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1.
Variable recruitments of striped bass were hypothesized to be caused by factors influencing growth and survival of larvae. Eggs and larvae were collected in the Potomac River from 1987 to 1989 and in the Upper Chesapeake Bay in 1988 and 1989 to estimate abundances, larval growth and survival rates, and environmental variability. Larval batch dates, ages, and growth and mortality rates were estimated from analysis of otolith daily increments. A retrospective analysis of Potomae River ichthyoplankton data from 1974–1977 and 1980–1982 provided additional estimates of larval abundances and vital rates for comparative purposes. Significant correlations betweens vital rates (growth and mortality) and abundances of striped bass larvae, and the Maryland juvenile recruitment index indicated that recruitment level may be fixed during the larval stage. The ratio of mean daily growth and mortality rates (G:Z) of larvae in the Potomac River for 1987–1989 was highest in 1987 when the juvenile index was relatively high, and was lower in 1988 and 1989 when juvenile indices were low. In the Upper Bay, mean larval growth rate, survival rate, and the G:Z ratio were highest in 1989 when the juvenile index also was high. In both tributaries, abundances of late-stage larvae (8 mm SL) were correlated with juvenile-stage recruitment indices. The retrospective analysis provided additional evidence that Potomac River larval abundances and G:Z ratios were positively correlated with juvenile recruitment indices in the 1974–1977 and 1980–1982 periods. Conditions favoring striped bass larval abundance and potential recruitment differed between the Potomac River and the Upper Bay. In the Potomac, late-stage larval abundances coincided with late-season water temperatures that were relatively warm, low river discharges and high, late-season densities of zooplankton prey, which favored larval growth. In the Upper Bay, the high abundance of late-stage larvae in 1989 relative to 1988 was attributed to a higher egg production that was coincident with high zooplankton abundances.  相似文献   

2.
We tested the hypothesis that the distribution and retention of larval smelt (Osmerus mordax) in the middle estuary of the St. Lawrence River is related to the maintenance of other planktonic organisms in the maximum turbidity zone (MTZ). We documented the horizontal and vertical distribution of larval smelt, macrozooplankton, and suspended particulate matter over four tidal cycles at each of three stations located along the major axis of the turbid upstream portion of the middle estuary. During summer, the turbid, warm, and low salinity waters of the two upstream stations were characterized byNeomysis americana, Gammarus sp. (principallyG. tigrinus), larval smelt,Mysis stenolepsis, andCrangon septemspinosus. The more stratified and less turbid waters of the downstream station were characterized by a coastal marine macrozooplanktonic community and the almost total absence of smelt larvae. Within the MTZ, the distribution ofN. americana coincided with the zone of longest average advective replacement times (null zone). Smelt larvae were distributed further upstream within the MTZ thanN. americana. Overall, larger larvae were distributed further upstream than smaller larvae. The relationship between turbidity and larval density at a specific time was weak (due to resuspension of sediments but not larvae), but the mechanism responsible for producing higher residence times for both sediment and larvae on a longer term basis appears the same. The daily movement and skewed nature of the null zone (due to the general cyclonic circulation of the middle estuary) defines a geographic zone over which the larval smelt population oscillates and remains despite the mean downstream velocities over the water column.  相似文献   

3.
Crab larval dispersal and, thus, adult population size can be influenced by oceanographic conditions, especially in highly dynamic and variable environments such as high-latitude estuaries. This study's primary goal was to understand larval timing, abundance, and distribution in relation to oceanographic effects between the more estuarine inner and more oceanic outer part of the subarctic estuary of Kachemak Bay (south-central Alaska, USA). Temperature and salinity measurements and plankton tows were taken along the boundary between the two bay parts from 31 March to 28 October 2008 on spring and neap tides. Summer water flow and stratification in Kachemak Bay were chiefly buoyancy driven, and predominant flow patterns were not affected by the large tidal range in the region. Larvae of seven brachyuran species were found over the sampling period, with seasonally different peak abundances. Larval spatial distribution patterns, presence of most larval stages for each species, and their seasonal timing and persistence within the water column suggest that most species are locally transported within or close to Kachemak Bay. The larval assemblage was correlated with seasonal changes in water temperature, and peak abundances of some species coincided with spring tides and/or frontal systems between the in- and outflow regions of the bay. The strong influence of freshwater on the local circulation pattern in the summer indicates that larval transport will likely be strongly affected by future changes in glacial melt and precipitation.  相似文献   

