Stories from a Coral Reef. Beginnings in Bermuda

Posted by on December 16, 2013
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Today’s post is the first of what I plan to be an occasional series of stories about coral reefs, coral reef biology, coral reef science, and so on.  I hope they will capture the imagination, because I am writing them for a specific purpose.  We are pushing this planet to become something very different to what it has been, with profound consequences for us as well as for many other parts of the biosphere.  We know how we are doing this.  We seem to understand the consequences of what we are doing.  Many of us are painfully aware of how soon they will come and how serious those consequences will be.  Yet, still we go on doing what we do.  As I wrote recently, we stand here stupidly, like deer in the headlights, waiting for the apocalypse.  And this is why I have decided to write these stories.

Coral reefs are perhaps the most sensitive of all ecological systems, and coral reefs are being very substantially altered by the stresses we are causing.  In Our Dying Planet, I detailed this story, and stated that by 2050, coral reefs as I knew them in the late 1960s will simply not be present anywhere on this planet.  Think what that statement means.  I’m not saying that some coral reefs will be degraded.  I’m saying that all coral reefs could be lost.  It’s like saying that ALL rain forests around the world will be clearcut.  We have never yet had that profound a global impact on any major ecosystem, yet we could eliminate coral reefs in just 37 more years!  There is still a vanishingly small window of opportunity for us to alter our behavior, reduce the impacts we are having on the planet, and help a few lucky reefs to persist and maybe to flourish, but we show little sign of wanting to take advantage of that window.  I have come to the conclusion that patiently explaining the cost of continuing present patterns of behavior is just not working to get us to move.  Like deer in the headlights, we stand, and we wait, and we watch, and then the window closes.  And so I turn to stories from a coral reef.  Because I believe that if we can reconnect with the natural world, then maybe we can come to actually appreciate, in a visceral way, that our civilization cannot survive on this glorious rocky planet hurtling through the universe if we do not take care to prevent human activities which degrade the capacity of ecological systems to sustain their integrity and resilience.  The biosphere is not simply here, one fact about our world; the biosphere makes it possible for us to be here.  Stories might help us to reconnect.  We need stories about all aspects of the natural world; my stories are mainly about coral reefs because I know them best.

Beginnings

I first began to learn about coral reefs during the five years of my childhood that I spent in Bermuda.  I did not know at the time that I was embarking on a lifetime career in coral reef science.  I left Bermuda at the age of 10, but I actually learned a few important things during those five years.  My family rented one wing of the main house on a small dairy farm on the south shore of Smith’s Parish, and, like children did back then, I spent most of my time when not at school playing outside.  Some of that play was simply hanging out at the cow barn, ‘helping’ to milk the cows, distributing feed, mucking out stalls, but much of it was simply exploring my amazing subtropical world.  I climbed trees, explored abandoned buildings, journeyed through the less-used part of the farm, all while immersed in a richly imagined amalgam of Tarzan, Roy Rogers and Captain Hook.  And whenever an adult could be dragged along, I spent time at the small beach at the base of the low cliff just a cow pasture away from our house.  Last week, I discovered on the web that I can now rent half that house for a Bermuda vacation at $600 per day, but the farm has been replaced by houses so the sense of ‘my own private beach’ is probably gone.  (Our house appeared to have changed very little over the years although it does seem to have had a fresh coat of paint.  I hope they have upgraded the plumbing as well.)

Tidepools as neighborhoods

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Our beach with rock ledges filled with tidal pools.  Photo © Bermudarentals.com

