Ann Bucklin and Dennis J. McGillicuddy
U.S. GLOBEC: Maintenance of Pseudocalanus spp.
populations on Georges Bank
The planktonic copepod sibling species, Pseudocalanus moultoni and P.
newmani, occur sympatrically during the spring and summer on Georges
Bank. Despite their marked morphological similarity, the species differ
in many aspects of their ecology, including: patterns of distribution and
abundance; preferred habitat; and seasonal timing of reproduction. In
comparison to P. newmani, P. moultoni is more abundant on the well-
mixed crest of Georges Bank within the 60 m isobath (Bucklin et al.,
1998, Mar. Biol., in press). We hypothesize that populations of P.
moultoni are maintained on Georges Bank by local reproduction and
recruitment, and that the species is differentially retained within the tidal-
mixing front located along the 60 m isobath by behavior (vertical
distribution) in relation to physical processes (dynamics of the tidal-
mixing front). This hypothesis will be tested by characterization of Bank-
wide, stage-specific distribution and abundance of P. moultoni and P.
newmani in relation to circulation patterns (based on Broad-scale Survey
samples collected from January to June, 1999) and three-dimensional
small-scale distributions in relation to advection and mixing in the tidal-
mixing front (during field experiments proposed for May and June,
1999). The goal of this work is to understand how P. moultoni may
persist and proliferate in the complex and variable flow field over
Georges Bank. The technical approach will be to identify all life stages of
P. moultoni using species-specific competitive PCR, and to perform
numerical modeling experiments using observed distributions in a known
physical field. A subsidiary goal is to evaluate molecular genetic
(mtDNA sequences) and biochemical (differential gene expression)
variation within P. moultoni, for possible use as indicators of rates of
exchange between Georges Bank and adjacent populations. The
significance of this project is to understand the interplay between
population dynamics and ocean processes in determining the distribution
and abundance of important members of the Georges Bank zooplankton