Showing papers in "Estuaries in 1988"
TL;DR: In this paper, an analysis of data relatingSpartina alterniflora Loisel to tidal elevations along the Atlantic and Gulf coasts demonstrated that although this species is primarily confined to the intertidal zone, its elevational limits do not correspond to a consistent elevation relative to a tidal datum in all marsh locations.
Abstract: An analysis of data relatingSpartina alterniflora Loisel. to tidal elevations along the Atlantic and Gulf coasts demonstrated that although this species is primarily confined to the intertidal zone, its elevational limits. of occurrence do not correspond to a consistent elevation relative to a tidal datum in all marsh locations. The variation in the vertical distribution of this species reported among marsh studies was attributed primarily to differences in mean tide range (MTR). A positive correlation between MTR and elevational growth range (r=0.91) demonstrated that theSpartina alterniflora zone expands with increasing tidal amplitude. Differences in MTR among marsh locations accounted for 70 and 68% of the statistical variation in the upper and lower limits, respectively, ofS. alterniflora growth. Among marshes of similar tidal amplitudes, the upper limit of occurrence ofS. alterniflora in northern marshes was significantly lower than that in marshes at lower latitudes. These results, in combination with regional differences in plant species distribution across the upper intertidal zone, suggested that some of the variation in the upper limit was due to latitudinal differences in growth conditions and/or differences in interspecific competition. Local and regional differences in other factors such as salinity, nutrients, or physical disturbance may have also contributed to the variation in the limits of growth relative to a tidal plane within and among marshes.
235 citations
TL;DR: In this article, the current status of the concentration of these contaminants in Gulf of Mexico coastal areas removed from point sources of input was determined in sediment and oysters to provide information on the current state of the contamination.
Abstract: Polynuclear aromatic hydrocarbons (PAH), chlorinated pesticides, and polychlorinated biphenyls (PCB) concentrations were determined in sediment and oysters to provide information on the current status of the concentration of these contaminants in Gulf of Mexico coastal areas removed from point sources of input. Coprostanol analyses of sediments showed that anthropogenic materials are associated with the sediments at all 153 stations sampled. The levels of contaminants encountered are low compared with areas of known contamination. Average PAH concentrations are nearly the same in oysters and sediments, although the molecular weight distribution is different. Average DDT and PCB concentrations are higher by a factor of 10 to 130 in oysters as compared to sediments. Continued sampling and analyses will allow for long-term trends in the concentrations of these contaminants to be determined.
189 citations
TL;DR: In this article, the authors measured the dry weight of macroorganic matter (MOM), soil bulk density, pH, humic matter, and extractable P in natural and transplanted estuarine marsh soils.
Abstract: 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.
156 citations
TL;DR: In this article, structural and functional characteristics of the Swartvlei estuary fish community are described, and the diets of 18 fish species, based on the analysis of 1,648 stomach contents, are presented.
Abstract: Structural and functional characteristics of the Swartvlei estuary fish community are described. The detritivore group of fishes comprised 49% of the total catch biomass, zoobenthivores 25%, herbivores 18%, piscivores 6%, and epifauna/zooplanktivores 2%. The diets of 18 fish species, based on the analysis of 1,648 stomach contents, are presented. Selection by Swartvlei estuary fishes for zoobenthic invertebrates and aquatic macrophytes in different habitats was calculated using the linear index of selection. Results indicated a strong positive selection for epifaunal invertebrates and poor utilization of infauna and plants. Plant consumption by herbivorous fishes in the estuary centered around filamentous algae and diatoms growing onZostera capensis, rather than seagrass leaf material. The detrital base for both eelgrass- and sand-dominated areas in the Swartvlei estuary is emphasized, and most of the fish biomass was supported directly or indirectly by detritus. Large catches (mass per unit effort) in the macrophyte-free upper reaches site were attributed to the tidal input ofZostera leaves and associated algae to the area and its subsequent utilization by fishes through the detrital food chain.
87 citations
TL;DR: Trophic groups were used to investigate broad patterns and predict species interactions of macrobenthic assemblages in Calcasieu Estuary, Louisiana as discussed by the authors, showing that surface-deposit feeders were dominant in the upper estuary, subsurface-depositional feeders dominated the lower estuary and a trophically well-mixed assemblage inhabited the middle estuary.
