Annual routines and life history of the amphipod Onisimus litoralis: seasonal growth, body composition and energy budget

Abstract

The scheduling of life history events over the year is a central characteristic of organisms in seasonal environments. Here, we report on seasonality in growth rate and cellular energy alloca- tion, as well as timing of maturation, egg production and brood release, through a full annual cycle of Onisimus litoralis, a lysianassoid amphipod dominating soft bottoms in the intertidal zone in the high Arctic. We observed that O. litoralis follows a semelparous 2 yr life cycle, with growth and devel- opment mainly taking place in summer, but with slow growth also in winter, which with the lack of energy reserves suggests that it feeds year-round. The importance of the spring bloom of phytoplank- ton in fueling growth and development is reflected in carbohydrate and protein content. Relatively stable lipid content and no build-up of energy stores prior to egg production indicate income breed- ing. Seasonal differences in energy consumption are apparent, with higher consumption in summer, but as a result of increased energy content during summer, the energy budget remains relatively sta- ble during the whole year. The life history observed is similar to that of previous studies, but our observations do not support iteroparity, which has been suggested by others. Parental care, through a 'start pack' of energy to the offspring and the ability to time the brood release to favorable condi- tions, add flexibility to the life history strategy. Easy access to the species and a good understanding of its biology support further use of O. litoralis as an indicator species for environmental change in the Arctic.