Spatial and temporal variability of SeaWiFS chlorophyll a distributions west of the Antarctic Peninsula:: Implications for krill production

ScaWiFS chlorophyll a distributions between 1997 and 2004 were investigated in relation to sea-ice dynamics for waters west of the Antarctic Peninsula (55-75 degrees S, 50-80 degrees W) in order to better understand the reproductive patterns and recruitment success of the Antarctic krill, Euphausia superba. Climatology patterns showed that the Bellingshausen Sea and Marguerite Bay region usually had higher chlorophyll a concentrations, which persisted throughout austral spring and summer, compared with more northern regions along the Antarctic Peninsula and the western Scotia Sea. These predictable and long-lasting phytoplankton accumulations could provide krill with the food levels required for successful reproduction and larval survival. Unusually high krill reproduction in 2000/2001 was coincident with above-average chlorophyll a concentrations throughout most of the study area and resulted in the largest juvenile recruitment (in 2001/2002) since 1981. High larval densities (up to 132 ind m(-3)) at the shelf break along the Antarctic Peninsula may have resulted, in part, from krill spawning in the Bellingshausen Sea. In general, ice-edge blooms were only a significant feature in the southern sectors of our study area, particularly in the Bellingshausen Sea and, thus, may not support krill reproduction in the northern Peninsula region as previously believed. Instead, phytoplankton blooms during spring in the northern region appeared to be governed by shelf-break processes, such as upwelling of iron-rich deep water. Interannual differences in sea ice also probably contributed to the variability in larval krill abundances observed in Marguerite Bay. Sea ice melted early in 2000/2001, allowing elevated phytoplankton blooms to develop. In contrast, sea ice persisted throughout spring and summer 2001/2002 limiting phytoplankton accumulation, particularly in southern Marguerite Bay. Thus, the early and extended availability of elevated chlorophyll a concentrations during spring and summer 2000/2001, particularly in the vicinity of Marguerite Bay and to the south in the Bellingshausen Sea, as well as reduced sea ice in coastal areas, likely supported the unusually high densities of larval krill observed during fall in waters west of the Antarctic Peninsula. (C) 2007 Elsevier Ltd. All rights reserved.