Blooms of phytoplankton along the west coast of India associated with nutrient enrichment and the response of zooplankton

Abstract

Incidents of blooms of phytoplankton, discolourations of coastal estuarine waters and swarms of zooplankton are regular features along the west coast of India These are generally concomitant with changes in the chemical properties of coastal waters This area is subject to episodic introduction of nutrients during the summer monsoon period (June-September) through river run-off and coastal upwelling Responses of phyto- and zooplankton to such inputs are often predictable and have been observed to form persistent patterns in numerous investigations Along the west coast of India regular blooming of Noctiluca, during or immediately after the onset of the monsoon, occurs following increases in phytoplankton populations Intermittent blooms of species of diatoms and dinoflagellates are also common Spectacular bloom formations of Trichodesmium is a regular phenomenon during the later part of the NE monsoon season At times, these blooms cover hundreds of kilometres Very often successions of phyto- and zooplankton communities could be traced During upwelling period, nutrient-rich cold subsurface waters occur in coastal areas and sometimes penetrate river mouths leading to high abundance of both phyto- and zooplankton Cladocerans, amphipods, pteropods, tunicates and herbivorous copepods are some the common zooplankton organisms which swarm following phytoplankton abundance Apex communities are usually dominated by chaetognaths, siphonophores and medusae