Major pathways by which climate may force marine fish populations

Climate may affect marine fish populations through many different pathways, operating at a variety of temporal and spatial scales. Climate impacts may work their way bottom up through the food web or affect higher trophic levels more directly. In this review we try to disentangle and summarize some of the current knowledge made available through the rapidly increasing literature on the topic, with particular emphasis on the work within the Global Ocean Ecosystems Dynamics (GLOBEC) programme. We first consider different classification schemes and hypotheses relating climate through physical features of the ocean to population patterns. The response of a population or community to climate may be linear or non-linear, direct or indirect. The hypotheses may be classified according to the form of physical features in operation as being related to mixing, advection or temperature. The bulk of the paper is devoted to a region-by-region presentation and discussion of examples relating climate variability to marine fish populations. It is slanted towards the North Atlantic and North Pacific, but the tropical Pacific is also covered. By means of different categorization methods we compare climate responses between ecosystems. We conclude that the use of such classification schemes allows for a more precise description of the various ecosystems particular properties and facilitates inter-regional comparison.