Influence of environmental settings on the prevalence of Trichodesmium spp. in the Bay of Bengal

Abstract

Trichodesmium, an important marine nitrogen-fixing cyanobacteria, is widespread in tropical waters and contributes substantially to the global chemical cycles by new production. The interesting and intriguing feature of Trichodesmium blooms is the suddenness with which the blooms appear and disappear. A well-defined periodicity and annual rhythm of Trichodesmium blooms in the Indian south central coastal environments of the Arabian Sea between February and May is well documented. However, not much is known for the Bay of Bengal. Analysis of the surface water samples collected from the merchant vessels plying between Chennai and Singapore at regular intervals (February 2000 to September 2002) to study the variations in the micro-phytoplankton community indicated that Trichodesmium persists for a large part of the year in the south-eastern part of the Bay of Bengal. Remotely sensed images from 1997 to 2003 also indicated the prevalence of Trichodesmium in the south-eastern part of the Bay during the winter months and in the west (west Bay of Bengal and east Arabian Sea) during summer. This raises the possible role of physical forcing in the dispersal and seeding of Trichodesmium. The prevalence of stratified conditions in the Bay of Bengal almost throughout the year can be one of the causative factors facilitating the preponderance of Trichodesmium. The inter-annual variations observed indicate that the tracking of Trichodesmium will be useful in understanding the biogeochemistry of the region.