Abstract: Trophic groups were used to investigate broad patterns and predict species interactions of macrobenthic assemblages in Calcasieu Estuary, Louisiana. Macrobenthic assemblages of the estuary were numerically dominated by deposit-feeding species. Surface-deposit feeders were the most abundant macrobenthos of the upper estuary, subsurface-deposit feeders dominated the lower estuary, and a trophically well-mixed assemblage inhabited the middle estuary. There were periodic shifts in species dominance within each region, but the shifts were without temporal pattern and seldom led to changes in trophic structure of the region. The macrobenthic assemblages of the upper estuary were dominated by several early-colonizing species which switched feeding modes with changes in water flow, suggesting that disturbances in the upper estuary had a direct effect on macrobenthic communities. Disturbances also may have eliminated macrobenthic species before they could establish a well-mixed community. The presence of trophically mixed communities in the middle estuary probably was indicative of fewer disturbances there. The dominance by subsurface-deposit feeders in the lower estuary probably indicates that sedimentary food in Calcasieu Lake was seldom utilized at the sediment-water interface. Rather, most food became buried and was available only to subsurface-deposit feeders.
82 citations
TL;DR: A habitat suitability index (HSI) model, developed for the American oyster,Crassostrea virginica, along the Gulf of Mexico, was field tested on 38 0.1-ha reef and non-reef sites in Galveston Bay, Texas as mentioned in this paper.
Abstract: A habitat suitability index (HSI) model, developed for the American oyster,Crassostrea virginica, along the Gulf of Mexico, was field tested on 38 0.1-ha reef and nonreef sites in Galveston Bay, Texas. The HSI depends upon six (HSI1) or, optionally, eight (HSI2) variables. The six variables are percent of bottom covered with suitable cultch (V1), mean summer water salinity (V2), mean abundance of living oysters (V3) (a gregarious settling factor), historic mean water salinity (V4), frequency of killing floods (V5), and substrate firmness (V6). The optional variables are the abundance of the southern oyster drillThais haemostoma (V7), and the intensity of the oyster pathogenPerkinsus marinus (V8). The HSI values were lowest at high and low salinity sites and highest at intermediate-salinity sites. To validate the model, the hypothesis that the output of the HSI model was correlated with oyster density was therefore tested. A significant correlation was found between HSI1 and oyster density (Kendall Tau Beta correlation coefficient, τ=0.674, p<0.001, n=38); however, a statistical independence problem exists with the above test, that is, oyster density is both the independent standard for the test and a variable in the model. A regression model was constructed to test the relationship between log-transformed oyster density values (dependent variable) and the other variables of the model (independent variables). Most variation (r2=0.72, r=0.85) in the log-transformed density values were explained by a regression model that contained V2, V4, V5, V6, V7, and V8 as independent variables. The regression model was useful in constructing a modified HSI model (MHSI). A significant correlation (τ=0.674, p<0.05, n=10) was found between MHSI1 values and oyster densities from reefs closed to harvesting. The MHSI improves upon the original model by (i) simplifying the model structure, (ii) removing the requirement to measure V3, (iii) accounting better for the negative effects of high salinity, disease, and parasitism upon oysters, and (iv) eliminating the statistical independence problem by dropping V3 from the model. The MHSI should be tested against a new, independently-collected data set.
69 citations
TL;DR: In the El Verde Lagoon, a small coastal lagoon with an ephemeral inlet on the Pacific Coast of Mexico, the water column was slightly heterotrophic, with an annual P/R ratio of 0.89 as discussed by the authors.
Abstract: Plankton metabolism andRuppia maritima biomass were measured seasonally during 1982–83 in El Verde Lagoon, a small coastal lagoon with an ephemeral inlet on the Pacific Coast of Mexico. Total net aquatic primary production was 521 g C m−2 y−1. The water column was slightly heterotrophic, with an annual P/R ratio of 0.89. Our analysis indicates that tropical and subtropical coastal lagoons with restricted or seasonal inlets have generally higher net aquatic primary productivity levels than lagoons with permanently open inlets. We hypothesize that this is due to retention of nutrients and plankton stocks during the dry season. The seasonal pattern of water column metabolism was related to rainfall and riverflow, with higher values generally occurring during the wet season. Net production and respiration were about three times lower during the 1982 dry season as compared to the 1983 dry season which received considerable rains due to abnormal climatic conditions. The biomass ofR. maritima ranged from zero to 620 g dry wt m−2. Growth occurred only during the dry season and there were two distinct biomass peaks representing two separate crops. The second crop was heavily epiphytized with nitrogen-fixing algae. There was an apparent succession in dominance of water column productivity over the year, withRuppia dominating during the dry season and phytoplankton more important during the wet season.
