Why Coral Reefs Around the Gili Islands Are Changing
Coral Reefs Around the Gili Islands
The coral reefs surrounding the Gili Islands have long been among the most accessible and rewarding dive destinations in Southeast Asia. Crystal-clear waters, healthy reef systems, and regular encounters with turtles and reef sharks made these islands a magnet for divers and snorkelers from around the world.
But if you have been diving here for years—as we have at Oceans 5 Gili Air—you will know that the underwater world is not the same as it used to be.
This is not a story about one single event. It is a gradual shift, built up over decades. A series of changes that, when put together, tell a clear story: the reefs around the Gilis are under pressure.
A Timeline of Change Underwater
To understand what is happening today, we need to look back.
Around the year 2000, divers regularly encountered grey reef sharks around the Gilis. These were not rare sightings—they were part of the ecosystem. But over time, they disappeared.
In 2008, large groups of mature white tip reef sharks vanished. Again, not overnight, but steadily enough that today, seeing one is no longer the norm but the exception.
By 2010, zebra sharks—once part of the marine life diversity—were gone.
In 2015, something else changed. The large schools of bumphead parrotfish, powerful reef grazers that play a critical role in reef health, disappeared from the area. These fish are essential: they control algae growth and help maintain the balance between coral and algae on reefs.
Then came 2022, when a turtle disease outbreak affected populations around the islands. Turtles, one of the most iconic species of the Gilis, suddenly showed signs of stress and illness.
In 2025, divers began noticing an unusual increase in Halimeda algae. By 2026, this had escalated into a much larger outbreak, with certain reef areas increasingly dominated by this calcifying green algae.
And this timeline doesn’t even include global coral bleaching events driven by rising sea temperatures.
Each of these moments might seem isolated. But they are not. They are signals.
What Is Driving These Changes?
There is no single cause. Coral reef ecosystems are complex, and when they change, it is usually the result of multiple stressors acting at the same time.
1. Overdevelopment on Small Islands
The Gili Air, Gili Meno, and Gili Trawangan are small islands. Their landmass is limited, and so is their capacity to support infrastructure.
Yet in recent years, development has accelerated rapidly. New accommodations, villas, and resorts are being built at a pace that raises serious questions about sustainability.
More rooms mean more tourists. More tourists mean more pressure on water, waste systems, and ultimately, the marine environment.
2. Coastal Construction and Beach Walls
One of the most visible changes above water is coastal construction.
Beach walls, land reclamation, and building too close to the shoreline disrupt natural coastal processes. Sand movement changes, erosion patterns shift, and sediment can be transported into the ocean.
Sediment is one of the biggest enemies of coral reefs. It reduces light penetration, smothers coral polyps, and creates conditions where algae can thrive instead.
3. Wastewater and Nutrient Runoff
As development increases, so does wastewater.
Without proper treatment systems, nutrients from wastewater seep into the ocean. Elevated nutrient levels change the chemistry of the water, often leading to algal blooms.
The Halimeda algae outbreaks seen in 2025 and 2026 are not random. They are symptoms of a system receiving too many nutrients.
This shifts the balance: instead of coral-dominated reefs, you get algae-dominated systems.
4. Increasing Numbers of Divers and Snorkelers
Tourism is the backbone of the Gili Islands. Diving and snorkeling are at the center of that economy.
But more people in the water means more potential for impact:
- Accidental contact with coral
- Poor buoyancy damaging reef structures
- Disturbance of marine life
Even when unintentional, the cumulative effect of thousands of visitors adds up.
5. Ignoring Regulations and Zoning Laws
Indonesia has clear regulations regarding coastal development and land zoning, especially within marine park areas.
The Gili Islands are part of the Gili Matra Marine Park, a protected area meant to balance conservation and tourism.
However, when regulations are not consistently enforced, or when zoning rules are ignored, development can exceed what the ecosystem can handle.
This is where the real problem begins—not just development, but uncontrolled development.
6. Changes in Water Chemistry
Rising pH levels and other chemical changes in the water can alter reef ecosystems. Combined with nutrient input and temperature stress, these changes create conditions where corals struggle and algae thrive.
Why These Changes Matter
It is easy to look at one missing species and think it is an isolated issue. But reefs are interconnected systems.
- Sharks regulate fish populations
- Parrotfish control algae
- Coral provides habitat for everything else
Remove one element, and the system shifts.
Remove several, and the entire ecosystem starts to transform.
The disappearance of grey reef sharks, white tips, zebra sharks, and bumphead parrotfish is not just about biodiversity—it is about losing balance.
The Economic Reality
Let’s be honest: the Gili Islands depend on tourism.
Diving, snorkeling, and beach holidays are the main drivers of the local economy. Without healthy reefs, that economy will suffer.
This is not an environmental issue alone. It is a business issue.
If reefs degrade:
- Divers will choose other destinations
- Snorkelers will have less to see
- The reputation of the islands will decline
And once that happens, recovery is not quick.
So What Can Be Done?
This is the most important question.
At Oceans 5, we believe that sustainability in a marine park cannot rely only on good intentions. It requires structure, regulation, and long-term thinking.
1. Introduce a Visitor Quota System
Marine parks around the world already use quota systems to control visitor numbers.
Look at destinations like Sipadan Island or the Galápagos Islands. These are not comparable in every aspect, but they share one key element: they limit access to protect the environment.
A quota system for the Gili Islands would:
- Control the number of daily visitors
- Reduce pressure on reefs
- Limit uncontrolled expansion of tourism infrastructure
It is not about stopping tourism—it is about managing it.
2. Control New Developments
A quota system would also indirectly limit new construction.
If visitor numbers are capped, there is less incentive to build more rooms. This creates a more stable and sustainable economic model instead of the current “wild west” approach.
3. Enforce Existing Regulations
Indonesia already has laws in place. The issue is enforcement.
Respecting zoning laws, coastal setbacks, and environmental regulations is essential. Without enforcement, even the best policies remain ineffective.
4. Improve Wastewater Management
Investing in proper wastewater treatment systems is critical.
Reducing nutrient runoff will directly impact algae growth and help restore the balance between coral and algae.
5. Educate Divers and Snorkelers
Better education leads to better behavior underwater.
At Oceans 5, we focus on:
- Neutral buoyancy training
- No-touch policies
- Environmental awareness
Small actions from individuals can make a big difference when multiplied across thousands of divers.
6. Support Local and Scientific Initiatives
Collaboration with universities, marine biologists, and conservation organizations provides valuable data and insight.
Long-term monitoring is essential to understand trends and measure the impact of any changes implemented.
A Choice for the Future
The Gili Islands are at a crossroads.
The current path—rapid, largely uncontrolled development—may bring short-term economic gains. But it risks long-term damage to the very environment that makes these islands special.
The alternative is a more controlled, sustainable approach:
- Managed tourism
- Enforced regulations
- Protected ecosystems
It requires cooperation between government, businesses, and the local community.
Final Thoughts
The changes we have seen over the past 25 years are real. They are measurable, and they are accelerating.
From the disappearance of key species to the rise of algae dominance, the reefs around the Gili Islands are telling us something.
The question is whether we are willing to listen.
Because if we don’t, the future of Gili Air, Gili Meno, and Gili Trawangan as world-class diving destinations is not guaranteed.
But with the right decisions—starting now—we can still protect this marine park for future generations.
And that is a responsibility we all share.