Phytoplankton community structure in the Drake Passage between the Magellan Strait and the Bransfield Strait

Abstract

During the Austral summer of 2001/02, phytoplankton biomass and species distribution were measured in the Drake Passage between the Magellan Strait and the Bransfield Strait region. Size-fractionated chlorophyll a (chl a) concentrations with species information were measured to investigate the relations between physico-chemical factors and phytoplankton community structure. Chl a values ranged from 0.14 to 2.42 mg chl a m-3 (mean of 0.93 mg chl a m-3) in the overall surface stations. The highest values of the chl a concentrations (1.08 - 2.42 mg chl a m-3) were found in the Magellan Strait and near Falkland Island in the Sub-Antarctic. Nanoplanktonic (<20 &micro

m) phytoflagellates were the important contributors for the increase of the chl a in the pelagic region. The nano-sized phytoflagellates accounted for more than 80% of the total chl a biomass in the pelagic regions of the Sub-Antarctic and the Antarctic. Mean chl a concentration in the Sub-Antarctic (0.92 mg chl a m-3) was 0.05 mg chl a m-3 lower than in the Antarctic (0.97 mg chl a m-3).