67 citations
TL;DR: A two-year trawl study of Laguna Joyuda, Puerto Rico, a small, polyhaline lagoon with restricted oceanic exchange, yielded 803 crabs belonging to sixCallinectes species, finding distributional patterns appear to be a result of complex interactions of habitat preferences and intra- and interspecific interactions among the crabs.
Abstract: A two-year trawl study of Laguna Joyuda, Puerto Rico, a small, polyhaline lagoon with restricted oceanic exchange, yielded 803 crabs belonging to sixCallinectes species.Callinectes danae was the most abundant (35.7%), followed byC. sapidus (21%),C. ornatus (12.6%),C. bocourti (12.1%),C. exasperatus (1.2%), andC. larvatus (0.4%). Abundances of different species differed more spatially than temporally despite very homogeneous salinities.Callinectes bocourti andC. sapidus were most abundant furthest from the lagoon’s inlet, whileC. danae andC. ornatus were most abundant near the inlet and in the center of lagoon. Juveniles were least abundant in the center of the lagoon. Size frequencies of most species showed common trends with high percentages of small crabs furthest from the inlet, and high percentages of larger crabs near the inlet and central parts of the lagoon. Distributional patterns appear to be a result of complex interactions of habitat preferences and intra- and interspecific interactions among the crabs.
63 citations
TL;DR: In this article, sediment oxygen uptake and net sediment-water fluxes of dissolved inorganic and organic nitrogen and phosphorus were measured at two sites in Fourleague Bay, Louisiana, from August 1981, through May 1982.
Abstract: Sediment oxygen uptake and net sediment-water fluxes of dissolved inorganic and organic nitrogen and phosphorus were measured at two sites in Fourleague Bay, Louisiana, from August 1981, through May 1982. This estuary is an extension of Atchafalaya Bay which receives high discharge and nutrient loading from the Atchafalaya River. Sediment O2 uptake averaged 49 mg m−2 h−1. On the average, ammonium (NH4+) was released from the sediments (mean flux =+129 μmol m−2 h−1), and NO3− was taken up (mean flux =−19 μmol m−2h−1). However, very different NO3− fluxes were observed at the two sites, with sediment uptake at the upper, river-influenced, high NO3− site (mean flux =−112 μmol m−2 h−1) and release at the lower, marine-influenced low NO3− site (mean flux =+79 μmol m−2 h−1). PO43− fluxes were low and often negative (mean flux =−8 μmol m−2 h−1), while dissolved organic phosphorus fluxes were high and positive (mean flux =+124 μmol m−2 h−1). Dissolved organic nitrogen fluxes varied greatly, ranging from a mean of +305 μmol m−2 h−1 at the lower bay, to −710 μmol m−2 h−1 at the upper bay. Total dissolved nitrogen and phosphorus fluxes indicated the sediments were a nitrogen (mean flux =+543 μmol m−2 h−1) and phosphorus source (mean flux =+30 μmol m−2 h−1) at the lower bay, and a nitrogen sink (mean flux =−553 μmol m−2 h−1) and phosphorus source (mean flux =+17 μmol m−2 h−1) in the upper bay. Mean annual O∶N ration of the positive inorganic sediment fluxes were 27∶1 at the upper bay and 18∶1 at the lower bay. Based on these data we hypothesize that nitrification and denitrification are important sediment processes in the upper bay. We further hypothesize that Atchafalaya River discharge affects sediment-water fluxes through seasonally high nutrient loading which leads to net nutrient uptake by sediments in the upper bay and release in the lower bay, where there is less river influnces.
60 citations
TL;DR: An undescribed juvenile lobster habitat in Nauset Marsh, Cape Cod is discovered and studied and may be an important nursery habitat for small juvenile lobsters.
Abstract: The habitats utilized by small juvenile (<40 mm carapace length, CL) lobsters (Homarus americanus) are poorly known. We discovered and studied an undescribed juvenile lobster habitat in Nauset Marsh, Cape Cod. Juvenile lobsters (X=26.7 mm carapace length, 6 to 72 mm, n=38) were collected from suction samples primarily 0144 01 in “peat reef” habitats during the period from August 1985 through October 1986. The reefs consisted of large blocks ofSpartina alterniflora peat that had separated from the marsh surface and fallen into adjacent subtidal marsh channels. The smallest lobsters (6 to 7 mm CL) were collected from peat reefs in October 1985, and April and July 1986. In these habitats, juvenile lobster density averaged 2.5 individuals m−2 (range 0–5.7) in suction samples. Peat reef habitats occur in other salt marshes in the northeastern United States and may be an important nursery habitat for small juvenile lobsters.
