Krill can shrink as an ecological adaptation to temporarily unfavourable environments

Because environments vary with both predictable patterns and with unpredict able but recurring events, ecologists have long been interested in the ecol ogical adaptations that organisms use to survive periods in which the envir onment may be exceptionally harsh. In the north-east 'Pacific, one example of this is periodic warming episodes. Here, we demonstrate for the first ti me that krill (Euphausia pacifica Hansen), which is a centrally important s pecies in coastal-upwelling systems, can survive periods of abnormally high temperatures by shrinkage between molts, even if food is plentiful. In add ition, we demonstrate that there is a high amount of individual variation i n growth rates of krill. Krill are centrally important within pelagic foodw ebs both worldwide and within the north-east Pacific, thus we explore the p otential ecological consequences of such shrinkage for both krill and their predators.