4.
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  相似文献   

5.
Estuarine species with wide geographic distributions often experience tidal regimes that vary significantly throughout their range. Plasticity in behaviors associated with the tide is expected to enable synchronization with local tides. The American horseshoe crabLimulus polyphemus typically inhabits estuaries and coastal areas with pronounced semi-diurnal tides that play a role in synchronizing the timing of spawning and larval hatching, but also lives in areas that lack significant tides and associated synchronization cues. We investigated the spatial and temporal pattern of adult spawning and larval hatching ofL. polyphemus in a microtidal coastal lagoon (Indian River Lagoon, Florida, USA). Spawning activity and larval abundance were monitored weekly February 1998–August 2000 at sites spanning 100 km of the lagoon. To identify possible synchronization cues for spawning and hatching success, the presence of adult and larvalL. polyphemus were related to environmental and hydrologic variables using logistic regression. The presence of spawning adults varied significantly among the sub-basins of the lagoon, with the highest densities occurring in the Banana River. Large spawning aggregations were not observed and densities never exceeded 6 m−2. Spawning occurred year-round but varied seasonally with episodes of increased mating activity in the early spring. The occurrence of mating pairs was episodic and was not synchronized among sites. Larval densities were low (4 m−3) and larvae were present at only 12 of the 21 sites. Hatching success was decoupled temporally from spawning activity, with peaks in larval abundance occurring approximately 8 wk after peaks in spawning. Larval abundance was associated with periods of high water. Reproductive activity of horseshoe crabs in the lagoon differs significantly from populations inhabiting areas with semi-diurnal and diurnal tides. These differences are likely due to the lack of periodic tidally-related synchronization cues and regular beach inundation.  相似文献   

6.
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.  相似文献   

7.
The relationships between egg production (spawning behavior), larval growth and survival, and environmental conditions that larvae encounter were investigated in the Patuxent River tributary of Chesapeake Bay in 1991. Striped, bass (Morone saxatilis) eggs and larvae occurred predominantly above the salt front where conductivity was ≤800 μmhos cm?1. There were three prominent peaks in egg production, each coinciding with increasing temperatures. Estimated growth rates of 6-d, otolith-aged cohorts, which ranged from 0.15 mm d?1 to 0.22 mm d?1 (mean=0.17 mm d?1), were not demonstrated to differ significantly from each other. Observed zooplankton densities and temperature did not significantly affect growth rates. Stage-specific cumulative mortalities of combined cohorts were calculated for eggs (Zstage=0.20=18.1%), yolk-sac larvae (Zstage=5.80=99.7%), and first-feeding larvae (Zstage=2.95=94.8%). The very high mortality of yolk-sac larvae suggests that dynamic during this stage may have had a major impact on subsquent recruitment. Cohort-specific mortality rates of larvae were variable, ranging from Z=0.045 d?1 to 0.719 d?1, and were strongly temperature-dependent. Cohorts that experiented average temperature <15°C or >20°C during the first 25 d after hatching had significantly higher mortality rates than those which experienced intermediate temperatures. Estimated hatch-date frequencies of larvae ≥8 mm SL indicated goo, very good, and very low potential recruitments for cohorst spawned during early-season (April 2–11), mid-season (April 12–24) and late-season (April 25–May 5), respectively. Because seasonal temperature trends and fluctuations are unpredictable, striped bass females cannot select a spawning time that guarantees their offspring will be exposed to optimum temperatures. Consequently, selection may have occured for spawning over a broad range of temperatures and dates, a behavior insuring that some larval cohorts will encounter favorable temperatures.  相似文献   

