Mastery through simplicity: Tide pool springtails, Anurida maritima

Anurida maritima

As if the tide pool surface was ice, hundreds of small gray animals skate and jiggle over the salt water. Not a single one of the animals is wet. None sink. In gusty wind their swarms blow back and forth within the confines of the rocks that wall the tide pools. In still air, the animals’ tremulous movement draws them into ever-shifting amoeboid shapes.

Anurida maritima, the “seashore springtail,” has a distribution that encompasses most of the rocky shores of the North Atlantic. This species’ daily rhythms are tuned to the tides. At low tide, the springtails disperse over the exposed rocks, scavenging for food (including discards from mollusc-throwing gulls, as I discovered a few weeks ago). About an hour before the rising tide submerges them, the springtails retreat to rocky crevices and huddle. When the tide reaches its full height, the animals are fully submerged. This rhythm seems to be controlled from within: they keep up the cycle of activity tuned to the tides even when removed to a lab.

Not many animals can be so amphibious. Oxygen, in particular, is hard to come by. Land animals have lungs adapted to air, sea creatures have gills that can extract oxygen from water. There is not much room for an “in between” state. Animals with lungs hold their breath underwater, then surface to gasp more oxygen. Marine animals exposed at low tide close their shells and trap doors to keep their gills moist. Springtails manage to break these rules and thrive by adopting the path of simplicity. Oxygen enters their bodies across their skin, so during high tide they wander in the open air without lungs. When submerged, the waterproof hairs on their bodies hold a layer of air close to the skin, like a diver’s air tank.

The springtails use more than their body hairs, though, to carry them through 3-4 hours of submergence at high tide. They seek out rocks whose undersurfaces allow several springtails to huddle within an air bubble. If they’re lucky (and clever) enough to find a good spot, the bubble keeps the animals oxygenated through the entire high tide cycle, acting like a lung into which oxygen diffuses from the sea water. By the end of the tidal cycle the bubble is depleted — it shrinks and eventually disappears — and the animals must tolerate low oxygen for a while. Then, when the waters recede, they are free to wander the wrack and see what washed up on the falling tide.

Relatively simple though this strategy may be, it is extraordinarily successful. Close inspection of rocks reveals the springtails wandering nearly every surface at high tide. There seem to be thousands of them in a single square meter. These close relatives of the insects may lack wings, internal breathing apparatus, and elaborate body appendages, but lack of anatomical sophistication has unlocked feeding and living opportunities for which no other creature seems able to compete.

Anurida maritima 2

 

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Ocean teenagers leaving their shed clothes everywhere

Small horseshoe crab shells have started littering the wrack line in Middle Bay, Maine. Every high tide brings more, sometimes half a dozen shells for every meter or so of wrack.

These are not dead crabs (the May full moon mating frenzy left plenty of those), but the discarded exoskeletons of molting juveniles. Young horseshoe crabs spend the first few years of their lives in the muddy bottom of the bay, just below the lowest reach of the tide. In August they molt, crawling head-first out of their old shells, then the animals swell up and harden their new armor. The cast-off shells wash ashore. Mature horseshoe crabs don’t molt, so these shed skeletons are all from growing youngsters. I’d guess the one in the photo is about two or three years old. This year’s hatchlings are still less than an inch across.

These are good things to find. Although the species is protected in Maine, horseshoe crab populations elsewhere have been hammered over the last decades by harvesting for bait and for bleeding (to yield chemicals used in human blood tests). Seeing new generations coming along is good news for the horseshoe crabs (who’ve been around largely unchanged for >400 million years) and for the migrant birds that depend on their springtime eggs for food.

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Great new book: “I Contain Multitudes” by Ed Yong

News flash: A fabulous new book about microbial life (which, it turns out, is all life) hit the shelves yesterday.

Ed Yong is an outstanding writer whose elegant, witty prose describes a revolution in biology. Our new understanding of microbes upends much of what we thought we knew about medicine, conservation, ecology, and many other fields. I Contain Multitudes takes us into the labs and the field sites where this revolution is unfolding. Ed not only delivers a book full of incredibly important ideas, he lets us inhabit the processes that gave rise to these ideas. Including the correct way to obtain an anal swab from a dangerous animal.

