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.

As part of an investigation of ribonucleic acid (RNA) content as an index of growth and nutritional condition of zooplankton in the field, we describe here a method for measuring RNA and DNA in ind~viduals, Stage N5 through adult, of the copepod Calanus finmarchicus. We used the technique to compare total RNA and DNA content and RNA:DNA ratios of C. finmarchicus copepodite stages cultured at different food densities. Copepods reared at growth-limiting phytoplankton concentrations (25 pg carbon 1-') were smaller, had lower RNA:DNA ratios, and contained less total RNA and DNA than did copepods reared in excess food (500 pg C I-'). This was true for each stage from C1 to C5. Stages C5 and C4 C. finmarchicus collected from Georges Bank and the Gulf of Maine were compared to those from the laboratory experiment. While RNA:DNA ratios of C5 and C4 individuals collected in May and June 1994 were intermediate between the 2 lab treatments, Stage C5 C, hnmarchicus collected in November 1993 had the lowest RNA:DNA ratlos of all copepods sampled. This seasonality of RNA:DNA ratios is most likely related to food availability and changing metabolic activity. Our data show that RNA is a useful index of physiological condition for C. finmarchicus.

We examined the effects of food concentration and temperature on nucleic acids and protein content of Calanus finmarchicus in order to evaluate the use of RNA as a growth rate index for this species. We measured RNA, DNA, and protein content of copepods reared from egg to adult stage in 5 combinations of food and temperature conditions (25 to 500 µg C l -1 , 4 to 12°C). At 8°C, DNA, RNA and protein content and RNA:DNA differed among food treatments during Stages N6 through to adult female. Protein:DNA ratios and RNA:protein ratios were significantly different among food levels for only 3 of the 8 stages examined. At excess food, DNA, RNA, and protein content and RNA:DNA ratios were inversely related to temperature for most stages from C1 onward, but the effect of temperature was relatively small over the range of temperatures investigated. The RNA:DNA and protein:DNA ratios increased with developmental stage whereas the RNA:protein ratio and growth rates (measured in terms of protein, nitrogen, DNA, and carbon content) declined with increasing stage. Although the relationship of RNA:DNA to growth rates was stage-specific, the two were related when standardized for temperature and developmental stage. RNA:protein ratios were directly related to growth rates regardless of stage, and the slope of the relationship increased with increasing temperature in a nonlinear fashion. Our results emphasize the importance of temperature and developmental stage for the relationship of growth rates to RNA concentration and RNA:DNA ratios. We propose 2 ways to estimate in situ growth rates of C. finmarchicus from RNA:DNA or RNA:protein ratios and environmental temperature.

An anomalous winter phytoplankton bloom was observed across the central Gulf of Maine during a winter cruise in late February 1999, but not during a similar mission to the same region in late February 2000. During the cruise in 1999, 0 to 40 m mean chl a concentrations were >2 µg l -1 , while in 2000 total chl a concentrations were <1.0, and > 5 µm size fractions were < 0.5 µg l -1. The presence of the bloom in 1999 could not be explained in terms of the critical depth hypothesis given conditions present at the time of the bloom. The large amount of colder, lower-salinity Scotian Shelf water present at the surface of the central Gulf of Maine in 1999 may have provided conditions suitable for the initiation of the bloom earlier during the winter. The presence of the winter bloom had a major effect on higher trophic levels. Zooplankton were >10 × more abundant in 1999 and included species typically not present in the central Gulf during winter. All developmental stages of planktonic copepods were present, including large numbers of older copepodid stages of species such as Calanus finmarchicus, indicating that the bloom had been proceeding for some time. RNA:DNA ratios of surface C. finmarchicus stage C5 and adult females were at or near maximum temperature-dependent values in 1999, but were considerably reduced in 2000. Egg production rates of C. finmarchicus were high in1999 but reduced in 2000. Both showed a curvilinear relationship with chl a. Analysis of gonads of females of other copepod species indicate similar between-year differences in reproductive rates. We suggest that the presence of the winter bloom in the central Gulf of Maine allows an extra generation of C. finmarchicus and other copepods to develop, leading to a buildup of the population during winter. This will have significant effects on downstream regions such as Georges Bank, which depend on re-supply from the Gulf of Maine.

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