8.
The seasonal abundance and spatial distribution of eggs and early larvae of the bay anchovy,Anchoa mitchilli, and the weakfish,Cynoscion regalis, were determined from plankton collections taken during 1971–1976 in the lower Chesapeake Bay. Eggs and larvae of the bay anchovy,Anchoa mitchilli, dominated the ichthyoplankton, making up 96% of the total eggs and 88% of all larvae taken. A comparison of egg and larval densities from the lower Chesapeake Bay to existing data from other East Coast estuaries suggested that Chesapeake Bay is a major center of spawning activity for this species.Anchoa mitchilli spawning commenced in May when mean water column temperatures approached 17°C and abruptly ceased after August. Eggs and early larvae presented a continuous distribution throughout the study area during these months. Eggs and larvae of several sciaenid species, especiallyC. regalis, ranked second in numerical abundance. Larval weakfish were consistently taken in late summer of each sampling year but peak abundance and distribution was observed in August 1971. Sciaenid eggs exhibited a distinct polyhaline distribution with greatest concentrations observed at the Chesapeake Bay entrance or along the Bay eastern margin. Analysis of sciaenid egg morphometry and larval occurrence suggested spawning activity of at least four species. Additional important species represented by eggs and/or larvae in the lower Chesapeake Bay wereHypsoblennius hentzi, Gobiosoma ginsburgi, Trinectes maculatus, Symphurus plagiusa andParalichthys dentatus with the remaining species occurring infrequently.  相似文献   

9.
Synoptic ichthyoplankton sampling was conducted on two transects, one on either side of Beaufort Inlet, North Carolina, during the winter immigration season of seven ocean-spawned, estuarine-dependent fishes;Brevoortia tyrannus (Atlantic menhaden),Leiostomus xanthurus (spot),Micropogonias undulatus (Atlantic croaker),Lagodon rhomboides (pinfish),Paralichthys albigutta (Gulf flounder),P. dentatus (summer flounder), andP. lethostigma (southern flounder). Densities and lengths of larvae were significantly different among sampling dates, with distance offshore, and between sides of the inlet. Flood-tide stage had minimal effect on larval densities and lengths except forP. albigutta andP. lethostigma. Changes in larval densities with distance offshore were not coherent among species; densities ofB. tyrammus increased offshore whereas densities of the other species decreased offshore. Average larval densities on a sampling date were coherent among species. Patterns in larval lengths were also coherent among the four non-flounder species. Larval densities outside of Beaufort Inlet were correlated with larval densities inside of Beaufort Inlet. Larval densities outside of Beaufort Inlet were also correlated with the north component of the wind, nearshore water temperature, and distance to the mid-shelf front. Differences in larval density across the inlet were significantly correlated with the east component of the wind. The patterns in larval densities outside of Beaufort Inlet were complex and apparently influenced by both the physical processes that supply larvae to the nearshore region and nearshore physical dynamics.  相似文献   

