MOLLUSKS AS A PROXY FOR ASSESSING ECOLOGICAL IMPACTS OF ARTIFICIAL REEFS: A COMPARISON OF DEAD AND LIVING MOLLUSK ASSEMBLAGES IN THE SUWANNEE REGIONAL REEF SYSTEM, FLORIDA

The construction of artificial reefs is an important reef restoration strategy. However, few studies have attempted to assess their impact on reef-associated soft-bottom benthic fauna. Time-averaged death assemblages (DAs), representing surficial skeletal remains of past communities provide a historical perspective on the local community. Some studies suggest that comparisons between mollusk living assemblages (LAs) and sympatric DAs can be used as a proxy for changes in natural reef environments with time. To our knowledge, the LA-DA approach has not been applied to artificial reefs. Here, we compared mollusk LAs and DAs in the Suwannee Regional Reef System (SRRS), Gulf of Mexico. Since deployment dates are known, SRRS can be used to examine ecosystem changes over well-understood time frames.

We test the hypothesis that the SRRS has impacted the local faunal communities over decadal time scales. Both mollusk LAs and DAs were sampled along transects by SCUBA at 1m, 10m, 25m, 50m and 75m away from the reef wall. In addition to identifying and counting live and dead specimens, the presence of drill holes was recorded to determine variations in drilling predation along transects.

We hypothesized that the composition of DAs will be unvaried along transects since DAs are likely to record community composition averaged over multi-centennial time-scales. Conversely, LAs were expected to vary in composition along transects. ­Consequently, predicting a high LA-DA discordance in reef proximity and an improved LA-DA concordance away from reefs.

Preliminary analyses suggest that DAs are homogenous along transects, suggesting that the impact of artificial reefs is not reflected in DAs, due to taphonomic inertia. Similarly, no major trends were seen in drilling predation. However, within a single reef system, DAs differ in faunal composition between transects, indicating that DAs can differentiate a fine-scale spatial variability in past communities. Species composition of LAs does not indicate homogeneity along transects, but due to a limited number of specimens available for pilot analyses, a more specific interpretation is not yet possible. The preliminary results tentatively suggest that decadal changes induced by SRRS may have already altered living mollusk communities, but are not reflected in the DAs.