A comparison of seasonal growth and development of the copepods Calanus marshallae and C. pacificus in the northern Gulf of Alaska.

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]