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Gibbous Europa
(Credit: Galileo Project, JPL, NASA)
Tonight is Yuri’s Night, when space enthusiasts around the world celebrate the first human trip to outer space made by Yuri Gagarin fifty two years ago. You can read about Yuri here. It is an excellent occasion to assess what is most exciting in space exploration. Unfortunately nobody has jumped forward to build a floating colony on Venus. Indeed NASA seems rather flat footed lately—building a series of colorless rockets and sending successive similar rovers to Mars. Fortunately there is one exciting mission which still has not definitively been cancelled because of budget stalemate.
Proposed Europa Clipper (NASA)
The Europa Clipper mission is a $2bn dollar project to launch a probe to Jupiter’s moon Europa, a large icy satellite covered in cracked ice. Europa is slightly smaller than Earth’s moon and has a thin oxygen atmosphere. It is one of the smoothest items in the solar system. Astronomers believe that an ocean of liquid water lies beneath Europa which is warmed by tidal flexing (a process which causes orbital and rotational energy to be converted into heat). The surface of Europa is bathed in exotic radiation which rips apart water molecules and leaves oxidants like hydrogen peroxide. All of this means that Europa is the most likely planet in the solar system to harbor unknown life. It has even been theorized that beneath the ice the ocean could have black smoker type environments–and just possibly thermal vent or “cold seep” ecosystems.
Artist’s concept of the cryobot and hydrobot probes (NASA)
Because of this, scientists have been anxious to get a closer look at the intriguing moon. Various proposals have been put forward for missions directly to the moon. The Pioneer and Voyager spacecraft took pictures of it as they flew through the solar system and subsequent missions also took readings and photos—but there has been no Europa-centric mission to really find out about the oceans below the cracked ice. One (amazing!) proposal was to send a nuclear powered melt probe to melt through the ice and sink to the bottom of the ocean, whereupon a mini-sub probe would emerge and explore the extraterrestrial ocean! That plan was shelved because it was too expensive (and nobody could figure out how to sterilize the probe). The proposed Europa Clipper mission is more modest but still quite amazing. Here’s how the Jet Propulsion Laboratory describes it:
The Europa Clipper mission would send a highly capable, radiation-tolerant spacecraft into a long, looping orbit around Jupiter to perform repeated close flybys of Europa.
The possible payload of science instruments under consideration includes radar to penetrate the frozen crust and determine the thickness of the ice shell, an infrared spectrometer to investigate the composition of Europa’s surface materials, a topographic camera for high-resolution imaging of surface features, and an ion and neutral mass spectrometer to analyze the moon’s trace atmosphere during flybys…The nominal Europa Clipper mission would perform 32 flybys of Europa at altitudes varying from 2700 km to 25 km.
That sounds amazing! Join me in lifting a glass to Yuri Gagarin and also join me in hoping that our moribund government funds this far-sighted mission to what might be life’s other home in the solar system!
Yuri Gagarin–the first human to go to space
The Snider-Pellegrini-Wegener fossil map which illustrates how scientists pieced Pangaea together
During the Permian era (around 300 million years ago) the strange slow dance of Earth’s tectonic plates brought together all the world’s major landmasses into the supercontinent Pangaea. Because of its very nature, Pangaea changed the world’s climate in bizarre ways. Baking hot deserts were so far from the coast that they never received rain. Landlocked seas boiled away and left great evaporitic deposits of strange minerals which we still mine and exploit. Huge mountains rose and fell as the continents crashed together.
Pangaea lasted for approximately 100 million years, during a time of tremendous biological upheaval and diversification. The worst mass extinction in the history of life took place during the continent’s heyday (The Permian-Triassic extinction event took place about 250 million years ago). After the great dying, he first dinosaurs and mammals walked the super continent. However this post is not a meditation concerning Pangaea (thankfully– since its history is extraordinarily complicated).
Triassic Pangaea by Richard Morden
The idea which excites me is that Pangaea was only a third of the Earth. The remainder of the globe was taken up by water. Between Laurasia and Gondwana there was a great wedge shaped ocean called the Tethys Ocean (indeed Pangaea looked somewhat like Pacman—as you can see on the beautifully illustrated map by Australian freelance illustrator Richard Morden). Named after a titaness who was the daughter of Uranus and Gaia, the Tethys radically changed shape as the continents separated. Through big parts of its history, large parts of the Tethys consisted of warm shallow continental shelves (which are ideal environments for fossil deposits). Paleontologists and Geologists thus know a great deal about the natural history of the Tethys Ocean.
