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1.
Estuarine rearing has been shown to enhance within watershed biocomplexity and support growth and survival for juvenile salmon (Oncorhynchus sp.). However, less is known about how growth varies across different types of wetland habitats and what explains this variability in growth. We focused on the estuarine habitat use of Columbia River Chinook salmon (Oncorhynchus tshawytscha), which are listed under the Endangered Species Act. We employed a generalized linear model (GLM) to test three hypotheses: (1) juvenile Chinook growth was best explained by temporal factors, (2) habitat, or (3) demographic characteristics, such as stock of origin. This study examined estuarine growth rate, incorporating otolith microstructure, individual assignment to stock of origin, GIS habitat mapping, and diet composition along ~130 km of the upper Columbia River estuary. Juvenile Chinook grew on average 0.23 mm/day in the freshwater tidal estuary. When compared to other studies in the basin our growth estimates from the freshwater tidal estuary were similar to estimates in the brackish estuary, but ~4 times slower than those in the plume and upstream reservoirs. However, previous survival studies elucidated a possible tradeoff between growth and survival in the Columbia River basin. Our GLM analysis found that variation in growth was best explained by habitat and an interaction between fork length and month of capture. Juvenile Chinook salmon captured in backwater channel habitats and later in the summer (mid-summer and late summer/fall subyearlings) grew faster than salmon from other habitats and time periods. These findings present a unique example of the complexity of understanding the influences of the many processes that generate variation in growth rate for juvenile anadromous fish inhabiting estuaries. 相似文献
2.
David L. Taylor Jason McNamee John Lake Carissa L. Gervasi Danial G. Palance 《Estuaries and Coasts》2016,39(5):1505-1525
This study evaluated the relative importance of the Narragansett Bay estuary (RI and MA, USA), and associated tidal rivers and coastal lagoons, as nurseries for juvenile winter flounder, Pseudopleuronectes americanus, and summer flounder, Paralichthys dentatus. Winter flounder (WF) and summer flounder (SF) abundance and growth were measured from May to October (2009–2013) and served as indicators for the use and quality of shallow-water habitats (water depth <1.5–3.0 m). These bioindicators were then analyzed with respect to physiochemical conditions to determine the mechanisms underlying intraspecific habitat selection. WF and SF abundances were greatest in late May and June (maximum monthly mean?=?4.9 and 0.55 flounder/m2 for WF and SF, respectively) and were significantly higher in the tidal rivers relative to the bay and lagoons. Habitat-related patterns in WF and SF abundance were primarily governed by their preferences for oligohaline (0.1–5 ppt) and mesohaline (6–18 ppt) waters, but also their respective avoidance of hypoxic conditions (<4 mg DO/L) and warm water temperatures (>25 °C). Flounder habitat usage was also positively related to sediment organic content, which may be due to these substrates having sufficiently high prey densities. WF growth rates (mean?=?0.25?±?0.14 mm/day) were negatively correlated with the abundance of conspecifics, whereas SF growth (mean?=?1.39?±?0.46 mm/day) was positively related to temperature and salinity. Also, contrary to expectations, flounder occupied habitats that offered no ostensible advantage in intraspecific growth rates. WF and SF exposed to low salinities in certain rivers likely experienced increased osmoregulatory costs, thereby reducing energy for somatic growth. Low-salinity habitats, however, may benefit flounder by providing refugia from predation or reduced competition with other estuarine fishes and macroinvertebrates. Examining WF and SF abundance and growth across each species’ broader geographic distribution revealed that southern New England habitats may constitute functionally significant nurseries. These results also indicated that juvenile SF have a geographic range extending further north than previously recognized. 相似文献
3.
The blue crab, Callinectes sapidus, is an ecologically and economically valuable species in Chesapeake Bay. Field surveys and laboratory experiments indicate that blue crab mortality is significant during severe winters. We applied a temperature and salinity-dependent survival model to empirical temperature and salinity data to explore spatial and interannual patterns in overwintering mortality. Harmonic regression analysis and geostatistical techniques were used to create spatially explicit maps of estimated winter duration, average temperature, average salinity, and resulting crab survival probability for the winters of 1990–2004. Predicted survival was highest in the warmer, saline waters of the lower Bay and decreased with increasing latitude up bay. There was also significant interannual variation with survival being lowest after the severe winters of 1996 and 2003. We combine the survival probability maps with maps of blue crab abundance to show how winter mortality may reduce blue crab abundance prior to the start of the harvesting season. 相似文献
4.
