Growth Rates Of Calanoid Copepods In The Northern Gulf Of Alaska, And Their Relationships To Temperature, Chlorophyll And Body Size

Abstract

The juvenile growth rate and development time of the dominant calanoid copepods in the northern Gulf of Alaska were investigated. The utility of the artificial-cohort method was successfully validated as the most practical approach for estimating copepod growth rates in this ecosystem. The underlying functional responses of growth rates to temperature, food concentration, and body size were thoroughly explored for Neocalanus flemingeri/plumchrus, Metridia pacifica, Calanus marshallae, C. pacificus and Pseudocalanus spp. These results lay the foundation for the calculation of copepod secondary production and ongoing ecosystem modeling activities for the northern Gulf of Alaska, and will contribute to the refinement of global models of copepod growth rates. In general, the rates of copepod growth were negatively size-dependent. However, a positive relationship between growth rate and body size within each stage emerged in response to food climate. The effect of temperature on growth rates was prominent, but confounded with food conditions and body sizes, which also vary with temperature conditions. Copepod growth rates were significantly related to chlorophyll a, and were frequently food-limited, particularly for later developmental stages during the summer. Compared to other co-occurring calanoid copepods, egg-carrying species (i.e. Pseudocalanus) tend to grow slowly to meet their unique life history strategy. Statistically, more variability in temperature corrected growth rates can be explained by composite nonlinear models that incorporate development stage and body size into the traditional Michaelis-Menten relationship. The species-specific comparisons of the measured growth rates with those predicted by global models of copepod growth suggested more direct measurements of copepod growth rates in various ecosystems are required for fully appreciating the global patterns of copepod growth. Caution should be used in the widespread application of those models for estimating copepod secondary production, especially in polar and sub-polar waters.