Disruption of Fish Reproduction in Hypoxic Coastal Waters: Potential - - PowerPoint PPT Presentation

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

Peter Thomas University 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 water O2 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 water O2 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

• rganisms
• 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 Pollution Disease Capture Photoperiod Temperature Water 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 1.7ppm 500 1000 1500

* *

• Vitell. (µg/ml)

Vitellogenin

Control 2.7 ppm 1.7 ppm 0.0 2.5 5.0 7.5

* *

E2 (ng/mL)

Estrogen

Control 2.7 ppm 1.7 ppm 0.0 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 1.7ppm 0.0 2.5 5.0 7.5 10.0

*

GtH (ng/ml)

GtH

Control 1.7 ppm

0.0 0.5 1.0 1.5 2.0

***

GnRH I mRNA level

GnRH GnRH fecundity

Model predicts decreased population size

Control 2.7ppm 1.7ppm 25 50 75

* *

Estrogen receptor

Relative ER1 α mRNA

Control 2.7ppm 1.7ppm 50000 100000 150000 200000

* *

Egg production

Fecundity

(eggs/fish)

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

LA Study area FL 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 N2 N1 H3 H2 H1

DO HIF-1 2 4 6 DO HIF-1 2 4 6 DO HIF-1 2 4 6

*

DO HIF-1 2 4 6

*

DO HIF-1 2 4 6

*

DO HIF-1 2 4 6 DO HIF-1 2 4 6

*

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 PensaBay 500 1000 1500 2000

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

* compared to Bridge

*

*

* * *

Vitellogenin ( µg/m)

hypoxic normoxic

P12 P13 P14 PB5 Trans Bridge PensaBay 500 1000 1500 2000

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

* compared to Bridge

*

*

* * *

Vitellogenin ( µg/m)

hypoxic normoxic

hypoxic normoxic

P12 P13 P14 PB5 Trans Bridge PensaBay 100 200 300

* compared to Bridge

* * * *

*

Fecundity (1000 Vitellogenic eggs/fish)

hypoxic normoxic

vitellogenin fecundity 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 N1 5 10

*

*

*

* *

GSI

Hypoxia in Estuaries: Hypoxia exposure causes reproductive dysfunction in females

Ovary size hypoxic normoxic

hypoxic normoxic

Ovary Function Oocyte Production

GtH

vitellogenin E2 ER Function fecundity

egg production and endocrine function impaired at hypoxic sites

P12 P13 P14 PB5 Trans Bridge PensaBay 1 2

* compared to Bridge

* * * *

Site plasma 11-KT (ng/ml)

hypoxic

normoxic

P 12 P 13 P 14 P B5 Trans Bridge Pensa Bay

hypoxia normoxic relative sperm production

Plasma 11-KT Sperm production

H1 H2 H3 H4 TR N2 N1

P12 P13 P14 PB5 Trans Bridge PenBay

1 2 3 4 5

* * * *

GSI

P12 P13 P14 PB5 Trans Bridge PenBay

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 impaired

Testis 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

C F

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

hypoxic zone sites Normoxic sites

Testis Ovary

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-5 2 4 6 8

Normoxic hypoxic until 2 wks before

Sampling Sites

Ovarian development (GSI)

Ovarian growth Testicular growth

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

1 2 3 4 Normoxic hypoxic zone sites

Sampling Sites

Testicular development (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-5

25 50 75 ac ac bc a b b b b bc

*

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

Normoxic 2 weeks before hypoxic

Ralative sperm 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

2007

hypoxic zone sites Very few mature eggs (low fecundity) at hypoxic zone sites

CTL1 CTL2 CTL3 C5 C6 C7 F3 F4 F5

10 20 30 40 50

Normoxic 2 weeks before hypoxic

Fecundity (103 eggs/fish)

Large eggs> 350 μm fecundity

Hypoxic zone sites

CTL1CTL2CTL3 C5 C6 C7 F3 F4 F5

1 2 3

***

a ac a ab bc ab ab ab ab

*Nested ANOVA

a-cFisher's PLSD test

GnRH mRNA levels

CTL-1 CTL-2 CTL-3 C5 C6 C7 F3 F4 F5

1 2 3

ac a a b b b bc b b

***

***P<0.001, Nested ANOVA;

a-cFisher's PLSD test

Relative ERα mRNA levels

Ovary Function Oocyte Production

GtH

vitellogenin E2

Fall 2007 Endocrine function decreased at hypoxic sites

GnRH

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

1 2 3 a ac ac

b b bc b b b

*

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

2 weeks before hypoxic

Plasma VTG levels (mg/mL)

GnRH mRNA

ER Liver Function ER mRNA vitellogenin 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

25 50 75 14% 24% Year 2006 Year 2007

Intersex fish (%)

Field Studies

Control Hypoxia Recovery

25.0% 27.6%

• Lab. experiments

Control Hypoxia Recovery

25.0% 27.6%

• Lab. experiments

How does hypoxia cause the croaker ovary to produce sperm?

Ovary Function Egg Production

GtH

vitellogenin Estrogen ER Liver Function fecundity Egg production Androgens (testosterone) Enzyme: aromatase Sperm production sperm

HYPOTHESIS: HYPOXIA

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

1 2 3

***

ac ac a bc b b bc b b

Ovarian AROM mRNA levels

hypoxic zone normoxic

Aromatase mRNA levels in females

Aromatase, decreased expression at hypoxic sites- could be related to masculinization 2007 field studies

Lab study-ovaries

Control Hypoxia 1 2 3

*

Aromatase mRNA levels

Control Hypoxia 10 20 30 40 50

Aromatase activity

(pmol/mg protein/h)

*

• Arom. mRNA
• Arom. activity

N1 N2 N3

25 50 75 100

• 52% males

Proportion of male (%)

N1 N2 N3 C5 C6 C7 F3 F4 F5

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

25 50 75 100

• N1

N2 N3 C5 C6 C7 F3 F4 F5

A D B C M L J E H I G F K A B C E F G H I J K L M N O 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 R

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% males 61% 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

20 40 60 80 100

Total Abundance (millions)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 Baseline 10 % Louisiana 25 % Louisiana 50% 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
• ther aquatic species. But information lacking on reproductive effects
• n 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