10.
The temporal and spatial distributions of salinity, dissolved oxygen, suspended particulate material (SPM), and dissolved nutrients were determined during 1983 in the Choptank River, an estuarine tributary of Chesapeake Bay. During winter and spring freshets, the middle estuary was strongly stratified with changes in salinity of up to 5‰ occurring over 1 m depth intervals. Periodically, the lower estuary was stratified due to the intrusion of higher salinity water from the main channel of Chesapeake Bay. During summer this intrusion caused minimum oxygen and maximum NH4 + concentrations at the mouth of the Choptank River estuary. Highest concentrations of SPM, particulate carbon (PC), particulate nitrogen (PN), total nitrogen (TN), total phosphorous (TP) and dissolved inorganic nitrogen (DIN) occurred in the upper estuary during the early spring freshet. In contrast, minimum soluble reactive phosphate (SRP) concentrations were highest in the upper estuary in summer when freshwater discharge was low. In spring, PC:PN ratios were >13, indicating a strong influence by allochthonous plant detritus on PC and PN concentrations. However, high concentrations of PC and PN in fall coincided with maximum chlorophyll a concentrations and PC:PN ratios were <8, indicating in situ productivity controlled PC and PN levels. During late spring and summer, DIN concentrations decreased from >100 to <10 μg-at l?1, resulting mainly from the nonconservative behavior of NO3 ?, which dominated the DIN pool. Atomic ratios of both the inorganic and total forms of N and P exceeded 100 in spring, but by summer, ratios decreased to <5 and <15, respectively. The seasonal and spatial changes in both absolute concentrations and ratios of N and P reflect the strong influence of allochthonous inputs on nutrient distributions in spring, followed by the effects of internal processes in summer and fall.  相似文献   

11.
Atlantic herring (Clupea harengus) larvae have been collected for resource monitoring purposes in the Sheepscot River in mid-coastal Maine during October–February, for the past 20 years. During this period, the larval population in the river has typically peaked in October-early November and has been composed of larvae derived from August–September spawning in eastern Maine and New Brunswick waters and from September-early October spawning along the central Maine coast. Larvae from eastern coastal spawning areas are transported to the river by the prevailing westerly coastal current. The appearance of small (≤15 mm SL) larvae in the river during December and January 1985–1989 suggested an additional time and area of origin. Aging procedures based on enumeration of daily otolith increments showed the majority of these small larvae were spawned from mid October to mid November when spawning usually occurs in western Maine coastal waters and in the vicinity of Jeffreys Ledge. Comparison of back-calculated hatching dates for small larvae collected in the river with wind direction and velocity data from mid October through November suggested that larvae were transported eastward against a weakened Gulf of Maine coastal current to the Sheepscot River by complex wind-driven surface currents that occur off the western Maine coast in the fall. *** DIRECT SUPPORT *** A01BY059 00003  相似文献   

12.
Three polyhaline subtidal marsh creeks in southern New Jersey were sampled with weirs and seines to determine seasonal patterns of utilization by fishes and macroinvertebrates. Sixty-four species of fish, 13 invertebrates, and the diamondback terrapin were collected in 69 weir and 57 seine samples from April to November 1988 and April to October 1989. Average abundance, biomass, and faunal composition were strongly seasonal with greatest abundances during spring and summer, and peaks in May and August. Sixteen species were represented by all life-history stages, including the five most important species by combined ranks of percent frequency, mean abundance, and mean biomass. These five species were important during spring, summer, and fall and included the fishes Menidia menidia and Fundulus heteroclitus, the shrimps Palaemonetes vulgaris and Crangon septemspinosa, and the crab Callinectes sapidus. In addition, there were distinct seasonal assemblages of other species which utilized the creeks primarily as young-of-the-year. Importnat species in spring collections included the fishes Clupea harengus, Alosa aestivalis, Alosa pseudoharengus, Pollachius virens, and Urophysics regia, while Leiostomus xanthurus, Pomatomus saltatrix, Paralichthys dentatus, Mugil curema, and Strongylura marina were important in the summer. Fall samples were best characterized by declining abundances of summer species. Thus, subtidal marsh creeks in southern New Jersey appear to be valuable nurseries for a variety of species which spawn over the continental shelf, as well as one of the most important habitats for estuarine residents.  相似文献   

