Wicomico River Research Articles

Salmonella enterica recovery from river waters of the Maryland Eastern Shore reveals high serotype diversity and some multidrug resistance

The Delmarva Peninsula, a major agricultural and recreational region for the U.S. states of Delaware, Maryland and Virginia, experiences recurrent salmonellosis disease. Previous studies point to water environments as a potential persistent environmental reservoir of Salmonella enterica. To evaluate this hypothesis, water from the four main rivers of the Maryland Eastern Shore on the Delmarva Peninsula was tested for the presence of S. enterica, and recovered isolates were characterized for antimicrobial resistance. Sampling was performed in autumn and spring to evaluate temporal persistence at twenty four sites along the Choptank, Nanticoke, Pocomoke and Wicomico Rivers. Water (10 L) was filtered through sterile modified Moore swabs in situ. Swabs were selectively enriched for S. enterica and presumptive salmonellae were confirmed by PCR amplification of the Salmonella-specific invA and hilA genes. The serogroup of 402 isolates was determined, followed by serotype characterization for 157 isolates selected to represent all the identified serogroups across all samples. S. enterica was isolated from all the rivers in both seasons and was detected in 35/46 (65%) of surface water samples, with equivalent recovery in spring (70%) and fall (61%). The likelihood of isolating S. enterica was higher for the Nanticoke and Pocomoke Rivers, χ2 (3, N = 46) = 12.75, p < 0.01. In total, 18 serotypes of S. enterica were identified, and serotype diversity differed between the fall and spring samplings. Newport was the most frequently isolated serotype, both overall and in the fall, identified in 8/46 samples (17%). Typhimurium was the predominant serotype in spring. Some temporal and biogeographic patterns were observed in S. enterica recovery, but 6/18 serotypes were identified in both seasons. The majority (84%) of isolates were pan-susceptible, including all those tested from the Wicomico River (N = 19). Twenty five isolates (16%) from 9 samples were resistant to at least one antimicrobial, including serotypes Typhimurium, Newport, Litchfield, III 17:z10: e,n,x,z15, III 60:I and IV_40:z4: z32: -. Of the isolates that were resistant to a single antimicrobial (N = 12), resistance was to streptomycin or sulfisoxazole. Thirteen isolates were multidrug resistant, nine exhibiting resistance to ampicillin, sulfisoxazole, tetracycline, amoxicillin/clavulanic acid, cefoxitin and ceftriaxone, and four to sulfisoxazole and tetracycline. The widespread presence and diversity of S. enterica in Delmarva rivers are concerning given the frequent use of rivers and tributaries as a source of irrigation and for recreation. Future research should seek to determine specific point sources of S. enterica for surface river waters, and risks associated with acquisition of antimicrobial resistance traits.

Gear and survey efficiency of patent tongs for oyster populations on restoration reefs.

Surveys of restored oyster reefs need to produce accurate population estimates to assess the efficacy of restoration. Due to the complex structure of subtidal oyster reefs, one effective and efficient means to sample is by patent tongs, rather than SCUBA, dredges, or bottom cores. Restored reefs vary in relief and oyster density, either of which could affect survey efficiency. This study is the first to evaluate gear (the first full grab) and survey (which includes selecting a specific half portion of the first grab for further processing) efficiencies of hand-operated patent tongs as a function of reef height and oyster density on subtidal restoration reefs. In the Great Wicomico River, a tributary of lower Chesapeake Bay, restored reefs of high- and low-relief (25–45 cm, and 8–12 cm, respectively) were constructed throughout the river as the first large-scale oyster sanctuary reef restoration effort (sanctuary acreage > 20 ha at one site) in Chesapeake Bay. We designed a metal frame to guide a non-hydraulic mechanical patent tong repeatedly into the same plot on a restored reef until all oysters within the grab area were captured. Full capture was verified by an underwater remotely-operated vehicle. Samples (n = 19) were taken on nine different reefs, including five low- (n = 8) and four high-relief reefs (n = 11), over a two-year period. The gear efficiency of the patent tong was estimated to be 76% (± 5% standard error), whereas survey efficiency increased to 81% (± 10%) due to processing. Neither efficiency differed significantly between young-of-the-year oysters (spat) and adults, high- and low-relief reefs, or years. As this type of patent tong is a common and cost-effective tool to evaluate oyster restoration projects as well as population density on fished habitat, knowing the gear and survey efficiencies allows for accurate and precise population estimates.

