Evaluating the ecological impact of an oil spill is a complex issue requiring coherently articulated examination of the sequence of interactions that link the cell, where contaminants exert their effects, to the ecosystem, where interactions with human activities arise. This sequence of interactions traverses the frontiers between scientific disciplines (chemistry, toxicology, physiology, and fisheries ecology). Using the common sole (Solea solea L.) as a model species for the coastal habitats polluted by the “Erika” oil spill, our research project attempted to define indices of functional integrity that characterised the consequences of fuel exposure at the different biological levels. The coupling of field observations with experimental laboratory work revealed how functional alterations which are readily observable within individuals and their organs are progressively obscured as investigation progresses towards more complex organisational levels. Some of the approaches and indices are proposed as instruments for evaluating the impact of contamination by hydrocarbons.

The influence of temperature and light on growth and photosynthetic physiology were investigated in embryos of Fucus evanescens grown at 5 or 20°C under irradiances of 15 or 150 μmol photons m−2 s−1 for 7–10 days. Growth was light-independent, but high-temperature embryos were always significantly larger than those grown at low temperature. Photosynthesis-irradiance responses were measured at growth temperature and a standard temperature (20°C) to isolate instantaneous effects of temperature from acclimation responses. Our data indicate that growth and photosynthesis are uncoupled during the early development of Fucus, and that acclimation of the photosynthetic light-harvesting apparatus occurred. Light-limited net photosynthesis (Psub-sat) responded similarly to high temperature and low light. Rates of Psub-sat were similar in embryos grown at 20°C (regardless of light) and at 5°C in low (c. 1.2 nmol O2 mm−3 min−1), whereas those of 5°C high-light embryos were lower (c. −0.04 nmol O2 mm−3 min−1). Changes in Psub-sat were associated with changes in initial slope of the photosynthesis-irradiance curve (α) and dark respiration. Differences in α were attributed to increased absorption due to increased chlorophyll a content and PSII reaction centre densities. Changes in α were also correlated with changes in fluorescence induction kinetics, with high-temperature and/or low-light embryos exhibiting higher ratios of variable: maximum fluorescence (Fv/Fm) than 5°C high-light embryos (c. 0.5 vs. 0.19). In contrast to Psub-sat, changes in light-saturated photosynthesis (Pmax) in response to growth under different temperature/light regimes did not confer metabolic compensation. Rates of Pmax were highest in 20°C high-light embryos (7.3 nmol O2 mm−3 min−1), lower in 20°C low-light and 5°C low-light embryos (c. 2.6 nmol O2 mm−3 min−1) and lowest in 5°C high-light embryos (2.3 nmol O2 mm−3 min−1). We suggest that the ability to achieve temperature-independent rates of Psub-sat may be important for fucoid embryos that recruit in intertidal microhabitats where photosynthesis is often light-limited.