Abundance and grazing effects of Cyclosalpa bakeri in the subarctic Pacific

Ecological effects of populations of the salp Cyclosalpa bakeri were studied in late summer of 1984, 1983 and 1988 during the Subarctic Pacific Ecosystem Research (SUPER) project at Station P in the northeast Pacific. Salps occurred largely in the top 60 m, with biomass values ranging from 76 to 3621 mg C m(-2). Three approaches were taken to estimate the grazing impact of these populations. C, bakeri removed from 1.6 to 136.6 % of daily primary production and 1.3 to 56.8 % of the diatom stocks in August 1988. On average, feeding rates of the salps predicted clearance of all particles greater than or equal to 5.0 mu m from 1.2 to 49.2 % of the water column per day in 1984 and 1988. Although excretion of dissolved N appears negligible, production of fecal C and N can be high, as much as 875 mg C and 110 mg N m(-2) d(-1) at the highest population density sampled. Although the salps probably do not have a significant grazing impact on the small cells (less than or equal to 5.0 mu m) which are responsible for most of the production, they may be important in controlling populations of diatoms which typically occur in late summer at Station P.