Time series of the abundance of the post-larvae of the crabsCancer magister andcancer spp. on the Southern Oregon coast and their cross-shelf transport

Using stationary zooplankton nets that fished the tidal current we measured the daily abundance ofCancer crab megalopae near the mouth of Coos Bay, Oregon, during the 1997 spring settlement season. During the spring of 1997, the coastal waters were dominated by a significant El Niño event. Sea surface temperatures (SST) were higher than normal, upwelling indices were an order of magnitude smaller than during the two previous springs, and upwelling favorable winds were weak. Daily catches ofCancer magister megalopae ranged from 0 to 78 with 61% of the total catch occurring during four pulses. Peak catches tended to occur every 13.6 d close to 13.8 d average period between spring tides. Significant cross correlations were found between the maximum daily tidal range and the catch ofC. magister megalopae; large catches tended to occur 4 to 7 d after the spring tide. Daily catches ofCancer oregonensis andCancer productus ranged from 0 to 307 with catch significantly positively cross correlated to the maximum daily tidal range at a lag of ?5 days suggesting that the largest catches tended to occur after the spring tides. We hypothesize that a tidally-generated phenomenon internal waves, transportedCancer megalopae shoreward and caused the observed variation in their abundance in Coos Bay.     

The impact of yellow shore crabs,<Emphasis Type="Italic">Hemigrapsus oregonensis</Emphasis>, on Early Benthic Phase dungeness crabs,<Emphasis Type="Italic">Cancer magister</Emphasis>, in intertidal oyster shell mitigation habitat

Dungeness crab (Cancer magister) megalopae recruit to northeastern Pacific coastal estuaries, and settle into intertidal and subtidal habitats where they molt into Early Benthic Phase (EBP) crabs, and are dependent on epibenthic structure for shelter from predation. Given the importance of shell refuge to their post-settlement ontogeny, the U.S. Army Corps of Engineers began constructing intertidal plots of oyster shell in the Grays Harbor estuary, Washington, to enhance recruitment and mitigate losses of subtidalC. magister entrained and killed during extensive dredging efforts. When shell habitat was newly constructed, settlement and survival ofC. magister were high, and expectations for the mitigation project were met. During the first several years (1992-1997), plots greater than 1 yr postconstruction were colonized by yellow shore crabs,Hemigrapsus oregonensis (often≥75 crabs m⁻², and abundance of EBPC. magister was reduced to nearly zero. While some predation of settling megalopae byH. oregonensis does occur, the relationship between these species is characterized by density-dependent competitive interactions. Laboratory observations of competition for shell habitat indicate thatH. oregonensis are dominant over EBPC. magister and can evictC. magister from refuge spaces. Field experiments show that high densities of the former cause, the latter to emigrate from shell, and suggest detection and avoidance of areas with high densities ofH. oregonensis by settlingC. magister megalopae. More recently (1998-2001), abundance ofH. oregonensis has declined dramatically within plots of oyster shell, apparently due to recruitment failure, and patterns ofC. magister abundance and production have returned to levels consistent with original expectations of the mitigation project. Both intraspecific and interspecific competition for space are significant factors effecting population, regulation ofC. magister when they are strongly dependent on refuge from predation. Efficacy of constructed oyster shell plots as a mitigation tool may hinge on the population dynamics of a species previously considered of little consequence to the target species.     

Seasonal abundance and vertical distribution of crab larvae in Delaware Bay

Larvae of 15 species or genera of crabs were collected and identified during a six month (May 26 to October 28, 1978) study in the mouth of Delaware Bay. Seasonal abundance and vertical distribution of each species were investigated. Most species studied had peak abundance in July and August except forCancer irroratus andOvalipes ocellatus which showed peak occurrence in May and June, respectively. Larvae of species strongly dependent on estuarine habitats, such asUca spp.,Pinnixa chaetopterana, andP. sayana, showed a tendency to congregate in near-bottom waters where net flow of water is landward, thus favoring retention within the estuary. Larvae ofOvalipes ocellatus, Cancer irroratus, andCallinectes sapidus were more common at the surface. This vertical distribution suggests that these larvae are flushed out of the estuary. The mechanisms of recruitment and replenishment of adult populations within the estuary would therefore depend on migration of megalopa and juveniles. *** DIRECT SUPPORT *** A01BY019 00006     

