Category Archives: scientific_programme

Lead Proponents: Katrin Rehdanz (Kiel Institute for the World Economy and Christian-Albrechts-Universität zu Kiel CAU), Martin Quaas (CAU, Kiel)

Consortium 5 “Services of the Ocean” aims to investigate social and economic consequences of ocean acidification and to quantify them. Thus, stakeholders will be able to recognize consequences of their behaviour as well as ways to reduce climate change or adapt. Based on the scientific evidence, politics, economy and society can take joint action. They shall ensure that the oceans continue to provide food and energy, promote recreation and health, drive the tourism as an economic factor, or – and this service is considered to be economically most important – store carbon dioxide from the atmosphere and thus slow down climate change.

Model calculations show how the use of the seas impacts them and how the use options may change in the future. The focus is on the function of the ocean as a CO₂ sink and fishing.

In 2008, the oceanic content of carbon increased by 2.3 gigatons. This corresponds to 8.4 gigatons of CO₂. In the European Union Emissions Trading Scheme, a ton of CO₂ emissions is calculated with ten euros. If the ocean absorbs only one percent less CO₂ per year due to climate change, this would generate “costs” of about 0.84 billion euros. Such a development seems realistic. Reason number one is the fact that warmer water absorbs less CO₂ than colder. Secondly, many plankton organisms seem to form less calcium carbonate in a more acidified water and thus fix less carbon. The natural CO₂ storage device reaches its limits.

Will the future ocean provide enough food? Photo: Maike Nicolai, GEOMAR

Because it sits at the base of the marine food web, modifications in the plankton community evoked by climate change also affect fish stocks. But even some direct consequences for the extension of habitats, the growth or body functions of fish are known. At global and regional levels, biologists and economists therefore determine future changes to marine fisheries engage stakeholders in the discussion about possible options for adaptation or prevention.

More about the science of Consortium 5.

Lead Proponents: Katrin Rehdanz (Kiel Institute for the World Economy and CAU, Kiel), Martin Quaas (CAU, Kiel)

Ocean Acidification (OA) has been gaining increasing recognition in the policy circles recently, due to an increasing number of studies on biological and ecological impacts of OA (e.g. Turley et al. 2010). However, estimates of socio-economic impacts are still almost absent (Brander et al. 2009, Cooley and Doney 2009, Cooley et al. 2011, Narita et al. 2011), although such impacts constitute key information for formulating international policies for greenhouse gas emission reduction as well as for climate engineering and strategies for adaptation. Hence, research on socio-economic impacts of OA has strong policy relevancy.1
The oceans provide goods and services, which are used directly and indirectly by human societies and economies. These include food and health, energy, mineral resources and system services. Ocean services include ecosystem services (e.g. fish and seafood, biodiversity, tourism) as well as the role of the ocean in the climate system. Fig. 5.1 provides an overview of categories of ecosystem services including those of the ocean.

Among the economically most important ocean services are CO₂ storage (a regulating service) and fisheries (a provisioning service). In the year 2008, the oceanic carbon content increased by 2.3 +/- 0.4 Gigatons (Gt) of carbon, equivalent to 8.4 Gt CO₂ (Le Quéré et al. 2009). At the current price of about 10 Euros for a ton of CO₂ emissions in the European Union Emissions Trading Scheme, which is a very conservative estimate of the social costs of CO₂ emissions, a one percent decrease, or increase, of this service of the ocean would generate a cost, or value, of 0.84 billion Euros per year. The world-wide marine capture fisheries land about 80 million tons of fish per year, generating revenues of about 65 billion Euros per year, but also exerting a huge impact on marine ecosystems (World Ocean Review 2010).

Ocean acidification interacts with these economically important ocean resources and services (Fig. 5.2). Most directly, OA is a consequence of the use of the oceans as a sink of anthropogenic CO₂. However, the quantity of CO₂ stored in the oceans is also affected by ocean change, including the processes of acidification and warming, as ocean biogeochemistry is affected by these processes. These effects need to be quantified on a global scale and the associated uncertainties have to be assessed.

The way how fish stocks are managed influences the marine carbon cycle (Wilson et al. 2009) with potential impacts on marine CO₂ uptake and, hence, OA. There is thus a possible trade-off between the ocean’s provisioning service (fishery yield) and the ocean’s regulating service in terms of taking up anthropogenic CO₂. A close interaction of biogeochemical and ecological modelling with a socio-economic analysis is required to elucidate this potential trade-off in a quantitative way.

To ensure that scientific results will be used most effectively in adaptation and policy making, results of bio-geochemical models and socio-economic analyses have to be shared with affected stakeholders, preferably beginning at an early stage. In addition to valuing changes in ecosystem services in objectively derived monetary terms, it is advisable to let stakeholders value their perceived potential damage on their own. It is very likely that stakeholders are then much more willing to take ownership of the problem of OA, which greatly enhances the motivation for participating in mitigation and adaptation measures.

General objectives:

The general objective of Consortium 5 is to assess and quantify how OA interacts with the provision and use of ocean services, notably with the services of oceanic CO₂ storage and fisheries, to reduce the scientific uncertainties associated, and to inform stakeholders about potential impacts and engage them in discussions about options for adaptation.

For CO₂ storage, several studies already exist that quantify the effects in physical terms using global biogeochemical ocean models. Our main interest is to assess and reduce the uncertainties associated. Work package 5.1 will focus on uncertainty of model predictions and aims at improving the performance by means of data-based model assessment. Work package 5.2 will assess the effect of environmental variability on the oceanic carbon sink within a global biogeochemical ocean model.

The impact of potential consequences of OA on phytoplankton C:N ratios and hence on the food quality and food web dynamics will be investigated in Work package 5.3, which will also investigate potential effects of changes in fishing pressure on zooplankton mortality and, eventually, on the oceanic biological carbon pump.

The effect of OA on fisheries and other services is much less clear. Ocean acidification and warming (OAW) is likely to have an impact on the stock dynamics of commercially important fishes, as it will probably alter recruitment success, growth, size and extension of suitable habitats (Beaugrand 2009). OAW thus will have implications for fisheries catch potential via impacts on ecophysiology and plankton dynamics (Cheung et al. 2011). These effects on fish stocks and reproduction still have to be quantified in physical terms. To assess the economic impacts of OAW in fisheries, these effects have to be incorporated in ecological-economic models, and the economic effects in terms of changing fishing opportunities have to be assessed.