Quantitative Validation of a Habitat Suitability Index for Oyster Restoration

Habitat suitability index (HSI) models provide spatially explicit information on the capacity of a given habitat to support a species of interest, and their prevalence has increased dramatically in recent years. Despite caution that the reliability of HSIs must be validated using independent, quantitative data, most HSIs intended to inform terrestrial and marine species management remain unvalidated. Furthermore, of the eight HSI models developed for eastern oyster (Crassostrea virginica) restoration and fishery production, none has been validated. Consequently, we developed, calibrated, and validated an HSI for the eastern oyster to identify optimal habitat for restoration in a tributary of Chesapeake Bay, the Great Wicomico River (GWR). The GWR harbors a high density, restored oyster population, and therefore serves as an excellent model system for assessing the validity of the HSI. The HSI was derived from GIS layers of bottom type, salinity, and water depth (surrogate for dissolved oxygen), and was tested using live adult oyster density data from a survey of high vertical relief reefs (HRR) and low vertical relief reefs (LRR) in the sanctuary network. Live adult oyster density was a statistically-significant sigmoid function of the HSI, which validates the HSI as a robust predictor of suitable oyster reef habitat for rehabilitation or restoration. In addition, HRR had on average 103-116 more adults m^−2 than LRR at a given level of the HSI. For HRR, HSI values ≥0.3 exceeded the accepted restoration target of 50 live adult oysters m^−2. For LRR, the HSI was generally able to predict live adult oyster densities that meet or exceed the target at HSI values ≥0.3. The HSI indicated that there remain large areas of suitable habitat for restoration in the GWR. This study provides a robust framework for HSI model development and validation, which can be refined and applied to other systems and previously developed HSIs to improve the efficacy of native oyster restoration.

An integrated modeling approach for elucidating the effects of different management strategies on Chesapeake Bay oyster metapopulation dynamics

Eastern oyster abundance is at an all-time low, yet this species is a key component of many estuarine systems because it contributes to ecosystem function by providing habitat, improving water quality, stabilizing benthic and intertidal habitat, increasing landscape diversity and producing more oysters. Given the breadth of environmental benefits oysters provide, as well as their commercial and cultural importance, sustainable oyster production has become a priority in several regions, including the Chesapeake Bay. Current strategies include treating restored reefs as permanent sanctuaries, which provide long-term environmental benefits yet removes them from the fishery, or harvesting reefs on a rotational basis, which provides economic value yet decreases environmental benefits. The long term dynamics of these strategies is unknown. Oysters have a complex, biphasic life cycle (i.e., sessile adult and motile larval stages) and their viability is intimately tied to a suite of environmental factors including, but not limited to, flow regime, total suspended solids, temperature, salinity, and dissolved oxygen. In order to determine how different oyster management strategies affect oyster dynamics, we developed a multi-model approach that integrates a 2-D hydrodynamic model, a larval transport model, and a spatially-explicit, agent-based population dynamics model to simulate long term oyster dynamics. We applied our model to a ten reef system in the Great Wicomico River in the Chesapeake Bay, and simulated six different combinations of sanctuary and/or harvest management scenarios over an 8-year period. We evaluated the environmental and commercial benefits of each strategy. Our results indicated that sanctuary reefs are beneficial, and that the spatial position of sanctuary reefs strongly affected source-sink dynamics and must be considered before implementing a harvest regime. Simulations that did not consider the source/sink dynamics of the reefs yielded larger numbers of oysters for harvest in the short-term, yet resulted in a complete fishery collapse in the long term. Selective, rotational harvest, resulted in lower annual yield, but the fishery persisted throughout the eight year simulation. This integrated modeling approach helped reduce uncertainty within the study system and can help natural resource managers understand ecosystem-level processes leading to more informed decision making across spatial and temporal scales.

A Multi-module Approach to Calculation of Oyster (Crassostrea virginica) Environmental Benefits.

Environmental benefits are one of the motivations for management restoration of depleted bivalve populations. We describe a series of linked modules for benefits calculation. The modules include: oyster (Crassostrea virginica) bioenergetics, materials transport via the tidal prism, and benefits quantification. Quantified benefits include carbon, nitrogen, and phosphorus removal and shell production. The modules are demonstrated through application to the Great Wicomico River, a tributary of Chesapeake Bay, USA. Oysters on seven reefs (total area 2.8 × 10(5) m(2)) are calculated to remove 15.2, 6.2, and 0.2 tons per annum of carbon, nitrogen, and phosphorus, respectively, from the Great Wicomico. Oyster mortality contributes 108 tons per annum dry weight shell to the reefs.

