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1. Marine Heat Waves (MHWs) are episodes of anomalous warming in the ocean that can last from a few days to months. MHWs have different characteristics in terms of intensity, duration, and frequency and generate thermal stress on marine ecosystems. In reef ecosystems, they are one of the main causes of decreased presence and abundance of corals, invertebrates, and fish. The deleterious capacity of thermal stress often depends upon biotic factors such as resource availability (bottom-up control on predators) and predation (top-down control on prey). Despite the evidence of thermal stress and biotic factors affecting individual species, the combined effects of both stressors on the entire reef ecosystems are far less studied. 2. Here, using a food-web modeling approach, we estimated the rate of change in species’ biomass due to different MHW scenarios based on their physical characteristics. Specifically, we modeled the mechanistic link between species’ consumption rate and seawater temperature (thermal stressor), simulating species’ biomass dynamics for different MHW scenarios under different trophic control assumptions (biotic factor). 3. We find that total reef ecosystem biomass declined by 10% ± 5% under MHWs with severe intensity and top-down control assumption. The bottom-up control assumption moderates the total ecosystem biomass reduction by 5% ± 5%. Irrespective of the MHW scenario and the trophic control assumption, the most substantial biomass changes occur among top, meso-predators, and corals (5% to 20% ± 10%).4. Since habitat degradation may lead to reef ecosystems governed by top-down control on prey, our findings point to the critical importance of protecting reef ecosystems as a pivotal strategy to alleviate the impacts of thermal stress induced by MHWs. Overall, our results provide a unified understanding of the interplay between abiotic stressors and biotic factors in reef ecosystems under extreme thermal events, offering insights into present baselines and future ecological states for reef ecosystems.

Overtopping-type wave power conversion devices represent one of the most promising technology to combine reliability and competitively priced electricity supplies from waves. While satisfactory hydraulic and structural performance have been achieved, the selection of the hydraulic turbines and their regulation is a complex process due to the very low head and a variable flow rate in the overtopping breakwater set-ups. Based on the experience acquired on the first Overtopping BReakwater for Energy Conversion (OBREC) prototype, operating since 2016, an activity has been carried out to select the most appropriate turbine dimension and control strategy for such applications. An example of this multivariable approach is provided and illustrated through a case study in the San Antonio Port, along the central coast of Chile. In this site the deployment of a breakwater equipped with OBREC modules is specifically investigated. Axial-flow turbines of different runner diameter are compared, proposing the optimal ramp height and turbine control strategy for maximizing system energy production. The energy production ranges from 20.5 MWh/y for the smallest runner diameter to a maximum of 34.8 MWh/y for the largest runner diameter.

AbstractOcean warming is altering the biogeographical distribution of marine organisms. In the tropics, rising sea surface temperatures are restructuring coral reef communities with sensitive species being lost. At the biogeographical divide between temperate and tropical communities, warming is causing macroalgal forest loss and the spread of tropical corals, fishes and other species, termed “tropicalization”. A lack of field research into the combined effects of warming and ocean acidification means there is a gap in our ability to understand and plan for changes in coastal ecosystems. Here, we focus on the tropicalization trajectory of temperate marine ecosystems becoming coral‐dominated systems. We conducted field surveys and in situ transplants at natural analogues for present and future conditions under (i) ocean warming and (ii) both ocean warming and acidification at a transition zone between kelp and coral‐dominated ecosystems. We show that increased herbivory by warm‐water fishes exacerbates kelp forest loss and that ocean acidification negates any benefits of warming for range extending tropical corals growth and physiology at temperate latitudes. Our data show that, as the combined effects of ocean acidification and warming ratchet up, marine coastal ecosystems lose kelp forests but do not gain scleractinian corals. Ocean acidification plus warming leads to overall habitat loss and a shift to simple turf‐dominated ecosystems, rather than the complex coral‐dominated tropicalized systems often seen with warming alone. Simplification of marine habitats by increased CO2 levels cascades through the ecosystem and could have severe consequences for the provision of goods and services.

