Ecological responses of autotrophic microplankton to the eutrophication of the coastal upwelling along the Southwest coast of India

The primary ecological effects of the eutrophication of upwelling in the nearshore waters are the triggering and sustenance of phytoplankton (diatom) blooms. Here, we present the changes in the morphological characteristics and body size of microautotrophs associated with the nutrient enrichment of coastal upwelling along the southwest coast of India. The FlowCAM data of microautotrophs representing two time series locations in the coastal environment along the southwest coast of India at 18 weekly/biweekly frequencies showed the following features. The most significant response of the microautotrophs to the eutrophication associated with coastal upwelling during the Southwest Monsoon (June-September) was an increase in their mean bio-volume, either by increasing the individual cell size or by forming large colonies. During the Southwest Monsoon, large colonies of Thalassiosira (similar to 8 cells/colony), Thalassionema (> 16 cells/colony), and Asterionellopsis (> 8 cells/colony) become very abundant. Streptotheca formed large mat-like colonies (av. 192350 +/- 348 mu m(3)/individual), and Fragilariopsis grew as very long ribbons (av. 272997 +/- 5071 mu m(3)/individual). Large-sized Chaetoceros (av. 45715 +/- 1273 mu m(3)/individual) with longer setae were also plentiful during the Southwest Monsoon. All these changes in the morphology and life forms of microautotrophs would help them to rapidly assimilate nitrate under turbulent conditions during the Southwest Monsoon.

Automated summary

Research indicates that the nutrient enrichment of coastal upwelling along the southwest coast of India leads to changes in the morphological characteristics and body size of microautotrophs. During the Southwest Monsoon, these organisms form large colonies to better assimilate nitrate.