Variable Nitrification Rates Across Environmental Gradients in Turbid,Nutrient-Rich Estuary Waters of San Francisco Bay     

Julian Damashek  Karen L. Casciotti  Christopher A. Francis 《Estuaries and Coasts》2016,39(4):1050-1071

Understanding rates of nitrogen cycling in estuaries is crucial for understanding their productivity and resilience to eutrophication. Nitrification, the microbial oxidation of ammonia to nitrite and nitrate, links reduced and oxidized forms of inorganic nitrogen and is therefore an important step of the nitrogen cycle. However, rates of nitrification in estuary waters are poorly characterized. In fall and winter of 2011–2012, we measured nitrification rates throughout the water column of all major regions of San Francisco Bay, a large, turbid, nutrient-rich estuary on the west coast of North America. Nitrification rates were highest in regions furthest from the ocean, including many samples with rates higher than those typically measured in the sea. In bottom waters, nitrification rates were commonly at least twice the magnitude of surface rates. Strong positive correlations were found between nitrification and both suspended particulate matter and ammonium concentration. Our results are consistent with previous studies documenting high nitrification rates in brackish, turbid regions of other estuaries, many of which also showed correlations with suspended sediment and ammonium concentrations. Overall, nitrification in estuary waters appears to play a significant role in the estuarine nitrogen cycle, though the maximum rate of nitrification can differ dramatically between estuaries.  相似文献   

<Emphasis Type="Italic">Deepwater Horizon</Emphasis> Oil Spill Impacts on Salt Marsh Fiddler Crabs (<Emphasis Type="Italic">Uca</Emphasis> spp.)     

Scott Zengel  Steven C. Pennings  Brian Silliman  Clay Montague  Jennifer Weaver  Donald R. Deis  Michelle O. Krasnec  Nicolle Rutherford  Zachary Nixon 《Estuaries and Coasts》2016,39(4):1154-1163

The Deepwater Horizon oil spill was the largest marine oil spill in US waters to date and one of the largest worldwide. Impacts of this spill on salt marsh vegetation have been well documented, although impacts on marsh macroinvertebrates have received less attention. To examine impacts of the oil spill on an important marsh invertebrate and ecosystem engineer, we conducted a meta-analysis on fiddler crabs (Uca spp.) using published sources and newly available Natural Resources Damage Assessment (NRDA) and Gulf of Mexico Research Initiative (GoMRI) data. Fiddler crabs influence marsh ecosystem structure and function through their burrowing and feeding activities and are key prey for a number of marsh and estuarine predators. We tested the hypothesis that the spill affected fiddler crab burrow density (crab abundance), burrow diameter (crab size), and crab species composition. Averaged across multiple studies, sites, and years, our synthesis revealed a negative effect of oiling on all three metrics. Burrow densities were reduced by 39 % in oiled sites, with impacts and incomplete recovery observed over 2010–2014. Burrow diameters were reduced from 2010 to 2011, but appeared to have recovered by 2012. Fiddler crab species composition was altered through at least 2013 and only returned to reference conditions where marsh vegetation recovered, via restoration planting in one case. Given the spatial and temporal extent of data analyzed, this synthesis provides compelling evidence that the Deepwater Horizon spill suppressed populations of fiddler crabs in oiled marshes, likely affecting other ecosystem attributes, including marsh productivity, marsh soil characteristics, and associated predators.  相似文献   

Submergence and Herbivory as Divergent Causes of Marsh Loss in Long Island Sound     

Rebecca A. Schultz  Shimon C. Anisfeld  Troy D. Hill 《Estuaries and Coasts》2016,39(5):1367-1375

