Coral Disease, Monk Seals, Invasive Fish Among Marine Issues at HCA Conference

“The new green is blue,” says Sylvia Earle, the pioneering marine researcher who was a plenary speaker at this year’s Hawai`i Conservation Conference. And with a theme of Island Ecosystems: The Year of the Reef, the conference, held last July at the Hawai`i Convention Center in Honolulu and organized by the Hawai`i Conservation Alliance, offered dozens of marine-related presentations detailing the latest research on reefs and wetlands throughout the Pacific and on life within those habitats. The following is a summary of a handful of those presentations.

Coral disease expert Greta Aeby has discovered something startling amidst the seemingly pristine reefs of the Northwestern Hawaiian Islands. At French Frigate Shoals, two coral diseases are spreading. One of them has already devastated reefs in the Florida Keys, where between 1996 and 2000, it spread from 26 research stations to 131. At Australia’s Great Barrier Reef, the number of reefs with the syndrome grew from four in 1998 to 33 in 2003.

In 2002, none of the six reefs Aeby surveyed at FFS showed any disease, she said. The next year, Aeby found one Acropora reef with white syndrome and by 2005, it had spread to four reefs. That year, she marked 41 diseased coral colonies and by the next year, 19 of them were dead. As of 2006, the most recent year for which data is available, seven of the nine reefs surveyed at FFS had Acropora white syndrome, Aeby said. (While Aeby was denied a permit from the state Board of Land and Natural Resources to continue her work in 2007, Hawai`i Institute of Marine Biology researcher Evelyn “Fenny” Cox received a permit to continue Aeby’s work this year.)

In addition to the white syndrome, Aeby said she has found large lumpy growths on some of the Acropora corals at FFS. In 2005, she found five instances of these unusual growths, and 24 the following year. Over that time, she said, there had been a 62.5 percent increase in the number of tumors.

Throughout FFS, less than half a percent of the corals are affected with these tumors. However, at “tumor city,” a 12-by-14 meter area, 40.2 percent of the corals are affected by the disease. “That is mind-boggling,” she said, adding that the area includes a number of dead zones of deformed, dead coral colonies.

The clustering of the corals with growth anomalies suggests that the cause is some kind of infectious agent, she said. The tumors, she added, drain the corals of energy and depress their ability to reproduce.

Aeby said that the incidence of disease at FFS is similar to where the Florida Keys were in the 1970s. Since then, Acropora in the Florida Keys and in the Caribbean have become very rare, she said.

The spread of disease at FFS is of particular concern to Aeby since she says the area is the center of diversity and abundance for Acropora corals.
While news of the spreading disease at FFS has been well reported over the past two years, Aeby said that the looming threat of ocean acidification has brought some urgency to the need to understand and control what’s going on up there.

“We need to start acting now… We need to know more about diseases for management,” she said, adding that surgical intervention may be appropriate since corals regenerate.

In response to a question from the audience about the genotype of the corals in “tumor city,” Aeby noted that in Kane`ohe Bay off O`ahu, in the Main Hawaiian Islands, two types of zooxanthellae inhabit corals there and that bacterial communities differ among the two genotypes.

If the corals in “tumor city” all contained the same type of zooxanthellae, “that would offer an alternative explanation,” for the growths she said, adding, “I think we’re going to find a variety of reasons.”

By all accounts, the endangered Hawaiian monk seals of the Northwestern Hawaiian Islands need some kind of intensive care facility that gives pups and juveniles a better chance of surviving to adulthood.

Right now, with a relatively small number of adult females remaining and fewer than one in five pups surviving, Charles Littnan, a monk seal researcher with the National Marine Fisheries Service, said that the entire Hawaiian monk seal population is in “kind of a death spiral,” declining at a rate of four percent a year.

Of the total population of about 1,200 seals, “Juveniles are hit extremely hard… terrible, terrible survival” rates, he said.

So in 2006 and 2007, Littnan and other NMFS researchers ran an experimental captive care facility at Midway atoll. In total, they helped raise seven pups, two of which were born on Midway and quarantined at Kewalo basin on O`ahu for a few months.

The pups were fed herring and vitamins and were kept in captivity anywhere from 89 to 297 days. During their stay, the seals’ body weights improved up to 143 percent, Littnan said, adding that the longer they were kept, the more weight they gained.

One juvenile that was held only 23 days died from what Littnan believes was chronic nutritional stress combined with the stress of being in captivity. Although maintaining the facility was difficult at times, with winter storm surges nearly burying the seals’ fenced pen and tsunami threats forcing two evacuations, the remaining six seals got fat and were eventually tagged and released, Littnan said.

Initially, the seals lost weight; two continued to deteriorate while the rest stabilized and improved, he said. All of the released seals foraged in less than 20 meters of water at first, but dove progressively deeper as time went on. While control seals all fed in one area, the released seals fed all over, with one swimming to Kure island after a few weeks, Littnan said.
Despite the initial improvement of some of the seals, all of the animals, even the control seals, are now dead, Littnan said. Of the “captive care” seals, four disappeared while in good condition, even the “champion who went to Kure,” he said. One seal continued to deteriorate, and the last disappeared in poor condition. The deaths, Littnan said, were probably due to a catastrophic event, like a shark attack or debris entanglement.

While the results overall were abysmal, Littnan said, the project was not a failure of technique and there is still a strong case for doing more captive care. In the 1980s and 1990s, former National Oceanic and Atmospheric Administration researcher William Gilmartin had run a similar program and successfully released dozens of seals.

