1. Future oceans : temperature changes - hypoxia - acidification
Temperature rise, ocean acidification and expanding hypoxic zones in the ocean are the most prominent impacts on marine ecosystem health on the global scale. All three phenomena are at least partly related to the anthropogenic release of carbon dioxide and global climate change (WBGU 2006, Stramma et al. 2008). Changes in ocean temperature lead to shifts in the distribution ranges of many marine species. Dramatic biogeographical shifts have already been documented for zooplankton communities in the Northeast Atlantic, where warm-water species have moved 1000 km further north over the past 40 years, whereas cold-water inhabitants have contracted their range (Beaugrand et al. 2002, Hays et al. 2005). Via predator-prey interactions, these changes propagate along food chains and affect higher trophic levels including commercially important fish stocks. The retreat of Atlantic cod from the southern North Sea has also been related to temperature rise during the last decades (Beaugrand et al. 2003, Pörtner and Knust 2007, Pörtner et al. 2008). In addition, the warming of the ocean leads to the retreat of sea ice in Europe’s nordic seas including not only Arctic regions, but also the Baltic Sea, and it affects ocean stratification and current regimes. The impacts of these processes on marine ecosystems and biogeochemical cycles are still far from understood. Rising temperatures will also increase the risk of biological invasions by alien species (xenobiota) in European waters, since many invaders arrive by shipping from warmer origins.
Increasing carbon dioxide concentrations reduce the pH value in the ocean and the concentration of carbonate ions in seawater (Orr et al. 2005). This process of ocean acidification makes it more difficult for marine calcifying organisms, such as corals and certain plankton species, to produce their calcium carbonate skeletons (Ruttimann 2006). Ocean pH has already dropped by >0.1 units compared to pre-industrial levels, and models predict a further decrease by 0.6 units, should anthropogenic CO2 emissions continue at the present rate (Caldeira and Wickett 2003). Already by the year 2050, parts of the ocean will become undersaturated with respect to aragonite (a form of calcium carbonate) so that pteropods (pelagic molluscs, sea butterflies) will no longer be able to produce their shells (Orr et al. 2005).
Expanding hypoxic and anoxic conditions in the ocean are another burning issue of growing global concern (Stramma et al. 2008). Oxygen depletion is expected to affect large areas of coastal and marginal seas as well as low-latitude open oceans in the forthcoming decades. The United Nations Environment Programme recently identified oxygen depletion as the most eminent future threat to global fishery resources and marine ecosystems (UNEP 2004a, b). Consequently, in 2005 the Scientific Committee on Oceanic Research (SCOR) established a new Working Group on Natural and Human-Induced Hypoxia and Consequences for Coastal Areas. Hypoxia may affect fish stocks directly or via detrimental effects on important prey species such as zooplankton (Auel and Verheye 2007, Chan et al. 2008).
Recent results show that the reaction of marine ecosystems towards climate changes, including ocean warming, acidification and expanding hypoxic zones, is often not linear but may occur in abrupt reorganisations of marine communities (Scheffer and Carpenter 2003). It is now generally accepted that such regime shifts can transfer a marine ecosystem from one steady state to another as soon as certain thresholds of important key species are transgressed (Steele 2004). There is evidence that such a rapid shift from a predominance of cold-water to warm-water species occurred in the North Sea during the mid-1980s (Beaugrand 2004). Especially short-lived plankton species are often very sensitive indicators of climate change, because their nonlinear responses can amplify subtle environmental perturbations (Taylor et al. 2002).
2. Understanding biodiversity effects on the functioning of marine ecosystems
During the last decades, it has become increasingly clear that the biodiversity of an ecosystem and its functional features are intricately linked. However, while before the emphasis mainly lay on trying to understand how environmental constraints maintain and regulate diversity, during the last years the focus has shifted to the reverse question, namely how does the biodiversity of an ecosystem affect its functioning? This paradigm shift was brought about by the alarming decline in global biodiversity caused by human activities. If altered diversity seriously impacts the basic functions of ecosystems, we want to know whether this will have serious consequences for the goods and services provided by ecosystems to humans.
The main objective is to further our understanding of how interactions between species, both within and between trophic levels, affect the key functions of marine benthic ecosystems, namely biomass production and nutrient regeneration, and how these biodiversity effects on ecosystem functioning can be influenced by anthropogenic activities (pollution, fisheries activities).
Relationships between biodiversity and ecosystem functioning (BDEF) have now been documented and described for various terrestrial and marine ecosystems (Balvanera et al. 2006, Vanelslander et al. 2009b, Stachowicz et al., 2007). While these (largely descriptive) studies demonstrated that biodiversity generally enhances many process rates, it has not yet been able to resolve some of the most fundamental aspects of BDEF relationships (Reiss et al. 2009). Most available data suggest that trait differences between organisms are required to explain the observed patterns (Hillebrand & Matthiessen 2009). However, we still do not understand the actual mechanisms that underlie the observed relationships. In addition, it is unclear how representative our current, simplified models and experiments are of real, highly complex natural ecosystems. We also do not know how strong the relative effect of diversity on ecosystem functioning is in comparison with direct alterations of ecosystem processes by human mediated change. Anthropogenic environmental change after all does not only affect ecosystem functions via changes in biodiversity, but also directly by impacting on e.g. the overall availability and stoichiometry of resources, size and connectivity of habitats.
