Oyster Death Assemblages as Archives of Historical Information for Studying Long-Term Trends in Oyster Body Size

A lack of location-specific, long-term data is a common obstacle to assessing trends in condition of coastal habitats over time. Without historical monitoring records or other documentation, filling such data gaps can be difficult, but sedimentary records such as death assemblages (DAs; the accumulated, identifiable remains of organisms that lived in or near the habitat in the past) are relatively untapped, location-specific archives of ecological information from the past. In 2018, the Florida Department of Environmental Protection and the Paleontological Research Institution began a collaboration to study the use of oyster reef (Crassostrea virginica) DAs to address monitoring information gaps for oyster size. To-date, our project has sampled DAs from over 30 intertidal oyster reefs around Florida, radiocarbon dated most of the samples, and measured over 26,000 oyster shells. In the process, we found that C. virginica DAs are recent and high-resolution archives, with most samples from 15-35cm burial depth dating to within the last 80 years. We also developed a model to combine the DA data with real-time monitoring data on live oyster sizes from the same reefs to estimate reef- and locality-level size trends from as early as the 1960s to the present. This information is adding temporal context for our overwhelmingly short (~5-10 years) and recent (many post-2010) time series of live C. virginica size data. This case study demonstrates the potential utility of DA data for supplementing real-time monitoring data during the assessment and management of coastal habitats.