Biodiversity of chaetognaths of the Andaman Sea, Indian Ocean.

Abstract

Andaman Sea is a prominent biodiversity hotspot in the Indian Ocean. Stratified zooplankton collections were taken at 33 locations during 2003-2006. Average density of chaetognaths was 8.5/msup(3) in open ocean and 41.6/m sup(3) in coastal waters. Twenty species of chaetognaths, including two recently described species occur in the area. In the oceanic sector Sagitta enflata dominated the layer above thermocline followed by S. neglecta, S. bipunctata , S. pacifica , Pterosagitta draco, and S. regularis. In the depths from thermocline to 500 m, S. decipiens dominated followed by Eukrohnia fowleri. Aggregations of S. decipiens, a mesopelagic species, were occasionally found in the mixed layer (upto 9.9/m sup(3)) during Northeast monsoon associated with the upward movement of species. In the coastal waters either S. enflata or S. neglecta dominated. Recently described Krohnitta balagopali and Sagitta meenakshiae are endemic to the area. Maximum species diversity was observed at the thermocline. Invariably two clusters were found along each stratumat the 60 to 70% similarity level or higher. Latitudinally, species diversity increased towards south. Variability in the chaetognath community is influenced by unique physical features of the area