Rocky intertidal fishes

some fish out of water do just fine.


A trip at low tide to one or our rocky intertidal sites always yields an array of pleasures and some treasures. Maybe I’ll see my favorite bright red hermit crab! Or find an Aristotle’s lantern—the feeding apparatus of sea urchins, which may be all that’s left of the innards of a hapless urchin demolished by a crow. Or maybe I’ll catch a whelk in the act of laying eggs. Always fun.

Lurking under rocks and rockweed, I’ll find small, slender fishes. Sometimes called eels, or blennies, they are neither: in our area, they are usually gunnels or pricklebacks, and I will focus here on some that reside in the upper portion of the intertidal zone. They spend their entire lives in the intertidal zone, which means that they are not submerged in sea water for a significant portion of each day. Of course, the higher up in the intertidal zone they are, the longer the non-submerged period, which happens twice a day. Most fish can’t handle that; we even have an expression “like a fish out of water” to describe someone completely out of his or her element.

Gunnels and pricklebacks, however, deal with low tides just fine. They (and many other species of fishes, of many different kinds) are able to breathe air. Air-breathing fishes around the world accomplish this feat in lots of different ways: for example, some use their swim bladders, or various parts of the digestive tract, or special chambers above the gills. Gunnels and pricklebacks can breathe air, using both gills and skin, as they do in water. Their respiration is reported to be just as effective in air as it is in water, although prolonged stress might alter that.

To begin this discussion, let me present some basics about respiration (in either air or water). Respiration is all about 1) getting oxygen into the body and then to the cells where mini-organs called mitochondria do the work of oxidizing carbohydrates and creating energy to run the whole body, and 2) getting rid of carbon dioxide, which is one of the byproducts of oxidizing those carbos, so that the interior of the cells and of the body don’t become too acidic (which interferes with lots of processes). Both gills and skin perform these functions, but the relative roles of those organs differ among species.

Gills of most fishes are long, thin, and delicate, so as to expose lots of surface area for uptake of oxygen and elimination of carbon dioxide. But such gills tend to collapse when out of water. Intertidal fishes make what is called a ‘trade-off: they have gills that are shorter and not quite so delicate, thus reducing their tendency to collapse, but they sacrifice some of the surface area for diffusion of respiratory gases. Shorter, stouter gills also reduce the risk of desiccation in air.

Both gills and skin need to be kept moist in order for oxygen to diffuse in and carbon dioxide to diffuse out. So when the tide is out, these intertidal residents may dip in and out of tiny pools or roll in wet places, for example.

High cockscomb prickleback. Photo by Bob Armstrong

A common prickleback in our upper intertidal zone is known as the high cockscomb prickleback—named for the prominent ridge on top of its head. That ridge tends to lie flat, however, when this dark fish is not submerged, making confident identification difficult for non-experts, in most field conditions. In this species, females tend to be larger than males (at equal ages), and males compete for mating privileges with females. Large females are especially worth competing for, because they lay more eggs than small females. Eggs are laid under rocks, where the female takes care of them for about a month: coiling around the ball of stuck-together eggs, fanning them to increase flow of oxygenated water, and guarding.

We also see crescent gunnels in the upper intertidal zone. These are sometimes readily identified by the light-colored marks along the sides, but I’m told that some individuals are dark, so discriminating them from other dark species may not be easy in the field. Crescent gunnels have apparently been studied less than high cockscomb pricklebacks, but both parents (but sometimes one or none) often tend the eggs, which are laid under rocks. Most of the other gunnels and pricklebacks in our region are either relatively rare or occupy lower parts of the intertidal zone, and in some of these species, parental care is by the males.

Another small fish is common in the upper parts of the intertidal zone: the tidepool sculpin. As the name tells us, it typically lives in tidepools left by the receding tide. It’s an air-breather too, using the gills, mouth lining, and skin. Sometimes conditions in its home tidepool become low in oxygen or too acidic; this could happen especially at night when all organisms continue to respire and produce carbon dioxide but there is no photosynthesis to use that carbon dioxide. Or sunlight might make the pool too warm. Then these little sculpins often choose to leave their pools, either partially—just exposing the head to air—or fully, resting on nearby weeds or rocks or, occasionally, crawling to another tidepool. They are said to be quite good at homing…returning to their home pond if they are displaced.

This fish is unusual in that males and females copulate and the males’ sperm are deposited inside the female, but the eggs are actually fertilized after they are laid. This is obviously a contrast with most other fishes, in which males and females spawn by releasing sperm and eggs into the water. There is no parental care.