With the present focus, we aim at significantly advancing our understanding of how biodiversity affects the functioning of marine ecosystems, and especially how interactions within (horizontal) and between (vertical) trophic levels influence BDEF relationships.
3. Biological invasions
Species, subspecies or lower taxa introduced outside their natural past or present range (or of their natural dispersal potential) are named non indigenous species (NIS). Due to the globalization of human activities, intentional or unintentional introductions of marine species have become a priority issue for marine conservation. During the last century a consistent subset of NIS demonstrate their capability of spreading over a level that alter receiving ecosystems. IAS (Invasive alien species) have adverse effect on biological diversity, ecosystem functioning, socio-economic values and/or human health in invaded regions. Understanding biological invasions requires multidisciplinary expertise including taxonomy, molecular biology, biogeography, population ecology, ecological modeling and economics.
Invasive alien marine species are, unlike oil spills only get worse with time. While some progress is being made internationally on the 10,000 species estimated to be in transit around the world in the ballast water, effective solutions are a long way off; meanwhile the majority of vectors is being ignored. A systematic approach to invasive alien marine species is required to target the means and location of the most effective management actions. Cooperation among regional trading partners will be essential to effectively manage the threat (Bax et al., 2003).
There is a global need to train scientists in assessing key descriptors of biological invasions (i.e. abundance and distribution of non native species, vectors of introduction, impact on native communities, impact on habitat, impact on ecosystem functioning and energy flow) and find management solutions to NIS introduction and IAS spread (e.g. Pimentel et al., 2005). . PhD courses and research topic developed by the MARES doctoral programme will provide all necessary skills to answer to global (e.g. Ramsar Convention, Bern Convention, United Nations Convention on the Law of the Sea, IMO International Convention on the Control and Management of Ships’ Ballast Water and Sediments) and European conventions, directives and guidelines (EU strategy on invasive alien species, EC Regulation for use of alien and locally absent species in aquaculture, Regional Activity Center/ Specially Protected Areas for the Mediterranean UNEP - RAC/SPA guidelines) concerning the assessment and management of biological pollution in marine ecosystems. The goal of MARES PhD courses in biological invasion is to create a new research figure in Europe: the expert in marine biopollution assessment and control.
4. Natural resources : overexploitation, fisheries and aquaculture
Since the late 19th Century, the world catch has increased steadily and is now around 100 - 120 x 106 MT a year. However, analysis of global trends of the most important marine stocks in the world shows that the majority are overexploited or depleted. Historical reconstructions of marine fisheries biomass (The Sea Around Us Project) have documented order of magnitude declines in biomass of commercial species during the course of the 20th century. More recent analysis of Japanese longliner logbook catch per unit effort illustrate how abundance of large oceanic pelagics (bill fishes and sharks) has declined exponentially with increasing fishing effort since the 1960’s, and how high seas pelagic longline fishing activity has spread throughout the world’s oceans, moving to new fishing grounds as catch rates decline and areas are depleted of the top predators.
New and constantly improving technology (synthetic fibres, electronics, remote sensing), along with overcapitalization and subsidies are the driving forces behind the overexploitation of marine fisheries resources. The effects of overexploitation can be seen in decreasing mean size, the “fishing down the food chain” phenomenon as fisheries turn to species lower down the food chain as those higher up are depleted, loss of genetic variability, changes in community structure, loss of biodiversity and regime shifts (e.g. Pauly et al., 1998). We now know that loss of biodiversity, resulting in part from fishing activity, can alter the resilience of communities and ecosystems, making these more susceptible to global changes. Harmful fishing activities include direct impacts on habitat, leading to destruction of for example coral reefs, and discarding of undersized or unwanted species, as well as indirect effects on species interactions and ecosystem structure (e.g. Essington et al., 2006)
Marine fisheries have been adversely affected by ecosystem-level phenomena caused by fishing, yet these impacts are not generally considered in the management process. Traditional fisheries management is heavily based on models that ignore biological factors such as spawning behaviours, habitat and forage dependencies, and the apparent structure of marine ecosystems before human involvement. A range of different approaches are needed to better understand the interactions of fisheries (and aquaculture) with the environment and provide a scientific basis for the management of marine resources.
