Seasonal variation in the biomass, quantity and quality of agar from Gelidiella acerosa (Forsskal) Feldmann et Hamel (Gelidiales, Rhodophyta) from the Gulf of Mannar Marine Biosphere Reserve, India

SUMMARY The Gulf of Mannar on the southeast coast of India, which has recently been declared as biosphere reserve, is the main harvesting place of Gelidiella acerosa for the Indian agar industry. The biomass harvested from natural stocks was estimated to be over 10 000 tonnes dry weight (DW) in the last two decades and is a serious cause of concern on long term sustainability of this valuable resource from this region. The present study reports the seasonal variation in the biomass and agar yield and quality from G. acerosa in four different habitats such as Rameswaram (rocky intertidal), Ervadi (lower intertidal), Sethukarai (subtidal) and Krusadai Island (lagoon reef area). A maximum biomass of 260 ± 26 g DW m−2 was recorded from Ervadi, whereas Sethukarai showed the highest percentage cover (69.83 ± 4.83%) and density (208.20 ± 30.16 plants m−2). Biomass, percentage cover and density were lowest in Rameswaram and significantly lower (P