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Sea stars lost in the Salish Sea
And found in southeastern Alaska
Once upon a time, you could kayak the waters of the Salish Sea—around Seattle or Vancouver, off of Whidbey island, or Orcas, or Vashon—and find sea stars in a rainbow of colors. There were bright orange sea stars and others in salmon pink; some were pale yellow, many of them a rocky beige; some sported an almost luminescent blue. There were even purple ones. Most had five arms, some had six, and some had many more than that. There were sea stars visible in any clear water that was shallow enough to see the sea floor.
Indeed, you could walk any dock, and find sea stars on the pilings. They were abundant, too, on rocky shores, anywhere the tide sometimes reached, and the water was clean. If you thought to look, sea stars were everywhere.
Now there are almost none.
Sea stars, more commonly known as starfish, are echinoderms. Sea cucumbers are also echinoderms, as are sea urchins and sand dollars. The echinoderms are closely related to vertebrates1.
There are many species of sea stars along the West coast of North America. Rather, there used to be. Worldwide, there are over 1,900 species of sea stars2. Their incredible diversity of form and color reflects, to a large degree, differences between species.
Their radial symmetry—arms radiating outwards from a single central point—seems exotic to us. If they had the consciousness to consider it, our bilateral symmetry—two halves dividing us neatly into left and right—would probably seem exotic to them.
Sea star species have as few as five arms, or as many as fifty. Most are predators or scavengers, and many specialize on breaking into and eating bivalves, like clams. The ochre star (Pisaster ochraceus) is a particularly fierce and generalist hunter. Indeed, the ochre star has such remarkable impacts on the intertidal zones in which it lives, that it was the first species ever to be described as a keystone predator3.
Sea stars are also, among biologists, known charmingly as asteroids.
Millions of asteroids have died on the West coast of North America since 2013.
First, they lost interest in food. Then their arms twisted and contorted. Then they melted. Their tissues seemed to lose all coherence. Their arms and bodies oozed into puddles. It looked painful, and made some observers quite sad.
“Sea star wasting disease” is a name without a mechanism, a way for scientists and the public to feel like they know something, and are doing something about it. In fact, we know very little about what caused this mass die-off, although many hypotheses have been proposed. Maybe it was a virus—a densovirus, to be precise4. Or perhaps bacteria. Maybe it’s higher water temperatures doing the damage, due to a changing climate5. Some research finds that cooler water temperature does slow the progression of “sea star wasting disease,” but that in the end, all of the ochre sea stars with the syndrome die, no matter how cool the water6. Over 81% of individuals in this—again—textbook keystone predator species have died7.
Perhaps “sea star wasting disease” is due to a combination of several pathogens and environmental causes. Perhaps. But the sudden and rapid disappearance of nearly all of the sea stars does not seem natural.
In the last five years, I had, until last week, seen fewer than five sea stars, although I explore Pacific Northwest coasts regularly, and now live on the Salish Sea. It is yet another example of a way in which our world is less rich, less diverse, less biologically interesting, than it used to be.
I had the good fortune to be in southeastern Alaska this last week—west of Juneau and south of Icy Strait, in shallow water in a bay of Chichagof island. We were in a double kayak at low tide and the water was clear. In the sky, there were bald eagles and pigeon guillemots, gulls and goldeneyes. In the water, the feathery orange tentacles of red sea cucumbers, and the tall white stalks and fronds of the giant plumose anemone8 fairly glowed. A small run of salmon flashed their silvery scales. Sea otters floated and played on the surface. Clam shells littered the shallow sea floor, open and broken and scattered. But the other organisms that were not just present, but abundant, were sea stars.
There were bright orange ones and others in salmon pink; some were pale yellow, many of them a rocky beige; some sported an almost luminescent blue. There were even purple ones. Most had five arms, some had six, and some had many more than that.
I don’t know if the sea stars never died out there, or they did, and now they’re back. But they’re thriving now in the waters of southeast Alaska, and that gives me hope.
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Vertebrates and echinoderms are, for the vast majority of people, the most familiar taxa within Deuterostomia, and while not exactly sister to one another, they are close enough for our purposes. “Sister group” is phylogenetic-speak for “these two groups of organisms share a Most Recent Common Ancestor.” Choose any echinoderm, and any vertebrate—an ochre sea star and a kangaroo; a sea cucumber and a crow; a brittle star and a gorilla—and they are more closely related to one another than either are to any NON-deuterostome organism. Gorillas and brittle stars are thus more closely related to one another than either are to shrimp or spiders or squid.
Mah and Blake 2012. Global diversity and phylogeny of the Asteroidea (Echinodermata). PloS one, 7(4), p.e35644.
Paine 1966. Food web complexity and species diversity. American Naturalist 100: 65–75. Of the ochre sea star: “…of six local starfish species, it is the most catholic in its tastes.”
Hewson et al 2014. Densovirus associated with sea-star wasting disease and mass mortality. Proceedings of the National Academy of Sciences, 111(48): 17278-17283.
Several authors have suggested that increasing water temperatures are indicated, if not necessarily causal, in sea star wasting disease, including before the mass die-offs began, as in this 2009 paper: Bates et al 2009. Effects of temperature, season and locality on wasting disease in the keystone predatory sea star Pisaster ochraceus. Diseases of aquatic organisms, 86(3): 245-251.
Kohl et al 2016. Decreased temperature facilitates short-term sea star wasting disease survival in the keystone intertidal sea star Pisaster ochraceus. PLoS One, 11(4), p.e0153670. Indeed, other research found that neither warm water temperature nor high population density are likely to be causal in the die-offs beginning in 2013: Miner et al 2018. Large-scale impacts of sea star wasting disease (SSWD) on intertidal sea stars and implications for recovery. PLoS One, 13(3): e0192870.
Schiebelhut et al 2018. Decimation by sea star wasting disease and rapid genetic change in a keystone species, Pisaster ochraceus. Proceedings of the National Academy of Sciences, 115(27): 7069-7074. Also, research in California found that supplementing with magnesium chloride helped slow physical deterioration in afflicted individuals of a different species; the sample size was very low, however: Jaffe et al 2019. Sea star wasting disease demography and etiology in the brooding sea star Leptasterias spp. PloS one, 14(11): e0225248.