Tidal marsh degradation has been attributed to a number of different causes, but few studies have examined multiple potential factors at the same sites. Differentiating the diverse drivers of marsh loss is critical to prescribing successful interventions for conservation and restoration of this important habitat. We evaluated two hypotheses for vegetation loss at two marshes in Long Island Sound (LIS): (1) marsh submergence, caused by an imbalance between sea-level rise and marsh accretion, and (2) defoliation associated with herbivory by the purple marsh crab, Sesarma reticulatum. At our western LIS site, we found no evidence of herbivory: crabs were scarce, and crab-exclusion cages provided no benefit. We attribute degradation at that site to submergence, a conclusion supported by topographic and hydrologic data showing that loss of vegetation occurred only in wetter parts of the marsh. In contrast, at our central LIS site, our observations were consistent with herbivory as a driving force: There were substantial populations of Sesarma, crab-exclusion cages allowed plants to thrive, and vegetation loss took place across a variety of elevations. We also analyzed soil conditions at both sites, in order to determine the signatures of different degradation processes and assess the potential for restoration. At the submergence site, unvegetated soils exhibited high bulk density, low organic content, and low soil strength, posing significant biogeochemical challenges to re-colonization by vegetation. At the herbivory site, unvegetated soils had a characteristic “riddled-peat” appearance, resulting from expansion and erosion of Sesarma burrow networks. The high redox potential and organic content of those soils suggested that revegetation at the herbivory site would be likely if Sesarma populations could be controlled before erosion leads to elevation loss.  相似文献   

Structural and Functional Composition of Benthic Nematode Assemblages During a Natural Recovery Process of <Emphasis Type="Italic">Zostera noltii</Emphasis> Seagrass Beds     

Patrick Materatski  Anna-Maria Vafeiadou  Tom Moens  Helena Adão 《Estuaries and Coasts》2016,39(5):1478-1490

In 2008, the stable seagrass beds of the Mira estuary (SW Portugal) disappeared completely; however, during 2009, they have begun to present early symptoms of natural recovery, characterised by a strongly heterogeneous distribution. This study was designed to investigate the spatial and temporal variability patterns of species composition, densities and trophic composition of the benthic nematode assemblages in this early recovery process, at two sampling sites with three stations each and at five sampling occasions. Because of the erratic and highly patchy seagrass recovery and the high environmental similarity of the two sampling sites, we expected within-site variability in nematode assemblages to exceed between-site variability. However, contrary to that expectation, whilst nematode genus composition was broadly similar between sites, nematode densities differed significantly between sites, and this between-site variability exceeded within-site variability. This may be linked to differences in the Zostera recovery patterns between both sites. In addition, no clear temporal patterns of nematode density, trophic composition and diversity were evident. Nematode assemblages generally resembled those of other estuarine muddy intertidal areas, which have a high tolerance of stress conditions.  相似文献   

Influence of the Mississippi River on <Emphasis Type="Italic">Pseudo-nitzschia</Emphasis> spp. Abundance and Toxicity in Louisiana Coastal Waters     

Sibel Bargu  Melissa M. Baustian  Nancy N. Rabalais  Ross Del Rio  Benjamin Von Korff  R. Eugene Turner 《Estuaries and Coasts》2016,39(5):1345-1356

The presence of domoic acid (DA) toxin from multiple species of Pseudo-nitzschia is a concern in the highly productive food webs of the northern Gulf of Mexico. We documented the Pseudo-nitzschia presence, abundance, blooms, and toxicity over three years along a transect ～100 km west of the Mississippi River Delta on the continental shelf. Pseudo-nitzschia were present throughout the year and occurred in high abundances (>10⁴ cells l^?1) in the early spring months during high Mississippi River (MSR) flow (～20,000 m³ s^?1) but were most abundant (>10⁶ cells l^?1) when MSR discharge was relatively lower among the spring months. A high particulate toxin production (maximum reaching 13 μg DA l^?1) was associated with the high cell abundances and exceeded, by an order of magnitude, prior reports of particulate DA concentrations in Louisiana coastal waters. Differences in Pseudo-nitzschia peak times and its toxicity were correlated mainly with the timing and magnitude of MSR discharge and changes in associated parameters such as nutrient stoichiometry and salinity. A negative relationship between high MSR discharge and Pseudo-nitzschia and particulate DA concentrations was documented. These riverine dynamics have the potential to influence DA contamination in pelagic and benthic food webs in the coastal waters of the northern Gulf of Mexico.  相似文献   

