image: Omar Defeo, a professor at UdelaR, gives a lecture during the Oceanography session at FAPESP Day Uruguay
Credit: Karina Toledo/Agência FAPESP
By Karina Toledo | Agência FAPESP – Beaches around the world are undergoing a process of “crushing” due to a combination of rising sea levels caused by climate change and urbanization in coastal areas. This phenomenon not only profoundly affects the biodiversity living on the sand, but it also harms activities such as fishing and tourism. Additionally, it makes coastal cities more susceptible to the advance of the sea.
The warning was issued during the FAPESP Day Uruguay symposium, which began on November 13 in Montevideo, by Uruguayan marine scientist Omar Defeo, a professor at Uruguay’s University of the Republic (UdelaR).
“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 said in his presentation.
As the researcher explained, the coastal ecosystem can be divided into three zones: the dune (post-beach), which is the area above the high tide line where sand accumulates due to wind action, forming mounds or “sand mountains”; the beach (beach face), a strip of sand exposed during low tide and submerged during high tide; and the submerged part (foreshore), which extends from the lower limit of low tide to the zone where waves begin to break.
“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,” said the scientist.
In a study conducted in collaboration with Brazilian researchers supported by FAPESP (17/17071-9, 18/22036-0, 18/05099-9, and 18/19776-2), Defeo’s group demonstrated that when one of these three coastal zones is compromised by urbanization, the effects harm the entire ecosystem. The study, led by Brazilian researcher Guilerme Corte, analyzed biodiversity at 90 locations along 30 beaches on the northern coast of São Paulo, Brazil.
The results, published in the journal Marine Pollution Bulletin, show that the number of beachgoers is the most impactful urbanization variable and correlates negatively with species richness and biomass, especially in submerged areas. The presence of buildings on the sand and mechanical cleaning activities also reduce biomass and species richness. Interestingly, abundance (number of individuals) was higher in locations close to urban centers. According to the authors, this is due to an increase in opportunistic species, such as polychaetes, which benefit from the supply of organic matter associated with human activity.
“Above all, the study showed that human impacts aren’t restricted to the place where they occur [on dry sand]. Stressors such as construction and high numbers of visitors on the upper part of the beach negatively affect biodiversity in the lower and submerged areas,” he said.
Another study conducted by Defeo in partnership with Brazilian scientists and published in the journal Frontiers in Marine Science showed that one-fifth of the 315 beaches analyzed around the globe have intense, extreme, or severe erosion rates. The group analyzed the various factors behind the phenomenon, including sea level rise, wind patterns, and waves. “We observed that human activities play a significant role, particularly on reflective beaches [with a steep slope that causes waves to dissipate their energy abruptly on the beach] and intermediate beaches [which have characteristics of both reflective beaches and calm or dissipative beaches],” he pointed out.
Defeo’s presentation took place during the first scientific session of the symposium, which was dedicated to oceanographic sciences. Other participants included Marcelo Dottori from the University of São Paulo (USP), who moderated the panel; Cristiana Seixas from the State University of Campinas (UNICAMP); and Natália Venturini from UdelaR.
The opening ceremony of the event was attended by Alvaro Brunini, president of Uruguay’s National Research and Innovation Agency (ANII); Marcio de Castro, scientific director of FAPESP; Raul Machado, manager of the Foundation’s Institutional Relations Advisory and coordinator of the symposium; and Brazil’s ambassador to Uruguay, Marcos Leal Raposo Lopes.
For more information about the FAPESP Day Uruguay symposium, visit fapesp.br/week/2025/uruguay.