13.
During the 1992 spawning season of river herring, three sites in a tributary of the Rappahannock River, Virginia, were studied to characterize spawning and nursery habitats of alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) and to identify differences in habitat use along an upstream to downtream gradient. The sites were sampled (using drift and dip nets and a plankton sampler) and habitat variables were measured on a 5-d, four-time interval rotation: at the end of 5 d, each site had been sampled once at dawn, noon, dusk, and midnight. Considerable non-overlap in spawning seasonality was apparent between species. For both species, densities of river herring adults, eggs, and yolk-sac larvae were highest at the upstream site, indicating 1) that the upstream site is more important for spawning than downstream areas, and 2) these species do not use different spawning areas in this stream. Densities of post-yolk-sac larvae did not differ significantly among sites, indicating post-spawning dispersal to downstream areas. The upstream site was smaller in area, more acidic, had faster water flow, clearer water, more vegetation, and siltier substrate than the downstream sites. At times, pH levels in the upstream site were within the lethal range reported for blueback herring larvae. Possible reasons for selection of the upstream habitat include: 1) adults may migrate as far upstream as possible to avoid predation or potential competition with other species of fish for spawning habitat; or 2) adults may historically enjoy greater spawning success in the upstream habitat due to physicochemical features of this area. More study is needed to determine the reasons for river herring use of upstream habitats in Virginia streams.  相似文献   

14.
Exchanges of fish larvae between the inner continental shelf and estuaries can be critical to the functional significance of these habitats as nurseries. We sampled near-surface fishes on the inner continental shelf off New Jersey and in an adjacent estuary during the summer and fall of 2005 and 2006 to evaluate the occurrence and variation in these connections. Very few of the abundant taxa (Anchoa mitchilli, Brevoortia tyrannus, Urophycis regia, Etropus microstomus, Peprilus triacanthus, and Pomatomus saltatrix) were exclusive to either habitat but some did change in relative habitat affinity among seasons. For some species, this was indicative of a departure from the ocean for estuaries (e.g., Micropogonias undulatus) while others used both habitats during the summer and fall (e.g., Syngnathus fuscus, Scophthalmus aquosus, and A. mitchilli). Together, these observations confirm the high degree of connectivity between the near-surface larval fishes from the inner continental shelf and estuaries.  相似文献   

15.
Larval fish use of surf zone and nearshore habitats at northern latitudes has received little attention. Consequently, potential impacts of beach nourishment and other forms of disturbance are not well understood. This study, on a northwestern Atlantic coastline spanning May through July over 4 years, demonstrates that recently hatched larvae are common in both surf zone and nearshore habitats. Taxonomic compositions of surf zone and nearshore assemblages were similar to each other and those from an adjacent estuary. An influence of upwelling events was apparent in coincident changes in abundance and/or size of several species in the surf zone. Other changes over the late spring–summer transition, including buoyancy-driven flows from the Hudson River plume, demonstrate the dynamic nature of larval fish assemblages in the New York Bight area.  相似文献   

16.
Niche models applied in the context of future climate change predict that as regional temperatures increase, the distribution of tropical species will shift poleward. While range expansions have been documented for a number of species, there is limited information on the ecological impacts of shifts on native species. Recently, abundances of tropically-associated gray snapper (Lutjanus griseus) and lane snapper (Lutjanus synagris) have increased in seagrass nurseries in the northern Gulf of Mexico (GOM), concurrent with regional increases in sea surface temperature. We investigated effects of increased abundances of these species on abundance and growth of pinfish (Lagodon rhomboides), the dominant native species. Because juvenile pinfish and snappers share common prey, predators, and habitat, the high degree of niche overlap suggests an equally high potential for competition. We used a multiple before–after control impact design to determine whether increased snapper abundances significantly affected abundance or growth of pinfish. Trawl surveys at six locations in the northern GOM in summer and fall 2010 were used to calculate pinfish and snapper abundances. We identified three locations with high snapper abundances and three locations with no snapper and compared pinfish abundance and otolith-determined growth rates in these locations before and after snapper recruitment. Paired t tests and two-way analysis of variance revealed no significant differences in pinfish abundance or growth in the presence of snappers compared to locations and seasons without snappers. We conclude that range expansions of tropically associated snappers have had no significant effect on abundance or growth of native pinfish in northern GOM seagrass habitats.  相似文献   

