Richard A. Cooper

Migrations and growth of deep-sea lobsters, Homarus americanus.

In distinct contrast to the restricted movements of coastal stocks of lobsters (Homarus americanus), those inhabiting the outer continental shelf undertake extensive seasonal migrations. Of 5710 tagged lobsters released on the outer continental shelf off New England from April 1968 to June 1969, 400 had been recaptured by April 1970. The distribution of the recoveries demonstrated shoalward migration in spring and summer and a return to the edge of the shelf in fall and winter. Deep-sea lobsters have a faster rate of growth than coastal lobsters; growth increments at molting and the frequency of molting are greater.

Disturbance and contrasting patterns of population structure in the brachiopod Terebratulina septentrionalis (Couthouy) from two subtidal habitats

Abstract The population structures of Terebratulina septentrionalis (Couthouy) from exposed upper rock surface and semi-cryptic rock wall habitats at 33 m depth in the Gulf of Maine differ. Over a 3-yr period, population densities were consistently higher in rock wall habitats. Although both populations were dominated by juveniles (1–4 mm shell length), size-frequency distributions constructed from upper rock surface and rock wall populations were significantly different, as a result of a greater frequency of large brachiopods (> 20 mm shell length) in rock wall populations. Prominent modes occurred at 14–15 mm shell length in upper surface populations and at 19–20 mm length in rock wall populations. Recruitment was higher in rock wall habitats where ambient light intensities were significantly lower than on upper rock surfaces. Differences in recruitment are either the result of larval selection for shaded rock walls or differential juvenile mortality between habitats. The larvae of Terebratulina settle on a diverse array of substrata. These include bedrock, sandy polychaete tubes and algae in upper surface habitats and bedrock, calcareous polychaete tubes, and ascidians in rock wall habitats. Individuals attached to polychaete tubes and algae in upper surface habitats do not attain large body size (> 13 mm shell length). It is suggested that these differences in population structure reflect the greater intensity of disturbance in upper surface habitats. For example, the cod, Gadus morhua (Linnaeus), ingests brachiopods attached to algae and polychaete tubes in this habitat. Gastropod predation affects brachiopods in upper surface habitats but not in rock wall habitats. Predation by gastropods and asteroids is not size-specific. These results are consistent with the hypothesis that predation contributed to the decline in the abundance and diversity of articulate brachiopods since the Mesozoic, and suggest that the restriction of recent populations to semi-cryptic rock wall and crevice habitats is, in part, controlled by disturbance.

Burrow construction and behavior of tilefish, Lopholatilus chamaeleonticeps, in Hudson Submarine Canyon

SynopsisDuring 22 daylight submersible dives in August 1979 numerous juvenile and adult tilefish, Lopholatilus chamaeleonticeps, were observed in and around vertical burrows in the clay substrate of portions of Hudson submarine canyon in depths from 110–230 m. The size and shape of the burrows varied considerably with the smallest juveniles occupying simple vertical shafts in the substrate. Larger fish were found in much larger burrows (up to 4–5 m in diameter and at least 2–3 m deep) that were funnel shaped in cross-section with the upper conical portions containing numerous smaller burrows of associated crabs. The range of burrow sizes observed suggests a regular sequence of burrow construction by tilefish and the associated crabs. Both juvenile and adult tilefish swam into the burrows head first and exited tail first. This behavior, which would preclude the possibility of ambushing prey, and evidence of predation by sharks and other tilefish, suggests that the burrow is a refuge from predators.Tilefish burrows appear to serve as a focus for biological activity. Species associated with the burrows included galatheid crabs, Cancer sp., Acanthocarpus alexandri, Homarus americanus, Heliocolenus dactylopterus and Conger oceanicus. Tilefish may play an important role in structuring outer continental shelf communities. They physically shape their environment and probably have significant biological interactions with the species that associate with their burrows.

