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排序方式: 共有446条查询结果,搜索用时 12 毫秒
21.
Zhao Sun Jean‐François Hamel Christopher C. Parrish Annie Mercier 《Ecology and evolution》2015,5(5):1117-1129
Classical optimality models of offspring size and number assume a monotonically increasing relationship between offspring size and performance. In aquatic organisms with complex life cycles, the size–performance function is particularly hard to grasp because measures of performance are varied and their relationships with size may not be consistent throughout early ontogeny. Here, we examine size effects in premetamorphic (larval) and postmetamorphic (juvenile) stages of brooding marine animals and show that they vary contextually in strength and direction during ontogeny and among species. Larger offspring of the sea anemone Urticina felina generally outperformed small siblings at the larval stage (i.e., greater settlement and survival rates under suboptimal conditions). However, results differed when analyses were conducted at the intrabrood versus across‐brood levels, suggesting that the relationship between larval size and performance is mediated by parentage. At the juvenile stage (15 months), small offspring were less susceptible than large ones to predation by subadult nudibranchs and both sizes performed similarly when facing adult nudibranchs. In a sympatric species with a different life history (Aulactinia stella), all juveniles suffered similar predation rates by subadult nudibranchs, but smaller juveniles performed better (lower mortalities) when facing adult nudibranchs. Size differences in premetamorphic performance of U. felina were linked to total lipid contents of larvae, whereas size‐specific predation of juvenile stages followed the general predictions of the optimal foraging strategy. These findings emphasize the challenge in gathering empirical support for a positive monotonic size–performance function in taxa that exhibit complex life cycles, which are dominant in the sea. 相似文献
22.
Agata Di Stefano Marina Verducci Luciana Ferraro Silja K. Hüsing 《Palaeogeography, Palaeoclimatology, Palaeoecology》2010,297(1):37-53
Integrated data of calcareous plankton and benthic foraminifers from the pre-evaporitic interval of Trave section (Central Italy) allowed the reconstruction of surface and bottom-water conditions in the Central Mediterranean during the interval from 7.61 to 6.33 Ma, preceding the Messinian Salinity Crisis.Our data point out a three-step paleoenvironmental evolution. During the first stage (7.61-7.02 Ma) benthic foraminiferal assemblages depict stable, well-oxygenated and ventilated bottom-water conditions, while the surface water records variable temperature and high nutrient conditions, probably associated with strong seasonality. The second stage (7.02-6.70 Ma) points to unfavourable bottom-water condition, triggered by deep-sea stagnation. This is witnessed by a significant decrease in oxygen concentration and biotic diversity, and by the presence of stress-tolerant taxa. A general warming of the surface water and a strongly stratified water column, characterized by an expanded mixed layer, are also recorded.From 6.70 Ma onwards (third stage), a prominent change to more restricted, low-oxygenated, hypersaline conditions at the sea floor is testified by the total disappearance of deep-dwelling planktonic foraminifers and the increasing abundance of stress-tolerant species. Calcareous plankton reflects high instability of the surface water in terms of nutrients, temperature and salinity. During this stage the environmental deterioration reaches intermediate depths in the water column.The initial change toward a step-wise isolation of the Central Mediterranean bottom-waters is probably related to a general warming, responsible for a first slowing-down of the vertical circulation, favouring stratification of surface and intermediate waters and stagnation of bottom-waters. This warming is related to the restricted connection between the Mediterranean Sea and the Atlantic Ocean, which occurred since 7.146 Ma.In the Trave section, the isolation of bottom-waters most likely occurred at the same time as in other Mediterranean sections. However, due to the presence of a hiatus it cannot be excluded that it occurred with a delay of ~ 100 kyr, probably related to the shallower paleodepth of the basin. 相似文献
23.
24.
