —

a represented by a single specimen

Nematodes were often collected (in settlement traps) from the water column above hypoxic or anoxic sediments

In normoxic conditions, they were found in the sediments.

(Wetzel et al. 2001)

•Most benthic recruitment is via meroplanktonic larvae.

•Amphipods and harpacticoid copepods rely on direct development and are characteristically absent from hypoxic areas.

•Benthic polychaete larvae are distributed throughout the water column regardless of low oxygen conditions.

•Paraprionospio pinnata, delayed settlement and remained in the water column until oxygen values returned to a level above 2.0 mg l-1.

•Barnacle cyprid larvae and holoplankton (e.g., chaetognaths) were reduced in densities below the pycnocline when oxygen concentrations were low.

•Species composition and abundance of organisms in the sediment reflected patterns of pelagic larval abundance.

•The supply of meroplanktonic larvae appears to determine the recovery population.

•Recovery of pericarideans, molluscs and echinoderms takes longer.

Farfantepenaeusaztecus

Brown Shrimp

Distance (km)20 40 60 80 100

Jan Feb Mar A

pr May Jun Jul A

ug Sep Oct N

ov Dec

100 Dep

th (m

)

spawning

spawning

postlarval

recruitment

emigration

(source: N. Rabalais, LUMCON)

Distance (km)20 40 60 80 100

Jan Feb Mar A

pr May Jun Jul A

ug Sep Oct N

ov Dec

100

spawning

postlarval

recruitment

emigrationD

epth

(m)

Litopenaeus setiferusWhite Shrimp

9590858075706560600

10

20

30

40

50

60

70

80

90

Year

Kilo

gram

s pe

r Hou

r

y = 137.04 - 0.97418x R^2 = 0.223

y = 69.224 - 0.10401x R^2 = 0.002

Roger J. Zimmerman and James M. Nance, 2001, Effects of Hypoxia on the Shrimp Fishery of Louisiana and Texas, 293-310 in N. N. Rabalais and R. E. Turner (eds.), Coastal Hypoxia: Consequences for Living Resources and Ecosystems. Coastal and Estuarine Studies 58, American Geophysical Union, Washington, D.C.

Figure 7. Trend in annual brown shrimp catch per unit effort (CPUE) from Texas and Louisiana from 1960 through 1998.

200001500010000500000

2000

4000

6000

8000

10000

12000

14000

Louisiana White ShrimpLouisiana Brown ShrimpLouisiana/Texas White ShrimpLouisiana/Texas Brown Shrimp

Hypoxia Area(Millions of Square Meters)

Met

ric T

ons

(tails

)y = 1756.2 - 2.5002e-2x R^2 = 0.062y = 3685.9 - 4.9392e-2x R^2 = 0.209y = 2107.4 - 1.5425e-2x R^2 = 0.021

y = 1.0910e+4 - 0.16224x R^2 = 0.400

Figure 6. July and August brown shrimp catch from Texas and Louisiana versus relative size of the hypoxic zone on the Louisiana shelf during the years from 1985 through 1997.

Roger J. Zimmerman and James M. Nance, 2001, Effects of Hypoxia on the Shrimp Fishery of Louisiana and Texas, 293-310 in N. N. Rabalais and R. E. Turner (eds.), Coastal Hypoxia: Consequences for Living Resources and Ecosystems. Coastal and Estuarine Studies 58, American Geophysical Union, Washington, D.C.

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SSSS SSSSSSSSSSSS ## #SSSSSS #

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S

Tx. La.Ms. Al.

0.0

20.0

40.0

60.0

80.0

100.0

0.0-2.0 2.0-5.0 >5.0

Dissolved oxygen (mg/l)

% A

rea

0.0

100.0

200.0

300.0

400.0

500.0

Mea

n C

PUE

(kg/

h)

% areamean CPUE

#

Ñ

Ñ

ÑÑ

#####

#########

#########

#

#

#

Ñ $

%

Ñ

$#

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19931992

Tx. La.

Ms. Al.

0 100 200 300 Kilometers

Summer 1993 HypoxiaSummer 1992 Hypoxia

Turtle Sightings ' Kemp's Ridley# Loggerhead% Green$ LeatherbackÑ Unid. hardshell

(Craig et al. 2001)

River discharge ↓Salinity in nursery area ↑Preferable nursery habitat for brown shrimp ↑Less hypoxia ↓Suitable habitat for brown shrimp offshore ↑

River discharge ↑Salinity in nursery area ↓Preferable nursery habitat for brown shrimp ↓More hypoxia ↑Suitable habitat for brown shrimp offshore ↓

…and the ultimate predator

Source: N. N. Rabalais, LUMCON

(Downing et al. 1999)

Gulf of Mexico shrimp landings (annual)and the area of wetland in each estuary (Turner, 1977)

Intact marsh

Increased edge

Open water

Shr

imp

yiel

d

Trajectory of Wetland DeteriorationPhotos: N. N. Rabalais, LUMCON

•Fishery yields have remained strong for the northern Gulf over the last 40 years. But….

•Menhaden production in years with widespread hypoxia were lower (log book analysis). (Smith 2001)

•Effects of hypoxia on distributions of nekton. (Several authors)

•Pattern of pelagic species becoming more abundant and some dominant demersal species declining in prominence within trawl bycatch, particularly between the 1930s and 1989. (Chesney and Baltz 2001)

•Other effects on nekton are probable.

•Other impacts of greater magnitude may have more significant effects than hypoxia on the community structure and secondary production of nekton.

•The effects of hypoxia on the nekton in the northern Gulf may be buffered by characteristics of the basin, the fauna and the ecosystem. These characteristics may partially offset some of the negative impacts of hypoxia seen in other systems by providing spatial and temporal refuges for demersalnekton.

• Many of the behavioral responses prey and predators to hypoxia documshelf are consistent with those in other areas.

• These developments are observed in many other coastal ecosystems, to lesser or greatersubstantially or distin

• The species may be different anduration may vary among regions, but these broadly described patterns are familiar patterns foincluding the Baltic, Black Sea an

of invertebrate and vertebrate ented for the Gulf of Mexico

degrees of detail, but in no ctly different ways.

d the degree of hypoxia or

r many stressed ecosystems, d the northern Gulf of Mexico.

2001

SUMMARY