Beneath the rough/choppy/tumultuous waves of the Bay of Bengal, a kaleidoscope of marine life thrives just 8-12 km off Chennai’s Neelankarai coast. In this column, you are invited to explore a world of vibrant colours and extraordinary creatures, captured during 11 dives between January 2021 and March 2023. From the sunlit shallows at 12-18 meters to thriving natural and artificial reefs, these underwater ecosystems are teeming with life—each species a testament to the ocean’s boundless creativity and resilience.
Chromodoris geminus:
It is closely related to terrestrial snails and slugs, collectively known as Gastropods. These colourful sea-slugs are called nudibranchs, coming from the Latin nudus; ‘naked’ and the Ancient Greek bránkhia; ‘gills’. The white hair-like structures on the left-hand side are the gills through which they breathe, and the two yellow rice grain-like structures on the right-hand side are the sensory organs through which they find food, communicate, and sense changes in water pressure and vibrations.
Nudibranchs have evolved with distinct and vibrant colours to let potential predators know they are poisonous if consumed. First observed at a dive site named ‘Big Rock’, where large underwater rock structures create dense habitats. Such rock structures are spread across the southern Coromandel Coast, also providing important fishing grounds for traditional fishermen.
Elysia marginata:
This sea slug is of the Sacoglossan group and smaller than the size of my palm. Like a lizard that sheds its tail to escape predators, this sea slug has the ability of autotomy, separating its head from the rest, and regenerating its entire body and heart — possibly to escape from predators or remove parasites.
While feeding on algae, they absorb and store the energy-producing cells of green algae known as chloroplasts, subsequently photosynthesizing sunlight into energy like most plants do. This ability is unique in the natural world - as most animals are dependent upon active feeding to gain energy, including us humans.
While photographing both these sea slugs, a strong current was passing between the big rocks. Swaying with the current and holding on to the rock structure, they fed on sea sponge and algae deposits quite unaffected by my camera’s presence.
Hydrophis schistosus:
Commonly known as the Hook-nosed sea snake, this species is one of the most venomous snakes found in Tamil Nadu. While sightings are rare on land, they are quite common off the coastline. This snake like most others is not aggressive in character — swimming up close, inspecting its reflection in my camera lens, and then inspecting me. I had no feelings of fear or threat as this animal was purely inquisitive and curious.
Unlike land-dwelling snakes that are flat on the ground, the tail of this sea snake is laterally flattened, much like the tail-fin of a fish, so that it can swim and propel itself swiftly through water. They are known to dive up to 100 meters in depth, with the ability to stay underwater for up to five hours before re-surfacing to breathe. Another unique evolutionary trait of this species is that they are viviparous; meaning that unlike most reptiles that lay eggs on land, this species gives birth to live young ones while in the ocean.
Barrel Sea sponge:
This ant-hill looking creature is among the earliest multi-cellular animals on the evolutionary chain of events. Bound to the seabed and unable to move — they lack complex nervous, digestive, or circulatory systems, and rely on filtering water through their porous bodies to obtain food and oxygen, and remove waste materials. Many species have inner skeletons made of Calcium carbonate, similar to shells and exoskeletons of more advanced marine life forms such as clams, mussels, crabs and lobsters. Most species feed on bacteria and other microscopic organisms, while some establish symbiotic relationships with photosynthesizing micro-organisms within their porous layers.
Feather sea star:
Pictured here is a feather star, perched on top of a Red sea fan coral. These feathered stars are closely related to the starfish family, including sea urchins and sea cucumbers. These animals are not fish at all, but a much more primitive group of species that don’t possess gills, scales, fins or blood. They maintain a ‘water vascular system’ — instead of blood, using water to pump nutrients in and out of their bodies.
Their feather-like arms are used to propel themselves, curl up into a ball, and move up and down the water column, even climbing rock structures toward a better feeding position or avoiding predators. They swim through short bursts of energy that appear like the furling and unfurling of a garden flower through the course of a day. Their feather-like arms catch plankton, organic matter, and other microscopic nutrients from the water and push them towards a mouth-like structure at the base of its feathers. They’re also able to regenerate lost limbs/feathers!
Among all the species listed here, it’s truly amazing how the regenerative and symbiotic capabilities built through millions of years of evolution — stand as testament to the resilience of the ocean and all her life forms.
(Abhinav Sitaraman is an ecologist and photographer having done research on mammals at the Field Museum of Natural History in Chicago. He is also a scuba diver off Chennai's coastline.)