Comparison of copepod communities during upwelling and non-upwelling in the summers from 1992 to 2010 in Tosa Bay, western Japan

Copepods were collected using a Norpac net (0.315 mm mesh aperture, 0.45 m mouth diameter) in the summers from 1992 to 2010 at Stn A (700 m depth) in Tosa Bay, western Japan. Among the summer samples collected in July and August, there were 19 net samples during periods of upwelling and 27 net samples during periods of nonupwelling, judged by criteria of water temperature. Total abundance of adult copepods in the upwelling samples was not significantly different from the abundance in the non-upwelling samples, while the number of species and species diversity in the upwelling samples was lower than in the non-upwelling samples. Adults of four species (Calanus sinicus, Clausocalanus parapergens, Paracalanus parvus s.l. and Corycaeus affinis) in the upwelling samples were significantly more abundant than those in the non-upwelling samples. The changes of the copepod community structure during periods of upwelling may be produced because of increases of species preferring low water temperatures and decreases of species preferring warm water temperatures.