The Daily Bucket is a regular feature of the Backyard Science group. It is a place to note any observations you have made of the world around you. Rain, sun, wind...insects, birds, flowers...meteorites, rocks...seasonal changes...all are worthy additions to the bucket. Please let us know what is going on around you in a comment. Include, as close as is comfortable for you, where you are located. Each note is a record that we can refer to in the future as we try to understand the patterns that are quietly unwinding around us.
August 2014
Salish Sea, Pacific Northwest
One of the sites I've been checking for seastars since spring is under this dock. The rocky slope in its shade is popular with invertebrates sensitive to dessication or light, so there's always a wealth of marine life there.
Up until July that included seastars, in particular the Ochre Star (Pisaster ochraceus), the most common seastar in the Pacific Northwest. In July, instead of shiny plump brightly colored seastars (on left, June), approximately one third were dying from Seastar Wasting Syndrome (on right). By August, no Pisaster under the dock were present except for the one in this photo: limp, mushy, falling to pieces and smelling rotten.
Seastar Wasting Syndrome is not new. Outbreaks have been observed periodically over the past century, and seastars have rebounded each time. What's different this time is the scale of the outbreak, both over a larger geographic range and in percent mortality. Hypotheses for the cause of this extreme episode include a warming sea temperature, the decline in ocean pH or other stressors, pathogens spread by human activity, or cyclical population changes, but no one knows at this point (it is not radiation from Fukushima though). The specific pathogen has not been isolated yet either.
However, when a species is decimated in an ecosystem, there is a ripple effect.
(All photos by me. In Lightbox...click to enlarge)
Interestingly, only seastars are affected by the pathogen causing SWS. Other species get wasting diseases, but so far limpets, chitons, snails, anemones, sponges, tunicates, crabs, barnacles etc are unaffected by this large-scale epidemic...no mortality has been observed either in the field or in the lab and they don't "catch" it from contact with a sick seastar.
So it's still very colorful under the dock.
A Lined Chiton grazes on red coralline algae:
and this Cloning Anemone is perfectly healthy:
Seastars belong to the phylum Echinodermata, which also includes sea urchins, brittle stars and sea cucumbers, none of which are affected by SWS. These Orange Sea Cucumbers, tentacles retracted at low tide, are as numerous as always:
A vast hatching of whelks caught my attention a few days ago under the dock. Whelks are sensitive to solar radiation and can be expected in this shady spot, but there were many newborns amongst the adults.
I know these baby whelks hatched right here. Whelks lay eggs, mostly through the spring, and after 3 months, tiny baby whelks break out and crawl away. Whelks do not have a drifting (planktonic) larval stage. These are the Frilled Dogwinkle (Nucella lamellosa), the most common in these parts:
The Frilled Dogwinkle, and its cousins the Channeled Dogwinkle, the Striped Dogwinkle and the Leafy Hornmouth, who I also saw here under the dock, feed primarily on barnacles. They drill a hole right through the shell, insert their proboscis and eject digestive fluids, dissolving and then consuming the barnacle body. Whelks are ruthless carnivores.
Here they are feeding on the large Gooseneck Barnacles, as well as the more numerous volcano-shaped Acorn (smooth) and Thatched (ridged) barnacles:
Big whelks feed on big barnacles and baby whelks feed on young tiny barnacles. Below you can see hundreds of tiny white acorn barnacles newly settled onto the shells of older barnacles, some of which look still occupied.
Amongst the recognizably snail-shaped older whelks, there are many more newborn whelks busily eating tiny Acorn barnacles. There were thousands within an arm's reach here. It was quite a spectacle!
Now here's the thing. The primary predators of whelks are seastars and crabs (birds less so). If seastars disappear, will these whelks proliferate, and if so, will barnacles be devastated? or will crabs increase in population since they aren't competing for food? Will the Frilled Dogwinkles then become more frilly, since that is an adaptation against crushing by crabs? What will happen to the mussel, oyster, urchin and limpet populations, ordinarily preyed upon by seastars? For example, Lined Chitons aren't common, but I saw quite a few under the dock...are there more surviving now? The questions beget further questions.
The Ochre Star in particular is considered a keystone species. Its absence will affect the marine ecosystem here in many ways.
Until the population recovers as it may. Overall, numbers are down in every site I've been checking, but at the first place I observed SWS, I've been seeing a few healthy Pisaster. Are they resistant individuals or are these colonizing the headland from depth or elsewhere? I'm continuing my observations of seastars, and starting to take note of changes in other species as this epidemic continues.
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What are you observing in nature where you live? What's there more of, or less of?
"Spotlight on Green News & Views" is posted every Saturday at 1:00 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.
