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We examined feeding by the blue crab, Callinectes sapidus on the softshell clam, Mya arenaria (their shells gape at both ends) and the Atlantic rangia clam, Rangia cuneata (their shell margins shut tightly). The maximum sizes of both species that could be opened by crabs was determined, along with techniques used by crabs to open and eat them. The largest softshell clam eaten was significantly larger than the largest rangia that could be opened. Provided with five softshell clams in each of five size groups at the start of a 14-day experiment, crabs on Day 1 ate proportionately more intermediate-sized (4-5 cm) clams, then larger clams (5-7 cm), smaller clams (3-4 cm), and the largest clams (7+cm) in that order; this pattern continued throughout the first three days, by which time nearly all clams had been eaten. We provided two or three size classes of softshell clams to four size classes of crabs (small, medium, large, and jumbo) and gave two size classes of rangia to two sizes of blue crabs (small, jumbo) and videotaped the crabs' feeding techniques. Blue crabs used 11 techniques to open softshell clams compared with 5 used to open rangia. When opening softshell clams, small and medium crabs pried, pulled apart, and bored into shells frequently, cracking and crushing next most frequently. Large and jumbo crabs cracked and crushed most frequently, followed by prying and pulling shells apart. Twisting the siphon and clam body was also common. Differences in clam shell morphology and strength imply that softshell clams are more easily fed upon by blue crabs than are rangia clams. Size provides partial protection from blue crab predation in that small blue crabs might not be able to feed easily on large softshell clams and perhaps only the largest blue crabs can open large rangia. L'alimentation du crabe bleu Callinectes sapidus a partir de deux especes de clams, Mya arenaria, clam a coquille molle (a coquille beant aux deux extremites) et le clam rangia Rangia cuneata (a coquille fortement fermee) a ete examinee. Pour les deux especes, la taille maximum qui peut etre ouverte par des crabes a ete determinee, ainsi que des techniques utilisees par les crabes pour les ouvrir et les ingerer. Le plus grand clam a coquille molle mange etait significativement plus grand que le plus grand clam rangia qui a pu etre ouvert. Dans une experience de 14 jours, on a fourni 5 clams a coquille molle a chacun des cinq groupes de taille. Le jour 1, les crabes mangent dans l'ordre les clams de taille intermediaire (4-5 cm), puis les grands clams (5-7 cm), les clams les plus petits (3-4 cm) et les plus grands (7+cm). Ce modele se poursuit pendant les trois premiers jours, temps au bout duquel pratiquement tous les clams ont ete manges. Nous avons donne deux ou trois tailles de clam a coquille molle a quatre classes de taille de crabes (petit, moyen, grand et jumbo) et deux tailles de rangia a deux tailles de crabes (petit et jumbo) et nous avons filme les techniques d'alimentation. Les crabes bleus utilisent 11 techniques pour ouvrir les clams a coquille molle et seulement 5 pour ouvrir les rangia. Pour ouvrir les clams a coquille molle, les crabes petits et moyens forcent, dechiquetent et percent les coquilles frequemment, cassant et ecrasant moins souvent. Les crabes grands et jumbo cassent et ecrasent plus souvent puis forcent et ecartent les coquilles. Tordre le siphon et le corps du clam est aussi assez frequent. Des differences dans la morphologie de la coquille et sa solidite impliquent que les clams a coquille molle sont plus aisement consommes que les clams rangia. La taille procure une protection partielle contre la predation par les crabes bleus, donc les petits crabes bleus ne seraient pas capables de se nourrir facilement de clams a coquille molle et seulement les plus grands crabes peuvent ouvrir les grands clams rangia.

The effects of competitor pressure and prey odor on foraging behavior of the rock crab, Cancer irroratus (Say), were investigated. The Jonah crab, Cancer borealis (Stimpson), was chosen as the interspecific competitor because it shares resources with C. irroratus. Four treatments were tested for their effect on foraging: the presence or absence of a competitor and two types of prey odor; body odor (living mussel) and tissue extract (dead mussel tissue). The presence of Jonah crabs did not influence location time, search time, prey size selected, or handling time of the rock crabs. However, rock crabs responded differently to the presence of body odor and tissue extract cues. The presence of extract odor decreased the time to locate prey while increasing the number of prey manipulated and prey size selected. When prey body odor was present, rock crabs displayed less investigative behaviors than in the presence of extract odor, illustrated by reduced location time. Extract odor provided a stronger and more attractive cue than body odor, but increased prey manipulation and search time. Extract odor induced increases in manipulation and searching for prey but canceled out the benefits of decreased location time, resulting in crabs from both treatments displaying similar search times. These elevated behaviors may be associated with foraging for injured and cracked prey or may indicate an area of conspecific feeding.