The remainder of the globe was a single world ocean called Panthalassa (or the Panthalassic Ocean). If you looked at Earth from outer space from a particular angle it would have been entirely blue (which is fitting for “Panthalassa” was not named after any god or goddess but from a Greek neologism meaning “universal sea”). The Panthalassa is not so well known as the Tethys. As Pangaea broke apart almost the entire ocean floor was subducted underneath the North American and Eurasian plates. However Geologists sometimes find tiny distorted remnants which were one part of the gigantic world sea.
A Black Smoker Geothermal Vent
The African Plate and the Indo-Australian Plate meet together deep beneath the surface of the Indian Ocean in a long line of tectonic divergence known as the Central Indian Ridge (CIR). As new seafloor is created hydrothermal vents pour out molten hot fluids rich with minerals and an alien landscape is formed. The hot minerals precipitate to form high cylindrical chimneys called smokers and strange communities of life form along these structures. This ecosystem is entirely based upon chemosynthetic archaea (ancient one-celled life forms which take energy directly from the oxidation of inorganic compounds). Great communities of eyeless shrimp, giant tubeworms, and annelids support themselves on the archaea. Among the strange creatures is a very weird gastropod mollusk, the scaly-foot snail (Crysomallon squamiferum), which is different from every other mollusk (and indeed every other animal) because of the material it uses for its bizarre scale-mail armor.
The Scaly Foot Gastropod (Crysomallon squamiferum)
The scaly foot gastropod has an armored foot which is covered in little scales made of iron sulfides. Additionally the deep-sea snail has a triple layer shell. The outermost shell layer is composed of iron sulfides, the middle is a thick protein coat, and the inner shell layer is composed of aragonite (a calcium carbonate).
I wish I could tell you more about the habits of this snail but since it is found in super heated water at the bottom of the Indian Ocean, it has not been extensively studied. However, The US military is interested in the creature as a possible inspiration for next generation composite military armor so maybe we will all learn more about the scaly foot snail.
Detail of the Foot Armor of Crysomallon squamiferum
Life around a Cold Seep
This week Ferrebeekeeper has been concentrating on the theme of discovering new life—a search which is very much ongoing even in today’s used-up overpopulated Anthropocene world. This concept has taken us to the mid levels of the ocean and the mountain jungles of Thailand and Vietnam to encounter species unknown (like this mystery sea slug, the tiny parasitoid wasp, and even a large hoofed mammal). However what is even more shocking is that our world features entire ecosystems rich with life that have only just been discovered.
A photograph of a pool of brine on the bottom of the ocean
A cold seep is an ecosystem on the bottom of the ocean formed around hydrocarbon-rich fluids which seep out of the earth and either “bubble up” or pool at the bottom of the ocean. The geography of such areas is alien to our perceptions: black pools of asphalt, barite chimneys, and undersea lakes of dense brine (which traps hydrocarbons and sulfites) are surrounded by otherworldly “reefs” of tube worms and benthic mollusks. The tube worms symbiotically partner with bacteria capable of “feeding” off the hydrocarbons while the mollusks filter feed on the archaeobacteria. Whole communities of grazers, scavengers, and predators then form around this base. Such communities are remarkable because they do not rely on photosynthesis as a source of energy and nutrients (much like more famous “black-smoker” ecosystems which are also chemotrophic ecosystems—but which form around hot volcanic vents). Cold seeps themselves were only discovered in 1983! Now that oceanographers know what to look for, cold seeps are being discovered in locations where we would never have looked for large complicated webs of life.
A Map of the collapsing Larsen Ice Sheet
In 2005, an oceanographic research team studying the seas once covered by the Larsen ice shelf (a melting shelf of ice located off the eastern side of the Antarctic Peninsula) discovered a cold seep community thriving in a glacial trough 850 meters (2,800 feet) beneath the ocean’s surface. The scientists found great mats of bacteria living on methane. These bacterial mats were in turn grazed on by strange bivalve mollusks and brittle sea stars. To quote EOS (a journal of the American Geophysics Union):
These results have implications for the discovery of life in extreme environments, including those found beneath the enormous extent of existing ice shelves and large lakes that lie beneath the Antarctic Ice Sheet. Because of its restricted conditions, the seafloor beneath ice shelves may provide a suitable, widespread habitat for chemotrophic systems; given this, there may be many more such habitats waiting to be discovered beneath existing ice shelves….The seafloor beneath Antarctica’s floatingice shelves covers more than 1.54 million square km [Drewry, 1983], an area of the same order of magnitude as the Amazon basin of Brazil or the Sahara desert.
