Disruption of Fish Reproduction in Hypoxic Coastal Waters: Potential Impacts on Coastal

Fisheries Worldwide

Peter ThomasUniversity of Texas at Austin

Hypoxia

Hypoxia – when dissolved oxygen ≤ 2.0mg/l, (~ 30% of normal oxygen levels), too low to support most marine life.

Anoxia – occurs when the bacteria use up the rest of the oxygen, suffocating even themselves.

Fresh water: lighter

Sea water: heavier

1.Stratification of water column ● oxygen in water column used by marine organisms, ● bottom layer cannot be re-oxygenated ● seasonal increase in oxygen consumption with temp., biomass increase

O2

Warmer water: lighter

Colder water: heavier

No mixing

Surface water

Bottom waterO2

plankton

How coastal hypoxic zones form

Fresh water: lighter

Sea water: heavier

2. Increased nutrient load- eutrophication ● plankton production increases● dead plankton and waste products fall into bottom layer ● bacteria digest dead organisms, waste – consuming

remaining O2

O2

No mixing

Surface water

Bottom waterO2

Nitrogen, phosphorous from fertilizers, etc.

Bacteria consume O2

O2

O2

O2

O2

How coastal hypoxic zones form

plankton

Global distribution of hypoxic systems associated with anthropogenic nutrient inputs

Diaz and Rosenberg, 2008. Science 321

● hypoxic regions have tripled in past 30yrs- Major Global Change

● over 400 coastal hypoxic regions worldwide, covering 250,000 km2

● Major concern Long term ecological impacts unknown

Assessment of long term effects of increased coastal hypoxia on marine ecosystems and fishery resources

• Necessary for the development of effective management strategies

• Requires knowledge of longterm biological effects of exposure to sublethal hypoxic conditions in marine organisms

• However, information lacking on hypoxia effects on physiological processes that affect fisheries stocks such as reproduction

Gonadal Function

Egg Production

GtH

vitellogenin

ER Liver function

E2

Brain

pituitary

Gonadotropin releasing hormone (GnRH)

Gonadotropin

PollutionDiseaseCapture

PhotoperiodTemperatureWater chemistry (pH) social

Environmental stimuli

Primary regulators Stressors

+ ve -ve

Control of the Reproduction in Fish

females

Sensitive stages:

● sex differentiation

● Puberty

● egg and sperm production and gonadal growth

● egg and sperm maturation, reproductive success

fecundity

Population Size

Hypoxia?

Gonadal Function

Egg Production

GtH

vitellogenin

ER Liver function

E2

control 2.7ppm 1.7ppm0

500

1000

1500

**

Vite

ll. ( µ

g/m

l) Vitellogenin

Control 2.7 ppm 1.7 ppm0.0

2.5

5.0

7.5

**E 2

(ng/

mL) Estrogen

Control 2.7 ppm 1.7 ppm0.0

2.5

5.0

7.5

10.0

* *GSI

Ovary growth

Laboratory studies: Effects of chronic hypoxia on egg production and endocrine function

Control 2.7ppm 1.7ppm0.0

2.5

5.0

7.5

10.0

*

GtH

(ng/

ml) GtH

Control 1.7 ppm0.0

0.5

1.0

1.5

2.0

***GnR

H I

mR

NA

leve

l

GnRH

GnRH

fecundity

Model predicts decreased population size

Control 2.7ppm 1.7ppm0

25

50

75

* *

Estrogen receptor

Rel

ativ

eER

1α

mR

NA

Control 2.7ppm 1.7ppm0

50000

100000

150000

200000

**

Egg production

Fecu

ndity

(egg

s/fis

h)

Estuarine Hypoxia: High rainfall in 2003 resulted in extensive and persistent hypoxia throughout East Bay, Florida

LA

Study areaFL

AL

SC

MS GA

5 km

30o20‘

87o00‘87o10‘

Pensacola Bay

Gulf of Mexico

Escambia Bay

Santa Rosa Sound

East Bay

N

S

W E

30o30‘

H4

N2N1

H3

H2

H1

DO HIF-10246

DO HIF-10246

DO HIF-10246

*

DO HIF-10246

*DO HIF-1

0246 *

DO HIF-10246

DO HIF-10246

*

TR

2 normoxic sites

4 hypoxic sites

Thomas et al., Proceedings of the Royal Society, London B. 2007

Question: Does environmental hypoxia exposure disrupt reproduction in Atlantic croaker?