Fish,Macroinvertebrate and Epifaunal Communities in Shallow Coastal Lagoons with Varying Seagrass Cover of the Northern Gulf of Mexico     

Rachel B. McDonald  Ryan M. Moody  Ken L. Heck  Just Cebrian 《Estuaries and Coasts》2016,39(3):718-730

Coastal lagoons are ubiquitous along coastlines worldwide. Here, we compare the abundance of epifauna, seagrass-associated macroinvertebrates, and small fish across a gradient of seagrass cover in shallow coastal lagoons of the northern Gulf of Mexico. Two of the lagoons had little or no seagrass cover (0–18.8 %), and four had high cover (83.8–97.5 %). All of the lagoons were partially covered with fringing marsh. We hypothesized that, due to habitat redundancy between seagrass beds and fringing marshes, seagrass-associated fish and macroinvertebrates would not be largely reduced despite the large differences in seagrass cover among the lagoons. Our results support this hypothesis. For most sampling dates, we did not find significant differences in fish and macroinvertebrate abundance among the lagoons and, when we did, several highly vegetated lagoons did not have larger abundances than sparsely vegetated lagoons. The extreme shallowness of the lagoons studied (<1 m) may also provide further protection from large predatory fishes in the absence of seagrasses. Our results also suggest that marsh detritus, by providing habitat for epifauna and helping maintain prey availability, may further temper reductions in seagrass-associated fishes and macroinvertebrates following seagrass decline. The results highlight the importance of marsh-bordered, shallow lagoons as habitat for small fish and macroinvertebrates regardless of seagrass cover. This study contributes to the characterization of habitat redundancy in coastal ecosystems and pinpoints the importance of considering all habitats in concert for the proper understanding and management of coastal ecosystems.  相似文献   

Spatial and Temporal Variations in <Emphasis Type="Italic">Pyrodinium bahamense</Emphasis> Cyst Concentrations in the Sediments of Bioluminescent Mangrove Lagoon,St. Croix,USVI     

Paula E. Reidhaar  Chad S. Lane  Claudia R. Benitez-Nelson  Douglas W. Gamble 《Estuaries and Coasts》2016,39(3):682-694

Mangrove Lagoon, located on the island of St. Croix, US Virgin Islands (USVI), is one of few actively bioluminescent lagoons in a location experiencing significant anthropogenic impacts. The bioluminescence is due to an abundance of the dinoflagellate Pyrodinium bahamense in the water column. We recovered surface sediments and sediment cores from Mangrove Lagoon to analyze the spatial distribution and temporal variability of P. bahamense cysts in this system. Surface sediment P. bahamense cyst concentrations ranged from 0 to 466 cysts g^?1 dry sediment, with higher abundances associated with elevated surface water nutrient concentrations and a mixed terrestrial–marine organic matter source regime. In combination with available bioassay data, we hypothesize that phytoplankton utilize nutrients rapidly and subsequent decay of organic matter makes nutrients available for dinoflagellates at the sediment–water interface in the eastern and northern quadrants of the lagoon. However, the nutrients are rapidly exhausted during counterclockwise lagoon circulation resulting in the decline of primary productivity and dinoflagellate abundance in the western quadrants. Downcore profiles suggest that P. bahamense blooms have been occurring for decades, declining in recent years. No cysts were present in sediments predating dredging activities of the 1960s that created Mangrove Lagoon. Recent reductions in cyst abundance may be the result of limited primary productivity caused by restricted water exchange with Salt River Bay due to shallowing of a sill at the mouth of the lagoon. This research highlights the need for more comprehensive geochemical and fossil analyses to better understand long-term ecological variability and inform conservation efforts of these unique habitats.  相似文献   

Wetland Loss,Juvenile Salmon Foraging Performance,and Density Dependence in Pacific Northwest Estuaries     

Aaron T. David  Charles A. Simenstad  Jeffery R. Cordell  Jason D. Toft  Christopher S. Ellings  Ayesha Gray  Hans B. Berge 《Estuaries and Coasts》2016,39(3):767-780

