CORAL REEF SUB-FOSSIL ASSEMBLAGES SUGGEST EARLY REEF LOSS IN BELIZE

Caribbean coral reef ecosystems have rapidly degraded due to climate change and local human stressors since large-scale monitoring began 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 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 and urchins preserved in a 3.5m-long core from two reefs within the central lagoon of Belize. Bivalve composition was assessed via relative abundance of shell valves, while urchin composition was assessed via the accumulation rate of spines measured by weight. In both cores, there is a notable shift in dominance from epifaunal to infaunal bivalves over time, indicating a loss of hard substrate including corals. Interestingly, these changes are largely due to an increase in chemosymbiotic deposit feeders, indicating a shift to low-oxygen environments. However these chemosymbiotic genera are not present in both cores. In contrast, 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, being consistently rare. The transition from infaunal to epifaunal bivalves occurs in tandem with a decline in the abundance of large (>2mm) coral fragments in the cores, together suggesting a loss of coral and/or declines in coral growth in this region of Belize. Continuing analyses will allow us to more accurately pinpoint the timing and drivers of observed change. These trends mirror those that have been previously observed from reef matrix cores from Caribbean Panama, suggesting region-wide declines in reef environmental conditions and ecosystems during the Anthropocene.