53 citations
TL;DR: The Delaware Estuary, bounded by the states of Delaware, New Jersey and Pennsylvania, is located in one of the most complex urban industrial regions in the United States as mentioned in this paper, and water pollution of the estuary was observable over two centuries ago and progressively worsened until after World War II.
Abstract: The Delaware Estuary, bounded by the states of Delaware, New Jersey and Pennsylvania, is located in one of the most complex urban-industrial regions in the United States. Water pollution of the estuary was observable over two centuries ago and progressively worsened until after World War II. Four distinct governmental responses to the pollution have led to the vastly improved water quality of today. A fifth-generation response, now being initiated, is oriented toward remaining problems, including toxic contamination of the water column, bottom materials and aquatic life. Changes in water quality and the institutional responses to pollution are traced to demonstrate the evolutionary process of water pollution control.
TL;DR: In this paper, a model for subtidal oyster reef development is proposed that accounts for sea level rise, biodeposition, and the harvesting activity of man, which is attributed to intense harvesting activity during the last century.
Abstract: Wreck Shoal is a subtidal oyster reef located in the James River estuary, Virginia. This estuary has moved upstream and landward in response to rising sea level. The recent geomorphic history of Wreck Shoal is analyzed based on bathymetric records from the 1850’s to the 1980’s. The data indicate that the shallow oyster reef areas have lost elevation in the last 130 yr. This is attributed to intense harvesting activity during the last century. The late Holocene evolution of Wreck Shoal is developed based on the results of sub-bottom profiles and coring data. These suggest that the Wreck Shoal oyster reef has developed on the ridge and swale topography of a point-bar formed during the late Pleistocene epoch. Contemporary biodeposition processes on Wreck Shoal are evaluated. The results indicate that sediments of biogenic origin (fecal and shell material) potentially accumulate at rates in excess of 50 cm 100 years−1. A model for subtidal oyster reef development is proposed that accounts for sea level rise, biodeposition, and the harvesting activity of man. The model is verified with field observations of reef elevation and radiocarbon dates of oyster shell material. The implications of these results are that oyster reefs should be considered a renewable natural resource, and therefore managed accordingly in concert with the oysters.
TL;DR: The data suggest that several common crab and snail inhabitants of eelgrass meadows are capable of preying on eel Grass seeds and seedlings, but that this activity may be influenced by the availability of an alternative food source.
Abstract: Ten species, including crustaceans, molluscs and fish, were examined for predacious activity onZostera marina L. seeds and seedlings. Predation was examined initially by offering seeds or seedlings as a sole food source for a maximum period of one week. Species exhibiting predation of 10% or more of the seeds or seedlings were tested further with bits of clam or scallop as an alternative food source. In these experiments, animals were tested in each of three conditions: 1) alternative food plus seeds or seedlings; 2) alternative food alone; 3) seeds or seedlings alone. In the initial experimentsOvalipes ocellatus, Pagurus longicarpus, andPanopeus herbstii preyed on seeds, andIlyanassa obsoleta, Littorina littorea, andP. longicarpus preyed on seedlings. Limited predation occurred, however, when these animals were presented with seeds or seedlings plus an alternative food. These data suggest that several common crab and snail inhabitants of eelgrass meadows are capable of preying on eelgrass seeds and seedlings, but that this activity may be influenced by the availability of an alternative food source.
TL;DR: It is concluded that the decreased oxygen consumption observed in infested mussels is not due to limitation of oxygen availability, but rather reflects a real metabolic response to the presence of the symbiont and the concomittant deprivation of food to the host.
Abstract: Filtration rates and oxygen consumption rates were measured in mussels (Mytilus edulis) with and without pea crabs (Pinnotheres maculatus). Noninfested mussels had a significantly higher rate of oxygen consumption per hour (0.578 ml±0.012) than did infested mussels (0.352 ml±0.012). There was no significant effect of pea crab size on mussel respiration. Filtration rates of infested mussels were significantly lower than those of uninfested mussels. Assimilation efficiency was not significantly affected by pea crab infestation. The relationship between body size and oxygen consumption inP. maculatus is given by the following equation: {ie264-1} W0.626, where {ie264-2} is oxygen uptake (ml h−1), and W is dry weight (g). There was no difference between the sexes. It is concluded that the decreased oxygen consumption observed in infested mussels is not due to limitation of oxygen availability, but rather reflects a real metabolic response to the presence of the symbiont and the concomittant deprivation of food to the host. The effect is probably reversible, that is, damage can be compensated for after the symbiont has vacated the mussel, depending upon the period of infestation. Our results indicate that the mussels infested by pea crabs may be at an energetic disadvantage relative to mussels without pea crabs.
