Saving the Jewels of the Trees

posted in: February 2002 | 0

Inside in a small room on the campus of the University of Hawai`i at Manoa, three miniature mountain rain forests are in full production: Every eight hours it rains for about three minutes, day and night alternate every twelve hours, and temperatures simulate those found along the slopes of the Wai`anae range of west O`ahu (one at 1,600-feet and two at 2,500-feet elevation).

Step into the room and the first thing you notice is the loud hum of the machines – souped-up, extra-large refrigerators, really — that make these duplicated environments possible. With these environmental chambers, Michael Hadfield, zoology professor and director of the university’s Kewalo Marine Laboratory, supports some of Hawaii’s most precious and perhaps least-appreciated wildlife: snails. Tree snails. More than 850 of them.

Like a peddler showing off a box full of precious jewels, Hadfield removes a small terrarium and lifts off the net. Carefully, he pulls out a branch. Clinging to the leaves like Christmas ornaments are brilliantly colored, fingernail-sized snails. “Look at this little gem,” whispers Hadfield as he points to one. His eyes aglow, he uses phrases like “caramel gold,” “vanilla almond fudge,” and “chocolate syrup swirl” to describe the various species’ shells.

To say Hadfield is passionate about these snails is an understatement. “How could you have trouble convincing anyone that these snails need protection?” he asks. He, for one, needs no convincing. Yet, when it comes to funding, he notes, “charismatic quadrupeds and pretty feathers beat you out.”

Two species in his collection exist nowhere else, he says: Achatinella apexfulva, which numbers about 10 individuals, and Achatinella fuscobasis, of which Hadfield holds about 270. Hadfield is especially proud of the latter species, which began with a seed population of ten snails in 1991. “It was pretty scary, but they’re just growing in leaps and bounds.”

The entire genus of Achatinella, which consisted of roughly 40 (there’s some debate concerning the exact number) different species of tree snails endemic only to the island of O`ahu, has been listed as federally endangered since 1981. Of those, at least half are believed to be extinct. Hadfield, who’s watched three of those species go extinct, is fighting to save the survivors.

“It certainly wasn’t my goal in life to build the world’s largest snail zoo. But with the rates of extinction, I didn’t have a choice,” he explains. Hadfield originally came to Hawai`i as a marine biologist in 1968. In 1973, he began studying land snails when he realized how fast the remaining achatinelline snails were disappearing. He kept having to climb higher and higher into the Wai`anae mountains to find one shrinking species, Achatinella mustelina.

“At this point in history, we’re doing search and rescue,” describes Hadfield. “We find species which are on the brink of extinction. So we bring them into the lab and keep them going.” But, he notes, “we’re maxed out. We can’t fit in anymore chambers and our chambers are full of snails. We’ve saturated the power supply in there. In fact, I get cited for illegal extension cords.”

The preciousness of his goods takes a toll on him. “We have two species in that one room in that one university which no longer exist in nature. If that building burns down, two species vanish right on the spot. I would just love to spread that risk.” After an unsuccessful effort to get the Honolulu Zoo to take on part of the project, Hadfield is optimistic about a plan by the U.S. Fish and Wildlife Service to take the funds initially set aside for the zoo and spend them instead to build a snail-rearing facility at Olinda, Maui, where the state has a captive-rearing facility for birds.

From Riches to Rarities

Several million years ago, stuck to the feathers or feet of far-traveling birds, a few small land snails arrived to the Hawaiian Islands. That handful of snails eventually evolved into more than 1,000 different species unique to the islands of Hawai`i. “In the 1800s,” says Hadfield, “populations were so thick you could just grab them by the handful. They talk about Achatinellas hanging from ie`ie like bunches of grapes. Estimates were thousands per tree.”

Today, tree snails persist in isolated pockets of moist or wet mountain forests above 1,500 feet. The Wai`anae range has only one species left: Achatinella mustelina, according to Hadfield. “You find five snails here, and you walk half a mile and you may find another dozen. Our impression is that those populations are still declining.”

Several factors have been blamed for the massive decrease: Huge levels of shell collecting in the 1800s led to the destruction of many populations. Current threats include habitat change and loss. Forest clearing, agricultural development, grazing, fire, and construction projects kill snails and destroy their habitat. It appears that some snail species have clear preferences for certain native plants. And in some cases, an entire colony can live on a single tree without ever leaving it.

Introduced predators have also been key in the extinction of Achatinella. In 1955, Euglandina rosea, a predatory snail (also known as the rosy wolf snail), was introduced from Florida in an effort to control the giant African snail. Following the mucous trails of other snails, the cannibalistic Euglandina will climb trees and bushes to find and devour its prey. Just as ravenous are rats, which in some areas have wiped out more than 80 percent of snail populations, says Hadfield.

The Achatinellas take a long time to reach sexual maturity, and once they do, they have a low reproductive rate, giving birth to live young. This makes them further vulnerable to outside threats. “When we started doing field demographic studies, we were really amazed because it turned out that compared to other snails, these things have really slow growth rates,” explains Hadfield.

“They were growing one to two millimeters a year. And it meant that at maturity they were at the earliest four years old. It just takes them forever to start reproducing. And the next thing was that their reproductive rate was really low. A lot of land snails are egg-layers, and they’ll lay 25 to 40 eggs at a time. And here were our achatinellids that were not reproducing until an average of about five years old, and then the birth rate was about four offspring a year.”

