Low tide explorations

a plethora of crabs, siphoning sponges, and other intertidal delights

June brought some good low tides, lower than minus four feet, so out we went to look at the rocky intertidal zone. This is always a little voyage of discovery, seeing some old ‘friends’ and finding some new ones. But I sure wish that some nice intertidal biologist would come with us, to answer our many questions!

We went out on two consecutive days, to two different sites. These two places differed greatly in the composition of the invertebrate community. For instance, at one site, the false white sea cucumber was overwhelmingly abundant, but at the other site, it was very rare…although the big orange sea cucumber was common there. The little black ‘tar-spot’ cucumbers were extremely plentiful at the first site, but they were not common at the second one. Crabs were hard to find at the first site but common, and of several different species, at the other. Such differences might be due, in part, to the difference in the amount of exposed bedrock habitat vs cobbles, but a real intertidal biologist could probably suggest some other possible explanations for the differences.

I picked up a big whelk shell and had a brief look at a bright red hermit crab rapidly retreating into the top of the shell’s spiral. This Pacific red hermit had found a shell so big that it could disappear entirely from view. Nice for protection, but the shell was so big compared to the crab that there was no way the crab could move its big house from one place to another.

Carefully turning over rocks, we often exposed small fish called pricklebacks. People erroneously or confusedly call them all sorts of names: blennies, eels, snakes, worms, wigglers, flippers, and whatnot. Pricklebacks, and the much less common crescent gunnels, can survive a low tide in damp, protected spots (such as under rocks, where ravens and gulls can’t grab them), because they can breathe through their skin.

Among the several kinds of crab were some brown ones totally covered with short bristles (helmet crabs, I think). We picked up one, only to find that it was an empty shell—the crab was gone. The shell was undamaged, but it was easy to lift open the back of the shell and view the interior. This crab had molted its old shell (along with the barnacles clinging to the legs), pulled its legs and eye and other parts free, and backed out. Now it had to produce a new hard shell, which must take some time, leaving the soft-bodied crab very vulnerable to predators. And the cost of making a new hard shell must be considerable. But a critter with a hard external skeleton can only grow by shedding the old one and making a new one.

Perched among the stubby fronds of an alga were several hairy snails—not very big, with very bristly shells. Something new for us! The usual kind of hairy snail appears to have a short life. After a larval stage, a young snail is male for the first year of its adult life. In its second year, it becomes female (while retaining the penis, just behind one eye), mates with a young male, lays eggs, and dies. An interesting way to go about things—I have to wonder what factors favored the evolution of this life history.

At one site, we found several crumb-of-bread sponges, yellowish in color, encrusting the rock. They break apart easily, hence their common name. I’ve read that a good diagnostic feature is their odor, said to smell like exploded gunpowder. Sponges are multicellular animals that have a very long fossil record, back to the earliest evolution of animals. They feed by pumping in water through small pores and passing water currents though the body, filtering out microorganisms. Several volcano-like structures are scattered over the body of this sponge; water currents and undigested food exit the sponge via these openings. The body is laced with glassy spicules made of silica but, nevertheless, it is eaten by various molluscs and other things. It simply can spread over the rock, but it can also reproduce sexually. However, unlike most sponges, this one has separate sexes.

Under a few flat rocks, there were several small, grub-like animals with no visible appendages that we’d not seen before. With long-distance help from an expert, these were identified as sandpeanuts, a kind of polychaete worm. It usually lives in the sediment below the mid-tide level and feeds on small bits of debris caught by its little tentacles. Without a hand-lens, we could not see the numerous tiny bumps and hairs that are distributed all over the body, nor did we discern the many ill-defined body segments. The feeding apparatus and gills at the front end can be retracted, so they are not visible when the animal is exposed by a low tide. No wonder we had a hard time figuring out what it might be!

I came upon a charming scene—a father with two small children (and a friendly dog) had found a small rock crab. The father carefully picked it up, showing the kids how to avoid the big pincers at the front end. After they all looked at the crab, it was gently placed back where they found it, and it wedged itself tightly between two rocks. What a good example of how to teach exploring kids.

