Reef damage more limited than suspected

A new study from Carl Meyer and Kim Holland of the Hawai’i Institute for Marine Biology encompassing four protected marine sites in Hawai’i reveals that snorkelers and scuba divers only have a low impact on coral reef habitants at these sites and that the impact is limited to comparatively small areas.

The study, funded by NOAA Fisheries and the Department of Land and Natural Resources’ Division of Aquatic Resources, is based on secret observations of snorkelers and scuba divers at four marine life conservation districts: Honolua-Mokule’ia on Maui, Kealakekua Bay on the Big Island, Manele-Hulopo’e on Lana’I, and Pupukea on O’ahu’s North Shore.

These are areas created with the overarching goal of maintaining an environment in pristine or near pristine condition“, says Meyer. “One of the ironies is that because it’s such a nice area, a lot of people want to come and visit it, and that sets up the potential for the original goal of marine protected areas to be undermined by overuse.

The researchers used handheld Global Positioning System (GPS) units to map the movements of swimmers in the water and identify “hot spots” where the highest amount of contacts with reefs and other substrate took place. They found that divers and snorkelers use no more than 15 percent of the total reef habitat at each studied site and that the visitors stay within comparatively small areas associated with access points.

Although Hawai’i marine protected areas were heavily used in comparison to those in other geographic locations, this did not translate into high recreation impact because most fragile corals were located below the maximum depth of impact of the dominant recreational activity (snorkeling),” according to the report.

The Meyer and Holland study provides information on a subject suffering form a severe shortage of reliable data.

A lot of work on marine protected areas has focused on what the marine life is doing, not people,” saysMeyer, who hopes that information from the study will be used to create designated access points and boat moorings to focus activities away from the most sensitive parts of the reefs. By looking at a dive site’s topographical features, it is possible to predict where snorkelers and scuba divers are most likely to proceed from an access point.

If you manage those access points somehow, you can determine where people go,” Meyer explains.

200px PillarCoral Reef damage from snorkelers and scuba divers not widespread in Hawaii

Boat access vs. shore access

According to data retrieved from the study, boat access has a lower impact per dive than shore access, for several reasons. People that dive and snorkel from a boat do not access the site from land so there is no wading involved, but information and supervision also seem to play a major role.

Divers and snorkelers on tour boats are instructed on proper reef behaviour before going into the water and they are also monitored by dive tour staff.

If people are doing things they are not supposed to be doing, I’ve seen them intervene, and that separates boat-based activities from shore-based,” says Meyer.

Shore-based snorkelers and divers may of course receive instructions from shops where they rent their gear, but they will not be as strictly supervised during the actual dive as those who access from tour boats. There is less on-site management at dive spots accessed from shore, Mayer says.

According to the study, most of the substrate contacts between reef and humans occurred at shoreline access points where people waded to enter and exit the ocean. Even in such areas, the reef impact level was low since the contacts mainly involved sand or rocks where no coral grew. (The study does however point out that we “cannot rule out that (coral) colonization is being prevented by continued trampling.”) Only 14 percent of the contacts were between humans and live substrates, such coral, coralline algae, or invertebrates living attached to the substrate, and less than 1 percent of the contacts caused apparent damage, e.g. tissue abrasions or broken branches. Most of the damage was caused by snorkelers accessing from the shore. Scuba divers do however have a greater average impact on coral per dive than snorkelers, chiefly because scuba divers stay down longer each dive, explore a larger area, and venture deeper down.

Impact would be slashed in half if 16% of visitors stopped acting like morons

As in many other parts of the world, a major part of the damage is caused by a comparatively small part of the population.

One of things we noticed is that about half of the physical impacts that we observed in these areas [shoreline access points] resulted from only 16 percent of the people who are using it,” Meyer says. “There is a subset of people who have a much higher impact. If you can reach that 16 percent, you could literally halve the existing impact.”

Meyer suggests placing educational signs at popular dive sites and letting volunteers provide visitors with information and advice.

Only few places are heavily impacted by tourist, but those places are of high commercial and recreational value

Although coral trampling only damages a very small part of Hawai’i's total reef resources, the damage naturally tend to take place along beaches and at offshore sites of high recreational value.

The state of Hawai’i’ is heavily dependant on its $800 million ocean recreation industry and managing even heavily visited areas is therefore imperative for the long-term financial stability of this island state and its inhabitants.

According to Ku’ulei Rodgers, another scientist with the Hawai’i Institute for Marine Biology, increased visitor use results in a clear pattern of decreasing coral cover and lower fish populations since popular reefs can’t recover from damages while being continuously trampled.

It can do really heavy damage to have people standing on the reef, but the good news is there are few places where there is a heavy impact from tourists. It’s mostly concentrated in places like Waikiki and Hanauma,” she said.

During the last fiscal year, the lower beach at the renowned snorkelling site Hanauma Bay was visited by 780,000 people. This can be compared to the areas studied by Meyer and Holland where the most heavily visited site, Kealakekua, was visited by roughly 103,300 snorkelers and 1,440 divers annually. Honolua-Mokule’ia received 84,000 snorkelers and 2,050 divers, Pupukea 47,700 snorkelers and 22,500 divers, and Manele-Hulopo’e a mere 28,200 snorkelers and 1,750 divers.

Closure, permit only or mandatory guides

In some situations, education and information simply isn’t enough. Last year, people straying onto unmarked coastal trails and trampling reefs at two popular snorkelling coves (the Aquarium and the Fish Bowl) forced managers of the ‘Ahihi-Kina’u Natural Reserve Area in South Maui to close much of the reserve’s 2,045 acres.

It was a big step for us,” says Bill Evanson, Maui District natural area manager for the Department of Land and Natural Resources (DLNR).

The closure took place in October and will be in effect for two years to give damaged areas a chance to recover. An advisory board is currently considering whether to allow future access by permit only or through guided hikes. Before the closure, the ‘Ahihi-Kina’u Natural Reserve received 700 to 1,000 visitors a day.

The ‘Ahihi-Kina’u reserve was created for conservational reasons and is home to some of Hawai’i's oldest reefs. Within the reserve, you can find rare anchialine ponds as well as numerous extraordinary geological and archaeological features.

Even though the reserve has only been closed since October last year, there are already noticeable signs of recovery.

We’re seeing that many of the tide pools and coves where there used to be people are inhabited by fish in numbers and variety we haven’t seen, says Evanson. Fish aren’t being scared away by the presence of people. Now they are able to feed, hide from larger predatory fish and breed.