Ecological measurements of phytoplankton communities in the Arabian Sea water off Kerala and Karnataka coasts (South India)

Phytoplankton diversity, abundance and distribution were studied in the Arabian Sea water off Kerala and Karnataka coasts. The study was carried out from November 2009 to October 2011 on a seasonal basis and the relationship between physico-chemical characteristics of coastal waters and phytoplankton communities were analyzed statistically at sixteen sampling sites. During the study, Shannon-Weiner diversity index (J') varied from 3.271 to 4.139, Pileou's evenness (J') ranged from 0.935 to 0.980 and Margalef's richness index (d) varied from 6.511 to 12.021. The seasonal variation of H' showed high diversity during post-monsoon season followed by pre-monsoon and monsoon seasons, respectively. Based on NMDS analysis, the similarity of the phytoplankton of the sampling sites belonging to the same shoreline exhibited high species similarity. The phytoplankton abundance was positively related to pH, temperature, salinity, chlorophyll-a and nutrients and negatively correlated with dissolved oxygen, turbidity and silicate. Out of the 185 species of phytoplankton identified, the diatoms, namely Cymbella aspera, Licmophora abbreviata and Skeletonema costatum were found to be dominant while Oscillatoria limosa was the prevailing cyanobacterium.