Ocean warming and acidification: organisms and their changing role in marine ecosystems

We investigate how climate change affects marine polar organisms directly and, thereby, their interactions and ecosystem functioning.

Objectives and Challenges

Organisms responding to warming and acidification are found in all groups and phyla, among autotrophs, heterotrophs, calcifiers and non-calcifiers. Animals in particular specialize on state and variability of their environment and hence are sensitive to conditions outside their normal range. Recent interdisciplinary research at molecular, physiological and ecological levels of biological organization (see details in ANNEX) has identified key mechanisms of animal response to climate change. These mechanisms require further investigation in order to elaborate the capacity and limits of acclimation and adaptation processes and the associated reasons for projected shifts in ecosystem species composition during climate extremes.

The climate regime is one major driver of functional specialization from gene to organism, thus shaping organism fitness, which is reflected e.g. in growth performance, fecundity and the capacity to perform relevant behaviours. Solely integrated analyses from molecule to ecosystem allow to identify cause-and-effect, functional constraints and trade-offs associated with adaptation and their consequences for biogeography and ecosystem functioning. The species inventory of a given ecosystem results from the interplay of environmental conditions, evolutionary adaptation and the immigration of pre-adapted species. Accelerated environmental change topples the delicate balance between selective and adaptive forces, when species elimination and replacement are out of equilibrium, causing change or loss of ecosystem functioning. Understanding ecosystem change, thus, requires understanding of organism response. Differential responses of organisms affect their interactions and might thereby explain changes at even higher levels as in marine food webs.

The challenges are to:

• elaborate the climate dependent evolution and functioning of selected key polar marine organisms and their ecosystems
• identify critical stages in the life cycle of selected organisms (e.g. eggs, larvae, adults) based on performance measures as indicators of sensitivity to ocean warming and acidification
• analyse physiological mechanisms defining performance levels and sensitivity and estimate acclimation capacity (gene expression capacity) for those mechanisms as the background of functional plasticity
• quantify impact and tolerance thresholds (tipping points) for various species and the consequences for their interactions
• compare responses and mechanisms in different populations of a species (e.g. in a climate gradient) reflecting potential for evolutionary adaptation (genetic differences)

Implementation

This work package focuses on selected species (e.g. among plankton, benthic invertebrates, fish and mammals) in Antarctic and Arctic oceans in general and of specific ecosystem compartments in particular, such as the head-down benthic community recently discovered at the underside of the Antarctic Riiser Larsen Ice Shelf, or the deep reefs at high latitudes, which are among the most vulnerable to Global Change. We use a comparative approach across latitudes to develop a deeper mechanistic cause-and-effect understanding of organism and ecosystem responses to variable climates and to ocean acidification. Organism effects to be identified include those causing shifts in material fluxes, food quality and food web structure. Organism effects may also lead to changing species abundance, biodiversity and, last not least, modified availability of marine living resources.

We integrate field and experimental studies to elucidate the impact of climate factors like temperature and CO₂, and the responsive mechanisms that set the performance of individual organisms, the genetic structuring of species and species complexes as well as species-to-species interactions. The respective analyses will range from effects of present change to those of climate variability in the past (TOPIC 3), the latter via studies of proxies (stable isotopes, trace metals) in lifetime growing hard structures or via phylogenetic trees. Remote sensing through marine mammals will identify hot spots of biological activity and reveal their own biogeography and acoustic behaviour. We will investigate across latitudes (in cooperation with WP 1 and WP 3), how selected species cope with changing environments and how this influences the flux of energy and organic matter, in the euphotic layer where zooplankton feed and reproduce, in deep water layers where dominant species over-winter, and in the benthos of open waters and under the ice shelf of polar areas.

An integrated approach across levels of biological organization identifies the molecular underpinning of climate dependent organismal performance associated with key processes like oxygen supply and food consumption in animals, energy budgeting and turnover, ion and acid-base regulation and stress resistance. Genomic and thus bioinformatics approaches in combination with systems biology identify differential gene expression patterns, gene clusters and regulatory networks as well as new candidate genes for further functional characterisation. Through the respective cellular functions protein structure and functional capacity as well as molecular networks and regulatory or signalling pathways define whole organism performance, tolerance and capacity to acclimate or adapt to change. Finally, implications of organism level processes for ecosystem structure and functioning are elaborated as potentially crucial for an understanding of ecosystem resistance.

We explore how specific performance, adaptability and sensitivity of our model species define their competitiveness and interaction patterns, and how changes at this level modify aggregate ecosystem-level processes that may finally add up to significant ecosystem transitions. The synoptic identification of physiological and ecological mechanisms operative across levels of biological organisation will provide a solid basis for a cause and effect understanding as well as for future scenarios and models of organism and ecosystem functioning and response to change.

Through studies of succession, population growth and competition, ecosystem transitions will be identified depending on the specific performance, adaptability and sensitivity of member species, their interactions and aggregate ecosystem-level processes. In specific examples, the identification of physiological and ecological mechanisms operative across levels of biological organisation will provide a solid basis for a cause and effect understanding as well as for future scenarios and models of organism and ecosystem functioning and response to change.

Milestones

• Likely scenarios for future climate development in different Polar Regions (Peninsula, Weddell Sea, Arctic waters) to generate realistic input data for abiotic experimental settings (year 1 in cooperation with other WP´s).
• Standardised methodologies for long term experiments (e.g. CO₂) and associated analyses (molecular, cellular, whole organism to field studies) (year 1).
• Key mechanisms that define sensitivities in relevant species, identification of corresponding threshold levels and links between organism response and ecosystem change (year 2-3).
• Modules for conceptual models of mechanisms in acclimation and adaptation and their consequences for population genetic structure (year 4).
• Contribution to mechanistic models of combined thermal and ocean acidification effects at the ecosystem level, naming uncertainties and probabilities and perspectives on new ecosystem states (year 5).

Deliverables

• Relate environmental change (e.g. ice conditions, ocean physico-chemistry) to principal ecological determinants, i.e. organism performance including calcification, population genetic structure as well as to ecosystem matter cycling, resistance and transition.
• Identify the physiological levers linking species biogeography, life history and fitness, energy budgets and metabolism, gene functions and regulatory networks depending on environmental and climate restrains.
• Define organism bio-recorders – high resolution archives of environmental change, recorders of evolutionary pathways and propensities in polar and temperate climates – that contribute to characterizing the relations between climate, climate variability, and genetic structures of key species, changing species interactions and biodiversity patterns across latitudes.
• Contribute to conceptual and quantitative models explaining climate forcing of ecosystems and linking mechanisms and processes at genetic, physiological and ecosystem levels.
• Specify organism mediated ecosystem change: past, present and future; contributions to vertically integrated, mechanism based modelling (environment – physiology – population dynamics – ecosystem functioning in polar and temperate latitudes).