Radical changes in the Wadden Sea fauna and flora over the last 2,000 years

Humans have interacted with the Wadden Sea since its origin 7,500 years ago. However, exploitation, habitat alteration and pollution have strongly increased since the Middle Ages, affecting abundance and distribution of many marine mammals, birds, fish, invertebrates and plants. Large whales and some large birds disappeared more than 500 years ago. Most small whales, seals, birds, large fish and oysters were severely reduced by the late 19th and early 20th centuries, leading to the collapse of several traditional fisheries. In the 20th century, conservation efforts have enabled some breeding birds and seals to recover. But other species declined further due to continuing exploitation, habitat destruction, pollution and eutrophication. Moreover, complex three-dimensional habitats such as oyster banks, Sabellaria reefs and subtidal eelgrass beds have been lost completely. In contrast, several opportunistic species such as gulls, polychaetes, green algae and exotic invaders increased during the 20th century. Taken together, multiple human impacts have caused dramatic losses of large predators and habitat-building species in the Wadden Sea over the last 500 years. Although still of high natural value and global importance, the Wadden Sea is a fundamentally changed ecosystem. On the other hand, reduced hunting pressure, increased habitat protection and reduced river pollution have enabled the recent recovery of several species and an increase in environmental quality. These successes, together with a historical vision of what was once possible, should guide current and future conservation, restoration and management efforts towards a more sustainable interaction between man and the sea.     

Predictive ecosystem research in the Wadden Sea

Predictive ecosystem research needs a pluralistic approach. Retrospective studies reveal the initial causes of ongoing ecological change. In the Wadden Sea, inherent ecosystem stability may be falsely assumed, because the effects of modern coastal architecture and of anthropogenic eutrophication to some extent complement each other. Expected environmental changes often have corresponding phases in the past which may serve as a model to predict ecological implications. Historically, quantitative ecology entered the Wadden Sea, via fisheries research, from the oceanic side. Quantified material fluxes may reveal imbalances which are indicative of the rough direction of ecosystem change. For ecosystem research to contribute to the maintenance of the Wadden Sea as a centre of coastal organisms, quantitative knowledge of resources and ecosystem metabolism must be supplemented by qualitative knowledge of habitat requirements and species interdependences. Qualitative ecology entered the Wadden Sea from the landward side. Extending this approach to anticipatory field experiments may help to predict ecological changes at the species level.     

Human impacts on fisheries resources and abundance in the Danish Wadden Sea, c1520 to the present

For the past 30 years, the Danish Wadden Sea area has been protected by fishery and hunting regulations, pollution controls and settlement restrictions. Nevertheless, todays Wadden Sea is a depleted ecosystem when we compare it with past abundance and diversity of marine animal populations. This review indicates that the abundance of finfishes has undergone a long-term decline since the seventeenth century. The review also indicates a trajectory of ecological decline since the early twentieth century that seems to be related to: (1) fishing extractions which focused on undersized fish throughout the first half of the twentieth century; (2) habitat destruction, which was most marked in the first half of the twentieth century; and (3) pollution, which was worst in the third quarter of the twentieth century. Historical investigation reveals that we need to fundamentally revise present-day baselines about the potential species richness and abundance of the Wadden Sea.     

Coast of change: habitat loss and transformations in the Wadden Sea

In the southern North Sea, coastal people commenced with habitat conversions 1,000 years ago. Partly interrupted in late medieval times by large-scale inundations of marshland, progressive embankments transformed the landward half of the amphibic transition zone between a limno-terrestric and a brackish-marine ecosystem into arable land and freshwater lakes. Sea walls rigidly separated the land from the sea. Dynamic transitional habitats have vanished. Areal loss has diminished the capacity of the Wadden Sea to dissipate wave and tidal energy. A coastal ecosystem once rich in marsh plants, seagrass and diatoms on mud flats became transformed into one with less autochthonous phototroph production, dominated by sandy tidal flats, and dependent primarily on allochthonous plankton supply. The large estuaries have been dredged to serve as shipping canals, and have lost most of their former retention and filter capacity. Riverine loads are now flushed right into the North Sea. Symptoms of a syndromatic coastal habitat degradation are diagnosed, leading to a decline in natural habitat diversity. The conventional on-line coastal protection may not achieve a sustainable coastal habitat configuration. At sedimentary coasts immobilised by dikes and petrified shores, a more flexible response to sea level rise is recommended.     

