Scientists discover why sea urchins are dying off from US to the Caribbean.

A ciliate known as philaster is responsible for the sea urchin die-off. Photograph: Pascal Pochard-Casabianca/AFP/Getty Images. Theguardian.com

Marine biologists at a Florida university say they have solved the mystery of a mass die-off of long-spined sea urchins from the US to the Caribbean.

The scientists blame a microscopic, single-cell parasite for the die-off, which took hold early last year. Affected Diadema antillarum urchins lose their spines and suction, then succumb to disease.

The researchers, from Tampa’s University of South Florida (USF), also suspect the organism, a ciliate known as philaster, might have been responsible for wiping out about 98% of sea urchins in a similar episode in the region in the 1980s.

“I was like, ‘Yes, we have to figure this out,’ because in that 80s die-out, just the loss of this one species of urchin completely changed the fate of coral reefs,” Mya Breitbart, professor of biological oceanography at USF, told the Tampa Bay Times of the day she was invited to research the die-off in March last year.

Breitbart and a team including scientists from Cornell University and the US Geological Survey cracked the case within four months. Their study was published last week in the peer-reviewed journal Science Advances.

They identified the culprit by collecting samples from 23 sites around the Caribbean, including Aruba, the US Virgin Islands and Puerto Rico, and observing organisms attached to the sea urchins, which are known as the “lawnmowers” of coral reefs for their ability to consume decay-causing algae.

They were able to prove philaster was to blame by placing the organism in tanks with healthy, laboratory grown urchins and watching about 60% of the sample die with the same symptoms exhibited in the marine environment.

Breitbart said what surprised them most was the speed at which they were able to home in on the prime suspect.

“All of us on our team have been working on marine diseases for a long time, and this just doesn’t happen. This is really unprecedented to figure it out,” she said.

The cause of the 1980s die-off was not established at the time and may never be known, Breitbart said, because no samples from that outbreak still exist.

But the scientists did identify similarities between the two events, and say the outcome is the same: coral reefs clogged with algae and starved of nutrients, further adding to their precarious state.

Reefs in the Caribbean were already suffering from the fast-spreading and highly contagious stony coral tissue loss disease, scientists warning more than a decade ago that the entire reef system was in danger of collapse.

While there is no known method to eliminate philaster or protect sea urchins from it, Breitbart said, she is hopeful that further research will provide a breakthrough. Her team in Tampa has established a laboratory farm to study the organism, which is not harmful to humans.

“We’re excited to share this information with everyone, from reef managers to additional scientists so we can explore it further and try to stop its spread,” she said.

 

Bracing for a Bullfrog Invasion

By JOSIE GARTHWAITE

NYTimes,

Kenneth H. Thomas/Photo Researchers On the move in coming decades: the American bullfrog.

The consequences of climate change for animals can seem very direct, as with polar bears in a warming Arctic. Others involve leaps, like the case of an invasive bullfrog: by 2080, it could splash into some of South America’s most ecologically rich protected areas, disrupting unique hotbeds of biodiversity. At least, that’s the prediction of a new study in the journal PLoS One.

Worldwide, researchers have increasingly been focusing on how a changing climate has altered or is likely to alter migration patterns and the habitats that different species may find hospitable.

For example, one recent study suggests that more than a million giant king crabs have ventured into the warming waters of Palmer Deep in the Antarctic shelf in recent decades, destroying native sea life. (Colder waters may have kept these “skeleton-crushing predators” at bay for more than 14 million years, the report said.)

Another, a meta-analysis published in the journal Science, found that a host of animal and plant species are moving to cooler, higher altitudes at a striking speed (an average of eight inches per hour). They have moved farthest in regions where the most warming has occurred, the report said.

And then there’s Lithobates catesbeianus (or Rana catesbeianus), commonly known as the American bullfrog.

Working out of universities in Argentina, Brazil and Colombia, the authors of this latest study have mapped species distribution models against climate models, information about biological preserves and sites where the species currently lives.

The result is a prediction of what places are more likely to be invaded by 2080. If the climate changes as anticipated, it appears that a bullfrog invasion will subside in portions of central western Brazil, Argentina, Paraguay and Bolivia. But it will increase in parts of northern Brazil, southeastern Colombia, eastern Peru and southern Venezuela, the researchers project.

The American bullfrog is a particularly vexing trespasser. “Bullfrogs are superfrogs, very adaptable and seemingly immune to most of the causes of amphibian decline,” said Peter B. Moyle, associate director of the Center for Watershed Sciences at the University of California, Davis. “They live in a wide variety of habitats, colonize new ones readily, and eat everything that fits into their mouths.”

If that seems like an overstatement, consider the United States Geological Survey’s summary of the species’ diet, which includes birds, rodents, frogs, snakes, turtles, lizards, and bats. In short, “they are voracious eaters who will also prey on their own young,” the survey says,

Dr. Moyle noted that the American bullfrog gets so big that people around the world have embraced them for culinary purposes (frog legs), even in Europe, “home of the original edible frog.”

Endemic to the eastern United States and Canada, the species has been introduced in more than 40 countries and four continents, including more than 75 percent of South America.

As areas where the American bullfrog has already taken up residence become less hospitable in a changing climate, the researchers, led by Javier Nori of the Universidad de Córdoba, anticipate that protected forest areas will become more suitable for the species.

Unless steps are taken to prevent the invasion, the authors write, climate change could enable the American bullfrog to thrive in areas of the Andean-Patagonian forest, eastern Paragua and northwestern Bolivia, where the species has not yet been reported.

The authors’ concern is especially high for the Atlantic Forest, a biodiversity hot spot in tropical South America. “Continuous monitoring of the native biodiversity in this biome should be a priority since L. castesbeianus is likely to colonize reserves more efficiently under climate changes,” they write.

Dr. Moyle said the study is of the sort that should be carried out for other species worldwide because “it demonstrates that we can predict alien invasions.”

The American bullfrog has a record that even Cortés might envy. But beyond its history, there are additional reasons that the species seems likely to colonize new territory.

“Amphibians rely on external temperatures, moisture levels, rainfall to regulate their own conditions,” said Robin Moore, an amphibian conservation officer for Conservation International. “They have semi-permeable skin, so even slight changes in rainfall can really affect them. Given their reliance on external temperatures and climate, as the climate changes, they are going to move.”

For native species, the arrival of the American bullfrog often means new competition, predation and the rapid spread of deadly disease among amphibians.The bullfrog is a carrier of amphibian chytrid fungus, Dr. Moore said, “possibly the most devastating disease to affect an entire class of animals, certainly vertebrates.”

According to the International Union for Conservation of Nature, based near Geneva, nearly half of all amphibians are now at risk of extinction for many reasons, climate change among them. Dr. Moore described it as an enormous conservation challenge.

Dr. Moyle said the latest study was quite thorough in its climate modeling and predictions and suggested that this could make it more convincing for policymakers.

But even good models have their limitations.“It is important to keep in mind that these are predictions,” he cautioned, noting that they are based in part on a big assumption: that the areas that conservationists need to protect in 50 years will be the same areas protected for their biodiversity today. “It is unrealistic to assume no change,” he said.

In an e-mail, the study’s authors also emphasized, for example, that their models do not take into account the dispersal capability of the bullfrog and its interactions with other organisms. So while this type of modeling is useful for pinpointing areas prone to invasion and providing management guidelines, Dr. Nori’s team wrote, more work is needed.

The scientists called on governments to redouble their efforts to collaborate with universities, research institutions and environmental groups to address “an imminent biological invasion of the bullfrog in the continent.”