Introduction to the special issue: The global state of the ocean; interactions between stresses, impacts and some potential solutions. Synthesis papers from the International Programme on the State of the Ocean 2011 and 2012 workshops

Pollution in the Arctic Ocean: An overview of multiple pressures and implications for ecosystem services

The Arctic is undergoing unprecedented change. Observations and models demonstrate significant perturbations to the physical and biological systems. Arctic species and ecosystems, particularly in the marine environment, are subject to a wide range of pressures from human activities, including exposure to a complex mixture of pollutants, climate change and fishing activity. These pressures affect the ecosystem services that the Arctic provides. Current international policies are attempting to support sustainable exploitation of Arctic resources with a view to balancing human wellbeing and environmental protection. However, assessments of the potential combined impacts of human activities are limited by data, particularly related to pollutants, a limited understanding of physical and biological processes, and single policies that are limited to ecosystem-level actions. This manuscript considers how, when combined, a suite of existing tools can be used to assess the impacts of pollutants in combination with other anthropogenic pressures on Arctic ecosystems, and on the services that these ecosystems provide. Recommendations are made for the advancement of targeted Arctic research to inform environmental practices and regulatory decisions.

Climate Change Effects on Aquaculture Production: Sustainability Implications, Mitigation, and Adaptations

Aquaculture continues to significantly expand its production, making it the fastest-growing food production sector globally. However, the sustainability of the sector is at stake due to the predicted effects of climate change that are not only a future but also a present reality. In this paper, we review the potential effects of climate change on aquaculture production and its implications on the sector's sustainability. Various elements of a changing climate, such as rising temperatures, sea-level rise, diseases and harmful algal blooms, changes in rainfall patterns, the uncertainty of external inputs supplies, changes in sea surface salinity, and severe climatic events have been discussed. Furthermore, several adaptation options have been presented as well as some gaps in existing knowledge that require further investigations. Overall, climate change effects and implications on aquaculture production sustainability are expected to be both negative and positive although, the negative effects outweigh the positive ones. Adapting to the predicted changes in the short-term while taking mitigation measures in the long-term could be the only way toward sustaining the sector's production. However, successful adaptation will depend on the adaptive capacity of the producers in different regions of the world.

A transition to sustainable ocean governance

Human wellbeing relies on the Biosphere, including natural resources provided by ocean ecosystems. As multiple demands and stressors threaten the ocean, transformative change in ocean governance is required to maintain the contributions of the ocean to people. Here we illustrate how transition theory can be applied to ocean governance. We demonstrate how current economic and social systems can adapt to existing pressures and shift towards ocean stewardship through incorporation of niche innovations within and across economic sectors and stakeholder communities. These novel approaches support an emergent but purposeful transition and suggest a clear path to a thriving and vibrant relationship between humans and the ocean. Oceans provide important natural resources, but the management and governance of the ocean is complex and the ecosystem is suffering as a result. The authors discuss current barriers to sustainable ocean governance and suggest pathways forward.

Oceans provide important natural resources, but the management and governance of the ocean is complex and the ecosystem is suffering as a result. The authors discuss current barriers to sustainable ocean governance and suggest pathways forward.

Eelgrass (Zostera marina) Food Web Structure in Different Environmental Settings

This study compares the structure of eelgrass (Zostera marina L.) meadows and associated food webs in two eelgrass habitats in Denmark, differing in exposure, connection to the open sea, nutrient enrichment and water transparency. Meadow structure strongly reflected the environmental conditions in each habitat. The eutrophicated, protected site had higher biomass of filamentous algae, lower eelgrass biomass and shoot density, longer and narrower leaves, and higher above to below ground biomass ratio compared to the less nutrient-enriched and more exposed site. The faunal community composition and food web structure also differed markedly between sites with the eutrophicated, enclosed site having higher biomass of consumers and less complex food web. These relationships resulted in a column shaped biomass distribution of the consumers at the eutrophicated site whereas the less nutrient-rich site showed a pyramidal biomass distribution of consumers coupled with a more diverse consumer community. The differences in meadow and food web structure of the two seagrass habitats, suggest how physical setting may shape ecosystem response and resilience to anthropogenic pressure. We encourage larger, replicated studies to further disentangle the effects of different environmental variables on seagrass food web structure.

The Southern Ocean ecosystem under multiple climate change stresses--an integrated circumpolar assessment

A quantitative assessment of observed and projected environmental changes in the Southern Ocean (SO) with a potential impact on the marine ecosystem shows: (i) large proportions of the SO are and will be affected by one or more climate change processes; areas projected to be affected in the future are larger than areas that are already under environmental stress, (ii) areas affected by changes in sea-ice in the past and likely in the future are much larger than areas affected by ocean warming. The smallest areas (<1% area of the SO) are affected by glacier retreat and warming in the deeper euphotic layer. In the future, decrease in the sea-ice is expected to be widespread. Changes in iceberg impact resulting from further collapse of ice-shelves can potentially affect large parts of shelf and ephemerally in the off-shore regions. However, aragonite undersaturation (acidification) might become one of the biggest problems for the Antarctic marine ecosystem by affecting almost the entire SO. Direct and indirect impacts of various environmental changes to the three major habitats, sea-ice, pelagic and benthos and their biota are complex. The areas affected by environmental stressors range from 33% of the SO for a single stressor, 11% for two and 2% for three, to <1% for four and five overlapping factors. In the future, areas expected to be affected by 2 and 3 overlapping factors are equally large, including potential iceberg changes, and together cover almost 86% of the SO ecosystem.

Critical indirect effects of climate change on sub-Antarctic ecosystem functioning

Sub-Antarctic islands represent critical breeding habitats for land-based top predators that dominate Southern Ocean food webs. Reproduction and molting incur high energetic demands that are sustained at the sub-Antarctic Prince Edward Islands (PEIs) by both inshore (phytoplankton blooms; “island mass effect”; autochthonous) and offshore (allochthonous) productivity. As the relative contributions of these sustenance pathways are, in turn, affected by oceanographic conditions around the PEIs, we address the consequences of climatically driven changes in the physical environment on this island ecosystem. We show that there has been a measurable long-term shift in the carbon isotope signatures of the benthos inhabiting the shallow shelf region of the PEIs, most likely reflecting a long-term decline in enhanced phytoplankton productivity at the islands in response to a climate-driven shift in the position of the sub-Antarctic Front. Our results indicate that regional climate change has affected the balance between allochthonous and autochthonous productivity at the PEIs. Over the last three decades, inshore-feeding top predators at the islands have shown a marked decrease in their population sizes. Conversely, population sizes of offshore-feeding predators that forage over great distances from the islands have remained stable or increased, with one exception. Population decline of predators that rely heavily on organisms inhabiting the inshore region strongly suggest changes in prey availability, which are likely driven by factors such as fisheries impacts on some prey populations and shifts in competitive interactions among predators. In addition to these local factors, our analysis indicates that changes in prey availability may also result indirectly through regional climate change effects on the islands' marine ecosystem. Most importantly, our results indicate that a fundamental shift in the balance between allochthonous and autochthonous trophic pathways within this island ecosystem may be detected throughout the food web, demonstrating that the most powerful effects of climate change on marine systems may be indirect.