Adaptation of phytoplankton communities to mesoscale eddies in the Mozambique Channel

An investigation of phytoplankton pigment and absorption characteristics was undertaken during three research cruises in the Mozambique Channel to elucidate community structure and examine the adaptation of populations to mesoscale features at the surface and the deep chlorophyll maximum (DCM). Total chlorophyll a concentration (TChla) at the surface was determined to be greater in cyclonic eddies than in anticyclones, while TChla in divergence and shelf zones were similar to cyclones, with frontal zones being slightly lower. TChla at the DCM was similar for all categories, although there was a tendency for anticyclones to have lower TChla. Prokaryotes were the most significant phytoplankton group at the surface, with small flagellates also being of secondary importance, while flagellates dominated at the DCM. A few shelf stations, and frontal and shelf stations close to the shelf, displayed high TChla and diatom domination, particularly at the DCM. Absorption properties and photopigment indices revealed that prokaryote dominated communities had high chlorophyll-specific absorption coefficients, a large range in the proportion of TChla within the total pigment pool and a high proportion of photoprotective carotenoids. Diatoms had low chlorophyll-specific absorption, a relatively high proportion of TChla, and elevated proportions of photosynthetic carotenoids and chlorophyll c. Flagellate dominated communities had intermediate chlorophyll-specific absorption, a lower proportion of TChla, elevated photosynthetic carotenoids and intermediate chlorophyll c.