P12 P13 P14 PB5 Trans Bridge PensaBay0

500

1000

1500

2000

1.3ppm 1.4ppm 1.9ppm 3.0ppm 1.2-4.8ppm 4.9ppm 4.6ppm

* compared to Bridge

* * * * *

Vite

lloge

nin

(µ g

/m)

hypoxic

normoxic

P12 P13 P14 PB5 Trans Bridge PensaBay0

500

1000

1500

2000

1.3ppm 1.4ppm 1.9ppm 3.0ppm 1.2-4.8ppm 4.9ppm 4.6ppm

* compared to Bridge

* * * * *

Vite

lloge

nin

(µ g

/m)

hypoxic

normoxichypoxic

normoxic

P12 P13 P14 PB5 Trans Bridge PensaBay0

100

200

300* compared to Bridge

* * **

*

Fecu

ndity

(100

0Vi

tello

geni

c eg

gs/fi

sh)

hypoxic

normoxic

vitellogeninfecundity

Similar to endocrine impairment seen in laboratory studies

H1 H2 H3 H4 TR N2 N 1 H1 H2 H3 H4 TR N2 N1

H1 H2 H3 H4 TR N2 N10

5

10

** * **

GSI

Hypoxia in Estuaries: Hypoxia exposure causes reproductive dysfunction in females

Ovary size

hypoxic normoxic

hypoxic

normoxicOvary Function

Oocyte Production

GtH

vitellogenin

E2 ERFunction

fecundity

egg production and endocrine function impaired at hypoxic sites

P12 P13 P14 PB5 Trans Bridge PensaBay0

1

2* compared to Bridge

* ** *

Site

plas

ma

11-K

T (n

g/m

l)

hypoxic

normoxic

P 12 P 13

P 14

P B5

Tran

s

Brid

ge

Pens

aBa

y

hypoxia

normoxic

rela

tive

sper

m p

rodu

ctio

n

Plasma 11-KTSperm production

H1 H2 H3 H4 TR N2 N1

P12 P13 P14 PB5 Trans Bridge PenBay0

1

2

3

4

5

* * **

GSI

P12 P13 P14 PB5 Trans Bridge PenBay0

1

2

3

4

5

* * **

GSI

H1 H2 H3 H4 TR N2 N1

Hypoxia in Estuaries: Hypoxia exposure also causes reproductive dysfunction in males

hypoxicc normoxic

Spermatogenesis impairedTestis size

H1 H2 H3 H4 TR N2 N1

1st evidence for reproductive /endocrine impairment in fish exposed to environmental hypoxia

Question:Does large scale hypoxia cause similar reproductive impairment in fish in the Gulf of Mexico hypoxic zone covering 1000s of square miles

- much greater potential impact on fisheries

Mississippi-Atchafalaya Drainage Basin• “top 10”river flow- stratification

• drains 41% of continental US

• Nitrogen loading tripled since 1950s

eutrophication

Hypoxia in the northern Gulf of Mexico

1989

1990

1993

1994

1995

1997

1989

1990

1993

1994

1995

1997

Mapping since mid 1980’s:increased from 5,000 km2 - 16,000 km2

Dissolved oxygen ≤ 2.0 mg

2nd largest coastal hypoxic zone in the world

Dissolved oxygen ≤ 2.0 mg

CTL

normoxic

Hypoxic from late spring until mid September

Hypoxic region on Louisiana continental shelf- 2006-2008

CF

In fall 2007 : 3 control sites and 6 hypoxic sites along two transects 120km apart were sampled

hypoxic zone sites

Normoxic sites

TestisOvary

hypoxic zone sites

Normoxic sites

Fall 2007 Croaker gonads undeveloped at hypoxic sites

Gonadal growth impaired at hypoxic sites in both females and males

CTL-1CTL-2CTL-3 C-5 C-6 C-7 F-3 F-4 F-50

2

4

6

8

Normoxic

hypoxic until 2 wks before

Sampling Sites

Ova

rian

dev

elop

men

t(G

SI)

