In the vast tropical Pacific Basin islands, corals reef ecosystems are one of the defining marine habitats, critical for maintaining biodiversity and supporting highly productive fisheries. These reefs are also vital for tourism and armoring exposed shorelines against erosion and other storm-related effects. Since the 1980’s, there has been growing evidence that these Pacific Basin coral reef ecosystems are highly vulnerable to the combined effects of both climatic and non-climatic stressors. Observations of widespread bleaching in the region has been linked to acute temperature stress, and the heightened recurrence intervals and intensity of storms has been correlated to recent climate-change induced impacts. Ocean acidification is another ubiquitous stressor with dramatic consequences to biological systems. In this paper we describe what sets this region apart from other coral reef regions around the world, and highlight some examples of the diverse response to ocean acidification threats and associated socio-economic impacts.
Climate Change, Ocean Acidification, and Ocean Warming
Thermal-stress events associated with climate change cause coral bleaching and mortality that threatens coral reefs globally. Yet coral bleaching patterns vary spatially and temporally. Here we synthesize field observations of coral bleaching at 3351 sites in 81 countries from 1998 to 2017 and use a suite of environmental covariates and temperature metrics to analyze bleaching patterns. Coral bleaching was most common in localities experiencing high intensity and high frequency thermal-stress anomalies. However, coral bleaching was significantly less common in localities with a high variance in sea-surface temperature (SST) anomalies. Geographically, the highest probability of coral bleaching occurred at tropical mid-latitude sites (15–20 degrees north and south of the Equator), despite similar thermal stress levels at equatorial sites. In the last decade, the onset of coral bleaching has occurred at significantly higher SSTs (∼0.5 °C) than in the previous decade, suggesting that thermally susceptible genotypes may have declined and/or adapted such that the remaining coral populations now have a higher thermal threshold for bleaching.
Diatoms are silicifying phytoplankton contributing about one quarter to primary production on Earth. Ocean acidification (OA) could alter the competitiveness of diatoms relative to other taxa and/or lead to shifts among diatom species. In spring 2016, we set up a plankton community experiment at the coast of Gran Canaria (Canary Islands, Spain) to investigate the response of subtropical diatom assemblages to elevated seawater pCO2. Therefore, natural plankton communities were enclosed for 32 days in in situ mesocosms (∼8 m3volume) with a pCO2 gradient ranging from 380 to 1140 μatm. Halfway through the study we added nutrients to all mesocosms (N, P, Si) to simulate injections through eddy-induced upwelling which frequently occurs in the region. We found that the total diatom biomass remained unaffected during oligotrophic conditions but was significantly positively affected by high CO2 after nutrient enrichment. The average cell volume and carbon content of the diatom community increased with CO2. CO2 effects on diatom biomass and species composition were weak during oligotrophic conditions but became quite strong above ∼620 μatm after the nutrient enrichment. We hypothesize that the proliferation of diatoms under high CO2 may have been caused by a fertilization effect on photosynthesis in combination with reduced grazing pressure. Our results suggest that OA in the subtropics may strengthen the competitiveness of (large) diatoms and cause changes in diatom community composition, mostly under conditions when nutrients are injected into oligotrophic systems.
Coral reefs distinctly illustrate the close relationship between biodiversity and ecosystem services. They are rich marine ecosystems, hosting extensive biological diversity, and yet that diversity and the ecosystem services provided are among the most endangered because of global changes. By reducing and altering coral reef biodiversity, global changes are endangering the lives of hundreds of millions of people. It was therefore appropriate that the ongoing workshop series ”Bridging the gap between Ocean Acidification and Economic Valuation” dedicated, during the International Year of Coral Reefs, its 4thedition in search of solutions inspired by the most recent data of the Natural, Economic and Social Sciences. This article summarizes the ecological and human importance of coral reefs, the reasons for their sensitivity to global changes, and presents the major conclusions of the workshop as well as policy options
Shallow coral reefs provide food, income, well-being and coastal protection to countries around the Indian Ocean and Asia. These reefs are under threat due to many anthropogenic stressors including pollution, sedimentation, overfishing, sea surface warming and habitat destruction. Ocean acidification interacts with these factors to exacerbate stress on coral reefs. Effective solutions in tackling the impact of ocean acidification require a thorough understanding of the current adaptive capacity of each nation to deal with the consequences. Here, we aim to help the decision-making process for policy makers in dealing with these future challenges at the regional and national levels. We recommend that a series of evaluations be made to understand the current status of each nation in this region in dealing with ocean acidification impacts by assessing the climate policy, education, policy coherence, related research activities, adaptive capacity of reef-dependent economic sectors and local management. Indonesia and Thailand, are selected as case studies. We also highlight general recommendations on mitigation and adaptation to ocean acidification impacts on coral reefs and propose well-designed research program would be necessary for developing a more targeted policy agenda in this region.
Food security, climate change, and their complex and uncertain interactions are a major challenge for societies and ecologies (1). Global assessments of predicted changes in crop yield under climate change, combined with international trade dynamics, suggest that disparities between nations in production and food availability will escalate (2). But climate change has already affected productivity. For example, weather-related factors caused declines in global maize and wheat production of 3.8% and 5.5%, respectively, between 1980 and 2008 (3). On page 979 of this issue, Free et al. (4) report a comprehensive analysis that indicates a 4.1% decline between 1930 and 2010 in the global productivity of marine fisheries , with some of the largest fish-producing ecoregions experiencing losses of up to 35%. Their spatial mapping can help to inform future planning and adaptation strategies.
