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16th International Conference Littoral22, 12-16 September 2022, Campus de Caparica (Portugal). Hundreds of millions of people worldwide directly rely on marine and coastal ecosystems for their food, livelihoods and ways of life, yet these ecosystems are subject to a variety of pressures (UNEP, 2006; Hoegh-Guldberg et al., 2015; Korpinen et al., 2019). These pressures include climate change - one of the most urgent challenges societies are currently facing, with “long-lasting or irreversible” adverse consequences predicted as a result (IPCC 2018). Healthy marine and coastal ecosystems are a pre-requisite for the continuing delivery of ecosystem services, such as the provision of food, climate regulation and carbon storage. Therefore, it is critical to achieve a more sustainable management and effective protection of such valuable ecosystems. Policy makers are increasingly aware of the adverse effects of climate change and environmental degradation on our coasts and oceans. As public opinion influence decision-making on the actions to take and contribute to the success of their implementation (Rasmussen et al., 2017), it is important to understand how well informed the public is about climate change impacts and solutions in marine and coastal systems. In recent years, significant efforts have been made by the scientific community to raise public awareness of climate change and the links between healthy marine and coastal ecosystems and ecosystem service provision, including their role in mitigating and adapting to climate change (Barracosa et al., 2019). However, there has been little consideration of how the public perceives the interlinkages between climate change and its effects on marine and coastal ecosystems. Instead, most efforts have addressed climate change perceptions (van Valkengoed et al., 2022) Mildenberger et al., 2019) and marine threats perceptions (Ankamah-Yeboah et al., 2020; Lotze et al., 2018), separately. In the scope of the research project on “Marine Coastal ecosystems Biodiversity and Services in a changing world” (MaCoBioS) funded by the European Commission, people’s views on climate change, the value of marine and coastal ecosystems and the threats facing they face, as well as potential management options were investigated. info:eu-repo/semantics/publishedVersion

Subtidal marine sediments are one of the planet's primary carbon stores and strongly influence the oceanic sink for atmospheric CO2. By far the most widespread human activity occurring on the seabed is bottom trawling/dredging for fish and shellfish. A global first-order estimate suggested mobile demersal fishing activities may cause 0.16–0.4 Gt of organic carbon (OC) to be remineralized annually from seabed sediment carbon stores (Sala et al., 2021). There are, however, many uncertainties in this calculation. Here, we discuss the potential drivers of change in seabed sediment OC stores due to mobile demersal fishing activities and conduct a literature review, synthesizing studies where this interaction has been directly investigated. Under certain environmental settings, we hypothesize that mobile demersal fishing would reduce OC in seabed stores due to lower production of flora and fauna, the loss of fine flocculent material, increased sediment resuspension, mixing and transport and increased oxygen exposure. Reductions would be offset to varying extents by reduced faunal bioturbation and community respiration, increased off-shelf transport and increases in primary production from the resuspension of nutrients. Studies which directly investigated the impact of demersal fishing on OC stocks had mixed results. A finding of no significant effect was reported in 61% of 49 investigations; 29% reported lower OC due to fishing activities, with 10% reporting higher OC. In relation to remineralization rates within the seabed, four investigations reported that demersal fishing activities decreased remineralization, with three reporting higher remineralization rates. Patterns in the environmental and experimental characteristics between different outcomes were largely indistinct. More evidence is urgently needed to accurately quantify the impact of anthropogenic physical disturbance on seabed carbon in different environmental settings and to incorporate full evidence-based carbon considerations into global seabed management.

Caribbean reefs have experienced unprecedented changes in the past four decades. Of great concern is the perceived widespread shift from coral to macroalgal dominance and the question of whether it represents a new, stable equilibrium for coral-reef communities. The primary causes of the shift—grazing pressure (top-down), nutrient loading (bottom-up) or direct coral mortality (side-in)—still remain somewhat controversial in the coral-reef literature. We have attempted to tease out the relative importance of each of these causes. Four insights emerge from our analysis of an early regional dataset of information on the benthic composition of Caribbean reefs spanning the years 1977–2001. First, although three-quarters of reef sites have experienced coral declines concomitant with macroalgal increases, fewer than 10% of the more than 200 sites studied were dominated by macroalgae in 2001, by even the most conservative definition of dominance. Using relative dominance as the threshold, a total of 49 coral-to-macroalgae shifts were detected. This total represents ~ 35% of all sites that were dominated by coral at the start of their monitoring periods. Four shifts (8.2%) occurred because of coral loss with no change in macroalgal cover, 15 (30.6%) occurred because of macroalgal gain without coral loss, and 30 (61.2%) occurred owing to concomitant coral decline and macroalgal increase. Second, the timing of shifts at the regional scale is most consistent with the side-in model of reef degradation, which invokes coral mortality as a precursor to macroalgal takeover, because more shifts occurred after regional coral-mortality events than expected by chance. Third, instantaneous observations taken at the start and end of the time-series for individual sites showed these reefs existed along a continuum of coral and macroalgal cover. The continuous, broadly negative relationship between coral and macroalgal cover suggests that in some cases coral-to-macroalgae phase shifts may be reversed by removing sources of perturbation or restoring critical components such as the herbivorous sea urchin Diadema antillarum to the system. The five instances in which macroalgal dominance was reversed corroborate the conclusion that macroalgal dominance is not a stable, alternative community state as has been commonly assumed. Fourth, the fact that the loss in regional coral cover and concomitant changes to the benthic community are related to punctuated, discrete events with known causes (i.e. coral disease and bleaching), lends credence to the hypothesis that coral reefs of the Caribbean have been under assault from climate-change-related maladies since the 1970s.