The Hidden Protectors of Our Beaches: The Role of Microbes in Safeguarding Coastal Waters

Environmental Microbiology a detailed analysis of these microbes in Stinson Beach, California. Their study sheds light on future environmental impacts and questions coastal management policies in the face of climate change.

Beaches: a threatened natural filter

Beaches function as a natural filtration mechanism at the interface between land and ocean. They play an essential role in the regulation of biogeochemical cycles. Grains of sand, much more than simple inert particles, form an environment where microbial communities capable of transforming or retaining chemical substances present in groundwater develop. These substances, from natural or anthropogenic sources, are potentially harmful to marine ecosystems. Jessica Bullington emphasizes that these processes are crucial for maintaining ecological balance. And this particularly in the face of the challenges linked to rising water levels and increasing climate disruptions.

The team conducted research at Stinson Beach, a high-energy beach north of San Francisco. In other words, it is a beach exposed to powerful and frequent waves, generally characterized by strong swell energy. Scientists have identified complex and varied communities there. They include bacteria such as Proteobacteria and archaea from the DPANN group.

Proteobacteria are a very diverse group of bacteria, essential in ecosystems, playing a key role in the degradation of nutrients and the regulation of environmental cycles such as nitrogen and carbon. Archaea of ​​the DPANN group are unicellular microorganisms, often tiny and dependent on other organisms, known for their ability to adapt to extreme environments and participate in complex biological processes, particularly in coastal aquifers. DPANN is an acronym that groups together several archaeal phyla, based on the initials of the main groups it includes.

Through their ability to degrade excess nutrients, these microorganisms limit the proliferation of harmful algae. They are also involved in greenhouse gas cycles. This role of purification is, however, fragile.

Resilience and fragility of microbes in the face of climate change

This study thus made it possible to examine the resilience of microbial communities living in the coastal aquifer in the face of environmental variations. Over two weeks, spanning a tidal transition between the wet and dry seasons, the researchers collected groundwater samples to analyze microbial composition using 16S rRNA gene sequencing. The results show remarkable stability of microbial populations despite daily tidal fluctuations and seasonal variations. However, an event ofovertoppingwhere intense waves penetrate the aquifer, resulted in significant reorganization of microbial communities. The DPANN Proteobacteria and archaea have seen their abundance and diversity altered. This fact could compromise their efficiency in the transformation of nutrients and the regulation of biogeochemical cycles.

These disturbances, which are becoming more and more frequent with rising water levels and intensifying storms, raise concerns about the sustainability of the ecosystem services offered by these microbes. For Christopher Francis, co-author, these complex communities could lose their ability to purify water if these disturbances increase. “ These microbes live in complex communities. Many have specialized roles that include nutrient processing and even greenhouse gas production or consumption “.

Rising sea levels, estimated between 0.3 and 1.2 meters by 2100 according to the IPCC, could intensify sea level events.overtopping. This will increase stress on these ecosystems on our beaches. A loss of these natural services could worsen environmental problems such as harmful algal blooms, fueled by excess nutrients. Another problem is the increase in greenhouse gas emissions. They come from disrupted microbial transformations.

What solutions to strengthen coastal resilience?

The results of the study provide the opportunity to better understand the functioning of underground estuaries and their response to environmental changes. As sea levels rise, beach sand will be pushed inland or erode. This will then change the hydrology, chemistry and microbial composition of groundwater.

Researchers emphasize the importance of preserving coastal microbial ecosystems by integrating them into environmental management policies. Alexandria Boehm warns: “A decline in the ability of microbes to purify water could have significant impacts on marine ecosystems and human health. » To prevent these scenarios, experts recommend targeted actions, including limiting coastal erosion through the restoration of dunes and mangroves. These natural barriers reduce the impact of waves and storms.

At the same time, rigorous management of wastewater and nutrient inputs is essential. Coastal areas and beaches receive a significant portion of human-caused nitrogen discharges. Reducing these inputs would limit environmental stress on microbial ecosystems. Finally, regular mapping and monitoring of underground estuaries must be developed to assess the impacts of climate change. The data from this study will make it possible to identify resilience thresholds and guide decision-makers in the development of appropriate policies. Interdisciplinary collaboration between scientists, managers and decision-makers will be crucial to protect these invisible but essential ecosystems.

Source: Jessica A. Bullington et al., “Microbial Community of a Sandy Beach Subterranean Estuary is Spatially Heterogeneous and Impacted by Winter Waves”, Environmental Microbiology (2024)