Core Projects
Thermal Adaptation and Limitation
The impact of environmental change on the Antarctic silverfish Pleuragramma antarcticum – Identifying physiological and ecological limits
This project is funded by the Deutsche Forschungsgemeinschaft (DFG); DFG project: MI 1391/1; DFG Priority Program SPP 1158 Antarktisforschung
Pleuragramma antarcticum is a key species in the Antarctic marine food web!
In the Antarctic marine ecosystem the Antarctic silverfish P. antarcticum (Notothenioidei, Perciformes) occupies a similar ecological position as krill (Euphausia superba) does.
P. antarcticum is the only pelagic shoal fish and dominates pelagic fish biomass in many Antarctic shelf areas by >90%. This fish represents a major trophic link between zooplankton and a multitude of predators, including seals, seabirds, penguins and piscivorous fishes, making P. antarcticum a key species in the Antarctic marine food web.
Climate change in the Antarctic is not a future scenario but a fact!
Climate change is most evident at the Antarctic Peninsula, where near sea surface temperatures did rise by about 3°C within the last 50 years (Turner et al. 2005, Int. J. Climatol. 25: 279-294). Increasing temperatures strongly altered sea ice conditions and sea water salinity. These primary effects of increasing temperature entail secondary effects, namely alterations in phyto- and zooplankton communities.
Such changes at the base of the food web include shifts in species abundance and composition, in species energy content, and in the size structure of the community. Organisms such as P. antarcticum depending on the plankton community as a food source might thus be affected by environmental change in multiple ways, directly at the physiological level as well as indirectly through the food chain.
Aim of the project
Indirect evidence suggests that P. antarcticum might be highly sensitive to direct effects of climate change, i.e. increasing temperature and reduced salinity, as well as to indirect effects such as alterations in prey composition and availability. Accordingly, this project involves experimental studies on physiological sensitivity of P. antarcticum to changing temperature and salinity regimes, as well as feeding experiments to investigate the impact of changes in prey availability, prey size, and prey energy content on survival and condition of P. antarcticum. This study will provide a comprehensive picture of the sensitivity of this Antarctic marine key species to environmental alterations driven by climate change.
Contact investigator:
Cooperation:
Prof. W. Hagen, University of Bremen
Prof. M. Peck, Institute of Hydrobiology and Fisheries Science, Hamburg
Temperature-dependent energy budget in fish: Relevance of ecological and physiological phenomena
The growth performance of a number of fish species living in cold polar waters lies below the range commonly found by marine fishes from temperate and boreal waters (e.g. Brodte et al., 2006). There has been a long-standing debate in polar biology whether these reduced performances are a mere temperature effect (e.g. Pörtner, 2006) since compared to other regions Antarctic waters display similar levels of food availability for benthic fish. This leads to the basic question how fish use the food available in the environment and convert it into matter and energy. Surplus energy is available for growth and reproduction only after the requirements for maintenance are met. Energy availability for growth and fecundity depends, on the one hand, on the energy coming in from food and on feeding efficiency and, on the other hand, on energy allocation in the whole organism. The present project is intended to develop and apply new techniques to monitor energy flow and allocation in the whole organism. In particular, this includes experimental work (acclimation and growth experiments, measurements of standard metabolism and specific dynamic action, digestive enzyme capacities) and non-invasive NMR measurements at cellular and whole organism levels to calculate energy allocation in closely related fish species of the family Zoarcidea from polar and temperate regions (Antarctic, Arctic, White Sea, North Sea). The results will be compared to field data on growth performance and fecundity in order to evaluate whether the energy budget model and the underlying physiological processes can explain the respective field observations.
Contact Investigators:
Dr. Christian Bock
Physiological match and mismatch in climate dependent distribution of boreal marine invertebrates
The physiological mechanisms, by which temperature and its oscillations shape biogeography, species survival, and energy expenditure for growth are addressed as crucial elements of climate effects on ecosystems. Such climate dependent physiological patterns are most adequately identified in marine aquatic species which cover wide latitudinal clines in temperate zones (Northern hemisphere) (Pörtner et al., 2001). Each population of these species (frequently genetically different from neighbouring populations) is adapted to a specific climate regime on a gradient between warm and cold climates and the associated seasonal and inter-annual variability of its physical environment. Comparison of populations of the lugworm Arenicola marina is intended for a comprehensive identification and quantification of physiological processes sensitive to climate change (e.g. Sommer et al., 2002). The adjustment of oxygen supply versus demand appears most crucial in thermal adaptation; therefore components of the oxygen transfer system, like haemoglobin functional properties, blood and tissue oxygenation, as well as parameters setting oxygen demand and organismic performance will be investigated in populations from the Atlantic, the North and White Seas. For each of those populations, climate oscillations beyond previous optima may lead them to the limits of their adaptational capacity, to be identified as a mismatch in demand vs supply capacities. Based on such physiological studies a cause and effect understanding is expected, how climate factors, molecular and cellular design as well as physiological and ecological performance are interrelated. Identification of the unifying trade-offs and constraints involved in thermal adaptation likely contributes to an understanding of how climate gradients and their oscillations shape ecosystem functioning during climate change scenarios.
