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

Highlights

• The present study describes environmental variables and coral bleaching in the Lakshadweep Sea.
• SST (Sea Surface Temperature) and pH were found to be responsible factors for coral bleaching.
• Among the islands studied, Kavaratti and Agatti islands are found with higher levels of NO3 and NO2 due to more anthropogenic activities.
• Narrow range of temperature in the Lakshadweep Sea for about 5 decades was noticed when compared with earlier reports.

Abstract

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; 0.052–1.522μm ol/L), nitrate (NO3; 0.293–14.867μm ol/L), in-organic phosphate (IP; 0.287–2.070μm ol/L), total phosphorous (TP; 1.919–5.200μm ol/L) and reactive silicate (RS; 3.791–19.422μm ol/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.

Kumaresan S., Shekhar S., Chakraborty S., Sundaramanickam A. & Kuly N., 2018. Environmental variables and nutrients in selected islands of Lakshadweep Sea; addressing coral bleaching. Regional Studies in Marine Science 22: 38-48. Article (subscription required).

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