L'aquaculture joue un rôle important dans la sécurité alimentaire et fournit des moyens de subsistance et des emplois à des millions de personnes dans les communautés côtières du monde entier. Cependant, le secteur aquacole en pleine croissance a également suscité des débats sur sa durabilité écologique à long terme, sa viabilité économique, les inégalités sociales potentielles et les problèmes de gouvernance. Nous avons étudié les défis et les opportunités perçus pour parvenir à une aquaculture durable du crabe de boue dans les régions côtières tropicales en utilisant l'étude de cas des fermes côtières de crabe de boue dans l'Andhra Pradesh, en Inde. Sur la base des perceptions et des données financières indicatives d'un échantillon de parties prenantes, nous avons étudié les résultats économiques potentiels dans différents scénarios représentant des niveaux de rendement, des facteurs de risque et des périodes de projet variables. Les principaux risques identifiés par les parties prenantes étaient associés à l'approvisionnement limité en graines de crabe de boue et au manque d'accès aux programmes de soutien gouvernementaux et non gouvernementaux. Il n'y a pas de tampons financiers, donc des épidémies majeures ou des conditions météorologiques extrêmes causées par le changement climatique entraîneraient une perte de moyens de subsistance. Cet article met également en évidence le facteur le plus critique déterminant le niveau de succès de l'élevage du crabe de boue étant le taux de survie du crabe qui est influencé par une variété de facteurs, y compris l'augmentation de la température de la surface de la mer. Les résultats de cette étude montrent que l'élevage de crabes de boue à petite échelle comporte moins de risques et une plus grande flexibilité que l'élevage de crabes de boue à grande échelle. Il pourrait s'agir d'une entreprise économiquement durable et servir d'outil de réduction de la pauvreté dans les pays en développement si un soutien et une formation en matière de microfinance sont disponibles. La acuicultura desempeña un papel importante en la seguridad alimentaria y proporciona medios de subsistencia y empleo a millones de personas en las comunidades costeras de todo el mundo. Sin embargo, el creciente sector de la acuicultura también ha creado debates en torno a su sostenibilidad ecológica a largo plazo, viabilidad económica, posibles desigualdades sociales y problemas de gobernanza. Investigamos los desafíos y oportunidades percibidos para lograr una acuicultura sostenible de cangrejo de fango en las regiones costeras tropicales utilizando el estudio de caso de las granjas costeras de cangrejo de fango en Andhra Pradesh, India. Con base en las percepciones y los datos financieros indicativos de una muestra de partes interesadas, investigamos los posibles resultados económicos en diferentes escenarios que representan diferentes niveles de rendimiento, factores de riesgo y períodos de tiempo del proyecto. Los principales riesgos identificados por las partes interesadas se asociaron con el suministro limitado de semillas de cangrejo de fango y la falta de acceso a esquemas de apoyo gubernamentales y no gubernamentales. No hay amortiguadores financieros, por lo tanto, los grandes brotes de enfermedades o las condiciones climáticas extremas causadas por el cambio climático conducirían a la pérdida de los medios de vida. Este documento también destaca que el factor más crítico que determina el nivel de éxito del cultivo de cangrejo de fango es la tasa de supervivencia del cangrejo, que está influenciada por una variedad de factores, incluido el aumento de la temperatura de la superficie del mar. Los resultados de este estudio muestran que el cultivo de cangrejo de fango a pequeña escala tiene menos riesgos y una mayor flexibilidad que el cultivo de cangrejo de fango a gran escala. Podría ser una empresa económicamente sostenible y servir como una herramienta para el alivio de la pobreza en los países en desarrollo si se dispone de apoyo y capacitación en microfinanzas. Aquaculture plays a significant role in food security and provides livelihoods and employment for millions of people among coastal communities worldwide. However, the growing aquaculture sector has also created debates around its long-term ecological sustainability, economic viability, potential social inequalities and governance issues. We investigated the perceived challenges and opportunities to achieving sustainable mud crab aquaculture in tropical coastal regions by using the case study of coastal mud crab farms in Andhra Pradesh, India. Informed by perceptions and indicative financial data from a sample of stakeholders we investigated the potential economic outcomes under different scenarios representing varying yield levels, risk factors and project time periods. The main risks identified by the stakeholders were associated with the limited supply of mud crab seeds and the lack of access to governmental and non-governmental support schemes. There are no financial buffers, therefore major disease outbreaks or extreme weather conditions caused by climate change would lead to a loss of livelihoods. This paper also highlights the most critical factor determining the level of success of mud crab farming being the crab survival rate which is influenced by a variety of factors including increasing sea surface temperature. The results of this study show that small-scale mud crab farming has fewer risks and higher flexibility involved than large-scale mud crab farming. It could be an economically sustainable enterprise and serve as a tool for poverty alleviation in developing countries if microfinance support and training are available. تلعب تربية الأحياء المائية دورًا مهمًا في الأمن الغذائي وتوفر سبل العيش وفرص العمل لملايين الأشخاص بين المجتمعات الساحلية في جميع أنحاء العالم. ومع ذلك، فإن قطاع تربية الأحياء المائية المتنامي قد خلق أيضًا مناقشات حول استدامته البيئية طويلة الأجل، وقابليته الاقتصادية، وعدم المساواة الاجتماعية المحتملة، وقضايا الحوكمة. لقد حققنا في التحديات والفرص المتصورة لتحقيق تربية مستدامة لسرطان البحر الطيني في المناطق الساحلية الاستوائية باستخدام دراسة حالة لمزارع سرطان البحر الطيني الساحلية في ولاية أندرا براديش، الهند. استنادًا إلى التصورات والبيانات المالية الإرشادية من عينة من أصحاب المصلحة، قمنا بالتحقيق في النتائج الاقتصادية المحتملة في ظل سيناريوهات مختلفة تمثل مستويات عائد متفاوتة وعوامل خطر وفترات زمنية للمشروع. ارتبطت المخاطر الرئيسية التي حددها أصحاب المصلحة بمحدودية المعروض من بذور سرطان البحر الطيني وعدم الوصول إلى خطط الدعم الحكومية وغير الحكومية. لا توجد حواجز مالية، وبالتالي فإن تفشي الأمراض الرئيسية أو الظروف الجوية القاسية الناجمة عن تغير المناخ ستؤدي إلى فقدان سبل العيش. تسلط هذه الورقة الضوء أيضًا على العامل الأكثر أهمية الذي يحدد مستوى نجاح زراعة سرطان البحر الطيني وهو معدل بقاء سرطان البحر الذي يتأثر بمجموعة متنوعة من العوامل بما في ذلك زيادة درجة حرارة سطح البحر. تظهر نتائج هذه الدراسة أن زراعة سرطان البحر الطيني على نطاق صغير تنطوي على مخاطر أقل ومرونة أعلى من زراعة سرطان البحر الطيني على نطاق واسع. يمكن أن يكون مشروعًا مستدامًا اقتصاديًا وأن يكون بمثابة أداة للتخفيف من حدة الفقر في البلدان النامية إذا توفر الدعم والتدريب في مجال التمويل الأصغر.