Sheep Creek Valley

nest-building, a song chorus, and a wildflower show

In early June, Parks & Rec hikers went up the Sheep Creek trail on a day of fitful rain showers and intermittent sunshine. This is a favorite trail, but it was clear that the trail could use some work! The uphill portion of the trail is seriously eroded by water coursing down the trail. The long traverse below the road is cut by deep erosional gullies and the edge of the trail is collapsing in spots. Along this stretch, cow parsnip overhangs and obscures the trail. Once in the valley proper, the going is easier, although several wind-shattered cottonwoods and sagging willows lie across the trail and there are more erosion cuts. Some of these things are easily fixed, while others are significantly more challenging.

This was a good time to go up into the valley, because it is rich in nesting, singing songbirds. Even though the P&R summer hikes begin well after the early-morning chorus of bird song (and my hearing is not as good as it once was), I identified the songs of twelve songbird species, plus hooters on the hillsides. One species, in particular, was a treat: Swainson’s thrushes commonly nest up there but they arrive later than the others; I don’t usually hear them until June. By that time, robins and fox sparrows are feeding chicks and juncos have fledglings.

swainson's-thrush-by-bob-armstrong
Swainson’s thrush with nest material. Photo by Bob Armstrong

Swainson’s thrushes nest all across northern North America and down along the Rockies. They spend the winter mostly in southern Central America and northern South America, although some go as far as northern Argentina. When they at last arrive here in spring, the female builds a nest, usually in the understory, lays her eggs and incubates them, while the male sings. But both parents tend the chicks. Hearing the song of that species is certainly a treat for me, but my favorite remains the ruby-crowned kinglet’s cheering carols from the canopy.

Right next to the trail we found a very large scat of a carnivore, full of fur and bones, artistically arranged. A wolf (or possibly a bear) had dined well, probably on marmot.

On this hike, some of the wild flowers were appearing—lots of buttercups, some chocolate lilies and miner’s lettuce, three kinds of violets, a few enchanter’s nightshade. Occasional salmonberry canes bore flowers, but there were wide stands of dead canes, some of which showed no evidence (?yet) of new canes coming up at the bases of the old ones. Does that bode ill for salmonberry production up here this year?

A special floral sighting was a clump of some kind of saxifrage, growing on boulder. We’d seen this on previous hikes too and noted the leaves with three sharp terminal teeth. That made identification simple—the three-toothed saxifrage. The leaf margins have scattered hairs, a feature that led us astray for a while, but consultation with real botanists eliminated the confusion and confirmed the name. This species is not common in our area, but it seems to be the only saxifrage here with three-toothed leaves. The white petals have reddish spots on them (so does another species, but that one has different leaves). It’s fun to try to figure out such things and learn new species; now if I can just remember all the distinguishing features…

Of course, having the right name is just a small part of any story! Many questions lie in wait for curious naturalists. What insects pollinate this plant? What is the function of the spots on the petals? Do the marginal hairs on the leaf deter some herbivores? Does this plant typically grow on rocks? And so on. That’s where the real interest and fun lie!

Just for fun of a different sort, on a completely different topic: I put up a peanut butter feeder on my deck this spring. A simple thing, it consists of a small block of wood with pits (for peanut butter) drilled into both sides of it. This dangles on a hook where I can see it easily, while lazing in my big comfortable chair. The chickadees found it almost immediately and visit it regularly. Did they know that this funny-looking thing might have food or are they just curious? Once there, one experimental peck would tell them there were goodies to be had, worth coming back for. For several weeks, I saw only chickadees there. Then the juncos began to come. Maybe they saw that the chickadees were making repeat visits and decided to check it out. They are considerably larger and much less acrobatic than chickadees, but they somewhat clumsily began to perch on top and reach down to the peanut-butter-laden holes. As time went on, they became more adept and more skillful at extracting several nice bites before losing their balance and fluttering down. Clearly they were learning how to exploit a new resource!

Occasionally other birds came too; a hairy woodpecker clung to the side of the feeder and reached quite easily over to the food source. A Steller’s jay sat on the deck railing, scoped out the situation, and flew straight at one of the gobs of peanut butter, snatching out a good mouthful on its way back to the railing. That worked, so it repeated the maneuver a couple of times. But it has not been seen again.

