Genetic structure of bay anchovy (Anchoa mitchilli) populations in Chesapeake Bay

To determine the genetic structure of the bay anchovy (Anchoa mitchilli) within Chesapeake Bay, 16 isozyme systems encoding 21 loci for 20 population were examined using horizontal starch gel electrophoresis. Contingency Chisquare analysis revealed significant allelic frequency differences at nine loci (AAT-1, AAT-2, ALD-1, CPK-2, GAP-1, GLY-1, LDH-1, MDH-1, and MDH-2). Two loci, ALD-1 and MDH-1, were responsible for nine of 14 tests not conforming to Hardy-Weinberg expectations, with some of these deviations attributed to possible scoring and/or sampling error. Estimates for mean average heterozygosity were relatively high, ranging from 0.40 to 0.096, with 33–57% of the loci polymorphic. A low F_st value (0.041) along with high genetic identity estimates (I=0.997) indicated little substructuring of bay anchovy populations within Chesapeake Bay.     

Inorganic carbon requirements of natural populations and laboratory cultures of some Chesapeake Bay phytoplankton

The rates of photosynthetic carbon fixation for some natural populations of Chesapeake Bay phytoplankton and for unialgal cultures of species isolated from those populations follow hyperbolic saturation kinetics with respect to total inorganic carbon concentrations. The apparent half-saturation constants, K_c, measured by ¹⁴C uptake are close to and in some cases larger than ambient concentrations of total inorganic carbon, indicating that inorganic carbon can be a limiting nutrient in eutrophic systems. Addition of bicarbonate ion to incubation bottles increased the measured ¹⁴C uptake rates by factors as high as 2.5 for natural samples and 4.5 for laboratory cultures.     

Structural components of eelgrass (Zostera marina) meadows in the lower Chesapeake Bay—Fishes

The structure of the fish community associated with eelgrass beds in the lower Chesapeake Bay was studied over a 14 month period. A total of 24,182 individuals in 48 species was collected by otter trawl with Leiostomus xanthurus (spot) comprising 63% of the collection, Syngnathus fuscus (northern pipefish) 14%, Anchoa mitchilli (bay anchovy) 9%, and Bairdiella chrysoura (silver perch) 5%. The density and diversity of fishes were higher in vegetated areas compared to unvegetated areas; fishes were more abundant in night collections Fish abundance and species number increased in the spring and early summer as both water temperature and eelgrass biomass increased and decreased in the fall and winter as temperature and eelgrass biomass decreased. Gill netting revealed some of the top predators in the system, especially the sandbar shark, Carcharhinus milberti. The fish community in the Chesapeake Bay was quite different from North Carolina eelgrass fish communities. Most notable was the rarity of the pinfish, Lagodon rhomboides, which may be a very important predator in the structuring of the epifaunal communities.     

Structural components of eelgrass (Zostera marina) meadows in the lower Chesapeake Bay—Decapod crustacea

Otter trawl collections of eelgrass habitats in the lower Chesapeake Bay during 1976–1977 produced 14 species of decapod crustaceans. These collections were dominated by palaemonid shrimp (Palaemonetes spp.), blue crabs (Callinectes sapidus), and sand shrimp (Crangon septemspinosa), each of which exhibited unimodal seasonal abundance curves with large summer peaks. Decapod abundance was positively correlated with plant biomass throughout the year. Decapod densities on vegetated bottoms were greater than on unvegetated bottoms, and nighttime abundance on each bottom type was greater than corresponding daytime abundance. Total decapod abundances in Chesapeake Bay eelgrass meadows appear to be much greater than those reported in North Carolina eelgrass or Gulf of Mexico turtlegrass habitats.     

Effects of Local Watershed Land Use on Water Quality in Mid-Atlantic Coastal Bays and Subestuaries of the Chesapeake Bay

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.     

Community structure of macrozooplankton in Trinity and Upper Galveston Bays

Macrozooplankton were sampled bi-weekly from October 1969 through May 1973 at 16 stations. Hydrological measurements, including water temperature and conductivity, accompanied each biological sample. Sampling sites and species were grouped by cluster analysis using Camberra-Metric measure of dissimilarity and flexible sorting. Two major seasons, based on taxon composition and abundance, were identified: A warm season (average water temperature above 22°C) dominated by larval and juvenile crustaceans, and a cool season with an abundance of larval fishes. Sites were more similar to each other within a year than they were between years. Differences between years correlated with variations in salinity and temperature. Community structure indices (Shannon-Weaver diversity, species richness and “evenness”) were applied to the seasonal data. Shannon diversity and “evenness” were positively correlated with each other, but richness values were often negatively correlated with the other two indices.     

