Blowin’ in the Wind: The Intertidal Zones of Vaippar

India’s intertidal zones are incredibly diverse both in the life they harbour and their very design — formed at the point where unique land and sea elements converge. Like a thumbprint, signature, or dosa, no two intertidal spaces look or feel the same. The intertidal zones of Vaippar, a small town in the Tuticorin district in Tamil Nadu, are surrounded by surreal land and sea features — jagged rocky coasts between long, sandy beaches. The land side of this intertidal zone is a seemingly never-ending landscape of salt pans interspersed with patches of Prosopis and grasses. The sea that ebbs and flows onto this intertidal zone is the Gulf of Mannar. The sea brings in nutrient-rich waters that support the diversity of algae and filter-feeding animals that live in the intertidal zone. From the land side, meandering seaward streams and water outlets from saltpans carry sediments onto the shoreline. These parts also experience the full force of another unsung architect of the coast — the wind.

In the shadow of the wind

The winds that blow over the sea energise the water to flow in different directions. Even the waves approaching the shore move at angles. As these waves move closer to the shore, they begin to conspire with the coastline to create currents of water that run parallel to the shore (longshore currents). The monsoon winds, thanks to their sudden switch in direction, have dramatic effects on longshore currents, and consequently, the Vaippar shoreline— flowing from the southwest until September and from the northeast starting in October. The southwest monsoon winds bring sandy sediments from the south, turning most of Vaippar into a long, uninterrupted sandy beach by September. The northeast monsoon takes the sand away and carries it to the south, exposing the beach rocks that line these shores. Sandy or rocky, Vaippar’s intertidal zones are bustling with life. 

Grains, shells, and the lives in between

Vaippar’s beaches have immense character. Large, coarse sand particles line most of the beaches; sheltered coves become deposition areas for more shells in a square metre than my mind could process. Living on the coarse shell-filled sands are a diversity of crabs. Red ghost crabs pop out of holes at regular distances, painting the beige beach with their Ferrari-red scuttles. Between them are crop-circle type patterns that decorate the beach, created by sand bubbler crabs. The tiny fingernail-sized sand bubblers pick up sand and roll it around in their mouths, taking in all the nutrients and discarding neatly balled sand in complex rows. Another filter-feeder that is generously distributed on this beach is the wedge clam. This remarkable bivalve uses its siphon (a tube-like feeding structure) to allow seawater to flow in, filtering out its food. Its diet consists of a healthy mix of decomposing organic matter and plankton. When the clam has fed enough, it quickly burrows itself in the sand to stay safe from potential predators and strong surges of water that may strand it too far inland. Who are the clams so afraid of? On most of my walks on the beach looking for wedge clams, I almost always find myself in the company of curlews, sandpipers, and whimbrels. All are birds with sharp, pointy beaks, built to probe the sand for crabs, clams, and any other invertebrates they can find in the sand.

Rocky sandcastles

When the northeast monsoon kicks in and carries sand away from Vaippar beach, incredible things happen. I have seen a spot outside the Aqua Outback resort (in Vaippar) drop in height by nearly 1-1.5 metres in a matter of days. The disappearance of the sand almost magically unveiled the jagged beach rocks that sat quietly underneath for the duration of the southwest monsoon. The beach rocks close to the high tide line are completely submerged underwater during high tide and completely exposed to air during low tide. Vast populations of tiny periwinkle snails inhabit these rocks, most the size of matchstick heads, which dot every surface and crevice. The beach rocks are also generously covered with barnacles and adorned at regular intervals with oysters. And if you stick around the rocks when the tide rises to cover them, you begin to see coin-sized anemone unfurl on the rocks.

The beach rocks further toward the water stay submerged until peak low tide. These mostly aquatic rocks are the homes of a diversity of algae: bunches of sea grape hang from the sides, carpets of Padina engulf the tops, and a myriad others grow in every nook and cranny of the beach rock. These algae-rich rocks are excellent places to spot crabs. On top of bare rocks, mottled lightfoot crabs (Graspus albolineatus) scuttle to escape crashing waves. The crabs’ long legs end with pointed tips, giving them the appearance of an eight-legged robot effortlessly walking on four pairs of high heels. With their carapace (upper shell) measuring roughly 4 cm in width and longish legs, these crabs are quite visible as they move on the tops of rocks, the sea behind them adding contrast. When they are on the side of a rock, however, the mottled deep greens and striations of black on their carapace camouflage these eight-legged runners beautifully. 

Human footprints in the sand

In and around Vaippar (and all over India really), human activity is affecting our coastlines at a frightful pace. Unlike the force of the monsoons, human-induced change isn’t part of a carefully balanced natural cycle. Human land-use changes further inland, and large-scale dams affect how rivers like the Vaippar bring sediments towards the shore. These nutrient-rich sediments settle around mangroves and are vital to their sustenance. Waves and wind push sediments flowing past the mangroves towards the sea to form dunes on the shoreline, which are important barriers that prevent coastal erosion. Other human activities on the shore, such as sandmining and the destruction of coastal vegetation, push this shoreline to change faster than it can recover.