Demography of Oysters Pre‐ and Postcollapse in Apalachicola Bay, Florida, Using Stage‐Based Counts

Abstract

The collapse of oyster populations and the fisheries they support has been a worldwide phenomenon, but studies of oyster demography in situ prior to and after the collapse have been rare. We used time series of stage‐based counts of eastern oysters Crassostrea virginica in Apalachicola Bay, Florida, to help understand how abundance and demographic rates may have changed in the decade after the 2012 collapse relative to the period before the collapse. We relied on a Bayesian hierarchical model in which the latent stage structure of the oyster population (i.e., densities of spat, sublegal oysters, and legal oysters) was governed by a system process and where the count data represented summaries of that latent structure. Count data were sufficient to conduct this on two large oyster bars that had some of the highest precollapse oyster densities. We also examined nine other bars with less data for any temporal trends in postcollapse abundance that might be associated with recent restoration efforts. Among the 11 bars examined, oyster densities were often increasing prior to the collapse and were very low, without detectable trends, afterward. Based on our demographic analyses, mortality rates of Apalachicola Bay oysters in the decade after the collapse generally exceeded (often greatly so) those during the precollapse period for all oyster stages. On the other hand, spat settlement rates apparently were increasing prior to the collapse and remained high during the postcollapse period. Simulations of postcollapse demography suggest that without improved survival rates, further declines of the oyster population can be expected. We discuss these findings in light of ongoing restoration and management efforts and suggest ways in which rapid transitions to undesirable socio‐ecological regimes might be avoided in the future.

Collapsed oyster populations in large Florida estuaries appear resistant to restoration using traditional cultching methods—Insights from ongoing efforts in multiple systems

“…Alternative hypotheses related to oyster population decline, including cascading predatory responses (Kimbro et al 2017), recruitment overfishing, discard mortality, virulent disease (known or unknown), freshwater inflow, climate change, or some combination of these, remain largely unassessed and impossible to address with available data. The reasons for the 2012 collapse and the decade-plus period of low oyster abundance are uncertain (Camp et al 2015;Kimbro et al 2017;Pusack et al 2018;Johnson et al 2023) and have been debated in courts as high as the U.S. Supreme Court (Kelly 2019; Barnett 2021).…”

Climate Change: Effects on Salinity in Florida’s Estuaries and Responses of Oysters, Seagrass, and Other Animal and Plant Life

“…It also coincided with high levels of oyster predators, such as crabs and conchs; parasites, such as worms, snails, and sponges (Figure 4); and pathogens, such as Perkinsus, a group of parasitic protists (single-celled organisms) that infect certain marine animals. Research showed the oyster population collapse was likely related to decreased survival of juvenile oysters (Pine et al 2015;Johnson et al 2023). Additionally, results from field experiments demonstrate that as the salinity in Apalachicola increased, so did the presence of an oyster predator called oyster drills (Kimbro et al 2017).…”

“…It is possible that this lower survival of juvenile oyster was made worse by high salinity or other environmental conditions (Camp et al 2015;Kimbro et al 2017). However, links between salinity and oysters are not clear (Fisch and Pine 2016), and juvenile survival appears to have remained low in the 2012-2022 period despite variable and more normal water conditions (Johnson et al 2023). Increasingly it seems that the oyster population in Apalachicola Bay experienced a shift to a much lower (and less valuable) population level (Johnson, Pine, and Camp 2022).…”

“…Increasingly it seems that the oyster population in Apalachicola Bay experienced a shift to a much lower (and less valuable) population level (Johnson, Pine, and Camp 2022). Ultimately it is not known what role high salinity may have played in that initial population shift (Johnson et al 2023), but it is possible it played one since salinity and temperature are key environmental factors that structure oyster populations (Love et al 2021). An earlier decline in oysters in Apalachicola Bay was documented by Petes, Brown, and Knight (2012).…”