Author of Coqui Report Underscores
Ecological Risks of Invading Frogs
“Study says coqui isn’t ecological scourge,” read the headline in the Honolulu Advertiser on August 28. The article, by former Advertiser reporter Timothy Hurley, discussed a report on the coqui by Karen H. Beard of Utah State University and William C. Pitt of the U.S. Department of Agriculture’s Wildlife Research Center in Hilo, published in the September issue of Diversity & Distributions.
But did the headline, the story, or both overstate the findings of the report’s authors?
According to Beard, who wrote her dissertation on the coqui in its native Puerto Rico, the newspaper report “didn’t capture the subtleties of our article.”
“Because the coqui is such a potentially serious issue for Hawai`i,” Beard continued, “the purpose of our article was to pull together preliminary data that we have and point out the most serious threats and the areas of research that we need more information on.”
Some of that research is already being done by Beard and Hans Sin, a graduate student advised by Beard and Pitt. For example, although coqui generally inhabit areas where few native birds are found today, their range does include areas where many endemic invertebrates remain. “We’re pulling together a more detailed analysis of the coqui’s diet,” she said. “Is the coqui eating endemic invertebrates? Over 50 percent of what they eat is not endemic. They eat lots of ants and amphipods, and none of those are endemic. But they also eat lots of mites, beetles, and diptera. Some of those are endemic. Because the coqui eat so much, they can have a serious impact even if the percentage of endemics they eat is small.”
The indirect effects of coqui predation is another effect that Beard and Sin are looking into. The impact of the coqui is not measured just by what it eats, but also by what its prey eats – or would eat. “That’s another area that needs to be investigated. It’s not just what they’re eating,” Beard said, “but what their prey is eating, too, and how this may impact some ecosystem processes. We know that coqui do significantly impact some ecosystems.” Their study focuses on two sites: one a relatively pristine lowland forest in Puna and the other a more degraded forest.
What about the coqui as prey? In its native Puerto Rico, hawks, owls, and native snakes feed on coqui. In Hawai`i, when Beard has examined stomachs of rats and mongooses, coqui remains have turned up in just three of 22 mongoose examined. “Mongooses and rats aren’t likely to reduce coqui densities in Hawai`i,” Beard says. And, as she and Pitt point out in their article, coqui in Hawai`i also don’t have any of the lizards or large predaceous invertebrates that compete with them for the same food sources.
In short, Hawai`i has few factors that could control coqui populations naturally, which helps explain the phenomenal densities measured in Hawai`i: more than 20,000 coqui per acre in some places, two-and-a-half times the highest coqui densities recorded in its native Puerto Rico.
So, will the coqui eventually eat themselves out of house and home? “Densities might drop in the future,” says Beard, “but I don’t think they’ll disappear. Even though in some areas of Hawai`i their densities are more than twice what they are in Puerto Rico, they could easily sustain themselves, but it would be a problem ecologically and culturally.”
One of the potential problems resulting from such high coqui densities in Hawai`i is a change in the availability of nutrients in the forest. In her work in Puerto Rico, Beard found that coqui increased “nutrient availability on the forest floor and plant growth rates.”
“If coqui have these fertilization effects in Hawai`i,” Beard and Pitt write, “they could influence ecosystem properties and potentially alter floral and faunal species compositions. For example, it has long been known that fertilization effects can change plant species composition and influence the colonization of new species, including invasives. This has especially been found to be the case in Hawai`i, where native species show high tolerance of low resource environments compared to exotics and where studies have shown that exotic plants become more abundant in soils where nutrients are abundant.”
What about getting rid of coqui? While eradication is probably out of the question for some parts of Hawai`i, Beard and Pitt offer some suggestions that beleaguered homeowners might take to heart. Based on observations of coqui in Puerto Rico, they write, “removal of low-lying habitat structure, such as fallen woody debris, might be an effective management strategy for reducing densities in Hawai`i.”
Bananas, heliconias, and gingers are a virtual welcome mat for the frogs. “These non-native, largely ornamental species provide forage and breeding habitat for coquis wherever planted,” Beard and Pitt write. “Removing large-leaved, mostly non-native species and replacing them with small-leaved, native species should reduce coqui densities.”