Alteration of estuarine shorelines associated with increased urbanization can significantly impact biota and food webs. This study determined the impact of shoreline alteration on growth and movement of the estuarine fish Fundulus heteroclitus in a tributary of the Delaware Coastal Bays. Fundulus heteroclitus is abundant along the east coast of the USA, and is an important trophic link between marsh and subtidal estuary. The restricted home range of F. heteroclitus allowed discrete sampling, and fish growth comparisons, along 35–65-m long stretches of fringing Spartina alterniflora and Phragmites australis marsh, riprap, and bulkhead. Fundulus heteroclitus were tagged with decimal Coded Wire Tags. Of 725 tagged F. heteroclitus, 89 were recaptured 30–63 days later. Mean growth rate (0.06–0.15 mm day?1 across all shoreline types) was greatest at riprap, lowest at Spartina and Phragmites, and intermediate at bulkhead, where growth was not significantly different from any other shoreline. This suggests that discernible environments exist along different shoreline types, even at the scale of tens of meters. No difference in movement distance was detected at different shoreline types; most individuals displayed a high degree of site fidelity. Forty-seven percent were recaptured within 5 m of their tagging location, although alongshore movements up to 475 m were recorded. Estimates of relative F. heteroclitus productivity, using relative density data from a concurrent study, were highest along Spartina and Phragmites, intermediate at riprap, and lowest at bulkhead. Therefore, despite greater growth rates along riprap than at vegetated shores, armoring reduces abundance sufficiently to negatively impact localized productivity of F. heteroclitus. 相似文献
5.
C. Michael Wagner 《Estuaries and Coasts》1999,22(2):304-312
Species richness declines to a minimum (artenminimum) in the oligohaline reach of estuaries and other large bodies of brackish water. To date, observations of this feature in temperate estuaries have been largely restricted to benthic macroinvertebrates. Five years of seine data collected during the summers of 1990–1995 in the major tidal tributaries to the lower Chesapeake Bay were examined to see if this feature arose in estuarine fish assemblages. Estimates of numerical species richness (alpha diversity) and rates of species turnover between sites (beta diversity) were generated via rarefaction and detrended correspondence analysis. Two spatial attributes of the distribution of littoral fish species along salinity gradients in the tributaries of the lower Chesapeake Bay were revealed: (1) a species richness depression in salinities of 8–10% and (2) a peak in the rate of species turnover associated with the tidal freshwater interface (salinities of 0–2%). Expression of the minimum is influenced by the physical length of the salinity gradient and the interaction between a species’ salinity preferences and tendency to make long excursions from favorable habitats. 相似文献
6.
Barbara A. Muhling Carlos F. Gaitán Charles A. Stock Vincent S. Saba Desiree Tommasi Keith W. Dixon 《Estuaries and Coasts》2018,41(2):349-372
Estuaries are productive and ecologically important ecosystems, incorporating environmental drivers from watersheds, rivers, and the coastal ocean. Climate change has potential to modify the physical properties of estuaries, with impacts on resident organisms. However, projections from general circulation models (GCMs) are generally too coarse to resolve important estuarine processes. Here, we statistically downscaled near-surface air temperature and precipitation projections to the scale of the Chesapeake Bay watershed and estuary. These variables were linked to Susquehanna River streamflow using a water balance model and finally to spatially resolved Chesapeake Bay surface temperature and salinity using statistical model trees. The low computational cost of this approach allowed rapid assessment of projected changes from four GCMs spanning a range of potential futures under a high CO2 emission scenario, for four different downscaling methods. Choice of GCM contributed strongly to the spread in projections, but choice of downscaling method was also influential in the warmest models. Models projected a ~2–5.5 °C increase in surface water temperatures in the Chesapeake Bay by the end of the century. Projections of salinity were more uncertain and spatially complex. Models showing increases in winter-spring streamflow generated freshening in the Upper Bay and tributaries, while models with decreased streamflow produced salinity increases. Changes to the Chesapeake Bay environment have implications for fish and invertebrate habitats, as well as migration, spawning phenology, recruitment, and occurrence of pathogens. Our results underline a potentially expanded role of statistical downscaling to complement dynamical approaches in assessing climate change impacts in dynamically challenging estuaries. 相似文献
7.
