Wednesday, February 12, 2014

SEA STARS WINKING OUT


Sea stars (you may know them as starfish) are prominent features of the marine environment all over the world. They are especially prominent in Pacific Northwest waters, where our species are among the largest, most diverse and best studied. In fact, the Pacific Northwest marine environment shelters the highest diversity of this group (class Asteroidea, phylum Echinodermata) anywhere in the world.

Perhaps this prominence made even more startling the discovery in 2013 that sea stars were dying off in great numbers in our waters. Sunflower stars (Pycnopodia helianthoides) were the first to be discovered. This largest of all sea stars is a top-level predator in our intertidal zone, eating just about everything smaller than it, so its disappearance could have profound ecological effects.

Just as important and much more abundant, the ochre sea star (Pisaster ochraceus) has long been known to control the distribution of mussels in the intertidal zone. By preying upon them in the lower intertidal and thus opening up substrates that would otherwise be completely covered by mussels, the sea stars provide habitat for many other species. The ochre sea star has been called a keystone species because of its importance. This species too has been dying off, in many cases completely disappearing from areas where it was once abundant.

These echinoderms are dying from sea star wasting disease, which causes the animal to deteriorate rapidly. Lesions form on the outer surface, and the arms begin to writhe around and eventually pull loose, spilling the internal organs. Death follows very soon, the animal turning to mush. This is a horrible thing to see, and you’ll have to go online elsewhere to see photos of it, as this is a family blog.


Other sea stars known to be affected include the sun stars (Solaster spp.). Some common species seem to be less affected or perhaps not at all, for example the blood star (Henricia leviuscula), leather star (Dermasterias imbricata) and bat star (Patiria miniata). Why would this be? Like everything else about this puzzle, no one knows.

The animals are being monitored in many areas now, both from shore and under water, and as spring comes and the intertidal begins to be exposed more during the daytime, it will be even easier to determine the fates of sea star populations all along the coast. Divers and remote underwater cameras have reported mass mortality in numerous places, with sea stars going from common to virtually absent in a shockingly short time, as if an epidemic swept through them en masse. Their dermal ossicles (the only hard part of a sea star) litter the bottom in some areas where they were once common.



Dead and dying animals have been brought into several laboratories, where efforts are being made to determine what pathogen(s) might be causing this disease. Earlier die-offs of sea stars were blamed on higher than usual ocean temperatures, but that’s not the case now.

So far, no bacterium or virus has been incriminated in these searches, but the search goes on. Stay tuned for more about this ongoing and very disconcerting drama.

Dennis Paulson

7 comments:

Emonicaljenkins said...

This is absolutely tragic. Sea stars are magnificent and i hate that they are dying off so drastically. I am quite eager to find out what is causing the decline of the beautiful creature. Looking forward to the research!

awerdel said...

That is interesting to learn that higher water temperatures are not causing the deaths, it will be even more interesting to find out the actual cause.

KimberlyLow said...

There are a lot of sea life animals from where I live back in Hawaii and I have seen starfish before, however I never knew that so many species of the echinoderms have been dying out because of diseases and other ecological effects. I hope more can be found out about why this might be and find ways to help.

Anonymous said...

It disheartens me to know that there is still so little known about what is destroying the starfish, especially as a keystone species. I woudl hate to sit by and watch so many of our ocean habitats be destryoed because of a single disease!

Rae Nathan said...

I think it's very unfortunate the rate at which sea stars are disappearing because soon enough they may not heavily populate the PNW which is very unfortunate.

Alec Scott said...

I think it is incredibly interesting and as said before tragic that something so devastating has hit an area with such a diverse population that has been studied so extensively and to have an unknown come through and begin to wipe out such a group while leaving so many puzzled is both fascinating and terrifying for a creature that everyone can appreciate.

Slater Museum of Natural History said...

Thanks for your concerns, everyone. All of us who live on the Pacific coast are hoping to gain understanding of this phenomenon, although it may be beyond our ability to prevent it from happening.