Marine fisheries in coastal ecosystems in many areas of the world have historically removed large-bodied individuals, potentially impairing ecosystem functioning and the long-term sustainability of fish populations. Reporting on size-based indicators that link to food-web structure can contribute to ecosystem-based management, but the application of these indicators over large (cross-ecosystem) geographical scales has been limited to either fisheries-dependent catch data or diver-based methods restricted to shallow waters (<20 m) that can misrepresent the abundance of large-bodied fished species. We obtained data on the body-size structure of 82 recreationally or commercially targeted marine demersal teleosts from 2904 deployments of baited remote underwater stereo-video (stereo-BRUV). Sampling was at up to 50 m depth and covered approximately 10,000 km of the continental shelf of Australia. Seascape relief, water depth, and human gravity (i.e., a proxy of human impacts) were the strongest predictors of the probability of occurrence of large fishes and the abundance of fishes above the minimum legal size of capture. No-take marine reserves had a positive effect on the abundance of fishes above legal size, although the effect varied across species groups. In contrast, sublegal fishes were best predicted by gradients in sea surface temperature (mean and variance). In areas of low human impact, large fishes were about three times more likely to be encountered and fishes of legal size were approximately five times more abundant. For conspicuous species groups with contrasting habitat, environmental, and biogeographic affinities, abundance of legal-size fishes typically declined as human impact increased. Our large-scale quantitative analyses highlight the combined importance of seascape complexity, regions with low human footprint, and no-take marine reserves in protecting large-bodied fishes across a broad range of species and ecosystem configurations. 相似文献
Comparative use of shelter use by three sympatric species of combtooth blenny (Ecsenius stictus, Glyptoparus delicatulus, and Salarias patzneri) was studied among micro-atolls in the lagoon at Lizard Island (14°42′S, 145°30′E), northern Great Barrier Reef, Australia. Blenny species used different sized holes; however, the average diameter and depth of holes used by the smallest and largest species differed by only 4 and 25 mm, respectively, indicating interspecific differences in suitable refuge can be very subtle. Both hole diameter and depth were positively related to total length of fish, suggesting use of holes relates to interspecific differences in body size. Total abundance of blennies was best explained by a general linear model that included either the number of holes or total habitat area on individual micro-atolls, predictor variables that were positively correlated with each other. However, the relative importance of variables differed among the three species, feeding area being most important for S. patzneri, feeding area and number of holes for E. stictus, and variance in hole diameter being the best explanatory variable for G. delicatulus abundance. The number of blenny species on a micro-atoll was best explained by variance in hole diameter, emphasizing the influence of refuge size variety in fish diversity. It is likely that subtle habitat partitioning, which relates to interspecific differences in body size, contributes to the co-existence of blenny species within the same microhabitat, but presence of holes is unlikely to regulate abundance of these fish. 相似文献
Previous studies suggested environmental exposures, including mercury (Hg) and lead (Pb), may be related to Wegener's granulomatosis. In this study, investigations were extended to include the measurement of heavy metals in blood samples from patients diagnosed with Wegener's. Diagnosis was confirmed by using the 1990 Classification Criteria for Wegener's granulomatosis established by the American College of Rheumatology (ACR). Using commercial lab testing, whole blood heavy metal screenings were obtained from patients, and results were then compared with validated subject self-report questionnaire estimates of exposure. Thirty-eight Wegener's patients were enrolled; 10 of the 38 exhibited abnormal lab values. In those 10 subjects 3 had elevated nickel (Ni), 7 with increased cobalt (Co), 3 with higher manganese, 1 with elevated copper, and 1 with increased Hg. Overall, the questionnaire results did not correlate with the blood heavy metal analysis. Approximately 26% of Wegener's subjects in this study displayed abnormal heavy metal levels. These findings are likely underestimates since blood levels are an insensitive means for assessing total body burden of heavy metals. From these preliminary studies it appears that elevated Co is a common finding in Wegener's patients but Ni and Hg were also found to be increased. The proportion of patients with abnormal heavy metal levels is more than expected by chance alone. In order to yield more definitive results, further analysis is needed with a larger data set, more controls and more sensitive measurements (hair, urine, or nail samples). 相似文献
The spatial scale of similarity among fish communities is characteristically large in temperate marine systems: connectivity is enhanced by high rates of dispersal during the larval/juvenile stages and the increased mobility of large-bodied fish. A larger spatial scale of similarity (low beta diversity) is advantageous in heavily exploited systems because locally depleted populations are more likely to be "rescued" by neighboring areas. We explored whether the spatial scale of similarity changed from 1970 to 2006 due to overfishing of dominant, large-bodied groundfish across a 300 000-km2 region of the Northwest Atlantic. Annually, similarities among communities decayed slowly with increasing geographic distance in this open system, but through time the decorrelation distance declined by 33%, concomitant with widespread reductions in biomass, body size, and community evenness. The decline in connectivity stemmed from an erosion of community similarity among local subregions separated by distances as small as 100 km. Larger fish, of the same species, contribute proportionally more viable offspring, so observed body size reductions will have affected maternal output. The cumulative effect of nonlinear maternal influences on egg/larval quality may have compromised the spatial scale of effective larval dispersal, which may account for the delayed recovery of certain member species. Our study adds strong support for using the spatial scale of similarity as an indicator of metacommunity stability both to understand the spatial impacts of exploitation and to refine how spatial structure is used in management plans. 相似文献