 

Dandelions

a surprisingly mysterious “weed”

Their cheery, bright yellow flower heads adorn the roadsides in late spring, before the compulsive mowing machines decapitate them. Foraging deer, bears, and human herbivores make use of their good nutrition. Bees and other insects visit the showy flower heads for nectar and pollen.

Dandelions seem to be everywhere in spring—roadsides, trailsides, some gardens, and even out on the rocky sea stacks. That widespread distribution led someone to ask if they are taking over the whole country. The simple answer is No. Dandelions are very good at colonizing open ground. They belong to a suite of weedy plants that specialize in colonizing disturbed sites—an ecological way of life known as ‘ruderal’. Their numerous air-borne plumed seeds waft about, sometimes for long distances, and a lucky few will land on disturbed ground such as roadsides, trailsides, and gardens (to the dismay of gardeners who have just weeded out the ‘last’ dandelion from their vegetable beds). So although a glance at our roadsides might make it seem like dandelions are taking over, unless all native habitats are disturbed by removing the original vegetation and rumpling the soil, dandelions are not going to take over everyplace.

The dandelions we see along the roads and trails probably belong to the species Taraxacum officinale, which originated in Eurasia and has become naturalized here. It has been on this continent for several hundred years, either brought over (intentionally or not) by immigrants from Europe or somehow by seeds blown over the ocean. In that time span, this dandelion has managed to spread all over North America in disturbed habitats.

When seeds are produced, the flower stem elongates, to raise the seed head above much of the surrounding vegetation. Each seed bears a long-stalked, puffy ‘parachute’ that catches any available breeze that might carry it to a new spot for colonization. Both the structure of the seed and parachute and the stem elongation are dispersal adaptations that aid the species’ ruderal strategy. But those adaptations are just part of the story.

Taraxacum officinale is generally known to be obligately asexual, producing seeds without pollination. That would mean that all offspring would be just like their mother—essentially forming a clone identical to her. The ability to reproduce asexually is another feature that helps to make the ruderal way of life successful—one plant can start a whole new population.

However, endless asexuality tends to reduce genetic diversity, which would eventually lead to considerable uniformity among all the individuals in a population. And that, in turn, as we know from what happens to genetically uniform crops when stricken by certain afflictions, can lead to catastrophic failure for the whole population. That somehow has not happened for dandelions, for various reasons. Mutations may occur, so that some offspring are a bit different from their mothers, and new asexual clones get started. Researchers have found that there is a further complication: the asexual dandelions are generally triploid (with three sets of chromosomes instead of the usual two sets) and during the process of seed formation there may be some recombination of genes between chromosomes, thus adding to the genetic diversity of the population. There is even a hint that pollination may (rarely) occur, such that some resulting seeds have been produced by sexual means, introducing still more genetic diversity to the population. In any case, as a result of mutation and occasional recombination, any population of dandelions is likely to be comprised of many clones.

All of that, however, leaves open a major evolutionary question about dandelion flowers. The function of flowers is sexual reproduction—attracting pollinators that convey pollen from one plant to another. But if the introduced dandelions reproduce without sex (at least almost always), why do they make such attractive floral displays? The bright yellow inflorescence is comprised of many small flowers, which offer nectar and pollen to insect visitors; production of flowers, pollen, and nectar is costly of energy. So why do it if reproduction is not sexual? It might be that dandelions engage in surreptitious sex more often than is thought to happen. Or perhaps the beautiful yellow inflorescence is a legacy of the past, reflecting the sexual reproductive habits of the ancestors of the present, clonal species.

In Southeast Alaska, besides the Eurasian dandelion, there are also two native species of dandelion that typically live in alpine and subalpine habitats; one of these is known to be obligately sexual, requiring pollen transfer between flowers. Bees and other flower-visiting insects might not discriminate between the native and the invasive species and may visit both in quick succession. Hand-pollination experiments have shown that pollen transferred from the invader to the sexually reproducing native species can result in some seed production, so genes from the invader may be assimilated by the native species. Such hybridization tends to obscure the distinction between the species. There is also a possibility that viable pollen from T. officinale could interfere with seed production in the native dandelion species (as has been reported for a similar situation in Japan).

The genetics of dandelions can be complex, and the taxonomy of the genus is quite confusing, with differences of opinion about which variants to call separate species. For now, suffice it to say that T. officinale is a highly successful ruderal, one that brightens our landscape with color.