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

UNDERWATER DRAMA

One night late in December, a small group of us decided to check out Puget Sound at Seahurst during a minus 1.5 foot low tide. At extreme low tides, you can find all sorts of marine invertebrates close up and personal. Unfortunately, low tides occur at night during the winter, so you have to go out with a strong flashlight and, most of the time, bundled up in parka and rain gear to have this experience. We were lucky: moderate temperature, no wind, no rain at 10 pm. The water was calm and clear as a windowpane, and the exposed beach was covered with critters.

It takes a while to get the hang of it. You have to distinguish stationary animals, many of them sessile filter-feeders, from multi-hued rocks and gravel and sand. Many of them are exposed by the receding tide, while others shelter in crevices, among algal fronds, or under rocks. On this visit, we looked mostly on the surface, as there were very few rocks of the right size to turn. But by doing this, you can find many more critters, including several species of fishes. But always replace the rocks carefully!

Mollusks of numerous kinds, including limpets, lined chitons (Tonicella lineata) and rock oysters (Pododesmus cepio), were scattered over the large boulders that were exposed by the low tide. There were scattered plumose anemones (Metridium senile) hanging down obscenely from rocks and Christmas anemones (Urticina crassicornis) looking like prettily patterned blobs. We found one attached to a movable rock, so we took it out in a foot of water to let it expand. We came back to it 10 minutes later, and it was nicely expanded for photos.

As we were photographing it, a kelp crab (Pugettia producta) approached from stage right. It came up to the anemone and started feeling in its tentacles. We wondered if it might be snipping them off to eat, but we couldn't be sure. More likely it was feeling for organic matter left among the tentacles, perhaps part of the anemone's last meal. Several times after inserting a cheliped among the tentacles, it brought it back to its mouth. After a short while of doing this, it started running one of its longer legs through the tentacles, almost in a grooming manner. Perhaps the leg was able to detect food particles?

 

Presumably the thick chitin of the crab's legs protected it from the anemone's stinging cnidocytes, and a coating of anemone mucus might have conferred additional protection.

As we were watching this, a red rock crab (Cancer productus) approached the kelp crab, and it scuttled away about a meter and sat among the eelgrass. The second crab didn't interact with the anemone but then found a dead Dungeness crab (Cancer magister), perhaps to check it out as dinner, but our lights may have scared it away. We had earlier found a pair of Dungeness crabs mating in an eelgrass bed.

Sea stars were the most conspicuous megafauna appearing in our lights, including sunflower stars (Pycnopodia helianthoides), many of them young, and ochre sea stars (Pisaster ochraceus), with fewer mottled sea stars (Evasterias troschelii). We turned one Pycnopodia over that had a hump in the middle and found what I thought was a fish skull clutched in its hot little tube feet. We grabbed the skull and started pulling on it and out from what must be an amazingly large stomach came a spotted ratfish (Hydrolagus colliei) carcass, largely digested!

On a previous occasion at the same site, we had found a Pycnopodia that had ingested a whole rat. We assumed the rat had been dead in the water rather than that the starfish had gone on walkabout up in the rocks. This huge sea star really seems at the top of the intertidal Puget Sound food chain!

Dennis Paulson