TL;DR: In this article, the authors used a linear regression analysis of winter canvasback populations in the bay to detect annual and seasonal changes in distribution, showing a significant decline in the upper bay and middle bay populations, but no significant changes in the lower-bay and Potomac River populations.
Abstract: Baltic clams (Macoma balthica) were the predominant food items of 323 canvasbacks (Aythya valisineria) collected throughout Chesapeake Bay during 1970–1979. Natural vegetation constituted 4% of the food volume. Widgeongrass (Ruppia maritima) and redhead grass (Potamogeton perfoliatus) constituted the greatest percent volume and frequency of occurrence among the plant species, whereas wild celery (Vallisneria americana) constituted only a trace of the food volume. These results contrast with historical records of food habits of canvasbacks in Chesapeake Bay. Canvasback population estimates during the 1970’s were examined to detect annual and seasonal changes in distribution. Linear regression analyses of winter canvasback populations in the bay showed a significant decline in the upper-bay and middle-bay populations, but no significant changes in the lower-bay and Potomac River populations. The changes in winter distribution and abundance of the canvasback appear related to changes in natural food availability, which is the result of altered environmental conditions.
TL;DR: In this article, the authors show evidence for anaerobic, sulfide oxidation in bottom waters of the Upper Chesapeake Bay bottom waters, which is consistent with possible biological mediation.
Abstract: Upper Chesapeake Bay bottom waters are stratified in the summer. In the water column below the pycnocline, anoxic and sulfidic conditions exist. Hydrogen sulfide concentrations approach 60 μM or greater and elemental sulfur is also present. Water samples brought on board ship, exposed to light, and not treated with formaldehyde show rapid sulfide decomposition which is significantly faster than sulfide oxidation by molecular oxygen. The data presented show evidence for anaerobic, sulfide oxidation. The kinetics of the decomposition are consistent with possible biological mediation. Hydrogen, peroxide produced by microorganisms may be the chemical oxidant responsible for the oxidation. Alternately, solid metal oxides such as colloidal manganese oxide phases may be reponsible.
TL;DR: In this paper, the macrofauna assemblages in Calcasieu Lake estuary (Louisiana) were sampled at 11 sites from October 1983 through November 1985, and the sites were numerically dominated by subsurface-deposit feeders, consisting mostly of polychaetes.
Abstract: Macrobenthic assemblages in Calcasieu Lake estuary (Louisiana) were sampled at 11 sites from October 1983 through November 1985. The sites were numerically dominated by subsurface-deposit feeders, consisting mostly of polychaetes. Greater densities of macrofauna were collected at the northern (upper) stations of the lake than were collected in West Cove or the southern stations. Abundances of polychaetes, oligochaetes, and amphipods at the upper lake stations accounted for most of the differences among stations. The numerical dominance by detritivores (97% of the fauna) and lack of strong sediment or salinity gradients across the estuary, resulted in an absence of temporal pattern in trophic structure of the macrofauna.
TL;DR: In this paper, the seasonal cycling of fine sediment in the upper reaches of a macrotidal estuary and its possible consequences for the behaviour of a contaminant which partitions between dissolved and particulate forms are investigated theoretically.
Abstract: The seasonal cycling of fine sediment in the upper reaches of a hypothetical macrotidal estuary and its possible consequences for the behaviour of a contaminant which partitions between dissolved and particulate forms are investigated theoretically. The simplest one-dimensional models are used as a starting point for future studies: (a) a within-tide hydrodynamic (tidal) model, (b) an associated sediment transport model and (c) a tidally-averaged contaminant dispersal model. The calculations are made for a four-year period and show that a cyclic migration of mobile sediment occurs in the upper reaches of the estuary. Sediment accumulates during spring to late summer, and is redistributed in the lower estuary during high runoff periods (autumn and winter). For a fluvial input of contaminant, the dissolved contaminant levels during summer are greatly depressed below conservative mixing values in the upper (turbidity maximum) region, whereas they are slightly enhanced in the lower reaches. During winter, the levels are substantially greater than conservative values except for a slight depression at very low salinities. Thus, sediment here acts as a source of contaminant for most of the salinity range. For a marine input of contaminant, levels are enhanced above the conservative mixing line at low salinities throughout the year, the effect being much larger during summer.
TL;DR: In this paper, the instantaneous flux of a nutrient is written in a constrained linear model as a function of time, and the model is rewritten as an unconstrained model, and net flux is shown to be a linear combination of the parameters of the model.
