The marine environment has played a key role in the history of life and today’s ocean continues its primordial function in the evolution of life and climate. The recognized species diversity in the oceans does not exceed 13% of all currently described living species – fewer than 250,000 – but this can be due partly to our lack of knowledge, especially concerning deep zones of the oceans and microorganisms, and partly to the fact that marine ecosystems and the way of life in such a continuous medium disperse more easily species and they are less predisposed to endemism. In contrast, marine biomass can be considerable. Climate disturbance has a direct role in the loss of biological diversity, and this loss contributes in turn to the deregulation itself.
Coral reefs are found in only a small percentage of global oceans, between 0.08 and 0.16%, but they shelter about one third of the marine species known today. This ecological success is due to a symbiosis between a coral and an intracellular microalga, commonly called zooxanthellae. “Organismic engineers”, they are the source of the largest biological constructions on the planet. Genuine oases of life, they support the direct sustenance of more than 500 million people in the world from fishing, but they engage human interest also for other reasons: protection of coasts against erosion, high value tourist areas… Ecological services from coral reefs are estimated at approximately 30 billion USD per year. Their growth depends on many factors (light, temperature, pH, nutrients, turbidity…). They are therefore extremely sensitive to the current changes in our environment: water temperature variability, ocean acidification, in addition to localized disruptions (pollution, sedimentation, coastal development, overfishing, marine shipping…). An increase of less than 1 degree above a threshold value is sufficient to cause bleaching. It breaks the coral symbiosis with their zooxanthellae throughout the populations, leading to the disappearance of the reef. Similarly, ocean acidification impedes the formation of coral skeleton and many other biological functions such as reproduction. We actually estimate that approximately 20% of the global coral reefs have already disappeared completely; 25% are in high danger; and 25% more will be threatened by 2050 if positive management action is not taken.
For thirty years, the ocean mean temperature has been incessantly increasing, which reinforces the intensity and length of coral bleaching. The period between 2014 and 2017 was marked by massive coral mortality in the various ocean basins, with an exceptional decline by more than 50% in the reefs on the Great Barrier Reef – the largest coral structure in existence. Coral resilience was compromised with a low recruitment rate of coral larvae, and the stress experienced was exacerbated by additional anthropogenic factors (pollution, overfishing, urbanization, tourism, ocean acidification, predation by corallivores, etc.). 2018 has been the warmest year for the oceans since records began, suggesting that coral bleaching could become a recurrent phenomenon in the years to come. In order to protect this natural heritage, which is home to more than a third of the global marine biodiversity and on which over 500 million people depend worldwide for their livelihoods, it is necessary and urgent for governments to take action, beyond local measures, towards reducing human impacts on climate.
Climate change is impacting the productivity of marine ecosystems and fisheries, while demand for fish for human consumption is increasing. Fish is the main source of animal protein for one billion people and is one of the most traded renewable resources in the world. Changes in physical and chemical characteristics of seawater affect individual metabolism, species’ life cycles, predator-prey relationships, and changes in habitat. Geographic distributions of fish (migration rate towards the poles is 72.0 ± 13.5 km/decade) and ecosystem dynamics could undergo profound disruption in the coming decades, impacting fisheries globally and jeopardizing food security in many southern countries. Maintaining healthy, productive marine ecosystems is a critical issue.
Debates on mitigation and adaptation measures to adopt against climate change are based on observations and estimations over a range of less than 250 years. A recent study by Clark and his collaborators, published in Nature Climate Change, covers extremely long term (over 10,000 years1) climate consequences. Their scope is linked to CO2 emissions. According to these scenarios, the temperature increase could exceed the 2°C limit, and a 2 to 4 meters per century sea-level rise could be expected in the next millennium. These results confirm the importance of keeping a large quantity of fossil resources untouched.
Marine and land ecosystems provide many benefits to society. Marine ecosystems are under increased pressure because of climate change, expanding human populations and needs. Increased pressures and associated impacts on ecosystems often render current management and conservation policies inappropriate to mitigate or regulate such pressures and maintain the level of ecosystem benefits provided. Integrated approaches centred on ecosystems can help assess synergies and trade offs for delivery of benefits provided by ecosystems for management options with different levels of usage and conservation. The ecosystem service framework can help structure the production of comprehensive assessments drawing from multi-disciplinary academic knowledge and management experience. Interaction and dialogue with stakeholders structured by a step-wise iterative ‘triage’ process can help ensure ecosystem assessment outputs are meaningful, salient (reflecting the interests of those involved), useful to management and policy concerns, needs and projects, and feasible under available knowledge and resources. The ecosystem service framework needs to be applied at regular intervals to gain an idea of how the benefits derived from ecosystems evolve in time. Using the ecosystem service framework in combination with the DPSIR framework to identify Drivers, Pressures, States, Impact, Response can provide very rich insights to discussions for establishment of management plans and policies for marine conservation, especially those aiming to mitigate or adapt to climate change pressure, for delivery of healthy ecosystems and associated human well-being.