Hypoxia conditions caused by the Green Noctiluca in the coral reef ecosystem of Tuticorin surface coastal waters along the Gulf of Mannar (Biological Paradise)

Abstract

Abstract The current study found that environmental variables triggered the sudden outburst of a high-density and thick mat-like algal bloom proliferated by Green Noctiluca on the coral reef surroundings in the coastal surface waters of the Tuticorin coast of the Gulf of Mannar (GoM). It is a distinguished heterotrophic dinoflagellate and bioluminescent organism in marine ecosystems. Coral reef ecosystem around the world have been waning severely in contemporary period. Climate change and disease epidemics are primarily responsible for coral devastation and other marine biodiversity. In this investigation, we report on considerable coral mortality due to a Green Noctiluca bloom on Kasuwar Island, Tuticorin Coast along Gulf of Mannar. The surface coastal waters have appeared as a strong bright green, and the microscopic laboratory analysis of the seawater samples exposed the existence of Green Noctiluca in high abundance and density. During the sample times, the mean concentration of Green Noctiluca was 3.98 × 105cells/L, associated with hypoxia and an abnormally elevated ammonia level in the Green Noctiluca bloom outburst zones. Hypoxic conditions (DO level less than 3mg/L) caused by harmful algal blooms can drive the destruction of corals, though they are reported rarely. The dissolved oxygen (DO) levels in bloom outburst zones declined below 3 mg/L. During the sampling periods, the Green Noctiluca bloom caused temporary low levels of dissolved oxygen in the fast-growing coral genera Acropora sp., Turbinaria sp., and Montipora sp., which were observed in the reef crest and reef slopes. Therefore, it is likely that shallow-water coral reefs will be affected more often by episodic smothering conditions caused by harmful algal blooms. Due to global climate change, anthropogenic activities, and the enrichment of nutrients, more frequent and larger algal blooms are expected in the future. Furthermore, long-term observation and scientific studies are required to understand the mechanisms of highly sensitive marine ecosystems due to harmful algal blooms, their impacts on community composition, and the potential for subsequent revival and conservation of marine ecology and biodiversity.