Upwelling-driven nearshore hypoxia signals ecosystem and oceanographic changes in the northeast Pacific

Seasonal development of dissolved-oxygen deficits (hypoxia) represents an acute system-level perturbation to ecological dynamics and fishery sustainability in coastal ecosystems around the globe. Whereas anthropogenic nutrient loading has increased the frequency and severity of hypoxia in estuaries and semi-enclosed seas, the occurrence of hypoxia in open-coast upwelling systems reflects ocean conditions that control the delivery of oxygen-poor and nutrient-rich deep water onto continental shelves. Upwelling systems support a large proportion of the world's fisheries, therefore understanding the links between changes in ocean climate, upwelling-driven hypoxia and ecological perturbations is critical. Here we report on the unprecedented development of severe inner-shelf (<70 m) hypoxia and resultant mass die-offs of fish and invertebrates within the California Current System. In 2002, cross-shelf transects revealed the development of abnormally low dissolved-oxygen levels as a response to anomalously strong flow of subarctic water into the California Current System. Our findings highlight the sensitivity of inner-shelf ecosystems to variation in ocean conditions, and the potential impacts of climate change on marine communities.     

Ecosystem energetic implications of parasite and free-living biomass in three estuaries

Parasites can have strong impacts but are thought to contribute little biomass to ecosystems. We quantified the biomass of free-living and parasitic species in three estuaries on the Pacific coast of California and Baja California. Here we show that parasites have substantial biomass in these ecosystems. We found that parasite biomass exceeded that of top predators. The biomass of trematodes was particularly high, being comparable to that of the abundant birds, fishes, burrowing shrimps and polychaetes. Trophically transmitted parasites and parasitic castrators subsumed more biomass than did other parasitic functional groups. The extended phenotype biomass controlled by parasitic castrators sometimes exceeded that of their uninfected hosts. The annual production of free-swimming trematode transmission stages was greater than the combined biomass of all quantified parasites and was also greater than bird biomass. This biomass and productivity of parasites implies a profound role for infectious processes in these estuaries.     

Rapid worldwide depletion of predatory fish communities

Serious concerns have been raised about the ecological effects of industrialized fishing, spurring a United Nations resolution on restoring fisheries and marine ecosystems to healthy levels. However, a prerequisite for restoration is a general understanding of the composition and abundance of unexploited fish communities, relative to contemporary ones. We constructed trajectories of community biomass and composition of large predatory fishes in four continental shelf and nine oceanic systems, using all available data from the beginning of exploitation. Industrialized fisheries typically reduced community biomass by 80% within 15 years of exploitation. Compensatory increases in fast-growing species were observed, but often reversed within a decade. Using a meta-analytic approach, we estimate that large predatory fish biomass today is only about 10% of pre-industrial levels. We conclude that declines of large predators in coastal regions have extended throughout the global ocean, with potentially serious consequences for ecosystems. Our analysis suggests that management based on recent data alone may be misleading, and provides minimum estimates for unexploited communities, which could serve as the 'missing baseline' needed for future restoration efforts.     

Lagged effects of ocean climate change on fulmar population dynamics

Environmental variation reflected by the North Atlantic Oscillation affects breeding and survival in terrestrial vertebrates, and climate change is predicted to have an impact on population dynamics by influencing food quality or availability. The North Atlantic Oscillation also affects the abundance of marine fish and zooplankton, but it is unclear whether this filters up trophic levels to long-lived marine top predators. Here we show by analysis of data from a 50-year study of the fulmar that two different indices of ocean climate variation may have lagged effects on population dynamics in this procellariiform seabird. Annual variability in breeding performance is influenced by the North Atlantic Oscillation, whereas cohort differences in recruitment are related to temperature changes in the summer growing season in the year of birth. Because fulmars exhibit delayed reproduction, there is a 5-year lag in the population's response to these effects of environmental change. These data show how interactions between different climatic factors result in complex dynamics, and that the effects of climate change may take many years to become apparent in long-lived marine top predators.     

Ecological responses to recent climate change

There is now ample evidence of the ecological impacts of recent climate change, from polar terrestrial to tropical marine environments. The responses of both flora and fauna span an array of ecosystems and organizational hierarchies, from the species to the community levels. Despite continued uncertainty as to community and ecosystem trajectories under global change, our review exposes a coherent pattern of ecological change across systems. Although we are only at an early stage in the projected trends of global warming, ecological responses to recent climate change are already clearly visible.     