If you have a strong intellectual immune system — one that is skeptical of the overblown claims that sometimes spill from scientific discoveries — Ed is a great guide. He’s clear-headed about both big ideas and bad ideas. His is a refreshing rigor in a time of journalistic bombast.

And, if you’re looking to see the world with new eyes, sloughing away the tropes, voice, and stale hypotheses of textbooks, you’ll love this book. The Atlantic, where Ed works as a science writer, has a timely excerpt about the microbial dimension of Zika and mosquitoes.

I strongly recommend doing yourself a favor and getting your hands on a copy. And by “your hands” I mean the dozens of species that comprise the communal entity formerly known as your “self.”

 

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Living flypaper

On the edge of a mountain bog in Maine, a thumbnail-sized plant grows amid the mosses:

sundew

This is sundew, Drosera, a carnivorous plant, ready to ambush.

Darwin devoted twelve chapters of his 1875 book, Insectivorous Plants, to the anatomy, behavior, and physiology of a European species of Drosera. He writes:

During the summer of 1860, I was surprised by finding how large a number of insects were caught by the leaves of the common sun-dew (Drosera rotundifolia) on a heath in Sussex. I had heard that insects were thus caught, but knew nothing further on the subject… I gathered by chance a dozen plants, bearing fifty-six fully expanded leaves, … it was soon evident that Drosera was excellently adapted for the special purpose of catching insects, so that the subject seemed well worthy of investigation.

The results have proved highly remarkable; the more important ones being—firstly, the extraordinary sensitiveness of the glands to slight pressure and to minute doses of certain nitrogenous fluids, as shown by the movements of the so-called hairs or tentacles; secondly, the power possessed by the leaves of rendering soluble or digesting nitrogenous substances, and of afterwards absorbing them; thirdly, the changes which take place within the cells of the tentacles, when the glands are excited in various ways.

We now know that sundews are forced into a carnivorous mode of existence by the poor soils of the bogs in which they live. They are starved of nitrogen and, not being able to find any through their roots, resort to feasting on flying nitrogenous sources, aka insects. (If extra nitrogen is added to their roots, they back off from carnivory.) The “dew” on the plants’ leaves is sweet and sticky; the droplets lure and trap passing sugar-seekers. The plants’ movable hairs and leaves then draw their victims into the center of the rosette of leaves where glands digest then absorb the meal.

Insects also serve as pollinators of the sundew’s flowers. You’ll note that the flower stalks holding opening buds in the pictures above are very tall. Natural selection evidently says: don’t eat your pollinator for lunch.

My camera could not capture the full beauty of the sundew’s leaves. The following photo by “I, Petr Dlouhý” (generously shared under a Creative Commons license) gives a glimpse. The last thing a gnat sees before The End:

Drosera_rotundifolia_leaf

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Cold, cold bathing (duckling style)

The Labrador Current carries water from northern Greenland down the Canadian coast, then swirls its iciness into the Gulf of Maine. On the Maine shore, waiting for the splash, are common eider ducklings:

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During:

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After:

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whee that was fun, can we go swim now?

In the surf, the downy balls have no trouble. As a breaker approaches, they dive then pop back to the surface, paddling in the sea spume and froth.

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When they hatch the ducklings weigh just 70 grams. After ten weeks of growth those that have not been eaten by gulls and seals are nearly as heavy as adults, about 1600 grams. They accomplish all this while keeping their bodies at 40°C (104°F) despite the frigid water (10°C, 50°F on a good day in the early summer). Their diet must therefore be rich in protein and fat — crustaceans, and other sea animals — and their eiderdown coats tight.

Small avian endotherms have no trouble with the water. Surely I should take a dip and join them?

swim

I lasted a screamingly cold two minutes. The first minute was pure pain, the second was alarmingly numb. I salute you, eider ducklings.

These eiders in Maine live at the southern edge of a range that encompasses much of the northern coastline around North America and Eurasia. The species is listed as “near threatened” meaning that we have significant cause for concern about its future.