Our beach was a tiny thing, usually with quite strong wave action (as judged by a skinny kid standing 4 ft tall), more a case of scattered patches of sand among the rocks.  It was definitely not one of those sweeping curves of pink that built Bermuda’s tourist economy over the years.  It had some extensive rocky benches, with tidal pools, and it is in those pools that I began to learn about coral reefs.  You see, Dad liked to fish.  He was not particularly good at it, but he used to alternate between swimming with his mask and spear (no snorkels back then), or standing on the rocks using a hand-line baited with snails that he had bashed out of their shells.  My brother and I got to stay well back from the breaking waves, with our own hand-lines and the tiniest possible hooks, also baited with bits of snail.  We fished the tidepools, occasionally capturing sand gobies which we then struggled to free from the hooks and release, hopefully to survive.  (Actually my brother was four years younger than me, so mostly he just got in my way, although he does not remember it that way.)  Fishing for gobies can wear a bit thin after a while, but exploring what was in those tidepools… that never seemed to get boring.  I learned early that if you were quiet (younger brothers can be so disruptive), and watched carefully, there were lots of critters living there, busily going about their business.  Best of all, with a face mask you could get right into the pool and really see what animals were doing.

The bleeding tooth snails were abundant on the rocks, and were my preferred choice as bait.  Nerita peloronta is named the bleeding tooth because the inner edge of its aperture contains two tooth-like ridges, white in color and surrounded by a rather anemic orange color.  I knew the teeth were not really bleeding, but I still wondered why the snail had those teeth, what it did with them, and why the color around them was vaguely blood-like.  I also wondered why the snails would withdraw their eyestalks if you touched them, and how they could do this, and what it must feel like to have your eyes stuck out on the end of long stalks, yet be able to pull them deep inside your body, never mind pulling your whole body inside a shell and slamming the operculum shut like a trap door to keep little boy’s fingers out.  I also wondered how they crawled over the rocks, and what they were eating.  I did not kill them indiscriminately, but I knew they made good bait, even if Dad was so unsuccessful as a fisherman.

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Bleeding tooth Nerite, Nerita peloronta, a common intertidal mollusk in Bermuda, Florida
and most of the Caribbean.  Photo © Olivier Caro

The rocks around the tidepools were also occupied by limpets and chitons.  Somehow I knew these were distantly related to the bleeding tooth, and not particularly closely related to the gobies.  But limpets and chitons were nearly impossible to dislodge from the rock and they did not seem to do much either.  (I did not know that they moved about during high tide, feeding over the rock, and then usually returned to the exact same sites to rest at low tide, clamped down tight to the rock keeping moisture inside despite the warm sun.)  The bleeding tooths by contrast could be active whenever submerged.  This made them more interesting creatures to me, and that interest in animals that behave stayed with me into adulthood.

There were lots of other creatures in the tidepools, but I did not know much about most of them.  Occasional small corals of various types lived in the deeper pools, as did sponges, coralline algae and other sessile creatures which I knew were alive.  I did not know much more than that, and these creatures seemed so foreign that I could not connect with them.  I knew they were alive, but that was all.  Starfish moved slowly, and brittle stars more swiftly, but their radial design left me confused.  Where was the head?  Could they see?  Small crabs, by contrast, or the beautiful red and white banded coral shrimp (Stenopus hispidus) which I found one day, all had arms and legs, eyes, a mouth, and seemed to do animal things.  The banded coral shrimp was beautifully colored, and waved his claws and white antennae at me, signifying what, I did not know.  I certainly did not know that he would wave at passing fish, which would then pause, allowing him to clamber on and pick parasites off their surfaces, even between their teeth.  If I’d known that, I would have wondered how the fishes know to pause.  Indeed, I still wonder that.  Occasionally, I’d come across the newly shed shell of a large Sally Lightfoot crab, Grapsus grapsus, and somebody, perhaps my parents, told me about how crabs had to periodically shed their shells in order to grow bigger.  I tried to imagine what it would feel like to shed your skeleton and be all soft and floppy – I figured it made more sense to have your skeleton inside, but I also thought it might be fun to have all that armour on the outside.