The existing economic studies point to small impacts of OA on global welfare compared to the impact of climate change (Brander et al. 2009, Narita et al. 2011). However, on the regional or local level significant differences exist but little detailed knowledge exists. Work package 5.4 will focus on two specific environments taking into account location-specific characteristics and different levels of economic development. Moreover, while the aggregate effects on a global scale may be small, there may still be significant local changes in fisheries incomes (for example due to OAW-induced movement of fish stocks), and the effects may strongly depend on the management regime. Work package 5.5 will address these questions and quantify the aggregate and distributional effects of OAW on commercially important cod fisheries.

Differences exist among regions and countries regarding vulnerability and adaptive capacity. An indicator is location, since there is a strong regional variation in the ocean’s buffer capacity and the sensitivity to acidification. Affluence is another important factor. The adaptive capacity of a relatively rich country in the tropics may be higher and therefore the impacts lower, compared to a less developed country in the temperate climate zones. For a developing country in the tropics other issues such as increase in population, public health and education are likely to be more relevant. If OA would affect food security, it would be an additional reason of concern.

Even less is known about a potential feedback of fisheries on OA, although it is well known that fisheries exert a strong impact on marine ecosystems, and some effects on the oceanic carbon cycle have been quantified before (Wilson et al. 2009). A feedback on OA may exist if trophic cascades from fish preying on zooplankton and phytoplankton affect biological production and the oceanic biological carbon pump at a significant scale. Work packages 5.3 and 5.5 will cooperate in studying these feedback effects attempting quantification at the global scale.

Impacts on ecosystem services are region-specific and valuation is depending on local, social, and cultural circumstances. Also, impacts can only be quantified with substantial uncertainties, further complicating the process of adaptation and policy formation. However, adaptation strategies need to be knowledge driven and need to find a broad support among stakeholders. Work package 5.6 will approach this issue with a regional focus on the habitats of two interacting cod species in the North Atlantic.

Research approaches
:

The main research approach employed is numerical modelling, in particular using global biogeochemical models and ecological-economic models for fisheries.

In work package 5.1, data-based model assessment will be used to evaluate and calibrate global biogeochemical models used for predictions of oceanic CO₂-storage.

In 5.2, the impact of environmental uncertainties on carbon storage and acidification will be assessed using a global biogeochemical ocean model.

In 5.3, the impact of OA on biological processes and the feedback of varying fish stock abundances on OA will be studied by means of the UVic Earth System model.

In 5.4, the impacts of OA on mollusc fisheries at the German/Danish coast and its economic implications will be studied in numerical models.

In 5.5, an ecological-economic model of the different cod fisheries that incorporates the effect of OA on recruitment and fish growth will be used to study the efficiency and distributional impacts of OA under various management regimes. The feedbacks between fisheries and OA will be studied using a similar model at a global scale that is coupled to the Earth System model of 5.3.

In 5.6, involving stakeholders will be facilitated by aggregating the results from work packages in consortium 5 and consortium 4 into a comprehensible frame for presentation and discussion with stakeholders at two workshops (preferably related to the annual BIOACID meetings). Within the model frame, stakeholders will be encouraged to explore different scenarios with varying potential impacts on ecosystem services.

In addition, we will use empirical methods to assess the economic significance of OA effects.
In work package 5.4 we will employ a survey approach with choice experiments to evaluate potential negative values of OA on coral reefs and the related services in Papua New Guinea.

Work package 5.6 will additionally employ stakeholder participation approaches and will use discourse-based measures for evaluating OA impacts on ocean services and for deriving options for a resilient management.

Back to Scientific Programme BIOACID II

Lead Proponent: Dr. Felix Christopher Mark (AWI, Bremerhaven)

Ocean acidification is an additional stressor developing in parallel to ongoing climate warming. Future impacts of ocean acidification on organisms and ecosystems are expected to be greatest in Polar Regions, owing to enhanced CO₂ solubility in cold waters and body fluids and to the concomitant exposure of organisms to a strong warming trend. At the same time, thermal tolerance windows are narrower and thus sensitivities to combined stressor effects are likely to be higher in cold-adapted polar compared to temperate species. The expected rise in carbon dioxide concentrations and temperature in the oceans (800-1000 μatm and 1-2 °C, respectively, until the year 2100 (IPCC, 2007)) may thus prove to be particularly threatening to Arctic ecosystems.

As the oceans are warming, fish stocks are moving with the water masses of their preferred temperatures to stay within a physiologically optimal temperature range, provided further factors such as food availability and competition with other species allow for that. This has already been documented for several fish species of the North Sea, which have been moving northward at a rate of approximately 12 km per decade (Drinkwater 2009, Perry et al. 2005). In response to this warming trend, the North Arctic stock of Atlantic cod (Gadus morhua) has also shifted spawning areas to the north (Sundby and Nakken 2008) and expanded its range into the Barents Sea (Drinkwater 2009). For the greatest part of the year, juvenile Atlantic cod are now frequently found in the coastal waters of Spitsbergen (Olsen et al. 2010), leading to strong competition with native Polar cod (Boreogadus saida). Polar cod is a dominant fish species on the Arctic shelf and is considered a key species in Arctic ecosystems. It is not clear, however, how these two species will interact in the long term and whether the ecosystem’s species composition will change due to the range expansion of the Atlantic G. morhua into the Arctic (Renaud et al. 2011).

Ecosystem-level perspective of how species interactions are affected by the synergistic effects of shifting temperatures, CO2 and hypoxia levels, building on a mechanistic understanding. The integration of CO2 sensitivity on a thermal matrix as defined by the principles of oxygen- and capacity-limited thermal tolerance emphasizes how species-specific sensitivities and their minimal levels of performance influence the window of temporal and spatial overlap defining the temperature range of coexistence as well as the changes in relative performance. Graph modified from Pörtner and Farrell 2008, Pörtner 2010.

The effects of ocean warming on fish distribution and physiology have been studied and documented to some extent in Atlantic cod (e.g. Colosimo et al. 2003, Lannig et al. 2003, Loeng and Drinkwater 2007, Mueter et al. 2009, Pörtner et al. 2008, Pörtner et al. 2001, Rose 2005) and to a lesser extent in Polar cod (Gjosaeter and Ajiad 1994, Graham and Hop 1995, Hop and Graham 1995, Nahrgang et al. 2010). However, very little is known about how the physiology or distribution of these species is altered by the additional effects of hypercapnia. Moreover, we lack data about how hypercapnia will modify the interactions between species, which are already affected by the warming trend. Using Atlantic cod and Polar cod as model species, we therefore propose to study the competitive interaction between two currently coexisting Arctic fish species under the combined effects of ocean acidification and warming (OAW) in an Arctic ecosystem, the Kongsfjord in Spitsbergen.

