Functional spatial contextualisation of the effects of multiple stressors in marine bivalves

Abstract. Many recent studies have revealed that the majority of environmental stressors experienced by marine organisms (ocean acidification, global warming, hypoxia etc.) occur at the same time and place, and that their interaction may complexly affect a number of ecological processes. Here, we experimentally investigated the effects of pH and hypoxia on the functional and behavioural traits of the mussel Mytilus galloprovincialis, we then simulated the potential effects on growth and reproduction dynamics trough a Dynamic Energy Budget (DEB) model under a multiple stressor scenario. Our simulations showed that hypercapnia had a remarkable effect by reducing the maximal habitat size and reproductive output differentially as a function of the trophic conditions, where modelling was spatially contextualized. This study showed the major threat represented by the hypercapnia and hypoxia phenomena for the growth, reproduction and fitness of mussels under the current climate change context, and that a mechanistic approach based on DEB modelling can illustrate complex and site-specific effects of environmental change, producing that kind of information useful for management purposes, at larger temporal and spatial scales.</p

Moving Toward a Strategy for Addressing Climate Displacement of Marine Resources: A Proof-of-Concept

Realistic predictions of climate change effects on natural resources are central to adaptation policies that try to reduce these impacts. However, most current forecasting approaches do not incorporate species-specific, process-based biological information, which limits their ability to inform actionable strategies. Mechanistic approaches, incorporating quantitative information on functional traits, can potentially predict species- and population-specific responses that result from the cumulative impacts of small-scale processes acting at the organismal level, and can be used to infer population-level dynamics and inform natural resources management. Here we present a proof-of-concept study using the European anchovy as a model species that shows how a trait-based, mechanistic species distribution model can be used to explore the vulnerability of marine species to environmental changes, producing quantitative outputs useful for informing fisheries management. We crossed scenarios of temperature and food to generate quantitative maps of selected mechanistic model outcomes (e.g., Maximum Length and Total Reproductive Output). These results highlight changing patterns of source and sink spawning areas as well as the incidence of reproductive failure. This study demonstrates that model predictions based on functional traits can reduce the degree of uncertainty when forecasting future trends of fish stocks. However, to be effective they must be based on high spatial- and temporal resolution environmental data. Such a sensitive and spatially explicit predictive approach may be used to inform more effective adaptive management strategies of resources in novel climatic conditions

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

Short-term exposure to concurrent biotic and abiotic stressors may impair farmed molluscs performance

Global warming, through increasing temperatures, may facilitate the spread and proliferation of outbreak-forming species which may find favourable substrate conditions on artificial aquaculture structures. The presence of stinging organisms (cnidarian hydroids) in the facilities fouling community are a source of pollution that can cause critical problems when in-situ underwater cleaning processes are performed. Multiple stressor experiments were carried out to investigate the cumulative effect on farmed mussels' functional traits when exposed to realistic stressful conditions, including presence of harmful cnidarian cells and environmental conditions of increasing temperature and short-term hypoxia. Exposure to combined stressors significantly altered mussels' performance, causing metabolic depression and low filtering activity, potentially delaying, or inhibiting their recovery ability and ultimately jeopardizing organisms' fitness. Further research on the stressors properties and occurrence is needed to obtain more realistic responses from organisms to minimize climate change impacts and increase ecosystem and marine economic activities resilience to multiple stressors

Functional consequences of prey acclimation to ocean acidification for the prey and its predator

Ocean acidification is the suite of chemical changes to the carbonate system of seawater as a consequence of anthropogenic carbon dioxide (CO2) emissions. Despite a growing body of evidences demonstrating the negative effects of ocean acidification on marine species, the consequences at the ecosystem level are still unclear. One factor limiting our ability to upscale from species to ecosystem is the poor mechanistic understanding of the functional consequences of the observed effects on organisms. This is particularly true in the context of species interactions. The aim of this work was to investigate the functional consequence of the exposure of a prey (the mussel Brachidontes pharaonis) to ocean acidification for both the prey and its predator (the crab Eriphia verrucosa). Mussels exposed to pH 7.5 for >4 weeks showed significant decreases in condition index and in mechanical properties (65% decrease in maximum breaking load) as compared with mussels acclimated to pH 8.0. This translated into negative consequences for the mussel in presence of the predator crab. The crab feeding efficiency increased through a significant 27% decrease in prey handling time when offered mussels acclimated to the lowest pH. The predator was also negatively impacted by the acclimation of the prey, probably as a consequence of a decreased food quality. When fed with prey acclimated under decreased pH for 3 months, crab assimilation efficiency significantly decreased by 30% and its growth rate was 5 times slower as compared with crab fed with mussels acclimated under high pH. Our results highlight the important to consider physiological endpoints in the context of species interactions

Functional consequences of prey acclimation to ocean acidification for the prey and its predator

Ocean acidification is the suite of chemical changes to the carbonate system of seawater as a consequence of anthropogenic carbon dioxide (CO2) emissions. Despite a growing body of evidences demonstrating the negative effects of ocean acidification on marine species, the consequences at the ecosystem level are still unclear. One factor limiting our ability to upscale from species to ecosystem is the poor mechanistic understanding of the functional consequences of the observed effects on organisms. This is particularly true in the context of species interactions. The aim of this work was to investigate the functional consequence of the exposure of a prey (the mussel Brachidontes pharaonis) to ocean acidification for both the prey and its predator (the crab Eriphia verrucosa). Mussels exposed to pH 7.5 for &gt;4 weeks showed significant decreases in condition index and in mechanical properties (65% decrease in maximum breaking load) as compared with mussels acclimated to pH 8.0. This translated into negative consequences for the mussel in presence of the predator crab. The crab feeding efficiency increased through a significant 27% decrease in prey handling time when offered mussels acclimated to the lowest pH. The predator was also negatively impacted by the acclimation of the prey, probably as a consequence of a decreased food quality. When fed with prey acclimated under decreased pH for 3 months, crab assimilation efficiency significantly decreased by 30% and its growth rate was 5 times slower as compared with crab fed with mussels acclimated under high pH. Our results highlight the important to consider physiological endpoints in the context of species interactions. PeerJ PrePrints | https://dx.doi.org/10.7287/peerj.preprints.1438v1 | CC-BY 4.0 Open Access