PS 15-212 - Impacts of ocean warming and resource level on the energy budgets of Wadden Sea fish

Abstract: Water temperature is a major driver determining fishes’ ability to thrive/survive in a habitat. Over the last 20 years, mean water temperature in the western Dutch Wadden Sea has increased with >1.5°C resulting in a changing habitat function of this crucial fish nursery area. Survey data have elucidated species composition and changes therein, but much less is known about species physiology especially for noncommercial, yet ecologically important species. It is this lack of physiological insight that is currently limiting the understanding of relationships between changes in abiotic factors and the fish community in the Wadden Sea.

To better understand how environmental factors such as water temperature and resource availability affect life history processes at the individual level, we developed a species-specific, temperature dependent, energy budget model. The temperature dependence of the model adjusts physiological rates (maintenance and intake) based on size dependent temperature tolerance ranges and optimum temperatures for each physiological process. The model framework tracks the allocation of available energy from food to different life history processes such as maintenance, development, growth, and reproduction, as organisms grow and progress through different life stages.

The individual energetics of five species (Clupea harengus - herring, Sprattus sprattus - sprat, Gadus morhua - cod, Ciliata mustela - fivebeard rockling, and Chelon ramada - thinlip mullet) representing contrasting fish guilds were studied. We found that responses to environmental conditions varied among species and are depending on individual size. Increased resource levels generally led to larger body sizes and greater reproductive output, but higher temperatures often resulted in reduced physiological performance, particularly for boreal (cool temperature-favoring) species like cod. The results of this study suggest that some Wadden Sea species will be disproportionately affected by increasing water temperature. On-going increases in the order of 1.5°C, as occurred in the past twenty years, are predicted to position some species under suboptimal conditions for physiological processes. Conversely, warm temperature-favoring species, such as mullet, are predicted to mostly benefit from rising water temperature, giving rise to a changing ecological role for this species in the ecosystem. Our findings suggest that even small increases in water temperature can have significant effects on the physiology and life history of Wadden Sea fish species, which may ultimately impact their population dynamics and interactions with other species in the ecosystem.