Recruitment Enhancement as an Indicator of Oyster Restoration Success in Chesapeake Bay

Oyster ( Crassostrea virginica ) recruitment in Chesapeake Bay, USA, dropped precipitously as stocks declined (1920s–1985), then collapsed (1986–present). Occasional recruitment spikes occurred, driven primarily by seasonal drought. Recruitment spikes helped sustain the fishery at a small, variable level for years post-collapse, as fishers took advantage of these strong year classes. Historically, oyster recruitment was higher, more reliable, and more stock-driven, with weather exerting less, though still significant influence. Analysis of publicly available oyster spat (young juvenile oysters) settlement data revealed the reestablishment of a steadier, historic pattern of oyster settlement and recruitment potential in the Great Wicomico River (GWR), where local stocks have been greatly enhanced by a large sanctuary reef network constructed in 2004. In 2012, an oyster shellstring survey in the GWR revealed the highest mean oyster settlement for any Bay tributary since such surveys began nearly 70 years ago. This unprecedented recruitment enhancement is significantly correlated to the large stock on the sanctuary reefs and a strong indicator of restoration success and longterm sustainability, as these reefs are well past the average age of senescence (five years) for restored reefs. With the expansion of large-scale Eastern oyster restoration efforts in Maryland’s portion of the Chesapeake Bay, developing efforts in the northeastern states of Massachusetts, Connecticut, New York, and New Jersey, and similar efforts to restore the Olympia oyster in the Pacific Northwest (Oregon, Washington, British Columbia), these findings are particularly timely and applicable.

Oyster δ15N as a Bioindicator of Potential Wastewater and Poultry Farming Impacts and Degraded Water Quality in a Subestuary of Chesapeake Bay

Fertig, B.; Carruthers, T.J.B., and Dennison, W.C., 2014. Oyster d 15 N as a bioindicator of potential wastewater and poultry farming impacts and degraded water quality in a subestuary of Chesapeake Bay. Journal of Coastal Research, 30(5), 881–892. Coconut Creek (Florida), ISSN 0749-0208. Anthropogenic nitrogen contributes to water quality degradation, but it is difficult to distinguish sources once they are mixed in coastal ecosystems. Natural abundances of stable nitrogen isotopes (d 15 N) were measured in oyster (Crassostrea virginica) tissues (muscle, gills, and mantle) during summer 2006 to summer 2008 to identify nitrogen sources in Monie Bay (a subestuary of Chesapeake Bay) receiving freshwater inputs from three tributary creeks. The creeks (estimated flushing times: 3.5, 5.7, and 37.2 d) vary in size and potential nitrogen sources: septic systems and poultry operations (Monie Creek), crop fertilizer (Little Monie Creek), and wetlands, forest, or both (Little Creek). Grand mean oyster tissue d 15 N values (11.8 6 0.4% in muscle, 10.4 6 0.4% in gills, and 10.5 6 0.3% in mantle) indicated a mixture of human and animal sources. Potential nitrogen loss from denitrification (15.1–24.5%) likely did not substantially modify isotopic values, and d 15 N values were greater than would be expected from atmospheric sources, refuting these alternative explanations. Though dilute, spatial patterns supported the inference that human waste, poultry waste, or both entered Monie Bay from its watershed and the adjacent Wicomico River watershed (via mixing). Calculated nitrogen generation from poultry manure in the watershed (containing 2.5 3 10 3 people) was 2.9 3 10 4 to 1.0 3 10 6 kg of total nitrogen (TN) per year (equivalent to 6.8 3 10 3 –2.3 3 10 5 people), whereas throughout Delmarva Peninsula (containing 1.2 3 10 6 people) it was 3.9 3 10 6 to 1.3 3 10 8 kg TN y � 1 (equivalent to 9.0 3 10 5 –3.1 3 10 8 people). Conservatively estimated (based on 0.038 kg chicken � 1 y � 1 ), poultry in the Monie Bay watershed generated an amount of nitrogen equivalent to that generated by 263% of the human population. Throughout Delmarva Peninsula, poultry generated an amount of nitrogen equivalent to that generated by 76% of the human population. Estuaries commonly receive nutrients from both inside and outside their watersheds, and oyster d 15 N values elucidated this process locally.

