Significance of herbivorous reef fishes on reefs of the Gulf of Mannar, southeast India

Abstract

Reef fishes, especially herbivorous fishes, play key roles in maintaining the integrity of coral reef ecosystems. We selected four herbivorous reef fishes, namely Scarus ghobban, Siganus javus, Siganus canaliculatus and Siganus lineatus, and examined their feeding behaviour through gut content analysis and their abundance through underwater assessments on a patch reef in the Gulf of Mannar, southeast India during 2022–23. The results revealed that these fishes feed primarily on algae and seagrasses for these items made up more than 40% of their gut contents, with the exception of S. ghobban . And all four species feed on minimum amounts of other organisms, such as sponges, mollusks, crustaceans, etc., opportunistically or accidentally. The densities of these four species decreased within a year while the algal cover increased by around 1% presumably indicating the reduced grazing. This short-term study provides an insight into the importance of herbivorous fishes to maintain the delicate balance of the reef while warranting more focused long-term monitoring. It is apparent that the conservation of herbivorous species such as these four examined species is of critical importance in the context of global climate change in order to sustain the integrity of coral reef ecosystems in the Gulf of Mannar or elsewhere.