In this case study we intend to take into account species physiology, behaviour and life cycle and to investigate the hypothesis that these species will be impacted differently by OAW, with the result of future changes in their competitive interaction. In the coastal waters of Spitsbergen, Atlantic cod find themselves at the northern limit of their geographical distribution and thus at the lower end of their thermal tolerance range. The opposite holds true for Polar cod. Spitsbergen marks the southern boundary of its distribution range and the upper end of its thermal tolerance range. This implies that within the range of their coexistence around Spitsbergen, Atlantic and Polar cod are both energetically limited and their physiological performance should be highly susceptible to further stressors. The increasing concentration of carbon dioxide is clearly one of them (Pörtner 2010). From that perspective, it is our view that ocean acidification may be a critical factor controlling the interaction of coexisting species and that it is likely to determine the outcome of their different abilities to face OAW, i.e. be displaced or restricted to a less favourable habitat (Fig. 4.1, Abrams et al. 2008, Matthews et al. 2010).

For a holistic and integrative analysis of OAW, it is important to consider the different sensitivities and susceptibilities of the various life stages of the two species, as well as their interaction with their prey organisms and thus, their dependence on the food web.

Previous research on the effects of elevated CO₂ levels on marine fishes led to the general notion that due to their powerful mechanisms of ion regulation they are not particularly vulnerable to ocean acidification. Adult cod are able to compensate for acid-base disturbances (Larsen et al. 1997) and show no substantial effects of hypercapnia on physiological performance (Melzner et al. 2009a). However, studies in various species demonstrated chronic effects of environmental hypercapnia on juveniles (Moran and Stottrup 2010), and a sensitivity of eggs and early life stages that was higher than in adults. It must be mentioned, however, that all of these observations were reported for CO₂ concentrations beyond realistic ocean acidification scenarios (Ishimatsu 2005, Kikkawa et al. 2004). The resulting view that fish are largely insensitive to OA may therefore be premature.

In fact, recent findings demonstrated behavioural disturbances in tropical coral reef fishes exposed to hypercapnia levels according to ocean acidification scenarios (Munday et al. 2009c); as well as alterations in larval development of cod (Frommel et al. in press) and herring (Franke and Clemmesen 2011). Also, the hypothesis that sensitivity to thermal extremes is enhanced under projected ocean acidification levels was confirmed in coral reef fish (Nilsson et al. 2009, Pörtner and Farrell 2008). In general, sensitivity of fishes to ocean acidification may be higher at temperature extremes, a hypothesis to be tested in fishes from various climate zones. At the same time, the allometry of thermal limitation indicates that tolerance to temperature extremes varies across life stages and decreases with increasing body size (e.g. Pörtner et al. 2008, Pörtner and Knust 2007, Storch et al. 2011). Accordingly, sensitivity to OAW may also vary during ontogeny as recently seen in crustaceans (Schiffer et al. in prep). The consequences of these observations for larval recruitment also remain to be explored. This fragmented knowledge base clearly calls for a better understanding of how exposure to combined CO₂ and temperature scenarios contribute to shaping fitness windows. This includes the question whether all life stages respond similarly or whether some of them represent potential bottlenecks for population survival.

Most life stages of Atlantic and Polar cod feed on planktonic organisms (Levasseur et al. 1994, Lowry and Frost 1981, Renaud et al. 2011). Their availability and nutritional quality are a very important secondary effect of OAW, likely influencing development and performance of the early life stages of both fish species. Driven by climate change, plankton communities undergo well-documented shifts in composition and spatial ranges (Beaugrand et al. 2009), which, in a bottom-up control process, influences the biogeographic distribution of the fish stocks that prey upon them (Drinkwater 2009, Drinkwater 2006). In this respect, it is of considerable importance, that, by nature, invasive species are more likely to be generalists than specialists and thus might be more successful than natives at adapting to changes in food availability and composition (Dukes and Mooney 1999). In the coastal waters of Spitsbergen, this is mirrored in the diets of Atlantic and Polar cod (Renaud et al. 2011) that show a more varied food composition for Atlantic cod. This might prove advantageous for the fitness and potential of Atlantic cod to adapt to a changing climate.

The success of predation, and thus survival, also depends on dedicated behaviour of the predator and its prey. Studies in tropical coral reef fish revealed that exposure to increased CO₂ strongly disturbed avoidance behaviour in juveniles and, as a consequence, resulted in their enhanced predation. These behavioural changes are presumably elicited by hypercapnia effects on the central nervous system. By changing species behaviour, hypercapnia likely has the potential to overthrow the balanced food-web interactions in this particular ecosystem (Ferrari et al. 2011, Munday et al. 2009a, Munday et al. 2010). This aspect has never been studied in adult or juvenile temperate and boreal fish and therefore needs to be addressed in the interactions between Atlantic and Polar cod and their prey.
The Gadidae family comprises some of the commercially most important fish species in the North Atlantic, namely cod, haddock, pollack and whiting, and Polar cod has also been the target of substantial industrial fishery in the Arctic (FAO Fishery Statistic). The Atlantic cod is now the subject of intensive aquaculture in Norway. It is therefore clear that any shift in the population structure, caused by OAW could have far reaching effects not only on the ecosystem itself but also on fisheries. It has also been suggested that OAW may have deleterious effects on aquaculture (Guinotte and Fabry 2008). The socio–economic consequences of such scenarios need to be explored.

General objectives:

This consortium sets out to investigate how the combined effects of OAW will affect different life stages of the interacting fish species Gadus morhua and Boreogadus saida and their prey. Its strength lies in the integrative approach across levels of biological organisation, from the genome to the ecosystem. Tightly intertwined work packages, which will rely on several joint acclimation experiments, will allow a thorough analysis of putatively shifting species interactions and their implications at ecosystem and socioeconomic levels.

Objectives include addressing the question whether OAW affects interacting species differently due to divergent physiological optima and ranges, expressed in thermal tolerance windows and associated performance capacities and phenologies of specific life stages. Crucial mechanisms as well as causes and effects will become accessible from unravelling the connections between levels of biological organisation, from genomic, molecular to cellular, individual and population level. Scopes for acclimation (physiology and behaviour) and adaptation (evolution) that together define species resilience will be studied in various life stages (eggs, larvae, juveniles, adults) and the most sensitive one(s) identified. Functional determinants of individual fitness such as ion and acid-base regulation, mitochondrial energy metabolism and immune response will also be examined. Furthermore, it will be addressed how these processes as well as fitness may be influenced by food quality and availability.

This consortium will address the following questions:

• How will OAW influence species distribution, competitiveness and behaviour (WP 4.1 and 4.6)?

