Environmental monitoring of the Kavaratti lagoon, Lakshadweep Islands, Arabian Sea using larger foraminiferal distribution

Abstract

Coral reef environments are known for the proliferation of algal symbiont-bearing foraminifera, which are sensitive indicators of water-quality conditions that support reef development. Keeping this in mind, 18 sediment samples were collected in the Kavaratti lagoon of Lakshadweep in 2004. The foraminiferal distribution and abundance of the major genera Amphistegina, Calcarina, Amphisorus and miliolids were compared with those reported nearly three decades ago. The aim was to identify changes in the foraminiferal data within the lagoon over time, through time-gap-sampling, to be able to assess environmental stress if any. The total foraminiferal number (TFN) in the lagoon ranges between 45 and 983 specimens per gram of dry sediments. The average TFN in the northern part of the lagoon (506/g) is lower than that in the southern part of the lagoon (612/g). Amphistegina and Calcarina, both being algal-symbiont-bearing foraminifera, show the tendency to occupy shallower depths of the lagoon. Amphisorus prefer the northern part of the lagoon, due to the prevalence of comparatively stronger currents. Over the past three decades, TFN in the lagoon has on an average gone down from 65,667 in 1976 to 56,100 (present study) specimens per 100 g of sediments. The larger foraminiferal distribution in the Kavaratti lagoon has slightly but undisputedly undergone quantitative and distributional changes over the past three decades. The FORAM Index suggests conducive environment for coral growth in the lagoon. However, definite deterioration due to dredging in the northern lagoon is indicated by the assemblage. The study also records signatures of domestic discharge and predicts a larger impact on the corals since 2004 to 2024.