So science is only just beginning to apprehend the sorts of biomes which are found across huge swaths of Earth. There are even more remote areas which are wholly unknown—like Lake Vostok, a subglacial lake wholly isolated from the rest of Earth (including the atmosphere) for 15 to 25 million years. As continental drift and the Antarctic Circumpolar Current froze Antarctica, Lake Vostok was trapped beneath 4,000 m (13,100 ft) of ice, and it has remained so until this year (when an intriguing but sloppy Russian drilling expedition means to pierce the lake). What scientists discover beneath the other ice dwindling shelves, and what the Russians find beneath the East Antarctic Ice Sheet will have broader implications for how we conceive of life on Earth–and beyond.
A watercolor painting by of chemotrophic life by Karen Jacobsen, an artist who has traveled to the bottom of the ocean via bathysphere to record her impressions!
Biologists estimate that there are approximately 8.8 million species of eukaryotes (animals with complex cell structure) currently alive on Earth. So far, humankind has only cataloged 1.9 million species and entire biomes remain largely unknown to us.
Unknown Order of Nudibranch Sea Slug swimming in the depths off Monterey (Image Credit: NOAA/Monterey Bay Aquarium Research Institute)
To illustrate this point, here is a photograph of a completely unknown genus of nudibranch mollusk photographed 1 mile beneath the surface of the ocean near Davidson seamount (which is an extinct underwater volcano just off the coast of Monterey). I wish I could tell you more about the strange mollusk, but this photograph, taken from a robotic deep sea submersible in 2002 is pretty much all that humankind knows about this species. The mission photographed a huge number of other gelatinous creatures in the middle depths of the ocean, and in fact caused scientists to rethink the importance of such animals in the oceanic ecosystem. The Monterey Bay Aquarium Research Institute (MBARI) worked on the mission with the National Oceanic and Atmospheric Administration. Their website explains the robotic study by paraphrasing Bruce Robinson, an ecologist who pioneered the use of robot submersibles:
One of the most important discoveries has been the realization that gelatinous animals are important as grazers and predators that comprise a large percentage of the open ocean animal biomass. Robison estimates that gelatinous animals make up about 40 percent of the biomass in the deep sea water column.
Nudibranch mollusks are largely thought of as colorful predators of the tropical reef, so it is a big deal if they (together with other floating mollusks, cnidarians, and siphonophores) constitute such a substantial percentage of the biomass of the largest portion of the ocean. As an unscientific postscript I think the delicate translucent nudibranch is very beautiful with its alien and ghostlike (and, yes, gelatinous) features.
The same mollusk (Image Credit: NOAA/Monterey Bay Aquarium Research Institute)
Cast your imagination down to the bottom of the ocean—not at a beach or a bright coral reef just offshore, but the true ocean floor—the abyssal plains which cover much of Earth’s surface. Here vast flat swaths of mud lie in black silence. Only the occasional seamount or shipwreck breaks the monotony of plains as big as continents. Tides do not particularly affect the bottom of the ocean. The most violent storms do not perturb the waters. Even humankind’s restless activities, which have so much affected the rest of the planet, mean little here. At first it seems bleak, but soon enough you realize that life is everywhere here. There are spiderfish, lizardfish, deep sea octopuses, bizarre roving sea cucumbers, and all sorts of strange creatures, but we are not here for them. Instead we are concentrating on an inconspicuous worm-like animal. The tiny cylindrical creatures are only 5 cm (2 inches long) and they shimmer strangely when exposed to light. It would be reasonable to assume that they were worms or tiny sea cucumbers, but they are not. The benthic beasts are members of the aplacophora class of mollusks—the naked mollusks. They are presumed to be similar in appearance and nature to the basal mollusks from which the other classes of mollusks have evolved (although both fossil and molecular evidence is frustratingly exiguous). To look at aplacophorans is to see back to the Cambrian (540 million years ago) and to glimpse an even earlier era when the ancestors of the mollusks diverged from the annelids.