Contact Investigator:
Dr. Christian Bock
Cooperation:
Institute for Animal Physiology, Universität Münster
DFG-project: Po 278/11-2
DFG priority programme 1162 "The Impact of Climate Variability on Aquatic Ecosystems (AQUASHIFT)"
Evolution of hemocyanin
Evolution of haemocyanin and its influence on thermal sensitivity in cold adapted
Cephalopods – does form follow function?
Temperature, pH and oxygen concentration are the three most important parameters that influence oxygen-binding capacities of cephalopod blood and for survival at nearly -2°C, a cephalopod requires a highly specialised blood-gas exchange. By using extracellular haemocyanin, cephalopods possess a less effective respiratory protein than fish (which have intracellular haemoglobin). In order to successfully compete with fish, cephalopods have developed a high level of haemocyanin adaptability. Despite their prominent position in Antarctic food webs and being highly abundant, very little is known about Antarctic octopod physiology in general and specifically of the role of haemocyanin as a mediator between the organism and an extreme environment.
By means of an integrative physiological and molecular genetic approach, this study aims to shed light on the physiological adaptation as well as the phylogeny of octopodid haemocyanin during the adaptive radiation of these animals into Antarctic waters and to assist in explaining the recent biogeography of Antarctic octopods.
Evolution der Hämocyaningene und ihr Einfluss auf die Anpassungsfähigkeit kaltadaptierter Cephalopoden – form follows function?
Die drei wichtigsten Parameter, die das Sauerstoffbindungsvermögen von Cephalopodenblut bestimmen, sind Temperatur, pH und die Sauerstoffkonzentration im umgebenden Medium. Um bei Temperaturen um -2°C herum überleben zu können, müssen antarktische Cephalopoden einen hochspezialisierten Blut/Gas-Austausch besitzen. Cephalopoden benutzen das extrazelluläre Hämocyanin zum Sauerstofftransport im Blut, ein weniger effizientes respiratorisches Protein als zum Beispiel das der Fische, die Hämoglobin intrazellulär in ihren roten Blutkörperchen tragen. Um dennoch erfolgreich mit Fischen konkurrieren zu können, haben Cephalopoden ein hohes Maß an Anpassungsfähigkeit ihres Blutfarbstoffes entwickelt. Trotz ihrer weiten Verbreitung und wichtigen Stellung im antarktischen Nahrungsnetz ist recht wenig bekannt über die allgemeine Physiologie antarktischer Oktopoden und vor allem über die Rolle ihres Hämocyanins als Mittler zwischen Individuum und der extremen antarktischen Umwelt.
Die vorlegende Studie wird daher mit einem integrativen physiologischen und molekularbiologischen Ansatz versuchen, sowohl die physiologische Anpassung als auch die Phylogenie des Oktopoden-Hämocyanins während der Einwanderung dieser Gruppe in die antarktischen Gewässer näher zu beleuchten und damit zur Erklärung der Biogeographie antarktischer Oktopoden beitragen.
Publications: Melzner, F., Mark, F. C. and Poertner, H.-O. (2007) Role of blood-oxygen transport in thermal tolerance of the cuttlefish, Sepia officinalis. Integrative and Comparative Biology, 47(4):645-655.
Contact investigator:
Dr Felix Christopher Mark
Cooperation:
PD Dr Bernhard Lieb
Johannes Gutenberg University, Mainz
DFG project: MA 4271/1-1
DFP Priority programm SPP 1158 Antarktis
Life in cold oceans: activity dependent on extracellular ion regulation?
The physiological basis of temperature dependent distribution limits includes the specific role of extracellular ion concentration in setting limitations to lifestyle and life history evolution. The biogeography of marine crustaceans in cold oceans is related to the combined effects of extracellular Mg2+ levels [Mg2+]e and low temperature, which act synergistically to slow muscular activity in the cold (Spicer, Frederich et al., 2001). The highly active cephalopod molluscs may have overcome the constraint of high [Mg2+]e by slightly increasing the extracellular potassium concentration ([K+]e), thereby exploiting the antagonistic effects of magnesium and potassium. We attempt to develop quantitative knowledge on the temperature dependent effects of potassium and magnesium on animal life cycles as mirrored in changes of physiological performance, larval development, and growth rate. In addition, it appears most crucial to understand the biochemical mechanisms leading to the increased magnesium effect in the cold. Within crustacean phyla this work will focus on lithodid crabs, compared to boreal reptant crabs as well as boreal and Antarctic natant shrimps. Among cephalopods we focus on the boreal species Sepia officinalis for an analysis of principle mechanisms. From a more conceptual point of view, the study intends to explore whether limitations in ion regulation capacities and costs may play a role in setting the levels of biodiversity observed in extant Antarctic marine fauna.
DFG-project: SA 1713/1-1
Contact Investigators:
Astrid Wittmann
Dr. Franz Josef Sartoris
Cooperation:
Dr. Klaus Anger, BAH
Thermal tolerance in various stages of invertebrates with complex life cycles. Can we identify the bottleneck in life history causing large scale biodiversity patterns?