Food habits of two larval flies (Dolichopodidae: Diptera) in two gulf coast oligohaline tidal marshes

Food habits of two species of dolichopodid fly larvae, from two Gulf Coast oligohaline tidal marshes, were analyzed from monthly collections taken between June 1979 and May 1980. Larvae ofPelastoneurus abbreviatus Loew andThinophilus frontalis Van Duzee, taken from aJuncus roemerianus Scheele dominated marsh, fed predominantly on oligochaetes and nematodes.Pelastoneurus abbreviatus, collected in a nearbySpartina cynosuroides (L.) Roth marsh, also fed on oligochaetes but consumed more polychaetes than nematodes. By being predators and prey in turn, these larvae serve in the transfer of energy between benthic, aquatic, and terrestrial components of the marsh, system.     

Densities ofPenaeus aztecus,Penaeus setiferus,and other natant macrofauna in a Texas salt marsh

Habitat-related densities of natant macrofauna were compared between vegetated and nonvegetated areas in aSpartina alterniflora marsh on Galveston Island, Texas. The most abundant macrofauna were crustaceans,Palaemonetes pugio, Penaeus aztecus, Penaeus setiferus, andCallinectes sapidus, and small fish,Gobiosoma bosci, Lagodon rhomboides, Leiostomus xanthurus, Fundulus similis andMicropogonias undulatus. Excluding residentsP. pugio, G. bosci andF. similis, most of the macrofauna were transient juveniles of estuarine-dependent species. Among crustaceans,P. pugio, P. aztecus, andC. sapidus were significantly more dense in vegetated habitat, butP. setiferus was not consistently more abundant in either vegetated or nonvegetated habitat. Of 29 species of fishes, 14 were usually in vegetation, 11 were more often on nonvegetated bottom, and 5 were indifferent to either habitat. Much seasonal variability in abundances ofP. aztecus, P. setiferus, andC. sapidus, but notP. pugio, could be attributed to changes in temperature, salinity and water-level. Strong selection for vegetated habitat byP. aztecus was related to the historical water-level pattern coinciding with seasonal periods of marsh flooding. Apparently, high seasonal tides during the spring and fall facilitated access to vegetated habitat in the marsh and exploitation by transientP. aztecus. In contrast, strong selection for vegetation byP. pugio, abundant year-around in the marsh, was not similarly influenced by seasonal changes in water-level. Overall, habitat-related densities and physical interactions suggest that marsh physiography together with differences in tides may greatly determine the extent to which certain estuarine macrofauna utilize marsh habitats.     

Attempted hybridization of the grass shrimpPalaemonetes (Caridea,palaemonidae) with an evaluation of taxonomic characters of juveniles

Variation in morphological characters used to distinguish the three sympatric species ofPalaemonetes, i.e.,P. pugio, P. intermedius, andP. vulgaris, is suggestive of natural hybridization. Interspecific crosses among the species and intraspecific crosses of allopatric populations ofP. pugio were made to determine whether hybridization was feasible and to evaluate taxonomic characters of the juveniles. No interspecific matings produced larvae in the laboratory. Larvae, from intraspecific matings ofP. pugio andP. vulgaris were reared to 40 days of age. Larval survival rates, development time, and postlarval length ofP. pugio andP. vulgaris were not different, but juveniles ofP. pugio at 40 days after hatching were larger than those ofP. vulgaris. At 40 daysP. pugio had developed adult diagnostic features. However,P. vulgaris displayed sufficient variation in adult diagnostic features to resembleP. pugio in some cases. The intraspecific matings ofP. pugio from widely separated populations were fertile, but there was some indication of reduced reproductive compatibility in crosses involving Virginia females and Florida males relative to intrapopulational controls. *** DIRECT SUPPORT *** A01BY019 00002     