Cedar Bayou, a natural tidal inlet, was recently dredged to allow for direct water exchange between the Gulf of Mexico and Mesquite Bay, TX, USA. We quantified changes in densities of juvenile nekton (fish, shrimps, and crabs) and community structure in Mesquite Bay after Cedar Bayou was reopened by collecting samples at both control and impact sites using an epibenthic sled 1 year before (October 2013–April 2014) and after (October 2014–April 2015) opening. Significantly higher densities of total nekton were observed at the impact sites after opening using a before-after control-impact design. Red Drum (Sciaenops ocellatus), Atlantic Croaker (Micropogonias undulatus), post-larval penaeid shrimps (Farfantepenaeus aztecus, F. duorarum, and Litopenaeus setiferus), and Blue Crabs (Callinectes sapidus) were significantly more abundant at impact sites after Cedar Bayou was opened. Multivariate analysis showed a significant change in impact site communities after opening and was driven by an increased presence of estuarine-dependent species. Overall, this study demonstrates that opening tidal inlets, such as Cedar Bayou, and reconnecting Mesquite Bay to the Gulf of Mexico increased the presence of numerous estuarine-dependent species, many of which were not present or occurred at very low densities prior to reopening. Thus, reestablishing the historical connectivity between a productive estuary and the open Gulf of Mexico via Cedar Bayou should reinstitute natural nekton recruitment processes important to the Aransas, Mesquite, and San Antonio Bay regions. 相似文献
8.
Optimal benthic macrofaunal sampling protocol for detecting differences among four habitats in Willapa Bay,Washington, USA 总被引：1，自引：0，他引：1
As part of an effort to estimate estuarine habitat values with respect to ecological indicators of benthic macrofaunal community condition, an optimal (effective and least costly) sampling protocol (sample unit size [area x depth], sieve mesh size, and sample number [n]) was determined. The goal was to use four ecological indicators (number of species, abundance, biomass, and fish and crab prey abundance) to detect differences among four intertidal habitats in Willapa Bay, Washington, United States. The four habitats were eelgrass (Zostera marina), Atlantic cordgrass (Spartina alterniflora), mud shrimp (Upogebia pugettensis), and ghost shrimp (Neotrypaea californiensis). Four sample unit areas (0.005, 0.010, 0.015, and 0.020 m2), two sample unit depths (0–5 and 0–10 cm), and two sieve mesh sizes (1.0 and 0.5 mm) were evaluated. The optimal sampling protocol was defined as the least costly protocol capable of reliably (statistical power, 1?β≥0.80) detecting significant (α=0.05) differences among ≥4 of the 6 pairwise habitat contrasts by ANOVA on all four ecological indicators. The relative cost of each sampling protocol was estimated as a direct function of the sample unit size and number and the cost-in-processing-time ratios of 1 (5 cm deep):1.7 (10 cm deep) and 1 (≥1.0 mm macrofauna size fraction); 2.5 (≥0.5 mm macrofauna size fraction), which were taken from previous studies. The optimal sampling protocol was 15–20, 0.01-m2×5-cm deep, 0.5-mm mesh samples per habitat. 相似文献
9.