Karin Karlson Rutger Rosenberg 《Journal of experimental marine biology and ecology》2007,344(2):123-135
This study focused on effects from Monoporeia affinis reworking and ventilation activities on benthic fluxes and mineralization processes during a simulated bloom event. The importance of M. affinis density for benthic solute (O2, ΣNO2− + NO3−, NH4+ and HPO42−) fluxes and sediment reactivity (mobilization of NH4+ and HPO42−) following additions of organic material to the sediment surface was experimentally investigated using sediment-water and closed sediment (jar) incubations. Three different densities of M. affinis were used to resemble a low, medium and high density situation (1300, 2500 and 6400 ind. m− 2, respectively) of a natural amphipod community. The degradation of phytodetritus (Tetraselmis sp., 5 g C m− 2) added to the sediment surface was followed over a period of 20 days. Benthic solute fluxes of O2, ΣNO2− + NO3− and NH4+ were generally progressively stimulated with increasing number of M. affinis, while no such correlation was found for HPO42−. Solute fluxes were initially enhanced 1 to 2 days after the addition of phytodetritius, caused by mineralization of the most labile organic material and a food-stimulated irrigation by the amphipods. There was no effect from the activity of M. affinis on total denitrification (Dtot = Dn + Dw) or denitrification utilizing nitrate from coupled nitrification/denitrification (Dn) for any of the densities examined. Denitrification utilizing overlying water nitrate (Dw) was only about 10% of Dtot. Dw was significantly enhanced for the highest M. affinis density investigated. The reactivity of the sediment decreased progressively with increasing density of M. affinis and with time of the experiment. However, enhanced ammonium production at least 6 days after the organic addition indicated excretion of N-containing organic compounds by M. affinis. In conclusion, large spatial and temporal variations in density of M. affinis may be of significant importance for benthic solute fluxes and overall mineralization of organic material in Baltic Sea sediments. 相似文献
25.
Rebecca L. Taylor 《Journal of experimental marine biology and ecology》2007,341(1):60-69
Diatoms that produce toxic oxylipins can be detrimental to the reproductive success of aquatic invertebrates. Despite the potential importance of these toxins in shaping aquatic ecosystems, marine studies to date have focused almost exclusively on planktonic calanoid copepods. The current work examines the response of the benthic harpacticoid copepod, Tisbe holothuriae, to direct exposure to diatom-derived oxylipins and the short-term impact of oxylipin-producing diatom diets on reproductive success. The most toxic oxylipin was the polyunsaturated aldehyde (PUA) 2E,4E-decadienal with an LD50 of 9.3 μM for T. holothuriae nauplii. The least tolerant life-stage was the nauplius followed by adult males then adult females. Short-term exposure to PUA-producing diatoms (Skeletonema marinoi and Melosira nummuloides) in maternal diets had no significant impact on reproductive success compared with non-PUA-producing diets (Skeletonema costatum, Navicula hanseni, Phaeodactylum tricornutum and Tetraselmis suecica). The PUA producers had no negative impact on the survival and development of naupliar stages to adulthood. T. holothuriae expresses a higher degree of tolerance to PUA-producing diatoms than many planktonic calanoids, possibly reflecting a degree of adaptation to higher stress levels associated with the benthos. This is the first study to investigate the reproductive responses of harpacticoid copepods feeding on known PUA-producing diatoms. 相似文献
26.
Bryan L. Brown 《Hydrobiologia》2007,586(1):93-106
Both habitat heterogeneity and disturbance can profoundly influence ecological systems at many levels of biological and ecological
organization. However, the joint influences of heterogeneity and disturbance on temporal variability in communities have received
little attention despite the intense homogenizing influence of human activity. I performed a field manipulation of substrate
heterogeneity in a small New England stream, and measured changes in benthic macroinvertebrate communities for 100 days—a
period that included both a severe drought and a flood. Generally, community variability decreased with increasing substrate
heterogeneity. However, within sampling intervals, this relationship tended to fluctuate through time, apparently tracking
changes in hydrology. At the beginning of the experiment, community temporal variability clearly decreased along a gradient
of increasing substrate heterogeneity—a result consistent with an observational study performed the previous year. During
the subsequent weeks, droughts and flooding created exceptionally high variability in both hydrology and benthic macroinvertebrate
community structure resulting in the disappearance of this relationship. However, during the last weeks of the experiment
when hydrologic conditions were relatively more stable, the negatively sloped relationship between community temporal variability
and habitat heterogeneity reemerged and mimicked relationships observed both early in the experiment and in the previous year’s
study. High habitat heterogeneity may promote temporal stability through several mechanisms including stabilization of resources
and increased refugia from minor disturbances or predation. However, the results of this experiment suggest that severe disturbance
events can create large-scale environmental variability that effectively swamps the influence of habitat heterogeneity, illustrating
that a thorough understanding of community temporal variability in natural systems will necessarily consider sources of environmental
variability at multiple spatial and temporal scales.
Handling editor: L. M. Bini 相似文献
27.
