The Noctiluca algae is often reported to occur in patches or blooms in the Northern Arabian Sea. These striking green blooms often appear to glow at night due to a special phenomenon called bioluminescence, earning them the nickname ‘sea sparkle’. Unfortunately, these beautiful patches, indicate zones of decline because fish cannot thrive and sometimes die because of these blooms. Noctiluca voraciously eats one of the most important planktonic organisms at the base of the fish-food chain, namely diatoms, and also excretes large amounts of ammonia, linked with massive fish mortalities.
The success of Noctiluca was previously assumed to be linked with low oxygen and coastal pollution from major Indian cities along west coast. However, this link is strikingly denied by results of a new joint Indo-US study. Scientists from Indian National Centre for Ocean Information Services (INCOIS) under the Ministry of Earth Sciences (MoES), Govt. of India and National Oceanic and Atmospheric Administration (NOAA) – National Marine Fisheries Service (NMFS) under the US Dept. of Commerce worked together towards ‘Development of Predictive Capabilities for Marine Fisheries and Harmful Algal Blooms in Indian Seas’ to extensively collect samples and data. Sensors onboard satellites were used to observe the distribution of both diatoms and harmful Noctiluca. In addition, sea conditions, nutrients, and oxygen concentrations were studied with sensors attached to special free-floating and self-propelling Argo floats and chemical analyses of water samples were collected on board research vessels.
The study suggests that rather than effluents or chemical pollution, it is actually global warming conditions that are contributing to the observed abundance of Noctiluca in the Northern Arabian Sea. The warming climate will allow seawater layers to stratify more intensely. This will slow the upward transport of nutrients like silicate from the ocean bottom, lowering its concentration at the surface. Diatoms growing in surface water need both sunlight and silicate to build their glass skeletons and thus will fail to thrive when silicate becomes less available. On the other hand, Noctiluca remains unaffected by these changes and additionally will prey on the remaining diatoms. Remarkably, the waters in the study area were observed to have sufficient oxygen clearly opposing any linkage between low oxygen and Noctiluca growth. Intensifying global warming conditions, thus may be expected to disrupt the fish-food chain and cause a decline of fisheries in the region.
Further studies and monitoring are imperative to sustaining fisheries in the region. In this direction, INCOIS, Hyderabad is now setting up the MOSAIC (Marine Observation System Along Indian Coast) network of automated moored buoys to monitor and now-cast the water quality of the Indian coastal waters.
Further details are available at Lotliker, A.A., Baliarsingh, S.K., Trainer, V.L., Wells, M.L., Wilson, C., Udaya Bhaskar, T.V.S., Samanta, A., Shahimol, S.R. 2018. Characterization of oceanic Noctiluca blooms not associated with hypoxia in the Northeastern Arabian Sea. Harmful Algae, 74: 46-57, DOI: https://doi.org/10.1016/j.hal.2018.03.008.
Green colouration of sea surface with Noctiluca scintillans bloom in the northern Arabian Sea
