UTILIZING CORAL REEF SUB-FOSSIL ASSEMBLAGES TO ASSESS STABILITY AND CHANGE IN BELIZEAN REEF COMMUNITIES OVER THE PAST 800 YEARS PART A

Caribbean coral reef ecosystems have rapidly declined due to climate change and local human stressors since large-scale monitoring in the 1970s. However, less is known about reef health before monitoring began. Reef matrix cores can help fill this knowledge gap, as they provide records of reef communities and environments over the past centuries to millennia, prior to large-scale human disturbance. To obtain a more accurate baseline of reef ecosystem structure and functioning, and to track ecosystem change over the past 800 years, we assessed changes in the taxonomic and functional group composition of sub-fossil assemblages of bivalves, gastropods, and urchins preserved in 3.5m-long cores from two reefs within the central lagoon of Belize. Gastropod and echinoderms can be used to determine changes in coral reef communities linked to environmental changes. Here, we quantify changes in gastropod community composition via relative abundance of shells, in contrast, changes in urchin composition was assessed via the accumulation rate of spines measured by weight. In both cores, there is a notable dominance of microalgivore gastropods with large variation in proportions throughout, this could indicate ample hard substrate. Similarly, urchin composition shows little change through time, with the currently-common Echinometra spp. dominating throughout the past 800 years and Diadema antillarum, which suffered a mass mortality event in the 1980s and is currently undergoing another mortality event, being consistently rare. This contradicts what was previously thought about Diadema being the dominant genus until their mass mortality event. While there are no significant trends overall in these groups, the data we have supports other indicators of environmental change in these cores.