Crow with a prickleback. Photo by Bob Armstrong

These intertidal fishes face many risks in addition to desiccation and respiratory difficulties. Even though they have escaped the many predators in the open sea, there are opportunistic land-based predators that can find them. For example, ravens and crows fossick about in the rockweed and poke under rocks, sometimes coming up with a prize; mink delve into tidepools or turn over rocks. And we who love to explore the rocky intertidal inevitably do more damage than we would like.

Thanks to Dr. K. L. Martin, Pepperdine University, for helpful references and consultation.

What is there to see?

the art of noticing among the familiar

The Boy Scout/Crow Point trail is one that some of us walk several times a year. We get to know every rise and turn pretty well. One might think that a trail so familiar could not offer much in the way of interest. Yet it does, regularly—at least to those of us who look for things to pique and tweak the curiosity. Every season brings different things to be noticed.

One day in late August, as we emerged from the forested part of the trail, a ruckus arose out over the river behind us, somewhere near the Eagle Beach State Park parking lot. A horde of noisy crows took to the air and circled over the river, along with numerous gulls, and then disappeared from sight. I’ve never seen so many crows in a flock; there were at least a thousand of them (no exaggeration!). What would draw so many crows to that particular spot, and what would send them all up and away in such a flurry?

A little way before the junction where the Boy Scout trail splits off from the Crow Point trail, we commonly see a little flower that blooms late in the summer. On this day, there were just buds, some of them ready to open and show off the light blue, star-shaped flower. This small annual plant is known as star gentian (in one field guide) or marsh felwort (in another). It seems to favor areas of sparse, low vegetation, and we see it close to the trail. I’ve not noticed it elsewhere around here, although maybe I’ve just not been in the right place at the right time of year. Unfortunately, I have not found any information about its pollination biology, but I’d love to see what insects visit the flowers.

Recent high tides had stranded dozens of chum salmon carcasses and a few body parts alongside the trail and sloughs, which still harbored lively spawners. Many carcasses seemed to have spawned before they were stranded. The carcasses were interesting because all but one of them had intact skulls. However, several bodies had been ripped open, eggs taken from unspawned females, and a good portion of the muscle eaten. If bears had been feeding here, I would have expected to see some skulls opened up so the bears could eat the brains, which are full of fat (every neuron is coated with it). That’s what we often see at Steep Creek, especially on male salmon, which—lacking succulent eggs—have the next best stuff in the braincase. So when a bear happens to catch a male salmon, if it doesn’t reject the fish outright, it often crunches the skull for the brains. But that didn’t happen to these chum salmon by the sloughs. Those with torn-up bodies were, I presume, ripped up by birds—eagles and ravens, probably; they and gulls also took the eyes, as usual.

As we wandered out into the big flat meadow, we noticed an unusually heavy infestation of ergot on the beach rye. This fungus sends up conspicuous blackish spikes from the seed heads in late summer. It’s hallucinogenic and is thought to have been responsible, historically, for such madnesses as witch hunts; rye grain was commonly used for bread, especially by poor folks. In some stands of beach rye, there were twelve to fifteen ergot spikes on a single seed head and ninety-nine percent of the seed heads had at least one, while other stands had little infestation.

On the approach to the south-facing beach, near the edge of one of the spruce groves, there were yellowish, small piles of seed fragments and the occasional dropped seed. They lay beside the empty seed pods of chocolate lily. I’m guessing that a red squirrel ventured out of its grove and made a small feast of these seeds.

Little mixed flocks of sparrows fossicked about for grass seeds in the meadows, while some migrating warblers flitted in the bordering trees. I always enjoy that stand of red alders festooned with beautiful draperies of old-man’s-beard lichens, especially when high-lighted by an errant shaft of sunlight. Bright red fruits of baneberry, elderberry, and highbush cranberry made spots of color at the forest edge.

Tussock moth caterpillar. Photo by Bob Armstrong

I harvested a few of those so-called cranberries (they are not even related to true cranberries), with the thought of making some of that savory ketchup. When I spread out my collection on the kitchen counter in order to pick out some little stems and leaves that had found their way into my stash, I found a tiny hairy caterpillar, the kind that most of us call ‘woolly bears’. And that reminds me to say that these caterpillars with broad black and orange bands are not true woolly bears. They belong to another genus entirely (Lophocampa), distinguished from true woolly bears (genus Pyrrharctica) by the long white plumes emerging from the black bands. Both are the larvae of tiger moths but they tend to eat different kinds of leaves. The proper common name of the black and orange caterpillar in our area is the spotted tussock moth. What? Our caterpillars don’t (usually) have spots! But reportedly, in some areas, this species sports a row of black spots on its all-yellow back. And even some of our local specimens show some black spots on the orange/yellow band. In fact, the color pattern is extraordinarily variable across North America, for reasons unknown. Another mystery, for someone to unravel…