Abstract: Statistical aspects of estimating net fluxes of nutrients between a salt marsh and a tidal creek on a tidal cycle basis and an annual basis are explored. For individual tidal cycles, the instantaneous flux of a nutrient is written in a constrained linear model as a function of time. The model is rewritten as an unconstrained model, and net flux is shown to be a linear combination of the parameters of the model. Standard linear models techniques can be used to make inferences about net fluxes on a tidal cycle basis. Considering a year as a finite population of tidal cycles, annual net flux can be estimated using a regression estimator. In the case of the flux of dissolved nitrite plus nitrate, the marsh was found to be a statistically significant sink for nitrogen (in this form) from adjacent tidal creeks.
TL;DR: Cluster and nodal analyses identified four broad assemblages based on habitat: 1) an open marsh assemblage, 2) a creek assemblaging, 3) a eurytopic assembLage, and 4) an impoundment assemblAGE.
Abstract: Forty-eight core and grab samples were taken from two impoundments and an adjacent tidal creek and salt marsh during each of six sampling periods (January, June and November 1983; and January, April and July 1984). Habitats sampled within the impoundments included the perimeter ditch and shallow vegeted areas dominated byRuppia maritima, Spartina alterniflora, andScirpus robustus. The adjacent tidal creek bottom and low marsh ofS. alterniflora were sampled for comparison with the impoundment sites. Major differences in faunal composition and density of macrobenthic invertebrates were observed between habitats in this study. Macrobenthic density was highest (475 individuals 0.05 m−2) at the impoundment site dominated byScripus robustus, where oligochaetes were abundant. The open marsh site had a density of 254 individuals 0.05 m−2. Among unvegetated sites, density for all sampling periods was higher in Chainey Creek than in the perimeter ditches of the impoundments. The total number of taxa was highest for the open marsh and tidal creek sites. The impoundments contained vegetated sites which were inhabited by fewer species than nonimpounded sites, while the perimeter ditch sites were comparatively depauperate. Cluster and nodal analyses identified four broad assemblages based on habitat: 1) an open marsh assemblage, 2) a creek assemblage, 3) a eurytopic assemblage, and 4) an impoundment assemblage. The separation of faunal assemblages by sampling site rather than sampling period suggests that physical differences between habitats were important factors determining distribution patterns.
TL;DR: The role of tides in the redistribution of aquatic macrophyte primary production in the Swartvlei estuary was discussed in this article, showing that the amount of plant material transported during spring tides was 2 to 3 times greater than that carried during neap tides.
Abstract: The Swartvlei estuary possesses a prolific growth of both intertidal and subtidal eelgrass,Zostera capensis. During 1984 less than 12% of the eelgrass beds were located in the upper half of the estuary, yet deposition ofZostera/macroalgal wrack in this region, when the estuary was linked to the sea (open phase), was similar to that in the lower half. Over a period of 20 semidiurnal tidal cycles there was a net gain of 2.5 tonnes dry mass of plant material into the upper reaches. Export of aquatic macrophytes and filamentous algae from the lower reaches toward the sea over 20 tidal cycles amounted to 1.6 tonnes dry mass. The amount of plant material transported during spring tides was 2 to 3 times greater than that carried during neap tides. Shallowing of the estuary mouth due to sand deposition resulted in a decline in the tidal prism and a decrease in macrodetrital flux. Total export ofZostera and associated algae amounted to 0.87 g ash-free dry mass m−2d−1 and represented a monthly export of 18% ofZostera bed biomass. Deposition of plant wrack during the 1984–1985 closed phase amounted to 63 g dry mass per meter of shore per day at the lower reaches site but only 10 g m−1d−1 was recorded at the upper reaches site. The relatively low latter value was attributed to the absence of tidal action which transports macrodetritus from the lower and middle reaches into the upper part of the system. During the 1984 open phase 70 g m−1d−1 was deposited at the lower reaches site and 68 g m−1d−1 at the upper reaches site. The role of tides in the redistribution of aquatic macrophyte primary production in the Swartvlei estuary was therefore clearly underscored.
TL;DR: Differences in tissue concentrations of benzo(a)pyrene derived material were observed between crabs of various sex, maturity, and molt stages, suggesting that localized areas of contamination and episodic contaminant releases may result in xenobiotic body burdens in mobile/migratory species.
