Hydrographic, seasonal diversity, distribution and abundance of phytoplankton in coastal waters off Cochin - south-eastern Arabian Sea

Phytoplanktons are the key primary producers in the ocean; their growth mainly depends on various physico-chemical parameters. In this study, a total of 73 species of phytoplanktons from 48 genera were identified from Cochin coastal waters. Diatoms dominated the phytoplankton community followed by dinoflagellates. Asterionellopsis glacialis, Chaetoceros decipiens and Chaetoceros curvisetum were the major diatoms noticed during the study period. The results revealed relatively high species diversity in the pre-monsoon season when compared to monsoon and post-monsoon seasons. The hierarchical multidimensional scaling of phytoplankton communities using PRIMER 6 revealed maximum similarity between the species from stations 1 and 2 during monsoon season. The canonical correspondence analysis was done using PAST version 2.17c. The results showed that post-monsoon stations were characterized by high dissolved oxygen, low temperature, phosphate, ammonia and silicate. Phytoplanktons, such as Rhizosolenia sp., Thalasionema sp., Navicula sp. were found to be strongly linked to these parameters. A bloom of Skeletonema costatum was also observed during the study period.