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The banded coral shrimp, Stenopus hispidus, a circumtropical commensal shrimp which
removes ectoparasites from fishes.  Photo © Richard Ling

 Galapagos Grapsus

Sally Lightfoot crabs, Grapsus grapsus, are a common intertidal crab of the Americas and nearby islands.  These are chatting about the weather in the Galapagos.  Photo © Peter Sale

Best of all were the fishes.  The tidepools always had sand gobies in them, but occasionally they would contain more brilliantly colored fish as well.  Fish like the Sergeant Major, Abudefduf saxatilis which occurred in shimmering regiments in the water just beyond the edge of the rock shelf – water that I was allowed to swim in, with my face mask, on calm days.  Still, the sand gobies were always there, and we ‘interacted’ with them to a greater degree because they ate our bait.  They were probably Bathygobius soporator, but several other species occur there, and at 7 or 8 years old, I was not into counting fin rays or gill rakers, or checking to see whether the animal’s tongue was notched in order to figure out which species of sand goby I was watching.  They spent their time moving slowly about over the sand, occasionally taking a mouthful of sand, and winnowing it through their gills.  I guessed they were eating something in the sand.  Many years later, an Australian student of mine showed that similar gobies winnowed mouthfuls of sand allowing the large sand grains to fall out past their gills, while the much smaller crustaceans that lived among the sand were somehow kept and swallowed.  Sort of like taking a mouthful of tiny pebbles mixed in with even smaller bits of candy, swirling them around with your tongue, and then swallowing the candy while spitting out the pebbles – even if I had gill slits I think I’d find that a demanding task.

Frillfin_Goby

A common sand goby in tidal pools, Bathygobius soporatorPhoto © Marine Science Center

Those tidepools gave me an opportunity to see some of the creatures that lived on reefs up close, and taught me something about the different types of animal.  The surrounding rock sometimes showed its coral origins, retaining the skeletal features shared with the living corals nearby, and this taught me lessons too.  I understood that all rock in Bermuda was of coral reef origin.  I don’t know whether I learned this in school, or elsewhere, but I knew that Bermuda existed as a reefal structure that had grown on top of a volcano rising from the seafloor.  I understood that where there was evidence of coral in the rock above high tide level that was because of uplift in past ages.  I did not know the details or the complexity of the geology of Bermuda.

History told in the rocks

Bermuda lies well outside the tropics.  Its reefs are the most northerly coral reefs in the world, and exist only because the Gulf Stream brings warm water up from the Caribbean.  Of course, that water cools a bit along the way, and presumably because of the cooler water, Bermudian reefs are comprised of fewer species of coral than is the case in the Caribbean.  Most notably, Bermuda did not have the majestic elkhorn coral, Acropora palmata, which formed the shallowest part of Caribbean reefs, an immensely strong rampart of sturdy branches that faced into the waves.  (I put that sentence into the past tense, because very few of those ramparts now remain – white band disease has largely killed off A. palmata throughout the Caribbean and it is now on the IUCN Red List.)

Bermuda is a young reef formation.  The volcano itself, which rises 4270 meters from the ocean floor, was formed in at least two periods of activity between 45 and 33 million years ago.  The final push which saw a mountain rising perhaps 1 kilometer above sea level occurred during the Oligocene about 10 million years after modern coral reefs had first evolved during the Eocene.  This mountain did not subside to any significant degree, as I had been taught, but instead was eroded away by wind and rain during subsequent years.  Volcanic basalts, remnants of that eroded mountain are now at least 60 meters below sea level and buried by a thick cap of reefal limestone.

bermuda bathymetry NOAA

Bermuda showing calderas NOAA

Diagram showing the bathymetry of the Bermuda Rise and its four seamounts, and a photo of Bermuda showing the two large calderas, remnants of its volcanic origins.
Both figures courtesy NOAA.

