In the coral paradise of Lakshadweep, four species of this branching coral stand out on the richly coloured reef. Look inside its branches, and you’ll see a mini ecosystem of invertebrates, fish, and algae
Text by: Farai Divan Patel
In the coral paradise of Lakshadweep, four species of this branching coral stand out on the richly coloured reef. Look inside its branches, and you’ll see a mini ecosystem of invertebrates, fish, and algae
Coral reefs are bursting with life, but they are also dangerous places to live. Thousands of peering eyes from an array of potential predators scour the reef hungrily. One wrong move and you could be dinner. In this eat-or-be-eaten environment, reef organisms use all the hiding places they can find. In fact, the majority of reef species are small and cryptic, living inside the reef structure and within the coral that creates it.
Corals are fascinating organisms; each individual is tiny, but together they form colonies that build the foundation of the reef. Their hard calcium carbonate skeletons provide the structure that forms the huge variety of niches that support a mind-boggling array of marine life. There are numerous coral species, with more than 200 recorded in Indian waters (Venkatraman, 2006), and they are classified broadly into a few growth forms. For example, massive corals grow in large boulders, foliose coral produce structures resembling petals or leaves, while branching coral, as the name suggests, have a network of branches that vary in shape and size. Some coral species are always found growing in a particular form, while others are extremely variable, growing in various forms depending on environmental conditions.
In the Lakshadweep Islands, India’s very own coral paradise, there is one group of corals that is home to some very peculiar inhabitants. Pocillopora is a genus of mainly branching corals that form intricate growths on their branches, much like modern sculptures, and stand out even in the richly coloured reefs. These lump-like growths, called verrucae, are only observed on Pocillopora corals and are the reason for their common name, cauliflower corals. Five species in the genus are found in India, and four of these have been recorded in Lakshadweep.
Two of the species of Pocillopora corals found on Lakshadweep’s reefs are (1) Pocillopora damicornis and (2) Pocillopora verrucosa. The verrucae, from the Latin verruca meaning wart-like, can be observed as small lumps in the second image. Though their function is unclear, one study suggests that they could play a role in reducing light stress (Soto et al., 2018). Pocillopora colonies easily seen in Lakshadweep, in the Andaman and Nicobar Islands, and Gulf of Munnar. The size of the branches and the space between them depends on the habitat of the coral, with colonies in fast-moving, shallow water having shorter and more compact branches to prevent breakage. Photos: Neil Shah (1), Vardhan Patankar (2)
Cover photo: Neil Shah
When you encounter a Pocillopora colony on a reef, a dascyllus is the first inhabitant you will likely spot. These fish usually swim around the edges of the coral. This (1) cloudy dascyllus (Dascyllus carneus), for instance, quickly retreats into the colony’s protective arms if you venture too close. Although shy when humans approach, studies by Chase et al. (2014) show the dascyllus can improve coral growth by protecting the colony from coral-eating fish. This symbiosis, where both organisms benefit, is found all over reefs. Cloudy dascyllus is not completely reliant on Pocillopora to provide sanctuary, it also uses Acropora, another genus of branching coral. Swimming within the branches of these corals you may also encounter the wonderfully named (2) pixy hawkfish (Cirrhitichthys oxycephalus), (3) the blackside hawkfish (Paracirrhitus forsteri) and juveniles of a whole host of reef fish. Photos: Vardhan Patankar (1,3), Farai Divan Patel (2)
As you get closer to the coral and begin to peer between its branches, a strange selection of creatures will begin to appear. The coral protects a mini ecosystem of invertebrates, fish, and algae. These include brittle stars, snails, and numerous species of shrimps and crabs, like (1) hermit crabs, (2) hairy Cymo crabs, (3) Alpheus lottini or coral snapping shrimp, and (4) shrimp in the genus Saron. A. Lottini is part of a family (Alpheidae) that includes some of the loudest shrimp in the world. They produce a high-pressure bubble with their large front claw that they use to defend themselves and communicate. Photos: Vardhan Patankar (1), Farai Divan Patel (2,3,4)
Like the dascyllus, many of these crustaceans provide valuable services to their host colonies. Some are known to keep the coral free of sediment, while others are valiant defenders, posturing and approaching any nosy fish or inquisitive fingers with spread claws. Experiments have shown that the crabs of the genus Trapezia (1, 2 and 3), living inside Pocillopora are highly effective at guarding their homes from predators, including the ferocious coral-eating crown of thorns starfish. Photos: Farai Divan Patel (1), Vardhan Patankar (2); video: Vardhan Patankar
Looking even further into these coral sculptures you might, if you are lucky, see a large pinkish eye staring back at you. This belongs to one of the most unusual fish found in these reefs. Not much bigger than a finger, the (1) yellow spotted scorpionfish (Sebastapistes cyanostgm) is pink and, as its name suggests, has yellow polka dots. It uses the coral branches not only as a home but also as a hiding place from which it pounces upon unsuspecting fish. This fascinating critter is an obligate symbiont of branching corals, which means it is only found within these colonies. Another inhabitant you might spot is the (2) spotted coral croucher (Caracanthus maculatus), which is also a species of scorpionfish that has adapted to live within branching corals. Like other scorpionfish, these two species have dorsal fin spines through which they can release venom. However, neither is considered fatal to humans. Photos: Farai Divan Patel
Finally, observing the coral itself will reveal the individual (1) polyps, the organisms that together make up a coral colony. These can be seen as the small brown rings in the image on the right. Within these polyps is perhaps the most important symbiosis of the reef, the relationship between the coral and tiny photosynthetic algae known as zooxanthellae. These algae are what give the coral its fantastic colours and provide vital food to the coral host. However, in times of stress, the coral can bleach, ejecting the algae and turning a ghostly white (2). Despite repeated bleaching events, the branching corals around the Lakshadweep islands are making a comeback. If you are lucky enough to come across one, don’t forget to peer inside its branches. Photos: Neil Shah (1), Vardhan Patankar (2)
About the contributor
Farai Divan Patel
is an ecologist and activist based in Goa. He is currently working to research and conserve the coral reefs of India's west coast.