Algal turf scrubber (ATS) floways on the Great Wicomico River, Chesapeake Bay: productivity, algal community structure, substrate and chemistry(1).

Two Algal Turf Scrubber (ATS) units were deployed on the Great Wicomico River (GWR) for 22months to examine the role of substrate in increasing algal productivity and nutrient removal. The yearly mean productivity of flat ATS screens was 15.4 g · m(-2) ·d(-1) . This was elevated to 39.6g·m(-2) ·d(-1) with a three-dimensional (3-D) screen, and to 47.7g·m(-2) ·d(-1) by avoiding high summer harvest temperatures. These methods enhanced nutrient removal (N, P) in algal biomass by 3.5 times. Eighty-six algal taxa (Ochrophyta [diatoms], Chlorophyta [green algae], and Cyan-obacteria [blue-green algae]) self-seeded from the GWR and demonstrated yearly cycling. Silica (SiO2 ) content of the algal biomass ranged from 30% to 50% of total biomass; phosphorus, nitrogen, and carbon content of the total algal biomass ranged from 0.15% to 0.21%, 2.13% to 2.89%, and 20.0% to 25.7%, respectively. Carbohydrate content (at 10%-25% of AFDM) was dominated by glucose. Lipids (fatty acid methyl ester; FAMEs) ranged widely from 0.5% to 9% AFDM, with Omega-3 fatty acids a consistent component. Mathematical modeling of algal produ-ctivity as a function of temperature, light, and substrate showed a proportionality of 4:3:3, resp-ectively. Under landscape ATS operation, substrate manipulation provides a considerable opportunity to increase ATS productivity, water quality amelioration, and biomass coproduction for fertilizers, fermentation energy, and omega-3 products. Based on the 3-D prod-uctivity and algal chemical composition demonstrated, ATS systems used for nonpoint source water treat-ment can produce ethanol (butanol) at 5.8× per unit area of corn, and biodiesel at 12.0× per unit area of soy beans (agricultural production US).

Effects of age and composition of field-produced biofilms on oyster larval setting

Lack of success in restoring the native Eastern oyster, Crassostrea virginica, to Chesapeake Bay has been linked to the low occurrence of oyster larval setting in tributaries to the Bay. Among the many potential factors that could affect efforts to produce oysters through aquaculture or supplementation of shell beds is substratum condition. The present study examined larval setting on field-produced biofilms from Little Wicomico River (Virginia, USA) to assess whether bacterial community structure (examined by terminal restriction fragment length polymorphism, T-RFLP) or other characteristics of contemporary biofilms in this tributary (biofilm age and mass, algal abundance, and percentage organic matter) inhibited setting of larval oysters. The structure of the natural and heterogenous bacterial community in the biofilms and the success of oyster set were correlated, suggesting that specific microbial species may play a role in oyster setting. Larval set increased with biofilm age and mass, suggesting that established field-produced biofilms have no inhibitory effect. In contrast, the percentage of organic matter was negatively correlated with oyster set, whereas chlorophyll a concentration had no observed effect. The study expands prior knowledge by providing a more realistic timeframe for biofilm development (weeks as opposed to days), recounting effects of biofilms that are more representative of the natural dynamic and disturbance processes that would be expected to occur on submerged structures, and by incorporating seasonal and spatial variation. An important negative effect observed during the study period was heavy predation by Stylochus ellipticus on newly set oysters. Overall, the results of this study, which is the first assessment of the effects of biofilms produced naturally within a Chesapeake Bay tributary, suggest that the absence of large numbers of oysters in Little Wicomico River is not related to microbes or other specific characteristics of biofilms that develop on suitable setting substrata, but rather to heavy predation of newly set larvae.

