Estuarine production of juvenile dungeness crab (cancer magister) and contribution to the Oregon-Washington coastal fishery

Estuaries provide nursery habitat for juvenile stages of several commercial decapod crustaceans worldwide, and those in the Northeastern Pacific are viewed as providing this function for Dungeness crab,Cancer magister. It is difficult to ascertain the degree to which such estuarine production of juveniles eventually contributes to coastal adult populations and fisheries since there are no direct surveys of adult abundance. As other authors have done, we used fishery landings data to compute the long-term average contribution of 1 + juvenile crab populations reared in estuaries to future coastal fisheries. We focused on Oregon and Washington states, but grouped landings in two large geographic zones by combining fishery ports as adjacent to Large Estuarine Zones (LEZ; Grays Harbor and Willapa Bay, Washington, and both sides of the Columbia River) and Small Estuarine Zones (SEZ; all other ports in Oregon). Mortality estimates were used to reduce 1 + crab abundance to surviving legal males, and portrayed as percent of the fisheries. Trends in the SEZ indicate that an average of only about 5–7% of estuarine production adds to the coastal adult population and contributes about $0.7 million to the fishery. The contribution is 25–30% in the LEZ (but may be higher since interannual density varies up to 5 times) and is worth about $3.9 million based on present ex-vessel value. Analyses of crab distribution and density indicate that the majority of an estuarine population (50–80%) is located in lower side channels (LSC) in spring and summer where temperature is higher and prey within and on adjacent intertidal flats is high. The potential average dollar value of equivalent legal male crab produced from the juvenile population is about $180 ha^?1 in LSC (but $280 ha^?1 in Grays Harbor where long-term density is highest), and lower in other estuarine habitats ($50–100 ha^?1). Estuarine juvenile production provides a relatively stable source of recruits to coastal adult populations, and large systems in the LEZ are important nurseries. Since direct coastal settlement of larvae does occur but is highly variable, the estuarine contribution may be especially important when physical forcing or unusual events lead to low survival of the coastal 0+ cohort. An unusually long period of very low landings in the LEZ from 1981–1987 is interpreted in light of the Mount St. Helens eruption (1980) and subsequent transport and deposition of very fine silt fractions over much of the LEZ nearshore shelf that may have adversely affected several year classes of small, early benthic phase juveniles at that time.     

Swimming behavior of Dungeness crab,Cancer magister Dana,megalopae in still and moving water

In the Grays Harbor estuary, juvenile Dungeness crab (Cancer magister Dana) are found at higher densities in epibenthic shell deposits compared to open mud flat. Differences in predation rate between habitats have been suggested to be due to habitat preference and differential survival. Megalopae preferred shell over open space in still-water conditions. However, it is not known whether megalopae are able to select shell in flowing water since larval preference is known to differ between still and flowing water. Here we report the first experimental study of swimming behavior of Dungeness crab megalopae in a range of current velocities (0–40 cm s^?1) equivalent to natural flow in Grays Harbor estuary. Experiments were conducted in daylight using a recirculating flume. Megalopae swimming speeds ranged from 8.5 cm s^?1 (8 body lengths s^?1) in still water to 44.8 cm s^?1 (44 body lengths s^?1) at flow speeds of 40 cm s^?1, Neither swimming behavior nor sheltering behavior in shells showed any flow-related pattern. Megalopae spent a large proportion of time swimming against the current and made headway upstream against all current velocities tested. The results suggest that Dungeness crab megalopae are able to maneuver and actively search for settlement sites under current velocities found in natural habitats, including intertidal shell deposits, and support the hypothesis of active selection of shell by megalopae.     

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.     

