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Wild Shores: Life in a Tide Pool

When the tide goes out, take a walk along the shore and discover a fascinating range of marine animals and plants

By Sejal Mehta

We may love walks on the beach and the sound of waves crashing on the shore, but the sea also offers other hidden joys. All along the 7,500-km-long coastline of India, the rise and fall of the tide supports ecosystems that are rarely noticed.

When the water recedes, and human activity abates, a part of the shore only visible at low tide — the intertidal zone — becomes exposed. Due to the continuous ebb and flow of salty water, and exposure to harsh sunlight, the intertidal zone is a good place to explore marine biodiversity. At low tide, the wilderness on our shores is revealed, making this a nature trail like no other. Here are some of the most common creatures you’ll find in a tide pool on the shore, to get you exploring on your next seaside stroll.

A sponge's porous body enables it to absorb oxygen and food from the water flowing over it, while discharging waste into it. Photo: Sejal Mehta

A sponge's porous body enables it to absorb oxygen and food from the water flowing over it, while discharging waste into it. Photo: Sejal Mehta

Sea sponge

Some rocky shores look like gardens, with sea sponge ‘growing’ on the rocks. Interestingly, these animals were the inspiration behind the protagonist of the animated show, Spongebob Squarepants. If you see them, go closer and look at their skin. These primitive animals belong to a phylum called Porifera, which literally means ‘pore-bearing organisms’. Pores filter food in the form of bacteria, plankton, and other organic matter from the sea.

Fiddler crabs are usually 2-5 cm in size. They have five pairs of legs and a two claws; the large claw can be almost half its body weight. Photo: Abhishek Jamalabad

Fiddler crabs are usually 2-5 cm in size. They have five pairs of legs and a two claws; the large claw can be almost half its body weight. Photo: Abhishek Jamalabad

Fiddler crabs

These crabs are extremely entertaining to watch. Fiddlers get their name from the behaviour of the male of the species. Fiddler males have one very large claw, which they wave, to mark territory or to attract mates. This action resembles a person playing a fiddle. Usually found in mudflats and among mangroves, but also on other shores, this crab is the easiest to spot and identify for a shore beginner. In Japan, they are called shiomaneki, which loosely translates to ‘the one that beckons the tide’.

Sea anemones are typically found attached to a hard surface, but some species are also observed in sand or mud, while others will float on water. Photo: Sejal Mehta

Sea anemones are typically found attached to a hard surface, but some species are also observed in sand or mud, while others will float on water. Photo: Sejal Mehta

Sea anemone

Named after the anemone flower due its obvious resemblance, it’s easy to mistake a sea anemone for a plant. It has a flower-like organism on the surface (tentacles and an oral disc) and a trunk-like column that’s buried under the sand or attached to a surface (like a root). But this animal is classified under the phylum Cnidaria, which also includes jellyfish and corals. They’re found in the deep sea as well; remember the home Nemo lived in with this father in the animated film?

Endowed with a beautiful branching structure, sea fans usually anchor themselves in mud or sand. Photo: Sejal Mehta

Endowed with a beautiful branching structure, sea fans usually anchor themselves in mud or sand. Photo: Sejal Mehta

Sea fan

These creatures are colonial soft corals found predominantly in warm waters and around reefs both in the intertidal zone and in the deep. The tiny animals are called sea fans because of their resemblance to old hand-held fans. The fan-like body branches out, giving the impression of a tiny tree growing. They are found in glorious colours on Mumbai’s coasts.

Hoof-shield limpet

This little creature sits clamped on rocky surfaces in tide pools and it is easy to miss them if you’re looking for larger or more colourful creatures. But the limpet, which will probably be feeding when you find it, has interesting capabilities. Its scientific name (scutus unguis) comes from its shell, which looks like a shield — called ‘scutum’ — used by ancient Roman armies. It scrapes algae off rocks with a radula, a bristly tongue with rows of tiny teeth made of the mineral goethite set in a chitin matrix, resulting in one of the strongest biological materials known to humans.

The hoof-shield limpet (left), a variety of sea snail, uses its foot to firmly attach itself to a rock so that it cannot easily be displaced by the movement of the waves. Spiny skin and five arms usually characterise sea stars, but some species are known to grow up to 40 arms. Photos: limpet by Shaunak Modi; sea star by Sejal Mehta.

Sea star

Sea stars or starfish aren’t actually fish, but marine invertebrates. These are delightful creatures to come across on busy beaches because of how much pop culture has already endeared them to us. They’re usually found towards the edge of the intertidal zone, close to the water, clamped on rocks, moving slowly with their tube feet. These animals possess the power of regeneration, and some species can grow back even from one severed healthy limb.

In the right conditions zoanthid colonies expand rapidly, packed in tight clusters they can be mistaken for a carpet of coral (Photo: Abhishek Jamalabad).

In the right conditions zoanthid colonies expand rapidly, packed in tight clusters they can be mistaken for a carpet of coral (Photo: Abhishek Jamalabad).

Zoanthids

When open at high tide, these startling green creatures look like a bouquet of flowers scattered over rocky surfaces. These are also Cnidarians, and come under the same class as anemones, which is Anthozoa. Unlike anemones, zoanthids live in colonies, and are more like coral in that sense. When the tide rolls out, they retract their tentacles and close off, resembling a small jelly-like object. Some zoanthids can be extremely dangerous as they carry minute quantities of a marine toxin called palytoxin, which can paralyze or kill a human if it enters the body.

 

TIDEPOOL ETIQUETTE

  • Tread lightly. Watch your step when you walk in the intertidal zone. It is a home, a forest. A lot of animals attach themselves to rocks, or are buried in the sand.
  • Wear closed shoes with a firm grip. Rocky shores are also full of sharp barnacles and empty oyster shells. The intertidal area is slippery. Algae covered rocks can prove treacherous if you fall.
  • Don’t touch or pick up animals. And don’t treat these creatures as selfie props. Some creatures, like Conus or jellyfish, are venomous. Also, the animals you see could be in the middle of a hunt, or being hunted, laying eggs etc. and a slip in focus might be fatal to them. Some animals like sea stars, porcelain crabs, and sea cucumbers will literally dismember themselves if they feel threatened. Even with harmless intentions, we can stress an animal into this state.
  • Try not to move things. Some of these animals are territorial, or in search of perfect conditions for specific activities. They might not survive in another place.
  • Don’t take back souvenirs. Some of these animals are Schedule 1 species, and you could be arrested for taking them. Everything on a shore is used by something or goes back into the sand. Just like we wouldn’t want guests picking up our things when they visit, we should leave shore life as we find it. Sea shells are useful to many creatures, namely hermit crabs, leave them as they are.

Sejal Mehta
Sejal Mehta

is a writer and editor based in Mumbai, creating articles and fiction about science, wildlife, and travel. She is also founder at Snaggletooth, a nature-inspired merchandise brand.

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