Ocean distribution of dungeness crab megalopae and recruitment patterns to estuaries in Southern Washington State

We investigated the distribution of meroplankton and water properties off southern Washington and simultaneously measured time series of larval abundance and water properties in two adjacent estuaries, Grays Harbor and Willapa Bay. The cruise period, in late May 1999, coincided with large variation in the alongshore wind stress that caused dynamic change in the position of the Columbia River plume, coastal upelling and downwelling, and offshore phytoplankton production. In the coastal ocean, meroplankton groups responded differently to this wind event and the associated advection of water masses. Dungeness crab (Cancer magister) megalopae were largely indifferent to the wide salinity variation, and were found throughout the surveyed area in both plume and recently upwelled waters. Megalopae of kelp crab (Pugettia producta) and hermit crab (Pagurus spp). were more abundant in upwelled water and low numbers were caught in the plume water. Barnacle cyprids appeared to track the advective transport suggesting that they may be more passively dispersed. Within the estuaries, hydrography responded rapidly and synchronously to variation in wind stress. Intrusions of both plume and newly upwelled waters were detected at estuarine sites, depending on the type of water present at the coast, indicating a tight link between the estuaries and the coastal ocean in this region. A 90-d record ofC. magister megalopae abundance was made at 3 estuarine sites using light traps. The bulk of theC. magister recruitment was limited to a relatively brief period in late May through June. Within this window, megalopae occurred in distinct pulses of 3–5 d interspaced with periods of low or zero abundance.C. magister megalopae recruited to the estuaries over a wide range of wind forcing, and were transported into the estuary within varied water types. There were no periodic patterns indicative of spring-neap tidal variations in the abundance time series. Abundance was only weakly cross-correlated between the adjacent Grays Harbor and Willapa Bay estuaries, which contrasts with the more synchronous estuarine-coastal linkages measured for water properties. These results suggest the interaction of larval aggregation size in the ocean with estuary-ocean exchange processes likely controls patterns of estuarine recruitment.     

Upriver migration and abundance of naked goby (Gobiosoma bosci) larvae in the Patuxent River estuary,Maryland

Larvae of the naked goby,Gobiosoma bosci, were collected during the spring and early summer of 1977 in the upper tidal Patuxent River, Maryland. Larvae first appeared in the collections on May 5. Weekly night sampling at 26 stations covering 28 km of the Patuxent illustrated the upriver movement of larvae, at an estimated rate of about 1 km per day. Larval densities quickly reached high levels, with a maximum density of more than 6,000 larvae per 100 m³ at one station on June 16. By June 23, the mean larval density for the entire 28 km stretch of the river was 1,825 larvae per 100 m³. Length-frequency distributions of the larvae illustrate the growth of the larvae, continual recruitment into the population, and a gradient in mean population length over the sampling transect that was due to the presence of the smallest larvae in the lower stations.     