Locally, here in Maine, the situation was dire but has improved. Bradford Allen‘s review of eider biology in Maine reports that over-hunting in the late 19th and early 20th centuries reduced the population from tens or hundreds of thousands of birds to just four birds nesting on one sea island. At the time, many of Maine’s coastal islands were inhabited by people; nesting birds fared very poorly alongside hungry human settlers. By 2000, after several decades of hunting restrictions and the abandonment of Maine islands to well-fed tourists, the population had risen to 29,000 pairs nesting on over 300 islands.

Across North America, population trends are mostly unknown. Hunting continues. According to the Sea Duck Joint Venture, a collaboration among scientific and management groups:

Within North America, most sport harvest occurs along the Atlantic coast; with about 15,000 birds taken in Canada and about 23,000 in the New England states. They continue to be harvested commercially (80,000+ birds/yr) in Greenland, and this may not be sustainable.

BirdLife International reports that:

In Europe the population size is currently declining overall at a rate of >40% over three generations…Given the strong declines in the European population and a lack of compensatory increases in the North American population the overall population trend is thought to be declining moderately rapidly.

So although eider populations have rebounded from the edge of extinction in some parts of coastal Maine, their longer term future is uncertain. Current threats include oil spills, entanglement in nets, over-hunting, disturbance from expanding industrial activity, poisoning from mercury and other pollutants, predation by gulls and eagles, and nesting site disruption by development and tourism.

Maine’s history of near annihilation followed by recovery gives us reason for hope. If we can stay out of their way, young eiders will continue their 28 million year history of salt-water life.

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Now we see through a glass, (darkly, nope…) Tiffany, Chihuly

At the Museum of Fine Arts in Boston, light streams through vitrified pigmented sand:

From Louis Comfort Tiffany, Parakeets and Gold Fish Bowl, a piece made in about 1893. Tiffany’s use of glass to evoke the birds’ colorful and varied head patterns is stunning.

tiffany parrots

Sadly, the work now stands as an unwitting eulogy. By 1910 the Carolina Parakeet was extinct in the wild and the eastern US had lost its only native parrot. A few lingered for half a dozen years in zoos, but these individuals died without leaving offspring. Occasionally, the birds’ reflections surprise us with a gleam in museum galleries, but their light is almost entirely gone.

A few steps away, Dale Chihuly’s Lime Green Icicle Tower (2011) uses some of the same palate, but without direct representation and, I hope, presaging of extinction.

chihuly1

The piece is 40 feet high, about 10,000 lbs of glass in conversation with the sun, the museum’s atrium windows, and the vegetation outside. From some angles, inner and outer reflective surfaces combine and tangle. Intended or not, this creates a coda to Tiffany’s work: what we conceptualized as Nature is now, whether we like it or not, wrapped into Humanity. Understanding this, might we, perhaps, perhaps, snuff and shadow less light?

chihuly2

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A few bright spots in the dark woods

The many greedy layers of the forest canopy in Shakerag Hollow gobble the light. It is darker at ground level now than it is in mid-winter. Most understory plants are in hunker-down-and-sip mode.

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One or two species, though, know that the forest hosts summer-warmed bees. In sunflecks on the forest floor, these blooms burn holes in the daylong gloam.

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Tall bellflower, Campanula americana.

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White Avens, Geum canadense.

And, yet more brightness, students from Sewanee’s Young Writers’ Conference, taking a saunter, learning a few tales from the woods. Listening on all sides, perhaps, and filtering. Peering with me through the dim light.

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New England clam preparation, gull style

Drifts of smashed clam shells lie on the exposed rocks at the high tide mark.

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These are the leavings of aerial bombardment by herring gulls. As the tide recedes, mud flats are revealed and, buried in the gray ooze, quahog clams. These are big, heavy-shelled creatures, sometimes as large as my hand.

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Their interior surface is blushed with purple at one end. Beads made from this colored shells were used as wampam currency by some of the American Indians of this region and, later, by European settlers. In the 17th century, tuition at Harvard could be paid with “1,900 beads of purple quahog and white whelk.” The scientific name of the clam, Mercenaria mercenaria, derives from the species’ importance in human mercantile transactions.

Purple from gastropods was also highly valued on the other side of the Atlantic: Tyrian purple favored by the Imperial elites of the Mediterranean and, later, Christian bishops, came from sea snails. Lately, molluscs have fallen from favor as status symbols, a loss for human aesthetics, but a gain for clams and snails.

