Vertical distribution of calanoid copepods in a mature cyclonic eddy in the Gulf of California

Abstract

The distribution of calanoid copepod habitats in a cyclonic eddy in the Gulf of California was examined. Direct velocity observations revealed that the eddy extended to approximately 550 m depth and 150 km diameter. The established thermocline suggested that active vertical pumping was not occurring because the eddy was in mature phase. A copepod habitat located in the surface mixed layer, showed high abundances, dominated by Subeucalanus subtenuis (Giesbrecht, 1888), whose abundances decrease towards the centre of the eddy. A second habitat, situated in thermocline, had the highest abundances dominated by Nannocalanus minor (Claus, 1863) and Temora discaudata Giesbrecht, 1889. Another habitat, beneath the thermocline, was dominated by most of species recorded in thermocline, but with the lowest abundance. Results suggest that in the mature phase of a cyclonic eddy, the water column stratification induces layering of the calanoid copepod habitats, with the most propitious conditions for their feeding in thermocline.