Gregory C. Jensen

The competitive and predatory impacts of the nonindigenous crab Carcinus maenas (L.) on early benthic phase Dungeness crab Cancer magister Dana

We evaluate the potential competitive and predatory impacts of nonindigenous European green crab Carcinus maenas on native Dungeness crab Cancer magister in the northeast Pacific. The coastal estuaries of Washington State, USA, provide appropriate habitat for recently introduced green crab, yet these areas are important nursery grounds for Dungeness crab and contribute greatly to the coastal crab fishery. Juvenile Dungeness crabs are dependent on limited intertidal epibenthic shell for refuge habitat during early benthic life and experience increased mortality on open sand and mud as a result of predation by fish and birds. Early juveniles throughout the subtidal are similarly at risk due to predation by fish and especially adult conspecifics. Laboratory experiments and infrared video observations revealed that juvenile green crab displace Dungeness crab of equal size from shelters during one-on-one competition. Green crab also consistently win nocturnal foraging trials in which the species compete for fresh, damaged clams. Field and laboratory enclosure experiments show that juvenile Dungeness crab emigrate from oyster shell habitat as a result of competition and predation by adult green crab. Depending on the extent to which the two species overlap, interactions with the dominant nonindigenous species could have a negative influence on juvenile Dungeness crab survival and could conceivably impact recruitment to the fishery. However, current evidence indicates that the distribution of green crab in Washington State is far removed from nursery areas of Dungeness crab.

Gregarious settlement by megalopae of the porcelain crabs Petrolisthes cinctipes (Randall) and P. eriomerus Stimpson

Settlement was studied in two vertically separated populations of the filter-feeding porcelain crabs Petrolisthes cinctipes (Randall) and Pefrolisthes eriomerus Stimpson near Bamfield, British Columbia, Canada. Within their respective tidal levels, megalopae of each species settled preferentially in cages containing conspecific adults. In addition, P. cinctipes was induced to settle below its normal tidal level in response to caged adults; similar settlement preference was also found in the laboratory, thus, demonstrating the first example of gregarious settlement among the Decapoda. While not as critical as for sessile organisms, the use of conspecific cues by crabs insures settlement in a suitable location while helping maintain existing zonation patterns, and may enhance postlarval survival through protection imparted by the presence of adult crabs.

Competency, settling behavior, and postsettlement aggregation by porcelain crab megalopae (Anomura: Porcellanidae)

Gregarious settlement by megalopae of the porcelain crabs Petrolisthes cinctipes (Randall) and P. eriomerus Stimpson was investigated to determine possible means of attraction and postsettlement benefits. Megalopae of P. eriomerus were attracted to conspecific adults confined to chambers that prevented tactile or visual contact, suggesting that postlarvae respond to a waterborne cue. There was also clear evidence of an extended period of competency for settlement, since newly molted megalopae of P. cinctipes held with conspecific adults settled within 2–4 days while those without adults delayed settlement for 2–3 wk. Loss of swimming ability at settlement is followed by degeneration of the pleopods and color changes. Following settlement juvenile instars appear to gain protection by continuing to hide between and beneath conspecific adults; this behavior significantly reduced predation in a laboratory experiment.

Omnivory in the diet of juvenile dungeness crab, Cancer magister Dana

Abstract Juvenile Dungeness crab ( Cancer magister Dana) have always been considered strict carnivores; however, early instars have been observed ingesting filamentous, epiphytic diatoms in the field. To investigate the potential importance of diatoms in the diet of this species, wild-caught megalopae were raised to the third juvenile instar on a variety of dietary treatments. Although the animals that were fed only filamentous diatoms ( Melosira sp. and Grammatophora sp.) had intermolt periods 20–25% longer than those raised on mussel ( Mytilus sp.) flesh or a mix of diatoms and mussels, there was no difference in molt size increment between the treatments. This ability to utilize such alternative food resources at a lower trophic level may be especially important in years of high settlement into coastal estuaries, when large numbers of juvenile crab are known to cause dramatic reductions in prey densities.