Our study was designed to examine early life stage tarpon (Megalops atlanticus) recruitment, habitat use, and residency in coastal environments near the northern limit of their distribution in the western Atlantic Ocean. We employed a multi-faceted approach to (1) collect ingressing larval tarpon on nighttime flood tides at multiple sites, (2) document larval and juvenile tarpon use of natural high marsh pools, and (3) examine juvenile tarpon movement and behavior in managed marsh impoundments, all in the North Inlet-Winyah Bay estuarine system of South Carolina, USA. The timing of recruitment (June through November) and size of larvae (mean ± standard deviation = 23 ± 3 mm standard length [SL]) during estuarine ingress was similar to that reported from other subtropical locations in the region. Soon after recruiting into the system, larval and small juvenile tarpon (47 ± 25 mm SL) co-occurred in high marsh pools from July to November, and large juveniles (201 ± 34 mm SL) were also present in marsh impoundments during this same time period. An increase in tarpon length over time during their residency in high marsh pools and the relatively large size they attain in marsh impoundments indicate these environments may function as favorable nursery habitats. As water temperatures decreased during October and November, juvenile tarpon emigrated from these estuarine habitats. Tarpon appear to use a variety of estuarine habitats in coastal South Carolina from summer through late fall during their early life stage development. The fate of these individuals after they leave estuarine habitats at the onset of winter in this region is currently unknown. 相似文献
10.
The copepod Eurytemora carolleeae dominates vernal zooplankton biomass in the Chesapeake Bay estuarine turbidity maximum (ETM) region, where it is an important prey item for larval anadromous fish. Although there have been several zooplankton studies in the Chesapeake Bay ETM focused on spring, the importance of winter zooplankton populations for establishing these vernal conditions has not been investigated. We examined the abundance, distribution, and individual sizes of E. carolleeae in winter of 2007 and 2008 and we investigated the potential impact of varying winter conditions and rising winter temperatures on Eurytemora female carbon content, egg production rate, and generation time. We found higher abundances and larger individuals in the colder 2007 than in 2008 under similar freshwater flow conditions. Empirical estimates showed that overall zooplankton productivity was higher in 2007 than in 2008. Published recruitment indices for anadromous fish including white perch and striped bass were higher in 2007 than in 2008 in the study region. Based on these findings, we hypothesize that colder conditions resulted in larger individuals and therefore increased prey biomass available to larval fish. We further hypothesize that rising winter water temperatures will negatively impact trophic transfer of primary production to copepods and ultimately to fish. 相似文献
11.
Fish diets play a critical role in our understanding of aquatic trophic dynamics and are an important component in developing ecosystem-based approaches to fisheries management. Although large nektonic fishes exert top-down predator effects on the food web and typically support viable commercial and recreational fisheries, little is known about the diet of this guild. We evaluated the diets (6327 stomachs) of four nektonic predatory fishes (Pomatomus saltatrix [78–395 mm], Cynoscion regalis [91–520 mm], Morone americana [156–361 mm], and Morone saxatilis [82–785 mm]) in Delaware Bay and in the adjacent ocean. To assess ontogenetic, geographic, and interspecific variation in diets, observations from individual fish stomachs were clustered into species-size class groups, and dietary overlap was estimated using multivariate analyses. A shift in diet composition, as well as diversity, occurred along the estuarine gradient and into the adjacent ocean. Some prey were shared by most predators, including some crustaceans (dominated by Callinectes sapidus, mysids, and Palaemonetes spp.), fundulids (dominated by Fundulus heteroclitus), engraulids (dominated by Anchoa mitchilli), and clupeids (dominated by Brevoortia tyrannus). However, inter- and intra-specific variation in diet was observed as well. In particular, M. americana consumed fewer engraulids and clupeids, and many more and diverse types of invertebrates, while P. saltatrix consumed more clupeids and less invertebrates. The lack of overlap in diet between the four predators evaluated, and between size groups for each predator, supports previous evidence that these groups feed in trophic guilds defined by species and by size within a species. The highly variable diets for these predators suggest high resolution spatial data are necessary in order to quantify their most important prey and their role in coastal ecosystems. 相似文献
12.