The latitudinal gradient of increasing biodiversity from the poles to the equator is one of the most prominent but least understood features of life on Earth (Hillebrand 2004). Although most taxa show such a pattern, several evidences of an inverse trend have been reported for marine organisms (Valdovinos et al. 2003). However, taxa exhibiting planktotrophic larvae always show a clear decrease toward high latitudes (Astorga et al. 2003). Three main hypotheses have been proposed to explain the low frequency of planktotrophic species at high latitudes: 1) Mortality increases at high latitudes due to starvation, 2) Mortality increases because of increased vulnerability to predation, 3) Reduced tolerance of larvae to low temperature. The latter hypothesis has not been evaluated in spite of the evidences pointing to the effect of temperature on the distribution of planktotrophic species in the ocean and evidences of physiological constraints to evolutionary thermal adaptation in the ocean. Temperature is the main factor explaining the decrease in diversity of planktotrophic species at high latitudes.
In collaboration with Dr Miriam Fernandez (ECIM and Universidad Católica) the general hypothesis of thermal tolerance is tested in crab larvae along the Chilean coast. Parameters of thermal tolerance are measured from the organismic to the cellular level (Pörtner 2001) in planktotrophic larvae using the Majid crab Taliepus dentatus as a model. Crab larvae are excellent models because they show extended larval periods and are planktotrophic. Moreover, Brachyuran crabs show large ranges of distribution and seem to be particularly sensitive to temperature.
Financial support:
Alexander von Humboldt Stiftung
FONDECYT Project Nr. 3060050
Pew Ocean Institute for Marine Conservation
Contact Investigator:
Dr. Daniela Storch
External Cooperation:
ECIM, Las Cruces, Department of Ecology, Universidad Católica de Chile, Santiago
CO2 sensitivity and tolerance in marine fish and invertebrates
scheme of CO2 affected acid base regulatory processes
Anthropogenic CO2 emissions are acidifying the world’s oceans. Under business as usual scenarios reasonable estimates suggest that decreases in surface ocean pH of 0.7 - 0.8 units (increases in pCO2 by 2,000 ppm) can be expected during the next 300 years (Caldeira and Wickett, 2003, 2005). Both, the rate and intensity of this hypercapnia induced acidification are unprecedented in the evolutionary history of the last 30 million years and will certainly represent a forcing factor capable of restructuring entire marine ecosystems (Legendre & Rivkin, 2005). However, relatively little is known on how, and at what concentrations, hypercapnia will affect the functioning, the physiological and structural integrity of higher marine organisms (e.g. Pörtner et al. 2005).
At present, one line of investigations at the AWI focuses on hypercapnia tolerance mechanisms of high – power marine ectothermic animals, mainly teleost fish and cephalopods. Both taxa are characterized by high metabolic rates in concert with closed blood circulation systems and a high regulatory capacity. We believe that these features enable them to maintain physiological equilibria at relatively high water pCO2 values.
Experimental approaches also target the ion- and acid – base regulatory capacities of model organisms from temperate and polar seas. We currently attempt to quantify gill ion – exchange transporter activities, protein concentrations and mRNA expression patterns that enable acclimation to ocean hypercapnia and maintenance of stable extra- and intracellular pH values and ion concentrations. Long term, sublethal hypercapnia exposure experiments focus on determining whether increased costs for ion regulatory processes affect cellular / whole animal energy budgets and, eventually, growth and aerobic performance of our model species.
Contact Investigator:
Dr. Magnus Lucassen
Interaction of climate factors: CO2 and temperature
Illustration of oxygen limited thermal tolerance model
Conceptual analysis, confirmed by a series of first experiments in a crustacean, predicts that CO2 enhances sensitivity to thermal extremes and thus, climate sensitivity. CO2 accumulating in the ocean is expected to narrow thermal windows of animals and thereby enhance temperature dependent shifts in geographical distribution (Pörtner et al., 2005, Metzger et al., 2007). Concomitantly, through affecting similar physiological mechanisms CO2 will exacerbate long-term hypoxia effects.
These interactions and their functional consequences are quantified in various life stages of representative Crustaceans from a latitudinal cline, including lithodid species from the sub-Antarctic and sub-Arctic. As magnesium regulation plays a major role in setting biogeographical patterns in Crustaceans in polar areas (Frederich et al., 2001), the interaction between temperature, O2 and CO2 in relation to temperature dependent magnesium effects on whole animal performance are also studied.
Further study focuses on the impact of temperature-CO2 interactions on energy metabolism and stress tolerance of marine fish, the stenothermal Antarctic eelpout, P. brachycephalum and its eurythermal counterpart, North Sea eelpout, Zoarces viviparus. Our goal is to identify the trade-offs in adaptation processes and in organismic energy budgets which shape the width of ecological niches in organisms from various climates. For an analysis of potential shifts in energy metabolism and acid-base status, we combine standard metabolic studies of P. brachycephalum during acute and chronic temperature and CO2 exposure with in vivo 31P NMR spectroscopy.
Contact Investigators:
Dr. Franz Josef Sartoris
Dr. Gisela Lannig