Bermudian limestones (CaCO3) are generally less than 2 million years old because significant reef building did not begin at this site until the late Pliocene or Pleistocene.  The islands of Bermuda, all built of limestone, lie along the southern edge of the volcano that forms its base but they did not develop simply through occasional uplift of reefs as I understood.  Most of the rock above sea level is actually consolidated sand dunes rather than raised reef.  Those sand dunes were formed from the carbonate sands that any coral reef produces as its rock is worn away by wave action, by storms and by the active grinding, drilling and chewing of a myriad of bioeroders – creatures from fish to molluscs, worms and sponges that attack the rock, seeking the algal and bacterial food that lives just within its outer layers.  During the Pleistocene, sea level fluctuated from as much as 140 meters lower to 10 meters higher than today as glaciers waxed and waned, so reef development was frequently interrupted.  During cold periods, when North American glaciers were at their maximum, the low sea levels allowed for lots of reef erosion, and winds built immense dunes – the beaches were probably even more magnificent than they are today.  Ultimately, those dunes became consolidated into the fine-grained limestone that forms the topography and has been quarried and sawn into the flat tiles used to build the distinctive roofs of Bermudian houses.  As a child, I did not know the details, but I did understand that the island on which I lived had been built from the skeletons of tiny reef organisms.  I still am fascinated that the slow growth of tiny creatures, generation after generation can result in masses of rock like Bermuda, like the Great Barrier Reef, and like most of Florida and the Yucatan peninsula.  This world we live in has been around a very long time, and small actions by animals and plants can achieve great change.

A Mysterious Evening Walk

When I could not be at the beach, there were other animals available to keep me amused.  One of them gave me a lesson I did not understand until many years later.  The Bermuda crab, or Black-backed land crab, Gecarcinus lateralis, occurs in Bermuda, Florida and a wide swath of the Caribbean.  Unlike most crabs, this is a sturdy terrestrial soul that builds burrows up to a meter long in sandy soils.  Deep within its burrow, there is sufficient moisture to enable it to keep its gills moist.  It comes out to forage at night, and feeds primarily on vegetable matter.  To me, the Bermuda crab was a crab that lived in a burrow, and might come out if it was teased in the right way.  The right way required finding a stem of grass, preferably a long one with a seed head on top.  By crouching down, being very quiet, and poking the grass stem into the burrow, I could sometimes get the crab inside to swat at it, to grab it with one of its claws, and maybe to take a few steps towards the entrance.  Very rarely, I could get it to reach the burrow mouth, but I don’t think I ever got it to come outside.  My friends and I would spend what now seems like hours attempting to entice land crabs out of their burrows.  What we planned to do if a crab really came right out, I have no idea.  Why this was so entertaining fascinates me now.  Of course, we did not have Nintendos, X-boxes, Game-Boys or even television to keep us entertained, so I doubt many kids spend time in this fruitless pursuit today.  Fruitless it may have been, but it allowed us to explore, and to think about other creatures that shared our world.  Why did they dig burrows?  What did they do all day?  Why did they not live down at the beach?

Gecarcinus lateralis Jeff Higgott

Gecarcinus lateralis occurs in Bermuda (where it is called the Bermuda land crab), Florida, the Bahamas, and much of the Caribbean.  This one was photographed in Cuba, while it was feeding on a compatriot that had been run over by a car.  Photo © Jeff Higgott.

The big lesson came one evening, when contrary to our usual pattern, my parents took my brother and me and walked down towards the shore.  I’m not sure why we did that, but I think it was because a hurricane was coming, the seas were up, and it would be fun to go and watch the surf.  I know now that the evening in question was during spring tides (the highest tides of a month), but back then I did not even know there was such a thing as a spring tide.

Now the Bermuda land crab lives well away from the sea, and is quite common.  There were land crab burrows in our lawn, and all through the pastures.  This evening, it seemed as if every crab on the farm was out of its burrow, and moving down towards the ocean.  They had not been out when we went down to the shore, but as we were heading home in the twilight, there were crabs everywhere.  As the beam of our flashlight shone on them, they would stand up tall, stretch their two claws wide and high, open them and wave them menacingly at our ankles.  Switch off the flashlight, stand quiet, and they would settle down and recommence their oddly diagonal walk down towards the shore.  What were they doing, and why?

