Food depletion in mussel cultivation has been rarely studied and seldom demonstrated. In this study, concentrations of phytoplankton in and around a blue mussel Mytilus galloprovincialis raft culture unit in the Ría de Vigo were measured during a 2 wk study period in July 2004. Flow direction and current speed were measured using an Aanderaa current meter and fine-scale Acoustic Doppler Velcimeter probes at different positions in the raft. Flow speeds were reduced compared to outside the raft, but a clear tidal signal and significant flow velocities could still be observed inside the raft. At the upstream corners of the raft, a zone of high turbulence but reduced advection was observed. Concentrations of chlorophyll a (chl a) were measured on 3 different spatial scales. On a macro-scale, fluorescence profiles were taken inside and outside the raft on several occasions and there was depletion of chlorophyll inside the raft corresponding to ~80% of the outside concentration, whereas there was no depletion below the ropes. On a meso-scale, from just upstream to just downstream of the raft, fluorescence profiles, as well as water samples, at several depths revealed similar depletion, however, with larger depletion of size-fractionated chl a > 2 μm. On a micro-scale, water was sampled within 20 cm of the ropes using siphon mimics. In the middle of the raft, concentration profiles towards the mussel ropes could be observed at 2 depths, whereas less clear profiles were observed on the turbulent upstream corner. The present study documents food depletion in a mussel culture and emphasizes the importance of physical forcing and phytoplankton composition for food availability.

Measurements of the water clarification capacity of a nutrient extractive mussel farm in a eutrophic fjord in Denmark were used to optimize eutrophication mitigation capacity. Graphic: Camille Saurel, DTU Aqua

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The Paris Conference of Parties (COP21) agreement renewed momentum for action against climate change, creating the space for solutions for conservation of the ocean addressing two of its largest threats: climate change and ocean acidification (CCOA). Recent arguments that ocean policies disregard a mature conservation research field and that protected areas cannot address climate change may be oversimplistic at this time when dynamic solutions for the management of changing oceans are needed. We propose a novel approach, based on spatial meta-analysis of climate impact models, to improve the positioning of marine protected areas to limit CCOA impacts. We do this by estimating the vulnerability of ocean ecosystems to CCOA in a spatially explicit manner and then co-mapping human activities such as the placement of renewable energy developments and the distribution of marine protected areas. We test this approach in the NE Atlantic considering also how CCOA impacts the base of the food web which supports protected species, an aspect often neglected in conservation studies. We found that, in this case, current regional conservation plans protect areas with low ecosystem-level vulnerability to CCOA, but disregard how species may redistribute to new, suitable and productive habitats. Under current plans, these areas remain open to commercial extraction and other uses. Here, and worldwide, ocean conservation strategies under CCOA must recognize the longterm importance of these habitat refuges, and studies such as this one are needed to identify them. Protecting these areas creates adaptive, climate-ready and ecosystem-level policy options for conservation, suitable for changing oceans.

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We review and compare four broad categories of spatially-explicit modelling approaches currently used to understand and project changes in the distribution and productivity of living marine resources including: 1) statistical species distribution models, 2) physiology-based, biophysical models of single life stages or the whole life cycle of species, 3) food web models, and 4) end-to-end models. Single pressures are rare and, in the future, models must be able to examine multiple factors affecting living marine resources such as interactions between: i) climate-driven changes in temperature regimes and acidification, ii) reductions in water quality due to eutrophication, iii) the introduction of alien invasive species, and/or iv) (over-)exploitation by fisheries. Statistical (correlative) approaches can be used to detect historical patterns which may not be relevant in the future. Advancing predictive capacity of changes in distribution and productivity of living marine resources requires explicit modelling of biological and physical mechanisms. New formulations are needed which (depending on the question) will need to strive for more realism in ecophysiology and behaviour of individuals, life history strategies of species, as well as trophodynamic interactions occurring at different spatial scales. Coupling existing models (e.g. physical, biological, economic) is one avenue that has proven successful. However, fundamental advancements are needed to address key issues such as the adaptive capacity of species/groups and ecosystems. The continued development of end-to-end models (e.g., physics to fish to human sectors) will be critical if we hope to assess how multiple pressures may interact to cause changes in living marine resources including the ecological and economic costs and trade-offs of different spatial management strategies. Given the strengths and weaknesses of the various types of models reviewed here, confidence in projections of changes in the distribution and productivity of living marine resources will be increased by assessing model structural uncertainty through biological ensemble modelling.