Geology and biology of Oceanographer submarine Canyon

Abstract We investigated Oceanographer Canyon, which is on the southeastern margin of Georges Bank, during a series of fourteen dives in the “Alvin” and “Nekton Gamma” submersibles. We have integrated our observations with the results of previous geological and biological studies of Georges Bank and its submarine canyons. Fossiliferous sedimentary rocks collected from outcrops in Oceanographer Canyon indicate that the Cretaceous—Tertiary boundary is at 950 m below sea level at about 40°16′N where at least 300 m of Upper Cretaceous strata are exposed; Santonian beds are more than 100 m thick and are the oldest rocks collected from the canyon. Quaternary silty clay, deposited most probably during the late Wisconsin Glaciation, veneers the canyon walls in many places, and lithologically similar strata are present beneath the adjacent outer shelf and slope. Where exposed, the Quaternary clay is commonly burrowed by benthic organisms that cause extensive erosion of the canyon walls, especially in the depth zone (100–1300 m) inhabited by red crabs (Geryon) and/or jonah crabs (Cancer). Bioerosion is minimal on high, near-vertical cliffs of sedimentary rock, in areas of continual sediment movement, and where the sea floor is paved by gravel. A thin layer of rippled, unconsolidated silt and sand is commonly present on the canyon walls and in the axis; ripple orientation is most commonly transverse to the canyon axis and slip-faces point downcanyon. Shelf sediments are transported from Georges Bank over the eastern rim and into Oceanographer Canyon by the southwest drift and storm currents; tidal currents and internal waves move the sediment downcanyon along the walls and axis. Large erratic boulders and gravel pavements on the eastern rim are ice-rafted glacial debris of probable late Wisconsinan age; modern submarine currents prevent burial of the gravel deposits. The dominant canyon megafauna segregates naturally into three faunal depth zones (133–299 m; 300–1099 m; 1100–1860 m) that correlate with similar zones previously established for the continental slope epibenthos. Faunal diversity is highest on gravelly sea floors at shallow and middle depths. The benthic fauna and the fishes derive both food and shelter by burrowing into the sea floor. In contrast to the nearby outer shelf and upper slope, Oceanographer Canyon has not been extensively exploited by the fishing industry, and the canyon ecosystem probably is relatively unaltered.

Seasonal Abundance of the American Lobster, Homarus americanus, in the Boothbay Region of Maine

Abstract Estimates of the abundance of the American lobster, Homarus americanus, in the inshore fishing grounds of Maine were made at monthly intervals by diver biologists from August 1965 through August 1967. Pairs of divers searched 540 m2of ocean bottom at the 6-12-m and 18-24-m depth intervals at two stations in the Boothbay Region of Maine. Comparative estimates of lobster abundance were made at adjacent depths of 30-60 m from the research submersibles PC-8 and Deep Diver. The relatively constant estimates of lobster abundance shoaler than 24 m suggest that large scale seasonal movements into and out of the shallow onshore fishing grounds does not occur. Size structure and sex ratio of the lobster population shoaler than 24 m was defined from collections made by the divers during periods of maximum (September) and minimum (February) bottom water temperatures. Mean carapace lengths by sex are similar for the September and February samples. Males and females range in size from 5-90 mm. A 50:50 sex rati...

Trace metal concentrations in offshore, deep-water seaweeds in the western North Atlantic ocean☆☆☆

Abstract Ambient, natural levels of selected heavy metals were assayed from deep, offshore populations of attached seaweeds from 1980 through 1983 from Pigeon Hill, 37 km from the nearest shoreline in the Gulf of Maine, and from Block Island, 23 km from the nearest mainland in Rhode Island Sound. Concentration levels of barium, cadmium, chromium, copper, mercury, lead and zinc were low when compared with concentration values published for a variety of seaweeds from the eastern and western North Atlantic. Values from Pigeon Hill and Block Island provide baseline data for long term monitoring of a relatively pristine, offshore, benthic community in the western North Atlantic.