Assessing coral reef health in North Ari Atoll (Maldives Archipelago) using different indices: Amphistegina Bleaching, FORAM and SEDCON Indices.

Coral reefs are fragile biodiversity hotspots that are exposed to various natural and human induced stressors. In June 2015, a severe El Nino caused a major coral bleaching event in the Maldives. In September 2018, in the framework of the Conférence Universitaire de Suisse Occidentale (CUSO), Earth Surface Processes and Paleobiosphere (ESPP) doctoral school, a survey was conducted on three islands undergoing different management regimes: Rasdhoo a local community island, Vihamafaaru an uninhabited island and Mayaafushi a resort island. The goal of the CUSO course was to assess the ecological status around these three islands and compare results with those compiled during the International Union for Conservation of Nature (IUCN)-REGENERATE Cruise carried out prior to the bleaching in April-May 2015 (Pisapia et al., 2017; Spezzaferri et al., 2018). Assessments are based on three indices: The Amphistegina Bleaching Index (ABI), which denotes the degree of photic stress, the FORAM Index (FI), which is related to the water quality and indicates that the environment can support calcifying organisms and the SEDiment CONstituents (SEDCON) Index which indicates the degree of bioerosion. Amphistegina spp. are large benthic foraminifera that host diatom symbionts and, similarly to corals, are susceptible to photo-oxidative stress, induced by solar irradiance and high temperatures which induce bleaching. Hallock et al (2006, and references therein) showed that signs of bleaching in Amphistigina precedes the visual evidence of bleaching in corals. Indeed this was evident in 2015, the ABI evaluated in April-May 2015 indicated photic stress, preceding the coral bleaching that occurred in June (Spezzaferri et al., 2018). The 2018 results show that the reef community has not yet fully recovered and continues to be stressed.The FORAM (FI) and the SEDCON (SI) Indices are related to local water quality and bioerosion in the environment and give a time-averaged measure of the environmental status within months to few years. The 2015 FI values showed the strong influences of the management regimes (FI value ± 7.28, uninhabited island, ± 5.025, resort island and ± 5.075 in local community island). Environmental deterioration was revealed by the 2018 data, with both FI and SI values relatively uniform across three management regimes islands (e.g., medians of FI 4.08±0.12; and SI 3.01±0.4).All three indices confirm ongoing environmental degradation, consistent with visual observations of degraded coral cover between 2015 and 2018. Therefore, this study, therefore, highlights the potential application of these three indices in future coral-reef-management. References:Pisapia, C., El Kateb, A., Hallock, P., &amp; Spezzaferri, S., 2017. Assessing coral reef health in the North Ari Atoll (Maldives) using the FoRAM Index. Marine Micropaleontology, 133, 50-57.<li>Ramirez, A., 2008. Patch reefs in Biscayne National Park, FL: Sediments, foraminiferal distributions and a comparison of three biotic indicators of reef health: M.S. Thesis, University of South Florida, Tampa, USA, 137pp.</li><li>Spezzaferri, S., El Kateb, A., Pisapia, C., &amp; Hallock, P., 2018. In situ observations of foraminiferal bleaching in the Maldives, Indian Ocean. Journal of Foraminiferal Research, 48(1), 75-84.</li>