• Will food web mediated OAW effects influence the vulnerability of species (WP 4.5, 4.8, 4.9)?

• Which life stages are most susceptible to OAW and contribute most to ecosystem level effects (WP 4.1, 4.4, 4.5, 4.6 and 4.7)?

• How do OAW effects become manifest on different levels of biological organisation, how are they linked and interdependent across levels of organisation (WP 4.1, 4.2, 4.3, 4.4, 4.5 and 4.7)?

Research approaches:

Each of the nine work packages in this consortium will engage with a specific level of biological organisation to have their results integrated into a projection of responses at ecosystem level and their socioeconomic consequences in consortium 5 (WP 5.6).
Experiments will be conducted at various laboratories. At the Alfred Wegener Institute in Bremerhaven, Germany, adult and juvenile fish as well as copepods will be kept in specifically designed OAW acclimation systems that were refined (and in part already acquired) during BIOACID I. Cultures of larval and juvenile fish and pteropods will be set up under laboratory conditions at the University of Bergen, Norway and of juvenile fish, pteropods and copepods at the AWIPEV laboratory in Ny-Alesund, Spitsbergen. Fish and copepods will be caught from wild populations with RV Heincke around Spitsbergen and Norway in 2012 and 2013 in close cooperation with our Norwegian project partners in Bergen and Tromsø. We will further include fish and eggs from Norwegian aquaculture and also rely on various life stages cultured at the Sven Lovén Centre for Marine Sciences in Kristineberg, Sweden (Atlantic cod adults, eggs, larvae) and the National Cod Breeding Centre in Tromsø (Polar cod adults, eggs, larvae).

Work packages 4.1, 4.2, 4.3, 4.6 and 4.7 will rely on juvenile animals from common incubations of juvenile Atlantic cod (spring 2013) and Polar cod (spring 2014) at various temperature-pCO2 combinations at the Alfred Wegener Institute. These incubations (organized by WP 4.1) will thus serve as a central hub for several work packages, ensuring thorough connections between the work packages while at the same time reducing the effort and number of individuals needed per incubation.

To trace individual acclimation histories for each juvenile fish, individuals from all stocks will be tagged and populations screened for their bandwidth of growth and other environmental adaptation-relevant physiological performances (‘whole organism phenotype’, WP 4.1), as well as for genetic variability (‘genotypes’, WP 4.3). The studies will also define the diversity of responses from which selection and further adaptation will be possible, increasing the resolution and accuracy for predictions at the population level. Analysis of transcriptomic responses (WP 4.3) along with adaptations of the proteome (WP 4.2) will provide information on adaptation mechanisms, which become manifest at cellular and systemic levels.

Consideration of within population diversity will increase the resolution and accuracy for predictions at the population level. Such predictions also require the identification of the most sensitive life stages and transition phases, including reproduction, fertilisation success, egg and larval development and larvae to juvenile metamorphosis (WP 4.4 and 4.5). Species-specific differences and shifts in performance characters are hypothesized to shape interactions within food webs (WP 4.5 and 4.6). CO₂ may affect such processes due to changes in relative performance and in behaviour. WP 4.6 will set out to identify behavioural changes in juvenile fish and elucidate the neuronal underpinning of OAW effects on behaviour using MRI and NMR spectroscopy.

For an inclusion of food web effects, we will integrate the copepods and pteropods reared under the same schemes of OAW in WP 4.8 and WP 4.9 and quantify prey uptake, catch rate by juvenile cod (WP 4.6) as well as potential changes in their food quality (WP 4.8 and 4.9).
To this end, work packages 4.8, 4.9, 4.4, 4.5 and 4.7 will conduct joint experiments on copepod and pteropod performance, on the responses of eggs and fish larvae to CO₂ and changing food availability, one to be carried out in summer 2013 at AWIPEV in Ny-Alesund, in spring/summer 2014, Bergen, Norway, and at the AWI facilities. Experiments will be carried out in close collaboration with our external co-operators. For testing the role of such phenomena under field conditions, these work packages will also join BIOACID consortium 1 during the common mesocosm studies (KOSMOS) in Gullmar Fjord, Kristineberg, Sweden, in spring and summer 2013.

In cooperation with the bridging WP 5.6 in consortium 5, we will finally address the socio- economic implications for fishery and aquaculture and establish their societal relevance. To do so, we will connect to an international network of ocean acidification researchers who already investigate the socioeconomic aspects of OAW. This will provide a means to further extrapolate from the findings of this consortium and disseminate them to the public.

Back to Scientific Programme BIOACID II

Lead Proponent: Dr. Dirk de Beer (Max-Planck-Institute for Marine Microbiology, Bremen)

The acidification of the oceans due to rising carbon dioxide concentrations in the atmosphere can be predicted quite well. In contrast, its effects on biodiversity and biological functions are still difficult to foresee. For organisms with long life spans, it is difficult to estimate, if and how these organisms and their communities will adapt to the future pH decrease. This can definitely not be addressed by short-term laboratory experiments. For example, in a short-term experiment, the initial stress responses can blur possible acclimatization mechanisms. Furthermore, evaluations of evolutionary consequences by short incubations could also be very uncertain.

Consortium 3 focuses on natural reefs such as those created by tropical corals or cold-water corals or mussels. These animals depend on calcification.
If more CO₂ is dissolved in sea water and thus less carbonate ions are available, reefs might be endangered or even erode – growth is only possible at high energetic costs or the more acidic water might affect the calcium carbonate structures. Oases of biodiversity and spawning or nursery areas of important fish species could be lost this way.

Three locations in the Arctic, the temperate and the tropical climate serve as natural laboratories. At CO₂ sources off Papua New Guinea, mussel reefs in the North and Baltic Seas and at the cold-water coral reefs off the Norwegian coast, the scientists study microbes, micro- and macro-algae, invertebrates and the corals or the mussels themselves in connection with the carbonate chemistry of the water and nutrients. With their different living conditions, the natural reefs can be used as windows to the future. This allows to determine changes of physiology and fitness of the organisms, the composition of species, and finally of the reef ecosystem.

Measurements and long-term experiments in the laboratory accompany the observations and experiments. Population surveys provide insights into how locals use the fragile ecosystem and how they will cope with expected changes, particularly the potential economic losses.

Cold-water coral reef in Arctic climate.
Photo: JAGO-Team, GEOMAR

More about the science of Consortium 3.

