An Integrative Perspective on Fish Health: Environmental and Anthropogenic Pathways Affecting Fish Stress

Abstract

Multifactorial studies assessing the cumulative effects of natural and anthropogenic stressors on individual health are crucial to understand how organisms and populations cope with environmental change. Such studies are rare in marine ecosystems, partly due to the challenge of studying interactions between multiple stressors. Here, we tested direct and indirect causal pathways through which environmental stressors affect the health of wild gilthead seabream (Sparus aurata) in Mediterranean costal lagoons using an integrative partial least squares path modelling (PLS-PM) approach. We monitored the bio-chemical features of ten Mediterranean lagoons ecosystems and assessed their consequences on fish physiology. We integrated information on 10 environmental variables and 36 physiological variables into seven latent variables reflecting lagoons features and fish health. These variables concerned fish lipid reserves, somatic structure, inorganic pollutant load, and individual trophic and stress levels. This approach explained 30% of the total variance of the whole data studied. More importantly, 54% of fish stress was explained by the dependent lagoon features, fish age, fish diet, fish reserve, fish structure and fish pollutant load latent variables included in our model. We identified direct negative consequences of lagoon eutrophication on fish health (oxidative stress, immune function and stress hormone levels), and found indirect antagonistic effects, mostly via a reduction of inorganic pollutant loads. Increasing eutrophication was associated with increasing growth rates as well as higher energetic reserves in fish. These effects were mediated by a shift from detrital terrigenous-based towards carnivorous diets. Such benefits were nonetheless balanced-out by increase individual stress and individual with higher growth rates appearing to pay short-term costs (ie. oxidative stress and immunity). This integrative study sheds light on how individuals deal with contrasting environments and multiple ecological pressures. A similar framework for studying complex multifactorial interactions should prove useful for other species, stressors and ecosystems.

Keywords: Ecosystem, PLS-PM, Eco-physiology, Direct and indirect effects, Fish health, Stress, Coastal lagoon, Mediterranean