Summary of Abstract Submission

Abstract Submission No. IO50-09-0031PresentationPoster

VARIATIONS IN FOOD WEB DYNAMICS IN THE THERMAL FRONTAL ZONE IN THE ARABIAN SEA

J. Mukherjee*1, V. V. S. S. Sarma1

1 National Institute of Oceanography, India

ABSTRACT :

Oceanic fronts are rich in nutrients and are generated by drastic changes in thermodynamic properties. They are thus amongst the highly productive regions in the marine environment. To examine the trophic dynamics, five frontal zones were studied in the North-Eastern Arabian Sea during winter (2014). Content and isotopic composition of carbon and nitrogen of plankton were analysed to evaluate trophic levels (TL). Sea surface temperatures within the fronts were found to be cooler by 0.2 to 1.2oC. They were richer in nutrients and phytoplankton biomass than non-frontal zones. The 15N of phytoplankton were relatively enriched suggesting that nutrient inputs through vertical mixing supported their growth. Rates of nutrient uptake, primary and export production were higher within the fronts than outside suggesting that frontal zones are highly productive sites. Content of carbon and nitrogen per cell were significantly higher in phytoplankton and zooplankton in fronts compared to outside (by 15 to 30%) suggesting that availability of high nutrients enhanced uptake rates and primary production. Based on isotopic composition of carbon and nitrogen of plankton, we found that diatoms formed the base of the food web and catered to the dietary needs of zooplankton. The mean trophic levels were lower in the frontal zones (1.2 to 1.4) compared to the non-frontal zones (1.6 to 1.8), suggesting faster response of plankton to nutrient enrichments in the former than the latter. The longer TL in the non-frontal zone was attributed to existence of microbial loop that led to longer response time for zooplankton.