Group formation stabilizes predator-prey dynamics

Theoretical ecology is largely founded on the principle of mass action, in which uncoordinated populations of predators and prey move in a random and well-mixed fashion across a featureless landscape. The conceptual core of this body of theory is the functional response, predicting the rate of prey consumption by individual predators as a function of predator and/or prey densities. This assumption is seriously violated in many ecosystems in which predators and/or prey form social groups. Here we develop a new set of group-dependent functional responses to consider the ecological implications of sociality and apply the model to the Serengeti ecosystem. All of the prey species typically captured by Serengeti lions (Panthera leo) are gregarious, exhibiting nonlinear relationships between prey-group density and population density. The observed patterns of group formation profoundly reduce food intake rates below the levels expected under random mixing, having as strong an impact on intake rates as the seasonal migratory behaviour of the herbivores. A dynamical system model parameterized for the Serengeti ecosystem (using wildebeest (Connochaetes taurinus) as a well-studied example) shows that grouping strongly stabilizes interactions between lions and wildebeest. Our results suggest that social groups rather than individuals are the basic building blocks around which predator-prey interactions should be modelled and that group formation may provide the underlying stability of many ecosystems.     

Consistent patterns and the idiosyncratic effects of biodiversity in marine ecosystems

Revealing the consequences of species extinctions for ecosystem function has been a chief research goal and has been accompanied by enthusiastic debate. Studies carried out predominantly in terrestrial grassland and soil ecosystems have demonstrated that as the number of species in assembled communities increases, so too do certain ecosystem processes, such as productivity, whereas others such as decomposition can remain unaffected. Diversity can influence aspects of ecosystem function, but questions remain as to how generic the patterns observed are, and whether they are the product of diversity, as such, or of the functional roles and traits that characterize species in ecological systems. Here we demonstrate variable diversity effects for species representative of marine coastal systems at both global and regional scales. We provide evidence for an increase in complementary resource use as diversity increases and show strong evidence for diversity effects in naturally assembled communities at a regional scale. The variability among individual species responses is consistent with a positive but idiosyncratic pattern of ecosystem function with increased diversity.     

Ecosystem remodelling among vertebrates at the Permian-Triassic boundary in Russia

The mass extinction at the Permian-Triassic boundary, 251 million years (Myr) ago, is accepted as the most profound loss of life on record. Global data compilations indicate a loss of 50% of families or more, both in the sea and on land, and these figures scale to a loss of 80-96% of species, based on rarefaction analyses. This level of loss is confirmed by local and regional-scale studies of marine sections, but the terrestrial record has been harder to analyse in such close detail. Here we document the nature of the event in Russia in a comprehensive survey of 675 specimens of amphibians and reptiles from 289 localities spanning 13 successive geological time zones in the South Urals basin. These changes in diversity and turnover cannot be explained simply by sampling effects. There was a profound loss of genera and families, and simplification of ecosystems, with the loss of small fish-eaters and insect-eaters, medium and large herbivores and large carnivores. Faunal dynamics also changed, from high rates of turnover through the Late Permian period to greater stability at low diversity through the Early Triassic period. Even after 15 Myr of ecosystem rebuilding, some guilds were apparently still absent-small fish-eaters, small insect-eaters, large herbivores and top carnivores.     

复杂泄漏方式下的海上溢油行为归宿数值模拟及应用

为对海洋溢油风险及其生态环境损害影响进行评估,及时制订溢油事故应急反应决策,基于油粒子追踪法建立多源泄漏、移动泄漏等复杂泄漏方式下海上溢油行为归宿的数值模拟方法,包括海面溢油在风和海流作用下的迁移、扩散、蒸发、溶解、乳化、分散等行为动态和风化过程,并以接连发生在大连新港附近的两起船舶溢油事故作为多源泄漏的典型案例进行应用研究.结果表明,海面油膜时空分布模拟结果与调查监测数据符合较好,油污影响范围与观测报道结果基本吻合.     

典型海洋生态系统中关键种的研究进展

随着人类对生态环境和生物多样性保护意识的增强，基于食物网结构和物种间相互作用的关键种(Keystone species)这一概念一经提出就引起了广泛关注和讨论，相关研究亦成为国际生态学研究的热点。本文从关键种概念起源出发，探讨了关键种定义中丰度与作用的不成比例性、在实际应用中存在的模糊性和无法量化等问题，综述了不同类型海洋生态系统中关键种的特点和共性问题，探讨人类作为超级关键种(Hyperkeystone species)对海洋的影响，并尝试提出人类应当如何理性看待关键种及其在海洋生态系统中的功能和作用。     

