A Space- and Time-Scale Characterization of Circulation and Mixing over Submarine Banks, with Application to the Northwestern Atlantic Continental Shelf

Vertical distribution of sea scallop larvae was studied from pump samples in mixed, stratified, and frontal areas of Georges Bank. The extent of larval aggregation was positively related to the degree of water column stratification. In mixed areas larvae were distributed evenly over the 40 to 50 m water column, while in stratified waters larvae showed subsurface peaks in concentration above the pycnocline. Where the pycnocline was well developed, differences in the larval centre of mass (ZCM) were associated with differences in the position of the pycnocline. Food for sea scallop larvae was measured as the concentration of chlorophyll a < 15 Km and particles 2.5 to 16 pm. In stratified areas food was usually greatest within the upper 10 m. Sea scallop larvae were most concentrated below 10 m and d~d not aggregate in relation to food concentration. The capacity of sea scallop larvae for depth regulation on Georges Bank appears limited, since there were no die1 differences in the ZCM, and sizedependent differences in vertical distribution were weak and inconsistent.

Section: Discussionmentioning

confidence: 99%

Sea scallop larvae Placopecten magellanicus on Georges Bank: vertical distribution in relation to water column stratification and food

Tremblay¹,

Sinclair²

1990

“…The circulation on Flemish Cap is characterized by a weak anticyclonic circulation (ca 3 to 5 cm S-' residual circulation) that can be disrupted by storms (Hill et al 1975, Hayes et al 1977, Ross 1980, Kudlo et al 1984. Loder et al (1988) reported a mean annual recirculation time of 67 to 78 d for near-surface waters along the 400 m isobath and a mean residence time of 32 to 40 d for near-surface waters within the 400 m isobath. They concluded there is sufficient residency time to be favourable to biological processes.…”

Section: Peak Spawningmentioning

confidence: 99%

Seasonal development of invertebrate zooplankton on the Flemish Cap

Anderson¹

1990

Flem~sh C a p was dominated by the calanoid copepod Calanus finmarchicus It const~tuted 37 to 69 % of all zooplankton sampled with coarse mesh nets (0 333 and 0 505 mm) and 15 to 33 % In fine mesh nets (0 165 mm) dunng March to August O w~n g to its large size, C finmarchjcus dominated the biomass of all specles sampled in both coarse and fine mesh samples The domlnant copepod species in flne mesh samples (0 165 mm) were Oithona s~mllis and 0 atlanOca which together compnsed 20 to 4 2 O/a of all specles sampled C finmarcl~icus formed a d~screte populahon on Flemish C a p with peak spawning in mid-Aprll beginning first in waters 5 200 m depth Peak biomass occurred In late May and probably early June coincident w~t h peak abundance of late-stage copepodites Significant differences were observed in the rate of C finmarchicus developinent and absolute abundance among years sampled on Flemish Cap Differences in development were related to differences in the seasonal h e a t~n g of surface waters on Flemish Cap in different years It is hypothes~zed that these differences in rate of development and absolute abundance of C finmarchlcus and other copepods w~l l have a significant effect on larval fish feedlng, growth and survival

“…The bank is typified by a large, well-known, mean residual clockwise gyre with a recirculation time (about 56 d) near its annual average residence time of 54 d (Flagg 1987, Lynch & Namie 1993. Variations in current suggest that in summer, when the gyre is at its strongest, residence time exceeds recirculation time, while in winter residence time tends to be about half and recirculation time about double the summer values (Loder et al 1988). It is thought that this gyre helps to retain larvae of fish on the bank (Bumpus 1976).…”

Section: Three Populations With Different Larval Habitatsmentioning

confidence: 99%

Veligers from different populations of sea scallop Placopecten magellanicus have different vertical migration patterns

Manuel¹,

Gallager²,

Pearce³

et al. 1996

ABSTRACT. Veligers spawned by adults collected from 3 different populations (Georges Bank, Passamaquoddy Bay and Mahone Bay, all on the northeastern coast of North America) of giant scallops Placopecten nlagellanicus were maintained for 2 mo in replicated, 9.5 m deep, polyethylene mesocosms with a 1.5"C thermal gradient at mid-depth and a 12/12 photoperiod. The populations came from varied hydrographic regimes that might require vel~gers to have different vertical migration patterns if they are to be in an appropriate area for settlement when they reach competency. Veligers from all population~ were found in shallower depths at night than during the day, developed strong bio-convective cells when numbers were high at the surface and were seldom found below the thermocline until about 21 d after spawning. Under similar conditions, veligers from the 3 populations exhibited significantly different vertical migration patterns and depth distributions. These patterns of vertical distribution are unlikely to be due to differences in buoyancy, growth rate, food density, settlement preference or mesocosm effect, and they differ substantially from patterns of mussel veligers raised according to the same protocol. Such differences may reflect selection for different behaviors in different populations, arguing for an active and genetically controlled component to vertical movements of scallop veligers. The observed patterns of vertical distribution could produce marked differences in horizontal transport in the various physical regimes; increased self-recruitment seems the most likely explanation for the intense selection required to fix such behavior in populat~ons.