Biodiversity and China's new Great Wall

Coastal armouring and the reclamation of intertidal areas through the use of seawalls and other artificial structures has been practiced for thousands of years, but its recent expansion in China and elsewhere in Asia has been unprecedented in its rate and intensity. One result has been the recent loss of nearly two‐thirds of tidal flats in the Yellow Sea, a globally unique ecosystem of high ecological value. The severe effects on biodiversity of the recent large‐scale coastal land claim activities in China are well documented, yet some recent studies have emphasized the ecological opportunities provided by such artificial coastal infrastructure in China, in some cases suggesting that the ecological impacts of coastal infrastructure should be reconsidered due to benefits to some rocky shore species in a changing climate. This is cause for concern because, while studying the “new ecology” arising from coastal modification is useful, broad conclusions around the ecological role or conservation gains from seawall construction without adequate contextualization underplays the ecological consequences of large‐scale coastal land claim, and could potentially undermine efforts to achieve biodiversity conservation. Here, we clarify the characteristics of seawall construction in China and summarize the environmental damage and some broadscale impacts caused by this type of infrastructure expansion on the endangered Yellow Sea tidal flats ecosystem. We also highlight the urgent need for all coastal development plans to consider how coastal wetlands and ecosystem functionality can be maximally retained within the development precinct.     

Habitat preferences of an endangered insect species,Cepero’s ground-hopper (<Emphasis Type="Italic">Tetrix ceperoi</Emphasis>)

Preventing the global decline in biodiversity is a major task for conservation biologists. Although habitat loss has been identified as a key factor driving extinction processes, our knowledge on the habitat requirements of many endangered species, particularly invertebrates, is still sparse. We present a feasible method to study the microhabitat preferences of insect species. In Central Europe, the endangered Cepero’s ground-hopper, Tetrix ceperoi, is believed to have its only remaining natural habitats in dune slacks of the Wadden Sea Islands. Our results suggest that this species performs an active habitat choice of damp, bare patches with high temperatures. While ponds and fens in dune slacks provide large areas of damp bare ground and algal mats, grasslands, degraded dune slacks and the transitional zone between salt marsh and dunes are less suited as habitats. The major threat for T. ceperoi is found in the succession of its pioneer habitats due to the reduced natural dynamics. In industrialized countries, pioneer habitats and species are threatened substantially by coastal protection and floodplain regulation. This is only compensated in part by anthropogenic creation of secondary habitats, such as different kinds of pits or coal heaps. Nevertheless, there is a strong need for restoration of dynamic habitats by floodplain revitalization and dune slack restoration.     

Neues Leben im Weltnaturerbe Wattenmeer. Globalisierung unter Wasser

Globalization under water: Alien species in the Wadden Sea World Heritage Recent investigations reveal an increasing number of non‐native species in the Wadden Sea which profit from warmer water temperatures caused by global change. These exotic species achieve highest occurrence and densities in shallow waters near the low tide water level. In this tidal zone, a highly diverse species community of algae and invertebrates became established and will continue to alter in composition. This leads to enhanced complexity of biogenic habitats and to a prevalence of filter feeding organisms. Thus, we observe a fundamental change of the whole Wadden Sea ecosystem which is without return.     

Predation rates on semi-natural grasslands depend on adjacent habitat type

Spillover in ecological systems, that is the dispersal or foraging of organisms across habitat borders, can affect ecosystem functioning and food web interactions of local communities. While spillover of organisms from perennial habitats into agricultural fields received some attention in the context of ecosystem service provisioning, the spillover into semi-natural habitats has rarely been addressed, although spillover of generalist predators or competition for pollinators can have consequences for nature conservation. We studied predation rates of ground-dwelling predators on 20 calcareous grasslands, with either coniferous forest or a crop field as adjacent habitat. As prey items we exposed 32,000 ladybird eggs on the grasslands. Within two study periods (June to September) predation rates were higher at warm compared to cool days, but did not depend on the study period itself or the distance from the edge where prey items were placed. In each study period we found higher predation rates when coniferous forest was the adjacent habitat, however, only on cool days. On warm days, prey items were consumed to very high extents (often 100%), which did not allow the detection of possible differences between adjacent habitat types. The higher predation rates on grasslands adjacent to forests can be explained by predator spillover from forests to grasslands. We conclude that semi-natural habitats provide not only ecosystem services in adjacent human dominated habitats, but are also exposed to antagonistic spillover effects. Such antagonistic spillover should be considered in conservation strategies for semi-natural habitats.     