Zooplankton dynamics in an intertidal salt-marsh basin

We determined tidal, diel (day-night), and diurnal (day to day) patterns of occurrence for the summer zooplankton assemblage in an intertidal salt marsh basin at North Inlet Estuary, South Carolina. In one time series, 153 μm pump and 365 μm net collections were made every 1–2 h during four consecutive tidal cycles. Taxonomic composition remained unchanged throughout most of the 48-h period, but densities and proportionalities of individual taxa were highly variable. Recurring patterns of abundance were observed and taxon-specific relationships with the tidal and diel cycles were indicated. Zooplankton were not uniformly distributed within flooding-ebbing water masses and distributions could not be explained by simple passive advection with the tides. Diel differences in densities of copepods and bivalves resulted from behavioral responses to changing light conditions. Large pulses of crab and shrimp larvae originating from nocturnal hatching events within the intertidal basin exited but did not return during the next flood tide. Higher densities of postlarval decapods on flood tides indicated settlement and recruitment to the shallow basin. In a second time series, replicated collections of the 153 μm and 365 μm assemblages were made during the daytime ebb tide every 1–3 d from May through October 1991 to determine relationships between diurnal changes in depth, salinity, and temperature and zooplankton composition and abundance. Diurnal variations in densities and proportionalities were less than those observed during the 48-h study and patterns were not regular. For most taxa, relationships between depth and abundance were the same in both time series. During periods of reduced salinity, densities of copepods,Uca zoeae, and barnacle nauplii decreased and densities ofUca megalopae andPenaeus postlarvae increased. However, zoeae emerged and postlarvae recruited throughout the 5-mo period, indicating that considerable flexibility in responses and tolerances existed within the populations. The diversity of life-history strategies and behavioral adaptations found among the zooplankton assures continuous occupation of flooded intertidal habitats. We suspect that the evolution and maintenance of temporally staggered recurring patterns of occurrence results in reductions in the competition for resources.     

Seasonal occurrence of larval and juvenile fishes in a Virginia Atlantic coast estuary with emphasis on drums (Family sciaenidae)

The seasonal occurrence and relative abundance of larval and juvenile fishes, particularly members of the family Sciaenidae, from a Virginia Atlantic coast estuary were determined from ichthyoplankton and otter trawl collections made from March 1979 to March 1980. The larvae of 19 species in 14 families were identified in the ichthyoplankton. Larvae of the engraulid, Anchoa mitchilli (bay anchovy), and the atherinid, Menidia menidia (Atlantic silverside), dominated the samples and made up 13 and 22%, respectively, of the 9,440 larvae collected. Peak occurrence of all larvae was from May to August. The juveniles of 28 species in 19 families were identified from otter trawl collections. Juvenile sciaenids numerically dominated the trawl collecions and made up 68% of the trawl catch. Juvenile density peaked during September through December.     

Abundance and dispersal potential of horseshoe crab (<Emphasis Type="Italic">Limulus polyphemus</Emphasis>) larvae in the Delaware estuary

The distribution, abundance, and dispersal patterns of horseshoe crab (Limulus polyphemus) trilobite larvae were determined from 671 plankton tows taken near a spawning beach in lower Delaware Bay, New Jersey, in 1998 and 1999. In both years, peaks in larval abundance occurred during periods of rough surf (>30 cm wave heights). Planktonic larvae were significantly more abundant nocturnally than during the day, but there was no evidence of a lunar component to larval abundance. Larvae were strongly concentrated inshore; trilobites were 10–100 times more abundant in the immediate vicinity of the shoreline than they were 100–200 m offshore. The strong tendency ofLimulus larvae to remain close to the beach suggests that their capability for long-range dispersal between estuaries is extremely limited. We suggest that limited larval dispersal potential may help explain previously observed patterns of genetic variation among the Mid-Atlantic horseshoe crab populations.     

Composition and distribution of larval fishes in New Jersey high marshes

The surface of the salt marsh is an important, but largely unrecognized, site for fish reproduction and larval growth. In an attempt to determine the composition and distribution of fishes utilizing these habitats, we sampled larval and juvenile fish with plankton nets, dip nets, and traps at a variety of microhabitats (tidal and nontidal ponds and ditches and the marsh surface) in three New Jersey high marshes. Two of the three marshes had been altered for mosquito control. During April to September 1980, we collected over 2,400 larvae and juveniles. All study sites were dominated by the larvae of the resident killifishes (Fundulus heteroclitus, Cyprinodon variegatus, F. luciae, andLucania parva) and less commonlyMenidia beryllina. However, the occurrence and abundance of each species varied with microhabitat. Larval production in all three marshes peaked during June–July, but extended from May until September. In most instances juveniles of the dominant fishes had microhabitat preferences similar to the larvae. High marshes may be more important for fish production than previously recognized because they serve as nursery areas for the resident killifishes.     

