Stronger Ocean Rules Could Shield Pacific Marine Life From Climate Losses, Study Finds

Stretching across the waters of Colombia, Costa Rica, Ecuador and Panama, the Marine Corridor of the Eastern Tropical Pacific, known as CMAR, is one of the world’s most ambitious experiments in transboundary ocean conservation. Established in 2004, the corridor links a chain of oceanic protected areas, including Cocos Island, Gorgona, Coiba, Malpelo and the Galápagos, with the goal of safeguarding the migratory highways of sharks, rays, sea turtles and marine mammals. A new open-access study published in Discover Oceans suggests that this celebrated network faces a difficult future under climate change, but also delivers a strikingly hopeful message: how well the region manages fishing and enforcement will largely determine how much marine life survives the coming decades.

An international team led by Juliano Palacios-Abrantes of the Institute for the Oceans and Fisheries at the University of British Columbia, together with colleagues from Fundación MarViva, the Charles Darwin Foundation and partner institutions across the region, set out to answer a deceptively simple question. If the countries of the Eastern Tropical Pacific improve their fisheries management and conservation enforcement, can they buffer their marine ecosystems against the impacts of a warming ocean? The answer, drawn from an unusually detailed modelling exercise, is a qualified yes, with an important caveat: neither conservation nor fisheries management alone is enough, and the two must advance in parallel.

The scientific challenge is formidable. The Eastern Tropical Pacific is a region of high endemism and extraordinary migratory species, from tunas and billfishes to scalloped hammerhead sharks that move between island sanctuaries. It is also a region where climate stressors converge. Surface temperatures are projected to rise by up to 0.96 degrees Celsius by 2050 under a high-emission scenario, while oxygen minimum zones, already a defining feature of the region, are expected to expand and shoal. Warmer, less oxygenated water compresses the vertical habitat available to pelagic species, disrupts trophic interactions across the food web and shifts species distributions, often poleward toward the Humboldt Current system. On top of these pressures, illegal, unreported and unregulated fishing has historically undermined the conservation benefits that the protected areas were designed to deliver.

To explore how these forces might interact, the researchers built their analysis around a dynamic bioclimate envelope model, or DBEM, operating on a half-degree grid across the exclusive economic zones of the four member countries, ten marine protected areas and the adjacent high seas. The model ingests spatially explicit outputs from three Earth System Models contributed to the sixth phase of the Coupled Model Intercomparison Project, from the Geophysical Fluid Dynamics Laboratory, the Institut Pierre-Simon Laplace and the Max Planck Institute. These inputs, including temperature, oxygen, salinity, net primary production and ocean currents, are translated into habitat suitability indices for each of 42 species identified as priorities during stakeholder workshops held in December 2023 and May 2024. The model then simulates population growth, adult and larval dispersal through advection-diffusion-reaction equations, and even the effect of warming and oxygen loss on individual growth through a generalized von Bertalanffy growth sub-model.

What makes the study distinctive is its treatment of management. Rather than assuming regulations on paper translate into protection at sea, the team co-developed five scenarios with regional stakeholders, capturing everything from the status quo, in which fishing mortality runs roughly 30 percent above sustainable levels and protected cells still experience 20 percent of that pressure, to a future in which all rules are respected and fishing everywhere occurs at maximum sustainable yield. Intermediate scenarios tested the consequences of implementing only conservation measures or only fisheries reforms, and of abandoning enforcement altogether, which the model represented as fishing mortality 50 percent above sustainable levels inside and outside protected areas.

The projections are sobering. Under continued status quo management, biomass of the region’s key species holds roughly steady through 2030 under the low-emission SSP1-2.6 pathway but begins declining by 2050 under the high-emission SSP5-8.5 pathway. Regional patterns diverge sharply from this overall trend. Panama’s exclusive economic zone fares worst, with projected biomass losses of around 13 percent by 2030 and losses reaching 20 percent around Coiba by 2050, while Ecuador’s insular waters and the Galápagos Marine Reserve show near-zero change, albeit with low confidence across the climate models. By mid-century, most sub-regions are projected to lose between 7 and 15 percent of their biomass relative to a 1951 to 2014 baseline.