Two specimens of the aplacophoran Simrothiellidae (photographed by G. Rouse)
The aplacophoran shine because of tiny calcareous spicules embedded in their skin. There are about 320 known species split between two clades: the caudofoveates and solenogasters. To quote the University of California Museum of Paleontology website, “Caudofoveates are burrowers that feed on detritus and bottom-dwelling microorganisms, while solenogasters feed on cnidarians. Both groups have a radula and lack true nephridia.” There is an even more important distinction between the two different clades: whereas solenogasters are hermaphrodites, caudofoveates have two genders, and reproduce by external fertilization.
Epimenia australis (Photo by R. Willen)
The depths of the ocean are known to harbor animals which have vanished from the rest of the Earth long ago, and such is believed to be the case with aplacophorans. For a half billion years they have gone about their business in a part of the world which is resistant to outside change. The next time you fly across an ocean, imagine all of the naked mollusks in the muck at the very bottom and think about the vast amount of time they have been there.
An Adult Female Blanket Octopus
“Blanket octopus” sounds like an endearing nursery game, but the blanket octopuses are actually pelagic hunters which have adapted to living in the ultra-competitive environment of the open ocean. There are four species of blanket octopuses (Tremoctopus) which can be found ranging from the surface to medium depths of open tropical and subtropical seas worldwide. Because they often live far from any land, some of the methods which other octopuses use to escape predators do not work very well for them. Fortunately Blanket octopuses have adapted in their own unique bag of tricks.
An Adult Female Blanket Octopus
Blanket octopuses are named after the distinctive appearance of adult female octopuses which grow long transparent/translucent webs between their dorsal and dorsolateral arms. Blanket octopuses use these webs as nets for hunting fish, but they can also unfurl and darken their nets in order to appear much larger than they actually are. Since blanket octopuses do not produce ink and can not camouflage themselves as rocks, coral, or sand, they rely heavily on their blankets. As a last resort they can jettison the blankets as a decoy and jet away while the confused predator attacks the highly visible membranes.
Blanket octopuses exhibit extreme sexual dimorphism. Whereas the female octopus can grow up to 2 meters (6 feet) in length, the male octopus is puny and does not grown longer than a few centimeters (1 to 2 inches). Males store their sperm in a modified quasi-sentient third right arm, known as a hectocotylus. During mating this arm detaches itself and crawls into the female’s reproductive vent. As soon as the hectocotylus is detached the male becomes unnecessary and dies.
Male Blanket Octopus
Tiny males and immature females do not have blankets, but they utilize another trick to protect themselves. Because they hunt jellyfish and other hydrozoans, the little octopuses are immune to the potent venom of the Portuguese man o’war. The octopuses tear off stinging tentacles from the man o’war and wield them in their tentacles like little whips to ward off predators.
An amazing illustration of a blanket octopus sheltering in a Portuguese man o’war’s tentacles
The Mountains of Antarctica as seen from the Southern Ocean
The great Southern Ocean which swirls in a clockwise circle around Antarctica is home to many of the Earth’s largest animals. Blue whales come here to gorge on vast schools of krill. Among the icebergs and the towering waves, southern elephant seals (the largest member of the order Carnivora) fight duels to build their harems, and highly intelligent killer whales hunt together in pods. There are populations of sperm whales living in the Southern ocean as well and these leviathans dive to the cold floor of the world hunting for the world’s largest mollusk, a huge cephalopod which can only be found in the Southern Ocean. In fact this bizarre creature, the colossal squid (Mesonychoteuthis hamiltoni) is also the world’s largest invertebrate. Also known as the Antarctic squid or the giant cranch squid, the colossal squid lives in the abyssal depths. Unlike other squid, the colossal squid does not have tentacles–its powerful arms are studded with sharp hooks (much like the long-extinct belemnites). Some of these hooks swivel while others have three barbs in the manner of a fish spear.
The Colossal Squid (Mesonychoteuthis hamiltoni)
The measurements of the colossal squid are staggering. Its eye alone (the largest of any known creature) measures 27 centimetres (11 in). A fully grown adult squid is estimated to be 12–15 metres (39–49ft) long. Although giant squid have longer tentacles, the colossal squid a long stout mantles and are thus much more massive. Their upper weight limits are unknown but are well over 500 kg (+1000 lbs).
The colossal squid is believed to be an ambush predator, which lurks in the depths waiting for chaetognatha, other squid, and benthic fish (such as the Patagonian toothfish) to pounce upon. It is hypothesized that they have a slow metabolism and do no need great reserves of food (unlike the energetic endothermic sperm whales which prey on them). The colossal squid are believed to be sexually dimorphic—the females become much larger than the males.
