Zooplankton distribution and dynamics in a North Pacific eddy of coastal origin: 1. Transport and loss of continental margin species

Zooplankton from coastal/continental margin environments can be transported long distances seaward into the subarctic North Pacific by the large (100-200 km diameter) anticyclonic eddies that form annually in late winter along the eastern margin of the Alaska Gyre. One recurrent region for eddy formation is off the southern tip of the Queen Charlotte Islands (near 52degreesN 132degreesW). Eddies from this source region (termed 'Haida eddies') propagate westward into open ocean waters during the subsequent 1-3 years, often to about 140degreesW, occasionally to mid gyre. Each eddy contains a core of anomalously low density water, and produces an upward doming of the sea surface detectable by satellite altimetry, thereby aiding repeated ship-based sampling. The zooplankton community in the eddies is a mixture between shelf/slope species (transported from the nearshore formation region) and subarctic oceanic species (which colonize the eddy from the sides and below). This paper reports sequential observations (late winter, early summer and fall seasons of 2000, and early summer and fall of 2001) of the abundance and distribution of continental-margin zooplankton in the Haida eddies that formed in late winters of 2000 and 2001. Shelf-origin species declined in abundance over time. Species that appeared to have a continental slope origin sometimes declined but sometimes persisted and flourished. Transport and retention within the eddy appeared to be especially effective for species that undergo diel vertical migration.