Summary of Abstract Submission

Abstract Submission No. IO50-05-0044PresentationPoster

SHIFT IN SIZE STRUCTURE OF PLANKTON OFF ALAPPUZHA, SOUTHWEST COAST OF INDIA, ASSOCIATED WITH UPWELLING AND MUD BANK EVENTS DURING THE SOUTHWEST MONSOON

Karnan, C*1, Jyothibabu, R1, Madhu, N.V1, Balachandran, K.K1, Pandiarajan, R.S1, Anjusha, A1

1 CSIR-National Institute of Oceanography, Regional Centre, Kochi, India

ABSTRACT :

Mud bank is a unique coastal oceanographic phenomenon that occurs along the southwest coast of India during the Southwest Monsoon (June - September), characterized by relatively turbid and calm waters and facilitating successful fishing activities. This study presents the prominent temporal difference in the size structure of plankton components observed off Alappuzha during the low-nutrient Preżmonsoon and high-nutrient Southwest Monsoon (mud bank/upwelling) conditions. Water samples were collected from two locations off Alappuzha during one mud bank period (July 2013) and one non-mud bank period (April 2014), and analyzed using a Flow Cam. The result showed a significant increase in the mean biovolume of plankton cells during the mud bank/upwelling period (av. 307917 µm³) as compared to the Pre-monsoon period (av. 42560 µm³).The elevated concentrations of macro-nutrients during the upwelling/mud bank period significantly increased the occurrence of larger diatoms such as Fragilaria and Chaetoceros, facilitating a short food chain favorable for the high stock of fishes. On the other hand, smaller plankton forms were abundant during the Pre-monsoon period, favoring a long and complex food chain, which is less efficient in supporting a large fish stock. We propose the noticeable increase in the size of the plankton as one of the reasons for the exceptional fishery stock associated with the upwelling/mud bank events that occur off Alappuzha during the Southwest Monsoon.