A Comparison of Larval Fish Assemblages in the Temperate Zone of the Northeast Pacific and Northwest Atlantic Oceans
Numerical classification is used to examine broad scale spatial patterns in the larval component of the ichthyoplankton off the west and east coasts of the United States, based on data collected during extensive surveys over several years. The multispecies spatial patterns that emerged imply the existence of persistent and geographically distinct larval fish assemblages off both coasts. Four assemblages were identified off the west coast. They include a coastal assemblage that was restricted to coastal and continental shelf waters mainly off Washington and Oregon; a slope/transitional assemblage that occurred largely along the shelf edge and slope; a Columbia River plume assemblage that was associated with the Columbia River plume during summer; and an oceanic assemblage that prevailed in deep water beyond the shelf edge and for which northern and southern components were apparent during winter and spring. The east coast assemblages include a Gulf of Maine and Georges Bank assemblage; an oceanic assemblage that was associated with the continental shelf edge and slope; and a Middle Atlantic Bight assemblage that occurred along the shelf from Cape Cod, Massachusetts, to Cape Hatteras, North Carolina. Northern, southern, inshore, and offshore components of the Middle Atlantic Bight assemblage were apparent at certain times of the year. In general, the boundaries to the assemblages are fluid, and seasonal variation in occurrence and abundance of species within assemblages is strong. The distribution of the larval fish assemblages reflects spatial structure in the oceanographic environment and, in some instances, can be related to specific hydrographic features. Among the fish taxa in both regions, adaptation of the spawning patterns to the prevailing oceanographic conditions is apparent. Co-evolution among the fishes spawning strategies within the complex and variable marine ecosystems may have given rise to the high degree of structure observed in the ichthyoplankton spatial patterns and to the larval fish assemblages themselves. It is not possible to conclude from this limited study that the multispecies larval fish assemblages are independent ecological entities that enhance survival of the constituent species. Further investigations of finer scale spatial patterns within the larval fish assemblages and among different ontogenetic categories, as well as consideration of the zooplankton, of which fish larvae form only a small part, are necessary to understand fully the multispecies spatial patterns that prevail.
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Document Type: Research Article
Publication date: 1993-09-01
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