Observations of Blue Crabs (Callinectes sapidus, Rathbun 1896) on Shell Bar Oyster Reef, Great Wicomico River, Virginia

Blue crabs (Callinectes sapidus, Rathbun 1896) were sampled with commercial crab pots on Shell Bar oyster reef in the Great Wicomico River, VA, from May through October during 2006 and 2007. Weekly catch per unit effort (CPUE), sex ratio, and size (carapace width, measured in millimeters) were evaluated in the context of water temperature (measured in degrees Celsius), salinity, and daylength (measured in hours) conditions on the reef. The total number of crabs collected in 2006 and 2007 was 5,221 and 3,303, respectively. Blue crab CPUE was highest from mid-June through mid-September at water temperatures at or more than 26°C, with maximum CPUEs observed in late July. The overall annual ratio of females to males was 0.47 in 2006 and 0.60 in 2007. Males made up more than 50% of the catch at Shell Bar reef from May through August. The observed sex ratio shifted from male dominated to female dominated as salinity increased, whereas water temperature and daylength decreased seasonally. Female crabs (median carapace width (CW), 142–144 mm) were approximately 20 mm in CW larger than males (median CW, 125 mm) in both years. Annual average CPUE (13.42 crabs per pot; SE = 1.57) and maximum CPUE (32.06 crabs per pot) was twice as high in 2006 as it was in 2007. The observed interannual differences in crab CPUEs may be the result of an enhanced forage base on the reef in 2006 relative to 2007. Approximately 9 million cultchless oysters (40–80 mm in shell height) were planted on Shell Bar reef between May and October 2006 as part of a concurrent oyster rehabilitation program.

Oyster (Crassostrea virginica, Gmelin 1791) Population Dynamics on Public Reefs in the Great Wicomico River, Virginia, USA

We describe oyster population trends in the Great Wicomico River, VA, from 2000 through 2009 using quantitative fishery independent survey data collected using a stratified random design. The seven public reefs examined cover a total of 2.8 3 10 5 m 2 and vary in individual size from 1.36 3 10 4 to 7.16 3 10 4 m 2 . The river is functionally divided by a sand spit into upriver and downriver regions. Oyster densities on the upriver reefs were typically an order of magnitude higher than densities on the downriver reefs within the same time period. Throughout the system, the highest observed densities were coincident with high annual recruitment events (2002, 2006). Recruitment events were usually followed by high mortality, with small percentages of the population reaching $3 y of age. A predictive stock-recruit relationship is absent; rather, population demographics appear to be dominated by periodic high recruitment events. In the absence of seed removal, biomass maxima follow 1-2 y after recruitment maxima. Standing stock for the system varied between 1.56 3 10 6 g and 3.63 3 10 7 g in 2005 and 2006. Year-specific age-at-length relationships were estimated from demographics data. Length demographics were recast as age demographics to estimate mortality. Observed proportional mortality between young of the year and age 2 oysters was approximately 0.88 for the 2006-y class, which is slightly higher than the 0.62-0.71 observed for the 2007-y class. The ability to estimate age specific mortality accurately allows the construction of shell (habitat) budgets for the individual reef systems. The Great Wicomico oyster population appears to be maintained by episodic and extraordinary recruitment in the face of high mortality—the latter driven by disease (predominantly Perkinsus marinus) epizootics. The shell resource is modest, equivalent to little more than a monolayer several centimeters thick. Over short timescales (years), the available shell resource oscillates in concert with mortality. The shell accretion rate on upriver reefs is consistently 4-5 times greater than that observed on downriver reefs. Periodic modest shell planting has maintained the habitat base (the shell resource) throughout the system over decadal scales.

Oysters Booming on New Reefs, But Can They Survive Disease?

A group of researchers is claiming an unprecedented restoration of oysters in the Great Wicomico River, a small tributary of the Chesapeake Bay. Thanks to a large network of reefs created in 2004, a booming population of native oysters has taken hold, the group reports in a paper published online by Science this week. Some researchers herald the accomplishment as a model for restoration, but others say that the new populations have yet to prove they can survive now-endemic diseases.

Oysters Booming on New Reefs, But Can They Survive Disease?

Thanks to a large network of reefs created in 2004, a booming population of native oysters has taken hold in the Great Wicomico River, a small tributary of the Chesapeake Bay, researchers report in a paper published online by Science this week.

Unprecedented Restoration of a Native Oyster Metapopulation

Native oyster species were once vital ecosystem engineers, but their populations have collapsed worldwide because of overfishing and habitat destruction. In 2004, we initiated a vast (35-hectare) field experiment by constructing native oyster reefs of three types (high-relief, low-relief, and unrestored) in nine protected sanctuaries throughout the Great Wicomico River in Virginia, United States. Upon sampling in 2007 and 2009, we found a thriving metapopulation comprising 185 million oysters of various age classes. Oyster density was fourfold greater on high-relief than on low-relief reefs, explaining the failure of past attempts. Juvenile recruitment and reef accretion correlated with oyster density, facilitating reef development and population persistence. This reestablished metapopulation is the largest of any native oyster worldwide and validates ecological restoration of native oyster species.