Beard is adamant that neither she nor Pitt wanted their article to be taken as giving an ecological pass to the coqui. “That’s not what we intended,” says Beard. “I just wanted to present what we know about coqui from Puerto Rico as well as what we’re learning about it in Hawai`i – we just wanted to have that information in one location, and were hoping to point out some really important research areas. There’s a little we do know, and so much more we don’t know. That’s what I wanted to point out.”
Deepwater Corals:
Black vs. White
Carijoa riisei is a relatively recent marine invader whose common name, snowflake coral, conjures up images of pristine white landscapes. But when the feathery white tentacles of this octocoral blanket vast stretches of dead and dying black coral trees in the deep waters of the `Au`au channel off Maui, the sight is anything but beautiful.
Last month, Samuel E. Kahng, a graduate student in oceanography at the University of Hawai`i, and his advisor, Ricky Grigg, published an article in the journal Coral Reefs that laid out in grisly detail the effect of C. riisei on Hawai`i’s black corals.
From the time the species was discovered in Hawaiian waters – in 1972 at Pearl Harbor – up to around 2000, C. riisei (formerly known as Telesto riisei) “was thought to be a relatively benign introduction occupying an underutilized habitat,” Kahng and Grigg write. In 2001, however, surveys of black coral beds showed them being overrun with the invasive octocoral.
From November 2001 through September 2004, Kahng and colleagues made three surveys of the deepwater black corals, used in jewelry and harvested commercially by a small community of divers. The areas most heavily covered by snowflake coral were between 80 and 105 meters deep. There, Kahng and Grigg note, more than 60 percent of all black coral colonies were at least partially overgrown with the snowflake coral. At depths less than 70 meters, less than 10 percent of the black coral was affected. In even shallower waters, the snowflake coral could still be found, but only deep within the black coral colonies, “on the shaded undersides of ledges and coral heads.”
Deeper than 110 meters, the snowflake coral was scarce and was not seen at all at depths beyond 115 meters.
Kahng and Grigg found older black coral colonies generally had greater infestation of C. riisei than younger ones. This, they write, suggests that “size and exposure through time increase the cumulative probability of C. riisei settlement and overgrowth.” Also, the snowflake coral was found settling on shells of hammerhead oysters and on black coral skeletal surfaces laid bare by sponges, leading them to postulate that “certain epifauna facilitate C. riisei settlement onto black corals.” Once the snowflake coral settles in, it can quickly spread vegetatively and smother its host. The snowflake coral preys on the same small size class of zooplankton as the black coral feeds on, suggesting that it may complete with the black coral for food as well, Kahng and Grigg write.
Black corals are by no means the only corals affected by C. riisei. In 2003 and 2004 surveys, the authors note, the invader was seen “colonizing large areas of more level and gently sloping substrata…, overgrowing large beds of scleractinian plate corals … and creating an underwater ‘prairie’ of white polyps.” The snowflake coral actually had settled on the undersides of the plate corals, they write, with the polyps extending upward into the water column.
But the black corals, which are economically far more valuable than the other affected species, are the special focus of Kahng and Grigg’s work. They note that C. riisei “may significantly alter the population dynamics of black corals.” At present, most of the black corals taken by divers are no deeper than 75 meters, where C. riisei infestation is fairly light. It is the deeper colonies that are more heavily affected, and “this deeper population has been traditionally regarded as a reserve of large, highly fecund black coral colonies. With the C. riisei invasion of the `Au`au Channel, black corals there now incur mortality from both invasion and harvesting.”
Last spring, the Scientific and Statistical Committee of the Western Pacific Fishery Management Council learned of Kahng and Grigg’s work, which had been submitted for publication nearly a full year earlier. Members of that panel regarded the findings as so significant that they recommended that the council close the fishery. Not only was there the threat of C. riisei to contend with, there were also indications that recruitment of black coral colonies had declined, starting sometime between 1998 and 2004, when a survey of black coral beds found “no babies,” according to Frank Parrish, a scientist with the NMFS Pacific Islands Fisheries Science Center. Mortality has increased in addition to recruitment diminishing, and there are significant differences in the population structure of the coral beds now as opposed to the condition they were in before they were harvested, he noted. “We need to be suspicious,” he said.
