Environmental variables and nutrients in selected islands of Lakshadweep Sea; Addressing coral bleaching

An observational investigation on the environmental variables in the coral reef ecosystem of the Lakshadweep Sea was made with reference to coral bleaching. The investigation was done during 2014-2015 in selected islands of Lakshadweep Sea. The environmental variables recorded were sea surface temperature (SST; 28.1-31.5 ° C), salinity (34.0-38.36 psu), pH (7.9-8.3), dissolved oxygen (DO; 3.19-7.70 mg/L), total organic carbon of water (WTOC; 1.6-3.20 ppm) and net primary productivity (NPP; 0.440-2.060 mgC/m3/hr). Nutrients of nitrite (NO2; 0.052-1.522μmol/L), nitrate (NO3; 0.293-14.867μmol/L), in-organic phosphate (IP; 0.287-2.070μmol/L), total phosphorous (TP; 1.919-5.200μmol/L) and reactive silicate (RS; 3.791-19.422μmol/L) were also recorded. PCA showed positive loadings for salinity, DO, NO2, IP, TP, and RS in the Lakshadweep Sea. Currents and their divergence patterns influencing the upwelling in the nearshore islands might be the sources for the availability of nutrients. Data were treated statistically (linear regression) to understand the interrelationship between the variables. DO was found normal, indicating that the waters of the Lakshadweep Sea are well mixed and aerated. Nutrients such as NO2, NO3, IP and RS in Kavaratti and Agatti islands were found higher indicating that these islands are under the influence of anthropogenic activities. Cluster analysis revealed clear groupings among the islands. Agatti and Kalpetti islands were grouped together indicating more similarity in the values of environmental variables than with other islands. SST was found in the higher range over a study period and also over to the past ∼5 decades as per records and pH was found at the lower level in majority of the assessments. The unvaried ranges of SST and pH (P >0.01) might have favored bleaching of the corals in the Lakshadweep Sea. The nutrient levels recorded presently besides the other variables will serve as the baseline data for future investigations in the Lakshadweep Sea.