Effect of Multiple Stressors on marine organism predicted and quantified through bioenergetic mechanistic models

Anthropogenic pressure on coastal ecosystems is vast and diverse, simultaneous impacts such as pollution, eutrophication and fishing pressure nowadays add up and interact with the effects of climate change (e.g., global warming, acidification and sea level rise). The magnitude of these effects on marine species and their replies can vary and the possible changes can depend on: i) species life-histories (LH) traits, ii) local environmental conditions and iii) contextual presence of more than one anthropogenic related stressor. The study of a single anthropogenic disturbance or Climate Change-derived alteration on multi-level ecological responses is misleading and generates unrealistic conclusions, and for this reason is actually recognized as the main limitation of the current ecosystem management approach. These climate change stressors exert negative effects on marine biota as single stressors, but at the same time they are also likely to have interactive effects on biodiversity and ecosystem functioning that are difficult to predict. Although the ecosystem based management (EBM) approach focuses on ecosystem equilibria, to provide realistic management measures for important activities at sea such as conservation, fisheries and aquaculture, there is a need of quantities. While ecological research has begun to document the individual effects of these various stressors on species and ecosystems, research into the cumulative and interactive impacts of multiple stressors is less frequent. This need is still cited as one of the most pressing questions in ecology and conservation. The effect of stressors on marine organisms has been frequently assessed using the Scope for Growth (SFG) approach, which lead to a static snapshot of the current physiological status of a target organism, used as an indicator of the ‘health’ of the ecosystem. In the last decade, eco-physiological studies have focused on linking the effect of climate change on species distributions based on organisms' physiological limits and, in some cases, with the overall relationship between environmental factors and physiological performance. In addition, past modelling efforts largely based on correlative Species Distribution Models (SDMs) also known as “bioclimatic envelope models”, “ecological niche models” or “habitat suitability models” used known occurrences of species across landscapes of interest to define sets of conditions under which species are likely to maintain populations. However, effective conservation management required models able to make projections beyond the range of available data. One way to deal with such an extrapolation is to use a mechanistic approach based on physiological processes underlying climate change effects on organisms. One such bio-energetic model, which has been successfully applied for modelling species distributions, is the Dynamic Energy Budget (DEB) model, which is able to deal with multiple stressors and other environmental parameters that are expected to affect the individual performance such as growth and reproduction. While Chapter 1 was dedicated to frame of general topic of the present thesis, Chapter 2 experimentally investigated the effects of a novel prey and a chronic increase in temperatures on functional traits and global fitness of the whelk Stramonita haemastoma. In Chapter 3, we applied a new approach using DEB models to investigate the effects of an anthropogenic pollutant on Life-History (LH) traits of marine organisms, providing stakeholders and policy makers an effective tool to evaluate the best environmental recovery strategy. In Chapter 4 we used DEB models to determine the effect of changing environmental conditions and pollution on the Indo-Pacific Perna viridis aquaculture. In Chapter 5 we proposed a DEB application to study the link between future COP21 predicted temperature scenarios and varying food availability on LH-traits of some Mediterranean fishery and aquaculture target species, exploring the efficiency of Integrated Multitrophic Aquaculture as a potential management solution. A spatial contextualization of model outcomes allowed translating those results into useful figurative representations. Through Chapter 6 we investigated the site-specific effects of environmental changes represented by Ocean Acidification and hypoxia on the functional and behavioural traits of the mussel Mytilus galloprovincialis. Finally, in Chapter 7 we presented a proof-of-concept study using the European anchovy as a model species to show how a trait-based, mechanistic species distribution model can be used to explore the vulnerability of marine species to environmental changes. Scenarios of temperature and food were crossed to generate quantitative maps of selected mechanistic model outcomes.