Corals of St. Martin's Island, Bangladesh: An illustrative guide

Abstract

Corals are invertebrate animals that belong to the phylum Cnidaria, a diverse and fascinating group of colorful creatures. Cnidarians come in a wide range of hues, sizes, and shapes, but what sets them apart is that they all have a main body cavity with a one mouth opening surrounded by stinging tentacles. Each coral animal is known as a polyp, and the majority of them live in colonies made up of hundreds to thousands of genetically identical polyps. The original polyp produces copy of itself during a process known as budding, which is how the colony is created. Both "hard corals" and "soft corals" are generic categories of corals. Hard corals, also referred to as "reef building" corals, are represented by about 800 species. Soft corals, such as sea fans, sea feathers, and sea whips, lack the hard internal calcareous skeleton of the hard corals that gives them their rock-like appearance, instead, they develop wood-like cores for support and fleshy rinds for protection. St. Martin’s Island is the only coral-bearing island in Bangladesh where corals have colonized a rocky reef that surrounds the island. The rocky reef with its coral communities protect the island from severe oceanic waves, storm surges, and beach erosion. This unique rocky reef that surrounds St. Martin’s Island also provides important spawning, nesting and nursery grounds for many marine vertebrate and invertebrate species. There are a variety of corals found on St. Martin’s Island. In the present study, a total of 46 coral species were identified that belong to 13 families. Among the 46 corals, most of the species belong to the family Merulinidae (21 species), Poritidae (12 species), and Acroporidae (3 species). Rest of the coral species belong to families Lobophylliidae (1), Plesiastreidae (1), Psammocoridae (1), Leptastreidae (1), Oulastreidae (1), Dendrophylliidae (1), Coscinaraeidae (1), Cladiellidae (1), Sarcophytidae (1), and Melithaeidae (1). All of the coral species belong to two subclasses of anthozoans, Hexacorallia (43 coral species) and Octocorallia (3 species). Most of the species belong to Order Scleractinia (43 species) and rest 3 species belong to Malacalcyonacea (3 species). The most abundant hard coral genera on St. Martin’s Island are Dipsastraea, Porites, Goniopora, Favites, and Platygyra. Cladiella australis, Lobophytum mortoni, Melithaea ryukyuensis species belong to the soft corals. About 15% of hard coral bleaching has commonly happened during monsoon and pre-monsoon periods because of high rainfall, a great quantity of freshwater input from upstream, a tremendous amount of sedimentation, global warming, and ocean acidity. It is time to implement a comprehensive environmental monitoring strategy that will support the development and implementation of sound conservation and restoration management plans for ecologically sustainable management of coral resources on St. Martin’s Island.