The distribution of the chaetognath population and its interaction with environmental characteristics in the Bay of Bengal and the Arabian Sea.

Abstract

The Bay of Bengal (BoB) and the Arabian Sea (AS), the two major ocean basins in the north Indian Ocean, share similarities in geographical and meteorological characteristics but differ in hydrographic characteristics and biological production. The BoB is traditionally considered a less productive region than the AS. Chaetognatha, a major taxon of carnivorous mesozooplankton, often rank second in abundance to copepods and thus play a pivotal role in the pelagic food web of this region. We studied the influence of environmental variables on the distribution and the diversity of chaetognaths in these two ocean basins. Of the 21 species observed during the study, Flaccisagitta enflata dominated in the mixed layer to the thermocline, Decipisagitta decipiens from the bottom of the thermocline to 500 m and Eukrohnia fowleri below 500 m. Mesoscale and basin-scale processes such as eddies, gyres and upwelling had a profound influence on the abundance in the upper layer, while the presence of an oxygen minimum zone in the mid-depth layers had a crucial effect on the vertical distribution of the chaetognath population. Despite the variation in the controlling factors on chaetognath populations in the BoB and AS, the patterns of depth-specific abundance were similar