| Summary: | The calanoid copepod genus, Pseudocalanus, is an important secondary producer and widespread throughout the northern hemisphere. While ecologically important, previous work with this genus has been limited due to difficulties in morphometric identification. Here, Pseudocalanus species composition and distribution were examined in the Bering Sea through sequencing of the mitochondrial CO1 gene of 642 individuals from 10 locations. Phylogentic trees of inter- and intra specific diversity demonstrated that in the spring of 2010 (March-June), four species of Pseudocalanus co-existed at various locations across the shelf. Species composition in the middle shelf (50-100 m depth) was significantly different from composition on outer shelf/slope (≥200 m depth). Correlation of species composition with salinity and the chlorophyll maximum depth indicated that environmental factors influence distribution and highlighted the importance of species-specific approaches to ecological research involving the Pseudocalanus genus. Differences between the middle shelf and outer shelf/slope populations extended to the intraspecific level in two of the four species. Although high haplotypic diversity was observed in all Pseudocalanus spp., a weak structure between the middle shelf domain and offshore stations was seen only in P. acuspes and P. minutus. This indicates that while there may currently or previously been some barriers, gene flow is possible across the shelf. Evidence of mixed intraspecific and divided interspecific variations, in addition to correlation with environmental conditions, highlighted the importance of a species-specific approach to future research of this genus and will assist in creating greater accuracy in the modeling of an ecosystem-wide response to climate change.
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