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As the tide falls, herring gulls gather quahogs from the mud, then fly to the rocky shore:

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Just before they reach the rocks, the birds oar their wings to gain altitude, then toss the clam from their beak toward the ground:

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The clams accelerate as they fall, but also move horizontally, carried by the forward momentum of the gulls’ flight. The birds know exactly when to release their clams, the crack of  impact always falls on rock, even when birds release the clam while still winging over mud or grass. Like humans who can throw a newspaper from a moving bike and always hit the mark, gulls are well-practiced at lobbing their food at the best shell-splitting rocks. On this short stretch of coastline, the birds have three favorite sites and each one is smothered in shell remains.

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The violence of the fall is enough to break open the hard shells of the quahog clams:

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Gulls quickly consume clam’s innards, a sizeable meal for a bird (a few large quahogs are enough to make a chowder that will fill a human belly). But the clam’s afterlife continues beyond gull gizzards. Within minutes of a gull’s departure, springtails colonize leftovers, munching on protein and fat:

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Then, when the tide returns, algae colonize the leftover shells, gastropods graze over calcium-rich surfaces, and small fish and crabs take refuge under shelly eaves.

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Gulls are not the only foragers. People — “clammers” — also follow the tide, raking the mud for quahogs and soft-shelled clams.

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Clams are the third largest fishery in Maine, one rife with controversy about the right way to manage clams in the face of invasive predatory green crabs, warming waters, and pollution.

While humans fret (with good reason), herring gulls play (also, I think, with good reason). On warm days, the birds drop then re-catch clams seemingly for the joy of it. The feelings of clams about all this are, as yet, unstudied by students of animal behavior. Complete the aphorism, The unexamined clam is

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End Times and the interrogative mood.

My phone tells me:

earthhasstopped

Questions ensue:

In what way could this be OK? Can we imagine ways in which this might not be OK? Does the use of “Unfortunately” and OK in the same statement evince an emotionally mature mélange of acceptance and willingness to move on, or is it simply a sign of careless typing? To whom should we REPORT? Would the recipients of the REPORT care? Does the Android operating system have a way of reaching said recipients and, if so, can I buy the messaging upgrade? Can I REPORT other occurrences that alarm me or cause me anxiety? Or should I, in those anxious moments, be more OK? Where, finally, is the UNDO button?

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Grassland birds

In a hay meadow near Brunswick, Maine:

Bobolink, taking a break from his jumbled singing flights over the field.

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Savannah sparrow, keeping an eye on neighboring males.

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According to the North American Breeding Bird Survey, neither species has been faring well. The bobolink has declined by about 2% per year since the 1960s. The savannah sparrow’s decline is about 1.25% per year.

North American Breeding Bird Survey trend for bobolink, then savannah sparrow (“index” on the vertical axis is a measure of the number of birds seen along annual survey routes):

boblink suvey wide

sav graph surveywide

These declines are typical for meadow species in North America. According to a review by ornithologist Jon McCracken, birds that nest in upland grasslands have, in the last century, “experienced the most pronounced declines of any other group of birds on the North American continent.”

In the last few decades, intensification of agriculture — earlier hay-cutting, more frequent hay-cutting, conversion of grass to alfalfa — has drastically reduced breeding success of these species. Before that, in the mid-1900s, regrowth of forests on former agricultural land was the main cause of the decline of grassland birds. This followed the 1800s and early 1900s, the heyday of hay in eastern North America. Early European colonists cleared large areas of forest, opening grassland. Then, as American agriculture moved to the midwest and heating oils replaced firewood, grasslands in eastern North America declined as forests regrew (and grasslands in the midwest declined as they were plowed for grain crops).

Given the great variability of grassland acreage over the last centuries, the “right” or desirable amount of bird-friendly grassland in the region is obviously hard to state. But the combined effects of early hay cutting (goodbye nests) and land conversion (hello alfalfa fields and housing subdivisions) suggests that, if we want to maintain populations of these species, we’ll need more (and better) grassland than we now have. The economics of farming makes this a significant challenge. Stiff competition from industrialized meat and milk businesses mean that hay meadows are not money-makers, hence the long-term decline.

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