Exploring the Coral Reefs of Goa’s Grande Island

India’s west coast nurtures many marine ecosystems and their associated fauna. From sandy beaches, estuaries, and mangroves to coral reefs and other open ocean habitats, the coastline showcases a vibrant display of marine ecosystems and coastal niches. Among these habitats are two coastal islands off the northern coast of Goa, namely Grande and Saint George Islands. Collectively referred to as Grande Island, the group is situated three nautical miles (approximately 5.5 km) from the urban centre of Vasco Da Gama.

On land, the island group is covered in wild shrubs with sporadic coconut trees. Underwater, there exists a different and dynamic world. A few metres below the waves, Grande Island reveals its gem — a thriving coral reef habitat — quietly tucked within the commercially important and popular coastline of Goa. Spread over 12 sq. km. encircling the island, the reef is home to 19 genera of reef-building corals that support over 120 species of reef fish and 37 genera of reef-associated invertebrates. Recreational divers have also spotted migratory and resident megafauna such as sea turtles, stingrays, and nurse sharks.

Grande Island’s significance is not restricted to the ecology of the coral reef habitat. It is one of the pioneering destinations for India’s SCUBA dive tourism industry, with operations spanning over two decades. Many of India’s most experienced and proficient dive professionals can trace their dive beginnings to this reef. Grande Island’s reef continues to support one of the longest-running and most accessible SCUBA tourism operations in the country.

A grand urban reef

“Coral reef” elicits a distinct and typical image of a thriving mass of different shapes and sizes of corals, with even more diverse and colourful marine life surrounding them. Incidentally, the coral reef habitat of Grande Island is not among them. This lesser-known habitat may not hold ground in its glamour quotient, but its USP lies in its ability to thrive in turbid, low-light environments that experience heavy sediment loads from nearshore activities. Such habitats are increasingly being termed urban coral reefs, as they are close to urban spaces and subject to high anthropogenic (human) stressors.

The Grande Island coral reef habitat consists of two kinds of reefs: 1) a fringing reef that runs from mid-way along the northern border of Grande Island, continuing westward until the Saint George Island curves in, and 2) patchy reefs that are located sporadically along the southern margins of the two islands, within smaller coves or valleys formed by the separation of rocky outcrops from the main landmass. The entire reef is characterised as a silty coral reef habitat. The coral cover encircling the island consists of metre-wide whorls of thin, crusted plate corals, and massive and sub-massive structured coral mounds interspersed with rocks with encrusted coral growth. The structural complexity of the coral reef — with expanses of filamentous algae and sargassum growth — supports a generous diversity of reef-associated fauna.

Denizens of Grande’s reefs

Diving at Grande Island on a regular day, you might spot: a blue-lined grouper (Cephalopholis formosa) giving you a side-eye from its territorial crevice; white-cheek monocle breams (Scolopsis vosmeri) following you like surveillance units; bubblefin wrasses (Halichoeres nigrescens) darting around corners as you swim through the yellow-silver clouds of goldstripe ponyfish (Karalla daura). If the stars have aligned to reward you with good visibility, you might see large-bodied cloudy groupers (Epinephelus erythrurus), blue-barred parrotfish (Scarus ghobban), fine-lined surgeonfish (Acanthurus grammoptelis), and masked triggerfish (Sufflamen frenatum) in the distance. Hermit crabs and molluscs (such as gastropods and bivalves) dominate the rock and gravel substrate at most dive sites, while a few other areas can be described as sprawling sea urchin cities. Strikingly colourful nudibranchs, pistol shrimps, and crabs add to the bustle of the reef. However, exercising caution while diving and observing the reef is important because what is beautiful may also be dangerous. Friendly neighbourhood moray eels (Gymnothorax spp.), scorpionfish (Scorpaenopsis spp.), and red lionfish (Pterois volitans) have a knack for making unexpected guest appearances at Grande.

Threats, challenges and resilience

There are very few locations where you surface from a dive and hear a commercial plane descending right over you. Fifteen minutes into your return boat journey, you’re surrounded by water sports activities, shipping vessels docking at the Mormugao Port, and an oil slick floating across the coastal waters surrounding the island.

Situated close to urban landscapes, Grande Island faces enormous challenges. Heavy sedimentation from terrestrial run-off makes the water perpetually turbid, restricting the sunlight available to photosensitive life forms such as corals. Limited sunlight restricts coral growth, providing an ideal environment for algae to take over. An unprecedented rise in the popularity of SCUBA diving amongst tourists has led to uncontrolled growth in local dive tourism operations, increasing the risk of unmanaged or unregulated interactions with the fragile reef. Other commercial and tourism activities around the island add to the pressures faced by the ecosystem, some of which include engine oil seepage, debris, discard of single-use plastics, and noise pollution. More recently, increasing accessibility to SCUBA gear and affordable spear guns have introduced additional pressures in the form of recreational fishing. While still in its nascent stages, spearfishing using SCUBA tanks can significantly reduce fish biomass on a coral reef, affecting the ecological abilities of the habitat to resist frequent disturbances.

Considering all these dynamic challenges and threats, one wonders how this ecosystem sustains itself in the face of multiple stressors. While coastal island reefs such as Grande Island will certainly not be as attractive or vibrant as their atoll and oceanic island counterparts, they seem to be resilient. The many human-induced pressures and disturbances this urban reef sustains today could have disastrous consequences on the popular reefs of India’s archipelagos. But what makes the Grande Island habitat so formidable? Is there an innate ability within Grande’s hard corals to survive repeated and prolonged stress exposure? Research groups are just beginning to understand the ecosystem functioning of the Grande Island habitat and asking questions that might shed light on its ability to survive in such a dynamic environment. While these reefs can be considered resilient, there is a pressing need to investigate the degree of impact that increasing human activities have and will continue to have on this habitat.

Recognising the importance of such unique habitats to the coastal and marine biodiversity along India’s coastline, steps need to be taken to conserve the coral reef of Grande Island. Currently, the island, the coral reef habitat, and its ecosystem services are largely unmanaged. Protecting Grande Island’s unique habitat requires management plans that conserve its marine biodiversity and safeguard the ecosystem services (like tourism and support for livelihoods) arising from this reef.

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Karan and Phalguni work with the marine programme at the Wildlife Conservation Society - India. One of the projects focuses on assessing the impact of SCUBA dive tourism on coral reef habitats and strengthening the management of coral reef habitats along India’s west coast.