Scary Critters?

Spring 2007

This is an article from WaveLength Magazine, available in print in North America and globally on the web.
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by Helen Hess

A sea kayaker who is skilled in navigation, physically fit, ready for the weather and even has a bombproof roll, may nonetheless be unprepared for an encounter with a dangerous animal. Virtually none of us will ever be in a position to fend off a shark from our boats. However, most paddlers suffer the indignities of barnacle scrapes, jellyfish stings, or urchin punctures somewhere along the way. While the threats they pose are minor and easily addressed with the most basic first aid, it makes sense to be aware of these marginally dangerous marine invertebrates. Not only as a safety issue, but also because they are pretty cool critters.

Barnacles are among the easiest-to-ignore inhabitants of the shoreline. Found in marine environments all the way into the uppermost reaches of the intertidal, most of us walk right over them without giving them a second thought. Encased in a sturdy shell, they look like little white volcanoes, tightly closed to reduce water loss when they’re exposed to air during low tide. The shell is made of calcium carbonate, the same mineral that snails use to make their shells; indeed, this superficial similarity to snails caused them to be originally classified as mollusks by early 19th-century naturalists. However, they are actually crustaceans, relatives of lobsters, shrimp and crabs, beloved by gourmets and the film industry alike.

Every ocean-themed animated movie seems to include a colorful crustacean character, full of personality. Think of the fussy cleaner shrimp in Finding Nemo or Ariel’s friend Sebastian in The Little Mermaid. How can barnacles, which don’t even have a face, claim kinship with such expressive, antennae-waving media darlings? The secret is in the larvae. While adult barnacles live permanently attached to rocks, pier pilings, boat bottoms, or any reasonably hard object they find—even whales or sea turtles—the babies swim in the currents, waving tiny, jointed appendages, just as baby crabs, lobsters and shrimp do. After weeks of living in the plankton and growing to perhaps a millimeter in length, barnacles head for the bottom and snuffle around looking for a good place to attach.

Given that it’s a life-long commitment they’re making, they rely on their senses of smell and touch to pick a promising site, ideally somewhere bumpy, near other barnacles, but without the smell of predatory snails. They may not look impressive, but barnacles have a pretty sophisticated nervous system, giving them powers of subtle discernment. Once they’ve picked out a spot, they glue themselves to the bottom by their heads, secrete a shell, and use their jointed legs to kick food particles into their mouths for the rest of their lives, which may last many, many years in the case of some deep-water species. If you look closely at a group of barnacles submerged in a tide pool, it’s possible to see their feeding structures, called cirri, beating rhythmically, bringing in a tasty meal of microscopic algal cells.

After I finish a long paddle, I always intend to gracefully unfold from the cockpit and step lightly out onto the shore, my joints flexible, my muscles springy. But rubbery legs and numb feet are usually the reality, which can make negotiating the rocky intertidal a challenge. A barnacle-encrusted shore is a mixed blessing indeed; their rough shells provide footing that isn’t slippery, but if you do happen to take a spill, those sharp edges will make fast work of exposed skin, much like a cheese grater on a hunk of mozzarella. But don’t blame the barnacles; they’re stuck there forever, standing on their heads, waiting inside their shells, staying moist until the tide comes in.

While barnacles pose a hazard along the shores, be on the lookout for jellyfish in the open water. The largest jelly in the world, the lion’s mane jellyfish, with its red bell and slender brown tentacles, can be found in cold water along both coasts of North America. Drifting gracefully, trailing hundreds of tentacles behind them, these creatures seem to have become more common in recent years. Harmless moon jellies are also common along both North American coasts.

A bit larger than a hockey puck and fringed with short, white tentacles, their gelatinous bodies are transparent enough for us to clearly see the four pouches of their stomach.

Jellyfish and their relatives, sea anemones and corals, are carnivorous and use a specialized mechanism to capture animal prey.

