The upcoming coastal road in Mumbai, with a plan that involves reclamation across multiple shores, could be a threat to the coastal ecosystem.

The piece of land on the shore that reveals itself only at low tide is known as the intertidal zone. This ever-changing shore is a dynamic habitat, adaptive, resilient and vulnerable all at once.

In this article, meet the denizens of the intertidal zone and their different homes on the prime real estate in the city.

For a city that is fixated with its housing, real estate opportunities and acquiring homes with a view, finding a space to call your own in Mumbai carries its own form of trauma. If the rents and EMIs don’t knock the life out of you, it’s the negotiations on the transactions that will. In this milieu, the citizens that have a prime piece of the pie are shore creatures – and they navigate it with the expertise and eloquence that we humans regularly deny our land spaces.

Having said that, the threat of Mumbai’s upcoming coastal road, which involves reclamation across multiple shores along the city’s coast, no longer looms in the distance but is terrifyingly close, stomping the intertidal zone, rock by rock. The consequence is an erasure of a major swathe of an ecosystem.

The piece of land that reveals itself only at low tide is known as the intertidal zone. It’s where animals that can survive only in the conditions that are unique to this space (ebb and flow of saline water, varying temperatures) live and grow.

It would be easy for us to dismiss the intertidal as an empty piece of land, one that is washed clean over every few hours by the waves. But we’d be wrong.

The intertidal zone is a neighbourhood that criss-crosses with many lives at street-corner hangouts, room-sharing, private condos. The ever-changing shore is a dynamic habitat, adaptive, resilient and vulnerable all at once.

Here, we meet a few of the shore homeowners. This is by no means a comprehensive list – far from it – thankfully, the more we walk the intertidal, the more life we find living in it. For now, these are just a few animals whose houses you can stop by for a chat.

Hermit crabs: the relentless fighters for ‘bigger and better’ houses

If you watch a hermit crab trudge across the intertidal, you know that housing is a weight it literally carries on its shoulders. While these are crustaceans, under the phylum Arthropoda, these aren’t true crabs (the ones with short abdomens and hard shells). Hermits have long abdomens and soft bodies that make them vulnerable but are still designed to twist and fit into shells.

Which is why they carry around shells discarded by other animals (like snails) – as their homes. Their bodies have adapted to this form of life – their eyes rest on long stalks so they can take in their surroundings, their feet and abdomen have appendages that fix into the shell they choose (so don’t try and pry them out of their shells, you might hurt them, or cost them a limb).

Increasingly, because of the way our shores are changing, hermits have been known to make do even with the trash we leave behind.

When hermits outgrow their shell, they find larger ones, and in some cases, fight other hermits over truly remarkable real estate. Relentless strugglers, like us humans, hermit crabs will always have a bigger, better real estate opportunity on the horizon.

Barnacles: sticky squatters

If you’ve walked on a rocky shore at low tide, and had the unfortunate experience of slipping on the moss-covered rocks, chances are your bleeding hands or legs have met acorn barnacles and their sharp-as-knives shells.

These animals attach themselves to rocks on the shore and are seen in abundant numbers – from the highest hide-tide zones downwards to the surf zone. They grow on almost everything near the shore including submerged jetties, pillars, even living organisms like oysters, gastropods and other marine animals. Weirdly enough, these aren’t gastropods, but crustaceans (same family as crabs!), part of a class called Cirripedia (meaning ‘hairy foot’).

As larvae, these creatures swim around freely but later attach themselves head-first to a substrate, developing the conical shell-like structure around them, which remains closed in the absence of water.

They’re active when submerged in water, so at low tide, one can see them open to feed inside tide pools. Specially-paired appendages called cirri reach out through the ‘mouth slit’ and the animal uses these to sieve food particles from water. There are 900 species of barnacles, including the goose barnacle that can be seen on Mumbai’s shores (called so because of the white colour and the shape of the covering).

These barnacles have come in from things floating in from the ocean to the shore and this can include driftwood to manmade cast-offs. In the deep ocean, you’ll see barnacles growing on whales and ships. They’re unpopular with sailors as they grow on the bottom of ships and slow down the speed, thus increasing fuel consumption. They also do the same to other animals in the water, like turtles and whales and on the shore, wreak significant havoc on piers, jetties, pipes, cables.

Cratena: the art of war

Certain sea slugs, like some species of Cratena, live on their food. This gorgeous white and orange little animal lives on creatures called hydroids.

Hydroids are often mistaken for plants due to their appearance – the ‘stalk’ is attached to the substrate and the rest of the animal seems to branch out. Part of the phylum Cnidaria (which also hosts jellyfish, sea anemone, corals), hydroids belong to the class Hydrozoa, which means ‘water animals’ in Greek. They possess polyps – individual sessile animals, with tentacles, mouth and a gut. They are colonial animals and like most cnidarians, possess stinging cells called nematocysts.

This doesn’t really worry the Cratena, in fact it uses its home in many different ways: it lays eggs on hydroids, feeds on the polyps and even stores its stinging cells to use as a defense against a predator. The cells are stored in tiny sacs on the tips of their cerata (outgrowths that appear like flames on the sea slug) and are discharged when the animal is attacked. According to a study, some species of sea slugs prefer to eat hydroids that have also just had their fill.

Study author Trevor Willis speculates that it’s a way for the animals to get calories from plankton while also not overeating hydroids, which they depend on for shelter, in addition to nourishment.