New distribution record of globally threatened Ocean Turf Grass Halophila beccarii Ascherson, 1871 from the North Andaman Islands highlights the importance of seagrass exploratory surveys

Abstract

Halophila beccarii, listed as ‘Vulnerable’ on the IUCN Red List, aids in seagrass and mangrove succession, acts as a substrate stabilizer and provides feeding grounds for mega-herbivores like dugongs. This species was first recorded from the Andaman & Nicobar Islands in 2015, and its distribution status within the archipelago remains under-investigated. We report a new distribution record of H. beccarii from the North Andamans and shed light on its inter-island distribution. H. beccarii was recorded from a mixed meadow comprising of Cymodocea rotundata (20.5 ± 28.8%, mean seagrass cover), Thalassia hemprichii (16.3 ± 23.3%, mean seagrass cover), and Halodule pinifolia (6.3 ± 12.1%, mean seagrass cover) at Pokkadera, North and Middle Andaman district. H. beccarii had the highest mean seagrass cover (30 ± 34.7%) and shoot density (103.5 ± 68.3 shoots/ m2) among sympatric seagrass species. We also recorded eight seagrass-associated macrofaunal groups (gastropods, bivalves, polychaetes, foraminiferans, nematodes, brachyurans, decapods and asteroids) from the infaunal and epibenthic micro-habitats within the meadow. Infaunal macrobenthos had a much higher density (73.5 ± 129.7 individuals/m2) than the epibenthic macrofauna (0.4 ± 1.5 individuals/m2), possibly influenced by the seagrass canopy structure and biomass. Overall, gastropods were the most dominant macrobenthic faunal group (overall mean 95.0 ± 106.1 individuals/m2). The present findings emphasize the need for more exploratory surveys to understand H. beccarii distribution in the Andaman & Nicobar archipelago to identify priority conservation areas.