Impacts of upstream drought on downstream oysters in Apalachicola Bay

Laura E. Petes

NOAA Climate Program Office

Apalachicola Oysters

• 90% of oysters for state of Florida, 10% of oysters for U.S.

• Rapid growth rates and high reproductive output

• Adapted to brackish conditions (mix of fresh and salt water), natural timing of freshwater input

• Reefs provide complex habitat to fish and invertebrates

1909

Drought Effects on Bay

CP

DB

EB

CP=Cat Point, DB=Dry Bar, EB=East Bay

Feb. 20, 2007

http://drought.unl.edu/dm/monitor.html

Salinity in Apalachicola Bay

Data from ANERR

CP

DB

EB

Nov. 20, 2007

http://drought.unl.edu/dm/monitor.html

Salinity in Apalachicola Bay

Data from ANERR

CP

DB

EB

Mar. 28, 2008

http://drought.unl.edu/dm/monitor.html

Salinity in Apalachicola Bay

Data from ANERR

CP

DB

EB

Predictions of increased salinity on

oysters1.Reduced survival, growth, and condition of oysters;

increased prevalence of disease

2.Range expansion of marine predators (e.g. oyster drills)

Dermo Disease

• Protozoan parasite (Perkinsus marinus)

• Host-to-host transmission; waterborne infective stages abundant in summer

• Thrives in high salinity

• Can cause sublethal effects and mortality

Salinity Impacts on Oysters• Collected at Dry Bar; acclimated at ambient

salinity

• Randomized into 4 salinity treatments (9, 17, 25, 33 ppt)

• 10 large, 10 small oysters per tank

• Held at ambient temperature (15°C Winter; 25°C Summer) for 5 weeks

• Measured mortality and disease load

Mortality

Weighted Prevalence

None

Moderate

Conclusions

• High salinity (17-25 ppt) leads to oyster mortality

• High mortality from Dermo disease in Summer due in part to increased infection severity

Implications:

• Drought and reduced freshwater input will lead to more summer die-offs of oysters

• Consistent with field data (~50% mortality)

Predatory Oyster Drills

• Stramonita haemastoma (Florida rock snail)

• Direct fertilization; lay egg masses

• Common predators of oysters in the Panhandle

• Increase in number in Apalachicola Bay during periods of high salinity

Salinity Impacts on Predators

• Predation under different salinity treatments (9, 17, 25, 33 ppt)

• One oyster drill and five oysters per container

• Oyster mortality and source (predation vs. disease) quantified; dead oysters replaced daily

Predator Weight Gain

*All oyster drills in 9 ppt died within 48 hours!!!

Question: What are the effects of salinity on oyster drill hatching success?

Experimental Set-Up:

• Egg capsules separated and sorted into groups of 20

• Salinity treatments (9, 17, 25, 33 ppt)

• Hatching quantified weekly– Unhatched egg capsules white– Hatched egg capsules clear

Oyster Drill Hatching Success

Conclusions

• Oyster drills and their egg capsules have low tolerance for fresh water

Implications:

• Both predation and disease important drivers of mortality

• Freshwater input would limit predation

Implications for Watershed Management

Freshwater input is important for oysters due to:– Lowering disease-related mortality– Decreasing the number of oyster predators

Future studies should address timing and magnitude of freshwater releases necessary for oysters

Water resource and fishery management will become increasingly difficult with climate change

Acknowledgments

• FSU students: Alicia Brown, Carley Knight, Ryan Corley • Wakulla Co. teachers: Margy Callaghan, Russell Herron • FSUCML staff• ANERR staff• Virginia Institute of Marine Science