Biological-Physical Processes Determining Pseudocalanus Spp. (Crustacea; Copepoda) Distribution And Abundance On Georges Bank In The Northwest Atlantic

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The planktonic copepod sibling species, Pseudocalanus moultoni and P. newmani, co-occur on Georges Bank (Northwest Atlantic), but differ in Spring-time evolution of distribution and abundance. Previous studies have described Bank-wide species’ distribution and abundance in monthly snap-shots from January to June of 1997 and 1999, using species-specific PCR (SS-PCR) to discriminate the sibling species. Numerical models were used to infer the biological sources and sinks implied by the observed changes in abundance between monthly surveys and the flow during the intervening periods. Based on such observation, visualization, and modeling, the two species appeared to have distinct sources in the early spring, but overlapping distributions by early summer, with the springtime increase for both species driven by a complex mixture of hydrodynamic transport and species-specific population dynamics. New observations have examined distribution and abundance of the two species at smaller scales. We describe here studies of Pseudocalanus spp. vertical distributions with respect to stratification and mixing, and the distributions of other biological, chemical, and physical moieties in the water column. Field collections were done along transects in two areas: across a tidal-mixing front on Georges Bank, and along in near-shore water of western Gulf of Maine. Both field studies demonstrated that water column stratification and stratified flow may differentially affect the two Pseudocalanus spp. The previously observed differences in Bank-wide patterns of P. moultoni and P. newmani may result from processes at small-scales, including different vertical distributions under stratified conditions, different responses to turbulence, and different micro-habitat preferences