Did You Know? Starfish and How They Regenerate

In September 2019, newspapers around Galicia in northwest Spain reported an unusual marine phenomenon: Thousands of starfish had appeared along the Atlantic coastline, almost overnight, and were consuming the region’s clams, cockles, and mussels en masse. “They eat everything in their path,” a fisherman from the region was quoted saying in a story by Stephen Burgen in The Guardian. “And they like shellfish, the same as the rest of us.” The fisherfolk were distraught, locals were upset, and none could comprehend how the innocuous starfish could cause such decimation.

We think of starfish as relatively harmless — and they are, for the most part — but to cast them as merely beach accessories would be a grave injustice. For these are intriguing creatures, with bodies that can do extraordinary things, and minds we are yet to understand.

For starters, they are among the few species on the planet that can regenerate their arms. They can do this because of two reasons: Because they house their vital organs in their central disc, and because they have what scientists call ‘indeterminate stem cells’.

To understand what this means, let us first understand what stem cells are, and why parts of the scientific community are obsessed with them. “During embryonic development,” explains an article on the National Science Foundation website, “cells of most animals take on a particular identity —they become blood cells, lung cells, bone cells, etc. and keep these identities forever.”

A precious few however, fall into the indeterminate stem cell category, and have the ability to divide and create cells of any kind — a valuable trait to possess. Humans too have them, but only during the foetal stage.

Sea stars on the other hand, retain indeterminate stem cells throughout their lives, enabling them to regrow most parts of their bodies, even vital organs. This process can take anywhere between months to years, depending on the extent of the damage and the availability of resources such as food.

There are over 2,000 species of sea stars on the planet. They are found in saltwater systems, ranging from tropical tide pools to the frigid sea floor of the Atlantic. Most have five arms, though there are species with six, twelve, even upwards of twenty arms, such as the sunflower sea star. In India, sea stars are seen along the coastline, from the protected waters of the Gulf of Kutch Marine National Park in Gujarat, to the bustling beaches of Girgaum Chowpatty, where MLOM (Marine Life of Mumbai) conducts walks to introduce the city’s human residents to their marine counterparts.

For a closer look at sea stars, diving in the waters around Havelock and Neil islands (both in the Andamans) are a favoured option. The waters of this region are inhabited by dainty blue stars, cushion stars, and the infamous crown-of-thorns, a species that feeds on coral polyps. “We see plenty of sea stars in various stages of regeneration while diving,” says marine biologist Chetana Purushotham. “On rocks, hidden in crevices, amidst coral or sandy pools, with their stubby arms in the process of regrowth.”

They are resilient creatures, but not immune to harm. Whether diving, or taking a walk along the coast, Purushotham advises against handling sea stars for two reasons: Some species, like the crown-of-thorns, have venomous spikes that can cause a painful allergic reaction. And secondly, “because picking up a sea star causes immense loss of energy to the animal.” Sea stars, she explains, stiffen under stress as a defence mechanism, making it much harder for predators to consume them whole. It is a decent enough strategy for dealing with potential hunters, but it falls short when dealing with humans, especially in groups, with phones and cameras. Delight in viewing them, but from afar, give the wondrous sea star your undivided attention, and watch carefully: You might catch their tubular feet in action as they gracefully move away.