Study links global warming with huge algae patches in Arabian Sea, fish mortalities

Global warming is resulting in massive patches of an algae species in the Arabian Sea that is eating up the planktons and excreting large amounts of ammonia leading to fish mortalities, a joint study conducted by institutes of India and the US has found.

The Noctiluca Algae is often reported to occur in patches and blooms in the Northern Arabian Sea.

The study also denies any link between the growth of the algae to low oxygen and coastal pollution from major Indian cities along the west coast.

These algae patches -- some as big as one-fourth the size of Mumbai -- are observed in the sea north off Mumbai and stretch as far as the Oman coast.

The 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," says the study.

Plankton is a very crucial element in the ocean food-chain.

The joint study was conducted by scientists from Indian National Centre for Ocean Information Services (INCOIS) under the Ministry of Earth Sciences (MoES) and the US government's National Oceanic and Atmospheric Administration (NOAA) - National Marine Fisheries Service (NMFS).

"Earlier, studies had linked the growth of the algae to low oxygen and coastal pollution from major Indian cities along the west coast. However, this link is strikingly denied by results of a new joint Indo-US study," said SSC Shenoi, Director of INCOIS.

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 study said.

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, the study adds.

The study also finds that the waters in the study area were observed to have sufficient oxygen, clearly opposing any linkage between low oxygen and Noctiluca growth.