© 1991 by The Society for Integrative and Comparative Biology
Amphipod Life Histories: Community Structure, Impact of Temperature on Decoupled Growth and Maturation Rates, Productivity, and P:B Ratios1
Institute of Marine Science, School of Fisheries and Ocean Sciences, University of Alaska Fairbanks Fairbanks, Alaska 99775-1080
Data are presented on northern Bering Sea benthic amphipod growth rates and age at maturity, indicating that high latitude species grow slowly, require 2 to 4 years to mature, reach a large size, and have long lifespans. Data are also presented demonstrating predation by benthic amphipods on newly metamorphosed juveniles of a potential space competitor, the northern sand dollar Echinarachnius parma. Such facultative predation by the predominantly herbivorous amphipods may, in part, explain the existence of alternative benthic communities in the eastern Bering Sea. Incorporation of the high latitude results into a review of benthic amphipod life histories revealed several important patterns. Amphipod growth rates and molting rates appear to be decoupled, resulting in small adults at warm temperatures and large adults at lower temperatures. We posit that molting rate is temperature- sensitive, that at warm temperatures molting occurs rapidly regardless of limited instar tissue growth, and that the amphipods reach sexual maturity after a fixed number of molts. Alternatively, gonad development is also temperature-dependent and may drive maturation, regardless of the number of molts experienced. Amphipods have linear or exponential growth rates, as opposed to the familiar asymptotic curve. Consequently, secondary production is highly dependent upon the proportion of large individuals in the population, in contrast to organisms with asymptotic growth in which production is largely determined by the proportion of young, growing individuals present. Production in amphipods is significantly correlated with standing stock. P:B ratios are not correlated with production in amphipods, and probably are not in other organisms with linear or exponential growth rates, and thus appear to have no comparative value other than as a possible index of generation times.