17.
Pacific herring early life stages provide good model systems for studying effects of suspended sediments on estuarine organisms. To investigate effects on the herring larval stage, we used environmentally relevant particle concentrations for San Francisco Bay (200?C400?mg/L of particles <50???m in size) and exposure times of 16?h in a novel two-pump sediment suspension mesocosm. There were no mortalities during the 16-h suspended sediment incubation. Following sediment exposure, larvae were cultured in sediment-free water for up to 10?days during which survival and condition were measured. None were affected by previous sediment treatment. Four criteria for larval condition included growth, heart rate, prey capture, and critical swimming velocity. These results provide a framework for implementing regulatory decisions on anthropogenic activities such as dredging.  相似文献   

18.
Fish abundance and environmental data collected over ten years (1980–1989) from the middle Thames estuary, England, were analyzed to detect temporal trends in fish populations and relationship with environmental parameters, and to assess water quality. Fish were collected from the cooling water intake screens of West Thurrock power station, situated 35.5 km below London Bridge, in the mid-estuary. Marine species abundance were highly seasonal, with peaks in December–March for herring (Clupea harengus), sprat (Sprattus sprattus), 3-spined-stickleback (Gasterosteus aculeatus), and poor cod (Trisopterus minutus); July–August for flounder (Platichthys flesus); and September–December for sand goby (Pomatoschistus minutus), whiting (Merlangius merlangus), bass (Dicentrarchus labrax), plaice (Pleuronectes platessa), and dab (Limanda limanda). Bimodal seasonal patterns of peaks or unclear seasonality in abundance characterized marine estuarine-dependent sole (Solea solea), Nilsson's pipefish (Syngnathus rostelattus) (April/May and September/October), and pouting (Trisopterus luscus) (May and November/December); the estuarine smelt (Osmerus eperlanus) (October and January) and the catadromous eel (Anguilla anguilla) (June and October). There was substantial variation in the abundance of common species over the period of ten years, with herring, sand goby, flounder, and plaice showing a stable abundance in 1980–1984, increasing sharply in 1985–1986, and then decreasing successively through the remainder of the decade (1987–1989). The first half of the decade was a period of higher abundance for less tolerant species such as smelt, sprat, and poor cod, while the second half showed higher abundances of species tolerant to harsh environmental conditions such as sand goby, flounder, eel, and plaice. A general pattern of stable fish populations with a slight trend of deterioration was found to emerge over the years, related to the number of species and quantities of common species. Multivariate techniques of principal component and canonical correspondence ordinations were used for assessing relationships between fish populations abundance and environmental variables. The most significant environmental variables correlated with fish species were temperature and dissolved oxygen. High abundances of flounder were associated with high temperature, while high abundance of poor cod, sprat, herring, and 3-spined-stickleback were associated with high dissolved oxygen, flow, ammonical nitrogen, and low temperature. Plaice, whiting, sand goby, bass, and dab were preferentially found in high salinity and suspended solids, while smelt and sole were likely to prefer average values or showed no clear preferences.  相似文献   

19.
Results of laboratory feeding experiments suggest that oyster (Crassostrea virginica) larvae select small phytoplanktonic organisms (<10 μm) over larger-celled forms from natural estuarine assemblages, but that little selection occurs within the small phytoplankton fraction. Laboratory-reared larvae grazed each of five small-celled phytoplankton groups enumerated (coccoids, centrate diatoms, pennate diatoms, dinoflagellates, and flagellates) at rates proportional to phytoplankton group densities in controls (no larvae added). Larval grazing rates (number of cells removed per larva per hour) were inversely proportional to both larval density and experimental duration.  相似文献   

20.
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.  相似文献   

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