Late stage bivalve larvae in a well-mixed estuary are not inert particles

Depth-specific sampling at a single location was used to examine the vertical distribution of pediveliger larvae of bivalve mollusks in the York River, an estuary of Chesapeake Bay, Virginia. The water column at the sampling site was usually well mixed, lacking consistent temperature or salinity gradients for larvae. Four species showed strong vertical stratification when collected simultaneously at three depths. Pediveliger stage larvae of a clam (Cyrtopleura costata), an oyster (Crassostrea virginica), and a shipworm (Bankia gouldi) were most abundant near the benthos, and least abundant near the surface. A mussel (Geukensia demissa), showed the reverse trend, with most pediveliger larvae near the surface. Tidal stage had a slight effect on two species (C. costata andC. virginica), but only to increase the relative abundance of larvae near the benthos during flood tide. Otherwise, neither tidal phase nor light levels (night versus day) had detectable effects on distribution patterns. Sampling very close to the sediment-water interface provided no evidence that pediveliger larvae spent a significant proportion of their time in this location. While the behavior of precompetent bivalve larvae may tend to retain them within an estuary, that of competent-to-metamorphose pediveliger larvae does not appear to have that function. Pediveliger larvae may regulate their depth to best locate potential settlement substrate. Such an hypothesis is consistent with adult habitat zones of at least some of these species in Chesapeake Bay. Removing competent-to-settle larvae from analyses of larval distributions in estuaries will enhance or clarify depth distribution patterns observed for earlier-stage larvae.     

A comparison of dispersal strategies in two genera of brachyuran crab in a secondary estuary

Seasonal occurrence and vertical distribution of larvae of two genera of brachyuran crab were studied in a secondary estuary flowing into Delaware Bay. Spawning in the xanthid crabRhithropanopeus harrisii occurred earlier with peak abundance of larvae in June and with a distinct decline in abundance in August. In contrast,Uca spp. larvae reached peak abundance in August. All zoeal stages ofR. harrisii were collected in the river suggesting that larvae of this species are retained in secondary estuaries near areas of prime adult habitat. Only zoea stage I larvae and megalopa ofUca spp. were collected in the river indicating that larvae of these speies may be flushed into the Delaware Bay and may not return to secondary estuaries near areas suitable for adult habitat until the megalopa stage is reached. It is not clear if this dispersal pattern is an active or passive process. *** DIRECT SUPPORT *** A01BY019 00004     

Larval production of the caridean shrimp,Crangon septemspinosa,in waters adjacent to Chesapeake Bay in relation to oceanographic conditions

Plankton samples of the MECCAS- (Microbial Exchanges and Coupling in Coastal Atlantic Systems) Project, taken in February, June, and August 1985 and April 1986, were analyzed to study the spatio-temporal distribution of sand shrimp, Crangon septemspinosa, larvae of Chesapeake Bay. With up to 250.9 larvae m^?3, results confirm C. septemspinosa as a very abundant decapod larval form in early spring in the study area. The overwhelming majority (94.5%) of the larvae occurred in April 1986; a second minor peak of larval production was observed in February 1985. The first two larval stages comprised 81.1% of the collected larvae, and complete series of all developmental stages including juveniles were obtained in June 1985 and April 1986. Newly hatched larvae occurred over a wide range of salinities (22.00–33.60‰), while more advanced forms were found mainly at higher salinities (>30‰). High larval abundances (>50 larvae m^?3) were obtained between 10°C; another considerably smaller peak in abundance occurred at temperatures ranging from 2.7°C to 4.5°C. Compared to other developmental stages, high abundances of the first two larval stages were collected at the highest chlorophyll concentrations. The significance of phytoplankton as a possible energy source for early stages of planktonic larvae and the role of phytoplankton as a possible chemical stimulus for larval release is discussed in terms of stomach and mouthpart structure and larval sensitivity to their chemical environment. *** DIRECT SUPPORT *** A01BY066 00016     

