DISTRIBUTION AND SUB-BOTTOM FEATURES OF HOLOCENE OYSTER DEPOSITS IN THE YORK RIVER, VIRGINIA AND THE RATE OF DEGRADATION OF OYSTER SHELL

Oyster populations in the Chesapeake Bay have declined precipitously during the past century due to several factors, including overharvesting, increased sedimentation, and disease. By researching the distribution of Holocene oyster deposits, we can develop a baseline for restoration. This study addresses three research questions focusing on oyster shell deposits located near the Catlett Islands in the York River (southeastern Virginia): 1) how has the percentage of oyster bottom changed over the past 100 years, 2) how much time is represented by the buried shell deposits, and 3) how long does oyster shell remain on the bottom of the river before it starts to degrade? To answer the first question, side scan sonar and single beam seabed classification were used, along with a video sled and grab samples to ground truth these data. We collected data along seven transects, covering an area of 173,250m². By mapping the bottom and comparing it with historic data collected by the Baylor Survey in 1894, we were able to quantify how bottom type has changed due to increased sedimentation and overharvesting of oysters. For the second part of the project, we mapped the sub-bottom in this same region by computing sub-bottom profile data and collecting three sediment cores. We have also dated shells from the cores to estimate how long shell deposition occurred in this area. The final part of this research involved a taphonomic experiment on shell degradation. A range of oyster types and sizes (n > 100) were deployed in the York River to determine the weight of shell organic content lost after one year. Given the prevalence of oyster restoration techniques that rely on cultch deployment and the fact that oyster spat do not settle on extremely degraded shell, this research will help determine how long, after deployment, oyster shell can remain viable for restoration. Preliminary results suggest that the percentage of oyster bottom in the York River has dramatically declined over the past 100 years.