Carcinus Maenus Research Articles

Ecology of beach wrack in northern New England with special reference to Orchestia platensis

The northern New England beach wrack community with special reference to the cosmopolitan amphipod crustacean, Orchestia platensis, was examined at estuarine and open coastal habitats. Beach wrack was dominated by the plant genera Ascophyllum, Zostera, Spartina and Chondrus, and was most abundant during spring and late summer. Animal community numbers, biomass and frequency in fresh to moderately decomposed wrack were dominated by O. platensis throughout the year at all habitats; oligochaetes and Collembola were also important. The abundance of O. platensis showed high spatial and temporal variability, with low abundance generally associated with decreased amounts of wrack during colder months. An exception was the winter presence of the species at one estuarine habitat, in patchy aggregations within gravel-cobble refuges. The abundance of O. platensis averaged 1280 (0.04 m 2) −1, with a maximum of 7040 (0.04 m 2) −1. The life cycle of O. platensis is bivoltine, with summer-hatched young reaching maturity within 1 month. Laboratory studies indicate females with up to 4 broods (30 days) −1, averaging 18 eggs brood −1. Orchestia platensis is omnivorous, eating fresh plant tissue, live oligochaetes, Limulus eggs and diatom ‘fuzz’. The rate of laboratory consumption of algae and Zostera was 0.05 mg plant mg −1 wet body weight day −1. Presumptive predators of O. platensis are juvenile green crab, Carcinus maenus, and the earwig. Anisolabis maritima. The mobility, aggregation and aggressiveness of O. platensis assist the species in establishing and maintaining populations in the rigorous wrack habitat. The general competitive superiority of O. platensis over its congener, O. gammarella, and the co-occurrence of these species on both eastern and western Atlantic shores is discussed.

RELEASE OF HATCHERY‐REARED BAY SCALLOPS (Argopecten irradians) ONTO A SHALLOW COASTAL BOTTOM IN WATERFORD, CONNECTICUT

ABSTRACTSurvival and growth of hatchery‐reared bay scallops (Argopecten irradians) transferred to a shallow coastal area in outer Jordan Cove, Connecticut, were monitored by SCUBA during the summer and fall of 1979. In all, 47,000 bay scallops were released over 4 sequential seedings. Based on slopes derived from linear regression models the time to 50% loss of bay scallops from the release areas was less than one day for juveniles ≤22 mm and ≥6 days for scallops ≥24 mm. Significant (α = 0.05) reductions in the rate of loss occurred as scallop size increased at release. Scallops released with shell heights >45 mm had the lowest rates of loss. Both predation and dispersion effected these loss rates. Predation of scallops was attributed to the following benthic invertebrates: 6 species of crabs (Cancer borealis, Cancer irroratus, Carcinus maenus, Callinectes sapidus, Pagurus pollicarpus, Pagurus longicarpus), lobsters (Homarus americanus), 2 species of oyster drills (Urosalpinx cinerea and Eupleura caudata) and sea stars (Asterias forbesi). These predators contributed to most of the losses of bay scallops ≤22 mm and at least 20–50% of the losses in scallops ≥24 mm. Dispersion consisted of a northwest drift of scallops across the field study areas, which was probably enhanced by current patterns. Growth of bay scallops from October 3–24 was 0.26 mm/day and the rate of growth slowed as the water temperature dropped below 15°C.

Changes in permeability in the shore crab, Carcinus maenas (L.), as a response to salinity

1. 1. With a change in salinity Carcinus maenus changes its permeability to salts. 2. 2. This adaptation takes place in two stages: (a) a very quick response to external changes in salinity and (b) a gradual adaptation which may be connected with a change in internal concentration. 3. 3. Both reactions proceed more slowly at a lower temperature (5°C) than at a higher temperature (20°C). The temperature does not greatly influence the final permeability.

Cadmium Poisoning in Fundulus heteroclitus (Pisces: Cyprinodontidae) and other Marine Organisms

In acute toxicity bioassays with [Formula: see text] at 20 C and 20‰ salinity, the concentrations fatal to 50% of the organisms of various marine species in 96 hr ranged between 0.32 and 55.0 mg/liter Cd2+. The order of sensitivity was: sand shrimp, Crangon septemspinosa (0.32); hermit crab, Pagurus longicarpus (0.32); grass shrimp, Palaemonetes vulgaris (0.42); common starfish, Asterias forbesi (0.82); common soft-shell clam, Mya arenaria (2.2); green crab, Carcinus maenus (4.1); Atlantic oyster drill, Urosalpinx cinerea (6.6); eastern mud snail, Nassarius obsoletus (10.5); sandworm, Nereis virens (11.0); striped killifish, Fundulus majalis (21.0); blue mussel, Mytilus edulis (25.0); sheepshead minnow, Cyprinodon variegatus (50.0); and mummichog, Fundulus heteroclitus (55.0). Mummichogs were more susceptible to cadmium exposures at 20 C than at 5 C and at 5‰ salinity than at 15, 25, or 35‰. Additional studies with mummichogs clearly demonstrated that 96 hr was not sufficient to adequately evaluate cadmium toxicity to this species. Mummichog whole body cadmium residues determined by atomic absorption provided a useful index of cadmium body burden among fish surviving exposure. However, cadmium residue data from dead mummichogs were of limited worth owing to accumulation after death.