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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."]

A giant among the smaller majority

Coconut crab (Birgus latro) on Guadalcanal, Solomon Islands [Canon 1D MKII, Canon 16-35mm, speedlight Canon 580EX]

While I can honestly say that there is no animal that I find uninteresting, none is higher on my list of the most amazing animals than the coconut crab (albeit this top place in my ranking is shared by many.) The first thing that you will notice about this crustacean is of course its size – it is huge. In fact, with the maximum leg span of 1 m (~3 ft) and weight of 3 kg (6.6 lb), it is the largest invertebrate animal you will find on land. There exist larger marine crustaceans, and there are many much larger cephalopods, but on dry land the coconut crab is the undisputed champion. It is also incredibly long-lived, for a terrestrial invertebrate, reputedly capable of reaching the ripe age of 40 years.

The chelae (“claws”) of coconut crabs are incredibly powerful, capable of cracking open a coconut shell [Canon 1D MKII, Canon 16-35mm, speedlight Canon 580EX]

From the taxonomic point of view, coconut crab (Birgus latro) is more closely related to hermit crabs (infraorder Anomura) than true crabs (infraorder Brachyura), and you can tell that by, among other things, the presence of only 4 pairs of walking legs (true crabs have 5 pairs.) Another giveaway is its life cycle – following a brief period as pelagic larvae, young coconut crabs carry a shell, just like other hermits. Only after reaching the size of about 10 mm the young abandon the shell, and begin to resemble the adults.

Legs of coconut crabs are of different length, perfectly adapted for climbing coconut trees [Canon 1D MKII, Canon 16-35mm, speedlight Canon 580EX]

The transition to the terrestrial lifestyle is more complete in the coconut crab than in any other land hermit. Not only did this species eschew a protective shell of a snail, thanks to its hard, resistant to water loss abdomen, but its senses are more akin to those of insects than crustaceans. All other terrestrial hermit crabs can only detect smells if the air humidity is very high – their olfactory organs are still those of an aquatic animal, and can only respond to chemical cues if they are dissolved in water. Coconut crabs, on the other hand, can smell things in dry air, indicating the development of land-adapted olfaction.

Like all arthropods, coconut crabs need to molt periodically, and the process takes place in a deep underground burrow [Canon 1D MKII, Canon 100mm, speedlight Canon 580EX]

Despite the common name, coconut crabs don’t feed only on coconuts. Like many decapod crustaceans, they are opportunists and will eat anything organic that they can put their powerful claws on (so powerful are their claws that you can easily lose a finger if you are not careful when playing with one.) In addition to cracking coconuts, they have been known to hunt shore birds sitting on their nests at night, steal dog food from people’s backyards, and will gladly eat any kind of carrion. This last habit had them implicated in the disappearance of the famed pilot Amelia Earhart, and you can sometimes hear speculations that her body might have been dismembered and eaten by coconut crabs somewhere around the archipelago of Kiribati after her plane’s crash.
Even if true, it is the crabs that suffer more from our appetite for crustacean flesh than the other way around. Their meat is purportedly deliciously coconutty, and there is plenty of it in an animal of their size. Nor surprisingly, they have been overharvested within most of their range around tropical islands of the Pacific and Indian Ocean, and have virtually disappeared from many places where they used to be common. Many countries that still have these magnificent animals now have laws protecting them, or at least limiting their harvest (one of them is the United States, which protects the crabs on the island of Guam), but an official conservation assessment of this species across its entire range has never been done. Therefore, the coconut crab is still listed as Data Deficient by the IUCN Red List, and its trade is not regulated by CITES. Hopefully this will change in the near future, it would be an unforgivable tragedy to lose this wonder of crustacean evolution.

Live young coconut crabs for sale at a seafood market on Okinawa, Japan [Canon PowerShot SX100 IS]

The benefits of constant rain

Even in the middle of the day, forests of New Guinea can appear dark, saturated with water and engulfed in a perpetual mist. [Canon 1Ds MkII, Canon 16-25mm]

I am not a big fan of cold, rainy days, like the one we are having today in Boston, and so I need to remind myself that this type of weather actually produces one of the richest, life-friendly environments imaginable. Not in Massachusetts, however, but in the mountains of Papua New Guinea.

In 2009 I spent a couple of months on the islands of New Guinea and New Britain, conducting a survey of katydids and related insects, which revealed that over 60% of katydid species there were new to science. This blew my mind, but I was also astounded by the preponderance of organisms and behaviors that I always thought of as quintessentially aquatic, which I nonetheless found on land.

Male of a yet unnamed, new species of tree frog (Oreophryne sp. n.) guarding a clutch of eggs in the Muller Range of PNG [Canon 1Ds MkII, Canon 100mm macro, 2 speedlights 580EX]

Few places are more humid than rainforests of New Guinea. Annual rainfall in some areas reaches seven thousand millimeters, or even a staggering twelve thousand millimeters (or nearly forty feet) per year! The atmosphere is saturated with moisture, and thick mats of mosses and lichens trap and store huge amounts of water. Yet at the same time many parts of the island are virtually devoid of streams, rivers, or any large bodies of standing water. This is due to the geological composition of its surface, which in many places consists of karst, a formation in which the underlying limestone layers have been dissolved, forming countless sinkholes and fissures. This prevents the accumulation of surface water, forcing organisms that rely on its presence for their reproduction and development to find other solutions.

A semi-terrestrial naiad (nymph) of a damselfly (Papuagrion sp.) on a Pandanus leaf. [Canon 40D, Canon MP-E 65mm, 2 speedlights 580EX]

Frogs are organisms whose early development requires an aquatic habitat, an inconvenient remnant of their early evolutionary history. In most species females lay their eggs in streams and ponds, and developing tadpoles use their gills to breathe under water. But on New Guinea, where surface water is scarce, many species have evolved strategies that allow them to bypass a free-living tadpole stage entirely. Rather than laying hundreds or thousands of small eggs and leaving them to their own devices in the water, they produce a handful of very large eggs and take care of them until they are ready to hatch. Each egg contains enough nutrients, in the form of a large yolk reserve, that allows the embryo inside to complete its development into a tiny, independent froglet. Unlike reptile or bird eggs, frog eggs lack a hard, water-impermeable shell, and risk their desiccation if not protected and moistened regularly. For this reason, one of the parents stays with the eggs and safeguards them throughout their development. In frogs of the genus Oreophryne, the male guards the eggs suspended in a clutch underside a leaf, and leaves them during the day to go hunting for insects, but comes back every evening to moisten them with water and shield them from harm. After a few weeks, young frogs are ready to become independent, and break the walls of their miniature aquatic cradles.

Pink, terrestrial amphipod crustacean from the Muller Range of PNG [Canon 40D, Canon MP-E 65mm, 2 speedlights 580EX]

But tadpoles with terrestrial development were not the only animals that seemed out of place on the forest floor of New Guinea. High in the mountains of the Muller Range we found damselfly nymphs crawling on leaves of Pandanus trees, and below, in the leaf litter, pink amphipod crustaceans mingled with ants and beetles. I also saw in those forests land crabs, flatworms, and sea anemones. Well, the last ones turned out to be strange mushrooms of the genus Aseroë, but for a second I almost believed in the existence of terrestrial sea anemones – if they were to live on land, rainforests of New Guinea would probably come closest to their underwater habitat.

Ok, now I feel a little better about the rain behind the window.

(You can read more about the amazing life forms on New Guinea in my book “Relics: Travels in Nature’s Time Machine”, from which I took a fragment of this text.)

Sea anemone mushrooms (Aseroë sp.) from New Britain [Canon 1D MkII, Canon 24-105mm]