Established in 1995, Mexico's Cabo Pulmo Marine National Park is slightly more than 7,000 hectares of coastal waters in the Gulf of California, offshore from the small village of Cabo Pulmo. The park’s establishment followed a period of determined lobbying by the village’s 100 or so residents, who had become alarmed at overfishing and declines in the area’s marine life.
The reserve is no more than 5 kilometers (3 miles) wide and measures just 14 kilometers (almost 9 miles) north to south. And yet its impact on the marine life within it, such as these Devil Rays, has been profound – so much so that researchers have dubbed it “the most successful marine reserve in the world.”
Despite its small size, the park boasts an impressive density and diversity of species. The reef contains 11 of the 14 hard coral species in the Gulf of California, and supports a recorded 154 invertebrate species as well as 226 species of fish, including these Panamic Porkfish, which school on the reefs.
Marine mammals, such as humpback whales, are regular visitors.
Several other open ocean species feed in the reserve’s waters, including a small colony of California sea lions. The reserve also provides nesting grounds for leatherback and olive ridley sea turtles.
The effects of the reserve were not immediately apparent. In 1999, a survey showed mean fish biomass in the area was not statistically different from that in open-access fishing waters elsewhere in the Gulf of California.
Ten years later, the situation in much of the gulf remained the same. In Cabo Pulmo, however, it had all changed; there had been a huge increase in fishes. As detailed in a paper due out in the online journal PLoS One on August 12, the increases were across all trophic levels, and led to a fourfold increase in biomass across the board.
Indeed, at 4.2 tonnes per hectare, fish biomass in Cabo Pulmo may constitute the highest recovery of any marine reserve in the world. The density of some species, such as these Devil Rays, is now sometimes so great that even from the air their density is overwhelming.
“You can’t even really see from this photograph, but these rays are four or five deep in places,” says Grant Galland of Scripps Institution of Oceanography, who is a co-author of the PLoS One paper. “You couldn’t possibly get any kind of accurate count from underwater.”
"It's a little like stepping back in time when you dive in the water," says Galland, pointing out that Cabo Pulmo's waters contain sights -- such as large aggregations of Bull Sharks, Tiger Sharks, and Blacktip Sharks -- seen only rarely in most waters today.
Once, while diving in the reserve, Galland says it suddenly went dark, almost as if the sun had gone out. He looked up to see a huge school of Bigeye Crevalle Jack fish, such as the ones pictured here, which had effectively blocked out the light. Pelagic fish that also aggregate on reefs, these jacks eat small fishes and some crustaceans.
A Crown-of-Thorns sea star begins to prey on a coral, as a Coral Hawkfish looks on. The sea star is among the species that have grown in numbers in the Cabo Pulmo Marine Park, but there is no fear of it forming the massive groupings that have devastated parts of the Great Barrier Reef in Australia.
In the eastern Pacific, says Galland, the species is “not nearly as dangerous.” Individual Crown-of-Thorns tend to be isolated and predators lurk. The hawkfish, which lives its entire life within the coral, is likely not watching idly; researchers believe it is possible the fish protects its home by biting small pieces off the coral’s would-be predator.
The Giant Conch (Strombus galeatus) has long been an important fishery species in the region, valued for its meat and its shell as far back as Incan times. But it is today found very rarely on reefs elsewhere in the Gulf. In Cabo Pulmo, however, it has recovered rapidly. “It takes just five minutes of diving to see them in numbers you just don’t see elsewhere,” Galland says.
According to Galland, many factors have contributed to the reserve’s effectiveness. “It is relatively small, and its establishment and enforcement are the result of local involvement, ensuring compliance and support,” he points out. Those commercial activities that are permitted – tourism, fishing on the reserve’s fringes – are small-scale.
Even so, why the park should have been such a success – how long-lived species such as this Gulf Grouper could have apparently exploded in number (and even in size) in such a short time – remains something of a mystery. “But it may be,” suggests Galland,“ the simple fact that the reserve is where the food is.”
One fascinating side-effect of the reserve has been a previously unknown change in the behavior of the Sabretooth Blenny. Normally a visual and behavioral mimic of the Cortez Rainbow Wrasse, it ‘tricks’ much larger fishes into thinking that, like the wrasse, it is completely harmless, only to take a bite out of its unsuspecting victim and quickly swim away.
However, this strategy only works if there are more wrasses than Sabretooth Blennies, so that potential victims are less likely to assume they are about to be bitten.
Sabretooth Blennies have multiplied prodigiously since the establishment of the park. Within the reserve, the species’ appearance and behavior has changed: it no longer attempts to mimic the wrasse and instead forms schools of as many as 120 fish such as the one pictured here.
Writing in the journal Coral Reefs in March this year, Galland and colleagues observed that these groups of blennies “aggressively attacked large fishes, including top predators … in such large numbers and with such ferocity that they affected the behaviors and movements of these much larger fishes, displacing them from the area.” Such rapid and localized change is without known precedent.
The existence of the park has been a boon for the local economy. Fishers, at the Park’s boundaries, can take advantage of the growing fish populations inside. Tourism, too, has developed, with visitors from the United States and elsewhere in Mexico keen to take advantage of the diving opportunities the reserve offers.
Its very success, however, could prove its greatest threat, with the announcement of plans for a mega-resort just 4 kilometers (2.5 miles) north of Cabo Pulmo. The village’s residents hope to be able to stave off the development and to maintain the small scale of the reserve as a way to perpetuate its extraordinary success. In this photo is David Castro of the Castro family, "one of the most outspoken families during the declaration of the Park and since," says Galland.