^226Ra evidence for the ecosystem shift over the past 40 years in the North Pacific Subtropical Gyre

Surface seawater was collected for ~(226)Ra measurement in the North Pacific Subtropical Gyre from July to October, 1999 and October to December, 2003. Combined with the historical data reported for this sea area, a declined trend of surface ~(226)Ra concentrations was observed since 1960s, indicating the ecosystem shift in response to global warming. On one side, the enhanced stratification of the upper water column resulting from global warming reduced the ~(226)Ra input from the depth, on the other, the temporal increase of biological production resulting from the climate-related ecosystem structure change strengthened the ~(226)Ra removal from the surface ocean. Both the physical and biological processes resulted in the decrease of surface ~(226)Ra concentrations in the North Pacific Subtropical Gyre. The temporal trend of surface ~(226)Ra concentrations was consistent with the trends of chlorophyll a, silicate, phosphate and primary production previously reported. This study provided ~(226)Ra evidence for the ecosystem shift under global change.     

Ecosystem size determines food-chain length in lakes

Food-chain length is an important characteristic of ecological communities: it influences community structure, ecosystem functions and contaminant concentrations in top predators. Since Elton first noted that food-chain length was variable among natural systems, ecologists have considered many explanatory hypotheses, but few are supported by empirical evidence. Here we test three hypotheses that predict food-chain length to be determined by productivity alone (productivity hypothesis), ecosystem size alone (ecosystem-size hypothesis) or a combination of productivity and ecosystem size (productive-space hypothesis). The productivity and productive-space hypotheses propose that food-chain length should increase with increasing resource availability; however, the productivity hypothesis does not include ecosystem size as a determinant of resource availability. The ecosystem-size hypothesis is based on the relationship between ecosystem size and species diversity, habitat availability and habitat heterogeneity. We find that food-chain length increases with ecosystem size, but that the length of the food chain is not related to productivity. Our results support the hypothesis that ecosystem size, and not resource availability, determines food-chain length in these natural ecosystems.     

The trophic fingerprint of marine fisheries

Biodiversity indicators provide a vital window on the state of the planet, guiding policy development and management. The most widely adopted marine indicator is mean trophic level (MTL) from catches, intended to detect shifts from high-trophic-level predators to low-trophic-level invertebrates and plankton-feeders. This indicator underpins reported trends in human impacts, declining when predators collapse ("fishing down marine food webs") and when low-trophic-level fisheries expand ("fishing through marine food webs"). The assumption is that catch MTL measures changes in ecosystem MTL and biodiversity. Here we combine model predictions with global assessments of MTL from catches, trawl surveys and fisheries stock assessments and find that catch MTL does not reliably predict changes in marine ecosystems. Instead, catch MTL trends often diverge from ecosystem MTL trends obtained from surveys and assessments. In contrast to previous findings of rapid declines in catch MTL, we observe recent increases in catch, survey and assessment MTL. However, catches from most trophic levels are rising, which can intensify fishery collapses even when MTL trends are stable or increasing. To detect fishing impacts on marine biodiversity, we recommend greater efforts to measure true abundance trends for marine species, especially those most vulnerable to fishing.     

Confronting the coral reef crisis

The worldwide decline of coral reefs calls for an urgent reassessment of current management practices. Confronting large-scale crises requires a major scaling-up of management efforts based on an improved understanding of the ecological processes that underlie reef resilience. Managing for improved resilience, incorporating the role of human activity in shaping ecosystems, provides a basis for coping with uncertainty, future changes and ecological surprises. Here we review the ecological roles of critical functional groups (for both corals and reef fishes) that are fundamental to understanding resilience and avoiding phase shifts from coral dominance to less desirable, degraded ecosystems. We identify striking biogeographic differences in the species richness and composition of functional groups, which highlight the vulnerability of Caribbean reef ecosystems. These findings have profound implications for restoration of degraded reefs, management of fisheries, and the focus on marine protected areas and biodiversity hotspots as priorities for conservation.     

广西红树林生态系统的常见物种

红树林湿地是链接陆地与海洋的重要枢纽,地貌特征独特,内部构造复杂多样,集海洋与陆地的普遍性与特殊性于一体,具有强大的包容性,为数以千计的海洋生物提供了生存、觅食、繁衍的环境。本文主要从食用红树林生物、广西红树林鸟类和昆虫3个方面重点介绍广西红树林生态系统中的常见物种。     

Impacts of biodiversity on the emergence and transmission of infectious diseases

Current unprecedented declines in biodiversity reduce the ability of ecological communities to provide many fundamental ecosystem services. Here we evaluate evidence that reduced biodiversity affects the transmission of infectious diseases of humans, other animals and plants. In principle, loss of biodiversity could either increase or decrease disease transmission. However, mounting evidence indicates that biodiversity loss frequently increases disease transmission. In contrast, areas of naturally high biodiversity may serve as a source pool for new pathogens. Overall, despite many remaining questions, current evidence indicates that preserving intact ecosystems and their endemic biodiversity should generally reduce the prevalence of infectious diseases.     