Effects of Shoreline Alteration and Other Stressors on Submerged Aquatic Vegetation in Subestuaries of Chesapeake Bay and the Mid-Atlantic Coastal Bays

Submerged aquatic vegetation (SAV) provides many important ecosystem functions, but SAV has been significantly reduced in many estuaries. We used spatial–statistical models to identify estuarine shoreline characteristics that explain variations in SAV abundance among subestuaries of the Chesapeake Bay and mid-Atlantic Coastal Bays. We summarized digital spatial data on shoreline construction, shoreline land use, physical characteristics, watershed land cover, and salinity for each subestuary. We related SAV abundance to shoreline characteristics and other stressors using univariate regression and multivariate models. The strongest univariate predictors of SAV abundance were percent shoreline forest, percent shoreline marsh, the percentage of shoreline that is 5–10 m tall, percent riprap, the percentage of subestuary area <2 m deep, percent herbaceous wetland, and percent shrubland. Shoreline marsh, bulkhead, and shoreline forest had different effects on SAV in different salinity zones. Percent riprap shoreline was the most important variable in a regression tree analysis of all the subestuaries, and percent deciduous forest in the watershed was the most important variable in a separate regression tree analysis on the mesohaline subestuaries. Subestuaries with <5.4 % riprap followed a significantly different temporal trajectory than those with >5.4 % riprap. SAV abundance has increased steadily since 1984 in subestuaries with <5.4 % riprap, but has not increased since 1996–1997 in subestuaries with >5.4 % riprap. Some shoreline characteristics interact with larger-scale factors like land cover and salinity zone to affect the distribution of SAV, while the effects of other shoreline characteristics are consistent among subestuaries with different salinities or local watershed land covers. Many shoreline characteristics can be controlled by management decisions, and our results help identify factors that managers should consider in efforts to increase SAV abundance.     

Harmful algal blooms in the Chesapeake and Coastal Bays of Maryland, USA: Comparison of 1997, 1998, and 1999 events

Harmful algal blooms in the Chesapeake Bay and coastal bays of Maryland, USA, are not a new phenomenon, but may be increasing in frequency and diversity. Outbreaks ofPfiesteria piscicida (Dinophyceae) were observed during 1997 in several Chesapeake Bay tributaries, while in 1998,Pfiesteria-related events were not found but massive blooms ofProrocentrum minimum (Dinophyceae) occurred. In 1999,Aureococcus anophagefferens (Pelagophyceae) developed in the coastal bays in early summer in sufficient densities to cause a brown tide. In 1997, toxicPfiesteria was responsible for fish kills at relatively low cell densities. In 1998 and 1999, the blooms ofP. minimum andA. anophagefferens were not toxic, but reached sufficiently high densities to have ecological consequences. These years differed in the amount and timing of rainfall events and resulting nutrient loading from the largely agricultural watershed. Nutrient loading to the eastern tributaries of Chesapeake Bay has been increasing over the past decade. Much of this nutrient delivery is in organic form. The sites of thePfiesteria outbreaks ranked among those with the highest organic loading of all sites monitored bay-wide. The availability of dissolved organic carbon and phosphorus were also higher at sites experiencingA. anophagefferens blooms than at those without blooms. The ability to supplement photosynthesis with grazing or organic substrates and to use a diversity of organic nutrients may play a role in the development and maintenance of these species. ForP. minimum andA. anophagefferens, urea is used preferentially over nitrate.Pfiesteria is a grazer, but also has the ability to take up nutrients directly. The timing of nutrient delivery may also be of critical importance in determining the success of certain species.     