海岸带区域陆海统筹生态安全研究

海岸带既是区域经济发展的黄金地带,亦是陆海系统交互胁迫的敏感区域,快速城镇化与工业化导致海岸带关键生态系统服务受损、生态网络格局紊乱、珍稀物种安全保障空间萎缩等重大生态安全问题。以闽三角海岸带珍稀物种-栖息地系统为研究对象,从“多物种-多生境-多尺度”视角出发,基于陆海统筹理念系统评估了闽三角海岸带珍稀物种-栖息地系统的脆弱性,建立了基于物种水平的海岸带生态保护与修复网络,构建了海岸带陆海统筹生态安全“一张图”。研究结果表明：(1)高强度围填海驱动下,闽三角红树林与水鸟栖息地脆弱性显著增加,高脆弱区域主要集中于九龙江河口、厦门同安湾和泉州湾;(2)闽三角生态安全网络由12条水鸟迁徙廊道和11个生态节点组成,其中影响陆海统筹生态安全的生态节点4个,预警生态节点3个;(3)闽三角海岸带未来安全韧性生境(水鸟栖息地与文昌鱼、中国鲎低脆弱生境较密集的区域)分布于云霄红树林保护区、东山岛近岸、九龙江河口、厦门大嶝海域、围头湾、深沪湾。本研究能够为设计规划未来韧性海岸带“受损海水-滨海湿地-珍稀物种”一体化修复与保护的生态安全格局,保障陆海统筹生态安全提供理论支撑和一体化解决方案。     

Are aliens threatening European aquatic coastal ecosystems?

Inshore waters of European coasts have accumulated a high share of non-indigenous species, where a changeable palaeoenvironment has caused low diversity in indigenous biota. Also strongly transformed modern coastal ecosystems seem to assimilate whatever species have been introduced and tolerate the physical regime. Adding non-native species does not have any directional predetermined effects on recipient coastal ecosystems. The status of being a non-native rather refers to a position in evolutionary history than qualify as an ecological category with distinct and consistent properties. Effects of invaders vary between habitats and with the phase of invasion and also with shifting ambient conditions. Although aliens accelerate change in European coastal biota, we found no evidence that they generally impair biodiversity and ecosystem functioning. More often, invaders expand ecosystem functioning by adding new ecological traits, intensifying existing ones and increasing functional redundancy.     

No consistent diversity patterns in terrestrial mammal assemblages along rural-urban forest gradients

Urbanization is increasing worldwide, fragmenting, isolating or destroying native habitats with a subsequent loss of biodiversity, structural and compositional changes of biotic communities and weakening of the functioning of biological processes and ecosystem services. In urban ecosystems, terrestrial mammals provide important functions and services, but we do not have a synthesis of the impacts of urbanization on terrestrial mammals. Terrestrial mammals are vulnerable to habitat loss and modification caused by urbanization, thus we hypothesised that the abundance and diversity of mammals would decrease as urbanization progresses. In addition, due to the declining number of predators and thus to decreasing predation pressure in urban habitats, we assumed that herbivore and omnivore mammals would gain dominance. To clarify the inconsistency of previous urbanization studies on terrestrial mammals, we synthetized and re-evaluated published results by meta-analysis. Based on 50 rural-urban comparisons, terrestrial mammals were not significantly more abundant or diverse in rural than urban habitats. This was not only found at the community level, but also at the level of taxonomic groups (carnivores, marsupials, rodents), feeding habit (carnivorous, herbivorous or omnivorous species) or at the level of their interactions. Our results suggest that the studied urban-dwelling mammal species are probably well adapted to environmental conditions and pressures accompanied by urbanization via individual-level adaptation.     

The Biodiversity of the Mediterranean Sea: Estimates,Patterns, and Threats

The Mediterranean Sea is a marine biodiversity hot spot. Here we combined an extensive literature analysis with expert opinions to update publicly available estimates of major taxa in this marine ecosystem and to revise and update several species lists. We also assessed overall spatial and temporal patterns of species diversity and identified major changes and threats. Our results listed approximately 17,000 marine species occurring in the Mediterranean Sea. However, our estimates of marine diversity are still incomplete as yet—undescribed species will be added in the future. Diversity for microbes is substantially underestimated, and the deep-sea areas and portions of the southern and eastern region are still poorly known. In addition, the invasion of alien species is a crucial factor that will continue to change the biodiversity of the Mediterranean, mainly in its eastern basin that can spread rapidly northwards and westwards due to the warming of the Mediterranean Sea. Spatial patterns showed a general decrease in biodiversity from northwestern to southeastern regions following a gradient of production, with some exceptions and caution due to gaps in our knowledge of the biota along the southern and eastern rims. Biodiversity was also generally higher in coastal areas and continental shelves, and decreases with depth. Temporal trends indicated that overexploitation and habitat loss have been the main human drivers of historical changes in biodiversity. At present, habitat loss and degradation, followed by fishing impacts, pollution, climate change, eutrophication, and the establishment of alien species are the most important threats and affect the greatest number of taxonomic groups. All these impacts are expected to grow in importance in the future, especially climate change and habitat degradation. The spatial identification of hot spots highlighted the ecological importance of most of the western Mediterranean shelves (and in particular, the Strait of Gibraltar and the adjacent Alboran Sea), western African coast, the Adriatic, and the Aegean Sea, which show high concentrations of endangered, threatened, or vulnerable species. The Levantine Basin, severely impacted by the invasion of species, is endangered as well.This abstract has been translated to other languages (File S1).     