Climate change, observed as warming sea surface temperatures, is expected to impact the Eastern coast of Canada at a rate higher than the global average. Changes in marine abiotic conditions will impact the growth and performance of economically important bivalve species, creating an increasingly uncertain future for the bivalve aquaculture industry. Site-selection for new farms, and the management of extant ones could mitigate these potential impacts, but the implementation of this planning process is dependent on stakeholder support and engagement. Recognizing the importance of stakeholder input in management decisions, this research analyzed the perspectives of farmers, researchers, and managers from Nova Scotia (NS) and Prince Edward Island (PEI) on the relationship between climate change and bivalve aquaculture. Stakeholder perspectives were analyzed using a semi-quantitative interview method (Q methodology). These perspectives indicated the need for a higher level of integration both between stakeholder groups, namely farmers and managers, and management tools and climate change. Increased understanding between farmers and managers could be achieved through the use of researchers as knowledge brokers, collaborating and communicating with both groups. Making use of management tools, such as the ecosystem approach to aquaculture, required insurance, and adaptive management, governmental bodies on both a federal and provincial level can act as channels by which uncertainty generated by climate change can be further reduced. In summary, stakeholder perception can be used by marine planners to adapt to these foreseen changes, and to promote the expansion of this industry.
Experiments have shown that increasing dissolved CO2concentrations (i.e. Ocean Acidification, OA) in marine ecosystems may act as nutrient for primary producers (e.g. fleshy algae) or a stressor for calcifying species (e.g., coralline algae, corals, molluscs). For the first time, rapid habitat dominance shifts and altered competitive replacement from a reef-forming to a non-reef-forming biogenic habitat were documented over one-year exposure to low pH/high CO2 through a transplant experiment off Vulcano Island CO2 seeps (NE Sicily, Italy). Ocean acidification decreased vermetid reefs complexity via a reduction in the reef-building species density, boosted canopy macroalgae and led to changes in composition, structure and functional diversity of the associated benthic assemblages. OA effects on invertebrate richness and abundance were nonlinear, being maximal at intermediate complexity levels of vermetid reefs and canopy forming algae. Abundance of higher order consumers (e.g. carnivores, suspension feeders) decreased under elevated CO2 levels. Herbivores were non-linearly related to OA conditions, with increasing competitive release only of minor intertidal grazers (e.g. amphipods) under elevated CO2 levels.
Our results support the dual role of CO2 (as a stressor and as a resource) in disrupting the state of rocky shorecommunities, and raise specific concerns about the future of intertidal reef ecosystem under increasing CO2 emissions. We contribute to inform predictions of the complex and nonlinear community effects of OA on biogenic habitats, but at the same time encourage the use of multiple natural CO2 gradients in providing quantitative data on changing community responses to long-term CO2 exposure.
Climate change, represented by ever-rising ocean temperatures, is a mounting threat to the marine ecosystem and its services. This is most evident in the longitudinal and depth-related migrations of the ectothermic species. Although the impacts of climate change on the marine ecosystem of the Arabian Gulf are expected to be exacerbated—owing to its semi-enclosed basin that limits species range shift, extreme environmental conditions, overfishing, and pollution—very few studies have been carried out to evaluate such impacts. Here, we conduct a systematic review of literature over the period 1950–2018 to assess the status of knowledge about climate change impacts on the Arabian Gulf's marine ecosystem and fisheries resources. We found that this region suffers a significant research gap in this critical subject, with only a handful of studies that explicitly addresses the effects of climate change. Our finding raises an urgent need for initiating long-term monitoring programs, along with establishing effective transboundary institutions to advance the current knowledge in climate change.
Ocean acidification (OA), the global decrease in surface water pH from absorption of anthropogenic CO2, may put many marine taxa at risk. However, populations that experience extreme localized conditions, and are adapted to these conditions predicted in the global ocean in 2100, may be more tolerant to future OA. By identifying locally adapted populations, researchers can examine the mechanisms used to cope with decreasing pH. One oceanographic process that influences pH, is wind driven upwelling. Here we compare two Californian populations of the coral Balanophyllia elegans from distinct upwelling regimes, and test their physiological and transcriptomic responses to experimental seawater acidification. We measured respiration rates, protein and lipid content, and gene expression in corals from both populations exposed to pH levels of 7.8 and 7.4 for 29 days. Corals from the population that experiences lower pH due to high upwelling, maintained the same respiration rate throughout the exposure. In contrast, corals from the low upwelling site had reduced respiration rates, protein content, and lipid‐class content at low pH exposure, suggesting they have depleted their energy reserves. Using RNA‐Seq, we found that corals from the high upwelling site upregulated genes involved in calcium ion binding and ion transport, most likely related to pH homeostasis and calcification. In contrast, corals from the low upwelling site downregulated stress response genes at low pH exposure. Divergent population responses to low pH observed in B. elegans highlight the importance of multi‐population studies for predicting a species’ response to future OA.