POPULATION-STRUCTURE, GROWTH, AND FECUNDITY OF THE KELP FOREST MYSID HOLMESIMYSIS-COSTATA IN MONTEREY BAY, CALIFORNIA

Field and laboratory studies were made in Monterey Bay, California, on Holmesimysis costata, an ecologically important mysid crustacean in W est Coast kelp forests that is currently being used as a water quality indicator organism. Nearly all the mysids were found in the upper por tions of the kelp canopy. Relative abundance, size, and male/female/ju venile frequency of occurrence varied substantially throughout the 2-y ear study. Abundance, ranging monthly from 254-3,359 individuals per 3 00-l sample, correlated with sea-water temperature the first year, but not the second. Laboratory growth rate, determined by measuring carap ace length, was approximately linear for the first 37 days after hatch ing(16 mu m day(-1)), after which it increased and became more variabl e until sexual maturity was reached at 62 days (females 41 mu m day(-1 ), males 35 mu m day(-1)). Brooding females were collected thoughout 1 year, but highest fecundities (maximum 45 juveniles in 1 female) occu rred between May and August. Mean field fecundities (27.4 +/- 6.6 juve niles per female) were higher than those of laboratory-reared females (16.4 +/- 4.3). These results indicate that there is high year-round p roduction of these mysids, with peak production in summer when predati on by recruiting rockfishes would be most intense.