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MS Thesis Defense: Greg Sorg

April 6, 2017 @ 9:00 am - 12:00 pm

Greg Sorg MS Thesis Defense titled Identifying Sustainable Alternative Substrates for Subtidal Oyster Reef Construction with Updates to Recommendations Made in 1904The M.S. Thesis Defense of Greg Sorg will be presented at Murray Hall, in the 3rd floor conference room #3204 of the Marine Sciences Department, UNC at Chapel Hill and live broadcast to UNC Institute of Marine Science (IMS) in Morehead City, NC. This event will be held on Thursday, April 6th, 2017 at 9:00 AM.

Title: Identifying Sustainable Alternative Substrates for Subtidal Oyster Reef Construction with Updates to Recommendations Made in 1904

Abstract: Wild stocks of the eastern oyster Crassostrea virginica are at historic lows.  Efforts to restore oyster populations requires the addition of substrate for larval settlement, and oyster shell has long been the preferred substrate.  As restoration efforts have ramped up, competition for oyster shell has driven up restoration costs.  These considerations have led to increased use of alternative substrates, often limestone-based rock because of its similarity to oyster shell mineralogy.  Non-carbonate substrates, such as granite rock and recycled concrete, have also been used to create reef foundations.  To date, there has been no systematic comparison of the long-term efficacy of different reef foundation materials to promote sustainable oyster populations.  Long-term testing is needed because CaCO3-based materials are susceptible to heavy infestation by carbonate bioeroders, such as Clionid sponges, that can collapse previously productive oyster reefs.  For this experiment in the Newport and North River estuaries in Carteret County, NC, 80 small oyster were constructed of CaCO3-based (loose oyster shell, small marl cobble) and non-CaCO3 based (recycled concrete, small granite cobble).  Niels Lindquist (UNC-IMS) and Dave Eggleston (NCSU-CMAST) initiated this project and reef construction occurred in 2012.   Oyster demographics, Clionid infestation of oysters and the substrates, and a characterization of predation sources on juvenile oysters were tracked over time.  Regression tree analyses indicate estuarine location and reef foundation composition interact to determine the fate of oyster communities, as long as 54 months after reef construction.  High salinity sites in both estuaries experienced elevated levels of oyster settlement on all reef types; however, intense predation on juvenile oysters prevented the development of mature oyster communities.  In upper, less-salty regions in both estuaries, freshets created safe zones for oysters, encouraging the establishment of robust and likely sustainable oyster communities on all substrate types.  Oyster populations struggled to persist at mid-estuarine sites, where even large freshets of 2014 and 2015 failed to eradicate boring sponges.  At one mid-estuary site in the Newport River, concrete and granite substrates delayed heavy infestation by boring sponge on oyster communities, and at 54 months post reef creation, granite-based reefs had large, size-diverse oyster populations with relatively low levels of boring sponge infestations.  Salinity is likely to increase in estuaries from rising sea levels, climate change, and direct anthropogenic modifications to estuarine hydrology (i.e. dredging). The continued use of CaCO3-based materials for restoration efforts, especially in regions already suitable for persistent oyster pest communities, is counterproductive to the intended purpose of restoring oyster populations.


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