Automated oyster shucking: Part III. Orientation efficiencies of an oyster orientation and transfer system

Many oyster handling and processing devices require oysters to enter in a specific orientation. Unfortunately wild caught oysters exhibit great variability in shape and configuration. Thus, orienting them automatically is challenging. Orientation and transfer devices were developed and the efficiency of both orienting single wild caught oysters from the Chesapeake Bay region and transferring them from the orientation device to an exit conveyor were determined. The computer program, OYSORS, developed to control the orienting device was found to be able to orient only 51% of the oysters within ±0.35 radians when using only the basic program and 68% when using the basic program plus the Adjust modification. The total orientation and transfer system efficiency using the Adjust algorithm was determined for oysters from three oyster bars in the Chesapeake Bay Region: Tangier Sound, Wicomico River, and Potomac River. The total system was found to be able to orient and transfer oysters while holding their orientation within ±0.35 radians for between 50 and 66% of the oysters depending on the origin of the oysters. The transfer system alone was shown to be able to transfer oysters from the orienter to the exit conveyor within an allowable deflection of ±0.17 radians in 75–95% of the oysters depending on the origin of the oysters. It was shown that the transfer system was actually able to correct the orientation of some of the oysters incorrectly oriented by the computer program OYSORS.

A genetic test for recruitment enhancement in Chesapeake Bay oysters, Crassostrea virginica, after population supplementation with a disease tolerant strain

Many of the methods currently employed to restore Chesapeake Bay populations of the eastern oyster, Crassostrea virginica, assume closed recruitment in certain sub-estuaries despite planktonic larval durations of 2–3 weeks. In addition, to combat parasitic disease, artificially selected disease tolerant oyster strains are being used for population supplementation. It has been impossible to fully evaluate these unconventional tactics because offspring from wild and selected broodstock are phenotypically indistinguishable. This study provides the first direct measurement of oyster recruitment enhancement by using genetic assignment tests to discriminate locally produced progeny of a selected oyster strain from progeny of wild parents. Artificially selected oysters (DEBY strain) were planted on a single reef in each of two Chesapeake Bay tributaries in 2002, but only in the Great Wicomico River (GWR) were they large enough to potentially reproduce the same year. Assignment tests based on eight microsatellite loci and mitochondrial DNA markers were applied to 1579 juvenile oysters collected throughout the GWR during the summer of 2002. Only one juvenile oyster was positively identified as an offspring of the 0.75 million DEBY oysters that were planted in the GWR, but 153 individuals (9.7%) had DEBY ×wild F1 multilocus genotypes. Because oyster recruitment was high across the region in 2002, the proportionately low enhancement measured in the GWR would not otherwise have been recognized. Possible causes for low enhancement success are discussed, each bearing on untested assumptions underlying the restoration methods, and all arguing for more intensive evaluation of each component of the restoration strategy.

Induction of Skin Ulcers in Atlantic Menhaden by Injection and Aqueous Exposure to the Zoospores ofAphanomyces invadans

Abstract The infectivity and role of Aphanomyces invadans in the etiology of skin ulcers in Atlantic menhaden Brevoortia tyrannus were investigated with two laboratory challenges. In the first experiment, Atlantic menhaden received subcutaneous injections with secondary zoospores from one of three cultures of Aphanomyces: WIC (an endemic isolate of A. invadans in Atlantic menhaden from the Wicomico River, Maryland), PA7 (an isolate of A. invadans from striped snakehead Channa striata (also known as chevron snakehead), infected with epizootic ulcerative syndrome from Thailand), and ATCC-62427 (an isolate from Atlantic menhaden from North Carolina). Fish were injected with 1.9 × 102 (WIC-low), 1.9 × 103 (WIC-high), 5.2 × 102 (PA7), or 6.0 × 102 (ATCC-62427) zoospores and held in static water at 23.5°C (6‰ salinity) for 21 d. Both low and high doses of WIC caused incipient, granulomatous lesions after 5 d. Fish injected with the high-dose WIC died within 7 d. All fish injected with the low-dose WIC were dead...