Distributional patterns of blue crabs (Callinectes sp.) in a tropical estuarine lagoon

A two-year trawl study of Laguna Joyuda, Puerto Rico, a small, polyhaline lagoon with restricted oceanic exchange, yielded 803 crabs belonging to sixCallinectes species.Callinectes danae was the most abundant (35.7%), followed byC. sapidus (21%),C. ornatus (12.6%),C. bocourti (12.1%),C. exasperatus (1.2%), andC. larvatus (0.4%). Abundances of different species differed more spatially than temporally despite very homogeneous salinities.Callinectes bocourti andC. sapidus were most abundant furthest from the lagoon’s inlet, whileC. danae andC. ornatus were most abundant near the inlet and in the center of lagoon. Juveniles were least abundant in the center of the lagoon. Size frequencies of most species showed common trends with high percentages of small crabs furthest from the inlet, and high percentages of larger crabs near the inlet and central parts of the lagoon. Distributional patterns appear to be a result of complex interactions of habitat preferences and intra- and interspecific interactions among the crabs.     

Comparison of fish and macroinvertebrate use of<Emphasis Type="Italic">Typha angustifolia,Phragmites australis</Emphasis>, and treated<Emphasis Type="Italic">Phragmites</Emphasis> marshes along the lower Connecticut River

Since 1965 large areas of lower Connecticut River tidelands have been converted from high diversity brackish meadow andTypha angustifolia marsh to near monocultures ofPhragmites australis. This study addresses the impact ofPhragmites invasion on fish and crustacean use of oligohaline high marsh. During spring tides from early June through early September 2000, fishes and crustaceans leaving flooded marsh along 3 km of the Lieutenant River, a lower Connecticut River tributary, were captured with Breder traps at 90 sites, equally distributed amongPhragmites, Typha, and treated (herbicide and mowing)Phragmites areas. Pit traps, 18 per vegetation type in 2000 and 30 each inPhragmites andTypha in 2001, caught larvae and juveniles at distances of up to 30 m into the marsh interior. There were no significant differences in fish species compositions or abundances among the vegetation types. Size distributions, size specific biomasses, and diets ofFundulus heteroclitus, the numerically dominant fish, were also similar. The shrimpPalaemonetes pugio was more abundant inPhragmites than in other types of vegetation, whereas the fiddler crabUca minax was least numerous inPhragmites. Mean numbers ofF. heteroclitus andP. pugio caught per site event were positively correlated with increasing site hydroperiod. Significantly moreF. heteroclitus were captured along the upper reach of the river where marsh elevations were lower than farther downstream. MoreF. heteroclitus and fewerP. pugio andU. minax were captured during the day than at night. A relatively small number of larval and juvenileFundulus sp. were captured in pit traps, but consistently fewer inPhragmites than inTypha, suggesting thatTypha and brackish meadow marshes may provide better nursery habitat. Vegetation was sampled along a 30 m transect at each trap site in 2000. Plant species diversity was greatest in treatedPhragmites areas and lowest inPhragmites sites.     

The abundance of fish larvae in estuaries: Within-tide variability at inlet and immigration

The larvae of winter spawning fishes immigrating through Beaufort Inlet into the Pamlico Sound estuarine system (North Carolina, United States) were passively sampled during 14 flood tides and nine of the following ebb tides. Five taxa were abundant in the catches. Pelagic species were represented by Atlantic menhaden, Brevoortia tyrannus. Nonpelagic taxa were represented by Atlantic croaker, Micropogonias undulatus, spot, Leiostomus xanthurus, pinfish, Lagodon rhomboides, and flatfishes of the genus Paralichthys. The sampling was continuous and the sample duration varied between 4 min and 32 min. The longest samples furnished the most accurate and precise estimates of the mean tidal abundance. Sampling 10 min each hour of the tide was the most efficient protocol for determining the mean tidal abundance. The abundance patterns was shown to differ according to the pelagic or nonpelagic behavior of the larvae. Analyses suggested the nonpelagic taxa rely on astronomical tides and vertical migrations synchronous with the direction of the tide flow to be transported upstream in the estuary. These larvae were not dependent upon the strength of the tide to penetrate the inlet. In contrast, menhaden larvae seemed to rely primarily on strong food tides to enter the estuarine area, probably because the vertical positioning of the species within the water column is not dependent upon the direction of the tide. However, if larvae were present outside of the inlet, strong flood tides indiscriminately brought pelagic and nonpelagic species into the estuary.     