Ovarian growth Testicular growth

CTL-1CTL-2CTL-3 C-5 C-6 C-7 F-3 F-4 F-50

1

2

3

4 Normoxic

hypoxic zone sites

Sampling Sites

Test

icul

ar d

evel

opm

ent

(GSI

)

** **

Fall 2007

Thomas & Rahman, Proceedings of the Royal Society, London B. 2011

zone sites

Normoxic site C transect F transect

2007,2008 Reproductive impairment in males at hypoxic sites

CTL1CTL2CTL3 C-5 C-6 C-7 F-3 F-4 F-50

25

50

75

acac

bc

a

b bb bbc

*

DO (mg/L) 4.1 5.2 4.8 5.5 4.3 4.5 6.1 5.9 6.2Sampling Sites

Normoxic 2 weeks before hypoxic

Ralat

ive sp

erm

pro

. (%

)

CTL CTL CTL C C C F F F

Spermatogenesis and sperm production decreased at hypoxic zone sites

Sperm production

Hypoxic zone sites

normoxic

Reproductive impairment in females at hypoxic sites

Normoxic site C transect F transect

2007hypoxic zone sites

Very few mature eggs (low fecundity) at hypoxic zone sitesCTL1CTL2CTL3 C5 C6 C7 F3 F4 F5

0

10

20

30

40

50Normoxic

2 weeks before hypoxicFecu

ndity

(103 e

ggs/

fish)

Large eggs> 350 μm

fecundity

Hypoxic zone sites

CTL1CTL2CTL3 C5 C6 C7 F3 F4 F50

1

2

3

***

aac

a

abbcab ab ab ab

*Nested ANOVAa-cFisher's PLSD test

GnR

H m

RN

A le

vels

CTL

-1

CTL

-2

CTL

-3 C5

C6

C7 F3 F4 F5

0

1

2

3

ac aa

b b bbc

b b

******P<0.001, Nested ANOVA;

a-cFisher's PLSD test

Rel

ativ

e ER

α m

RN

A le

vels

Ovary Function

Oocyte Production

GtH

vitellogenin

E2

Fall 2007 Endocrine function decreased at hypoxic sitesGnRH

CTL-1CTL-2CTL-3 C-5 C-6 C-7 F-3 F-4 F-50

1

2

3

aac ac

bb

bc

bb b

*

DO (mg/L) 4.1 5.2 4.8 5.5 4.3 4.5 6.1 5.9 6.2Sampling Sites

2 weeks before hypoxic

Plas

ma

VTG

leve

ls (m

g/m

L)

GnRH mRNA

ER Liver

Function

ER mRNAvitellogenin

fecundity

Reproductive impairment due to endocrine disruption at hypoxic sites

Some ovaries from hypoxic zone sites contain spermatogenic cells:

Suggests masculinization under hypoxic conditions

2006, 2007 Evidence for Ovarian Masculinization

Percent ovaries masculinized

Suggests masculinization caused by hypoxia exposure

0

25

50

75

14%24%

Year

200

6

Year

200

7

Inte

rsex

fish

(%)

Field Studies

Con

trol

Hyp

oxia

Rec

over

y

25.0% 27.6%

Lab. experiments

Con

trol

Hyp

oxia

Rec

over

y

25.0% 27.6%

Lab. experiments

How does hypoxia cause the croaker ovary to produce sperm?

