Taphonomic Disparity in Foraminifera as a Paleo-indicator for Seagrass

Seagrass meadows are a key component of marine ecosystems that play a variety of prominent geobiological roles in modern coastal environments. However, seagrass itself has low preservation potential, and consequently seagrass meadows are hard to identify in the rock record. In this study we combine observational taphonomic data from a modern sparse seagrass meadow with actualistic taphonomic experiments, in order to test whether taphonomic disparity (i.e., evenness in the distribution of taphonomic grades among multiple individuals) in the larger benthic foraminiferan Archaias angulatus has potential as a paleo-indicator for seagrass dominated communities. Our observational study demonstrates that sparse seagrass meadows possess a higher proportion of both pristine and highly altered tests than non-seagrass settings. Our taphonomic experiments, conducted over a six-month period, demonstrate a greater magnitude of bioerosion and diversity of bioerosion types in foraminifera deployed within sparse seagrass patches, than those deployed in patches without any seagrass cover. Although our experimental results in particular have high variability, these combined approaches provide a link between pattern (high taphonomic disparity) and process (higher rates of bioerosion) in developing the taphonomic signature of seagrass meadows. On the basis of these results we suggest several taphonomic criteria that could be used to identify seagrass meadows in the rock record. These criteria are potentially species-independent, and so may have greater utility as seagrass proxies than invertebrate indicator species that frequently have limited temporal or spatial distributions.