May 2, 2017
Salish Sea, Pacific Northwest
A few days ago I went out for my first count of seastars of the year. I have to wait until well into spring to do this — I need a low tide during daylight hours and a day that isn’t stormy since I use a kayak to access the rocky shoreline seastars inhabit. I chose an ebbing tide approaching its lowest point; I’ve found that’s optimal because the seastars crawl high on the rocks during high tide for food and are still galloping downward as the tide goes out … and that’s a long way for a seastar when there’s an especially big tidal range, over 10 feet on this day. Seastars, like all echinoderms, will die if they dry out. Summer season is a triple whammy for them: not only are there more daylight hours, with warm temperatures, but the lowest tides occur during the daytime in the Pacific Northwest in summer.
Seastar Wasting Syndrome is a periodic disease of Echinoderms that hit North American west coast populations with unprecedented virulence beginning in late 2013. While epidemics have run through echinoderms before, this one has been catastrophic, wiping out over 90% of seastars overall, and in some places completely. Some species have been hit harder than others. I’ve been doing inventories since 2014 at sites I can reach easily near my home in the Salish Sea, and since I count at the same sites regularly, I’ve been able to get a good longitudinal picture of the progression of this epidemic locally.
The Daily Bucket is a nature refuge. We amicably discuss animals, weather, climate, soil, plants, waters and note life’s patterns.
We invite you to note what you are seeing around you in your own part of the world, and to share your observations in the comments below.
Each note is a record that we can refer to in the future as we try to understand the phenological patterns that are quietly unwinding around us. To have the Daily Bucket in your Activity Stream, visit Backyard Science’s profile page and click on Follow.
|
Previous years’ observations:
In late spring 2014 I was seeing some dead and dying seastars, and it got significantly worse over the summer. For example, at the Sinibaldi/Olson headland they went from 64 in early June, to 40 in July to 0 in August and September. I’m using the earliest numbers as a baseline since I wasn’t counting before then, and that’s likely pretty close to typical pre-epidemic populations since the warmer water temperatures of summer hadn’t kicked in yet. Biologists have identified a particular densovirus as the pathogen causing the disease and studies have shown both by geographical surveys and laboratory experimental testing that water temperature is directly linked to SSWS.
At the beginning of 2015, my observations showed an approx 90% drop in numbers from early 2014 at all eight sites I survey, and those numbers declined over the season. Seastars were rare or absent (Daily Bucket report 2015) and there were few juveniles. I did see a good variety of species, if in small numbers.
Population counts in 2016 showed a definite improvement, with many juveniles and numbers increasing to about a third of my baseline counts at most sites (Daily Bucket report 2016). The numbers continued lower at more protected sites (Landau headland, Aleck Bay, Odlin) than at sites swept by strong currents (Sinibaldi/Olson, Richardson, Agate Rock). During the summer last year however I was seeing some signs of ecosystem effects. Seastars are carnivores and we’d expect to see a cascade effect from their absence: more of their direct prey (like mussels and urchins) and less of what those feed upon. I didn’t see much change in mussels and barnacles but I did see lots more urchins in the intertidal. However these are anecdotal observations, and I can’t say what’s going on in subtidal communities.
May 2, 2017 observations, conclusions to follow:
Landau headland
3 Pisaster (all purple) adult, healthy
Sinibaldi/Olson headland
26 Pisaster (1 orange, 2 mixed, 23 purple) adult or near adult, healthy
3 Henricia (one a baby), healthy
The following photos are from along the Sinibaldi/Olson headland.
Six feet above the water level, with another hour before slack, these four Pisaster below will have been out in dry air for about 10 hours before the next tide covers them. Evidently they are healthy enough to withstand that, in a wet crevice.
Besides Pisaster, only other species I saw on this day was Bloodstars (Henricia). Surrounding this baby Bloodstar below is an array of algae. From left to right, Sea Lettuce (green), Seersucker kelp (light brown), Desmarestia (dark bown, above), Pink Coralline algae (pink, encrusting), Split kelp (light brown, above), Tar Spot (purplish black, encrusting), more Sea Lettuce, and one of my very favorites, Iridescent algae (the iridescent sheets). The nutrient-rich waters of the Salish Sea support a tremendous variety of photosynthesizers, and that’s not even talking about the microscopic phytoplankton!
Preliminary seastar conclusions, beginning of 2017 season:
Numbers are stable compared to last year. We are a long ways from pre-epidemic populations but at least we’re not losing ground. However we haven’t gotten into really warm summer weather yet. Counts later in the season will indicate how resilient these survivors of the initial epidemic wave are. Since most of the seastars are adults, they were alive in 2014 when the populations crashed. Why did they survive? They might have descended into deeper, colder water. They might have intrinsically superior immune systems. No one really knows. I haven’t seen many young seastars of any species, which is worrisome, however researchers on the Oregon coast (oregonstate.edu/...) have been documenting unusually high numbers of juveniles.
Habitat seems to be important. Landau headland is small and tucked far into a large bay. It doesn’t get much current flow, as you can see by the masses of floating seaweed we are kayaking through in the photo above the fold. It was around this headland I first saw many disintegrating seastars in June 2014 — a really horrible sight. The numbers have not recovered there as well as at other sites. Across the bay from Landau’s, the Sinibaldi/Olson headland projects further out into tidal currents and the water is much deeper. The seastar density was originally much higher here. While seastars were completely wiped out there by the end of the first summer, they have recovered better than at Landau’s since then.
Diversity of species is way down. I haven’t seen a Sunflower seastar (Pycnopodia) in three years! Those huge many-legged colorful critters used to be a common sight in many habitats. They were voracious predators of many invertebrates, including other seastars. One concern about the SSWS epidemic has been what effects there would be on the marine ecosystem, where Pisaster in particular is a key factor. So far, the biggest effect I’ve seen and heard about, in Puget Sound (urbanmarineecology.org/...) and the California coast (news.nationalgeographic.com/...) is a big increase in sea urchins. Biologists are watching for cascade effects.
Besides documenting seastars, I’m always on the lookout for other marine life in the ecosystem. Here are some other highlights of our trip.
The summer season is just beginning, and I’ll be out kayaking as often as I can. Reports will follow :)
Time for you to share what you’re seeing in your natural neighborhood . . .
"SPOTLIGHT ON GREEN NEWS & VIEWS" IS POSTED EVERY SATURDAY AT 5:00 PM PACIFIC TIME AND WEDNESDAY AT 3:30 ON THE DAILY KOS FRONT PAGE. IT'S A GREAT WAY TO CATCH UP ON DIARIES YOU MIGHT HAVE MISSED. BE SURE TO RECOMMEND AND COMMENT IN THE DIARY. |