Handley, J. C. | bioRxiv Science

bioRxiv2022

Age variability and time averaging in oyster reef death assemblages

A lack of temporal context for paleoecological data from molluscan death assemblages (DAs) makes integrating them with monitoring data from living communities to inform habitat management difficult. Here we illustrate this challenge by documenting the spatial and stratigraphic variability in age and time-averaging of oyster reef death assemblages. We radiocarbon dated a total of 573 oyster shells from samples of two burial depths on 28 oyster reefs around Florida and found 1) that spatial and stratigraphic variability in DA sample ages and time-averaging are of similar magnitude, and 2) that the shallow oyster reef DAs are among the youngest and highest-resolution molluscan DAs documented to-date, with most having time-averaging estimates of decades or less. This information increases the potential usefulness of the DAs for habitat management because measured indicators can be placed in temporal context relative to monitoring data. More broadly, the results highlight the potential to obtain decadal-scale resolution from oyster bioherms in the fossil record.

paleontology↗

bioRxiv2022

Assessing the utility of death assemblages as reference conditions in a common benthic index (M-AMBI) with simulations

Incorporating paleontological data into the methods and formats already familiar to conservation practitioners may facilitate greater use of paleontological data in conservation practice. Benthic indices (e.g., Multivariate - AZTI Marine Biotic Index; M-AMBI) already incorporate reference conditions and are a good candidate for integration. In simulations of living communities under constant and changing environmental conditions, we evaluate the capacity of death assemblage reference conditions to replicate M-AMBI values when used in place of reference conditions from the final ten generations of the simulation or all five hundred simulated generations. Reference conditions from all death assemblage scenarios successfully replicated correct remediation decisions in the majority of simulation runs with environmental change and stability. Variations in M-AMBI values were due to overestimated richness and diversity in the death assemblages but effects of changes to these parameters varied across scenarios, emphasizing the importance of evaluating multiple metrics. Time averaging was largely beneficial, particularly when environmental change occurred and short-term ecological observations (ten generations) produced incorrect remediation decisions. When the duration of time averaging is known, death assemblages can provide valuable long-term perspectives with the potential to outperform temporally constrained baseline information from monitoring the living community. Supplementary materialAll R code used to produce the simulation, analyze outputs, and create figures is available at: https://doi.org/10.5281/zenodo.6355921. The simulated data is also available at this location. Supplementary figures and analyses referred to in the text are available at the end of this document.

ecology↗