Tidal wetlands are affected by sea level rise. In the tidal freshwater stretches of estuaries in the temperate zone, willows (Salix spp.) form tidal freshwater forests above the mean high water level. Willows tolerance to prolonged periodic flooding in riverine systems is well documented, whereas effects of tidal flooding on willows are largely unknown. Flooding stress may play a major role in regeneration failure of willows in tidal forest stands along estuarine shores, and juvenile willows might be specifically affected by partial or total submergence. To assess the tolerance of juvenile willows to tidal flooding, we conducted a mesocosm experiment with cuttings from Salix alba and Salix viminalis, which are both characteristic species for tidal freshwater forests in Europe. Cuttings originating from either fresh or brackish tidal forest stands were grown under four tidal treatments with up to a tidal flooding of 60 cm. A general tolerance to a tidal flooding of 60 cm was observed in chlorophyll fluorescence, growth rates, and biomass production in both willow species. Overall, S. alba showed higher leaf and shoot growth, whereas S. viminalis produced more biomass. S. alba with brackish origin performed worst with increasing tidal flooding, suggesting a possible pre-weakening due to stressful site conditions in tidal wetlands at the estuarine brackish stretch. This study demonstrates that juvenile willows of S. alba and S. viminalis tolerate tidal flooding of up to 60 cm. It is concluded that tidal inundation acts as a stress by causing submergence and soil anaerobiosis, but may also act as a subsidy by reestablishing aerobic conditions and thus maintaining willows performance. Therefore, we suggest investigations on Salix tidal flooding tolerance and possible effects of willows on tidal wetland accretion under estuarine field conditions. 相似文献
13.
Larvae of Atlantic croaker Micropogonias undulatus enter Mid-Atlantic Bight estuaries annually between September and February. A high prevalence of ectoparasitic crustacean infection of ingressing larval M. undulatus was observed in Chesapeake Bay; this ectoparasite was identified as a species of Lepeophtheirus within the copepod family Caligidae from analysis of cytochrome oxidase I sequences and scanning electron microscopy. Between 2007 and 2011, seasonal differences in prevalence were observed, with higher infection rates on fall ingressing larvae (20 % mean monthly infection rate) than in larvae entering the estuary in the winter (monthly infection rate of 6 %); the head region had the highest parasite attachment rate, being observed in 78 % of the infected fish. The potential effects of this ectoparasite on larval M. undulatus could include reductions in feeding (and thus growth) and increased susceptibility to predation. 相似文献
14.
Seagrass populations have been declining globally, with changes attributed to anthropogenic stresses and, more recently, negative effects of global climate change. We examined the distribution of Zostera marina (eelgrass) dominated beds in the York River, Chesapeake Bay, VA over an 8-year time period. Using a temperature-dependent light model, declines in upriver areas were associated with higher light attenuation, resulting in lower light availability relative to compensating light requirements of Z. marina compared with downriver areas. An inverse relationship was observed between SAV growth and temperature with a change between net bed cover increases and decreases for the period of 2004–2011 observed at approximately 23 °C. Z. marina-dominated beds in the lower river have been recovering from a die-off event in 2005 and experienced another near complete decline in 2010, losing an average of 97 % of coverage of Z. marina from June to October. These 2010 declines were attributed to an early summer heat event in which daily mean water temperatures increased from 25 to 30 °C over a 2-week time period, considerably higher than previous years when complete die-offs were not observed. Z. marina recovery from this event was minimal, while Ruppia maritima (widgeongrass) expanded its abundance. Water temperatures are projected to continue to increase in the Chesapeake Bay and elsewhere. These results suggest that short-term exposures to rapidly increasing temperatures by 4–5 °C above normal during summer months can result in widespread diebacks that may lead to Z. marina extirpation from historically vegetated areas, with the potential replacement by other species. 相似文献
15.
Global sea level rise (SLR) will significantly alter coastal landscapes through inundation and erosion of low-lying areas. Animals that display area fidelity and rely on fringing coastal habitats during multiple life stages, such as diamondback terrapins (Malaclemys terrapin Schoepff 1793), are likely to be particularly vulnerable to SLR-induced changes. We used a combination of empirical nest survey data and results from a regional SLR model to explore the long-term availability of known nesting locations and the modeled availability of fringing coastal habitats under multiple SLR scenarios for diamondback terrapin in the MD portion of Chesapeake Bay and the MD coastal bays. All SLR scenarios projected the rapid inundation of historically used nesting locations of diamondback terrapins with 25%–55% loss within the next 10 years and over 80% loss by the end of the century. Model trajectories of habitat losses or gains depended on habitat type and location. A key foraging habitat, brackish marsh, was projected to decline 6%–94%, with projections varying spatially and among scenarios. Despite predicted losses of extant beach habitats, future gains in beach habitat due to erosion and overwash were projected to reach 40%–600%. These results demonstrate the potential vulnerability of diamondback terrapins to SLR in Chesapeake Bay and underscore the possibility of compounding negative effects of SLR on animals whose habitat requirements differ among life stages. More broadly, this study highlights the vulnerability of species dependent on fringing coastal habitats and emphasizes the need for a long-term perspective for coastal development in the face of SLR. 相似文献
16.