Factors influencing spatial and annual variability in eelgrass (Zostera marina L.) meadows in Willapa Bay, Washington, and Coos Bay, Oregon, estuaries

Environmental factors that influence annual variability and spatial differences (within and between estuaries) in eelgrass meadows (Zostera marine L.) were examined within Willapa Bay, Washington, and Coos Bay, Oregon, over a period of 4 years (1998–2001). A suite of eelgrass metrics were recorded annually at field sites that spanned the estuarine gradient from the marine-dominated to mesohaline region of each estuary. Plant density (shoots m^?2) of eelgrass was positively correlated with summer estuarine salinity and inversely correlated with water temperature gradients in the estuaries. Eelgrass density, biomass, and the incidence of flowering plants all increased substantially in Willapa Bay, and less so in Coos Bay, over the duration of the study. Warmer winters and cooler summers associated with the transition from El Niño to La Niña ocean conditions during the study period corresponded with this increase in eelgrass abundance and flowering. Large-scale changes in climate and nearshore ocean conditions may exert a strong regional influence on eelgrass abundance that can vary annually by as much as 700% in Willapa Bay. Lower levels of annual variability observed in Coos Bay may be due to the stronger and more direct influence of the nearshore Pacific Ocean on the Coos Bay study sites. The results suggest profound effects of climate variation on the abundance and flowering of eelgrass in Pacific Northwest coastal estuaries.     

Patterns of estuarine use by juvenile English sole (Parophrys vetulus) and Dungeness crab (Cancer magister)

Extensive trawl surveys were conducted in two large estuaries (Grays Harbor and Willapa Bay) on the Washington coast during 1983–1987, and in adjacent areas of the open coast. These surveys have shown that both English sole and Dungeness crab rely heavily on these estuaries as nursery areas, although the pattern of utilization differs substantially. Juvenile migration patterns can show substantial interannual variability and can only be delineated by concurrent surveys in both coastal and estuarine areas, conducted over a period of several years. English sole eggs and Dungeness crab larvae are released in coastal waters. Larvae of both species transform to the benthic stage in both coastal and estuarine areas, but most English sole eventually migrate into the estuaries during the first year of life, even if initial settlement is along the open coast. By the time English sole have attained a length of 55 mm (TL), most of them are found in estuaries. English sole begin emigrating from the estuaries at about 75 mm, and few remain there during the second year of life. In contrast, Dungeness crab appear to remain in the area of initial settlement throughout the first year of life. Growth is substantially faster in estuaries where 0+ crab reach a mean size of about 40 mm carapace width (CW) by September, with those off the coast are only about 14 mm CW. Juveniles remain in the area of settlement over their first winter but, in contrast to English sole, most coastal 1+ crab immigrate to estuaries to join siblings that settled there the previous year. By September of the second year, crab at about 100 mm CW emigrate to the open coast where they reach maturity. Advantages to juvenile stages that reside in estuaries are discussed in terms of accelerated growth at higher temperatures and potentially greater food supplies than found nearshore along the coast.     

Interactions between human communities and estuaries in the Pacific Northwest: Trends and implications for management

This paper explores social, and economic aspects of coastal communities crucial to the management of estuaries in the Pacific Northwest. These aspects include the changing demographics and economies of coastal communities, and the public perceptions, attitudes, and values pertaining to estuarine ecosystems. Information from Willapa Bay and Grays Harbor in Washington and Tillamook, Yaquina, and Coos Bays in Oregon shows that the coastal communities are growing more slowly than the states overall., that the populations are relatively old, and that, although the local economies continue to rely on them, the extractive natural resource industries (fishing, aquaculture, agriculture, forest products) are declining in importance relative to tourism, recreation, and retirement industries. These trends suggest that human uses of the estuaries are changing in character, and altering the management problems. Coastal residents choose to live in these communities to enjoy the views and scenery, to experience rural living, to be near the ocean, and to recreate outdoors. People express coherent perceptions of risks to the estuaries, especially the threats of declining fish habitats, oil spills, shoreline development, invasive species, and logging in upland areas> Residential land values are enhanced by the presence of wetlands and forests and are diminished by the presence of hazardous waste sites. We conclude that, if recent trends in population age structure, income sources, and employment status continue, public attitudes and values will move towards stronger environmental protection. Because ecosystem management involves local public participation and collaboration, estuarine managers will be faced with both increased demands and opportunities.     