In Situ Effects of Shoreline Type and Watershed Land Use on Submerged Aquatic Vegetation Habitat Quality in the Chesapeake and Mid-Atlantic Coastal Bays

Submerged aquatic vegetation (SAV) is an ecologically and economically valuable component of coastal estuaries that acts as an early indicator of both degrading and improving water quality. This study aimed to determine if shoreline hardening, which is associated with increased population pressure and climate change, acts to degrade SAV habitat quality at the local scale. In situ comparisons of SAV beds adjacent to both natural and hardened shorelines in 24 subestuaries throughout the Chesapeake and Mid-Atlantic Coastal Bays indicated that shoreline hardening does impact adjacent SAV beds. Species diversity, evenness, and percent cover were significantly reduced in the presence of riprap revetment. A post hoc analysis also confirmed that SAV is locally affected by watershed land use associated with increased population pressure, though to a lesser degree than impacts observed from shoreline armoring. When observed over time, SAV recovery at the local level took approximately 3 to 4 years following storm impacts, and SAV adjacent to natural shorelines showed more resilience to storms than SAV adjacent to armored shorelines. The negative impacts of shoreline hardening and watershed development on SAV shown here will inform coastal zone management decisions as increasing coastal populations and sea level rise drive these practices.     

Delaware Bay and Chesapeake Bay populations of the horseshoe crabLimulus polyphemus are genetically distinct

The Delaware Bay contains the world’s largest population of horseshoe crabs, which constitute an ecologically significant component of this estuarine ecosystem. The North Atlantic speciesLimulus polyphemus has an extensive geographical distribution, ranging from New England to the Gulf of Mexico. Recent assessments of the Delaware Bay population based on beach spawning and trawling data have suggested a considerable decrease in the number of adult animals since 1990. Considerable debate has centered on the accuracy of these estimates and their impact on marine fisheries management planning. Compounding this problem is the lack of information concerning the genetic structure of Atlantic horseshoe crab populations. This study assessed patterns of genetic variation within and between the horseshoe crab populations of Delaware Bay and Chesapeake Bay, using both Random Amplification of Polymorphic DNA (RAPD) and DNA sequence analysis of the mitochondrial cytochrome oxidase I gene (COI). We examined 41 animals from Delaware Bay and 14 animals from the eastern shore of Chesapeake Bay. To provide high quality, uncontaminated genomic DNA for RAPD analysis, DNA was isolated from hemocytes by direct cardiac puncture, purified by spin column chromatography, and quantified by agarose gel electrophoresis. RAPD fingerprints revealed a relative paucity of polymorphic fragments, with generally homogeneous banding patterns both within and between populations. DNA sequence analysis of 515 bases of the 5′ portion of the mitochondrial COI gene showed haplotype diversity in the Chesapeake Bay sample to be significantly higher than in the Delaware Bay sample, despite the larger size of the latter. Haplotype analysis indicates minimal contemporary gene flow between Delaware Bay and Chesapeake Bay crab populations, and further suggests that the Delaware Bay population is recovering from a recent population decline.     

On the spatial structure of currents across the Chesapeake and Delaware Canal

The Chesapeake and Delaware (C&;D) Canal is a man-made waterway connecting two of the largest estuaries on the east coast of the United States: Chesapeake Bay and Delaware Bay. A set of current meter data collected during April–May 1975 along two cross-sections of the C&;D Canal was used to examine the spatial distributions of the currents at tidal and subtidal time scales. The different responses of the Chesapeake and Delaware Bays to tidal and wind forcing produce significant differences in sea level fluctuations between the two ends of the canal. These alongcanal surface slopes produce significant barotropic current fluctuations at both tidal (semidiurnal and diurnal) and subtidal (2-d to 3-d) time scales. Under the influence of bottom friction, the barotropic currents near the surface are stronger than those at depth, but these currents do not exhibit significant lateral variations across the canal. On the other hand, the long-term flow in the canal exhibits strong lateral variability with eastward flow off the south shore of the canal and westward flow off the north shore of the canal. The lateral structure of the long-term flow may carry significant implications for the long-term exchange of material between the two bays.     

Changes in submerged aquatic macrophyte populations at the head of Chesapeake Bay, 1958–1975

Submerged aquatic plant populations in the Susquehanna Flats of the Chesapeake Bay were followed for 18 years. An exotic species, eurasian water milfoil,Myriophyllum spicatum, increased dramatically from 1958 to 1962; at the same time the dominant native species declined. After 1962, milfoil populations declined and the native rooted aquatics gradually began to return to their former levels. In the late 1960's all species declined and in 1972 almost disappeared from the Susquehanna Flats. These fluctuations may have been related to several interrelated environmental factors in the Chesapeake Bay, including tropical storms, turbidity, salinity and disease. The utilization of the Susquehanna Flats by waterfowl appears to be related to the abundance and species composition of the submerged macrophytes present.     