The importance of chemical cues in the foraging behavior of the rock crab, Cancer irroratus, was investigated. Crabs were presented with mussel prey located upstream, downstream, or cross-stream. Trials were conducted under both light and dark conditions. With the prey upstream, the crabs exhibited the shortest search time and 100% searching success. There was a significant difference between flow direction treatments, but there were no significant differences between light and dark treatments. When presented with mussel extract and a seawater control, crabs approached the source of the current. Analysis of search patterns revealed differences in search time, path length and straightness, and total number of turns. Chemoreception was the predominant mode of prey detection and was used in guiding crabs to their prey. Large variabilities in the search path and search path parameters were exhibited, and there was no fixed search pattern for orientation toward food while foraging. It is suggested that rock crabs employed both chemotaxis and rheotaxis for locating odor sources.

Rock crabs,Cancer irroratus, respond to food odors in low concentration as measured by changes in antennular flicking rate. The responses of rock crabs to prey odor were tested in the presence and absence of visual cues to determine the role of chemical cues in prey recognition. Crabs were attracted to the source of mussel odor introduced into one arm of a Y maze. Natural and artificial prey shells and resin boxes were presented to crabs with and without the presence of mussel extract. The crabs were able to see, handle, and manipulate these objects. Crabs opened and consumed contents that emitted chemosensory cues and ignored identical objects that did not. Rock crabs were attracted to food odors and are capable of utilizing chemical cues to detect, locate, and identify food items.

The Jonah crab is an underutilized species in the mid-Atlantic region, and use of the whole, frozen crab would broaden marketing options for this seafood product. We monitored quality changes in whole cooked crabs held in a blast freezer for up to 50 weeks. A sensory evaluation panel determined the point at which detectable differences appeared in the product. Microbiological testing was conducted at selected intervals to assess bacterial content. In a triangle test, frozen experimental samples of leg meat were first differentiated from frozen controls at approximately 24 weeks. No significant difference was defected in body meat for up to 33 weeks’ storage. Microbial quality was acceptable throughout the experiment.

The sensitivity of the rock crab Cancer irroratus to extract of the freeze-dried mussel Geukensia demissa was measured using changes in the crabs' antennular flicking rate (AFR). Concentrations of 10―6 to 10―13 g 1―1 of extract were tested. The antennular flicking rate increased significantly at all concentrations down to 10―10 g 1―1. Nondirected feeding behavior was observed at a concentration of 10―6 g 1―1. At concentrations of 10―11 g 1―1 and below, the increase in flicking rate was not significant, although detection of the extract appeared to occur. A linear relationship exists between the ratio of AFR before introduction of extract to AFR after introduction of the extract and the log concentration of the extract.

Mechanical advantage and relative chela size of Jonah (Cancer borealis) and rock (Cancer irroratus) crabs were compared from locations along the east coast of North America, from Nova Scotia to Florida, to determine whether attributes of the chelae varied by sex, size class, or latitude. There was no relationship between mechanical advantage and sex. However, males of both crab species had larger chelae than females of comparable body size. There were no differences in mechanical advantage among size classes in the Jonah crab, nor was there a relationship between mechanical advantage and latitude, although mechanical advantage varied among the populations sampled. Relative chela size increased with the size of the crab and differed by site among populations sampled. The mechanical advantage of rock crab claws differed among size classes, varied according to site, and increased with latitude. The relative chela size of rock crabs also increased with size class and differed among sites. Differences may be attributed to pressures related to prey choice and availability, substrate preference, and habitat choice and availability, as well as competition and predation.

