The oceans store a substantial fraction of carbon as calcium carbonate (CaCO3) and organic carbon (Corg) and constitute a significant component of the global carbon cycle. The Corg and CaCO3 flux depends on productivity and is strongly modulated by the Asian monsoon in the tropics. Anthropogenic activities are likely to influence the monsoon and thus it is imperative to understand its implications on carbon burial in the oceans. We have reconstructed multi-decadal CaCO3 and Corg burial changes and associated processes during the last 4.9 ky, including the Meghalayan Age, from the Gulf of Mannar. The influence of monsoon on carbon burial is reconstructed from the absolute abundance of planktic foraminifera and relative abundance of Globigerina bulloides. Both Corg and CaCO3 increased throughout the Meghalayan Age, except between 3.0–3.5 ka and the last millennium. The increase in Corg burial during the Meghalayan Age was observed throughout the eastern Arabian Sea. The concomitant decrease in the Corg to nitrogen ratio suggests increased contribution of marine organic matter. Although the upwelling was intense until 1.5 ka, the lack of a definite increasing trend suggests that the persistent increase in Corg and CaCO3 during the early Meghalayan Age was mainly driven by higher productivity during the winter season coupled with better preservation in the sediments. Both the intervals (3.0–3.5 ka and the last millennium) of nearly constant carbon burial coincide with a steady sea-level. The low carbon burial during the last millennium is attributed to the weaker-upwelling-induced lower productivity.

Global climate change has aggravated the severity of space competition put up by marine sponges in the tropical coral reef ecosystems. We report here an outbreak of coral-killing sponge Clathria (Microciona) aceratoobtusa (Carter, 1887) over live coral colonies of the genus Turbinaria in an unprotected reef (mainland patch reef) in the Gulf of Mannar in India. An outbreak of this orange-reddish sponge was observed during an explorative dive in April 2020. Live coral cover in the reef was 62.06% (SD±3.36), which was dominated by the genus Turbinaria with 82.31%. Among the total of 549 Turbinaria colonies counted in five transects, 21.86% (n = 120) of colonies were found infested by the sponge. As the mainland patch reef lies outside the boundary of marine protected area, it is exposed to human-induced threats, apart from climate change implications. This report would serve as an evidence to indicate the intensity of the space competition waged by sponges in a disturbed reef ecosystem.

Starfish are echinoderms that live among corals and occur from the supra-littoral to the hadal zone. Deviation from pentamerism is a rare phenomenon in starfish and was observed in the red-knobbed starfish (Protoreaster linckii) collected from the Tuticorin coast, India. Eighty-five specimens were collected and, among these, one was found to be abnormal and had only four arms. The reasons for this abnormality may be due to the changes that occur during larval metamorphosis or caused by an abnormal regeneration of the arm.

This is the first record of Grammonus robustus from Indian waters. Five specimens measuring 132–233 mm standard length were collected from the by-catch landed by a deep sea trawler from waters 150 to 200 m deep off the Tuticorin coast in the Gulf of Mannar. The detailed morphometric and meristic characters are compared to known G. robustus material.

Neobythites stefanovi is recorded for the first time from Indian waters in the Gulf of Mannar. Two specimens were landed as by-catch in trawl gear at Tuticorin fisheries harbour, south-east coast of India, in March 2010. This is also the first record of the species outside the Red Sea, Gulf of Oman and Gulf of Aden, in the western Indian Ocean.

A new record on the occurrence of Neobythites multistriatus which hitherto had not been recorded from the Bay of Bengal is reported. Two specimens measuring 160 and 180 mm standard length were collected from the landings of a deep-sea trawler by-catch at depths of 200–250 m off the Tuticorin coast in the Gulf of Mannar (part of the Bay of Bengal) during March 2010. This is the first record of Neobythites multistriatus from the Bay of Bengal. The specimen is described and figured.

The striated fusilier Caesio striata, is recorded for the first time in Indian waters. A single specimen was caught in the Gulf of Mannar and landed at Tuticorin fisheries harbour in September 2010.