Abstract. Oyster reefs are among the world's most endangered marine habitats with an estimated 85% loss from historical levels worldwide. Oyster reefs offer diverse ecological and social services for people and natural environments; unfortunately, reefs are also highly sensitive to impairment from natural and human-induced disasters. Understanding the resilience of oyster reef communities to disturbance is key to developing effective conservation and restoration plans. Florida's Big Bend coastline (Gulf of Mexico coast from Crystal River to Apalachee Bay) supports large expanses of oyster reef habitat that have existed for thousands of years in a region that is one of the most pristine coastal zones in the continental US. We assessed trends in oyster habitat along the Big Bend region between 1982 and 2011 by examining changes in areal extent and distance of oyster reefs from shore. During our study period, we found a 66% net loss of oyster reef area (124.05 ha) with losses concentrated on offshore (88%), followed by nearshore (61%), and inshore reefs (50%). We also found that the spatial distribution of oyster reefs was moving inland. This rapid loss is likely a departure from historic geological succession. Multiple lines of evidence suggest that the primary mechanism for these observed losses in oyster reefs is reduced survival and recruitment, likely a result of decreased freshwater inputs which increases existing reef vulnerability to wave action and sea level rise. Once oyster reef substrate becomes unconsolidated and the nucleation site is lost, the regeneration of the oyster reef may not be reversible through natural processes. To test these predictions, we recommend restoration-based experiments to elicit the mechanisms of decline in order to foster longterm sustainability of estuarine habitat critical to oysters.

ABSTRACT. The Apalachicola Bay, Florida, eastern oyster (Crassostrea virginica) industry has annually produced about 10% of the U.S. oyster harvest. Today's simple individual-operator, hand-tonging, small-vessel fishery is remarkably similar to the one that began in the 1800s. Unprecedented attention is currently being given to the status of oyster resources in Apalachicola Bay because this fishery has become central to the decision making related to multistate water disputes in the southeastern United States, as well as millions of dollars in funding for restoration programs related to the Deepwater Horizon oil spill. The oyster fishery collapsed in 2012, leading to large economic losses and community concerns over the current and future status of oyster resources, ecosystem health, and local economic opportunities. We used best available data to assess what mechanism(s) may have led to the collapse of the Apalachicola Bay oyster fishery. We then assessed the efficacy of alternative management strategies (e.g., restoration, fishery closure) to accelerate oyster population recovery. Our results suggest that the Apalachicola Bay oyster population is not overfished in the sense that recruitment has been limited by harvest, but that the 2012 collapse was driven by lower-than-average numbers and/or poor survival of juvenile oysters in the years preceding the collapse. This reduction in recruitment not only reduced the biomass of oysters available to harvest, but from a population resilience perspective, likely reduced the amount of dead shell material available as larval settlement area. Although the Apalachicola Bay oyster fishery has proven resilient over its >150-year history to periods of instability, this fishery now seems to be at a crossroads in terms of continued existence and possibly risks an irreversible collapse. How to use the restoration funds available, and which restoration and management practices to follow, are choices that will determine the long-term viability of the Apalachicola Bay oyster fishery.

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Within the Big Bend region of the northeastern Gulf of Mexico, one of the least developed coastlines in the continental USA, intertidal and subtidal populations of eastern oyster Crassostrea virginica (hereafter referred to as "oyster") are a critical ecosystem and important economic constituent. We assessed trends in intertidal oyster populations, river discharge, and commercial fishing activity in the Suwannee River estuary within the Big Bend region using fisheries-independent data from irregular monitoring efforts and publicly available environmental data. We used generalized linear models to evaluate counts of oysters from line-transect surveys over time and space. We assessed model performance using simulation to understand potential bias and then evaluated whether these counts were related to freshwater inputs from the Suwannee River and commercial oyster fishing effort and landings at different time lags. We found that intertidal oyster counts have declined over time and that most of these declines are found in inshore intertidal oyster bars, which are becoming degraded. We also found a significant relationship between oyster counts and a 1-year lag on mean daily Suwannee River discharge, but including commercial fishery trips or landings did not improve model fit. It is unclear whether declines in intertidal oyster bars are offset by formation of new oyster reefs elsewhere. These results quantify rapid declines in intertidal oyster reefs in a region of coastline with high conservation value that can be used to inform ongoing and proposed restoration projects in the region.