Jeff Walters of the state Division of Aquatic Resources added in a later session on monk seals that managers need to do anything they can to improve juvenile survivorship, including developing a monk seal nursery hospital and rehabilitation center.

Shark Attacks

In most cases, monk seal pups are successfully weaned, NMFS researcher George Antonelis said in his presentation. But at French Frigate Shoals, where most pups are born, pup survival can be as low as 60 percent, the majority of the deaths due to shark predation.

So between 2000 and 2005, the NMFS removed 12 Galapagos sharks from FFS and the number of pups killed there dropped to about 10 a year. Since then, however, no sharks have been killed, in part because they have learned to stay away when humans are around. This year, instead of trying to kill the sharks, researchers have deployed electromagnetic, physical, and visual deterrents, and have also translocated seals to safer areas. Although three seals at FFS’ Trig Island and a total of nine seals at FFS were lost to sharks, only one of the deaths occurred after the deterrents were put in place. Antonelis added that 13 pups were successfully weaned at FFS.

While humans have filled, drained, or otherwise destroyed much of the state’s wetland habitats, tilapia, introduced here in the 1950s, are killing the native sea grass in those wetlands that remain. At the same time, the invasive fish may also be facilitating the growth of invasive algae. That’s according to research by University of Hawai`i graduate student Kim Peyton, who presented her results at July’s Hawai`i Conservation Conference.

Tilapia is one of five invasive species in sea grass habitats, said Peyton, whose research focused on the impacts tilapia were having on Ruppia maritima, a native seagrass and an important food source for native waterbirds. Most wetlands throughout the Main Hawaiian Islands have tilapia, whether Ruppia is present or not. But of the sites where Ruppia is absent, more than 50 percent of them have been invaded by tilapia.

At one such site in O`ahu’s Kawainui marsh, the largest wetland in the state, Peyton said she was surprised to see nothing green growing in the water. To determine whether the tilapia were to blame for the lack of vegetation, Peyton submerged fish exclosures around clumps of Ruppia, as well as fish cages containing Ruppia and either large or small tilapia at two study sites, one at Kawainui and the other at the Kawaiele wetland on Kaua`i.

Peyton found that large tilapia grazed on the Ruppia in the cages. In the cages containing small tilapia and in those without any tilapia, the Ruppia grew just fine, she found. “These results indicate that unfavorable water quality and/or sediment characteristics cannot explain the absence of Ruppia,” her abstract states.

“The tilapia are very good at removing vegetation,” she said. And because the native Ruppia is distinct from varieties in North America, “we are losing genetic diversity before we can understand it,” she said.

In similar experiments using a red invasive algae (Gracilaria salicornia) instead of Ruppia, Peyton found that the algae grew significantly in the presence of large tilapia because the fish grazed on the algae’s epiphytes (plants that grow on other plants).

Because tilapia are such prodigious grazers, Peyton said they are completely denuding coastal wetlands. And losing wetland plants is quite serious, she added, since they play such important roles in processing organic carbon and regulating water chemistry. She said that Ruppia, in particular, is not only a food source for waterbirds, but is habitat for `opae (native shrimp).

Do we want wetlands with plants and high water quality or do we want a “fish-poo” system, she asked the audience, adding that if resource managers want to improve Hawai`i’s wetlands, tilapia need to be controlled.

“We don’t expect to eradicate tilapia in Hawai`i,” since about five species of tilapia are established in a diversity of habitats in Hawai`i – from anchialine pools to coastal wetland ponds – and they are known to hybridize, she said.

Even so, the fish can be controlled with electrofishing (in fresh water), blasting caps that blow up their swim bladders, and other non-chemical means. Chemicals, she said, should only be used as a last resort.

“This is one [species] that we want the numbers to go down. If we can take that same energy [that we have put into depleting other fish species], we can do it,” she said.

Chris Bird and Rob Toonen of the Hawai`i Institute of Marine Biology, and fellow researchers Brendan Holland, Brian Bowen, and Steve Karl have recently studied the DNA of `opihi (Cellana spp.), an endemic limpet and popular local food item, to determine its population boundaries. All three `opihi species in Hawai`i have undergone a huge crash over the last century, Bird said in his presentation at the conference. Despite the state’s imposition of size limits on harvesting (a 1.25-inch minimum) in 1978, `opihi populations have not recovered, he said. While some have proposed using marine protected areas (MPA) to help improve populations, Bird said managers need to first know where `opihi larvae go so they can decide where to put the MPAs.

Since `opihi larvae are only .17 mm long, tagging them to find out their patterns of migration is out of the question. Instead, the researchers used differences in DNA to track different `opihi populations. They found that no larvae from the Northwestern Hawaiian Islands settle in the Main Hawaiian Islands, and that each of the MHI supports a distinct population of `opihi, which means than no larvae are crossing the oceanic gaps between islands, he said. `Opihi within each island, however, are genetically similar, they found.

Based on these results, Bird said, every island needs its own MPA. He also recommended some specific laws that could help the species: 1) Protect all subtidal `opihi (which would affect the species known as koele only), since adult `opihi don’t move; 2) protect all `opihi in current MPAs; and 3) protect all `opihi on all man-made shores, since those areas could not be considered cultural harvesting grounds.

— Teresa Dawson

Volume 19, Number 4 October 2008