Lead Proponent: Prof. Dr. Martin Wahl (GEOMAR, Kiel)

The distribution of species is a result of ecological, evolutionary, geological, oceanographic and climatic conditions. The characteristics of these species and their number determine the different roles and functions within the system and how the whole community might react to to stress and disturbances. Global factors such as temperature and pH and regional ones like salinity, eutrophication or oxygen concentration can disrupt the assemblage. Additionally, the immigration of new species, overfishing, pollution and structural changes of the coast mean further stress.

Previous studies have explored effects of individual stressors to individual species. Little is known about how a whole system reacts to a combination of factors: We know that there will be changes in marine communities – but not in which direction, to what extent and with what consequences for the ecosystem.

The consortium BIOACID 2 “Responses of benthic assemblages to interactive stress” will simulate a combination of climate change factors in communities that exist on the floor of the North and Baltic Sea. As most dominant parameters, the increase in temperature and decrease in pH in water (acidification) are focused on.

For the experiments, typical water plants and their dependant species were selected from the North Sea and from the Baltic Sea: the bladder wrack Fucus vesiculosus and the seagrass Zostera marina / Zostera noltii. Seagrass and wrack communities are widely distributed in both seas and play important roles as primary producers, carbon sinks, water purifiers, stabilizers of sediments, energy sources for microbes and herbivores and providers of substratum and structure of epibionts and juvenile fish.

To investigate how these communities alter due to climate change, benthocosms, experimental tanks equipped with a capacity of 4,000 liters, were set up in Kiel and in List (Sylt island). In the containers, temperature, pH, oxygen, salinity, light, CO₂ pressure, nutrients, and other control values can be adjusted precisely. Several three to four months long experiments in List and in Kiel help to better understand individual and interactive effects of a variety of stressors on the represented species.

Lead Proponent: Prof. Dr. Ulrich Sommer (GEOMAR, Kiel)

The ocean covers about two thirds of the earth’s surface. Marine plants and bacteria produce about half of the global biomass. Three “services” of the oceans are most important to mankind:

• The ocean absorbs carbon dioxide (CO₂) from the atmosphere and stores this greenhouse gas in the deep
• The ocean provides fish and other marine animals for food.
• The ocean represents an irreplaceable recreational value

Scientists have found out that plankton responds sensitively to ocean acidification. While some species are suffering from acidification, others seem to benefit if more carbon dioxide is dissolved in the sea water. These effects continue from the base of the food chain to its very end – for example if economically important fish species or fish stocks already threatened by overfishing find less food.

It is still unclear, how material and energy flows vary as a result of ocean acidification and how these variations may affect each other. In addition, the impact of other environmental changes, in particular rising temperatures, but also over-fertilization (eutrophication) and pollution as well as the reciprocal influences of these factors have been explored only partially yet. It is also uncertain if organisms are able to adapt to environmental changes through evolution. Laboratory experiments with various species suggest this, but studies under natural conditions are due.

Consortium 1 “Pelagic ecosystems ocean acidification” therefore aims to examine the effects of various environmental changes, in particular acidification and warming, to the whole ecosystem in the open water. In consequence, it is easier to better assess if and to what extent the ocean of the future can provide his “services”.

In several mesocosm experiments in the laboratory and in the field, BIOACID scientists simulate possible changes: The Kiel mesocosms – floating structures, each including up to 80 cubic metres of water – are employed in 2013 for studies in the Swedish Gullmar Fjord and 2014 in the North Atlantic Ocean in Gran Canaria. At GEOMAR Helmholtz Centre for Ocean Research Kiel, four laboratories with indoor mesocosms are used to learn how communities in the Baltic develop in autumn and summer under elevated temperature and CO₂ conditions.

More about the science of Consortium 1.

In so-called mesocosms, scientists simulate future ocean conditions.
Photo: Maike Nicolai, GEOMAR
Indoor-mesocosms allow experiments under controlled conditions.
Photo: Aleksandra Lewandwoska, GEOMAR

Back to Scientific Programme BIOACID I

Back to Scientific Programme BIOACID I

Overarching questions

• Which physiological mechanisms define sensitivity or tolerance of marine animals to ocean acidification and how do they set or modify performance levels and fitness?
• Can acclimation capacity (gene expression capacity) for such mechanisms explain physiological plasticity?
• How does acclimation or adaptation to new levels of CO₂ and temperature affect organism performance?
• In a comparison of species and their populations from temperate to polar climates, do they differ in their sensitivity or capacity to resist ocean acidification through acclimation or evolutionary adaptation? How do these findings relate to differences in temperature and associated ocean physicochemistry?
• Which life stages of functionally important marine organisms are most sensitive to ocean acidification and how does the level of sensitivity relate to the ontogeny of physiological mechanisms?

Ecosystem effects of ocean acidification include those on metazoan life. However, while ecosystem effects of warming trends have clearly been identified, those of ocean acidification are still equivocal. Within the next decades, elevated CO₂ levels are expected to affect marine water breathing animals directly through effects on the physiology and performance of the individual organism and indirectly through changes in food web structure. Emerging knowledge indicates that sensitivity to elevated CO₂ levels differs between animal phyla and species. It may also differ depending on geographical latitude and associated climate conditions. Effects may be large and potentially detrimental especially in life forms with a low metabolic rate, for examples among calcifying benthic macroorganisms (Wood et al., 2008) or in the deep sea. This hypothesis is in line with recent observations in habitats contaminated by natural CO₂ emissions, e.g. in volcanic areas around Ischia (Hall-Spencer et al., 2008). Initial findings suggest decreased growth and enhanced mortality of sensitive species such as among molluscs or echinoderms in response to a doubling of CO₂ from pre-industrial levels to 560 ppm (Shirayama and Thornton 2005), a value which is likely surpassed during this century. As effects of ocean acidification are expected on top of those of ocean warming, studying ecosystem effects of OA will thus need to consider both, the direct influence of ocean physicochemistry on individual organisms and species, and also the CO₂ dependent modulation of responses to temperature in particular.

For an in-depth cause and effect understanding, it is essential to unravel the physiological mechanisms that define whole organism sensitivity to ocean acidification (e.g. Pörtner et al. 2004, Fabry et al. 2008) and especially those, which synergistically interact with temperature effects on marine organisms (cf. Pörtner et al. 2005). A current hypothesis emphasizes a key role for the capacity of acid-base regulation in defining sensitivity (Pörtner, 2008 for review). Available data indicate that deviations of extracellular pH from its setpoint mediate several of the observed whole organism effects. Theme 2 will investigate how and to what extent these disturbances affect whole animal performance and how acclimation to various CO₂ levels can alleviate some of these effects. It will also address to what extent sensitivity to ocean acidification interacts with thermal stresses and is shaped by the specialization of organisms on ambient climate conditions according to latitude.

