Research Seminar: Greg Sorg

A research seminar presented by UNC Institute of Marine Sciences Graduate Student, Greg Sorg.

Seminar Title: Testing the Effectiveness of Alternative Substrates for Subtidal Oyster Reef Construction

Abstract: In North Carolina, the wild stock of Eastern oysters, Crassostrea virginica, is currently a fraction of the historic peak in the early 1900’s.  The NC Division of Marine Fisheries (NCDMF) as well as non-governmental agencies traditionally deploy mounds of loose oyster shell, and more recently marl in effort to restore local oyster populations. However, these two calcium carbonate materials are susceptible to infestations by common oyster pests including clionid boring sponges. Boring sponges excavate extensive galleries within living and non-living CaCO₃ material.  When present on live oysters, boring sponges cause a decrease in fitness of the oysters.  When present on substrates used in reef constructions, more rapid infestation of settled oysters by the boring sponge can occur.  In this study, we examined the effectiveness of 4 substrate types (2 CaCO₃ based, 2 non-CaCO₃ based) for their use in subtidal oyster reef foundations along a salinity gradient in two estuaries in Carteret County with particular interest in the sponge effect.  I will present initial analyses from long-term monitoring of the reefs 24 months, 28 months, and 36 months post-construction.  At the highest salinity site in each estuary all reefs experience high settlement by oyster spat; however, the high settlement is negated by intense predation. Moreover, at the lowest salinity sites in each estuary the maintenance of oyster populations with low incidences of boring sponge infestations is reliant on freshet (period of abnormally low salinity) occurrences.  At mid-estuarine sites, which freshets do not penetrate to or are infrequently occurring, boring sponge populations persist and thrive at the expense of oyster populations; however, non-CaCO3 based materials at mid-estuarine sites appear to delay heavy infestations of oysters by boring sponges.

This seminar will be held in Coker Hall seminar room 222 at the Institute of Marine Sciences in Morehead City and broadcast live to the Department of Marine Sciences seminar room G201 in Murray Hall, UNC – Chapel Hill.