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Tough as nails

Vernal pools are unique aquatic ecosystems, fleeting and unpredictable, but rich in animal life.

Vernal pools are unique aquatic ecosystems, fleeting and unpredictable, but rich in animal life.

Last night I finally managed to see the movie “Gravity”, which proves to me incontrovertibly that humans are not meant to stick their noses outside the protective layer of Earth’s atmosphere, despite having developed all kinds of high tech space gear (which, incidentally, seemed to have been designed primarily to kill Sandra Bullock’s character.) But this unexpectedly beautiful movie also made me think of a certain creature, whose amazing survival skills had lead NASA to use it to test the limits of life’s perseverance in outer space, long before somebody finally realized that people floating aimlessly in the cosmic void make for much better television.

To photograph fairy shrimp and other inhabitants of vernal pools directly in their habitat I used a complicated underwater setup with live video feed that allowed me to see what was in front of the lens. When I turned it on I was amazed how much life was there, it was almost as if I suddenly looked at a tiny coral reef.

To photograph fairy shrimp and other inhabitants of vernal pools directly in their habitat I used a complicated underwater setup with live video feed that allowed me to see what was in front of the lens. When I turned it on I was amazed how much life was there, it was almost as if I suddenly looked at a tiny coral reef.

As the first sunny days of March begin to melt away frozen remainders of winter in the northeaster United States, members of an ancient lineage of animals are getting ready to spring back to life. Throughout most of the year their habitat was as dry as a bone, but when the last patches of snow turned into water, leaf-packed depressions on the forest floor suddenly transformed into small, ephemeral ponds. Known as vernal pools, these fleeting bodies of water will be gone again by the time summer comes, but for now they create a unique aquatic ecosystem. Soon, the water is filled with thousands of tiny animals, at first not much larger than the point at the end of this sentence, but within a few weeks reaching the length of nearly a half of a pinky finger. They are the fairy shrimp (Eubranchipus vernalis), members of a group of crustaceans known as branchiopods, animals that were already present in the Cambrian seas half a billion years ago, before any plants even considered leaving water for terrestrial habitats.

Male fairy shrimp have massive, highly modified antennae, which they use to grasp and hold the female during mating.

Male fairy shrimp (Eubranchipus vernalis) have massive, highly modified antennae, which they use to grasp and hold the female during mating.

Looking at the delicate, soft body of a fairy shrimp it is hard to imagine how a lineage of organisms so seemingly fragile could have survived for so long. Take one out of the water, and it is dead within seconds. Let the oxygen level in the pond drop, and the entire population is wiped out. Given a chance, a single fish could probably do away with them all in a day, but luckily fish don’t do well in ponds that last for only a few months of a year. But fairy shrimps’ frailty is an illusion because where it counts they are as tough as nails.

In the northeastern United States several species of salamanders, such as this Spotted salamander (Ambystoma maculatum) from Westfield MA, share vernal pools with the fairy shrimp.

In the northeastern United States several species of salamanders, such as this Spotted salamander (Ambystoma maculatum) from Westfield MA, share vernal pools with the fairy shrimp.

If you live in a place as transient as a vernal pool, here now but gone in a few months, an environment of unpredictable duration and often uncertain arrival, you better have a solid survival strategy to build your life around. First, once the right environment appears, you must develop very quickly and reach reproductive maturity before the changing conditions kill you. Second, you need a method to keep your genetic line alive, even when the only habitat in which you can survive is gone. And third, plan for the unforeseeable cataclysms, such as sudden evaporation of the pool before you are ready to produce a new generation. Because, if you fail on any of these accounts, your species will not last past the first generation. Fairy shrimp, despite their unassuming physique, are master survivalists in the most hostile and unstable of habitats, and execute the three-step action plan flawlessly.

Male fairy shrimp (Eubanchipus vernalis).

Male fairy shrimp (Eubanchipus vernalis) from Estabrook Woods, MA.