Effects of anthropogenic ocean acidification on animal communities are expected on medium to long time scales, due to the progressive accumulation of CO₂ and due to long generation times. In variable environments (e.g. upwelling areas, Feely et al., 2008) not only the drift in mean physicochemical parameters but also enhanced amplitudes will require consideration in analyses of CO₂ effects. For an analysis of the interaction between specialization on various climates on the one hand and sensitivity to ocean acidification on the other hand, physiological studies (of e.g. performance and acid-base regulation) as well as investigations of gene expression patterns and population structure will be carried out in species and populations living in a climate gradient across latitudinal clines. Comparisons of fertilized eggs, juvenile and adult life stages will be essential to identify the bottlenecks of sensitivity throughout ontogeny as well as their physiological background. The physiological principles shaping performance may also control calcification, and thus the shell growth of bivalves and other calcifiers over time. Performance has been shown to link climate change to ecosystem effects of warming (Pörtner and Knust 2007). Performance characters like growth or foraging capacity are likely also involved in multistep processes affecting marine food webs. Here, species-specific responses and sensitivities cause various species of an ecosystem to be affected differently, resulting in changes in species interactions, population adaptability, food web structure and associated carbon fluxes. The work will include species of coastal areas and relevant to fisheries and other marine services. Theme 2 also includes approaches to test and further develop mechanistic concepts and models of effects of ocean acidification. This includes kinetic modelling of the mechanisms of ion and acid-base regulation for an improved quantitative understanding of effects, to generate a basis for a more comprehensive, mechanism based modelling approach.

Back to Scientific Programme BIOACID I

To address and better understand the chain from biological mechanisms, through individual organism responses, food web and ecosystem effects, to economic impacts, five consortia were established for BIOACID phase II:

• Consortium 1: Pelagic ecosystems under ocean acidification: Ecological, biogeochemical and evolutionary responses
• Consortium 2: Responses of benthic assemblages to interactive stress
• Consortium 3: Natural CO₂-rich reefs as windows into the future: Acclimatization of marine life to long-term ocean acidification and consequences for biogeochemical cycles
• Consortium 4: Effects of ocean acidification in a warming climate on species interactions at distribution boundaries: Mechanisms and consequences at ecosystem level
• Consortium 5: Ocean services

• The scientific programme of BIOACID I (October 2009 – September 2012)
• The scientific programme of BIOACID III (October 2015 – November 2017)

Five thematic areas have been identified which cover the range of processes from the base of the marine food chain to the community and ecosystem level, and of mechanisms from the sub-cellular to the whole organism level. In view of their distinct sensitivities to ocean acidification, calcification and carbonate dissolution processes will be the focal point of a separate theme. According to these research priorities the scientific programme of BIOACID I is structured as follows:

• Theme 1: Primary production, microbial processes and biogeochemical feedbacks
• Theme 2: Performance characters: Reproduction, growth and behaviours in animal species
• Theme 3: Calcification: Sensitivities across phyla and ecosystems
• Theme 4: Species interactions and community structure in a changing ocean
• Theme 5: Integrated assessment: Sensitivities and uncertainties

• The scientific programme of BIOACID II (September 2012 – August 2015)
• The scientific programme of BIOACID III (October 2015 – November 2017)

BIOACID III bridges between different branches of ocean acidification research and provide an assessment of short- to long-term responses and their underlying mechanisms at the level of organisms, populations, communities and ecosystems to multiple drivers leading up to ecosystem services.

Synthesis activities will be structured into three major themes. Each of them covers the range from organism responses to community and ecosystem effects, to biogeochemical impacts and consequences for ecosystem services. Also, each theme will contribute to the Integrated Assessment, which includes risk assessment as well as the development of future scenarios, management options and offering policy advice.

The scientific programme is devided into the following areas:

• Theme 1: Pelagic Ecosystems and Biogeochemistry
• Theme 2: Shifts in Benthic Ecosystems and their Services
• Theme 3: Ocean Acidification and Warming Impacts Across Natural Systems and Society: From Mechanisms to Sensitivities and Societal Adaptation
• Integrated Assessment

• The scientific programme of BIOACID I (October 2009 – September 2012)
• The scientific programme of BIOACID II (September 2012 – August 2015)

The Integrated Assessment (IA) is an overarching activity, which involves all BIOACID principle investigators. Information exchange for the Integrated Assessment will be active throughout the duration of the project. It will be guided initially by the theme leaders, followed up by the Integrated Assessment task force, which will commence its work after twelve months into the project (September 2016) and continue for six months after the end of the core project.

Integrated Assessment Members:
Ulf Riebesell, GEOMAR
Hans-Otto Pörtner, AWI
Thorsten Dittmar, Universität Oldenburg
Maren Voss, IOW
Martin Wahl, GEOMAR
Ulf Karsten, Universität Rostock
Felix Mark, AWI
Stefan Gößling-Reisemann, Universität Bremen
Kathrin Rehdanz, IfW
Martin Quaas, CAU
Wolfgang Koeve, GEOMAR
Felix Ekardt, Universität Rostock
Konrad Ott, CAU

Back to Scientific Programme BIOACID III

Theme leaders:
Felix Christopher Mark, AWI
Stefan Gößling-Reisemann, Universität Bremen

Theme members:
Daniela Storch, AWI
Catriona Clemmesen, GEOMAR
Martin Quaas, CAU
Felix Mark, AWI
Silke Lischka, GEOMAR
Hans-Otto Pörtner, AWI
Stefan Gößling-Reisemann, Universität Bremen

Marine ecosystems will be increasingly affected by the effects of ocean acidification and ocean warming, which can be exacerbated by further stressors such as hypoxia. Environmental change can either influence the physiology of plankton, marine fish and invertebrates directly across all life stages or affect them indirectly by changing the composition and quality of food web connections. This will alter the species abundance and composition of future ecosystems, entailing putative changes in ecosystem services for humans by e.g. affecting artisanal and industrial fisheries and the oceans’ value for recreation and tourism.

Many effects of ocean acidification and warming on organismal physiology can only be traced back from the organismal to cellular and molecular levels. Projecting species robustness and ecosystem resilience requires integration of these levels. Projecting future species composition at ecosystem level requires the integration and extrapolation of variable species responses. These responses are currently identified only for a number of selected taxa, and knowledge is especially needed for those species projected to be invasive and undergo changing interactions.

