Highlights
- Waters around the Grande Island (harboring patchy coral growth) along the central west coast of India experience low- O2, pH, and temperature during seasonal upwelling, while episodes of low- O2 and pH are observed during plankton blooms in the summer season.
- Changes in benthic communities and a steady decline in coral cover associated with a sharp increase in the macro-algae and rubble were observed at the Grande Island.
- Angria Bank, the offshore coral site, does not show extreme seasonal change in the environmental conditions, rather it shows open ocean biogeochemical characyteristics.
Abstract
The Western Indian Continental Shelf (WICS) experiences upwelling during the Southwest Monsoon (SWM), leading to deoxygenation and acidification of subsurface waters. The region has patchy growth of corals, e.g. in the Grande Island and Angria Bank. Measurements made during the late SWM of 2022 reveal that the shelf waters around the Grande Island were subject to varying environmental conditions, viz. lower temperature (21.3–26.1°C), oxygen (0–4.9 mL L−1) and pHT (7.506–7.927). Complete anoxia was associated with sulphide build-up to a maximum of 5.9 μmol L−1 at 17 m depth. An additional episodic condition (high temperature, low oxygen and pH) also occurred associated presumably with a plankton bloom in April 2017. Hence, unlike the offshore coral site Angria Bank, waters around the Grande Island experiences extreme changes in physico-chemical conditions (e.g. Ωarg ∼1.2–1.8 during October 2022) seasonally as reported here. The biogeochemical conditions are however not as intense (Ωarg = 0.6) as observed along the eastern boundary upwelling system of the Pacific Ocean.
Shirodkar G., Uskaikar H., Naqvi S.W.A., Pratihary A., Hussain A., Shenoy D. M., Gauns M., Manikandan B., Manjrekar S., Patil A., 2024. Seasonally varying biogeochemical regime around the coral habitats off central west coast of India. Marine Environmental Research 196: 106427. doi: 10.1016/j.marenvres.2024.106427. Article.