Functional trajectory models for assessment of transplanted eelgrass,Zostera marina L., in the Great Bay Estuary, New Hampshire

Functional trajectory models were used to assess the restoration of ecological functions in two transplanted eelgrass (Zostera marina L.) beds compared to three natural, reference beds in the Great Bay Estuary, New Hamsphire. Functional trajectory models describe the development of ecological functions over time in restored habitats relative to levels of function in natural habitats. We present the first application of trajectory models to transplanted seagrass and evaluate the utility of these models as a tool for assessing seagrass restoration. The project was an analysis of 9 yr of monitoring data, the longest monitoring of transplanted eelgrass to date. We used trajectory models to assess the time course of development of functions in transplanted beds by evaluating statistical trends, and to determine functional equivalence, defined as the time when functions in a transplanted bed reach an asymptote and are no more than 1 standard deviation below the reference mean. The functions modeled included primary production, 3-dimensional habitat structure, faunal use, and sediment filtering and trapping. Measured proxies for primary production and habitat structure increased logistically (sigmoidally) with time, reaching functional equivalence after 3 yr. In transplanted beds, trends in habitat use by infaunal invertebrates and fish were logarithmic, and values were functionally equivalent 2–4 yr after transplanting. We saw no trend in sediment filtering and trapping capacity of transplanted eelgrass over the 9 yr. Measures of function in both reference and transplanted beds fluctuated due to natural and anthropogenic disturbances. After reaching equivalence, measures of function in transplanted beds tracked those in reference beds, exhibiting long-term persistence and rebounding from disturbances similarly to reference beds. Trajectory models can illustrate the time course of eelgrass bed development, aiding the design of monitoring programs and the evaluation of ecological functional equivalence in seagrass restoration projects.     

Nitrogen,phosphorus and organic carbon pools in natural and transplanted marsh soils

Total nitrogen, phosphorus and organic carbon were compared in natural and transplanted estuarine marsh soils (top 30 cm) to assess nutrient storage in transplanted marshes. Soils were sampled in five transplanted marshes ranging in age from 1 to 15 yr and in five nearby natural marshes along the North Carolina coast. Dry weight of macroorganic matter (MOM), soil bulk density, pH, humic matter, and extractable P also were measured. Nutrient pools increased with increasing marsh age and hydroperiod. Nitrogen, phosphorus and organic carbon pools were largest in soils of irregularly flooded natural marshes. The contribution of MOM to marsh nutrient reservoirs was 6–45%, 2–22%, and 1–7% of the carbon, nitrogen and phosphorus, respectively. Rates of nutrient accumulation in transplanted marshes ranged from 2.6–10.0, 0.03–1.10, and 84–218 kmol ha^?1yr^?1 of nitrogen, phosphorus and organic carbon, respectively. Accumulation rates were greater in the irregularly flooded marshes compared to the regularly flooded marshes. Approximately 11 to 12% and 20% of the net primary production of emergent vegetation was buried in sediments of the regularly flooded and irregularly flooded transplanted marshes, respectively. Macroorganic matter nutrient pools develop rapidly in transplanted marshes and may approximate natural marshes within 15 to 30 yr. However, development of soil carbon, nitrogen and phosphorus reservoirs takes considerably longer.     

Changes in plankton community structure and function in response to variable freshwater flow in two tributaries of the Chesapeake Bay

The biomass of phytoplankton, microzooplankton, copepods, and gelatinous zooplankton were measured in two tributaries of the Chesapeake Bay during the springs of consecutive dry (below average freshwater flow), wet (above average freshwater flow), and average freshwater flow years. The potential for copepod control of microzooplankton biomass in the dry and wet years was evaluated by comparing the estimated grazing rates of microzooplankton by the dominant copepod species (Acartia spp. andEurytemora affinis) to microzooplankton growth rates and by calculating the percent of daily microzooplanton standing stock removed through copepod grazing. There were significant increases in phytoplankton and copepod biomass, but not for microzooplankton biomass in the wet year as compared to the dry year. The ctenophoreMnemiopsis leidyi was present during the dry year but was absent during the sampling period of the wet and average freshwater flow years. Grazing pressure on microzooplankton was greatest in the wet year, withAcartia spp. andE. affinis ingesting 0.21–2.64 μg of microzooplankton C copepod⁻¹ d⁻¹ and removing up to 60% of the microzooplankton standing stock per day. In the dry year, these copepod species ingested 0.10–0.73 μg of microzooplankton C copepod⁻¹ d⁻¹ with a maximum daily removal of approximately 3% of the microzooplankton standing stock. Potential copepod grazing pressure was significantly less than microzooplankton growth in the dry year, but was equivalent to microzooplankton growth in the wet year, implying strong top-down control of the microzooplankton community in the wet year. These results suggest that increased grazing control of microzooplankton populations by more copepods in the wet year released top-down control of phytoplankton. Reduced microzooplankton grazing, in conjunction with increased nutrient availability, resulted in large increases in phytoplankton biomass in the wet year. Increased freshwater flow has the potential to influence trophic cascades and the partitioning of plankton production in estuarine systems.     

