Professor Amanda Lombard and Dr Alejandra Vargas-Fonseca
Led by Professor Benjamin Halpern of the University of California – Santa Barbara’s National Center for Ecological Analysis and Synthesis, with co-authors Professor Amanda Lombard (National Research Foundation Chair of Marine Spatial Planning and research lead for the team from South Africa); and Dr Alejandra Vargas-Fonseca of Nelson Mandela University’s Institute for Coastal and Marine Research, the study is the most comprehensive forecast of cumulative human impacts on marine ecosystems to date.
The study points out stark projections
• Cumulative human impacts on oceans will rise by 2.2 to 2.6 times current levels by mid-century.
• In the tropics, impacts will nearly triple (up to 3.2 times).
• In the polar regions, already heavily stressed, impacts will climb by up to 2.5 times.
• Coastal habitats such as mangroves, seagrasses and salt marshes, crucial for storm protection, fisheries and carbon storage, will face the greatest losses.
“It’s sobering. And unexpected,” said Prof Halpern, “not because impacts will be increasing — that is not surprising — but because they will be increasing so much, so fast.” The very place people rely on most, the coasts, are at the greatest risk.
The study identifies ocean warming and loss of fish biomass from poorly managed fisheries as the most significant drivers of future impacts.
Other drivers studied were acidification, coastal disturbance, reduced oxygen, sea-level rise, primary productivity, nutrient and light pollution.
Prof Lombard adds that many other pressures, such as diseases, invasive species, wildlife strikes, entanglements, ghost fishing gear and noise pollution are also known to impact the ocean, but data were not available for the study to model into the future.
“More data on these pressures in urgently needed.” As human activity on the ocean and along the coast has intensified, so have impacts on the marine environment.
The scientists first tackled the challenge of understanding how these pieces fit together and add up to impact the ocean nearly 20 years ago, setting the stage for the current study.
They assert that without decisive action, many marine ecosystems could be pushed beyond their ability to cope, undermining the ocean’s capacity to provide food, regulate climate and support biodiversity.
The findings have profound implications for millions of people, especially in developing nations. Countries such as Togo, Ghana and Sri Lanka are among the most vulnerable due to their high dependence on marine resources and the rapid increases in projected pressures.
The world’s coasts are expected to bear the brunt of these increasing cumulative impacts — an unsurprising reality, the researchers say, given most human uses of the ocean are near coasts. Yet it’s also a “worrisome result nonetheless,” according to the paper, because the coasts “are where people derive most value from the ocean.” Additionally, many countries are dependent on the ocean for food, livelihood and other benefits. “Many of these countries will face substantial increases,” Prof Halpern said.
Prof Lombard is particularly concerned about coastal communities who rely on subsistence harvesting for livelihoods, many of these in African coastal regions where she currently works.
“Healthy marine species and habitats are fundamental to human well-being globally, but especially for coastal communities in Africa subsistence harvesters, artisanal fishers and families who depend on the sea will be among the hardest hit.”
The researchers stress the trajectory is not inevitable. Stronger climate action, improved fisheries management and protection of vulnerable coastal habitats could substantially reduce future impacts.
The authors contend that enacting policies designed to reduce climate change effects and to improve fisheries management could be effective ways to manage and reduce human impacts, given the outsize roles that ocean warming and biomass loss play in the estimate of future human impacts on the ocean.
Likewise, prioritising management of habitats that are expected to be heavily impacted — such as salt marshes and mangroves — could help reduce the pressures on them.
“Being able to look into the future is a super powerful planning tool,” Prof Halpern said. “We can still alter that future; this paper is a warning, not a prescription.”
The research mapped 10 key human pressures, from climate change to fisheries and land-based impacts, across 20 marine habitats at 10 km resolution. It was funded by the Belmont Forum under the MARISCO grant, led by Professor Helmut Hillebrand (Helmholtz Institute for Functional Marine Biodiversity, Germany), Prof Halpern and Prof Lombard.
The full article is available here: Science – Cumulative impacts to global marine ecosystems projected to more than double by midcentury.