Coral recruits settlement in Gulf of Mannar Marine Biosphere Reserve, India

Coral recruitment is one of the critical processes, leading to the recovery of coral reefs in the marine system. Density of coral recruits and their settlement sites in relation to the distribution of sediment hydrogen ion concentration (pH) and redox potential (Eh) was investigated in the selected islands of the Gulf of Mannar Marine Biosphere Reserve (GOMMBR). Among the island groups, the Mandapam group recorded the highest coral recruitment density (7.37±4.45m−2) followed by Vembar (4.26±4.64m−2), Keezhakarai (3.47±5.43m−2) and the Tuticorin group (1.79±2.55m−2). Among the groups of islands Bray-Curtis dissimilarity found 58.94 %, while the individual islands dissimilarity was 30.19 %. ANCOVA (ANalysis of COVAraians) results suggested that among the settlement sites, DRS (p>0.0001), SR (p>0.0001), NNR (p>0.011) and CCA (p>0.033) possessed suitable pH. Similarly, high coral recruit density on DRS (p>0.0001) SR (p>0.0001) and CCA (0.037) were found with suitable Eh for coral recruits. Non-New Recruitment sites (NNR) and coral rubble (CR) were not statistically significant. Overall average, settlement of coral recruits with prevailing sediment pH, observed with 7.21 to 7.49 and redox potential (Eh) 23.90 to 39.2 mV. Among different sites studied for the settlement of coral recruits, higher density of coral recruits found on dead reefs (DR) (22.08±14.71m−2) than crustose coralline algae (CCA) site (12.72±12.12m−2). Further studies are required to confirm the prevalence of these effects in recruits, which will enhance our understanding of settlement sites and improve the estimation of reproductive performance in relation to the phase shift and acidification in shallow water corals sediment-water flux.