As soon as the vernal pool forms, cysts containing fully formed shrimp embryos from the year before break open, and minute, swimming larvae emerge. They immediately start feeding on microscopic algae and bacteria already present in the water, and grow like crazy. During the first few days of their lives, baby fairy shrimp, known as nauplii, increase their length by a third and nearly double their weight every day. In about a month the animals are fully grown. One pair of the males’ antennae develops into giant, antler-like projections that help them catch and grasp their mating partners, while females grow big egg pouches on their abdomens. A few days later females start to lay at the bottom of the pool large clutches of cysts, eggs with embryos already developing inside, and die shortly after. Soon the water level in the pool begins to drop, and by June all traces of the once vibrant aquatic habitat are usually gone.

The body of a fairy shrimp is nearly translucent, which makes them invisible to a predator looking from above.

The body of a fairy shrimp is nearly translucent, which makes them invisible to a predator looking from above.

But inside the cysts hidden under a thin layer of soil the embryos are very much alive. They slowly continue their development, but can remain in the dormant state, out of the water, baking in the sun or being frozen in ice, for many years. Their outer shell is nearly waterproof, and quite sticky. This stickiness explains the sudden appearance of fairy shrimp in the most unexpected places, including old tires filled with water, after hitching a ride on the legs of birds and other animals. These cysts can live through being dipped in boiling water and liquid air (-194.35 °C, or -317.83°F), which is one of the reasons why these organisms are being used by NASA to test the survival of life outside of Earth’s atmosphere.
The following spring, if everything goes as planned, water of the melting snow awakens the dormant embryos, and within a few days they break the shell of their tiny survival capsules. But not all of them. Only a portion of the cysts responds to the first appearance of water, while others continue their slumber. If the pool dries prematurely, as it sometimes happens during a particularly warm spring, all early hatchlings die, and a second batch of larvae will emerge only if the pool fills up with water again. It has been shown that some cysts in a clutch will wait through eight cycles of wetting and drying before finally deciding to hatch. Fairy shrimp have evolved this ingenious strategy of hedging their reproductive bets in response to the erratic nature of their habitat, and it clearly serves them very well.

Fairy shrimp swim upside down, using 10 pairs of legs to propel themselves and collect bits of algae to feed on.

Fairy shrimp swim upside down, using 10 pairs of legs to propel themselves and collect bits of algae to feed on.

Footprint Cave, Belize

Africa in Mesoamerica – a beautiful, little pool on the floor of the upper chamber of the Footprint Cave; it even has an adjoining pool that looks like the Arabian Peninsula.

Africa in Mesoamerica – a beautiful, little pool on the floor of the upper chamber of the Footprint Cave; it even has an adjoining pool that looks like the Arabian Peninsula.

It has been a long while since the last update to this blog, mostly because of my hectic travel schedule (in fact, I am typing this on a shaky train ride). But it has been an interesting time, with lots of great photo ops. Last week I joined Alex Wild, John Abbott and Thomas Shahan in Belize to teach BugShot 2013, an intense course in tropical insect macrophotography. Aside from working with a friendly group of photography masters and enthusiastic students it was my first exposure to some of the most interesting members of the troglobitic Mesoamerican fauna as the workshop was held at the Caves Branch Lodge in central Belize, an area famous for its karst formations, replete with deep limestone caves.

The most famous cave in the area is the Footprint Cave, named after calcified Mayan footprints found in the deeper section of the cave, along with a number of artifacts and skeletal remains. The cave was looted in 1994, and many artifacts and remains are now gone, but you can still see there ancient fire places and shards of Mayan pottery. It was quite an unreal and humbling experience to sit next to a pile of ash that might be over 2,000 years old but still looks warm. The cave itself is stunningly beautiful, cathedral-like, with massive stalactites that shimmer in the light of the headlamp. The shallow Caves Branch River flows through it, and as you walk along its bed large catfish and shrimp follow your every step, looking for small aquatic invertebrates flushed from under the sand.

Female cave cricket Mayagryllus apterus, a species endemic to the Caves Branch system of Belize.

Female cave cricket Mayagryllus apterus, a species endemic to the Caves Branch system of Belize.

