A surreal depiction of the contrast between a healthy coral reef and sewage pollution.

Hidden Reef Dangers: How Sewage Pollution Affects Coral and Your Health

Rhea Morgan in Climate & Environment August 2025 • 4 min read.

"Uncover the alarming link between sewage, reef ecosystems, and the potential health risks lurking beneath the surface."

Coral reefs, vibrant ecosystems teeming with life, face increasing threats from human activities. Tourism, overfishing, and pollution from urban development all contribute to the decline of these underwater habitats. While the impact of bacteria on corals is well-documented, the role of yeasts, another type of microorganism, is less understood.

A recent study investigated the diversity of yeasts associated with corals in Brazilian reefs, focusing on the impact of sewage discharge on these microbial communities. The research aimed to identify the types of yeasts present in coral and evaluate how pollution affects their composition.

Zoanthids, soft corals often found in reefs, were the focal point of the study. These organisms, lacking a hard skeleton, are considered an intermediary between hard corals and sea anemones, and create microniches for various microorganisms, including yeasts. Understanding the yeast communities in these corals is crucial to assess the overall health of reef ecosystems.

The Unseen Impact: Sewage and Reef Yeast Communities

A surreal depiction of the contrast between a healthy coral reef and sewage pollution.

The study, conducted on reefs off the coast of Maceió, Brazil, compared yeast populations in two locations: one exposed to high levels of sewage (Ponta Verde reef) and another with lower levels of anthropogenic impact (Sereia reef). Researchers collected samples from three common zoanthid species—Palythoa caribaeorum, Palythoa variabilis, and Zoanthus sociatus—and isolated and identified the yeasts present.

The findings revealed a diverse community of yeasts, with 130 isolates identified belonging primarily to the phylum Ascomycota. Many of these yeasts had previously been found in human samples or are considered potential pathogens. This raises concerns about the potential health risks associated with exposure to these contaminated reefs.

Ascomycota yeasts were dominant, thriving on organic matter from coral compartments.
The Ponta Verde reef, affected by sewage, showed a less diverse, more homogeneous yeast population.
Several species identified had never been recorded in marine environments before.
Specific yeast species were more abundant in particular coral species, indicating potential host-microbe relationships.

One of the most significant observations was the difference in yeast communities between the two reef locations. The Ponta Verde reef, heavily impacted by sewage, exhibited a less diverse and more homogeneous yeast population compared to the Sereia reef. This suggests that sewage pollution can disrupt the natural balance of microbial life in coral ecosystems, favoring certain species over others.

Protecting Our Reefs, Protecting Our Health

This study underscores the urgent need to address sewage pollution in coastal areas to protect coral reefs and safeguard public health. By reducing pollution and preserving the biodiversity of these vital ecosystems, we can ensure the health of both the environment and the communities that depend on it.

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This article is based on research published under:

DOI-LINK: 10.1016/j.marpolbul.2017.08.050, Alternate LINK

Title: Diversity Of Culturable Yeasts Associated With Zoanthids From Brazilian Reef And Its Relation With Anthropogenic Disturbance

Subject: Pollution

Journal: Marine Pollution Bulletin

Publisher: Elsevier BV

Authors: Gustavo Vasconcelos Bastos Paulino, Ciro Ramon Félix, Leonardo Broetto, Melissa Fontes Landell

Published: 2017-10-01

Everything You Need To Know

What factors, beyond sewage, contribute to the decline of coral reef ecosystems?

Coral reefs are threatened by human activities, including tourism, overfishing, and pollution from urban development. A key aspect is the impact of sewage, which introduces harmful substances and alters the microbial balance, specifically affecting yeasts. These changes impact the overall health and biodiversity of reef ecosystems. It's also important to consider how other pollutants, like agricultural runoff and industrial waste, interact with sewage to exacerbate the effects on coral reefs.

Which specific coral species were examined in the study, and what role do they play in the reef ecosystem?

The research focused on zoanthids, soft corals that create microniches for microorganisms like yeasts. Samples were collected from *Palythoa caribaeorum*, *Palythoa variabilis*, and *Zoanthus sociatus* in two reef locations: Ponta Verde (high sewage) and Sereia (low sewage). Yeasts were isolated, identified, and compared between the sites to evaluate the impact of sewage on their diversity and composition. Future studies could examine the genetic adaptations of these zoanthids to polluted environments and how they influence yeast communities over longer periods.

How did sewage pollution affect the diversity and composition of yeast communities in the studied reefs, and what specific types of yeasts were identified?

The Ponta Verde reef, heavily impacted by sewage, had a less diverse and more homogeneous yeast population compared to the Sereia reef. This indicates that sewage pollution disrupts the natural balance of microbial life, favoring certain yeast species over others. A significant portion of the yeast isolates belonged to the phylum Ascomycota, with some species previously found in human samples or known as potential pathogens. The differences in yeast communities suggest that sewage pollution can disrupt the natural balance of microbial life in coral ecosystems, potentially leading to ecological imbalances. Further research could explore the specific mechanisms by which sewage components affect yeast metabolism and interactions within the coral microbiome.

What are the potential health risks associated with exposure to reefs contaminated by sewage, based on the yeast species identified?

The presence of yeasts previously found in human samples or known as potential pathogens raises concerns about potential health risks associated with exposure to contaminated reefs. Contact with contaminated water could lead to infections or other health issues for swimmers and divers. Understanding the specific health risks requires further investigation into the virulence and transmission pathways of these yeasts. The health risks extend beyond direct contact, influencing seafood safety if contaminated organisms enter the food chain.

What steps can be taken to mitigate the impact of sewage pollution on coral reefs and protect both the environment and human health?

Reducing sewage pollution in coastal areas is crucial for protecting coral reefs and safeguarding public health. Actions include improving wastewater treatment, reducing runoff from urban and agricultural areas, and implementing stricter regulations on pollution discharge. Preserving the biodiversity of these ecosystems ensures their resilience and the health of communities that depend on them. A broader integrated approach includes addressing climate change, promoting sustainable tourism, and supporting research into coral reef restoration techniques. Investing in advanced technologies for pollution monitoring and remediation can further enhance these efforts, ensuring long-term protection for both coral reefs and human populations.