The standing up tall and waving of claws is what every crab in creation does when disturbed.  It looks aggressive; looks like it means business.  In short, it is a defensive display that crabs have evolved which does the job it is intended to do.  It certainly stopped us.  And it stops most creatures smaller than us.  In a way, it’s part of a widely understood body language used by crustaceans (crabs and their kin), and by all vertebrates including us – stand tall, look as big as possible, display any weapons you possess – just think West Side Story.  Insects, related to crustaceans, do not do this so far as I know.  They tend to do things like suddenly exposing color patterns that resemble big eyes, or are simply suddenly bright.  Many fish spread all their fins and then turn sideways to the intruder.  Frogs, lizards and the hog-nosed snake puff themselves up by taking a couple of extra deep breaths; so does the puffer fish by swallowing water.  Birds fluff their feathers, and you and I raise the hair on the back of our necks – a rather futile enlargement technique – but our more hirsute mammalian relatives use the standing up of hair or fur very effectively in such circumstances.

So, those crabs were threatening us.  But what were they doing walking down towards the ocean.  I did not have an answer to that for many years (and I never again saw them doing this).  The Bermuda crab is one of a relatively small number of crustaceans that have invaded the land.  They are well adapted in many ways to their terrestrial life.  Their burrowing habit gives them the moist environment that they absolutely must have, because they breathe using feathery gills tucked inside that carapace.  They have almost succeeded in breaking their dependence on the ocean.  But not quite.  All crabs copulate and have internal fertilization.  In fact, at copulation the male crab delivers sperm to the female who then holds these sperm until she needs them sometime later.  Proper aquatic crabs copulate in the water, and usually just after the female has molted.  The Bermuda crab copulates on land, usually at the mouth of one of the animals’ burrows, and definitely not during a time soon after molting.  These crabs keep to themselves, deep in their burrows during that critical time.  Some time after copulation, the female ovulates, uses the stored sperm to fertilize her eggs, and then extrudes the eggs and fastens them in amongst her swimmerets – the tiny legs on her abdominal segments, segments that most people do not realize exist, because they are kept tucked up tightly under the crab’s body.  This again is exactly what aquatic crabs do, but the Bermuda crab does this on land.  The eggs develop for a time, packed in a moist space under the tucked up abdomen, but finally the time comes for them to hatch.  And that is what those crabs were doing.  They were walking down to the ocean on a spring tide evening.  Once there they would wade in just far enough to get their bellies wet, open their tucked up abdominal segments, wave the swimmerets around to disperse the eggs which would promptly hatch into tiny larvae that would swim, or be carried away on the outgoing tide.  Only after larval life was completed, would the few surviving young come back to shore, and wander up the hill, dig burrows and start the cycle all over again.  That it took me years to learn what was going on that evening makes the event that much more momentous for me.  At 9 or 10, I thought it was amazing that ‘all the crabs on the island were walking down to the sea’.  Now I know it was only the female crabs, and I know they were on an important mission.

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Nature encourages contemplation while opening young eyes and hearts.
Photo © Nowastewednesdays

My years in Bermuda gave me the opportunity to begin to know the seashore and the reef.  I learned about some of the animals, but I also began to learn about deep time, and complex geological processes.  I learned that it was possible to live on an island that had been built of rock manufactured initially by tiny corals.  If I had grown up somewhere else, I’d have learned fascinating things about that type of place.  In fact, I did just that when I moved from Bermuda to Canada.  I was intrigued by, and my parents never discouraged my interest in, the natural world.  I sense that most children, even today, are curious about the natural world, but I fear that many of them have no opportunity to let this curiosity have free rein.  They explore and they learn, but not about the real environment in which we all must live.  Coral reefs are full of stories, grand stories of mountain building and sea level rise and fall, smaller stories of simple creatures doing amazing things because that is who they are.  Reefs can teach us about time and space and about the amazing richness which is the biosphere, and life is made more wonderful because they are here.

Los-niños-corren-más-peligro-en-casa-que-en-la-naturaleza

Children are fascinated by the natural world, if we just give them the chance to explore it.
Photo © Porductos Ecologicos

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