One of the things that Sandra showed us was the direct consequences to shore life when a keystone species is suffering. In this case, the keystone species was the Purple Sea Star (Pisaster ochraceus),
a prominent predatory echinoderm. The wasting disease that we have seen in action has reduced numbers of this species as well as other asteroids (yes, that is a technical name for sea stars and their relatives). At the Willow Point Reef, this has led to a population boom in a species that they prey on. We saw thickets of purple and green sea urchins (pictured above) occupying relatively bald sandstone bedrock. Sandra pointed out that these regions were formerly covered in the large kelp Alaria
. Graceful as this winged kelp is to us, it is tasty to the urchins who are free to prey on the kelp as their population explodes absent the controlling presence of the sea stars. Sandra mentioned the voids left by Alaria
and the rich kelp beds in the area are being filled by Sargassum
, that bulby invasive brown seaweed.
Gumboot Chitons Everywhere
Despite its presence on Sandra’s species list, few of us expected to see so many big gumboot chitons filling the cracks and hugging the sandstone. The largest was somewhere north of 12 inches. This is a species that is hard to see on the shoreline. They spend most of the year in under the lowest tide line, moving up to exposed shore only to breed. This species, like most intertidal chitons is a “cow” (Sandra’s term for herbivorous grazers), consuming algae big (kelps) and small (diatomaceous crusts). Their enormous size does not happen overnight. Encased within the stubbly encompassing girdle are the same plates common to all chitons. These plates mineralize during regular, annual growth phases. Scientists can count the rings of growth in the plates much like the rings in of a tree to determine their age. It turns out they can live up to 40 years.
Colourful corals of Campbell River
Betty had mentioned being able to see corals on the shoreline in places on the island, but the point in front of the Panago seemed an unlikely place to find them. Happy little orange scleractinian corals (Balanophyllia elegans) ridged with calcite were spotting the ledges on the underside of the sandstone. Unlike most corals, it lacks symbiotic dinoflagellates/algae in its tissues, so it relies exclusively on indiscriminately stinging and capturing small creatures and floatsum that passes by its many tentacles.
Dead Man’s Fingers- The best common name
The deep forest green of Codium fragilis (
was a surprise to see in our region. This large, three-dimensional and dichotomizing green algae is one of a number of vastly different species that go by the common name “dead man’s fingers”. I’m beginning to think that different cultures have different ideas about the look of a dead man’s finger. These ones come straight out of a Dr. Seuss book, The flavourful shrub Decaisnea
seems to dwell in a purplish hue on the spectrum,
whilst those of those of the fungus Xylaria polymorha
must represent advanced decomposition. This is an introduced species.
Clionid Sponges and Giant Rock Scallops
Sandra showed us two really good examples of shell degradation by the activity of a tiny little sponge, Cliona. On the surface of both the Giant Rock Scallop (pictured above left) and the Hornmouth Snail (above right), we could see that the original mineral surface of these molluscs has been bored and thinned by the activity of Cliona. Excavating mineralized shell surfaces micrometers at a time by secreting enzymes to dissolve and loosen particles, this species is responsible for a lot of breakdown in the intertidal. While the pace might be slow, the product is voluminous. Carbonate mud (tiny particles of calcite) is produced by this activity. In the fossil record, we can see beds meters and meters thick composed almost exclusively of particles loosed by the activity of the “boring” sponges. Sandra mentioned the sponge as a pest from the perspective of aquaculture operations as it degrades the quality of oysters.
Honeycomb weathering or Bioeroders?
A number of shoreline members commented on the similarity of large cylindrical-to-hemispherical excavations at in the sandstones if Willow Point to patterns seen in shoreline sandstones on Hornby, Saltspring, Galiano and any number of other places where these rocks are found in proximity to the sea. There was mumblings of the word _Tafoni_, a term used to describe a type of honeycomb weathering in our area. To clarify: Honeycomb weathering happens above the hightide line to sandstones that are exposed to salt spray from the sea. The excavations that we were seeing in the sandstones at Willow Point were subtidal and were produced by the activity of invertebrates, most likely the sea urchins.
Species list. Modified barely from Sandra’s list based on what was seen and a few taxonomy changes. Please email me with corrections, additions and deletions. These are the things I remember seeing but between the 20 of us, there was likely more.