Aquaculture is already an important industry and is seen by some as a replacement for fisheries. However, commercial aquaculture relies heavily on fisheries (by)catch for oils and fish meal, which puts further pressure on fish stocks. Aquaculture intensification can be a focus of disease and parasites which can spread to natural populations. Escapes from farms and sea cages are also a source of genetic contamination which can threaten local populations. It can also be a source of nutrient pollution and can have direct destructive effects such as shrimp culture on salt marsh and mangroves ecosystems.
5. Ocean noise pollution
Anthropogenic sources of noise in the marine environment have increased in line with expansion in shipping, oil and gas exploration, infrastructure development, offshore renewable energy generation, naval sonar and research activities (e.g. Hastings & Popper, 2005, McDonald et al., 2006, Simmonds & McLennan, 2005). These sound sources vary in intensity and frequency and can result in chronic and acute impacts on marine organisms. Marine fauna that use sound for social interactions may have inter- and intra-specific communication masked or impeded. In addition, organisms that use sound for foraging may suffer direct impacts through masking or indirect impacts through alteration in prey distribution or habitat loss. The impact can also extend to changes in animal behaviour which can compromise their ability to regulate their diving physiology and result in death. In parallel with assessing and mitigating the impacts of underwater noise in the marine environment, bioacoustics presents the opportunity to use mammalian vocalisations for research using passive acoustics (Sueur et al., 2008). These techniques can provide significant insight into the biology and ecology of marine organisms as well as provide a valuable tool in impact assessment and conservation management. EU member states have legal obligations concerning the monitoring and protection of marine mammals and underwater noise represents one of the most significant threats to their conservation.
6. Habitat loss, urban development, coastal infrastructures and Marine Spatial Planning
The coastal seas are changing under the pressure from a growing human population, and conversion of shoreline habitat to urban development. Over the centuries, land reclamation, coastal development, overfishing and pollution have nearly eliminated coastal wetlands, seagrass meadows, shellfish beds, biogenic reefs and other productive and diverse coastal habitats (Lotze et al 2006, Airoldi & Beck 2007). Marine landscapes have been globally altered by the introduction of a variety of human-made infrastructures, such as seawalls, dykes, breakwaters, groynes, jetties, pilings, bridges, artificial reefs, offshore platforms, wind farms and tidal gauges (Glasby & Connell 1999; Bacchiocchi & Airoldi 2003, Bulleri & Chapman 2009). The extent and projected trend of this phenomenon are dramatic. In Europe, it is estimated that every day between 1960 and 1995, a kilometre of coastline has been developed, and nowadays an astonishing 22000 km2 of the coastal zone are covered in concrete or asphalt. More than 50 % of the Mediterranean coasts are dominated by concrete with > 1500 km of artificial coasts, of which about 1250 km are developed for harbours and ports (EEA 1999b). Similar examples occur in other parts of the world - e.g. USA (Davis et al. 2002), Australia (Chapman & Bulleri 2003), and Asia (Koike 1996) - where hundreds of kilometers of coasts are hardened to some extent. Marine artificial substrata will expand worldwide in almost every coastal locality. Indeed the population living on the coast is projected to double in the next 30 yr with an expected 75% of the world's populations residing in coastal areas by 2025 (EEA 1999a). Further , a major response to climate-change related impacts, notably inundation and flooding from sea level rise and storms, will be the further use of heavy engineering such as the building of artificial sea defences (Airoldi and Beck 2007). This will mean further losses of coastal habitats and their benefits to people (Knogge et al 2004). While the conservation challenges associated to the expansion of human infrastructures are well understood in terrestrial systems (e.g. Hobbs et al., 2006) urban ecology has not been as much a focus of marine science and management, and only few grasp the enormity and urgency of this scientific and socio-economic problem. However, some of the most obvious and economically important negative effects on native ecosystems are already being seen in the coastal zone (Turner et al. 1998, Airoldi et al. 2005, Devoy 2008, Bulleri & Chapman 2009).
The expansion of maritime activities and the increasing need of complying with international agreements on the protection of biodiversity have produced a growing interest on Marine Spatial Planning as a tool to manage uses of marine systems. The EU integrated maritime policy includes this tool as the means to reach the objectives established in the documents put forward until now: Green Book, Blue Book, Action Plan. Simultaneously, the Directive for a Marine Strategy (2008/56/EC) has now entered into force. This Directive establishes a time frame (2020) to reach a good environmental status of waters within European jurisdiction. More recently, the Roadmap for Maritime Spatial Planning [COM (2008) 791 final] establishes the advantages, approaches and principles for its implementation. At the same time, the European Commission (DG Maritime Affairs) is working on a specific document on maritime policy for the Mediterranean Sea, in which marine spatial planning will have a paramount role. The new maritime policies and the instruments of spatial planning are characterized by their applicability to Europe’s jurisdictional waters in their entirety, along a process that originally comprised the narrow coastal zone and is now reaching the external limit of the Economic Exclusive Zone and, in cases, the continental margin. In this context, integrated coastal zone management will be included in initiatives of wider scope.
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