Research at the University of Sydney has found that scuba-diving tourism – widely promoted as a sustainable way to experience coral reefs – is causing frequent and often hidden damage to fragile marine ecosystems.
The study, led by Dr Bing Lin from the University of Sydney's Thriving Oceans Research Hub in the School of Geosciences, analysed the behaviour of more than 700 scuba divers across tourism hotspots in the Philippines and Indonesia, including Bali.
It is published today in Conservation Letters .
Drawing on data from more than 300 hours of underwater observation, the researchers recorded 4981 reef contact events among 411 divers. Around 41 percent of these contacts caused observable damage to coral, from direct breakage to the stirring of sediment that can smother reef life.
On average, divers made 0.26 reef contacts a minute – roughly one every four minutes – and spent nearly two seconds of every minute in direct contact with the reef.
"This work documents the unsustainable underwater footprint of scuba diving tourism on coral reefs," said Dr Lin, who started the research during his PhD at Princeton University, completing it as part of his postdoctoral position at the University of Sydney.
A central finding of the study is that most damage is not deliberate. More than 80 per cent of damaging contacts were unintentional or unnoticed by the diver, revealing how routine tourism activity can quietly degrade reef systems over time. Further, most divers in the study self-reported very high pro-environmental attitudes, suggesting that they by and large care about reef conservation.
Overconfidence and psychological biases in divers
The study also uncovered several striking psychological patterns. First, around three-quarters of divers rated themselves as "above average" in their ability to avoid reef contact compared to their peers – an example of the illusory superiority effect, where people systematically overestimate their abilities relative to others.
Additionally, the study also documented the well-known Dunning-Kruger effect in divers, where people with lower skill levels disproportionately overestimated their competence.
This overconfidence translated into a major gap between perception and reality. In matched observations, divers underestimated how often they contacted the reef by nearly fivefold.
"Many divers believe they are careful and low impact, but our data shows a consistent mismatch between perception and behaviour," Dr Lin said.
The research identified several factors that were associated with increases in reef damage. Divers using underwater cameras, gloves or pointer sticks had higher contact rates, while peer behaviour also played a significant role – when one diver touched the reef, others were much more likely to follow suit.
Wildlife encounters – often the highlight of dive tourism – were found to significantly amplify damage. The presence of marine animals increased intentional reef contacts by 220 percent, unintentional contacts by 85 percent, and damaging contacts by 106 percent, often as divers approached or adjusted position to observe the wildlife.
The study also found that a small minority of divers accounted for a disproportionate share of total reef damage, suggesting targeted interventions could have considerable benefits.
"It's difficult to quantify the true scale of the reef contact problem," Dr Lin said. "But what is clear is that unregulated underwater tourism is an overlooked local driver of damage that adds to, and amplifies, other acute and chronic reef stressors."
Dr Lin's previous research, published in Nature Sustainability , has demonstrated the regionally detectable effects of coastal tourism, including scuba diving, on coral reefs across an entire archipelago.
With coral reefs already under pressure from climate change, pollution and overfishing, the findings highlight the need to better manage tourism impacts in heavily visited regions.
"Tourism is critical to many coastal economies, including those closely linked to Australia," Dr Lin said. "But without changes to diver behaviour, training and industry standards, it risks undermining the very ecosystems it depends on."
The researchers point to practical solutions – including improved buoyancy training, stricter controls on equipment use, stronger environmental briefings and higher standards in diver and dive-operator certification – to reduce cumulative damage.
"First and foremost, divers need to understand that they are a part of the problem before we can convince them to become a part of the solution," said Lin.
DOWNLOAD photos of divers plus the research at this link . VIDEO available on request.
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