Coral Bleaching at Kahekili Reef: Two Years Later

In November of 2015, I revisited the Kahekili Reef on the West shore of Maui. Some of the cauliflower coral was bleached snow white. A year ago, I reported that the coral seemed to be coming back. The white of the “snowballs” was more cream colored, and less shocking. Other colors such as green, blue, and brown were returning, but the intensity of the color seemed less than I recalled from visits prior to 2015.

In November of 2017, I was hopeful that the reef was recovering. However, a year later, I’m not so sure.

In November of 2018, I snorkeled Kahekili Reef for 11 days looking for unusual fish and taking inventory of changes. I saw an albino surgeonfish swimming with a few yellow specimens. The albino had sapphire red eyes. Wild type yellows have a dark red eye. Consulting Wikipedia, I found that albino fish have pink eyes.

After a few dives, I noticed that the population of small (~4 cm) sea urchins was very low. Only one coral head out of hundreds had several of the light-colored urchins (Echinoida). Most heads had none. Prior to 2015, the small urchins were in every nook and cranny, plus many appeared to be etching channels in old coral.

Then, I noticed the complete absence of larger (~10 cm diameter) spiny black and turkey-colored urchins. Where had they gone? Possibly divers harvesting them for uni? However, I did a quick search for sea urchin decline, and found a disturbing reference: “From a nutritional standpoint, sea urchin is one of the most prominent culinary sources of anandamide, a cannabinoid neurotransmitter.” Does this mean that eating uni will produce a similar effect to ingesting marijuana? Probably not, but it is possible that uni activates the dopamine system in the brain, humans’ built-in “reward circuit.”

I asked a few beach attendants about possible harvesting. They did not support this hypothesis—quite the contrary. They said that the decline was due to sunscreen washing off of people. So, I decided to sample another reef about 400 yards seaward from Olowalu (aka Mile Marker 14 on Highway 30). This is practically accessible only with a dive boat. The urchins, large and small, were abundant. Coral colors are vivid. The deck hands confirmed that the Kahekili Reef was known to be particularly sick. Coral colors are muted. Fish population is low and declining. This confirmed my observations.

What is going on? It seems that there are several possible causes for the decline of Kahekili Reef:

  • Overfishing of carnivorous fish, leading to overpopulation of algae grazers
  • Sunscreen poisoning the coral
  • Upwelling of partially treated wastewater from the West Maui treatment plant may be creating a dead zone in the water in the reef.

Overfishing of carnivores

The deck hands attributed the low population of urchins to a declining food chain that affects Kahekili Reef. About 10 years ago, the reef was designated a nonfishing zone for herbivorous fish. One could catch and retain carnivorous fish. This may have led to overfishing of predators. Indeed, I did not see a single barracuda or pencil fish on this trip. Five years ago, schools of pencil fish lurked just below the surface, especially noticeable on morning dives. I saw none this time. My eel count for two weeks was only four. This is down from about 3–6 per dive a few years ago. Also, I used to find numerous strands of fish line attached to hooks and lead weights in the reef. I found only one this visit. This may mean that fishing pressure is low due to the lack of suitable catch.

It is possible that overfishing for carnivorous fish leaves the algae eaters to grow unchecked. Herbivorous fish are much more mobile and can out-compete the urchins for algae.


Since Kahekili Reef is offshore of the Westin Ka’anapali Ocean Resort, I wondered about chemical poisoning. On the short flight over from California, I’d happened on an article in The New Times reporting that Palau has banned sunscreens, since they were damaging the coral reefs. The government of Palau plans to ban sunscreens containing any of 10 specific chemicals starting in 2020. This is in response to the rapid increase of these chemicals in Jellyfish Lake, a UNESCO World Heritage site.

A colleague pointed out that Hawaii’s governor had signed legislation on May 1, 2018 banning sunscreens containing oxybenzone and octinoxate, effective January 1, 2021. Oxybenzone has been linked to DNA damage, abnormal skeletal growth, and deformities.

A report by Haereticus Environmental Laboratory found that sunscreen chemicals caused bleaching, DNA damage, and ultimately death of coral when washed off beachgoers or discharged into wastewater treatment plants. For example, the lab estimates that 412 pounds of sunscreen were deposited daily in Hanauma Bay Nature Reserve on Oahu in 2015. The preserve attracts an average of 2600 swimmers per day.

Sun-protective clothing, including swimwear, would be a better choice than tubes of cream.


A wastewater treatment plant serving about 40,000 people in homes and resorts is located about a half-mile up-slope from Kahekili Reef. The plant processes about 3–5 million gallons of wastewater per day. The processed water is injected into four wells. Fluorescence tracer studies show that the processed water appears in Kahekili Reef with a transit time of about two months. Prior to injection wells, wastewater was treated with denitrification enzymes that convert amines and nitrogen oxides to nitrogen gas. The nitrogen gas bubbles are markers for the wastewater plume. The bubble field may be sufficient to sparge oxygen from the beach water.

In 2015 and at least five years before, the gas bubbles were located within the first 50 yards seaward of the north end of the Westin Ka’anapali Ocean Resort. In 2017, the bubbles had started to appear about 100 yards south of the original vent. In November 2018, the bubble field had extended another 100 yards south to the center of building two of the Westin resort complex.

Thousands of tourists lay out in the sun around the beautiful freshwater pools. Most are protected by sunscreen, which is washed off in swimming pools, showers, and tubs later in the day. It is not clear if the limited water treatment removes or renders harmless the chemicals in sunscreens.

Of course, discharging lots of fresh (low-salt) water into a marine environment will stress or even kill many organisms, especially the less mobile ones, that require salt water. This may explain the growing dead zone in the surf line of the reef.

In May of 2018, the County of Maui lost a petition to the Ninth Circuit Court of Appeals regarding the illegal operation of the West Maui water treatment plant. This November, it was easy to see significant construction equipment was operating within the facility.

I plan to keep you posted on the status of Kahekili Reef.

Robert L. Stevenson, Ph.D., is Editor Emeritus, American Laboratory/Labcompare; e-mail: [email protected]

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