FOOD-WEB INTERACTIONS IN THE PLANKTON OF LONG-ISLAND BAYS, WITH PRELIMINARY-OBSERVATIONS ON BROWN TIDE EFFECTS

We examined the relative importance of phytoplankton and ciliates as p rey for metazoan zooplankton, and the role of predation in regulating ciliate populations in 2 Long Island (USA) bays. Depth-integrated prim ary production (mg C m(-2) h(-1)) was dominated by nannoplankton < 5 m u m in diameter throughout the year, ranging from > 95% of total produ ction in mid-summer to an average of about 60% in winter and early spr ing. Predator exclusion and addition experiments conducted in microcos ms showed that the mortality coefficient of ciliates (d(-1)) from zoop lankton predation was higher when larger phytoplankton (> 10 mu m) con tributed less to total primary productivity. For adult copepods, an in crease in the percentage ciliate contribution compared to phytoplankto n contribution to total carbon intake also coincided with the higher p ercentages of small microalgal production. Egg production rates of Aca rtia spp. were positively correlated to the net growth coefficient of ciliates. In contrast, micrometazoa routinely obtained > 70% of their total carbon ration from phytoplankton, and at times during spring and summer, removed 23 to 52% of the total depth-integrated primary produ ction. In addition to protozoa, we suggest that micrometazoa, particul arly copepod nauplii, may serve as a trophic link between phytoplankto n and mesozooplankton in Long Island bays.