Comparison of intertidal habitat use and growth rates of two northern Puget Sound cohorts of 0+ age Dungeness crab,Cancer magister

Density, habitat use, and growth of intertidal 0+ age Dungeness crabs, Cancer magister, were examined at five northern Puget Sound (Washington, USA) sites between June 1984 and September 1987. Sampling was conducted biweekly during settlement, from June to September, and approximately monthly or bimonthly thereafter. Northern Puget Sound Dungeness crab populations appear to be largely supported by recruitment from inland parental stocks, but a smaller proportion of recruits originate from coastal or oceanic stocks, as evidenced by earlier settlement and larger size of the first instar. Settlement of Dungeness crabs in inland waters typically peaked in August, and interannual variation in year-class strength at settlement (measured as intertidal density) was low relative to that reported for coastal crab populations. Spatial and interannual differences in settlement densities were mediated by high postsettlement mortality, which varied inversely with habitat complexity. Seasonal densities were highest in mixed sand and gravel with an overstory of attached or drift macroalgae, intermediate in eelgrass (Zostera marina), and lowest on open sand. Postsettlement growth rates corresponded to seasonal water temperatures and were greatest for the coastal cohort that settled in May and June. This cohort was larger as first juvenile instars (7.2 mm carapace width, CW) and grew rapidly at summer temperatures in excess of 15°C to a size (>30 mm CW) that allowed emigration from intertidal to subtidal areas by September. The late summer cohort settled in August at 5.3 mm CW and soon after was subjected to decreasing autumn water temperatures. There crabs experienced little growth while over wintering in the intertidal, but growth rates increased in March, and the crabs emigrated in April and May, approximately 10 mo after settlement.     

The necessity for intertidal foraging by estuarine populations of subadult dungeness crab,Cancer magister: Evidence from a bioenergetics model

Complex intertidal habitats characteristic of northeastern Pacific coastal estuaries provide critical nursery environments for young-of-the-year Dungeness crab,Cancer magister, yet their role in supporting subsequent year classes remains unclear. SubadultC. magister (40–130 mm; 1+ and >1+ year classes), which reach densities as high as 4,300 crabs ha^?1 in subtidal channels during low tides, migrate during flood tides from subtidal refuges into intertidal habitats to forage. As with other brachyuran species that undertake extensive tidally-driven migrations, intertidal foraging may contribute significantly to the energy budget of subadultC. magister. In order to explore the energetic incentive for intertidal migrations by subadult crabs, we developed an ontogenetically-based bioenergetics model for crabs within Willapa Bay, Washington. The model showed that energetic demand varied spatially across the bay, with the highest average energetic demand of a population of subadult crabs (2.13×10⁶ kJ ha^?1) occurring in a habitat stratum termed lower side channel (LSC) and characterized by relatively little subtidal area and extensive intertidal flats. Comparison of model results with subtidal prey production revealed that the latter could not satisfy subadultC. magister energetic demands, especially in LSC where modeled crab predation depleted subtidal prey biomass within 17 simulation days. We estimate that 1 ha of subtidal crabs from LSC would minimally require an additional 1.6 ha of intertidal area to satisfy energetic demands without depleting prey biomass. Our model results support the assertion thatC. magister make regular migrations to forage on productive intertidal flats, and suggest that intertidal foraging may contribute significantly to the diet of subadult crabs in coastal estuaries.