Overcoming the coupled climate and biodiversity crises and their societal impacts.

Earth's biodiversity and human societies face pollution, overconsumption of natural resources, urbanization, demographic shifts, social and economic inequalities, and habitat loss, many of which are exacerbated by climate change. Here, we review links among climate, biodiversity, and society and develop a roadmap toward sustainability. These include limiting warming to 1.5°C and effectively conserving and restoring functional ecosystems on 30 to 50% of land, freshwater, and ocean "scapes." We envision a mosaic of interconnected protected and shared spaces, including intensively used spaces, to strengthen self-sustaining biodiversity, the capacity of people and nature to adapt to and mitigate climate change, and nature's contributions to people. Fostering interlinked human, ecosystem, and planetary health for a livable future urgently requires bold implementation of transformative policy interventions through interconnected institutions, governance, and social systems from local to global levels.

Healthy and diverse coral reefs in Djibouti - A resilient reef system or few anthropogenic threats?

Djiboutian coral reefs are poorly studied, but are of critical importance to tourism and artisanal fishing in this small developing nation. In 2014 and 2016 we carried out the most comprehensive survey of Djiboutian reefs to date, and present data on their ecology, health and estimate their vulnerability to future coral bleaching and anthropogenic impacts. Reef type varied from complex reef formations exposed to wind and waves along the Gulf of Aden, to narrow fringing reefs adjacent to the deep sheltered waters of the Gulf of Tadjoura. Evidence suggests that in the past 35 years the reefs have not previously experienced severe coral bleaching or significant human impacts, with many reefs having healthy and diverse coral and fish populations. Mean coral cover was high (52%) and fish assemblages were dominated by fishery target species and herbivores. However, rising sea surface temperatures (SSTs) and rapid recent coastal development activities in Djibouti are likely future threats to these relatively untouched reefs.

The current status of coral reefs and their vulnerability to climate change and multiple human stresses in the Comoros Archipelago, Western Indian Ocean.

Coral bleaching and various human stressors have degraded the coral reefs of the Comoros Archipelago in the past 40 years and rising atmospheric CO2 levels are predicted to further impact marine habitats. The condition of reefs in the Comoros is poorly known; using SCUBA based methods we surveyed reef condition and resilience to bleaching at sites in Grande Comore and Mohéli in 2010 and 2016. The condition of reefs was highly variable, with a range in live coral cover between 6% and 60% and target fishery species biomass between 20 and 500 kg per ha. The vulnerability assessment of reefs to future coral bleaching and their exposure to fishing, soil erosion and river pollution in Mohéli Marine Park found that offshore sites around the islets south of the island were least likely to be impacted by these negative pressures. The high variability in both reef condition and vulnerability across reefs in the Park lends itself to spatially explicit conservation actions. However, it is noteworthy that climate impacts to date appear moderate and that local human pressures are not having a major impact on components of reef health and recovery, suggesting these reefs are relatively resilient to the current anthropogenic stresses that they are experiencing.

Variation in size frequency distribution of coral populations under different fishing pressures in two contrasting locations in the Indian Ocean.

This study aimed to assess how the size-frequency distributions of coral genera varied between reefs under different fishing pressures in two contrasting Indian Ocean locations (the Maldives and East Africa). Using generalized linear mixed models, we were able to demonstrate that complex interactions occurred between coral genera, coral size class and fishing pressure. In both locations, we found Acropora coral species to be more abundant in non-fished compared to fished sites (a pattern which was consistent for nearly all the assessed size classes). Coral genera classified as 'stress tolerant' showed a contrasting pattern i.e. were higher in abundance in fished compared to non-fished sites. Site specific variations were also observed. For example, Maldivian reefs exhibited a significantly higher abundance in all size classes of 'competitive' corals compared to East Africa. This possibly indicates that East African reefs have already been subjected to higher levels of stress and are therefore less suitable environments for 'competitive' corals. This study also highlights the potential structure and composition of reefs under future degradation scenarios, for example with a loss of Acropora corals and an increase in dominance of 'stress tolerant' and 'generalist' coral genera.

Kenya.