Spatial and temporal distribution patterns of the macrozoobenthos assemblage in the salt marshes of Tejo estuary (Portugal) 总被引:1,自引:0,他引:1
The present study focuses on the spatial and temporal distribution of the macroinvertebrate community of the salt marsh areas
of the Tejo estuary, based on surveys conducted from autumn 1998 to summer 2000. Samples were collected quarterly in five
different intertidal areas along an elevation gradient in: mudflats, creek mouths, creeks, pioneer salt marsh areas and middle
marsh areas. A total of 36 benthic invertebrate taxa were identified. Insect larvae were the most well represented group,
with 10 taxa identified. Oligochaetes and ostracods were the most numerically abundant taxa, whereas bivalves dominated in
biomass. Benthic macroinvertebrate assemblages were dominated, both in number and biomass, by deposit feeders. Three distinct
macroinvertebrate assemblages were distinguished along the elevation gradient, based on species presence, density and biomass:
the unvegetated muddy areas with a macrobenthic assemblage composed mostly by infauna; the salt marsh pioneer areas of Spartina maritima in which several epibenthic taxa were found, as well as endobenthic taxa characteristic of muddy sediment; and the creek
margins, with epifauna taxa such as insect larvae and crustaceans and a low abundance of benthic infauna. Total biomass in
the unvegetated and Spartina areas was higher during spring and summer mainly due to the increase in biomass of Scrobicularia plana and Hydrobia ulvae. No decreases in the salt marsh macroinvertebrate biomass values were observed during the highest densities of their potential
nektonic predators (summer). This fact might indicate that macroinvertebrates are not a limiting resource for the nektonic
species, and that the natural biomass increment of these invertebrate species could be masking the predation/disturbance caused
by the nektonic species. 相似文献
28.
The aim of the study was to evaluate the long-term development of a hard bottom benthic assemblage over a period of 20 years
in an area off the mouth of a large river. The artificial reef of Fregene was selected because benthic assemblage data were
available for the period 1981–1992. This artificial reef is located in the mid Tyrrhenian Sea, 5 nautical miles north of the
two mouths of the Tevere River (Latium, Italy) and 1.5 nautical miles offshore from Fregene (Rome, Italy). The artificial
reef was deployed in March 1981 for fisheries enhancement in 10–14 m of water on a sandy-silty seabed. The Tevere River carries
suspended materials and a heavy load of organics since it transports Rome’s effluent, resulting in the eutrophic state of
area waters. Benthic sampling was conducted in 2001 by SCUBA diving; two standard surfaces of 400 cm2 were scraped from the vertical walls of the same uppermost block in four different periods. All organisms were identified
and counted. The methodology used is the same as that adopted in the previous periods, so that the 2001 data could be compared
with past collected data. The benthic assemblage was analysed by cluster analysis using the Bray-Curtis index and clustered
using the group average clustering algorithm. The SIMPER procedure was used to identify those taxa that characterize each
station group identified by cluster analysis. Changes in benthic assemblages and hydrological trends of the Tevere River were
investigated using the cumulative sum series method. The 20-year development of the benthic community, starting from the new
substratum, is composed of different phases characterised by different benthic assemblages. In particular five different phases
were distinguished: 1. Pioneer species recruitment (May 1981–June 1981); 2. Mytilus galloprovincialis (mussel) dominance (August 1981–November 1983); 3. M. galloprovincialis regression (July 1984–October 1985); 4. M. galloprovincialis absence (91–92); 5. Bryozoans bioconstruction dominance (2001). The dynamic succession of the observed benthic assemblages
exhibited a good relation with the Tevere River flow. The Tevere River flow, and the subsequent sedimentation process, seems
to have strongly influenced the benthic assemblage succession of the Fregene artificial reef.
Guest editors: G. Relini & J. Ryland
Biodiversity in Enclosed Seas and Artificial Marine Habitats 相似文献
29.
30.
Mayumi Yoshimura 《Biodiversity and Conservation》2007,16(7):2137-2148
We compared benthic invertebrate assemblages among headwater streams in several forest types in Japan. Forests were divided
into three clusters based on vegetation composition: old-growth broad-leaved forest, planted coniferous forest, and mixed
forest. The numbers of individuals and families and the diversity (Shannon-Wiener) of benthic invertebrate assemblages did
not differ significantly among the three forest clusters. However, principal components analysis of family abundance showed
differences in the benthic invertebrate assemblages among the three forest clusters. No environmental factors were correlated
with these differences. Benthic invertebrate assemblages differed depending on forest composition. The abundances of Taeniopterygidae
and Athericidae in old-growth broad-leaved forest were significantly greater than in planted coniferous forest. The abundances
of Heptageniidae, Baetiidae, Stenopsychidae, Uenoidae, Chironomidae, and Potamidae in planted coniferous forest were significantly
greater than in old-growth broad-leaved forest. If the remaining old-growth broad-leaved forest were to be converted to coniferous
plantation, species that inhabit old-growth forest may become extinct. 相似文献