Effects of distance between individual spawning oysters on fertilization success.

Investigators: David Bushek and John Quinlan, IMCS

Populations of the eastern oyster Crassostrea virginica are declining in many areas from decades of over harvesting, habitat loss/degradation and disease. With densities at record lows, recruitment failures are increasing. The introduction of a non-native oyster to Chesapeake Bay is being evaluated as a mechanism to increase fishery and aquaculture production and restore the ecologically important roles that oysters fulfill in the Bay. This project is part of a larger study to examine how gametes from the two species might interact if both are present. The flume experiments are an attempt to determine how gamete dilution over short distances (<12 m) might alter fertilization rates when population densities are low. Under hatchery conditions gamete densities that produce 5 to 10 active sperm in contact with each egg yield the highest fertilization rate. As sperm density declines so does fertilization rate. Gamete densities in the field have never been measured. Eggs and sperm can be introduced into the annular flumes at different points around the flume. As water circulates, gametes will become diluted until they begin to encounter each other. Simple logic suggests that gametes introduced further away from each other will dilute more than before encountering each other. If contact rates reach limiting levels, fertilization rate will decline. Results will hopefully provide a first estimate on minimal adult densities required for reliable fertilization to occur during the spawning season. As time and funding permit, we will also use the system to examine how gametes from the two species interact when introduced together. This work is funded by NOAA Chesapeake Bay Office.

Dave Bushek and Rachel Koehler calculate densities for flume experiments.

Day 2 larvae fertilized and grown in the flumes.

Andrea Kornbluh collects and washes larvae from the flumes.

Rachel Koehler washes oyster larvae collected from the flume experiments.

John Quinlan and Rachel Koehler plot up the experimental data.

One of the four annular flumes.