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Pseudocalanus are the numerically dominant calanoid species in coastal subarctic Pacific waters. We examined their juvenile growth rates, and explored their relationships to temperature, chlorophyll a and body size for Pseudocalanus spp. from 2002 to 2004 in the northern Gulf of Alaska. Generally, the monthly mean growth rates increased from 0.049 ± 0.007(SE) day−1 in March to 0.095 ± 0.016 day−1 in August, declining slightly to 0.074 ± 0.009 day−1 in October. Typically, growth rates at most stations were around 0.05 day−1, with no consistent or significant pattern between stations. After standardization to 5 and 10°C, the mean growth rates were 0.045 ± 0.002 day−1 and 0.075 ± 0.004 day−1 respectively, with growth rate decreasing with increasing development stage. Unlike other local calanoid copepod species, Pseudocalanus species tend to be more temperature-dependent than food-dependent, with composite statistical models describing at most 30% of the observed variability in growth rate. Interestingly, development time was comparable to other co-occurring calanoid copepods; however, growth rates of Pseudocalanus spp. were considerably lower. We demonstrate this with a new multi-species model that describes the growth rates of other egg-scattering copepods in this ecosystem, but to which Pseudocalanus does not fit. Thus, the egg-carrying Pseudocalanus species appear to employ a life history strategy optimized for slow growth at low chlorophyll that keeps individuals relatively small, and may therefore reduce visual predation upon them. [ABSTRACT FROM AUTHOR]

The juvenile growth rates and development times of subarctic Calanus marshallae and temperate/sub-tropical C. pacificus were investigated during nine cruises (May through October, 2001–04) in the northern Gulf of Alaska. The artificial cohort method based on a length-weight regression was used for growth estimates and the reciprocal of the molting rate for developmental time. The copepodite stage duration ranged from 3 to 16 days for C. marshallae (C1–C4) and 3–23 days for C. pacificus (C1–C5). Seasonally, copepodid growth rates increased from May to October, ranging between 0.055 and 0.291 day−1 (mean ± SE: 0.176 ± 0.008 day−1) for C. marshallae, while growth rates increased from August to October between 0.018 and 0.296 day−1 (mean ± SE: 0.142 ± 0.016 day−1) for C. pacificus. After standardization to 5°C (Q10 of 2.7), growth rate averaged 0.118 ± 0.007 day−1 and 0.075 ± 0.009 day−1 for C. marshallae and C. pacificus, respectively. Calanus marshallae growth rate is satisfactorily described by a Michaelis–Menten model using chlorophyll-a concentration (r2 = 0.33) after temperature correction, but the prediction improves with a composite nonlinear model combining body weight into the Michaelis–Menten function (r2 = 0.55). Considering the limited range of data available for C. pacificus, the combination of the data for both species suggests that C. pacificus has a similar functional response to growth despite the differences in the geographic and temporal distributions with C. marshallae. Measured juvenile growth rates of the two Calanus species in this study were comparable to other calanoid species in the same area and showed reasonable agreement to Calanus growth models but less with global copepod growth models. [ABSTRACT FROM AUTHOR]