The quiet rhythm of waves along the shore now carries a warning that feels both urgent and intimate. At a scientific gathering in Montevideo, researchers outlined how climate driven sea level rise and relentless coastal urbanization are reshaping beaches at a pace that threatens biodiversity, livelihoods, and the very stability of coastal cities. Speaking at the FAPESP Day Uruguay symposium, marine scientist Omar Defeo of Uruguay’s University of the Republic described a global process of beach crushing and the sweeping ecological consequences already underway.
The symposium, held on November 13, brought together researchers from Uruguay, Brazil, and Argentina to discuss the accelerating erosion of sandy shorelines. Defeo highlighted new findings from collaborations with Brazilian scientists supported by FAPESP, including large scale biodiversity surveys on the northern coast of Sao Paulo and global erosion analyses involving 315 beaches. Together, the results pointed to a single message: human pressure and climate driven forces interact across every layer of the coastal ecosystem.
The interconnected life of dunes, beaches, and submerged zones
Defeo explained that coastal ecosystems operate as three tightly linked zones, each exchanging sand and energy through wind, waves, and storms. When urbanization interrupts any one of these zones, the disruption reverberates throughout the system. Biodiversity declines first in submerged areas, the research shows, and then across the entire beach profile, especially where buildings encroach on dunes or where mechanical cleaning disturbs dry sand communities.
“These zones form an interconnected coastal ecosystem that’s essential for environmental balance. How are they interconnected? The wind carries sand from the dry area to the surf zone [the submerged part]. And when the waves advance, they bring the sediment back to the beach. This bidirectional movement generates a constant exchange in which one zone feeds the other. When a storm comes, the dune acts as a buffer. So when urbanization eliminates the dune, the result can be the destruction of seaside homes,”
A global pattern of erosion, with regional urgency
The group also examined erosion patterns at hundreds of beaches worldwide and found that one fifth show intense, extreme, or severe erosion. The drivers include sea level rise, shifting winds, and wave energy, but the influential role of human activity stood out, especially on reflective and intermediate beaches where built structures constrain natural sediment movement. Results from the Sao Paulo coast echoed this broader pattern: more beachgoers, more construction, and more mechanical cleaning were all associated with sharp drops in species richness and biomass.
“Almost half of the beaches will disappear by the end of the century. We in Uruguay, Brazil, and Argentina share these resources. Therefore, we must work in partnership with Brazilian scientists to manage and conserve coastal ecosystems,”
Defeo emphasized that impacts rarely remain where they begin. Foot traffic, shoreline buildings, and recreational pressure on dry sand degrade biodiversity even in the submerged zones, where many species support fisheries and broader food webs. At the same time, an increase in opportunistic species near urban centers hints at how human activity reshapes not only habitat structure but also ecological dynamics.
The session drew contributions from scientists across the region, including experts from the University of Sao Paulo, the State University of Campinas, and UdelaR. Their shared concern centered on the accelerating loss of natural buffers, the rising vulnerability of coastal cities, and the growing need for coordinated conservation strategies. For countries that share contiguous coastlines and interconnected ecosystems, Defeo argued, collaboration is becoming not just beneficial but essential.
The symposium’s opening ceremony included leaders from Uruguay’s National Research and Innovation Agency, FAPESP, and Brazil’s diplomatic mission, underscoring the binational commitment to scientific exchange. While no single study can reverse the global trajectory of sea level rise or urban expansion, the researchers stressed that understanding the full scope of coastal interactions is an indispensable foundation for protecting what remains. As Defeo’s warning made clear, the future of many beaches will depend on decisions made in the present.
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