Less reported, but equally important, says Daniel Chung of Kapi`olani Community College, are meteorological factors, namely drought and high temperatures. Chung, who has been recording snail populations on Oahu since the early 1970s and worked on the snail database for The Nature Conservancy, has noticed that during times of drought snail numbers fell dramatically. “That was across the board for all species, even the tiniest ones that you would swear that the Euglandina never eat, and in areas where there was no Euglandina at the time.”

In fact, Chung believes too much attention is paid to Euglandina as a culprit when more serious, far-reaching effects are taking place. For example, while most snail survivors are now in isolated high-elevation mountain peaks, in recent years Chung has also been finding colonies of Achatinella in wet, low-elevation gullies. “I’m not going to tell you where,” he adds. “It’s very weird. The gullies are the home of the Euglandina; they’re found there more than anywhere else.” Though Chung believes more research needs to be done, he strongly suspects global warming is causing the migration of tree snails into wetter and cooler patches.

A recent survey of a low elevation area of the Wai`anaes backs up his theory, he says. “We found Achatinellas crawling on the ground.” Something was causing them to fall of their perches. But there was no wind, says Chung. Nor did he see any rat marks, any nearby Euglandina, or any bite marks of Euglandina. “Their bodies were shrunken. This is a symptom you see when the snails suffer from drought. There’s a lot more going on than meets the eye. In high elevation sites you don’t usually see this.”

But in another recent survey of a high elevation site, Chung also found a sign of drying times. “We saw something I’ve never seen before in my life; and I’ve been coming here for years and years and years and I’ve seen pig damage. But the pigs were doing something very strange.” They were chewing up the tops of Ohi`a trees, which were full of Achatinellas, and spitting out the leaves all over the ground. “They were just annihilating habitat,” recalls Chung. “It turns out that pigs chew leaves for water when it’s dry-and this is at a mountaintop that supposedly is wet.”

Makua Valley Plan

Aside from his simulated rain forest, Hadfield does have a few other hopes for his snails. One, still in the works, includes two large greenhouses at the Lyon Arboretum. Air conditioners keep them mountain-top cool. Standing about six feet high are a variety of native trees, including the favored ohi`a tree, which seem to be preferred as perching spots for Achatinella. But ohi`a trees it turns out are temperamental, and Hadfield hasn’t mustered the nerve to put snails in the greenhouses yet.

More promising are the enclosures around the 4,190-acre Makua Valley, an amphitheater valley on the leeward side of the Wai`anae. Until September 1998, the Army had used the valley to conduct live-fire training, causing extensive habitat destruction. At that time, it suspended training after several fires were started by stray munitions.

The Army has recently resumed live-fire training at Makua, but Hadfield is hopeful that, by the end of the year, a so-called Implementation Plan will be in place to protect the valley’s precious natural resources, including the snails. Hadfield and his colleagues have been instrumental in developing that part of the plan addressing snails. They surveyed the area and genetically characterized all of the remaining populations of A. mustelina. By studying tiny snippets of DNA, they were able to analyze the degree of inbreeding in these small, remnant populations and determine which populations are genetically unique from the others. It turns out that A. mustelina is made up of eight genetically separate entities in the Wai`anae range.

“The Army is now charged with protecting populations of all of those,” says Hadfield. It is also providing support for his genetic work and supporting his captive breeding operations with a series of “enclosures.”

We visit the one such site that Hadfield’s group monitors. After a drive up a switch-back road, we hike a narrow footpath along weathered lava, eventually reaching the snail enclosure.

To keep out cannibal snails, hungry rats, and curious humans, many levels of defense have been implemented: walls of corrugated metal about four feet high fringed with barbed wire, a trough filled with rock salt, solar-powered electric wires with 12-volt zapping power, and bait boxes filled with rat poison both in and outside of the enclosure. Now in full operation for about a year, it’s been “working beautifully,” Hadfield says.

This particular enclosure is maintained by staff from the federal Fish and Wildlife Service and the state’s Natural Area Reserves System. A similar enclosure is maintained by Army biologists. The Army’s plan calls for more enclosures in each of the genetically unique areas, all funded by the Army.

Although live-fire has resumed, Hadfield remains optimistic. The snail enclosures are not close to the actual training area and a firebreak has been established. Also, adds Hadfield, the Army’s attitude “toward the whole Implementation Plan has become a lot more serious.”

Inside the 30-by-40-meter haven, in which native koa, pisonia, and ohi`a grow, about 20 A. mustelina don’t have to worry about cannibal snails or any other predators. Nor do they have to tolerate the less favored non-native plants, such as guava and Brazil pepper, that surround the enclosure.

Hadfield can’t say for sure whether population densities are higher within the enclosure, but he can say that mortality is lower. “So what we envision is developing methods like these enclosures or finding areas in the mountains that are so snail free we can start putting snails back into the mountains,” he says.

It’s a realistic goal, he believes. In 1991, he and his colleagues released nine lab-born Partulina redfieldii on a tree in Moloka`i. After a couple initial setbacks, the population is currently at 25.

But the search for survivors never stops. Turning over leaf litter during their periodic surveys, Hadfield and crew comb through empty shells for clues of what is or isn’t still around. A buzz spreads across the lab. After close inspection, a freshly empty shell found in the Ko`olau range appears to be from a species reported extinct in 1963.

“It’s not just exciting, it’s tantalizing,” says Hadfield. And the search continues.

— Gretel H. Schueller

Volume 12, Number 8 February 2002