CHENNAI: Ghost crabs that sidle on the east coast sands return home to find their habitat hostile, as splatters of thick gooey sludge from the oil spill have burrowed into the sands they dig into. Marine biologists say that the ocean ecosystem that lives on the sand and near the coast has been disturbed by the oil spill that happened last Saturday.
Fish that swim close to the coast, Olive Ridley turtles, hump back dolphins, the dark muzzles whose numbers have already dwindled over the years, Murex sea snails, nematodes and hundreds of microorganisms like rotifers and tardigrades that live between sand particles are among the several that keep the east coast alive. Marine biologists fear that toxins are entering the food web of the already degrading ecosystem.
“Starting from plankton, the small organisms ingest the toxins from the oil. Little marine insects could eat these tiny tar balls thinking it’s food,” said Rahul Muralidharan, a marine biologist.
“The smaller organisms easily absorb the toxins from their surroundings. If the toxins from the sludge have entered the interstitial microbes that live in the sand, they will enter the food web,” said K Venkataraman, ex-director, Zoological Survey of India.
The microbes that breed on the coast are consumed by insects, snails, worms and crabs on the shore. Small fish prey on these organisms and in turn, bigger ones eat the small ones.
The amount of toxin increases with higher and higher predators. One big fish will eat many small fish that eat several small insects that consume hundreds of microbes, each of which intrinsically pumps the toxins into the ecosystem.
This bio-magnification of the amount of toxins ensures that all organisms in the food web are affected. “While their food habits have gone toxic after the spill, they don’t even have conducive living conditions that nurture them,” he added.
The sludge oil that leaked from the ship has been deposited all along the high tide line. The inter-tidal organisms that live in the sand are more likely to be affected by the spill.
The oil that’s deposited on the sands prevents the entry of oxygen and food for these microbes, hence suffocating them. In addition, if the chemical dispersant used to break the layer of oil from the rocks mixes with the sludge making it denser than water, the toxins may get deposited on the ocean floor too. The crabs that spawn on the coast and the fish that spawn in the sands very close to the shore are at the risk of being affected.