SEASONAL STUDY OF PLANKTONIC COPEPODS AND THEIR BENTHIC RESTING EGGS IN NORTHERN CALIFORNIA COASTAL WATERS

Few investigations have examined the occurrence of zooplankton resting eggs in the sea bed of waters deeper than 20 m. In this study the dis tribution and abundance of planktonic copepods and their benthic resti ng eggs in coastal waters off northern California, U.S.A., were determ ined and related to environmental parameters (temperature, salinity, d epth, and sediment grain size). Sediment cores, net tows, and CTD prof iles were obtained in April and October 1989, and February, April, and October 1990. Water depths in the study area ranged from approximatel y 60 to 120 m. The mean abundance of eggs was as high as 1.2 x 10(5) m (-2) for Acartia clausi Giesbrecht and 1.9 x 10(5) m(-2) for Tortanus discaudatus Thompson and Scott. These egg concentrations those reporte d previously for shallower more protected regions. The abundance of eg gs in the sediments decreased with increasing depth of the water colum n. For the region as a whole, epos were least abundant in muddy sedime nts. The mean abundance of eggs in the sea bed also varied seasonally and annually. Benthic resting eggs of A. clausi were more abundant in April 1989 than in April 1990, and adults of the species were never fo und in the plankton samples. The lack of adults is not unusual since r esults of previous studies indicate that A. clausi is a cold-water spe cies, and in this region water temperatures are colder in summer, than in win-ter, due to upwelling. Temperature and salinity data indicated that the upwelling season had commenced by the time of the April 1990 : but not the April 1989 sampling. Thus, the reduced abundance of bent hic eggs in April 1990 may have been due to egg-hatching in st respons e to reduced temperatures. The results suggest that the presence of A. clausi in coastal waters off northern California is linked to recruit ment from benthic resting eggs.