Sea cucumbers: The moppers of the ocean floor

Sea cucumbers—marine organisms that resemble the vegetable in their shape and form—are found on the seafloors of the world’s oceans. As scavengers, they feed on algae, microbes, plankton and the dead and decaying organic matter that reaches the ocean’s dark benthic zone. These ‘janitors of the sea’, as they are called, keep the seafloor clean and benefit an unlikely ecosystem—the coral reefs. 

Scientists studying the tropical coral reefs of the Pacific Ocean around the Palmyra Atoll in French Polynesia have discovered that corals growing near sea cucumbers had fewer diseases and tended to die less compared to areas where sea cucumbers were absent. On further probing, they figured out that the cleaning act of the benthic dwellers had a role: the sea cucumbers, as part of their scavenger diet, devour coral disease-causing bacteria and the decaying ‘food’ that the bacteria thrived on. As a result, corals growing around them were relatively disease-free and healthy. 

Across the world, coral reefs—which support a quarter of marine life and many livelihoods—are in deep peril. As ocean temperatures rise, they succumb to acidification and bleaching, diseases, and pollution. While several attempts are underway to rejuvenate coral reefs and make them resilient to these changes, the authors say sea cucumbers could play a role in keeping the remaining corals healthy. 

That is, if sea cucumber populations themselves are healthy. As these marine organisms are considered a delicacy and used in traditional medicine in some parts of the world, they are overharvested and illegally traded. So much so that they are now entirely absent in some regions. In 2020, India became the first country to create the world’s first sea cucumber conservation area off the Lakshadweep coast, named in honour of Dr K K Mohammed Koya to conserve sea cucumbers, which enjoy protections similar to tigers or elephants in the country.