High focus on threatened species and habitats may undermine biodiversity conservation: Evidence from the northern Baltic Sea

Conservation policies and environmental impact assessments commonly target threatened species and habitats. Nevertheless, macroecological research provides reasons why also common species should be considered. We investigate the consequences of focussing solely on legally protected species and habitats in a spatial conservation planning context using a comprehensive, benthic marine data set from the northern Baltic Sea. Using spatial prioritization and surrogacy analysis, we show that the common approach in conservation planning, where legally listed threatened species and habitats are the focus of conservation efforts, could lead to poor outcomes for common species (and therefore biodiversity as a whole), allowing them to decline in the future. If conservation efforts were aimed solely at threatened species, common species would experience a loss of 62% coverage. In contrast, if conservation plans were based only on common species, threatened species would suffer a loss of 1%. Threatened species are rare and their ecological niches distinct, making them poor surrogates for biodiversity. The best results are achieved by unified planning for all species and habitats. The minimal step towards acknowledging common species in conservation planning would be the inclusion of the richness of common species, complemented by information on indicator species or species of high importance for ecosystem functioning. The trade-off between planning for rare and common species should be evaluated, to minimize losses to biodiversity.     

Larval habitat preferences of a threatened butterfly species in heavy-metal grasslands

Understanding the factors that determine habitat quality is of vital importance in ensuring appropriate habitat management. Here we used the Niobe fritillary (Argynnis niobe) as a study system to analyse the larval habitat preferences in a small network of heavy-metal grasslands in western Germany. The data were compared with the results of a previous study in coastal dune grasslands of the German North Sea. Based on this knowledge, we give management recommendations for the conservation of this threatened species. The key factors for the survival of A. niobe in heavy-metal grasslands were (i) open vegetation with a warm microclimate and (ii) sufficient host plants for the larvae. This reflects similar results from the previous study in coastal grey dune grasslands. However, in the heavy-metal grasslands, physiological stress generally slows down succession and favours the fritillary’s host plant, the metallophyte Viola calaminaria. As a result, the cover of the host plant was nearly twice as high in heavy-metal grasslands compared to the dune grasslands. Heavy-metal grasslands are of great significance for the conservation of A. niobe and overall butterfly diversity. Usually, the speed of succession in heavy-metal grasslands is slow and, hence, sites with high heavy-metal concentrations are characterised by relatively stable plant composition and vegetation structure. However, on soils with low heavy-metal content a loss of habitats of A. niobe and associated species of conservation concern may occur without management. On those sites sheep grazing seems to be an appropriate way to keep the habitats open and rich in violets.     

Major Changes in the Ecology of the Wadden Sea: Human Impacts, Ecosystem Engineering and Sediment Dynamics

Shallow soft-sediment systems are mostly dominated by species that, by strongly affecting sediment dynamics, modify their local environment. Such ecosystem engineering species can have either sediment-stabilizing or sediment-destabilizing effects on tidal flats. They interplay with abiotic forcing conditions (wind, tide, nutrient inputs) in driving the community structure and generating spatial heterogeneity, determining the composition of different communities of associated species, and thereby affecting the channelling of energy through different compartments in the food web. This suggests that, depending on local species composition, tidal flats may have conspicuously different geomorphology and biological functions under similar external conditions. Here we use a historical reconstruction of benthic production in the Wadden Sea to construct a framework for the relationships between human impacts, ecosystem engineering and sediment dynamics. We propose that increased sediment disturbances by human exploitation interfere with biological controls of sediment dynamics, and thereby have shifted the dominant compartments of both primary and secondary production in the Wadden Sea, transforming the intertidal from an internally regulated and spatially heterogeneous, to an externally regulated and spatially homogenous system. This framework contributes to the general understanding of the interaction between biological and environmental control of ecosystem functioning, and suggests a general framework for predicting effects of human impacts on soft-bottom ecosystems.     

