Nearly three out of four of the world’s marine protected areas (MPAs) are contaminated by sewage, according to a major new study which has underscored that in the ocean regions most critical for coral reefs and tropical marine life, the situation is far worse.

Research published in Ocean & Coastal Management by the Wildlife Conservation Society (WCS) and the University of Queensland found that between 87% and 92% of protected areas in key tropical regions are affected by wastewater pollution.

Startlingly, it describes the typical contamination levels inside these zones as running ‘ten times higher’ than in adjacent, unprotected waters.

The findings, drawn from an analysis of more than 16,000 MPAs worldwide, arrive at a pivotal moment for global ocean conservation – and cast a long shadow over the ambitious international commitment to protect 30% of the ocean by 2030.

Wastewater – the used water from homes and businesses that drains through sewage systems into rivers and ultimately the sea – carries a harmful cocktail of nutrients, pathogens, and chemicals a bear consequences for marine ecosystems that are well documented.

Previous research has linked wastewater pollution to coral reef decline, harmful algal blooms, and even Alzheimer’s-like brain disease in dolphins. For coastal communities, the stakes are as equally high. Polluted drinking water is estimated to claim up to 1.4 million lives each year through diseases such as cholera and typhoid fever, and inflict as much as $12 billion in economic losses.

The study has made clear its argument that designation as a protected areas – in reality – offers no defence against the threat of pollution, and rather in some cases acts to make it worse.

“What we found was striking,” said David E. Carrasco Rivera, lead author and PhD candidate at the University of Queensland. “Using global pollution data, we mapped wastewater exposure across thousands of protected areas and compared it to unprotected waters nearby. In region after region, the areas set aside for conservation were actually receiving more pollution than the areas with no protection at all.”

The research team analysed pollution exposure across 16,491 MPAs worldwide, with particular focus on 1,855 coastal protected areas – those located within 50 kilometres of the shore – across six tropical regions: Australasia and Melanesia, Mesoamerica and the Caribbean, the Coral Triangle, East Africa, the Indian Ocean, and the Middle East and North Africa.

Using a geospatial model, the researchers measured the volume of nitrogen from sewage reaching each protected area, then compared those levels to the unprotected waters nearby.

The pattern that emerged was consistent and troubling across every region studied.

The report suggests that it is the “fundamental limitation of marine conservation policy” that is at the heart of this issue. MPAs are ocean designations, but pollution originates on land. No amount of ocean-based management can intercept sewage flowing in from upstream catchments, agricultural runoff, or inadequate wastewater infrastructure in coastal towns and cities.

“Even a perfectly managed marine protected area will fail to achieve benefits for conservation and for people if wastewater keeps flowing in from upstream,” said Dr. Amelia Wenger, WCS Global Water Pollution Lead. “You cannot put up a barrier inside a protected area to stop pollution from coming in. The solution has to happen on land, upstream, and it has to be part of how governments plan and fund ocean protection. Right now, it’s not.”

Now, the study’s authors are calling on governments and conservation planners to integrate sewage and other land-based pollution into the design of MPAs, and into the metrics used to assess whether those protections are actually working.

They point specifically to the Global Biodiversity Framework – the international agreement underpinning the 30×30 goal across 23 interconnected targets – and warn that Target 3, the area protection goal, cannot succeed without parallel progress on land and sea use planning (Target 1), ecological restoration (Target 2), and pollution reduction (Target 7).

The research was supported by the Bloomberg Ocean Initiative and CORDAP.

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