Fish communities in tidal tributaries have received considerable attention, but the relative value of nontidal tributaries (having a tidal amplitude of <?5 cm) may represent an under-valued habitat. A multi-gear sampling approach was used to collect fish and macroinvertebrates from one tidal and two nontidal tributaries to describe and compare the respective nekton communities and habitat use patterns. Nekton communities in tidal and nontidal tributaries were markedly different even though habitats were similar (e.g., temperature, DO, depths, shoreline vegetation). While catch-per-unit-effort (CPUE) of estuarine-dependent species (e.g., red drum, spot, common snook) was lower in nontidal tributaries, the overall nekton CPUE was twice that of the tidal tributary, and the community was comprised mostly of freshwater marsh species (e.g., eastern mosquitofish, sailfin molly, bluefin killifish). Based on the life histories of the fishes that differed between tributary types, the proximity of coastal inlets and availability of effective larval transport mechanisms for estuarine-dependent species may be greater determinants of community differences than factors related to tributary size or shoreline habitat type. These results recognize smaller nontidal tributaries as undervalued nursery habitats and suggest the function as secondary nursery habitats is a critical service to the overall estuarine community. 相似文献
17.
Chesapeake Bay is the largest estuary in the USA and comprises vast areas of polyhaline to freshwater, tidal fish habitat. The Bay experiences large temperature differences between winter and summer, which in combination with the variety of salinities enables approximately 240 species of fish to be temporary inhabitants. This dynamic environment leads to an ever-changing prey field for predators. The goal of this study was to characterize the diet of one of the few resident, euryhaline predators within the tidal rivers in Virginia, Lepisosteus osseus (longnose gar). The top five prey species were Morone americana, Brevoortia tyrannus, Fundulus spp., Micropogonias undulatus, and Leiostomous xanthurus. The diet composition varied with the seasonal fish assemblages, length of L. osseus, water temperature, and salinity. L. osseus consumed a greater amount of marine and anadromous fishes (%W?=?59.4 % and %N?=?56.5 %) than resident fishes (%W?=?40.6 % and %N?=?43.5 %). The seasonal influx of anadromous or coastal spawning fishes appears to be an important prey source for L. osseus and most likely other piscivores in the tributaries of Chesapeake Bay. 相似文献
18.
Nutrient inputs have degraded estuaries worldwide. We investigated the sources and effects of nutrient inputs by comparing water quality at shallow (< 2m deep) nearshore (within 200 m) locations in a total of 49 Chesapeake subestuaries and Mid-Atlantic coastal bays with differing local watershed land use. During July–October, concentrations of total nitrogen (TN), dissolved ammonium, dissolved inorganic N (DIN), and chlorophyll a were positively correlated with the percentages of cropland and developed land in the local watersheds. TN, DIN, and nitrate were positively correlated with the ratio of watershed area to subestuary area. Total phosphorus (TP) and dissolved phosphate increased with cropland but were not affected by developed land. The relationships among N, P, chlorophyll a, and land use suggest N limitation of chlorophyll a production from July–October. We compared our measurements inside the subestuaries to measurements by the Chesapeake Bay Program in adjacent estuarine waters outside the subestuaries. TP and dissolved inorganic P concentrations inside the subestuaries correlated with concentrations outside the subestuaries. However, water quality inside the subestuaries generally differed from that in adjacent estuarine waters. The concentration of nitrate was lower inside the subestuaries, while the concentrations of other forms of N, TP, and chlorophyll a were higher. This suggests that shallow nearshore waters inside the subestuaries import nitrate while exporting other forms of N as well as TP and chlorophyll a. The importance of local land use and the distinct biogeochemistry of shallow waters should be considered in managing coastal systems. 相似文献
19.
