Development rates, nitrogen-and carbon-specific growth rates, size, and condition were determined for the copepod Calanus finmarchicus reared at 3 temperatures (4, 8, and 12°C) at non-limiting food concentrations and 2 limiting food concentrations at 8°C in the laboratory. Development rates were equiproportional, but not isochronal. Naupliar stage durations were similar, except for non-feeding stages, which were of short duration, and the first feeding stage, which was prolonged, while copepodite stage durations increased with increasing stage of development. Under limiting food concentrations at 8°C, development rates were prolonged but similar relative patterns in stage durations were observed. Body size (length and weight) was inversely related to temperature and positively related to food concentration. Condition measurements were not affected by temperature, but were positively related to food concentration. Growth rates increased with increasing temperature and increased asymptotically with increasing food concentration. At high food concentrations, growth rates of naupliar stages were high (except for individuals molting from the final naupliar stage to the first copepodite stage, in which growth rates were depressed), while growth of copepodites decreased with increasing stage of development. Neither nitrogen nor carbon growth rates, the former a proxy for structural growth, were exponential over the entire life cycle, but rather sigmoidal. Carbon-specific growth rates were greater than nitrogen-specific growth rates, and this difference increased with increasing stage of development, reflecting an augmentation in lipid deposition in the older stages. However, nitrogen and carbon growth rates were more similar under foodlimited conditions. Based on this study, we recommend that secondary production rates of Calanus finmarchicus and possibly other lipid-storing copepods not be estimated from egg production measurements alone, as has been suggested for other species of copepods, because growth, including structural growth, is not equivalent for all stages.

Omnivorous copepods are capable of discriminatory feedlng using mechano-and chemosensory mechamsms. The presence of phycotoxins in phytoplankton often results in reduced consumption of such potential prey by copepods, though it has not been clear if this is the result of dlscriminatory feeding by either tactile (mechanosensory) or chemosensory recognition of toxic prey, or perhaps a physiological response to ingested newotoxic compounds. In this study, experiments were performed to determine whether 3 species of marine copepods (Acartia tonsa, Centropages hamatus, and Eurytemora herdmani) that commonly CO-occur with toxic Alexandrium spp. dinoflagellates were capable of discriminating between cultured Alexandnum spp. strains on the basis of paralytic shellfish poisoning (PSP) toxin content, i.e. by chemosensory means, using Live fluorescently labeled cells. Additional experiments investigated whether toxic cells in mixtures with non-toxic alternate species of dlnoflagellates affected either prey selection or total carbon consumption rates of copepods, and whether daily carbon rations could be maintained on both toxic and non-toxic Alexandrium spp. monoculture diets. Results indicated that all 3 copepod species could discriminate between toxic and nontoxic Alexandrium spp cells by chemosensory means, suggesting that selective behavior, rather than physiological effects, governs the grazing response of copepods exposed to toxic prey. Prey selection in mixtures of several dinoflagellate species depended on whether the Alexandrium spp. cells present were toxic or non-toxic. C. hamatus and E. herdmani (but not A. tonsa) maintained daily carbon rations despite the presence of toxic Alexandrium spp., chiefly through increased consumption of alternate prey. For A. tonsa and C. hamatus, carbon rations were not equivalent between toxic and non-toxic Alexandrium spp. monoculture dlets, indicating strong aversions to PSP toxins, and the potential for physiological effects when no other food is a v d a b l e . In all experiments feeding behavior varied among copepod species, suggesting that grazing pressure on toxic Alexandrium spp, is not uniform throughout the zooplankton commumty. The grazer-deterrent effects observed have implications for the function of PSP toxins.

No abstract

Temporal variability in the distribution and abundance of North Atlantic right whales Eubalaena glacialis and their copepod prey, late-stage Calanus finmarchicus, was monitored at an oceanographic station in Grand Manan Basin of the lower Bay of Fundy for 29 h on 2 separate occasions. The vertical distribution of C. finmarchicus was measured at 1 / 2 h intervals with an optical plankton counter (OPC) and at 6 or 12 h intervals with a MOCNESS. Right whale abundance was estimated from periodic point scans. Late-stage C. finmarchicus exhibited diel vertical migration in the upper 100 m of the water column, but the bulk of the population remained at depths below 100 m throughout both the day and night and was likely in diapause. Diel vertical migration is unlikely to be influenced by right whales, but may instead be motivated by abundant, near-surface food resources and avoidance of visual predators. Right whale sighting rate was correlated with OPCdetected C. finmarchicus fifth copepodite (C5) abundance at mid-depths (90-140 m); variability in both right whale sighting rate and C. finmarchicus C5 abundance in this depth stratum appeared to have similar periodicity to that of the tide. Energetic considerations suggest that right whales continue to feed on deep, diapausing layers of C. finmarchicus during the night, but the occasional presence of exploitable near-surface concentrations of C. finmarchicus suggests that nighttime near-surface feeding might sometimes occur. KEY WORDS: Right whale · Eubalaena glacialis · Calanus finmarchicus · Diel vertical migration · Tides · Gulf of Maine · Bay of Fundy · Optical plankton counter Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 264: [155][156][157][158][159][160][161][162][163][164][165][166] 2003 Woodley & Gaskin 1996. The reliability of both right whale and C. finmarchicus aggregations in these regions provides an opportunity to study the unique trophic relationship between this predator and prey.Studies that have employed net sampling near right whales in the lower Bay of Fundy suggest that right whales feed on Calanus finmarchicus fifth copepodites (C5) (Murison & Gaskin 1989, Woodley & Gaskin 1996. Right whales forage during the day on C. finmarchicus C5 that aggregate in discrete layers deep in the water column just above a bottom mixed layer (Baumgartner & Mate 2003 this issue). Nighttime vertical migration to the surface by the copepods in these deep layers would have important implications for right whales. Surface feeding by the whales would be expected to have energetic benefits since transit time to shallower food resources is reduced. For a constant dive duration, reduced transit time increases feeding time, so comparatively more energy can potentially be acquired per dive when feeding near the surface than at depth.Surface feeding may also be accompanied by costs to the whales, however. Right whale exposure to the natural toxins that cause paralytic shellfish poisoning (PSP) may be enhanced by f...

Laboratory experiments suggest that toxic Alexandrium spp. cells are unpalatable to zooplankton grazers, and that toxic cells should be selectively avoided by zooplankton when feeding in mixtures of different prey species. Such avoidance, if practised in the wild, might contribute to harmful bloom formation by reducing losses of Alexandrium spp. due to grazing. In the spring of 1998 and 1999, during 'red tide' outbreaks in the southwestern Gulf of Maine, weekly experiments were performed using field collected natural water samples with ambient phytoplankton and dominant mesozooplankton grazers. The feeding response of Acartia hudsonica, Semibalanus balanoides nauplii, and Calanus finmarchicus was tested during various weeks in natural water samples with low concentrations of Alexandrium spp. (~1000 cells l -1 , typical natural concentrations for this region). Semibalanus sp. nauplii consistently avoided toxic Alexandrium spp. and other dinoflagellates. C. finmarchicus selectively fed on diatoms when they were abundant, and fed non-selectively on all dinoflagellates (except Ceratium spp.) when the spring bloom declined and dinoflagellates dominated. A. hudsonica non-selectively cleared Alexandrium spp. throughout the study periods. During spring Alexandrium spp. bloom formation, if non-selective grazers such as A. hudsonica dominate the zooplankton, Alexandrium spp. losses from grazing depend on grazer abundance (biomass); if selective feeders such as S. balanoides nauplii dominate, then Alexandrium spp. benefits from reduced grazing losses relative to alternative prey.