Correlation of measures of ambient toxicity and fish community diversity in a Chesapeake Bay Tributary, Maryland, USA: A biological, chemical, and geological assessment

AbstractA battery of water column and sediment toxicity bioassays measuring lethal and sublethal endpoints were employed with fish, invertebrates, vascular plants, and bacteria. Monthly water column bioassays were conducted with water from three stations in the South River, Maryland, USA, and from a reference station in the Wicomico River (Maryland, USA). Sediment bioassays were conducted with five discrete samples taken from each station. Water column assays indicated low‐level effects at the upstream stations in the South River. Animal species demonstrated higher responses than did plants. Chemical analyses revealed only trace levels of heavy metals. Sediment in the upper stations of the South River demonstrated significant toxicity to animal but not plant test species. Sediment chemistry indicated elevated levels of heavy metals and polycyclic aromatic hydrocarbons. The sediments are enriched with chromium, copper, iron, manganese, cadmium, and lead—above normalized background geochemical ratios. The toxicological risk ranking model identified a strong gradient from upstream to downstream. Toxicological risk scores for the downstream station in the South River were comparable to those for the reference station. The major source of contaminants in the South River is probably derived from a multitude of non–point sources associated with urbanization within the watershed. The upper stations are in a zone of deposition of riverine material, whereas the downstream station is dominated by open Chesapeake Bay dynamics.

Chronological changes in toxicity of and heavy metals in sediments of two Chesapeake Bay tributaries

Sediments are storage compartments for many toxicants and act as indicators of pollution. The objective of this research was to study the chronological changes in the toxicity and heavy metals concentrations in the sediments of Wicomico River (WR) and Pocomoke River (PR)—two Chesapeake Bay tributaries. The sediments were collected from four sites in both the rivers; sediment and porewater were separated and analyzed for toxicity using the marine luminescent bacteria— Vibrio fischeri (Microtox®). The most toxic site from each river was used for studying the chronological changes in toxicity and heavy metals concentrations. A mean sedimentation rate (7.5 cm/yr) was used for calculating the time scale. The sediments were collected at a depth of 23.0 cm and divided into three 10-yr periods. The sediment collected from the depth corresponding to the years 1965–1975 was the least toxic and contained the lowest amount of metals in both the rivers. The toxicity and heavy metal concentrations from this depth were used as the baseline data. Five heavy metals—all EPA priority pollutant—zinc, lead, copper, cadmium and arsenic were identified and measured both in the sediment and porewater. The results show an increase in both the toxicity and input of metals over the next 20 yr compared to the baseline data for both the rivers. The increases in toxicity and heavy metals concentrations appear to be related to increase in industrial and agricultural activity around WR and PR, respectively.

Integrated measures of ambient toxicity and fish community diversity in Chesapeake Bay tributaries

The goals of this study were to assess the results of a suite of sediment and water column bioassays in the framework of a toxicological risk ranking model and evaluate correlations of model output with fish community metrics. The test sites were located in four tributaries of Chesapeake Bay that are impacted on by industrial, urban and agricultural land use (Curtis Creek, Rock Creek, Fishing Bay and Wicomico River). The mortality, reproduction and growth rates in the water column assays indicated low-level chemical contamination impacts in Curtis Creek and Rock Creek. The results from the Wicomico River and Fishing Bay did not indicate contaminant impacts, but some borderline effects were seen. The sediment bioassays demonstrated greater toxicological responses than the water column assays. The sediments in the Curtis Creek and Rock Creek sites were contaminated with heavy metals and PAHs. The heavy metal concentrations were an order of magnitude lower in the Fishing Bay sediments and below detection in the Wicomico River sediments, except for zinc. The acid-volatile sulphides:simultaneously extractable metals (AVS:SEM) ratios were below 1 in all cases. All four systems had detectable petroleum hydrocarbon contamination. Organic contaminants were below detection for all analyses in the Wicomico River and Fishing Bay samples. The risk ranking model ranked Curtis Creek as the most toxicologically impacted site, followed by Rock Creek, Fishing Bay and Wicomico River, which were essentially equal. The diversity index for fish communities sampled by bottom trawl was significantly correlated with the toxicological risk scores for sediment. The toxicological results indicate sediment contamination effects on the deep water fish community in Curtis Creek and indicate that contaminant impacts are not likely to be a contributing factor to disturbed fish communities in Fishing Bay