While C. riisei might be implicated in this, another possible cause for the recruitment failure, Parrish suggested, might be too many mature trees being harvested.
The chief executive officer of Maui Divers, Robert Taylor, testified in opposition to any moratorium. Black coral accounted for 20 percent of his company’s annual sales, he said, amounting to some $15 million in revenue. “It would be very detrimental to our business if there is a moratorium on black coral,” he said, adding that it would probably result in layoffs of about 100 people.
Four divers – the entire population of black coral collectors – also testified in opposition to any closure of the beds.
At the council’s June meeting, Grigg himself, for 28 years head of the council’s Precious Corals Plan Team, objected to the proposed moratorium. It would kill the fishery, he said, since there could be no training of new divers for the duration of the closure and both full-time divers are now in their 60s. It would seriously impact the industry, he said, and in any event it was “not warranted by the data,” although he conceded, “It’s possible that there is a slight fall-off in recruitment.”
After hearing testimony, the council set up an informal meeting of industry, divers, scientists, and staff that came up with a compromise approach. The size of corals that could be taken was increased to either 4 feet in height or 1 inch in diameter at its base. The previous limit was 3 feet in height or ¾ inch at the base. The new limits conflict with state regulations on the take of black coral, but Francis Oishi of the Division of Aquatic Resources assured the council that the state would expedite changes in its rules to conform with the new federal requirements.
Notes from All Over
No Recourse on Oysters: Maryland and Virginia want to introduce an Asian oyster, Crassostrea ariakensis, to supplant depleted stocks of the native Eastern oyster, C. virginica in Chesapeake Bay. Their proposal comes after years of trying, without success, to rebuild stocks of the Eastern oyster.
Delaware and New Jersey haven’t yet given up hope of restoring native oyster populations to Delaware Bay, just above the Chesapeake, and they’re now worried that the Asian oyster will spread to the Delaware and eliminate any chance the native oyster might rebound. Plans to bring in the Asian oyster are premature, officials from these states say.
In a letter to Science, three fisheries experts – including two members of a National Academy of Sciences panel on non-native oysters in the Chesapeake – point out that adjacent states currently “have no recourse to prevent (or alter) such an introduction despite the likelihood of being affected by it.”
“Federal legislation,” they write, “could provide a mechanism to address this loophole by establishing a process for the governors of any states potentially affected by an intentional introduction to appeal to either the U.S. Fish and Wildlife Service or the National Marine Fisheries Service.”
BTS in OK: A brown tree snake was captured September 12 at the McAlester Army Ammunition Plant in Oklahoma. According to Dale Starry of the base’s Environmental Management Office, the snake was found as workers were unloading shipping containers from Guam. After being captured and killed, the snake, more than three feet long, was sent to the U.S. Geological Survey’s Science Center at Fort Collins, Colorado, where its identity was confirmed.
Exactly how the snake made it to Oklahoma is not known, Starry told Environment Hawai`i. “We don’t know if the containers came in by plane or by barge,” he said, although the containers were packed in Guam.
The incident isn’t the first time a brown tree snake has been reported in Oklahoma, he added. “We’ve had other reports of the brown tree snake here,” he said, “but no confirmed reports, so far as snakes being caught and killed.”
Brown tree snakes have decimated native bird populations in Guam and would be a major threat to Hawai`i if they ever established themselves here. As far as the snake posing an ecological problem in Oklahoma, “I seriously doubt it would,” he said. “We have all kinds of predators here that would feed on it, and a lot of other snakes – copperheads, cottonmouths, rattlesnakes – that already prey on the same things the brown tree snake would prey on. I just don’t see it causing a problem in Oklahoma.”
(*With this issue, Environment Hawai`i introduces a new occasional column addressing the impact of non-native species. Suggestions for future topics, comments, or responses are welcome: email them to [email]pattum@aloha.net.[/email])
— Patricia Tummons
Volume 16, Number 4 October 2005
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