The statistical analysis, a generalized additive model explaining 85 percent of the deviance in projected biomass change, identified management scenario as the strongest lever. Implementing fisheries regulations alone produced the largest single improvement relative to the unimplemented scenario, followed closely by full implementation of both conservation and fisheries rules. The high-emission climate pathway and the later 2050 time frame both depressed biomass independently, and MPA area exerted a strong but non-linear influence, suggesting that size alone does not determine a reserve’s climate resilience. Latitude mattered too, with biomass declining linearly as one moves northward through the corridor.

One of the most intriguing findings concerns the Galápagos, where implementing conservation rules alone sometimes appeared to yield slightly worse percentage outcomes than the status quo. The authors attribute this to what conservation scientists call the relative abundance protection paradox. Because the Galápagos reserve has already succeeded in rebuilding biomass, its baseline is higher, so climate-driven losses appear proportionally larger even though the reserve maintains more absolute biomass than less-protected areas. The pattern is a reminder that percentage comparisons can mislead, and that well-protected areas may be quietly doing exactly what they were designed to do.

The study also highlights the double-edged role of upwelling systems. Regions such as the Galápagos, which show the smallest projected losses, benefit from upwelling that delivers cool, nutrient-rich water to the surface, potentially acting as thermal refugia. Yet the same process can lift the upper boundary of the oxygen minimum zone closer to the surface, compressing habitat for tunas and billfishes that already face declining suitability in the region. Stronger currents projected under climate change may also scatter primary productivity offshore, weakening the food web that upwelling is supposed to sustain. The authors argue these zones should be managed as dynamic systems requiring continuous monitoring of oxygen and productivity rather than treated as stable sanctuaries.

The policy implications are direct. Fisheries management, the study finds, delivers a larger buffering effect than conservation because it regulates activity across entire exclusive economic zones rather than within smaller reserve boundaries, and reforms need not rely solely on effort limits. Shifting from high-bycatch gears such as longlines toward selective, low-impact methods, including the green-stick technique for tunas, would reduce mortality of sharks, billfishes and turtles while potentially raising economic returns for coastal communities. In Costa Rica, where the small but strictly protected Cocos Island coexists with the larger Bicentenario area that still lacks a management plan, targeted low-impact fisheries and stronger traceability measures could substantially amplify conservation gains. The authors also urge CMAR to move beyond its current non-binding structure, establishing a dedicated fisheries management body and thematic working groups on fisheries and tourism, the two most influential human uses in the region. Even under the most optimistic combination of mitigation and management, some biomass decline is inevitable, but the modelling makes clear that coordinated, enforced, transboundary action can meaningfully offset climate losses, offering a template as nations race to meet the Kunming-Montreal Global Biodiversity Framework’s 30-by-30 target.

Subject of Research: Climate change impacts and management resilience of marine biomass in the Eastern Tropical Pacific marine protected area corridor

Article Title: Climate change and ocean management shape marine biomass resilience in the Marine Corridor of the Eastern Tropical Pacific

Article References: Palacios-Abrantes, J., Clarke, T. M., Jiménez, A. B., Romero-Chaves, R., Villalobos-Rojas, F., Sánchez-Godínez, C., Viteri-Mejía, C., Martínez-Fernández, D., Moity, N., Ramírez, J., & Cheung, W. W. L. (2026). Climate change and ocean management shape marine biomass resilience in the Marine Corridor of the Eastern Tropical Pacific. Discover Oceans, 3(1), Article 38. https://doi.org/10.1007/s44289-026-00151-3

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00151-3

Keywords: marine protected areas, climate change, fisheries management, Eastern Tropical Pacific, CMAR, ocean warming, oxygen minimum zones, biomass projections, Galápagos, transboundary conservation, species range shifts, ecosystem modelling