As we walked deeper into the cave, leaving behind its large opening and eventually all traces of natural light, we began to discover a multitude of life forms that call this cave their home. Biologists explored Footprint Cave in early 1970′s, but little work has been done since. Many animal species found in the Caves Branch system are likely endemic, and some still await their formal scientific description. I was thrilled to see dozens of long-legged cave crickets Mayagryllus apterus, described only in 1993 from specimens collected in these caves. They were often accompanied by large, equally spindly amblypygids Paraphrynus raptator (Phrynidae), and apparently another, yet undescribed species of the family Charontidae is also present in the cave (and Gil Wizen might have found a third, possibly new amblypygid species). I was hoping to find some dinospiders (Ricinulei) there, alas, no such luck, but flipping rocks on the banks of Caves Branch River revealed a tiny, equally interesting arachnid, a pygmy vinegaroon (Schizomida). The species found in the Footprint Caves is a yet undescribed species of Schizomus, and I would love to be able to collect some specimens and describe them (I need to look into getting some permits for Belize).

A troglobitic isopod crustacean Troglophiloscia sp.; note its lack of pigmentation and eyes, characteristics typical of cave-dwelling organisms.

A troglobitic isopod crustacean Troglophiloscia sp.; note its lack of pigmentation and eyes, characteristics typical of cave-dwelling organisms.

Silk strands on the cave ceiling, produced by the larvae of predaceous fungus gnats (Keroplatidae: ?Macrocera sp.)

Silk strands on the cave ceiling, produced by the larvae of predaceous fungus gnats (Keroplatidae: ?Macrocera sp.)

Yet the most interesting organism in the cave was a fly. When we shone the light at the low celling of the cave we could see curtains of thin, glistening strands of sticky silk produced by larvae of predaceous fungus gnats of the family Keroplatidae; I have not been able to identify the species that lives in the Footprint Cave, but it is possibly a member of the genus Macrocera (Macrocerinae). The strands spun by the larvae are covered with droplets of oxalic acid, which trap and kill tiny flying insects, mayflies mostly, found in the cave. Members of a related subfamily Arachnocampinae found in Australia and New Zealand are famous for their bioluminescence, but the ones found in Belize are of the non-glowing variety. Still, it was a beautiful spectacle to see thousands of hair-like strands undulate gently in the breeze caused by a person walking several meters away.

The strands are covered with droplets of oxalic acid, which trap and kill unlucky insects, such as this mayfly, that brush against them in flight.

The strands are covered with droplets of oxalic acid, which trap and kill unlucky insects, such as this mayfly, that brush against them in flight.

Everybody was sad to leave the cave, which turned out to be the highlight of our photographic workshop, although the fauna of the rainforest that surrounded the lodge where we stayed was equally interesting. Not being able to collect anything was torture for me, but I hope that some day soon I will be able to come back to Caves Branch, this time wearing only my entomologist’s hat.

A new, yet unnamed species of the pygmy vinegaroon (Schizomus sp.) from the Footprint Cave.

A new, yet unnamed species of the pygmy vinegaroon (Schizomus sp.) from the Footprint Cave.

Blue land crab

Males of the blue land crab (Cardisoma guanhumi) from the Dominican Republic sport giant claws used in territorial display and combat. [Nikon D1x, Nikkor 17-35mm]

Males of the blue land crab (Cardisoma guanhumi) from the Dominican Republic sport giant claws used in territorial display and combat. [Nikon D1x, Nikkor 17-35mm]

Unable to break her ties to the sea, a female blue land crab cautiously approaches the edge of the beach to release her eggs during the full moon. Shecannot swim, thus she must be careful not to be swept away by the waves, and soon she runs back to her burrow in the forest. Her planktonic larvae will develop into tiny crabs in less than two months and then will leave the ocean to begin terrestrial life. [Nikon D1x, Nikkor 17-35mm, flash Nikon SB-28DX]

Unable to break her ties to the sea, a female blue land crab cautiously approaches the edge of the beach to release her eggs during the full moon. She
cannot swim, thus she must be careful not to be swept away by the waves, and soon she runs back to her burrow in the forest. Her planktonic larvae will develop into tiny crabs in less than two months and then will leave the ocean to begin terrestrial life. [Nikon D1x, Nikkor 17-35mm, flash Nikon SB-28DX]

[An excerpt from the book "The Smaller Majority."]