Ovary Function

Egg Production

GtH

vitellogenin

Estrogen ERLiver Function

fecundity

Egg production

Androgens (testosterone)

Enzyme: aromataseSperm production

sperm

HYPOTHESIS: HYPOXIA

CTL

-1

CTL

-2

CTL

-3

C-5

C-6

C-7 F-3

F-4

F-50

1

2

3

***

ac ac

a

bc

b b

bc

bbOva

rian

AR

OM

mR

NA

leve

ls hypoxic zone

normoxic

Aromatase mRNA levels in females

Aromatase, decreased expression at hypoxic sites- could be related to masculinization

2007 field studiesLab study-ovaries

Control Hypoxia0

1

2

3

*Aro

mat

ase

mR

NA

leve

lsControl Hypoxia

0

10

20

30

40

50

Aro

mat

ase

activ

ity(p

mol

/mg

prot

ein/

h)

*

Arom. mRNA

Arom. activity

N1 N2 N30

25

50

75

100

-----------------------

52% males

Prop

ortio

n of

mal

e (%

)

N1N2

N3

C5C6

C7

F3F4

F5

A D BC

M

L J EH

IGF

K

A

B

CE

F

GH

IJ

K

L

M

NO P

Q R

29°00?

Gulf of Mexico

LA MS

89°00?90°00?91°00?92°00?

Hypoxic zone

89°00?90°00?91°00?92°00?

D

N

A B C D E F G H I J K L M0

25

50

75

100

-----------------------------------------------------------

N1N2

N3

C5C6

C7

F3F4

F5

A D BC

M

L J EH

IGF

K

A

B

CE

F

GH

IJ

K

L

M

NO P

Q R

29°00?

Gulf of Mexico

LA MS

89°00?90°00?91°00?92°00?

Hypoxic zone

A B C D E F G H I J K L M N O P Q R0

25

50

75

100

50% males

-------------------------

------------------------------------------------

89°00?90°00?91°00?92°00?

D

N

Our samples Louisiana fisheries NOAA SEAMAP

Consistent male bias in sex ratio in fish from hypoxic zone

Sex ratio of Atlantic croaker

58% males 63% males61% males

east west

Conclusions: hypoxia field studies in northern Gulf of Mexico

• Egg and sperm production, endocrine function greatly impaired in both male and female croaker at hypoxic sites 120km apart, ~ 3-4000km2

• Evidence for intersex -masculinization of female gonads; male skewed sex ratio

• Results support hypothesis: hypoxia in the northern Gulf of Mexico significantly decreases egg and sperm production in croaker

Funded by NOAA NGOMEX research program

Potential Long-term Effects of Hypoxia-induced Decline in Reproductive Output on Fish Population Size.

Determining long term effects difficult

- Population affected by multiple factors that vary together and have interactive effects

-Separation of hypoxia effects from other factors is difficult. e.g fishing by catch

Population Modeling is a valuable approach

Modeling allows for systematic evaluation of multiple factors in a controlled world

Year of Simulation

0 20 40 60 80 100

Tota

l Abu

ndan

ce (m

illion

s)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8Baseline10 % Louisiana25 % Louisiana50% Louisiana

Rose et al. (2009) JEMBE

Modeling Results 1- Predicted Decline in Louisiana Population Size if 25-50% Croaker Exposed to Hypoxia

Average age 2+ abundance for model years 61-100 ranged from 81-83% of baseline abundance (17-19% reduction)

Modeling 2- A Second Model also Predicts a Decline in Croaker Population Size—Dr. Kenneth Rose

- Less dramatic decline than predicted in other simulation

Does Increased Hypoxia in Coastal Regions Threaten Fishery Stocks over the Long-term ?

-Most extensive study conducted on a coastal fish species, croaker, predicts long-term population decline.

-Hypoxia-induced reproductive impairment has been observed in other aquatic species. But information lacking on reproductive effects on coastal marine species.

- Difficult to detect hypoxia effects on size of fish populations from current stock assessments. Relevant data lacking. Clear evidence for a few fisheries.

Conclusion: Critical to examine commercially important marine fish in other coastal hypoxic regions worldwide for evidence of reproductive impairment in order to predict the long-term population effects