Ocean circulation off east Antarctica affects ecosystem structure and sea-ice extent

Sea ice and oceanic boundaries have a dominant effect in structuring Antarctic marine ecosystems. Satellite imagery and historical data have identified the southern boundary of the Antarctic Circumpolar Current as a site of enhanced biological productivity. Meso-scale surveys off the Antarctic peninsula have related the abundances of Antarctic krill (Euphausia superba) and salps (Salpa thompsoni) to inter-annual variations in sea-ice extent. Here we have examined the ecosystem structure and oceanography spanning 3,500 km of the east Antarctic coastline, linking the scales of local surveys and global observations. Between 80 degrees and 150 degrees E there is a threefold variation in the extent of annual sea-ice cover, enabling us to examine the regional effects of sea ice and ocean circulation on biological productivity. Phytoplankton, primary productivity, Antarctic krill, whales and seabirds were concentrated where winter sea-ice extent is maximal, whereas salps were located where the sea-ice extent is minimal. We found enhanced biological activity south of the southern boundary of the Antarctic Circumpolar Current rather than in association with it. We propose that along this coastline ocean circulation determines both the sea-ice conditions and the level of biological productivity at all trophic levels.     

Agricultural runoff fuels large phytoplankton blooms in vulnerable areas of the ocean

Biological productivity in most of the world's oceans is controlled by the supply of nutrients to surface waters. The relative balance between supply and removal of nutrients--including nitrogen, iron and phosphorus--determines which nutrient limits phytoplankton growth. Although nitrogen limits productivity in much of the ocean, large portions of the tropics and subtropics are defined by extreme nitrogen depletion. In these regions, microbial denitrification removes biologically available forms of nitrogen from the water column, producing substantial deficits relative to other nutrients. Here we demonstrate that nitrogen-deficient areas of the tropical and subtropical oceans are acutely vulnerable to nitrogen pollution. Despite naturally high nutrient concentrations and productivity, nitrogen-rich agricultural runoff fuels large (54-577 km2) phytoplankton blooms in the Gulf of California. Runoff exerts a strong and consistent influence on biological processes, in 80% of cases stimulating blooms within days of fertilization and irrigation of agricultural fields. We project that by the year 2050, 27-59% of all nitrogen fertilizer will be applied in developing regions located upstream of nitrogen-deficient marine ecosystems. Our findings highlight the present and future vulnerability of these ecosystems to agricultural runoff.     

Structural asymmetry and the stability of diverse food webs

Untangling the influence of human activities on food-web stability and persistence is complex given the large numbers of species and overwhelming number of interactions within ecosystems. Although biodiversity has been associated with stability, the actual structures and processes that confer stability to diverse food webs remain largely unknown. Here we show that real food webs are structured such that top predators act as couplers of distinct energy channels that differ in both productivity and turnover rate. Our theoretical analysis shows that coupled fast and slow channels convey both local and non-local stability to food webs. Alarmingly, the same human actions that have been implicated in the loss of biodiversity also directly erode the very structures and processes that we show to confer stability on food webs.     

Decline of the marine ecosystem caused by a reduction in the Atlantic overturning circulation

Reorganizations of the Atlantic meridional overturning circulation were associated with large and abrupt climatic changes in the North Atlantic region during the last glacial period. Projections with climate models suggest that similar reorganizations may also occur in response to anthropogenic global warming. Here I use ensemble simulations with a coupled climate-ecosystem model of intermediate complexity to investigate the possible consequences of such disturbances to the marine ecosystem. In the simulations, a disruption of the Atlantic meridional overturning circulation leads to a collapse of the North Atlantic plankton stocks to less than half of their initial biomass, owing to rapid shoaling of winter mixed layers and their associated separation from the deep ocean nutrient reservoir. Globally integrated export production declines by more than 20 per cent owing to reduced upwelling of nutrient-rich deep water and gradual depletion of upper ocean nutrient concentrations. These model results are consistent with the available high-resolution palaeorecord, and suggest that global ocean productivity is sensitive to changes in the Atlantic meridional overturning circulation.