Evidence for limited adaptive responsiveness to large-scale spatial variation of habitat quality

The ability of organisms to adapt their foraging behaviour to spatial variations in food availability and habitat quality is crucial to maximize energy intake and hence fitness. Under ideal conditions, habitat selection should result in a spatial distribution of individuals such that their fitness (energy reserves or condition) is roughly equal across habitats of varying quality. Using 11 yr of field data on Atlantic cod Gadus morhua distribution along the Greenland shelf, we investigated the foraging behaviour and life history of cod in heterogeneous environments. We combined information on energy reserves of cod with spatially resolved diet composition data to derive a measure of habitat quality and heterogeneity. Energy reserves in individual fish were best explained by the particular area they inhabited, whereas growth, population density, food quantity and interannual effects were of minor importance. Condition differed on relatively small spatial scales, at which cod would be capable of redistributing in favour of high-quality habitats. Our results indicate that particular areas may persistently allow higher fitness by sustaining high-conditioned individuals but suggest that replenishment of well-conditioned individuals in these high-quality habitats may take longer than expected. We conclude that cod exhibited limited scope in its behavioural response to spatial variation of habitat quality, leading to persistent spatio-temporal differences in energy reserves. Current climate change and fishing activities alter ecosystems and affect habitat heterogeneity, and the adaptive responsiveness of species to such changes in habitat quality is important in natural resource management

Effects of small-scale turbulence on lower trophic levels under different nutrient conditions

12 pages, 4 figures, 1 tableSmall-scale turbulence affects the pelagic food web and energy flow in marine systems and the impact is related to nutrient conditions and the assemblage of organisms present. We generated five levels of turbulence (2*10–9 to 1*10–4 W kg–1) in land-based mesocosms (volume 2.6 m3) with and without additional nutrients (31:16:1 Si:N:P µM) to asses the effect of small-scale turbulence on the lower part of the pelagic food web under different nutrient conditions. The ecological influence of nutrients and small-scale turbulence on lower trophic levels was quantified using multivariate statistics (RDA), where nutrients accounted for 31.8% of the observed biological variation, while 7.2% of the variation was explained by small-scale turbulence and its interaction with nutrients. Chlorophyll a, primary production rates, bacterial production rates and diatom and dinoflagellate abundance were positively correlated to turbulence, regardless of nutrient conditions. Abundance of autotrophic flagellates, total phytoplankton and bacteria were positively correlated to turbulence only when nutrients were added. Impact of small-scale turbulence was related to nutrient conditions, with implications for oligotrophic and eutrophic situations. The effect on community level was also different compared to single species level. Microbial processes drive biogeochemical cycles, and nutrient-controlled effects of small-scale turbulence on such processes are relevant to foresee altered carbon flow in marine systems.Access to installations was funded by the Large-Scale Facility of the University of Bergen and the Improving Human Potential Programme from the European Union through Contract No. HPRI-CT-1999-00056. This study was supported as part of the shared cost research project NTAP (Contract No. EVK3-CT-2000-00022) by the key action "sustainable Marine Ecosystems" of the European Community RTD Programme "Environment and Sustainable Development" and forms part of the ELOISE project cluster.Peer reviewe