Abstract: The blue crab,Callinectes sapidus, is an abundant and widely distributed species in the Chesapeake Bay. It also supports a valuable fishery. Minimal information concerning concentrations of toxic organic compounds in crustaceans of the southern Chesapeake Bay is currently available. As a consequence, a study to determine the tissue burdens and behavior of lipophilic polycylic aromatic compounds (PACs) in these organisms was undertaken. Highest concentrations of PACs were detected in hepatopancreas, followed by ovarian and muscle tissues. Extractable lipid levels in the tissues were positively correlated with organic xenobiotic concentrations. The major contaminants detected in blue crabs sampled from the southern bay were alkylated PACs, as opposed to unsubstituted polynuclear aromatic hydrocarbons which have been reported to predominate in molluscs and sediments of the bay. This dichotomy may be due to differences in contaminant bioavailability or in the relative abilities of the organisms to eliminate xenobiotics. Crabs from both heavily industrialized and relatively undeveloped areas, showed evidence of exposure. These data suggest that localized areas of contamination and episodic contaminant releases may result in xenobiotic body burdens in mobile/migratory species. Crabs acutely exposed to radiolabeled benzo(a)pyrene in the laboratory were capable of rapid bioaccumulation. After transfer to clean water, the organisms efficiently eliminated this material, although at a rate slower than that observed for accumulation. Evidence that ecdysis in crustaceans may affect the disposition of PACs was also witnessed in these experiments. Differences in tissue concentrations of benzo(a)pyrene derived material were observed between crabs of various sex, maturity, and molt stages.
TL;DR: In this paper, the spionid polychaete Paraprionospio pinnata altered the grain-size composition in its foraging area, and these alterations were reflected in grain size changes in the diet.
Abstract: Deposit-feeders often select for particles on the basis of grain size. The available pool of particles at the sediment surface may be modified both by deposit-feeder activity and by sediment transport, but the effects of these alterations on deposit-feeder diet composition have received little attention. In laboratory experiments the spionid polychaeteParaprionospio pinnata altered the grain-size composition in its foraging area, and these alterations were reflected in grain-size changes in the diet. After simulated transport of fine-grain sediments,P. pinnata diets also changed in grain-size composition. Field data were collected from 9 m depth in the lower Chesapeake Bay. A video camera, deployed near the bottom, identified times of sediment transport over a 6-h Period;P. pinnata were collected concurrently for gut analysis. Consistent with predictions from the laboratory experiments,P. pinnata ingested primarily small-grain sizes. During periods of no sediment transport this feeding pattern reduced the relative availability of small particles; larger sediments were incorporated into the diet. Sediment transport may resupply the foraging area with fine-grain particles which are then incorporated into the diet. On these small spatial and time scales, deposit-feeder activity may affect the availability of food resources.
TL;DR: The observed patterns indicate that some differential habitat utilization occurs and that overwintering female crabs are found preferentially in areas characterized by moderate energy regimes and fine, but sandy sediments.
Abstract: A study was conducted to define winter distribution patterns of blue crabs,Callinectes sapidus, in the lower Chesapeake Bay and to relate these patterns to environmental variation. During February 1986 a stratified random survey was conducted to examine the distribution of blue crabs with respect to three major habitat types: 1) high energy, wave- and tide-dominated, spits and shoals; 2) moderate energy, tide-dominated basins; and 3) variable energy, tide-dominated or quiescent channels (natural or cut). Each major habitat type was further stratified on the basis of location (to account for possible salinity effects), resulting in a total of 17 habitat-stratum combinations. Blue crabs exhibited significant differences in abundance among habitats. Crabs were most abundant in the basin habitat and least abundant in the shoal and spit habitat. A posteriori evaluations of abundance patterns in relation to sediment type and depth showed that crabs were significantly more abundant where sediments contained between 41 and 60% sand and at depths exceeding 9 m. The sampled population of blue crabs was dominated by mature females. There were no significant differences in crab sex ratios between habitats, but significant differences between two fixed sites sampled through the winter showed that there were proportionately more male crabs at the western site than there were at the eastern site. The observed patterns indicate that some differential habitat utilization occurs and that overwintering female crabs are found preferentially in areas characterized by moderate energy regimes and fine, but sandy sediments.
TL;DR: Water transport in Four League Bay is strongly influenced by the discharge of the Atchafalaya River and prevailing wind conditions as discussed by the authors, which resulted in an increase in water elevation and the inundation of adjacent marshes.
Abstract: Water transport in Fourleague Bay is strongly influenced by the discharge of the Atchafalaya River and prevailing wind conditions. In three 50-h intensive surveys, we measured transport through the major inlets of the bay during the three major river discharge/weather regimes of the year: strong frontal passage, high river flow, and calm, low river flow. Wind stress caused significant changes in both transport and water levels. North winds, dominant during winter frontal passages, caused a net export of water. During the high river flow survey, southeasterly winds created an opposing hydraulic pressure gradient in the Gulf of Mexico, diverting river flow into Fourleague Bay. This resulted in an increase in water elevation and the inundation of adjacent marshes. We believe that this high-discharge, southerly wind condition is the major mechanism leading to sheet flow and sedimentation on the marsh. Calm, low-discharge conditions, typical of late summer, produced classic tidally-dominated circulation.
