MOLLUSK FAUNAS AS INDIRECT INDICATORS FOR PALEO-SEAGRASS VEGETATION

Seagrass ecosystems play an important role in sedimentation processes and nutrient cycling and support local biodiversity by providing food and shelter for numerous associated organisms. These ecosystems have been around since the Late Cretaceous. In order to understand their emergence in geological time and their response to past perturbations we have to be able to recognize seagrass communities in the fossil record. However, seagrass itself hardly fossilizes and therefore we are searching for indirect indicators to recognize ancient seagrass vegetation.

In this contribution we review molluskan evidence for paleo-seagrass settings. Indicator species are rare since the majority of seagrass associated mollusks occur in other marine habitats as well. Furthermore, seagrass vegetation appears to be patchy, both spatial and temporal, resulting in mixed occurrences of seagrass and non-seagrass faunas. Often only the high abundance of certain mollusk groups and the general taxonomic composition of a fauna points to seagrass environments. However, the distribution of gastropod trophic guilds in species richness versus abundance data appears to yield patterns that may be very characteristic for the identification of fossil seagrass associated faunas.

We are currently applying Indirect Paleo Seagrass Indicators (IPSI’s) to a number of fossil and modern shelly samples from Indonesia, both from seagrass and non-seagrass environments. We also briefly review potential sedimentary and geochemical IPSI’s as well as fossil groups different than mollusks. Identifying seagrass environments enables us to assess diversity trends in such ecosystems through time and to study their response over time intervals with major environmental and climate change.