L. W. HardingJr. C. L. Gallegos E. S. Perry W. D. Miller J. E. Adolf M. E. Mallonee H. W. Paerl 《Estuaries and Coasts》2016,39(3):664-681
Climate effects on hydrology impart high variability to water-quality properties, including nutrient loadings, concentrations, and phytoplankton biomass as chlorophyll-a (chl-a), in estuarine and coastal ecosystems. Resolving long-term trends of these properties requires that we distinguish climate effects from secular changes reflecting anthropogenic eutrophication. Here, we test the hypothesis that strong climatic contrasts leading to irregular dry and wet periods contribute significantly to interannual variability of mean annual values of water-quality properties using in situ data for Chesapeake Bay. Climate effects are quantified using annual freshwater discharge from the Susquehanna River together with a synoptic climatology for the Chesapeake Bay region based on predominant sea-level pressure patterns. Time series of water-quality properties are analyzed using historical (1945–1983) and recent (1984–2012) data for the bay adjusted for climate effects on hydrology. Contemporary monitoring by the Chesapeake Bay Program (CBP) provides data for a period since mid-1984 that is significantly impacted by anthropogenic eutrophication, while historical data back to 1945 serve as historical context for a period prior to severe impairments. The generalized additive model (GAM) and the generalized additive mixed model (GAMM) are developed for nutrient loadings and concentrations (total nitrogen—TN, nitrate?+?nitrate—NO2?+?NO3) at the Susquehanna River and water-quality properties in the bay proper, including dissolved nutrients (NO2?+?NO3, orthophosphate—PO4), chl-a, diffuse light attenuation coefficient (K D (PAR)), and chl-a/TN. Each statistical model consists of a sum of nonlinear functions to generate flow-adjusted time series and compute long-term trends accounting for climate effects on hydrology. We present results identifying successive periods of (1) eutrophication ca. 1945–1980 characterized by approximately doubled TN and NO2?+?NO3 loadings, leading to increased chl-a and associated ecosystem impairments, and (2) modest decreases of TN and NO2?+?NO3 loadings from 1981 to 2012, signaling a partial reversal of nutrient over-enrichment. Comparison of our findings with long-term trends of water-quality properties for a variety of estuarine and coastal ecosystems around the world reveals that trends for Chesapeake Bay are weaker than for other systems subject to strenuous management efforts, suggesting that more aggressive actions than those undertaken to date will be required to counter anthropogenic eutrophication of this valuable resource. 相似文献
20.
Recruitment is a strong determinant of year class strength and adult population density especially for sessile benthic invertebrates where post-settlement mortality and competition are low or relatively stable over time. A series of surveys were undertaken to characterize recruitment and post-settlement processes for two species of burrowing shrimps, Neotrypaea californiensis and Upogebia pugettensis in order to determine how they influenced broader adult populations in US west coast estuaries. On average, U. pugettensis decapodids settled earlier (April–July), recruited almost exclusively to areas with conspecific adults, and grew more rapidly during their first summer than N. californiensis. Neotrypaea californiensis decapodids settled and recruited over a longer period (June–November) and were distributed across the tidal flat. While initially more abundant in areas with conspecific adults, they also either survived better or redistributed as small juvenile shrimp to areas where adults were absent. Linear relationships were found between abundance of newly recruited (0+ age class) shrimp and that of older 1+ shrimp a year later. Positive slopes were close to one for N. californiensis but less than one for U. pugettensis, suggesting lower survival. Annual recruitment varied dramatically but was more consistent for both species in Yaquina Bay. Patterns in strong recruitment years amongst estuaries, particularly for U. pugettensis, suggest the presence of multi-estuary metapopulations linked via larval dispersal. These results have important implications for shrimp population management including control for shellfish aquaculture, but also conservation of estuarine habitats due to the strong influence of these ecosystem engineers on the benthic community. 相似文献