IDENTIFYING POTENTIAL DRIVERS OF REGIME SHIFTS ON INDONESIAN CORAL REEFS UTILIZING BENTHIC FORAMINIFERA

The FORAM Index (FI) was developed to provide a simple metric to assess whether water quality supports coral recruitment and reproduction in Caribbean and Western Atlantic coral reefs. The FI was developed by Hallock and others (2003) based on observations of analogous requirements for both larger symbiont-bearing foraminifera and zooxanthellate corals. Use of the FI has since been successfully expanded to include myriad global reef locales, but its applicability to Indonesian reefs has been cautioned due to the presence of an endemic Indo-Pacific group of foraminifers – the Calcarinidae. Although the calcarinids are a large, symbiont-bearing group whose presence would result in favorable FI values, they are typically found in association with macroalgae rather than zooxanthellate corals, indicating degraded reef conditions.

This study is the first to report foraminiferal assemblages from Pulau Karangmajat, a remote Eastern Indian Ocean island located within the Mentawai Island chain, West Sumatra, Indonesia. Sediment samples were collected across fringing reef zones and analyzed for foraminiferal content. Ecological indices (i.e., richness, evenness, H’ diversity) and FI were calculated for each site. H’ diversity was moderate to low at all sites (2.02 - 6.46; avg. 3.08), and FI was extremely high (8 - 10). Calcarinids (Neorotalia calcar, Calcarina spp.) were very abundant at all sites accounting for 44%-95% of total species composition, and subsequently high FI values. This indicates water quality conditions are ideal for a healthy coral dominated system, yet dominance of calcarinid taxa suggests a shift from coral- to macroalgal-dominated reefs. Here it is proposed that reef degradation at this site is likely the result of failed coral recovery following climatic disturbances (eg. bleaching and upwelling events) due to the absence of herbivorous fishes, which control macroalgal populations, and not a consequence of decreased water quality. Utilization of indices like the FI in conjunction with analysis of foraminiferal assemblages may aid managers in deducing drivers of regime shifts on Indonesian coral reefs, and ultimately facilitate solutions for reef conservation and recovery following natural and anthropogenic disturbance.