Diffubenzuron (Dimilin) is used as an insecticide for control of the gypsy moth. Because it is a chitin synthetase inhibitor, it can be a potential threat to other arthropods, including crustaceans. We used a static renewal testing paradigm to determine the LC50 of Dimilin WP-25 to juvenile blue crabs (carapace width: 25–60 mm). Both molt stage of dose frequency effect toxicity. When we exposed the crabs at random molt stages, LC50=3.5 mg l−1. When crabs were exposed on the day of molt, LC50=300 μg l−1. If initial exposure occurred on the day of molt and the crabs were subsequently exposed to repeated doses, LC50=18.5 μg l−1. Effects were age and molt-stage sensitive. We include a review of the data available on Dimilin effects in the marine and estuarine environments.

Simultaneous activity recordings were obtained from individual organisms under identical conditions using a recirculating saltwater system containing a chamber with removable dividers to allow a maximum of 10 testing compartments. Ten infrared-sensitive photoresistor arrays beneath the testing area sensed activity in the individual compartments. Data were recorded on a 20 channel event recorder.Twenty common rock crabs, Cancer irroratus, were housed and tested for 5 mo under five different light regimes to ascertain the presence of daily or tidal periodicities. These crabs were tested simultaneously, but individually, in duplicate facilities permitting calculation of individual and total sample periodicity and allowing observation of differences in activity rhythms based on age, sex, stage of the molt cycle, or other factors. Key words: activity patterns, actograph, aquaculture, Cancer irroratus, circadian rhythms

Pagurus longicarpus (Say) migrates in autumn from a shallow estuary to deeper waters of Narragansett Bay, Rhode Island, when ambient water temperatures are between 10? and 4? C. Critical thermal minimum experiments indicated that crabs ceased locomotor activity at approximately 30 C and righting response at 1.5? C. When presented with different sub- strates, crabs used their walking legs and, occasionally, their chelae to scoop a depression in the substrate. They were not able to construct a proper depression in gravel and, although they succeeded in burying themselves in both mud and sand, they remained buried only in sand. Winter dredging seaward of an estuary in which hermit crabs were found in summer showed the greatest density of crabs at 16-18 m depth, buried in fine sand. No crabs were found several meters away at 20 m on a silty mud bottom. The water temperature was less than 20 C in all areas sampled. It is hypothesized that, as environmental temperatures decrease, hermit crabs move into deeper water and bury themselves in regions of sandy bottom. Overwintering in this manner might decrease the predation of hermit crabs by benthic organisms while the crabs are in a state of torpor.

Two populations of hermit crabs, Pagurus longicarpus , one from the testing location on Narragansett Bay and the other from the Pettaquamscutt River, an estuary 7·5 km to the south of that location, were tested for directional preferences in outdoor ‘Zugunruhe’ tanks. The estuarine population exhibited seasonal migrations into and out of the estuary and indicated a directional preference under sunny and partially cloudy skies. The Narragansett Bay population exhibited seasonal inshore-offshore movements and did not indicate a preferred direction. Relocation and retesting indicated that the directionality was fixed; therefore, homing was not involved. Attempts to phase-shift the biological clock regulating sun-compass mechanisms were only partially successful. Many of the crabs indicated no shift. It is hypothesized that the Pettaquamscutt River estuarine population randomly migrates into the estuary in the spring, at which time the direction of the estuary's mouth is learned. Several environmental features, including a sun-compass, are used when leaving the estuary in autumn.

Rock crabs, Cancer irroratus, from the Mid-Atlantic Bight, spend warmer months in deep water, migrating in fall to shallow waters to molt and mate. In doing so, they move from a habitat lacking solar cues to one with various LD ratios. Exposed to LD photoregimes, crabs entrain locomotor activity to a diel (24 h) periodicity. Most activity occurred in the dark period, with increases at artificial dawn and dusk. To examine whether crabs entrain to seasonal and nonseasonal photoperiods, they were tested for rhythmicity under a variety of photoperiods. Locomotor rhythms rapidly entrained to photoperiods with 6-h phase advances or delays and durations of less than or more than 24 h. Responses were strongest when the photoperiods corresponded to ambient photoperiods. It is proposed that C. irroratus possesses a weak endogenous rhythm and that activity is synchronized by exogenous cues, when they become available in the seasonal inshore migration.