This can be accomplished by meta-analyses and models that consider climate scenarios, multiple stressors and species interactions over time. Both have been included in the recent IPCC AR5 WGII report, based on emerging data of synergistic effects of ocean acidification and warming mainly for fish and marine invertebrates, including also estimates of economic impacts. A range of marine ecosystem services to human societies might be impacted by ocean acidification and warming. First results from BIOACID II show concern among affected stakeholders – ranging from fishers to tourism operators – is growing.

For fish stocks, which comprise the most important food provision service of the oceans, available data are still too patchy to support a high level of confidence in projection of ocean acidification and warming impacts and, so far, the effect of ocean warming alone has been modelled to project changes in catch potential. There is an urgent need to increase the level of knowledge and data available for modelling at the ecosystem level, including food webs and higher trophic levels such as fish to reliably project the synergistic effects of ocean acidification and ocean warming on marine ecosystems and their services to inform economists, political decision makers and society.

More about the science of Theme 3

Building on the knowledge and capacities of ocean acidification and warming effects on marine fish and invertebrates that were generated in BIOACID I and II, this theme sets out to integrate ecophysiological data across all levels of biological organisation (molecule – organism – population – ecosystem) for marine fish and invertebrates.

In an integrative manner, Theme 3 will build a database comprising ocean acidification and warming effects on marine fish and invertebrates from single metabolic pathways to life stage sensitivities and food web and ecosystem interactions. The database will be tailored to the specific needs of this theme and thus allow for a classification of positive and negative effects, of vulnerabilities as well as a parameterisation of effect sizes for several pCO2 ranges, thus making data available for meta-analyses and model information. Such efforts will be carried out within this theme by close cooperation between the different work packages, ranging from fisheries and bio-economic to social-ecological models. The results will then support an integrated assessment of risks associated with ocean acidification across all of BIOACID III.

The main objectives of this theme are:

• Identification of critical metabolic processes, key metabolic thresholds and sensitivity levels within and across several taxa
• Identification of most vulnerable life stages and transition phases of several major taxa to assess consequences for species and whole animal groups in life history
• Evaluation of OAW effects on species and food web dynamics
• Evaluation of OAW driven shifts in ecosystem functioning, habitat loss, marginalization and species replacement in ecosystems of high and low variability
• Meta-analyses and generation of input parameters for models
• Evaluation of trade-offs between ecological (stock size), economic (profits), consumer-related (harvest), and social (fishing effort) objectives for fishery management
• Quantification of uncertainties of OAW effects on commercially important fish populations, ecosystem resilience evaluation and suggestions for economically efficient adaptation of fisheries management
• Evaluation of impacts on ecosystem services and identification of stakeholder concerns and societal adaptation strategies to changes in ecosystem services provision

Research Approaches

In seven work packages, Theme 3 assesses vulnerabilities of marine ectotherms and their life stages from different taxa, habitats, and ecosystems. Based on this assessment, the risks for ecosystem services and affected human societies will be derived. The goal of these work packages is to develop a comprehensive picture of mechanisms causing effects, of the resulting sensitivity thresholds and effect sizes indicating vulnerability of various species and taxa, of effects on selected food-webs and ecosystems, and finally of the socio-economic consequences of ocean acidification and warming.

Led by specialists in their respective fields, the analyses of the work packages of this theme will be based on data available from BIOACID I and II and the current literature, with a specific interest on economically important species in boreal and Arctic latitudes. In a close cooperation between experimental biologists, (socio-) economists, and modellers, the results of the different meta-analyses will be directly incorporated into fisheries and bio-economic models, as well as social-ecological and socio-economic models.
All work packages will develop their own methods of data analysis and also contribute to a shared database, in which current knowledge will be entered and categorised. We will include all available studies that provide information on effects of PCO2 set by carbon dioxide bubbling and within the ranges of a) 500-650, b) 651-850, c) 851-1370, d) 1371-2900, e) 2901-10.000 and f) > 10.000 µatm.

The first level of analysis is directed towards organism responses, and strives to identify sensitive metabolic processes and threshold levels, as well as vulnerable life history stages in various taxa. Via the shared database, this data will then be passed on to the respective stock assessment and ecosystem models directly, as well as to the work packages of higher integration at species, taxon and community levels. The latter will also collect and evaluate ecological and physiological data available for marine ectotherms, yet with a focus on species interactions in food webs and the role and fate of selected taxa in their specific ecosystems. At the highest level of integration, the available data will be used to model and evaluate putative changes in ecosystem services and to develop and inform societal adaptation strategies. These models strive to evaluate the socio-economic costs and uncertainties of ocean acidification and warming for fish stocks and to inform ecosystem-based management and adaptation strategies. In this respect, this topic is directed to provide advice to economic and political decision-makers.

As there is an international recognition of the need for a higher level of certainty in predicting the socio-economic consequences of effects of ocean acidification and warming on marine ecosystems, this theme is also closely linked to the efforts currently made in the UK Ocean Acidification programme (UKOA) to create synergies and prevent parallel developments. Connections exist e.g. with the Centre for Environment, Fisheries & Aquaculture Science (CEFAS), the University of Strathclyde in Glasgow and the Plymouth Marine Laboratory.
Work packages and structure of Theme 3

Back to Scientific Programme BIOACID III

Theme leaders:
Martin Wahl, GEOMAR,
Ulf Karsten, Uni Rostock

Theme members:
Tal Dagan, CAU
Thorsten Reusch, GEOMAR
Birte Matthiessen, GEOMAR
Helmut Hillebrand, Universität Oldenburg
Frank Melzner, GEOMAR
Ulf Gräwe, IOW
Ulf Karsten, Universität Rostock
Martin Wahl, GEOMAR
Katrin Rehdanz, IfW

Ocean acidification is still an ongoing problem and has been the major research focus in BIOACID I and II as well as in numerous other research efforts worldwide. While a number of direct effects have been shown in the previous project phases, it became increasingly apparent that a simplistic approach is not suitable to reveal the real ecological importance of ocean acidification. 

As a consequence, in the second project phase we scaled up substantial along several dimension: complexity of the stress regime applied, incorporation of natural fluctuations, complexity of the biological system studied, and complexity of the responses assessed.

Using the novel Benthocosm system in Kiel (GEOMAR) and at the island of Sylt (AWI), the reactions of benthic communities (including macroalgae, mussels, seastars, gastropods, and crustaceans together with hundreds of associated species, e.g. ciliates, polychaetes, filamentous algae, microalgae, epibiotic bacteria) to the interacting factors warming, acidification, season as well as eutrophication and hypoxia. In the third phase of BIOACID, the diverse reactions of complex benthic communities to the multi-factorial and fluctuating climate change are modelled. Also, the socio-economical relevance of our findings shall be evaluated and recommendations developed for societal and economical decisions.

