EVALUATING DYNAMICS OF REEF TAXA ABUNDANCE AND ZONATION ON AN ALBORAN SEA COLD-WATER CORAL MOUND

Cold-water coral reefs (CWCs) are a hotspot of deep-sea biodiversity due to the interplay of local currents, nutrient availability, and sediment supply. Living coral concentrations tend to be highest towards the tops of the mounds where currents supply nutrients. These corals outcompete other reef taxa for resources, resulting in lower reef diversity near the mound top. 

This project analyzes CWC reef invertebrate diversity dynamics over the last ~13,000 years using a sediment core (GeoB 13729-1) collected from a CWC mound in the Alboran Sea in the Western Mediterranean. Our project aims to identify and quantify the primary groups of invertebrates in the core and relate the data to periods of coral growth and nutrient availability. This core was previously sampled at 10 cm intervals to extract invertebrate fossils, taken on the lower flank of the coral mound, where the biodiversity of non-coral invertebrates is expected to be higher. After sorting invertebrate fossils into five primary taxonomic groups, we found relatively low concentrations of non-coral, filter-feeding taxa on this part of the mound compared to cores from the mound top. We hypothesize that this is caused by a current that runs past the lower flank, supplying nutrients for coral growth, thereby suppressing reef biodiversity. Brachiopods, bryozoans, and barnacles are more abundant at higher depths within the core, peaking near the bottom. Conversely, echinoderm abundances are greater towards the top of the core, potentially reflecting an influx of grazing organisms as coral populations increased over time.