Long-term ecological assessment of faunal dynamics and production on a large, restored oyster reef in the Gulf of Mexico




Williams, Abby


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Crassostrea virginica oyster reefs, which are valued for providing essential fish habitat and other ecosystem services, were historically abundant throughout the Western Atlantic and U.S. Gulf of Mexico, yet have been severely degraded throughout their native range over the past century. The potential for oyster reefs to recover lost ecosystem services is a field that requires further research, in part due to the complex food webs that oyster reefs support by way of provision of high abundances of prey resources and habitat for vulnerable life stages of many fish and invertebrates. Because the majority of oyster reef restoration experiments are small-scale, it is unclear how fisheries benefits scale up for much larger restored reefs. Better understanding is needed on whether previous experimental findings are able to translate to large-scale restoration practices to advance our knowledge of oyster reef restoration. Half Moon Reef in Matagorda Bay, TX, was a large, historically productive reef rendered functionally extinct in the early 1900s due to overharvesting. In 2013, 23 of the original 200 ha were restored, followed by 4.5 years of ecological monitoring to assess faunal development and fisheries enhancement benefits. On a seasonal basis from July 2014 to January 2019, oysters were collected by hand from the restored reef while fish and macroinvertebrate samples were collected via suction sampling and modified epibenthic sled surveys on and off the reef. These data were used to assess oyster population and faunal community dynamics, including estimates of oyster disease and augmented faunal production from the restored reef. Data were also used to develop monitoring recommendations for key restoration metrics such as oyster population dynamics, oyster disease development, and faunal community development. Oyster population growth was typical of newly restored reefs, with the highest densities of newly settled oysters immediately post-restoration. Prevalence and severity of oyster infection by Perkinsus marinus were relatively low and indicative of early stage infection. After 1.5 years, faunal community composition on the restored reef was distinct from unrestored sites. Estimations of enhanced production were similar to previous studies except for stone crabs (Menippe adina), which were an order of magnitude higher than previous estimates (11.0 kg 10 m-2 y-1 versus 1.0 kg 10 m-2 y-1). Because restored reefs are generally small scale and monitored over a short timeframes of 1-2 years, this study provided the unique opportunity to assess longer-term thresholds of change in faunal metrics. Results indicated that monitoring timeframes of greater than 1 year may be required to properly document oyster population dynamics, faunal community succession, and seasonal dynamics of restored reef fauna. When reservoir reefs are distant from the restored reef, it may require greater than 4.5 years to observe the full onset of P. marinus (Dermo) disease within the restored oyster population. This study builds on previous meta-analyses of relatively small reefs monitored for short time scales encompassing a large geographic range by calculating the per-unit-area enhanced production of a large restored reef monitored over a relatively long time scale. Resource managers planning for future restoration projects in the Gulf of Mexico, particularly with the goal of enhancing faunal production of higher trophic levels, will benefit from assessments of large-scale restoration projects.





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