Growth and development of Pseudocalanus spp. in the northern Gulf of Alaska

• Published in: Journal of Plankton Research
• Main Authors: Liu, Hui, Hopcroft, Russell R.
• Format: Text
• Language: English
• Published: Oxford University Press 2008
• Subjects: ORIGINAL ARTICLES; Gulf of Alaska; Pacific; Subarctic; Alaska; Copepods
• Online Access: http://plankt.oxfordjournals.org/cgi/content/short/30/8/923; https://doi.org/10.1093/plankt/fbn046

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.