In this month’s “In Depth”, we discuss this report in which the Institute has contributed to and that highlights the “critical impact” on the ocean of stressors such as warming waters and overfishing, as well as the link between ocean health and human health.
On 8 June, coinciding with World Oceans Day, the United Nations released the third World Ocean Assessment (WOA III), the leading scientific report on the state of the marine environment, to which more than 550 experts from 86 countries have contributed, providing a global, cross-cutting and diverse perspective to the analysis. This is no routine document; the previous WOA, published in 2021, left a bittersweet taste due to a lack of specificity in certain sectorial indicators. This time, expectations were exceptionally high.
Following the collection, synthesis, and integration of the most recent scientific advances regarding the state of the oceans—and after a complex political validation process requiring the approval of all member states—the definitive text has been published, featuring prominent participation from the Institut de Ciències del Mar (ICM-CSIC).
Researchers from our centre have led and coordinated the chapter dedicated to the pelagic domain, the largest biome on the planet and, simultaneously, one of the least understood areas of the ocean.
"The pelagic domain is the open-ocean environment where organisms are not anchored to the seabed, but instead move with constant dynamics and mobility, utilising and connecting habitats that are vital for the global functioning of the entire planet," explains Marta Coll, a researcher at the ICM-CSIC and coordinator of this section.
From the sun-drenched surface to the nearly inaccessible hadal depths of over six thousand metres, the water column functions like a flawless climatic and biological machine. It provides us with living resources, energy, and thermal regulation essential for human survival, acting as the invisible lung of the Earth. However, the findings of this global evaluation confirm that we have fully entered the Anthropocene—the epoch in which human-driven changes have been drastically altering species distribution, productivity, and biodiversity since the Industrial Revolution. Finally, they highlight that our knowledge of this environment and its inhabitants remains partial.
New climate threats
The last five years have witnessed unprecedented technological advances. Thanks to oceanographic research vessels operating as motherships for underwater robots, the expansion of Argo biogeochemical floats, and environmental DNA (eDNA) techniques, science has managed to map previously invisible corners. Stable isotope analyses have allowed the food web to be mapped with unprecedented accuracy. Yet, holding up a more precise mirror has only served to confirm the severity of the Anthropocene’s scars. The latest climate models project a scenario marked by accelerated warming, the acidification of seas and oceans, oxygen loss, and extremely abrupt extreme phenomena, such as marine heatwaves, which until recently could not be accurately simulated.
Global warming has a significant impact, resulting in a phenomenon known as ‘trophic amplification’. Given that rising temperatures reduce the efficiency of energy transfer between different links in the food chain, small declines in phytoplankton biomass trigger massive losses at higher levels, directly affecting fish and marine mammals. A clear example of this environmental vulnerability occurred in 2023 with the arrival of the El Niño phenomenon, which halved industrial catches of the Peruvian anchoveta—the world's largest single-species fishery— that desestabilised the local economy and global aquaculture.
"We are observing profound changes in the physical and chemical state of the pelagic environment that are already affecting the efficiency of food webs," warns ICM-CSIC researcher Francisco Ramírez, who also participated in drafting the pelagic chapter. Ramírez points out that marine heatwaves are increasing in frequency and intensity, causing habitat compression for many species and worsening deoxygenation events and mass mortalities, as well as compounding the impacts of overfishing.
Furthermore, emerging pollutants such as microplastics are now widespread within the tissues of marine organisms, altering everything from carbon sinking rates to the food safety of humans who consume fish. Finally, the study warns of the critical situation facing chondrichthyans, or cartilaginous fish: three-quarters of the shark species studied are threatened with extinction due to overfishing and bycatch.
Lastly, the report highlights another major global issue: pollution. In this regard, ICM-CSIC researcher Vanessa-Sarah Salvo, from the ICM-CSIC’s EMBIMOS group, has co-authored the chapter examining the impacts of pollutants on marine ecosystems and the overall health of the ocean.
“Pollution continues to rise in all the world’s oceans, and the assessment highlights a particularly worrying increase in chemical pollution associated with plastics,” says Salvo. “These findings reinforce the need to tackle plastic pollution throughout its entire life cycle, including reducing production and preventing pollution at source.”
Finally, a specific chapter explores the intrinsic links between ocean health and human health. Elisa Berdalet, from the Plankton Ecology and Ocean Health group at the ICM-CSIC, explains:
“The sea provides us with food, medicines and spaces for health and wellbeing. However, at the same time, risks to people arise from human activity itself, such as exposure to pathogens and pollutants or the degradation of ecosystems. The chapter I have contributed to includes recommendations and priorities for protecting human communities from extreme marine events such as tsunamis, hurricanes or harmful algal blooms, some of which may be exacerbated by climate change.
Tools and global regulation
Despite everything, WOA III does not aim to be a mere chronicle of collapse, but rather a tool for transforming global governance. The text highlights the benefits of an effective fisheries management, which has enabled the sustained recovery of stocks that had historically suffered from severe overexploitation, such as Atlantic bluefin tuna. The regulatory horizon also faces monumental challenges in international waters. On one hand, the International Seabed Authority is still working on the uncertain regulation of deep-sea mining—a large-scale activity that threatens seabed communities, which are essential for carbon sequestration. On the other hand, the historic adoption of the BBNJ Agreement in June 2023 opens a window of hope for the conservation and sustainable use of biodiversity in areas beyond national jurisdiction through the creation of marine protected areas and the promotion of so-called 'blue corridors'.
Making these new international tools work will require filling the knowledge gaps that persist. For instance, nearly eighty per cent of zooplankton monitoring data remains inaccessible or partial, while socio-ecological research requires approaches that better connect human needs with the ecological limits of the planet in general, and the ocean in particular. For this reason, for the ICM-CSIC, having led these sections of the World Ocean Assessment reaffirms our institution's commitment to the frontier science and the United Nations, providing the necessary knowledge so that civil society and policymakers understand that the future of humanity depends, nothing more and nothing less, on the firmness with which we protect the ocean.