TL;DR: Macrobenthos were sampled at 27 sites on a seasonal basis from October 1981 through November 1982, and the results showed that although spatial and species groupings were weak, an underlying sediment-correlated structure persisted for all seasons as discussed by the authors.
Abstract: Macrobenthos were sampled at 27 sites on a seasonal basis from October 1981 through November 1982. Cluster analyses and principal components analyses indicated that although spatial and species groupings were weak, an underlying sediment-correlated structure persisted for all seasons. Weak station groupings resulted from great seasonal and local variability in abundance of several dominant taxa. The most widely distributed species varied the least in density over time. Species richness (number of species) and dominance were uncorrelated. Dominance was correlated with sediment organic content [% total organic carbon (TOC)] and % Mud. Species richness increased with increasing % TOC, reaching a maximum in the range 0.7 to 1.0% TOC (primarily sand stations). At higher organic levels (muddy, sand stations), species richness declined. Muddy sand stations were dominated byAmpelisca abdita. In this community, species richness was inversely correlated both with percent TOC and heavy metals concentrations. In both sand and mud communities, species richness was positively correlated with density (mean number individuals of all species per sample).
TL;DR: Results indicate that ambient population of N. incisa may go through several population “phases” resulting from temporal and spatial fluctuations in recruitment, individual growth and reproductive activity, which may depend on which phase the population is in at the time of disturbance.
Abstract: The infaunal polychaeteNephtys incisa is a dominant constituent of soft-bottom communities in nearshore New England waters. This study quantifies its population ecology under natural conditions and following disturbance (dredge material disposal). Five stations in central Long Island Sound (SREF, 1000E, 400E, 200E and CNTR) representing a gradient of increasing exposure to disposed materials were sampled quarterly for 26 months between May 1982 and June 1984. Population abundances declined continually for 2 years (from approximately 1,500 to 200 individuals m−2) following a peak of high recruitment. At CNTR, the population was decimated following disposal, and thereafter densities remained significantly below other stations. Population size-structure shifted from juvenile domination during the period of high abundance to adult domination as numbers declined. However, numbers of adults declined at 200E and CNTR following disturbance, relative to size-structure changes at other stations. Based on analyses of size-frequency distributions and tooth-rings in the jaws of individualN. incisa, eight cohorts (age-classes) were distinguished during the study period ranging from 3 months to 5 years in age. Growth was spatially and temporally variable; the average growth rate was approximately 15–20 mm (length) a year. Individual growth in most cohorts declined at 200E following disposal. Adults were reproductively active throughout the year, with two peaks in egg production, generally in the spring and fall. There were, however, spatial variations in the spawning cycle, which could influence larval recruitment. Results indicate that ambient population ofNephtys cicasa may go through several population “phases” resulting from temporal and spatial fluctuations in recruitment, individual growth and reproductive activity.Nephtys incisa's response to disturbance may depend on which phase the population is in at the time of disturbance (internal population conditions such as age/size structure) and factors external to the population (e.g., environmental influences on settlement and recruitment and/or the nature of the disturbance). Over 14 months of study, disposal of highly polluted dredge material had a negative impact on several population characteristics ofN. incisa at or near the disposal site (0 to 200 m away), but little or no effects on populations were detected 400 m to approximately 3 km away from the disposal area.
TL;DR: In this article, the longitudinal distribution of suspended matter and total dissolved, and particulate manganese in a small coastal plain estuary is described, and a within-estuary maximum is inversely correlated with river flow, and is a function of residence time in the estuary and resuspension in the upper estuary.
Abstract: The longitudinal distribution of total suspended matter and total, dissolved, and particulate manganese in a small coastal plain estuary is described. The distribution of manganese is a consequence of estuarine circulation; a within-estuary maximum is inversely correlated with river flow, and is a function of residence time in the estuary, resuspension in the upper estuary, and desorption from particles introduced from within the estuary or from the river. The turbidity maximum is similarly most pronounced during low river flows. The upper estuary (salinity <15‰), comprising a small percentage of the total estuary volume during low flow, receives material from the river and along the bottom from the lower estuary; this material is returned to the water column by resuspension and desorption from estuarine and riverine particles. The lower estuary tends to damp out these processes because of the greater volume and (residence) time available for mixing.