Research to date has suggested that both individual marine species and ecological processes are expected to exhibit diverse responses to the environmental effects of climate change. Evolutionary responses can occur on rapid (ecological) timescales, and yet studies typically do not consider the role that adaptive evolution will play in modulating biological responses to climate change. Investigations into such responses have typically been focused at particular biological levels (e.g., cellular, population, community), often lacking interactions among levels. Since all levels of biological organisation are sensitive to global climate change, there is a need to elucidate how different processes and hierarchical interactions will influence species fitness. Therefore, predicting the responses of communities and populations to global change will require multidisciplinary efforts across multiple levels of hierarchy, from the genetic and cellular to communities and ecosystems. Eventually, this may allow us to establish the role that acclimatisation and adaptation will play in determining marine community structures in future scenarios.

Assessing Biodiversity Declines Understanding human impact on biodiversity depends on sound quantitative projection. Pereira et al. (p. 1496 , published online 26 October) review quantitative scenarios that have been developed for four main areas of concern: species extinctions, species abundances and community structure, habitat loss and degradation, and shifts in the distribution of species and biomes. Declines in biodiversity are projected for the whole of the 21st century in all scenarios, but with a wide range of variation. Hoffmann et al. (p. 1503 , published online 26 October) draw on the results of five decades' worth of data collection, managed by the International Union for Conservation of Nature Species Survival Commission. A comprehensive synthesis of the conservation status of the world's vertebrates, based on an analysis of 25,780 species (approximately half of total vertebrate diversity), is presented: Approximately 20% of all vertebrate species are at risk of extinction in the wild, and 11% of threatened birds and 17% of threatened mammals have moved closer to extinction over time. Despite these trends, overall declines would have been significantly worse in the absence of conservation actions.