During the transition of juveniles from fresh water to estuarine and coastal environments, the survival of Pacific salmon (Oncorhynchus spp.) can be strongly size selective and cohort abundance is partly determined at this stage. Because quantity and quality of food influence juvenile salmon growth, high rates of prey and energy acquisition during estuarine residence are important for survival. Human activities may have affected the foraging performance of juvenile salmon in estuaries by reducing the area of wetlands and by altering the abundance of salmon. To improve our understanding of the effects of wetland loss and salmon density on juvenile salmon foraging performance and diet composition in estuaries, we assembled Chinook salmon (Oncorhynchus tshawytscha) diet and density data from nine US Pacific Northwest estuaries across a gradient of wetland loss. We evaluated the influence of wetland loss and density on juvenile Chinook salmon instantaneous ration and energy ration, two measures of foraging performance, and whether the effect of density varied among estuaries with different levels of wetland loss. We also assessed the influence of wetland loss and other explanatory variables on salmon diet composition. There was no evidence of a direct effect of wetland loss on juvenile salmon foraging performance, but wetland loss appeared to mediate the effect of density on salmon foraging performance and alter salmon diet composition. Specifically, density had no effect on foraging performance in the estuaries with less than 50 % wetland loss but had a negative effect on foraging performance in the estuaries with greater than 50 % wetland loss. These results suggest that habitat loss may interact with density to constrain the foraging performance of juvenile Chinook salmon, and ultimately their growth, during a life history stage when survival can be positively correlated with growth and size.  相似文献   

Influence of Environmental Factors on Spawning of the American Horseshoe Crab (<Emphasis Type="Italic">Limulus polyphemus</Emphasis>) in the Great Bay Estuary,New Hampshire,USA     

Helen Cheng  Christopher C. Chabot  Winsor H. WatsonIII 《Estuaries and Coasts》2016,39(4):1142-1153

The Great Bay Estuary, New Hampshire, USA is near the northern distribution limit of the American horseshoe crab (Limulus polyphemus). This estuary has few ideal beaches for spawning, yet it supports a modest population of horseshoe crabs. There is no organized monitoring program in the Great Bay Estuary, so it is unclear when and where spawning occurs. In this 2-year study (May through June, 2012 and 2013), >5,000 adult horseshoe crabs were counted at four sites in the estuary. The greatest densities of horseshoe crabs were observed at Great Bay sites in the upper, warmer reaches of the estuary. Peaks of spawning activity were not strongly correlated with the times of the new or full moons, and similar numbers of horseshoe crabs were observed mating during daytime and nighttime high tides. While many environmental factors are likely to influence the temporal and spatial patterns of spawning in this estuary, temperature appears to have the most profound impact.  相似文献   

Tide-Induced Variations in the Fatty Acid Composition of Estuarine Particulate Organic Matter     

Emily S. Antonio  Nicole B. Richoux 《Estuaries and Coasts》2016,39(4):1072-1083

The particulate organic matter (POM) in hydrodynamically variable habitats such as the lower reaches of estuaries can change in its content and quality on very short time scales (example, hourly), and these changes can potentially influence higher-level consumers in river-estuary-marine systems. Estuarine water samples were collected hourly for 12 h downstream in a small river to evaluate the fatty acid composition of POM over a tidal cycle. Fatty acid constituents of POM collected during the flood tide were dominated by the saturated, higher plant and bacterial fatty acids, whereas unsaturated, polyunsaturated, essential, and diatom-associated fatty acids dominated the POM collected during the ebb tide. Elevated algal biomass (as indicated by high chlorophyll a concentrations), diatom, and freshness indices in the POM indicated enhanced fresh autochthonous-origin materials that dominated the mixed organic pool during the ebb tide compared to more degraded detritus during the flood tide. Tidal retention of organic matter and algal primary production were the most influential factors that differentiated the fatty acid composition of estuarine POM over the short time scale. The results of this study have important implications on the quality of POM at the time of sampling, especially in estuaries where mixed organic pools have multiple inputs and are strongly influenced by tidal cycles.  相似文献