India’s deep seas are home to 4,371 species of fauna, reveals ZSI by Shiv Sahai Singh .
India is home to 4,371 species of deep-sea fauna, including 1,032 species under the kingdom Protista and 3,339 species under the kingdom Animalia, a recent publication by the Zoological Survey of India (ZSI) has revealed.

The deep-sea ecosystem is considered to be below a depth of 200 metres, where solar energy cannot support primary productivity through photosynthesis. This publication is the first detailed work on deep-sea organisms of the country.

Published by Ministry of Environment, Forest and Climate Change, the book titled ‘Deep Sea Faunal Diversity in India’ is the work of five authors and several other contributors over 41 chapters.

India is surrounded by the Arabian Sea, the Bay of Bengal, the Andaman Sea and the Laccadive Sea (Lakshadweep Sea). Of the 4,371 species, the maximum of 2,766 species has been reported from deep sea areas of the Arabian Sea, followed by 1,964 species from the Bay of Bengal, 1,396 species from the Andaman Sea, and only 253 species from the Laccadive Sea.

RIMS ship investigator
The authors behind the book point out that India is one of the countries that made a pioneering exploration in the deep Indian Ocean region in 1874 by commissioning a RIMS (Royal Indian Marine Survey) ship investigator, which conducted enormous studies in seas around India. “This RIMS investigator continued to work till 1926. After that, several other vessels, including vessels of the Indian Navy and scientists from the ZSI and other institutions, conducted deep sea explorations, gathering information about the fauna. This publication is a result of the work put together by several scientists across three centuries,” C. Raghunathan, ZSI Acting Director, one of the authors of the publication, said. The marine biologist said deep sea fauna had a vast diversity, starting from unicellular eukaryotes, sponges, corals, echinoderms and fishes, and also mammals.

Kailash Chandra, former ZSI Director, said that the deep sea ecosystem was the most unexplored ecosystem across the world. It included hydrothermal vents, submarine canyons, deep sea trenches, sea mounts, cold seeps, and mud volcanoes. “This publication, the first of its kind, provides baseline information on all groups of fauna and biological organisms in the Indian deep seas. Not only will this support our knowledge on conserving and managing deep sea faunal resources, but it will also pave way for their sustainable utilisation,” Dr. Chandra said.

31 species of sea mammals
There are 31 species of sea mammals which are found in deep sea ecosystem of Indian waters, including the Critically Endangered Irrawaddy Dolphin. Two other species, the Indo-Pacific Finless Porpoise and the Sperm Whale, are recorded as ‘Vulnerable’ in the International Union for Conservation of Nature (IUCN) classification.

The list of mammals includes Cuvier’s Beaked Whale and Short-beaked Common Dolphin, which dive as deep as 8,000 metres below the Earth’s surface.

Marine turtles
Out of the seven species of marine turtles found across the world, five species have been recorded from Indian waters. India is known as one of the best and largest breeding grounds for sea turtles, especially for Olive Ridley and Leatherback Turtles, across the world.

Indicative map of Deep-Sea fauna of Indian seas
Indicative map of Deep-Sea fauna of Indian seas

The publication’s chapter-wise description includes details of 36 species of sponges, 30 species of hard corals, 92 species of octocorals, 124 species of hydrozoans, seven species of jellyfish, and seven species of comb jellies.

The other deep-sea fauna found in Indian waters include, among others, 150 species of molluscs, including 54 species of cephalopods; 134 species of prawns; 23 species of lobsters; 230 species of echinoderms, 53 species of tunicates, 443 species of fishes and 18 species of sea snakes.

The other authors of the book are Honey U.K. Pillai, P. Jasmine and Tamal Mondal.

The publication comes days after the allocation of ₹4,000 crore was made for the Deep Ocean Mission by the government of India in the Union Budget for 2021-22.

Scientists pointed out that while the publication comes up with a baseline figure of 4,371 species, there is an urgent need for greater exploration of Indian deep seas. Most of the earlier explorations were carried to maximum depth of 2,000 metres, whereas parts of Indian seas are deeper than 6,000 metres, Dr. Raghunathan said.