Scientists have identified Vibrio pectenicida strain FHCF-3 as the bacterial pathogen causing the devastating illness that wiped out billions of sea stars, offering hope for recovery efforts.
For over ten years now, sea star wasting disease (SSWD) has been basically melting sea stars into goop — their spiny bodies just kinda turning into piles of disintegrating flesh. Researchers had first noticed and reported this strange and really destructive illness back in November 2013. Since then, it’s thrown ecosystems along the west coast of North America into a bit of chaos. And apparently, similar cases have popped up all over the world too, with more than 40 species hit.
Now, an international group of scientists say they’ve finally figured out the exact pathogen behind this whole thing. After four years digging through gene sequences and doing a ton of lab work, they’ve named it Vibrio pectenicida. More specifically, the strain FHCF-3 was shown to actually be causing SSWD. This discovery — which was recently published in Nature Ecology & Evolution — is kind of a big deal. It’s a key step toward (hopefully) figuring out how to help sea stars bounce back, and protect the ecosystems that kinda depend on them.
Devastating Impact of Sea Star Wasting Disease
Hakai Institute/Grant Callegari
The disease manefests with alarming speed and severety. At first, leisons usually show up on the sea stars’ bumpy outsides. Then, their mussels start to break down, making arms twist weirdly and sometimes even drop off. Deaths often happen just days after these signs show up.
SSWD hit the sunflower sea star (Pycnopodia helianthoides) especially hard. This big, multi-armed creature can grow up to 24 legs and comes in bright orange and purple colors. These “dinner-plate starfishes” dropped by more than 90% in the first few years of the outbreak. So by 2015, they were pretty much gone from the West Coast beaches, from Alaska all the way down to Mexico. This huge loss made the International Union for Conservation of Nature to list sunflower sea stars as critically endangered in 2020.
Ecological Consequences of Sea Star Decline
The ecological implications of SSWD are profound. Sea stars play an important role in their ecosystems. For instance, they primarily eat sea urchins, which feed on kelp roots. With sea stars absent, urchin populations have tripled, which has transformed once-lush, multi-story kelp forests into barren wastelands.
Kelp forests are critical habitats. Indeed, they support many ecologically, culturally, and commercially valuable species. These include sea otters, seals, porpoises, fish, lobsters, crabs, and shrimp. Kelp forests also produce oxygen through photosynthesis, helping to reduce methane levels in the atmosphere. Furthermore, they protect shorelines from tidal erosion. The ripple effects of sea star decline highlight the urgency of finding a vaccine and implementing recovery efforts
The Challenging Search for the Pathogen
Identifying the pathogen proved significant challenging. Initially, scientists, including marine ecologist Drew Harvell, suspected a virus. However, the actual culprit, Vibrio pectenicida, acts as a “sneaky critter”. Specifically, it show up on histology like no other bacteria. This might be due to its ability to produce an immune-inhibit toxins.
Harvell, a member of the international team, noted that they initially thought a virus caused the disease. Therefore, finding the pathogen in a more common group bacteria.. BTW, other hurdles hindered this bacterium’s identification. These included difficulty finding disease-free starfish for comparison, an apparent lack of visible pathogens in diseased tissue, and a general scarcity of knowledge regarding marine infectious diseases.
Identifying the Bacterial Culprit
Evolutionary ecologist Melanie Prentice was the one who led the breakthrough. Her team did a bunch of careful, controlled exposure experiments using sunflower sea stars that were bred in quarantine tanks. In these tests, they exposed healthy sea stars to tissue or fluids from infected ones. Pretty soon, the healthy stars started falling apart—arms twisting, then eventually dying off.
One of the most important experiments involved filtering or heat-treating the diseased stuff before exposing it. The starfish that got the filtered or heated material didn’t get sick at all. That was a huge clue—it meant the cause was probably bacterial, not viral, since viruses usually pass through filters or survive heat. (At least that’s what the team figured.)
They also did RNA sequencing on infected sea star samples from both the lab and the wild. Every time, they found V. pectenicida hanging around. Scientists already knew this bacteria as something that messes with scallop larvae and oysters, so it wasn’t totally new.
The final step was kind of the clincher. They isolated a strain called FHCF-3 from the sick sea stars and used it to infect healthy ones. Sure enough, the healthy stars started showing the same symptoms—legs twisting, melting, just falling apart. That’s when the team realized they’d nailed it. Marine disease ecologist Alyssa Gehman said the moment gave them “chills,” which honestly, yeah, sounds about right.
Climate Change: A Contributing Factor?
Researchers now know the immediate cause. However, they suspect that climate change might play a significant role in the outbreak. This is because they know Vibrio bacteria proliferate in warmer waters.
Some sunflower sea star populations still cling to life in British Columbia’s cold-water fjords. These areas may have temperatures too low for the bacteria to take hold effectively. This observation, therefore, supports the climate change hypothesis. Scientists like Gehman emphasize the need for further investigation into this temperature dependence.
Hope for Recovery
Figuring out the pathogen is honestly just the first step toward getting things back on track. With this discovery, scientists can now start doing culture-based experiments in the lab. Plus, they’ll be able to run wide-scale screenings to check how much of the pathogen is out there—both in labs and out in the field. Having this kind of info gives us a way better shot at saving starfish populations around the globe. In the end, it helps make sure they can keep doing what they do best: keeping marine ecosystems healthy and balanced, which, let’s be real, we all kinda rely on.