Distribution and abundance of early life history stages of the blue crab,Callinectes sapidus,in tidal marsh creeks near Charleston,South Carolina

A 16-month study of estuarine habitats in poly-, meso-, and oligohaline salinity regimes near Charleston Harbor assessed the distribution and abundance of megalopae and early crab stages of the blue crab,Callinectes sapidus. Blue crab were sampled with a plankton net and a cylindrical drop sampler. Blue crab were most abundant in plankton collections at night, accounting for 68% of the megalopae and over 88% of the juveniles collected in day and night tows combined. At night, densities of megalopae were greatest in surface samples, whereas densities in daylight collections were greater on the bottom. Juvenile densities were greatest on the bottom in both day and night collections, although catch rates at night were more variable than those of the megalopae. This suggests that megalopae, and possibly juvenile stages, experience a diel vertical migration. Results indicate that ingress to estuarine nursery areas occurs at the megalopal stage. Megalopal densities were highest at the polyhaline site, while juvenile blue crab were most abundant in the oligohaline area. Habitat utilization by juvenile blue crab was estimated using a cylindrical drop sampler and Venturi suction pump on three bottom types in the intertidal zone. Densities were greatest over the sandy-mud substrate, although catch rates were much lower than those reported for other geographical areas. These results suggest that juvenile blue crab do not occur in abundance on the marsh surface but remain on the creek bottom, possibly because creek physiography and large tidal amplitudes may restrict accessibility to the marsh surface.     

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.     

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.     

Oysters, crabs, and burrowing shrimp: Review of an environmental conflict over aquatic resources and pesticide use in Washington State’s (USA) coastal estuaries

Washington State’s coastal estuaries are productive shallow water environments that support commercial fisheries for Dungeness crabs (Cancer magister) and English sole (Parophrys vetulus) by providing 0+(settlement to age l) populations with critical refuge and foraging habitats until subadults migrate to the nearshore coast. Intertidalmudflats also constitute prime areas for commercial oyster (Crassostrea gigas) culture, an, important industry for the coastal communities of Willapa Bay and Grays Harbor that supply much of the nation's oysters. Conflicts over natural resources and estuarine utilization have arisen over the last 37 yr due to the use of carbaryl (an organo carbamate pesticide) by oyster growers on their grounds to control populations of burrowing thalassinidean shrimp (Neotrypaea californiensis and Upogebia pugettensis). Burrowing shrimp, which have an indirect negative effect on oyster survival and growth through bioturbation and sediment destabilization, are killed by carbaryl, as are 0+ and subadult Dungeness crabs, 0+English sole, and other non-target species prsent on the tideflats at the time of application. The pesticide is delivered at 9 kg ha^?1 directly to the mudflat as a wetable powder during low tides in July and August. Commercial crabbers and other groups who have economic, recreational, and environmental interests in the estuaries have generally opposed use of the chemical that oyster growers maintain is essential to sustain production levels. For years, government natural resource agencies that regulate the use of carbaryl lacked critical information needed to effectively manage the program. An Environmental Impact Statement (EIS) and Supplemental EIS have provided much of that data and helped shape management decisions with regard to establishing carbaryl concentration rates and total allowable spray area. Additional research is needed to develop more economically and environmentally sound policies for shrimp control based on burrowing shrimp-oyster interactions on an estuarine-wide scale. In this paper we review issues pertaining to oyster culture, the use of carbaryl to control burrowing shrimp populations, and effects on non-target species, drawing upon research from, published articles as well as unpublished data collected by the authors. We also discuss what is known of burrowing shrimp life history and ecology and emphasize the importance of integrating information on shrimp, such as timing of recruitment, variability in year class strength, and patterns of habitat use, into carbaryl control policies or alternative strategies that may be developed in the future. We recommend controlled experimentation be done to examine the ecological effects of delaying carbaryl application to some ghost shrimp beds until October after peak recruitment of 0+ ghost shrimp has occurred, allowing the number of hectares treated each year to vary based on fluctuations in pest population densities, and modifying the substrate by applying a dense layer of oyster shell to the mudflat (shell pavement) to reduce recruitment of ghost shrimp.     

