SEASONAL CONTRASTS IN THE DIEL VERTICAL-DISTRIBUTION, FEEDING-BEHAVIOR, AND GRAZING IMPACT OF THE COPEPOD TEMORA-LONGICORNIS IN LONG-ISLANDSOUND

We studied diel variability in vertical distribution, feeding behavior and grazing impact of female Temora longicornis in Long Island Sound on seven cruises from March to July. T. longicornis usually performed diel vertical migration characterized by deep residence during the day and ascent to near-surface waters at night for variable periods. The pattern of diel migration was independent of either the vertical distr ibution or relative abundance of chlorophyll in the water column. Ther e was no clear evidence linking the amplitude of vertical migration to food concentration. Rather, the amplitude of migration decreased towa rd the end of the season probably due to animals avoiding warm waters (> 17-degrees-C) near the surface. Gut pigment content showed diel var iation characterized by maximum values during, the nighttime. However, the estimated mean ingestion rate from the nighttime period was signi ficantly greater than that of the daytime period in only 2 of 11 compa risons indicating that this copepod usually fed throughout the day at about the same rate. The shape of the diel curve was usually similar f or females at 5 and 20 m. Usually there was no difference in gut conte nt of females with depth even when differences in chlorophyll with dep th were pronounced. Therefore, the diel variability in gut content was unlikely to result from continuous feeding in a vertically stratified food environment. Short-term (hourly) changes in chlorophyll concentr ation could not entirely account for changes in gut content over a die l cycle. We estimate that female T. longicornis removed daily < 1-34% of the phytoplankton stock and < 1-49% of the primary production in Lo ng Island Sound. Estimates of daily carbon rations indicate that a her bivorous diet can satisfy the metabolic requirements and support egg p roduction of T. longicornis throughout most of its season.