Seasonal Factors Influencing Copepod Abundance in the Maryland Coastal Bays

Maryland Coastal Bays differ in hydrography from river-dominated estuaries because of limited freshwater inflow from tributary creeks and more marine influence. Consequently, the copepod community structure may be different from that of the coastal ocean and river-dominated estuaries in the mid-Atlantic region. A 2-year study was conducted to describe copepod species composition and seasonal patterns in abundance and factors influencing the community structure. Seven copepod genera, Acartia, Centropages, Pseudodiaptomus, Parvocalanus, Eurytemora, Oithona, and Temora, in addition to harpacticoids were found. The copepod community was dominated by Acartia spp. (64%), followed by Centropages spp. (30%), unlike in river-dominated estuaries in the region where the copepod community is usually dominated by Acartia spp. followed by Eurytemora affinis. Acartia tonsa was the most abundant in summer and fall whereas Centropages spp., Temora sp., Oithona similis, E. affinis, and harpacticoids were most abundant in winter and early spring. Parvocalanus crassirostris and Pseudodiaptomus pelagicus were present in fall and winter but at relatively low densities. The highest mean density of copepods occurred in winter 2012 (36,437 m^?3) and the lowest in spring 2013 (347 m^?3). Low densities occurred through early summer (614 m^?3) coinciding with peak spawning by bay anchovy (Anchoa mitchilli). Bottom-up control via low phytoplankton biomass coupled with top-down control by ctenophores (Mnemiopsis sp.), mysids (Neomysis americana), and bay anchovy was probably responsible for the low copepod densities in spring and early summer. Temperature and salinity were also important factors that influenced the seasonal patterns of copepod species occurrence. The observed seasonal differences in the abundance of copepods have important implications for planktivorous fishes as they may experience lower growth rates and survival due to food limitation in spring/early summer when copepod densities are relatively low than in late summer/fall when copepod abundance is higher.     

Transient hydrodynamic and salinity simulations in the Chesapeake Bay network

A transient network model is applied to the Chesapeake Bay and its tributary estuaries. Calibration of the model is based on only three external parameters: a friction factor that is spatially described, and two global constants required to calibrate a dynamic dispersion relationship that depends on both the local salinity gradient and hydraulic conditions. The transient hydrodynamics and the transient salinity distribution of the Bay and its tributary estuaries are simulated for the period of one month and comparisons made between calculated and observed salinities.     

Genetic Classification of Natural Gases in the Oil—Gas Zone and Its Application in the Sichuan Basin

On the basis of the carbon isotopic compositions of methane(CH4) and its homologues and the differences in isotopic values for CH4 and ethane (C2H6) and the correlation and compositional char-acteristics of hydrocarbon gases, the author has proposed a genetic classification of natural gases in the oil-gas zone.They are classified as biogenetic and abiogenetic gases in terms of the types of hydrocarbon-generating precursors (or parent materials) and their thermal evolution stages.Biogenetic gases can also be further divided into two series: biochemical and thermochemical gases,with the lat-ter formed at different evolution stages.Gases generated from type-I and -II1 organic matter are called oil-series gases, those from type-III, coal -series ,and those type -II2,mixture-type gases.Gases generated from two or more than two types of precursors are called mixture-source gases.According to those mentioned above, natural gases from the major oil-gas pools in the Sichuan Basin have been discriminantly analyzed,and the results are concordant with the distribution and de-velopment of hydrocarbon-source rocks as well as with their characteristics, indicating a prospective application.