The Changeable Rocky Intertidal: 2013 v. 2018

The last five years have been a period of extremes for Pacific Northwest rocky intertidal ecosystems. We’ve all heard about sea star wasting syndrome, and persistent warm sea temperatures known as the blob. These unusual events are extreme enough that it’s reasonable to be curious about whether we might see changes in our familiar rocky intertidal communities. In the comparative photos below, you can take a look for yourself.

April 26, 2013- a time of high Pisaster abundance

This formation, shown at low tide, juts out of the sand onto an exposed surf swept shore on the northern Oregon coast. It’s tall enough and seaward enough to host pretty much all the intertidal zones. The zones you see here appear as horizontal bands distinguished by the color and texture of the organisms that call them home. For the sake of orientation, this view shows a northern exposure. The surf generally comes in from the west. This exposure gets pounded, but not with direct hits, usually. Here’s what I see in the image from spring 2013 (above). Below the zone of bare rock at the top, is a band of and green tufts and acorn barnacles, Balanus glandula. I’m not sure what the green tufts are. Cladophora perhaps? Lower, lies a bed of mussels, Mytilus californianus. The bed has a salt and pepper look dominated by pepper, the color of mussels. Below the mussels is an open looking band with a few clumps of goose-neck barnacles, Pollicipes polymerus, on the upper margin. The rest of this band is band is sparsely encrusted with thatched barnacles, Semibalanus cariosus. You’ll also see a few ochre stars, Pisaster ochraceus. Next, there is a zone inhabited by one or more species of brownish algae, that have defied my vain identification efforts, and giant green anemones, Anthopleura xanthogrammica. Below that is the low intertidal. It’s lowest reaches are only rarely exposed. Pinkish corallines are prevalent here. In this scene you also see lots of Pisaster stacked just above the sand-rock interface. Finally, protruding through the sand, are the branches of a somewhat buried but sand-tolerant red alga.

May 17, 2018- perhaps a bit less than five years after seastar wasting syndrome became widely noticed in the Pacific Northwest

Five years later, in the spring of 2018, the green tufts are missing, but the acorn barnacles, brownish here, are flourishing. The salt and pepper of the mussel bed is now dominated by salt. That doesn’t mean less mussels. The lighter color is the result of an encrusting layer of acorn, thatched, and buckshot barnacles, Chthamalus dalli. Below the mussel bed, goose-neck barnacles have filled most of the space between the mussel bed and the green anemones. Black flecks among the goose-necks are mussels that have found a home among them. Lower, the giant green anemones seem to be doing well. Any changes in the unidentified brownish algae and the corallines are open to interpretation. Pisaster are hard to find, and we see the persistent branching red, still poking out of the sand, even though the accumulation is a bit deeper than in 2013.

Want to try it on your own? This is another rock in the same vicinity. Here, The surfgrass covered surface takes a direct hit from the west swell. I’ll leave the comparison between spring 2013 and spring 2018 to you.

April 26, 2013- A lush growth of seagrass below the mussel bed and above the red turf
May 17, 2018

There are changes, and they aren’t restricted to the rocks in these photos. I’ve seen the patterns illustrated here repeated in other rocky places on the northern Oregon shore. But there is a question about causality. Without an experiment, lots of experiments, we’ll never know if what we see here is the result of direct and indirect effects of sea star wasting or warm sea temperature. And, there are other forces that shape rocky intertidal communities. Maybe some of them are mediating the changes. My impression is, the zones are more or less intact, but the communities, at the scale of the photos, are more changeable than I imagined in 2013, when I first got the idea to look for change.

This post looks at two points in time, five years apart. If I were you, I’d be asking what happened between 2013 and 2018. In a previous post on change, Comparative Photos Show Rocky Intertidal Changes Between 2013 and 2016, I provide photos and details relating to the progression. I think you’ll be surprised to see that the changes haven’t been gradual, or linear.

Are more changes on the way, maybe a return to familiar times? I don’t know much about the blob. I wonder if it’s gone, abating, only hiding. Pisaster ochraceus, is on the rebound. It’s strangely comforting to see them back in numbers, patrolling the lower edge of the mussel beds. In five years will intertidal communities appear more as they did in 2013? More like 2018? Or something novel?

starfish feeding on a mussel on a vertical wall in morning light
What’s ahead in the changeable intertidal?

To keep up with rocky intertidal news, the Multi-Agency Rocky Intertidal Network is a good source of information.

If you want to learn why I featured Pisaster so prominently here, I recommend this great animation.

Changing and/or Changeable


  1. In the 10 or so years that we’ve been visiting Oceanside I’ve seen the sea stars go from being abundant to not finding a single one this past spring when we were there. It’s depressing but I’m glad to hear that there he may be rebounding some places. It only makes sense: you can’t take a predator like that out of a system and not have consequences.

    1. Yes, I agree. Everything we know says there will be consequences. Pisaster ochraceus has been down since 2014 at least. Some other seastars, like sunflower stars, took an even harder hit. They are not coming back to great extent yet, as far as I know, is I expect effects to continue. Thank you for taking the time to share your observations from Oceanside!

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