Persistent spatial and temporal abundance patterns for the late-stage copepodites of Centropages typicus (Copepoda: Calanoida) in the US Northeast continental shelf ecosystem

The annual cycle of abundance and the monthly distributions of the copepodCentropages typicus are described for US NortheastContinental Shelf waters from samples collected on broadscale planktonsurveys during 1977-87. High numbers of the copepod were capturedthroughout the region during the autumn months in weak south-north andonshore-offshore abundance gradients. The highest individual stationdensities were found near the mouth of the major estuaries and the heaviestbroad-scale concentrations were usually located where bottom depth rangedfrom 20 to 39 m. Numbers declined throughout the ecosystem after winterarrived, less so in the southern half of the region whereC.typicus abundance remained high year round innearshore and midshelf waters between New York City and Chesapeake Bay. Thecopepod's abundance fell to much lower levels further north in the GeorgesBank and Gulf of Maine subareas, and disappeared entirely from shelf watersin the northernmost offshore region until summer. Interannual abundancevariability was substantial, but no long-term trend was detected. Analysesof samples collected from 1988 to 1996 on Georges Bank during early autumnindicate that abundance levels of C.typicus have beenhigh here in the 1990s, completely recovered from low density valuesmeasured there in 1986 and 1987. Temperature and food availability werefound to be the key factors that determine the copepod's distribution andannual abundance cycle. Mean abundance was high throughout the ecosystemwhere surface temperature was >9C andin regions where annual mean chlorophyll levels exceeded 1 mgm^-3. The copepod's abundance appeared to beindependent from variation in water column salinity.