On rocky shores, we walk past them, oblivious. Tide pools are microcosms of the sea, teeming with life. From just a few inches to a few feet in depth and diameter, these shallow pools of seawater are found in the intertidal zone – the area of the shore exposed only during low tides. A cursory peek reveals some forms of life: barnacles, a few snails and small fish. A deeper inspection reveals more: anemones, porcelain crabs, sponges, snail eggs, and if you’re lucky, sea stars!
Low tide exposes a colony of sea sponges in a tide pool off Mumbai’s Marine Drive. (Photo by Rizwan Mithawala)
A porcelain crab under a rock on one of Mumbai’s shores. (Photo by Rizwan Mithawala)
Porcelain crabs live up to their names. Beautiful and fragile, they will shed a limb if attacked, and escape, just like geckos do, leaving the tail behind. Living literally under a rock, these flat-bodied crustaceans are not true crabs but related to squat lobsters and hermit crabs (which, too, are not true crabs). They are a perfect example of carcinisation, an evolutionary process wherein a crustacean evolves into a crab-like form from a non-crab-like form.
Egg capsules of a predatory sea snail attached to a wrecked boat on Mumbai’s Chowpatty beach (Photo by Rizwan Mithawala)
In tide pools, the eggs of some marine animal or other are surely to be found, attached to rocks. These egg capsules, each containing 20-40 eggs, belonging to a species of predatory sea snail from the genus Murex, are abundant on Mumbai’s shores.
Elysia hirasei, a tiny sap-sucking sea slug, in a shallow tidepool on one of Mumbai’s rocky shores. (Photo by Rizwan Mithawala)
Plants don’t go looking for food. With their incredible ability to photosynthesize, they can stand in one place and eat sunlight. Animals move about, in different ways, seeking out plants, to eat them. These are among the rules that most life forms on Earth live by, except a few.
Pictured here is Elysia hirasei, a sacoglossan sea slug, or, simply, a sap-sucking sea slug. Living off the cellular contents of algae is all right, but many species in the genus Elysia are ‘solar-powered’! They sequester living chloroplasts from the algae they feed on, and use them for photosynthesis themselves. Experiments on one species have shown that it can go without eating for over nine months. The phenomenon is aptly called kleptoplasty, for the slugs are using stolen chloroplasts.
A sea anemone in a tide pool on one of Mumbai’s rocky shores. (Photo by Rizwan Mithawala)
A flower blooms in the seas, and also in tidepools along the shores. Though named after the very showy anemone flowers, sea anemones are very much animals, related to jellyfish and corals. What we usually notice of a sea anemone is the spirals of swaying tentacles surrounding an oral disc, with a central mouth, which is usually slit-shaped. Below that is a cylindrical trunk, under which is an adhesive, pedal disc, which attaches the anemone to the surface. The tentacles are armed with cnidocytes – a kind of explosive stinging cells also used by corals and jellyfish, among others – and triggered by touch, instantly paralysing prey, which is then moved to the mouth.
When it comes to reproduction, sea anemones are non-conformists: they don’t stick to one method, or one sex. While some species have separate sexes, others are sequential hermaphrodites, changing their sex at some stage in life. One species, Epiactis prolifera, starts life as a female, but later also develops testes, to spend the rest of its life as a hermaphrodite. Despite going to such extremes to reproduce sexually, sea anemones are also capable of reproducing asexually, and here, too, they have more than one trick up their sleeve (tentacle)!
On your next visit to a sea shore, enjoy the sunset, but also squat and look down. Spot these evolutionary marvels in tide pools, but don’t startle, touch or pick.
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About the author: Rizwan Mithawala is a Conservation Writer with the Wildlife Conservation Trust and a Fellow of the International League of Conservation Writers. He has previously worked as an environment journalist with a national newspaper.
Disclaimer: The author is associated with Wildlife Conservation Trust. The views and opinions expressed in the article are his own and do not necessarily reflect the views and opinions of Wildlife Conservation Trust.
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