Composition,habitats, seasonal changes and productivity of macroalgae in Grays Harbor Estuary,Washington

Twenty-nine taxa of macroalgae were collected from the Grays Harbor Estuary, Washington, from 17 April 1980 to 4 June 1981. Outer (oceanic) sites contained higher numbers of species than sites located in the inner portion of the estuary. Macroalgae were found in several habitats including attached to boulders, logs, tree roots, other algae, and angiosperms, as mats in sand, and drift.Fucus distichus ssp.edentatus andEnteromorpha intestinalis occurred at the greatest number of sites and were found throughout the year. The standing stock of the perennialFucus remained relatively consant, while that of anE. intestinalis andBlidingia minima var.subsalsa complex showed a significant peak between late spring and early summer as well as a winter minimum. The occurrence of most other taxa was highly seasonal. Net productivity rates for the most abundant macroalgal taxa were moderate to high relative to rates published for algae in other North American estuaries. It is concluded that, although inconspicuous, macroalgae may represent an important contributor of organic carbon to the Grays Harbor estuarine system.     

Oceanography of the U.S. Pacific Northwest Coastal Ocean and estuaries with application to coastal ecology

Ocean processes are generally large scale on the U.S. Pacific Northwest coast; this is true of both seasonal variations and event-scale upwelling-downwelling fluctuations., which are highly energetic. Coastal upwelling supplies most of the macronutrients available for production, although the intensity of upwelling-favorable wind forcing increases southward while primary production and chlorophyll are higher in the north, off the Washington coast. This discrepancy could be related to several mesoscale features: the wider, more gently sloping shelf to the north, the existence of numerous submarine canyons to the north, the availability of Columbia River plume water and sediment north of the river mouth, and the existence of a semi-permanent eddy offshore of the Strait of Juan de Fuca. We suggest that these features have important effects on the magnitude and timing of macronutrient or micronutrient delivery to the plankton. These features are potentially important as well to transport pathways and residence times of planktonic larvae and to the development of harmful algal blooms. The coastal plain estuaries, with the exception of the Columbia River, are relatively small, with large tidal forcing and highly seasonal direct river inputs that are low to negligible during the growing season. Primary production in these estuaries is likely controlled not by river-driven stratification but by coastal upwelling and exchange with the ocean. Both baroclinic mechanisms (the gravitational circulation) and barotropic ones (lateral stirring by tide and, possibly, wind) contribute to this exchange. Because estuarine hydrography and ecology are so dominated by ocean signals, the coastal estuaries, like the coastal ocean, are largely synchronous on seasonal and event time scales, though, intrusions of the Columbia River plume can cause strong asymmetries between Washington and Oregon estuaries especially during spring downwelling conditions. Water property correlation increases between spring and summer as wind forcing becomes more spatially coherent along the coast. Estuarine habitat is structure not only, by large scale forcing but also by fine scale processes in the extensive intertidal zone, such as by solar heating or differential advection by tidal, curents.     

Import of coastally-derived chlorophylla to South Slough, Oregon

Material transfer between estuaries and the nearshore zone has long been of interest, but information on the processes affecting Pacific Northwest estuaries has lagged behind other areas. The west coast of the U.S. is a region of seasonally variable upwelling that results in enhanced phytoplankton production in the nearshore zone. We examined estuarine-nearshore links over time by measuring physical oceanographic variables and chlorophylla concentration from an anchor station in South Slough, Oregon. Data was collected during 24-h cruises conducted at approximately weekly intervals during summer 1996 and spring 1997. The results demonstrate that the physical oceanography of this estuarine site was strongly influenced by the coastal ocean. Marine water reached the estuarine site on every sampled tide, and chlorophylla was clearly advected into the estuary with this ocean water. In contrast, phytoplankton concentrations were comparatively reduced in the estuarine water. There were, however, large fluctuations in the import of chlorophyll over the course of the summer. These variations likely reflect upwelling-generated phytoplankton production in the coastal ocean and subsequent cross-shelf transport to the estuary. Suspension feeding organisms in South Slough likely depend on the advection of this coastally-derived phytoplankton. The large allochthonous chlorophyll input measured for this system appears dissimilar from most estuaries studied to date. Previous investigations have focused on the outwelling and inwelling of materials in estuaries. We must now consider the influence of coastal upwelling and downwelling processes on estuarine material exchange.     

