IMPORTANCE OF CONTROLLING FOR SEDIMENT GRAIN SIZE WHEN ASSESSING TEMPORAL AND SPATIAL PATTERNS OF ECOLOGICAL QUALITY IN CONSERVATION PALEOBIOLOGY

As human activities continue to modify marine systems, environmental managers and policy makers have sought after metrics that can identify potentially degraded sites and track changes in ecological quality. Several Indices (e.g., AZTI Marine Biotic Index (AMBI)) have been developed to assess changes in benthic macroinvertebrate community dynamics in relation to anthropogenic stressors (e.g., heavy metal concentrations, total organic carbon). However, such indices, and the stressors themselves, may vary along environmental gradients (e.g., salinity, grain size). Unless the variation in index scores to environmental gradients is accounted for, the indices may not accurately reflect the response of benthic communities to anthropogenic stress. To illustrate the impact of grain size on molluscan community dynamics, we compiled a dataset of benthic surveys conducted in Long Island Sound, NY and CT, over the past four decades and calculated Shannon entropy and AMBI scores across a gradient from fine-grained mud to coarse-grained sand. Our results indicate that both indices correlate with grain size, irrespective of anthropogenic stress, confirming the need to account for variation in index scores caused by changes in grain-size when assessing ecological quality. To evaluate whether conservation paleobiology (CPB) studies account for this potentially confounding factor, we conducted a review of the CPB literature published in the last two decades aimed at assessing changes in community dynamics from anthropogenic stress or providing baseline information on ecological quality. We found that consideration of variation in index scores that can be explained by differences in grain size of samples is often not accounted for. To realize the full potential of CPB to provide meaningful information on benthic community response to anthropogenic stressors, we recommend including information on grain-size in studies to allow for grain-size normalization and cross-study comparisons.