MOLLUSK DEATH ASSEMBLAGES AS A BASELINE FOR ASSESSING COMMUNITY SHIFTS IN ARTIFICIAL REEFS: A COMPARISON OF DEAD AND LIVING MOLLUSK ASSEMBLAGES IN THE SUWANNEE REGIONAL REEF SYSTEM, FLORIDA

Artificial reefs represent an important reef restoration strategy, but few studies have attempted to assess their impact on reef-associated soft-bottom benthic fauna. Some studies in natural reef environments suggest that temporal changes in benthic communities can be examined by comparing living mollusk assemblages (LAs) and their sympatric death assemblages (DAs) – the latter representing surficial remains of past communities. To our knowledge, this approach has not been applied to artificial reefs. 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-defined time frames.

We test the hypothesis that SRRS has impacted 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 reefs. In addition to identifying and counting mollusks, presence of drill holes was recorded to determine trends in drilling predation along transects.

We hypothesized that composition of DAs will not vary 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, predicting high LA-DA discordance in reef proximity and improved LA-DA concordance away from reefs.

Analyses suggest that LAs differ drastically from DAs in terms of most abundant species and overall faunal composition. Poor live-dead fidelity suggests that faunal composition of local mollusk associations shifted notably in recent years and those changes are not yet reflected in DAs. LA is more concordant with DA at distal sites comparing to proximal sites indicating that changes in faunal composition occur in a limited halo around the reefs. DAs do not separate as proximal and distal in terms of species composition, showing no evidence of reef impact. Similarly, no predictable trends are seen in drilling frequency along transects. DAs in individual transects seem homogenous in terms of species composition. Different reefs have generally discernible composition. Based on these findings, it appears that DAs predate the reefs and reflect community structuring prior to reef deployment, thus providing a valuable baseline for the system.