Ingress of Brachyuran Crab Post-larvae to the Newport River Estuary

Planktonic larvae of estuarine species often develop in the coastal ocean and return to estuaries using favorable currents. This study investigated spatial distributions of brachyuran crab post-larvae during ingress to the Newport River estuary, North Carolina, USA (34°41′ N, 76°40′ W). Nearshore plankton tows were conducted across the inlet to the estuary. Settlement on passive ‘hog’s hair’ collectors was simultaneously monitored in each of four estuarine channels. Callinectes sapidus density was highest east of the inlet, whereas relative estuarine abundance was higher in western channels. In separate sampling with collectors at coastal and estuarine locations, spatial distributions of post-larvae were consistent through time but differed for C. sapidus, Uca spp., and Pachygrapsus transversus. The diel timing of C. sapidus settlement on collectors was determined at the coast and compared to previous studies of settlement in the estuary. Behavioral responses to environmental cues may alter transport pathways from those predicted by hydrodynamic models.     

Phytoplankton ecology of North Carolina estuaries

Numerous phytoplankton-oriented ecological studies have been conducted since 1965 in the extensive North Carolina estuarine system. Throughout a range of geomorphological estuarine types, a basic underlying pattern of phytoplankton productivity and abundance following water temperature seasonal fluctuations was observed. Overlying this solar-driven pattern was a secondary forcing mechanism consisting of a complex interaction between meteorology and hydrology, resulting in periodic winter or early spring algal blooms and productivity pulses in the lower riverine estuaries. Wet winters caused abundant nitrate to reach the lower estuaries and stimulate the blooms, whereas dry winters resulted in low winter phytoplankton abundance and primary production. Dinoflagellates (Heterocapsa triquetra, Prorocentrum minimum, Gymnodinium spp.) and various cryptomonads dominated these cool-weather estuarine blooms. Sounds were less productive than the riverine estuaries, and were dominated by diatoms such asSkeletonema costatum, Thalassiosira spp.,Melosira spp., andNitzschia spp., as were the most saline portions of riverine estuaries. Nutrient-limitation studies found that nitrogen was the principal limiting nutrient in these estuarine systems over a range of trophic states, with phosphorus occasionally co-limiting. Freshwater and oligohaline portions of large coastal plain rivers were often subject to summer blue-green algal blooms. Formation of these blooms on a year-to-year basis was also determined by meteorology and hydrology: wet winters or springs and consequent nutrient loading, coupled with low summer flow conditions and regeneration of nutrients from the sediments. Dry winters or springs resulted in less available nutrients for subsequent summer regeneration, and high flow conditions in summer flushed out the blooms. In recent years, there has been a dramatic increase in reported fish kills attributed to toxic dinoflagellate blooms, particularly in nutrient-enriched estuarine areas. This issue has become a major coastal ecological and economic concern.     

Green Crab Larval Retention in Willapa Bay,Washington: An Intensive Lagrangian Modeling Approach

The European green crab (Carcinus maenas) is invasive on the U.S. West Coast. This study uses a high-resolution circulation model to determine the likelihood that green crab larvae spawned in Willapa Bay, Washington could be retained by circulation and behavior long enough to reach maturity and resettle within the bay. A particle-tracking method (the “diffusive Lagrangian return map”) is presented that makes it possible to track the dispersion of hundreds of thousands of model larvae—each subject to three-dimensional advection, vertical turbulent diffusion, and imposed vertical migration behavior—over their full 30–50 days development time with modest computational resources. Larvae spawned in summer show significant retention (5–40%) in the southern and western portions of the bay, including the Stackpole shoals near the mouth, the area most likely to be colonized by late-stage megalopae arriving from the coastal ocean. Larvae spawned in spring show much less retention throughout the bay because of (1) increased flushing caused by increased river input relative to summer conditions and (2) longer development times caused by lower water temperatures. The role of larval swimming behavior is secondary to hydrodynamics in setting these spatial and seasonal patterns of retention.     