The Kenya coast is bathed by the northward-flowing warm waters of the East Africa Coastal Current, located between latitudes 1 and 5 degrees S. With a narrow continental shelf, the coastal marine environments are dominated by coral reefs, seagrass beds and mangroves, with large expanses of sandy substrates where river inputs from Kenya's two largest rivers, the Tana and Athi rivers, prevent the growth of coral reefs. The northern part of the coast is seasonally influenced by upwelling waters of the Somali Current, resulting in lower water temperatures for part of the year. The coast is made up of raised Pleistocene reefs on coastal plains and hills of sedimentary origin, which support native habitats dominated by scrub bush and remnant pockets of the forests that used to cover East Africa and the Congo basin. The marine environment is characterized by warm tropical conditions varying at the surface between 25 degrees C and 31 degrees C during the year, stable salinity regimes, and moderately high nutrient levels from terrestrial runoff and groundwater. The semi-diurnal tidal regime varies from 1.5 to 4 m amplitude from neap to spring tides, creating extensive intertidal platform and rocky-shore communities exposed twice-daily during low tides. Fringing reef crests dominate the whole southern coast and parts of the northern coast towards Somalia, forming a natural barrier to the wave energy from the ocean. Coral reefs form the dominant ecosystem along the majority of the Kenya coast, creating habitats for seagrasses and mangroves in the lagoons and creeks protected by the reef crests. Kenya's marine environment faces a number of threats from the growing coastal human population estimated at just under three million in 2000. Extraction of fish and other resources from the narrow continental shelf, coral reef and mangrove ecosystems increases each year with inadequate monitoring and management structures to protect the resource bases. Coastal development in urban and tourist centers proceeds with little regard for environmental and social impacts. With a faltering economy, industrial development in Mombasa proceeds with few checks on pollution and other impacts. In 1998 Kenya's coral reefs suffered 50-80% mortality from the El Niño-related coral bleaching event that affected the entire Indian Ocean. The institutional, human resource and legal infrastructure for managing the coastal environment has in the past been low, however these are rapidly improving with the revitalization of national institutions and the passing in 1999 of an Environment Act. Marine Protected Areas are the key tool currently used in management of marine ecosystems, and focus principally on coral reefs and biodiversity protection. New initiatives are underway to improve application of fisheries regulations, and to use Integrated Coastal Area Management (ICAM) as a framework for protecting marine and coastal environments.

Reefs and islands of the Chagos Archipelago, Indian Ocean: why it is the world's largest no-take marine protected area.

The Chagos Archipelago was designated a no-take marine protected area (MPA) in 2010; it covers 550 000 km2, with more than 60 000 km2 shallow limestone platform and reefs. This has doubled the global cover of such MPAs.It contains 25-50% of the Indian Ocean reef area remaining in excellent condition, as well as the world's largest contiguous undamaged reef area. It has suffered from warming episodes, but after the most severe mortality event of 1998, coral cover was restored after 10 years.Coral reef fishes are orders of magnitude more abundant than in other Indian Ocean locations, regardless of whether the latter are fished or protected.Coral diseases are extremely low, and no invasive marine species are known.Genetically, Chagos marine species are part of the Western Indian Ocean, and Chagos serves as a 'stepping-stone' in the ocean.The no-take MPA extends to the 200 nm boundary, and. includes 86 unfished seamounts and 243 deep knolls as well as encompassing important pelagic species.On the larger islands, native plants, coconut crabs, bird and turtle colonies were largely destroyed in plantation times, but several smaller islands are in relatively undamaged state.There are now 10 'important bird areas', coconut crab density is high and numbers of green and hawksbill turtles are recovering.Diego Garcia atoll contains a military facility; this atoll contains one Ramsar site and several 'strict nature reserves'. Pollutant monitoring shows it to be the least polluted inhabited atoll in the world. Today, strict environmental regulations are enforced.Shoreline erosion is significant in many places. Its economic cost in the inhabited part of Diego Garcia is very high, but all islands are vulnerable.Chagos is ideally situated for several monitoring programmes, and use is increasingly being made of the archipelago for this purpose.

The coral reef crisis: the critical importance of<350 ppm CO2.

Temperature-induced mass coral bleaching causing mortality on a wide geographic scale started when atmospheric CO(2) levels exceeded approximately 320 ppm. When CO(2) levels reached approximately 340 ppm, sporadic but highly destructive mass bleaching occurred in most reefs world-wide, often associated with El Niño events. Recovery was dependent on the vulnerability of individual reef areas and on the reef's previous history and resilience. At today's level of approximately 387 ppm, allowing a lag-time of 10 years for sea temperatures to respond, most reefs world-wide are committed to an irreversible decline. Mass bleaching will in future become annual, departing from the 4 to 7 years return-time of El Niño events. Bleaching will be exacerbated by the effects of degraded water-quality and increased severe weather events. In addition, the progressive onset of ocean acidification will cause reduction of coral growth and retardation of the growth of high magnesium calcite-secreting coralline algae. If CO(2) levels are allowed to reach 450 ppm (due to occur by 2030-2040 at the current rates), reefs will be in rapid and terminal decline world-wide from multiple synergies arising from mass bleaching, ocean acidification, and other environmental impacts. Damage to shallow reef communities will become extensive with consequent reduction of biodiversity followed by extinctions. Reefs will cease to be large-scale nursery grounds for fish and will cease to have most of their current value to humanity. There will be knock-on effects to ecosystems associated with reefs, and to other pelagic and benthic ecosystems. Should CO(2) levels reach 600 ppm reefs will be eroding geological structures with populations of surviving biota restricted to refuges. Domino effects will follow, affecting many other marine ecosystems. This is likely to have been the path of great mass extinctions of the past, adding to the case that anthropogenic CO(2) emissions could trigger the Earth's sixth mass extinction.