Grant's (1979) findings were based upon 2 years of sampling off the coasts of Virginia and New Jersey. The author stated that zooplankton volumes (biomass) varied seasonally--the maximum in spring and the minimum in fall. He also indicated that inshore and offshore volumes varied with the inshore highest in the summer, the mid-shelf highest in winter and spring, and the shelf edge highest in the fall. The author also noted that a north-south difference in volumes was apparent, with the southerly transect having higher values in fall and winter and lower in spring and summer. Grant (1979) also noted that, irrespective of the season, the Middle Atlantic Bight zooplankton tended to occur in three distinct communities: 1) a coastal community delineated by the Coastal Boundary Layer; 2) a mid-shelf community, and 3) an offshore community comprised of slope and occasional Gulf Stream species. Table III.B.1-1 lists the species group subclusters reported from Grant's (1979) work. Subcluster 1 is comprised of species groups A, B, and C which contain fauna that is associated most closely with the Coastal Boundary Layer. Group A is made up of predominantly summer-fall species and Group B is comprised of winter-spring species. Group C contains salps that, although important across all the shelf, are most abundant inshore. Subcluster 2 contains groups D, E, F, and I and demonstrates annual differences which were evident over the shelf and slope between the summer of 1977 and 1978. Groups D and F were most important in the summer of 1977, group I was important during the summer of 1977, and group E species were common during both 1977 and 1978. Subcluster 3 had groups G and H which were found predominantly offshore with species group G important during the fall of 1976 and group H found in spring of 1977. Species Group H is of particular interest because it contains the members of the Calanus finmarchicus-Sagitta elegans community. This community is indicative of southern New England or Gulf of Maine waters and is evidence of the extent of southern intrusion of northern waters into the Middle Atlantic Bight and the persistence of the faunal component after the extremely cold winter of 1977. The numerically important zooplankton species reported by Grant (1979) for the Coastal Boundary Layer over the entire Middle Atlantic Bight include Acartia tonsa, Centropages furcatus and Eucalanus pileatus in summer and fall, and Centropages hamatus, Temora longicornis, Tautanus discaudatus, Mysidopsis bigelowi and Crangon septemspinosa in winter and spring. The author also reports that Centropages typicus, Calanus finmarchicus, and Sagitta elegans are common over the mid-shelf in the Middle Atlantic Bight. The shelf-break and slope waters commonly contain the species Metridia lucens and Meganyctiphanes norvegica which, although spreading over the shelf in winter and spring, respectively, were restricted to pelagic (off-shelf) waters during the other seasons. Euphasia krahnii was restricted to the offshore stations (Grant, 1979). During the same study the neuston (those organisms living at or near the water's surface) was sampled to a depth of 10 to 12 cm. Diel migration patterns of neustonic species fell into three general categories: 1) no change over 24 hours (no diel migration), 2) increased abundance at night, and 3) crepuscular (dawn and dusk) peaks of abundance. The neuston species were reported to be reasonably predictable in the coastal waters, but unpredictable in mid-shelf and shelf-edge waters. This was attributed to dependence of the faunal community structure upon the incursion of southern New England waters or Gulf Stream warm-core eddies into the area and how recently it occurred (Grant, 1979; Cox and Wiebe, 1979). Grant (1979) attributes the neustonic layer with being a valuable nursery habitat for numerous trophically and commercially important species which have meroplanktonic larvae. The larvae of mid-Atlantic decapods and fish often were dominant numerically in the neuston community and are listed in Table III.B.1-2. Table III.B.1-2. Neustonic Larvae of Decapods and Fish captured in the Loligo and Illex, squids Callinectes sapidus, blue crab Merluccius bilinearis, silver hake Coryphaena hippurus, dolphin Mugil curema, mullet Scomber scombrus, Atlantic mackerel Peprilus triacanthus, butterfish Centropristis striata, black sea bass Source: Grant, 1979 Recently, extensive zooplankton sampling of the northeast coast of the United States has been conducted as part of the MARMAP (Marine Resources Monitoring, Assessment and Prediction) program. Sherman and Jones (1982) reported on the results of oblique tows with paired bongo nets in the Middle Atlantic Bight and southern New England. The authors reported that southern New England zooplankton demonstrated two peaks--a major peak in late winter-early spring and a minor peak in late spring to late summer--but the Middle Atlantic Bight zooplankters gradually increased to a single peak in late summer. The authors also stated that copepods were the predominant organisms in both areas with eight species--Calanus finmarchicus, Pseudocalanus minutus, Centropages typicus, Metridia lucens, Temora longicornis, Centropages hamatus, Acartia clausii, and other Acartia spp.--being dominant. Of the eight copepod species listed, Calanus finmarchicus, Centropages typicus, and Pseudocalonus minutus were most important in terms of percent dominance. Sherman and Jones (1982) reported that in both the southern New England and mid-Atlantic areas, P. minutus generally is dominant in winter and spring and is replaced by C. typicus in summer and into fall. Sherman et al. (1982) reported a zooplankton biomass (or displacement volume) as ranging from less than 25 cc/m3 in the colder months up to 75 cc/m3 during spring and/or summer in the southern New England area. They also reported the biomass of zooplankton in the mid-Atlantic gradually increasing from 10 cc/m3 in winter to about 55 cc/m3 in fall. The ichthyoplanktonic component of the meroplankton of the Middle Atlantic Bight was reported on by Smith et al. (1979). The authors note that spawning and subsequent planktonic larvae occur year-round, but most species spawn on a seasonal basis in response to environmental factors such as temperature. The entire Middle Atlantic Bight shelf waters are important as habitats for development of eggs and larvae, and no specific spawning areas were apparent. Table III.B.1-3 shows the months of occurrence of planktonic larvae of common mid-Atlantic marine fishes. |