Ecophysiological aspects of the coastal-estuarine distribution of acrochordid snakes

The Acrochordidae consists of three congeneric species of aquatic snakes distributed among fresh water and coastal marine environments in tropical southern Asia. The smallest species,Acrochordus granulatus, is euryhaline and the only acrochordid that permanently inhabits coastal seas and estuaries. The diving and metabolic physiology of this species is highly specialized and reflects the demands of estuarine environments. A capability for prolonged aerobic diving is attributable to low rates of oxygen consumption, high capacity for oxygen storage, nearly complete utilization of the oxygen stores, and cutaneous gas exchange. Recent studies indicate thatA. granulatus is primarily ammonotelic and requires a source of fresh water for elimination of nitrogenous wastes. The requirement for fresh water potentially limits seaward migration of populations due to the dependence of snakes on rivers or coastal rainfall. Adaptations for shallow-water diving conceivably further limit seaward migration, with the result that they have evolved as estuarine specialists that are restricted from deeper waters and the open ocean.     

Chesapeake Bay Plume Morphology and the Effects on Nutrient Dynamics and Primary Productivity in the Coastal Zone

To determine the effects of the Chesapeake Bay outflow plume on the coastal ocean, nutrient concentrations and climatology were evaluated in conjunction with nitrogen (N) and carbon (C) uptake rates during a 3-year field study. Sixteen cruises included all seasons and captured high- and low-flow freshwater input scenarios. Event-scale disturbances in freshwater flow and wind speed and direction strongly influenced the location and type of plume present and thus the biological uptake of N and C. As expected, volumetric primary productivity rates did not always correlate with chlorophyll a concentrations, suggesting that high freshwater flow does not translate into high productivity in the coastal zone; rather, high productivity was observed during periods where recycling processes may have dominated. Results suggest that timing of meteorological events, with respect to upwelling or downwelling favorable conditions, plays a crucial role in determining the impact of the estuarine plume on the coastal ocean.     

The distribution of hydroid sibling species on hermit crabs in estuaries in the Gulf of Maine

Estuaries in the Gulf of Maine contain disjunct, isolated populations of a number of invertebrate taxa typically distributed only sound of Cape Cod. These estuarine populations may either be remnants of a southern fauna that were stranded by Quaternary changes in water temperature, or they may have been established more recently via larvae that entered the estuaries from the open ocean. We tested these hypotheses by examining the distribution of sibling species of hydroids that are symbiotic on paguriid hermit crabs. These crab-hydroid species pairs differ greatly in their ability to colonize new areas through the water column. The hermit crabs possess a planktonic larva that can disperse great distances, while the hydroids have a crawling planula larva that is extremely limited in its dispersal capabilities. Consequently, estuarine hermit crab populations that lack their native hydroid symbiont are likely to have originated by larval colonization. Hydroid sibling species were identified on the basis of MDH electromorphs. Species identifications were confirmed through a limited number of test matings with colonies of known species identity. In three out of the four estuaries that we examined, shells inhabited by the southern hermit crab,Pagurus longicarpus, were occupied only by the local northern hydroid,Hydractinia polyclina. This pattern is consistent with a more recent establishment of the hermit crab populations through larval dispersal or transport. However, in Casco Bay, shells inhabited byP. longicarpus were occupied by a mixture of the northern hydroid,H. polyclina, and the southern hydroid,H. symbiolongicarpus, that is associated withP. longicarpus throughout the southern part of its range. Thus, theP. longicarpus population in Casco Bay may either be a relict of a former, more broadly distributed population of this crab in the Gulf of Maine, or if recently established, is likely to have originated by the introduction of adult crabs with hydroid-covered shells.