More about the science of Theme 2

The challenge for Theme 2 will be to feed the complex results into synthesising models to adequately exploit the newly achieved insights. The prime objectives of BIOACID III with regard to benthic ecosystems are the following:

• collecting and archiving all available data from the core experiments in BIOACID II but also from other BIOACID consortia and from published literature
• evaluating the potential for adaptation to environmental stress (also in an effort to compensate the inherent weakness of temporally restricted experiments)
• developing three different and complementary models with primarily descriptive but also some predictive intention
• developing a user interface allowing laymen to explore the impact of different aspects of global change on benthic communities
• assessing the awareness and responsiveness of the public to different ways of communicating the new information on global change impact and in particular ocean acidification

Research approaches
During a synthesis phase, we plan to pursue five parallel research lanes which complementarily and in close cooperation will deliver the essential pieces of the final picture.
The capacity of species (and, ultimately, communities) to adapt to a shifting environment will be evaluated based on an extensive meta-analysis of the rapidly growing body of literature. This capacity will help evaluating the trans-generation stress-sensitivity of a species.

Another potential buffering (or amplification) mechanism of stress is the associated shift in biotic interactions. In order to correctly weigh the importance of observed shift it is mandatory to have knowledge how much indirect and direct interactions contribute to the structuring and functioning of a community. This evaluation will be done using Structural Equation Modelling.

In an effort to project some of our findings onto a larger spatial scale, the interaction between climate change, Baltic hydrology and oceanography as well as the sensitivity and distribution of the ecologically and economically important bivalve Mytilus edulis will be modelled.

The multitude of data obtained from the series of core experiments in the Kiel Benthocosms will be used to assemble a new benthic model describing the drivers, interdependencies and responses of benthic communities under environmental pressure. The model is intended to describe the stress impacts at the organism to community level and to facilitate an evaluation of shifts in ecosystem services to be expected. The algorithms of the model will be incorporated into an interactive digital user interface.

A major challenge of global change impact research is to transport the new insights into public awareness. Ways to improve the “transport” of scientific insights into public awareness to increase societal acceptance for adaptation to ongoing environmental shifts shall be explored. We further expect that we will be able to extrapolate from shifts in ecosystem services to the socio-economic consequences of global change and provide valuable advice for managers and decision makers.

Work packages and Structure of Theme 2

Back to Scientific Programme BIOACID III

The goal of this consortium is to deepen and consolidate our understanding of ocean acidification effects and other stressors on plankton communities in terms of plankton ecology and biogeochemical functioning. This information will be implemented into an integrated assessment of ocean acidification effects on mainly pelagic ecosystem including possible feedback mechanisms.

We will synthesize the results of previous experiments obtained in BIOACID I and II and in related projects such as the Pelagic Ecosystem CO2 Enrichment Studies (PeECE) and Surface Ocean Processes in the Anthropocene (SOPRAN). Data-model synthesis will provide the necessary information on how to implement CO2/pH sensitivities into biogeochemical models that are used for regional to global scale simulations and future projections. These projections will provide a basis for better risk assessments, management options, and policy advice and will allow for evaluation of socio-economic consequences under different ocean acidification scenario

Theme 1 will address the following questions:

• What is the plankton community response to ocean acidification?
• Which biogeochemical impacts derive from changes in plankton community composition and activity?
• Are elemental budgets affected by ocean acidification?
• Which global ocean feedbacks might result from changes in ecological and biogeochemical states?

Research approaches

We will combine budget calculations, meta-analysis, and modelling to obtain a sound understanding of the effects of ocean acidification in combination with rising temperatures on the entire plankton food- web and fluxes of major elements.

The first step is a comprehensive review on the impacts of ocean acidification on marine planktonic communities, their vulnerabilities, and potential carry-on effects on higher trophic levels.

The second step is a network and meta-analysis aiming to assess the potential vulnerability of ocean acidification-induced changes in species composition and concomitant changes in the productivity of marine systems.

The final step is a dynamic modelling that synthesises information from the meta-analyses and improved process understanding at the community level. The findings will be extrapolated to the global ocean considering the complex interactions between atmospheric forcing, ocean dynamics, and biogeochemistry. Finally, three-dimensional scenarios will be generated on system-wide, large-scale responses on ocean acidification and other stressors.

Our synthesizing approach is essential to forecast how, when and where the impact of ocean acidification and co-occurring stressors act on the ecosystems and biogeochemistry of the ocean.

Workpackages and structure of Theme 1.

Back to Scientific Programme BIOACID III

Theme leaders:
Thorsten Dittmar, Uni Oldenburg
Maren Voss, IOW

Theme members:
Maarten Boersma, AWI
Kai Wirtz, HZG
Hans-Peter Grossart, IGB
Thorsten Dittmar, Universität Oldenburg
Ulf Riebesell, GEOMAR
Maren Voss, IOW
Andreas Oschlies, GEOMAR
Wolfgang Koeve, Julia Getzlaff, GEOMAR

To secure ecosystem properties and services in the future ocean we need to improve our understanding on response of pelagic communities to climate change, in particular to the emerging threat of ocean acidification.

In the recent years, a large effort has been set on elucidating responses to ocean acidification. Studies addressed responses from single organisms to plankton communities in experimental settings and in the ocean. These studies often included additional environmental factors, such as temperature or light.

A direct functional effect of ocean acidification was found for calcification which seems to be the most pH-sensitive process with decline by 25 per cent in projected acidification scenarios of the 21st century. Likewise, reproduction in decapod crustaceans, oyster and bryozoa seemed to be directly harmed when water pH drops below certain thresholds. Similarly, increased growth- and photosynthetic rates have been documented for elevated ocean acidification, most likely promoting photoautotrophic processes in algae with higher carbon assimilation rates in response to increased levels of dissolved CO2. Impacts of ocean acidification on traits such as elemental stoichiometry were also identified.
Ocean acidification and warming as combined stressors caused significant negative effects on calcification, reproduction, and survival of early life history stages of e.g. spider crabs and a significantly positive effect on photosynthesis.

It has to be clarified to what extend observations from experiments can be extrapolated to natural planktonic food webs and large biogeochemical cycles. Further uncertainties derive from the differing experimental set-ups. These have to be quantified in order to evaluate the significance of individual results.

To draw a more holistic picture, an integrative assessment of ocean acidification effects in combination with co-varying factors is urgently needed. Based on a review of empirical insights, more mechanistic process need to be described and substantiate model-based projections of how ocean acidification will impact on pelagic ecosystems and the services these provide.

More about the science of Theme 1