"This is shocking." An underwater pest is destroying a key oceanic species | Science

An abundance of sunflower starfish before the outbreak of "starfish disease" off the coast of Canada.

Neil McDaniel

By alex fox

An "underwater zombie apocalypse". This is how wildlife veterinarian Joe Gaydos of the University of California (UC), Davis, describes "starfish disease," a pest that has decimated more than 20 species of starfish from Mexico to Alaska since 2013. Now, a new study by Gaydos and his colleagues has more bad news: the disease has affected the sunflower star (Pycnopodia helianthoides), A key predator within algal forests, the most difficult of all. This species, which was once common, has disappeared from most of its range, sending shockwaves through the ecosystems it once called home. The team also found a worrying badociation between warmer ocean temperatures and the severity of the outbreak, suggesting that climate change could exacerbate future marine epidemics.

"This is shocking," says marine ecologist Mark Carr, of UC Santa Cruz, who was not involved in the study. "This is not just a population reduction, it's practically the loss of a key species in thousands of miles. We have never seen anything like this before. "

The starvation disease progresses from "what seems strange" to the "horror movie" for a few days. White lesions appear, then expand into fissures of fusion tissue. Limbs fall and crawl. And finally, the starfish disintegrates into a pale mound of decomposing flesh.

Scientists have not yet identified the pathogen responsible for the disease. Research suggests that the culprit is a virus, but which remains unknown. In previous decades, similar deaths have hit the west coast, but none has been so deadly in such a large area. Of the 20 species affected by the outbreak, laboratory tests showed that the sunflower star is among the most susceptible.

The sunflower star 24 meters wide and one meter lurks the forest of seaweed swallowing prey like sea urchins whole seaweed. As one of the leading invertebrate predators, these large stars help maintain balance in the algae forest ecosystem. If left unchecked, sea urchins can cut algae forests, leaving behind a depopulated and depressed underwater landscape. The sunflower star used to be a common sight underwater, but since its disappearance and the subsequent rise of hedgehogs, northern California has lost more than 90% of its seaweed forests, according to the Department of Fisheries and Wildlife of California.

The loss of these algae forests has left the other species that depend on them hungry, homeless or dead. In December 2018, California decided to extend the ban on recreational fishing for red abalone (Haliotis rufescens) After the surveys, the mollusks, which feed on algae, died of hunger in large quantities. Impacts on fish species are harder to quantify, but Carr says algae forests are vitally important not only as food, but also as habitat, especially for young fish that hope to evade predators.

A dying sunflower star infected with "starfish disease" in the Salish Sea off the coast of Washington State.

Jenn Collins

To badess the impact of starfish disease on the sunflower star, Drew Harvell, a colleague of Gaydos, a marine ecologist at Cornell University based in Friday Harbor, Washington, and other team members badyzed the counts of sunflower stars from nearly 11,000 shallow water dives and close to 9,000 bottom trawl surveys in deeper waters. Hundreds of citizen scientists trained to identify and record the presence of the sunflower star carried out the surveys in shallow waters, and the National Oceanic and Atmospheric Administration (NOAA) conducted the bottom trawl nets, which consist of systematically drag a network along the seabed to take samples from the navy. The Biodiversity.

These data sets extended almost a decade before the collapse of starfish and covered more than 3,000 kilometers of coastline. The researchers reported today in surveys in shallow and deep waters that showed stable populations followed by sharp declines in the sunflower star ranging from a population reduction of 60% to 100% in some areas after the onset of the disease of wear in 2013. Scientific advances.

"Many people expected sunflower stars to take refuge in deep waters where we could not count them," says Steve Lonhart, a NOAA seaweed ecologist based in Monterrey, California, who was not involved in the study. "We expected them to hide there, this research shows that hope was naive."

The occurrence of sea star disease also coincided with the 3-year warmest period recorded in the coastal waters of California (2014, 2015 and 2016), according to NOAA climatic researcher Nate Mantua in Santa Cruz, who did not participate in the study. To see if there was a connection between water temperature and disease, the study authors compared the sea surface temperatures of the times and places of each survey with the decrease in sunflower stars. His badysis found that the times and places of the greatest deaths coincided with the presence of abnormally warm water.

Mantua is the co-author of a 2018 article in the Bulletin of the American Meteorological Society Demonstrate that climate change played an important role in warming California's coastal waters from 2014 to 2016. Climatic projections indicate that these temperatures will become common in the 2050s.

"Many of these shoots are sensitive to heat. In the lab, starfish got sick earlier and died faster in warmer waters, "says Harvell. "An ocean that gets hot could increase the impact of infectious diseases like this one."

It is unlikely that declining seaweed forests in northern California will recover unless the sea urchins succumb to a pest of their own or their natural predators are restored. Harvell believes that the endangered sunflower star should receive strong consideration for being added to the US List of Endangered Species. UU., And that a formal recovery plan may be necessary.

"I'm more worried now than before reading this document," says Lonhart. "We could be observing the extinction of what was a common species only 5 years ago."

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