Individual cells throughout the skin of every tentacle each have a nematocyst packed inside. The nematocyst is a hollow sac, drawn out into a very long, barbed tube with an open tip, which is initially coiled up inside-out within the sac. When an unwary fish, shrimp, or hand of a kayaker brushes against the tentacle, the nematocysts fire, everting the tube and releasing toxin. The barbs help ensnare the prey and also make holes in the skin, allowing toxin to enter. The tentacles are densely covered with many thousands of nematocysts.

If you do blunder into a jellyfish, use a smooth rock or other object to carefully remove any tentacles sticking to your skin to stop more nematocysts from firing. The jellyfish toxins are proteins, and they may be rendered inactive in several ways. Meat tenderizer, which softens the protein in a tough steak, is commonly applied to jellyfish stings to offer relief. It can be mixed into a paste and left on for about 15 minutes. Also, a change in pH can inactivate the toxins; vinegar works well, but if you don’t keep it in your first aid kit, some claim that urine can be used in a pinch. You may want to consider whether the cure is worse than the problem before asking your paddling partner to pee on you.

Although Australia is infamous for fatal jellyfish stings, and dozens have been recorded over the years, our North American species are fairly benign, and while able to inflict painful stings and even leave welts, the ill-effects are typically not severe. Humans have tough skin that can be penetrated by only the most powerful nematocysts, which our local species just don’t have.

Sea anemones also have nematocysts on their tentacles that are even wimpier than those of jellyfish. An anemone tentacle feels sticky but never painful to your fingers. The nematocysts may attach with the little barbs, but they don’t puncture our thick skin. Curious about what would happen to thinner skin, I once put my tongue and lips on a sea anemone in a tidepool. It tasted salty, for sure, but also very weird, kind of metallic and tingly. I can’t recommend it.

While I don’t care for them, sea anemones are the favorite prey of many large sea slugs, or nudibranchs. Somehow the nudibranchs manage to gobble up their anemone prey without discharging the nematocysts. Adding to the mystery, the nudibranch is able to transfer the unfired nematocysts up onto its back and rely on them for defense against their own predators. So, in the category of advice you probably don’t need: don’t kiss sea anemones or nudibranchs either.

Barnacles look dull and unassuming even though they’re busy doing gymnastics inside their shells. Jellyfish look deceptively delicate even though they can pack a wallop. Sea urchins are creatures that actually do look fierce in all their spiky splendor. A sea urchin’s skeleton features a stony internal globe that houses their organs, with hundreds of spines attached via miniature ball-and-socket joints, complete with muscles and ligaments for each one. The spines are quite maneuverable and swing around freely to defend the urchins against predators and even help in walking. Although urchins don’t have brains, they still know which way is up, and if overturned, an urchin will use its spines and hundreds of flexible suckered tube feet to right itself. Thanks to a special type of connective tissue, the joints can also become instantaneously rigid, locking into place, which helps the urchin stay wedged in a safe crevice.

If you happen to step on an urchin, especially when it’s locked into place, those sharp spines will easily pass through neoprene booties and the soles of your feet, only then breaking off. What’s more, the entire urchin skeleton is covered with a thin layer of skin, so the spine that pokes into your foot also brings along with it some living tissue that your body recognizes as definitely alien. While some tropical species are mildly venomous, our North American species are merely sharp. Your immune system will ultimately take care of you, but the area around an embedded spine usually becomes red and swollen beyond expectations before finally expelling the spine fragment encapsulated in a blob of pus. You can soak the area in warm water to speed the process, and even coax the spine out with a sterilized needle.

Hopefully knowing about these minor hazards doesn’t raise your anxiety level, but instead makes a bad encounter less irksome because you carry along tidbits of information about the offending critter, what my Californian professor of invertebrate zoology referred to as “nickel knowledge.” Go forth and enjoy the small stuff during your paddling trips, and try to avoid getting scraped, stung or pierced.

Helen Hess teaches invertebrate zoology, among many other things, at College of the Atlantic in Bar Harbor, Maine. HHESS@coa.edu