A comparison of seasonal growth and development of the copepods Calanus marshallae and C. pacificus in the northern Gulf of Alaska |
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Authors: | Liu, Hui Hopcroft, Russell R. |
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Affiliation: | Institute of Marine Science, University of Alaska Fairbanks, AK 99775-7220, USA |
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Abstract: | The juvenile growth rates and development times of subarcticCalanus marshallae and temperate/sub-tropical C. pacificus wereinvestigated during nine cruises (May through October, 200104)in the northern Gulf of Alaska. The artificial cohort methodbased on a length-weight regression was used for growth estimatesand the reciprocal of the molting rate for developmental time.The copepodite stage duration ranged from 3 to 16 days for C.marshallae (C1C4) and 323 days for C. pacificus(C1C5). Seasonally, copepodid growth rates increasedfrom May to October, ranging between 0.055 and 0.291 day1(mean ± SE: 0.176 ± 0.008 day1) for C.marshallae, while growth rates increased from August to Octoberbetween 0.018 and 0.296 day1 (mean ± SE: 0.142± 0.016 day1) for C. pacificus. After standardizationto 5°C (Q10 of 2.7), growth rate averaged 0.118 ±0.007 day1 and 0.075 ± 0.009 day1 for C.marshallae and C. pacificus, respectively. Calanus marshallaegrowth rate is satisfactorily described by a MichaelisMentenmodel using chlorophyll-a concentration (r2 = 0.33) after temperaturecorrection, but the prediction improves with a composite nonlinearmodel combining body weight into the MichaelisMentenfunction (r2 = 0.55). Considering the limited range of dataavailable for C. pacificus, the combination of the data forboth species suggests that C. pacificus has a similar functionalresponse to growth despite the differences in the geographicand temporal distributions with C. marshallae. Measured juvenilegrowth rates of the two Calanus species in this study were comparableto other calanoid species in the same area and showed reasonableagreement to Calanus growth models but less with global copepodgrowth models. |
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