Marine macrophyte communities on the reef flat at Agatti atoll (Lakshadweep, India)

Abstract

The distribution, abundance and standing stock of macrophytes on the intertidal reef flat at Agatti atoll (Lakshadweep, India) were recorded in a total of 1234 quadrats in October 1993 and April 1994. Eighty seven species of macrophytes, including 16 new records, were observed on the different islands. The reef flat at Agatti can be divided into three zones partly correlated with physical factors. The upper zone is characterized by Thalassia hemprichii, Boergesenia forbesii, Gracilaria edulis and Valoniopsis pachynema, the middle zone by Gelidiella acerosa, Laurencia papillosa and Ceramium sp., and the lower zone by Ulva lactuca, Turbinaria ornata and Codium arabicum. Halimeda gracilis is dominant in both the middle and lower zone. The majority of algae exhibited patchy distributions, with seasonal fluctuations in their abundance. Species diversity increased with distance from the shore while percentage cover and species richness exhibited the reverse trend. Herbivory appeared significant with sea urchins as the major grazers. Algal abundance was reduced to one third in April mainly because of periodicity;governed by the monsoon. Macrophyte wet weight standing stock of Agatti reef flat was estimated to be 835 plus or minus 59 t (October 1993) and 686 plus or minus 77 t (April 1994).