Das Wattenmeer als gemeinsame Verantwortung verstehen

Understanding the Wadden Sea as a shared responsibility The Wadden Sea is the largest tidal flat system in the world, where natural processes run undisturbed. The World Heritage site is home to over 10,000 species of plants and animals, which continuously adapt to the ever‐changing dynamic area. 10–12 million migratory birds yearly rely on the Wadden Sea as a stopover. To ensure its protection, the three countries have been joining efforts for the sea's conservation since 1978, taking responsibility for this irreplaceable ecosystem and preserving it for the benefit of present and future generations. One of the cooperation's main pillars is the harmonised, cross‐border Trilateral Monitoring and Assessment Programme.     

Macroalgal blooms alter community structure and primary productivity in marine ecosystems

Eutrophication, coupled with loss of herbivory due to habitat degradation and overharvesting, has increased the frequency and severity of macroalgal blooms worldwide. Macroalgal blooms interfere with human activities in coastal areas, and sometimes necessitate costly algal removal programmes. They also have many detrimental effects on marine and estuarine ecosystems, including induction of hypoxia, release of toxic hydrogen sulphide into the sediments and atmosphere, and the loss of ecologically and economically important species. However, macroalgal blooms can also increase habitat complexity, provide organisms with food and shelter, and reduce other problems associated with eutrophication. These contrasting effects make their overall ecological impacts unclear. We conducted a systematic review and meta‐analysis to estimate the overall effects of macroalgal blooms on several key measures of ecosystem structure and functioning in marine ecosystems. We also evaluated some of the ecological and methodological factors that might explain the highly variable effects observed in different studies. Averaged across all studies, macroalgal blooms had negative effects on the abundance and species richness of marine organisms, but blooms by different algal taxa had different consequences, ranging from strong negative to strong positive effects. Blooms' effects on species richness also depended on the habitat where they occurred, with the strongest negative effects seen in sandy or muddy subtidal habitats and in the rocky intertidal. Invertebrate communities also appeared to be particularly sensitive to blooms, suffering reductions in their abundance, species richness, and diversity. The total net primary productivity, gross primary productivity, and respiration of benthic ecosystems were higher during macroalgal blooms, but blooms had negative effects on the productivity and respiration of other organisms. These results suggest that, in addition to their direct social and economic costs, macroalgal blooms have ecological effects that may alter their capacity to deliver important ecosystem services.     

海草生态学研究进展

海草床生态系统是生物圈中最具生产力的水生生态系统之一,具有重要的生态系统服务功能。作者根据海草生态学及相关领域的最新研究进展,对世界范围内海草床的空间分布、海草床的生态系统服务功能以及外界因素对海草床的影响等研究进展进行了综述。海草床生态系统服务功能主要包括净化水质、护堤减灾、提供栖息地和生态系统营养循环等。对海草床影响较大的外界环境因素包括盐度、温度、营养盐、光照、其他动物摄食、人类活动和气候变化等。海草普查、海草生态功能研究,影响海草床的主要环境因素,海草修复研究等将是我国海草研究的主要方向。     

Historical Changes in Marine Resources,Food-web Structure and Ecosystem Functioning in the Adriatic Sea,Mediterranean

The Mediterranean Sea has been strongly influenced by human activities for millennia. Although the environmental history of its surrounding terrestrial ecosystems has received considerable study, historical changes in its marine realm are less known. We used a multidisciplinary approach combining paleontological, archeological, historical, fisheries, and ecological data to reconstruct past changes in marine populations, habitats, and water quality in the Adriatic Sea. Then, we constructed binary food webs for different historical periods to analyze possible changes in food-web structure and functioning over time. Our results indicate that human activities have influenced marine resource abundance since at least Roman times and accelerated in the nineteenth and twentieth centuries. Today, 98% of traditional marine resources are depleted to less than 50% of former abundance, with large (>1 m) predators and consumers being most affected. With 37% of investigated species rare and 11% extirpated, diversity has shifted towards smaller, lower trophic-level species, further aggravated by more than 40 species invasions. Species providing habitat and filter functions have been reduced by 75%, contributing to the degradation of water quality and increased eutrophication. Increased exploitation and functional extinctions have altered and simplified food-web structure over time, especially by changing the proportions of top predators, intermediate consumers, and basal species. Moreover, simulations of species losses indicate that today’s ecosystems may be less robust to species extinctions than in the past. Our results illustrate the long-term and far-reaching consequences human activities can have on marine food webs and ecosystems.