Shell selection by the hermit crab, Pagurus hartae (McLaughlin & Jensen, 1996) (Decapoda, Anomura)

Most species of hermit crabs rely on gastropod shells to protect their uncalcified abdomens, and these mobile shelters help guard against predation, desiccation, and physical stresses (Hazlett, 1981). Shells are so essential that their availability has been considered a limiting factor for populations (Vance, 1972; Spight, 1977). The types of gastropod shells available also determine the size of hermit crabs present in an area (Markham, 1968). In shell-limited environments crabs are often forced to occupy inadequate shells, which in turn restricts not only their growth and fecundity but also increases their risk of predation (Sripathi et al., 1977). There is considerable evidence that hermit crabs do not enter gastropod shells at random, but select shells according to shell species and their associated characteristics of shape, epibionts, dimension, and weight (Grant & Ulmer, 1974). This differential shell preference may lead to a form of habitat partitioning that increases the likelihood of coexistence between similar hermit crabs (Vance, 1972). Pagurus hartae (McLaughlin & Jensen, 1996) is a tiny species (maximum carapace length 6 mm) found from the Queen Charlotte Islands, Canada to the Mexican border. It occurs subtidally under rocks and in crevices at depths of 6-635 m, and large assemblages can be found in parts of Barkley Sound on Vancouver Island, British Columbia, Canada (Jensen, 1995). The present experiment was undertaken to determine what types of shells this newly described species occupies in natural surroundings and whether they exhibit any preference for shell species.

A Unique Feeding Method by a Teleost Fish, the Fourhorn Poacher Hypsagonus quadricornis (Agonidae)

Fish rarely move inanimate objects when seeking prey, and those few that employ such foraging strategies typically use the mouth to grasp materials. The fourhorn poacher (Hypsagonus quadricornis), a benthic North Pacific species, displays a unique ability to manipulate objects and uncover prey by a method that does not involve the mouth. Rocks and shells are lifted and overturned using the fingerlike, free rays of the pectoral fins, leaving the mouth available for

STATUS OF EUALUS PUSIOLUS IN THE NORTHEASTERN PACIFIC, WITH A DESCRIPTION OF A NEW SPECIES OF EUALUS (DECAPODA: HIPPOLYTIDAE)

Abstract The presence of Eualus pusiolus (Krøyer, 1841) in the northeastern Pacific is confirmed, and a new species that has often been confused with E. pusiolus is described and illustrated. Eualus butleri, n. sp., is found inside hexactinellid sponges and is distinguished by an elongated basal article of the antennular peduncle that exceeds the stylocerite, slender pereopods, and pronounced sexual dimorphism, with males larger than females and bearing enlarged third maxillipeds. A key to all known northeastern Pacific species of Eualus is included.

Distribution, Abundance, and Habitat Associations of a Large Bivalve (Panopea generosa) in a Eutrophic Fjord Estuary

ABSTRACT Marine bivalves are important ecosystem constituents and frequently support valuable fisheries. In many nearshore areas, human disturbance—including declining habitat and water quality—can affect the distribution and abundance of bivalve populations, and complicate ecosystem and fishery management assessments. Infaunal bivalves, in particular, are frequently cryptic and difficult to detect; thus, assessing potential impacts on their populations requires suitable, scalable methods for estimating abundance and distribution. In this study, population size of a common benthic bivalve (the geoduck Panopea generosa) is estimated with a Bayesian habitat-based model fit to scuba and tethered camera data in Hood Canal, a fjord basin in Washington state. Densities declined more than two orders of magnitude along a north—south gradient, concomitant with patterns of deepwater dissolved oxygen, and intensity and duration of seasonal hypoxia. Across the basin, geoducks were most abundant in loose, unconsolidated, sand substrate. The current study demonstrates the utility of using scuba, tethered video, and habitat models to estimate the abundance and distribution of a large infaunal bivalve at a regional (385-km2) scale.

FEEDING BEHAVIOR OF THE HORNED SHRIMP, PARACRANGON ECHINATA (CARIDEA: CRANGONIDAE)

Abstract Stomach content analysis and behavioral observations reveal that the horned shrimp Paracrangon echinata is a lie-in-wait predator on smaller organisms, especially amphipods, polychaetes, and caridean shrimp. Prey is detected using the extremely thin third pair of pereiopods, captured with the subchelate first pereiopods, and ingested whole.

HEPTACARPUS PUGETTENSIS, A NEW HIPPOLYTID SHRIMP FROM PUGET SOUND, WASHINGTON

ABSTRACT A new shrimp, Heptacarpus pugettensis (family Hippolytidae), is described. This small striped species occurs under rocks in the low intertidal zone in Puget Sound and the San Juan Archipelago. The combination of a short rostrum and epipods on the first two percopods readily distinguish it from other members of the genus.