Differences in the gaping response and hemolymph pH of the eastern oyster

Crassostrea virginica and the Asian oyster Crassostrea ariakensis when exposed to hypoxic

environments

Sara A. Lombardi & Kennedy T. Paynter

Marine Estuarine Environmental ScienceUniversity of Maryland College Park, MD USA

Oysters and the Chesapeake Bay

Population decline of Crassostrea virginica 1% of historic population (Newell 1988)

Ecosystem service decline Before 1870: 6 day Bay filtration Now: approximately 325 days (Newell 1988)

Introduction of C. ariakensis as a solution? Increased comparisons

between the species Growth Perkinsis marinus infection (Dermo)

C. virginica and C. ariakensis during low oxygen

Harlan 2007

“C. ariakensis began gaping during the sparging process ….. The native oyster remained closed until 1-2 days before its death”

Why gape? Risk: Greater exposure to predators

Probably a physiological underpinning

Is gaping a response to release CO2? Acidic metabolic byproducts accumulating in the

hemolymph CO2 + H2O H2CO3 HCO3

- + H+

ObjectivesCompare the physiological responses of Crassostrea ariakensis and Crassostrea virginica to low oxygen

Assess gaping response after hypoxic exposure Frequency of gape Extent of gape Analyze correlations between gaping and external

water pH Inhibit gaping and assess hemolymph pH

Effect of time Effect of species

Gaping Study Methods Oysters from Horn Point Lab,

Cambridge, MD Starved for 1 week in 15ppt 25° C

water Respiration chambers filled and

sparged until oxygen concentration below 0.5mgL-1

Individual oysters were placed into a chamber which was then sealed

At periodic intervals, oyster gaping response was assessed 8-72 hours after hypoxic immersion the pH of

the water surround each oyster was analyzed.

Repeated Measure Analysis of Variance

Gaping Response

C. ariakensis gapes more often than C. virginica (p<0.0006)

12 hrs

10 days

Gape Distance

C. ariakensis gapes to a greater degree than C. virginica during early (0-72 hours) hypoxic exposure (p=0.0057)

Gaping and Water pH

Gaping is correlated with acidic external environments (p=0.034)

Hemolymph pH Methods Clamped using 2” binder clips and

placed on lab bench at ~25° C air temperature

Sacrificed at hr 0 (control), 2, 4, 6, 8, 10, 12, & 24

Dorsal and ventral side drilled Hemolymph sampled with 5ml glass

syringe pH analyzed with bench top meter

and micro pH probe Performed Perkinsis marinus analysis

Excluded those with P. marinus score greater than 1 from analysis

Two-way ANOVA

Hemolymph pH after clamping

Species: p<0.0001Time: p<0.0001Interaction: p=0.2934

Change in hemolymph pH after clamping

Species: p= 0.0214Time: p<0.0001Interaction: p=0.2934

**

Conclusions C. ariakensis gapes more often than C. virginica

(p<0.0006)

C. ariakensis gapes to a greater extent than C. virginica (p=0.0057)

Gaping is correlated with acidic external environments (p=0.034)

When gaping is prevented…

C. ariakensis hemolymph pH is more acidic than C. virginica (p<0.0001)

Conclusions and Implications

C. ariakensis may respond differently to low oxygen and different acid-base homeostatic abilities

Gaping may be a mechanism to prevent or limit metabolic acidosis in C. ariakensis

Next steps Assess pH over time simultaneously with

calcium and carbon dioxide concentration Assess hemolymph pH of gaping and

ungaped oysters when exposed to low oxygen Effect of gaping on hemolymph pH

Assess the effect of acidosis on adductor muscle function

References Acknowledgements

Funding Oyster Recovery Partnership National Oceanographic and

Atmospheric Administration – Chesapeake Bay Office

Army Corp of Engineers – Baltimore district

University of Maryland’s Horn Point Lab Oyster Hatchery Dr. Donald Merrit Stephanie Tobash Alexander

University of Maryland Paynter lab staff and

students

Dwyer J. J & Burnett L.E 1996. Acid-base status of the oyster Crassostrea virginica in response to air exposure and to infections by Perkinsus marinus. Biol. Bull. 190 :13-137

Newell R. I. E 1998. Ecological changes in Chesapeake Bay: Are they the result of overharvesting the American oyster, Crassostrea virginica? Understanding the estuary: Advances in Chesapeake bay research. Proceedings of a conference 29-31. Chesapeake Research consortium publication 129.

Harlan N.P. 2007 A comparison of the physiology and biochemistry of the eastern oyster, Crassostrea virginica, C. ariakensis. Masters of Science.

Stickle W.B., Kapper M.A, Liu L., Gnaiger E., & Wang S.Y. 1989. Metabolic adaptations of several species of crustaceans and Molluscs to Hypoxia: Tolerance and Microcalorimetric studies. Biological Bulletin 177:303-312