Weekend shoreline wonders

From an email by Randal Mindel to members of the Shoreline Group on May 13.

Last weekend saw the passing of a strong tide cycle that took the group out to lots of nearby beaches. Below are some photos and associated comments from observations made by group members.

We are now up to more than 290 species and 1220 observations in our iNaturalist project page. If for example you wanted to see all the nudibranchs our group has uncovered, you can search our project page and enter “nudibranchs” in the species field.

The next good tide cycle runs from May 22nd to 27th, so hopefully some of these observations will inspire you to get out for a walk in the open and uncrowded environments of our local shorelines.

Not from Russia, with nacre

Group member Ian managed to catch sight of the red-listed Haliotis kamtschatkana, the northern abalone up by Willow Point Reef in Campbell River. Despite what the specific epithet suggests, this species ranges over the northeastern Pacific Ocean. It was named after a colloquial seaway east of the Kamchatka Peninsula around the Aleutian Islands of Alaska, where, at least in 1865, this spectacular marine gastropod flourished. Today, on account of its edibility and beautiful shell, with its characteristic perforations and deep, nacreous lining, it is overexploited and endangered through much of its range. Ian’s photos above show a live northern abalone creeping along bedrock in the low intertidal. This species is red-listed in British Columbia, meaning it is functionally at serious risk of extirpation.

The following is from the provincial government’s description of red-listed species:

Red: Includes any native species or subspecies that have, or are candidates for, Extirpated, Endangered, or Threatened status in British Columbia. Extirpated taxa no longer exist in the wild in British Columbia, but do occur elsewhere. Endangered taxa are facing imminent extirpation or extinction. Threatened taxa are likely to become endangered if limiting factors are not reversed. Not all Red-listed taxa will necessarily become formally designated. Placing taxa on these lists flags them as being at risk and requiring investigation.”

All harvesting has been prohibited in the province since 1990. If you are interested in the conservation status, biology, traditional and commercial uses of this species, there is a fairly comprehensive COSEWIC report from 2009 available online here.

Mystery of the flaccid anenome

Group member Christine recently passed along a photo of a creature that has puzzled many of us in the shoreline group over time. I think Robin and Jennifer have commented on it and many of our outings include discussion of its enigmatic form. Metridium farcinatum, the giant plumose anenome is spectacular in water, where you can see its branched tentacles in a cauliflower-like mass that actively stings, paralyzes and consumes small creatures unfortunate enough to fall into its arms. Out of water, it looks completely deflated and defeated as it tries to retain water and avoid fatal dessication. Below you can see Christine’s observed specimen out of the water, with the tentacles retracted and the body tube just hanging at the mercy of gravity.

Another anenome that does this is Urticina, which has simple, unbranched tentacles. Adjacent to the first photo, you can see Metridium in its happy state, indiscriminately killing and eating everything that the current brings it. 

Our biggest intertidal flatworm

As Canadians, we are used to seeing a lot of the world’s biggest things. Usually, these show up in far-flung locations in range of the Trans-Canada or Yellowhead highways. Whether this is a giant hockey stick in Duncan or a giant nickel in Sudbury, they tend to draw people on novelty and a lack of competition. The same cannot be said for the giant flatworm. It lives right alongside giant sea cucumber and giant sea stars and giant sea urchins. How can it attract attention?

Kaburakia excelsa, about the size of a sand dollar, turned up on the underside of a sandstone slab recently. It is thought to feed on limpets (how?) as it walks slowly over its substrate using a dense array of tiny cilia. Unlike most marine worms, this flatworm does not have a fully developed digestive tract, so it passes food out through the same mouth that it takes it in with. You can see the entire tract in the second photo with a human hand for scale.

While this is large for the intertidal area in our region, it is certainly not the largest flatworm. You’ll be horrified to learn (or recall) that the honour goes to a species of tapeworm that is 90 ft long! That group of flatworms inhabits the intestinal tract of large mammals, including humans. They are considered parasites and have very detrimental effects on human health in many parts of the world. 

The savage sea star strikes again

Group member Mary M. sent along a picture that ties together themes from the last two email updates, wherein we considered the plainfin midshipman fish and the feeding habits of the purple sea star. I think the photo speaks for itself. We can add the midshipman to the list of unlikely items that the purple starfish eats. It should be noted that Pisaster ochraceus is considered a keystone species in our region. As a ravenous predator, it controls populations of prey species. This site from HHMI provides a visual demonstration of what happens to our intertidal flora and fauna absent the purple sea star. 

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