Lamellibrachia luymesi and Seepiophila jonesi are co-occurring species of vestimentiferan tubeworms found at hydrocarbon seepage sites on the upper Louisiana slope of
the Gulf of Mexico. Like all vestimentiferans, they rely on internal sulfide-oxidizing symbiotic bacteria for nutrition. These
symbionts produce hydrogen ions as a byproduct of sulfide oxidation, which the host tubeworm needs to eliminate to prevent
acidosis. The hydrothermal vent tubeworm Riftia pachyptila uses a high activity of P- and V-type H+-ATPases located in its plume epithelium to excrete protons. Unlike R. pachyptila, the seep species grow a posterior root, which they can use in addition to their plumes as a nutrient exchange surface. In
this study we measured the ATPase activities of plume and root tissues collected from L. luymesi and S. jonesi, and used a combination of inhibitors to determine the relative activities of P- and V-type H+-ATPases. We found that the total H+-ATPase activity of their plumes was approximately 14 μmol h−1 g−1 wet weight, and that of their roots was between 5 and 7 μmol h−1 g−1 wet weight. These activities were more than ten times lower than those measured in R. pachyptila. We suggest that seep tubeworms might use passive channels to eliminate protons across their roots, in addition to ATP-dependant
proton pumps located in their plumes and roots. In addition, we found strong differences between the types of ATPase activities
in the plumes of L. luymesi and S. jonesi. While the H+-ATPase activity of L. luymesi plumes is dominated by P-type ATPases, S. jonesi has an unusually high activity of V-type H+-ATPases. We suggest that S. jonesi relies on its high V-type H+-ATPase activity to drive carbon dioxide uptake across its plume surface. L. luymesi, on the other hand, might rely partially on bicarbonate uptake across its root. 相似文献
Regime shifts of major salinity constituents (Ca, Mg, Na, K, SO4, Cl, HCO3, and NO3) in the lower Salinas River, an agricultural ecosystem, can have major impacts on ecosystem services central to continued agricultural production in the region. Regime shifts are large, persistent, and often abrupt changes in the structure and dynamics of social-ecological systems that occur when there is a reorganization of the dominant feedbacks in the system. Monitoring information on changes in the system state, controlling variables, and feedbacks is a crucial contributor to applying sustainability and ecosystem resilience at an operational level. To better understand the factors driving salinization of the lower Salinas River on the central coast of California, we examined a 27-year record of concentrations of major salinity constituents in the river. Although limited in providing an understanding of solute flux behavior during storm events, long-term “grab sampling” datasets with accompanying stream discharges can be used to estimate the actual history of concentrations and fluxes. We developed new concentration–discharge relationships to evaluate the dynamics of chemical weathering, hydrological processes, and agricultural practices in the watershed. Examinations of long-term records of surface water and groundwater salinity are required to provide both understanding and perspective towards managing salinity in arid and semi-arid regions while also enabling determination of the influence of external climatic variability and internal drivers in the system. We found that rock weathering is the main source of Ca, Mg, Na, HCO3, and SO4 in the river that further enables ion exchange between Ca, Mg, and Na. River concentrations of K, NO3, and Cl were associated with human activities while agricultural practices were the major source of K and NO3. A more direct anthropogenic positive trend in NO3 that has persisted since the mid-1990s is associated with the lag or memory effects of field cropping and use of flood irrigation. Event to inter-year scale patterns in the lower Salinas River salinity are further controlled by antecedent hydrologic conditions. This study underscores the importance of obtaining long-term monitoring records towards understanding watershed changes-of-state and time constants on the range of driving processes.
We report nutrient addition bioassays at 18 stations in Chesapeake Bay (USA) to assess resources limiting phytoplankton growth.
Data were pooled from several sampling programs conducted from 1989 to 1994. Spatially, light and P limitation declined from
low salinity regions to high salinity regions, as N limitation increased. This spatial pattern was driven primarily by freshwater
inflows with high N/P and seawater inflows with low N/P. Seasonally, there was a marked progression of winter light limitation,
spring P limitation, and summer N limitation at mesohaline and polyhaline stations. The seasonal pattern appeared to be caused
by temperature, mixing, river discharge, and sediment P fluxes. At high salinity stations, we also observed winter N limitation
(caused by DIN depletion prior to spring nitrate delivery), and at lower salinity stations there was fall P limitation (caused
by reaeration of bottom sediments). At tidal fresh stations, turbidity and nutrient concentrations resulted in continuous
light limitation, except at some stations in summer. Interannual decreases in light limitation and increases in N and P limitation
appear to represent improvements in water quality.
Received: 31 October 1997 / Accepted: 18 December 1998 相似文献
Severe fluid forces are believed to be a source of injury and mortality to fish that pass through hydroelectric turbines.
A process is described by which laboratory bioassays, computational fluid dynamics models, and field studies can be integrated
to evaluate the significance of fluid shear stresses that occur in a turbine. Areas containing potentially lethal shear stresses
were identified near the stay vanes and wicket gates, runner, and in the draft tube of a large Kaplan turbine. However, under
typical operating conditions, computational models estimated that these dangerous areas comprise less than 2% of the flow
path through the modeled turbine. The predicted volumes of the damaging shear stress zones did not correlate well with observed
fish mortality at a field installation of this turbine, which ranged from less than 1% to nearly 12%. Possible reasons for
the poor correlation are discussed. Computational modeling is necessary to develop an understanding of the role of particular
fish injury mechanisms, to compare their effects with those of other sources of injury, and to minimize the trial and error
previously needed to mitigate those effects. The process we describe is being used to modify the design of hydroelectric
turbines to improve fish passage survival. 相似文献