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Wednesday, September 18, 2013

Starfish Population Decline A Mystery to Scientists

A starfish is pictured at low tide on Sanibel Island, Florida. (Alaskan Dude/Flickr)A diseased starfish. (Courtesy of Caitlin Del Sesto)A healthy group of starfish. (Courtesy of Caitlin Del Sesto)A healthy starfish. (Courtesy of Caitlin Del Sesto)

A massive starfish die-off from Maine to Florida, is concerning scientists who have no idea what is causing the decline.

This comes after a boom in their population just three years ago.

Here & Now speaks with a University of Rhode Island researcher, Caitlin Del Sesto about her own research about this particular issue.


  • Caitlin Del Sesto, starfish researcher and graduate student at URI.



It's HERE AND NOW, and there is a big mystery developing along the East Coast. Starfish populations have collapsed from Maine to Florida, and scientists have no idea why. Caitlin Del Sesto was one of the first people to notice the problem last year, when she was an undergraduate at the University of Rhode Island. She's now a grad student and part of a team of scientists researching the issue. She joins us from Rhode Island Public Radio. Caitlin, welcome.

CAITLIN DEL SESTO: Thank you, thanks for having me.

HOBSON: So I understand that Rhode Island was sort of ground zero for this, and you were among the first to notice that starfish numbers were dwindling. What were you seeing?

SESTO: Well, I was working on an undergraduate project in one of my classes, and I collected about 10 sea stars from the bay, and you know, I put them into the tank and within five days to a week they had literally just melted apart. Their arms just kind of basically crawled away from the center of the body until they detached.

HOBSON: And this was also happening as far south as Florida, right?

SESTO: Right. We have gotten some reports from as far south as Florida. What they're seeing is in a different species, but we're thinking that it could be possibly the same issue going on.

HOBSON: Well, what is the issue? Explain what we know so far about what might be causing this.

SESTO: So we know very little about what's going on. In doing research for my project, I found some reports from the West Coast. You know, there was only a handful of them from the '70s, '80s and the '90s. It seems to be, you know, every decade or so there was some sort of mass die-off, but no one had really figured out what the cause of it was.

There were suggestions that it could be bacteria-related or that it could be tied to climate change, warming events. But again, it wasn't able to be explored. So, you know, we are really taking this opportunity to try and figure out what the cause is. We're not even sure if it's a bacteria versus a virus or even possibly a fungus, and we're not sure if sea stars, as invertebrates, they're more sensitive to environmental change, especially in the inter-tidal communities, where you find them, we're not sure if this could be an indicator of some sort of change going on in the environment and if that, you know, these sea stars are just the first species that's showing an impact.

HOBSON: Well, what do you mean a change in the environment? Like what kind of thing are you talking about?

SESTO: Well, we're not sure if it's tied to a warming event. You know, some people suggested that a lot of things got kicked up during Sandy and the recent weather events that we've been having. But again, no one really has any concrete ideas. So right now we're actually running some trials at the graduate school to try and narrow down some conditions that may show to increase the speed of degradation from the disease or slow it down, basically just trying to manipulate temperature, salinity, even population density within our tanks to see what is seeming to trigger this response in the sea stars.

HOBSON: Now, there was an explosion of population of starfish just three years ago, right?

SESTO: Right, right, and a lot of times what happens is when you see these massive population blooms, you're increasing the competition for food and for nutrients, and you're also - by having so many animals in such close contact with each other, as soon as one of them starts to get sick, some - an illness or disease can spread through an entire population extremely fast.

So that's kind of what we're thinking is happening right now, is just that because they were so many of them, when a disease got into the population, it was just able to run rampant, basically, on their numbers.

HOBSON: What could this mean for the ecosystem? Who feeds on starfish?

SESTO: So not many animals feed on starfish. Every now and then you'll see seagulls trying to go at them, but as invertebrates they don't really have much meat to their bodies. The more important thing is they're prey items. Adult sea stars feed primarily on blue mussels, which are found all over the inter-tidal zone here, especially in Rhode Island.

Now, if you remove a sea star, they're a keystone predator. So once you remove that predator from the food chain, you get this explosion in the population level below it. So you in that case would get an explosion of blue mussel population, which you might not think is an issue, but if you are allowing one level to overgrow and to experience this population boom, then they're out-competing other animals that are also trying to inhabit that same space, and you lose a lot of the diversity, and it changes the structure of the ecosystem itself.

HOBSON: Is there any indication that this could be related to what is killing off all these dolphins along the East Coast right now?

SESTO: I would say probably not, just because a lot of times when you have diseases in invertebrates, it's very unlikely that you would see something similar in a large mammal like that. You don't often get the crossover between groups like that. So that's why we're trying to make people aware that it's not a health issue to us as humans, it's more of just a concern for ecosystem balance.

But I can't see it being related to dolphins, most likely.

HOBSON: Caitlin Del Sesto is a graduate student at University of Rhode Island. She's part of a collaborative research effort to find out what is killing the starfish. Caitlin, thanks.

SESTO: Thank you so much.

HOBSON: And you're listening to HERE AND NOW. Transcript provided by NPR, Copyright NPR.

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