A rare specimen of colossal squid
There is a reason that so much of this article is couched in ambivalent language such as “estimated”, “believed” and “probably”: colossal squid live in an environment where humankind can barely venture. The colossal squid are fast enough and clever enough to usually evade our nets, lines, and traps (although fishermen trying to catch Patagonian toothfish hooked a 450 kg (990 lb) specimen which was about 39 feet (13 m) long). Additionally our submarines and submersible robots are too slow and noticeable too stalk the squid in the abyssal depths. Other ocean creatures do not suffer from the same problem. Juvenile colossal squid are eaten by beaked whales, elephant seals, sharks, toothfish, and even albatrosses, however the adult squid are so large that only massive sleeper sharks and giant sperm whales can threaten them. Sperm whales are often covered with scars from their battles with the giants but the whales easily have the upper hand. Sperm whale stomachs have been found filled with hooks and beaks (which coincidentally were much larger than those found on the largest squid specimens recovered by humans to date).
Man O’ War (Photograph by Enrique Talledo)
The Portuguese man o’ war (Physalia physalis) is not a jellyfish, in fact it is not a discreet animal at all, but instead a siphonophore—a colonial medusoid made up of specialized animal polyps working together as an organism. These siphonophores have stinging tentacles which typically measure 10 metres (30 ft) in length but can be up to 50 metres (165 ft) long. Being stung by a man o’ war does not typically cause death, but sailors and mariners who have survived the experience assert that it taught them a new definition of agony.
Glaucus atlanticus
But the fearsome man o’ war is not the subject of this post. Instead we are concentrating on the animal which feeds on the man ‘o war (as well as other siphonophores which drift in the great blue expanses of the open ocean). One is inclined to imagine that men o’ war are eaten only by armored giants with impervious skins and great shearing beaks (and indeed the world’s largest turtles, the loggerheads, are the main predators of siphonophores), however another much less likely predator is out there in the open ocean gnawing away at the mighty stinging colonies. Glaucus atlanticus, the blue sea slug, is a tiny shell-free mollusk which lives in the open ocean. The little nudibranch only grows up to 3 cm in length but it hunts and eats a variety of large hydrozoans, pelagic mollusks, and siphonophores (including the man o’ war).
Glaucus atlanticus eating velella colony animal
Although not quite as gaudy as its lovely cousins from tropical coral reefs, Glaucus atlanticus is a pretty animal of pale grey, silver, and deep blue with delicate blue appendages radiating out from its six appendages. The little mollusks live in temperate and tropical oceans worldwide. They float at the top of the water thanks to a swallowed air bubble stored in a special sack in their gastric cavity. Because of this flotation aid, the slug is able to cling upside down to the surface tension of the waves. Since it is entirely immune to the venomous nematocysts of the man o’ war, the sea slug can store some of the man o’ wars venom for its own use. The tendrils at the edge of Glaucus atlanticus’ body can produce an extremely potent sting (so it is best to leave the tiny creatures alone, if you happen to somehow come across them).
Glaucus atlanticus inshore
Each and every Glaucus atlanticus is a hermaphrodite with a complete set of sex organs for both genders. Incapable of mating with themselves they ventrally (and thoroughly) embrace another blue sea slug during breeding, and both parties then produce strings of eggs. The hatchling nudibranchs have a shell during their larval stages, but this vestige quickly disappears as they mature into hunters of the open ocean.
Sealife Mosaic from "the House of the Dancing Faun" in Pompeii (ca. 1st century AD)
So much of Roman artwork is lost. Except in remarkable circumstances, Roman paintings, textiles, and drawings were too fragile to survive the long centuries of neglect. Almost all are now long gone. Fortunately the Romans were masterful mosaic artists and mosaics are durable. Many mosaics concerning all sorts of aspects of classical life have lasted through the millennia. Some of these tile artworks present the loves of gods or the wars of men but quite a few are more humble and show the aftermath of a banquet or fishermen hauling in a day’s catch . Since Romans ate a huge amount of seafood, it is no surprise that many mosaics showcase mollusks of one sort of another. Here is a gallery of Roman mosaics featuring octopuses, squids, bivalves, or snails. I have tried to add as much information as I could but some of the photos I found were poorly labeled
Marine Life Mosaic from House viii in Pompeii demonstrating the vermiculatum technique (ca. 2nd century BC)
Detail of a Roman bath mosaic depicting a murex. (ca. late second to early first century BC)
Floor mosaic from "House of the Faun" Pompeii: Cat with bird, ducks, and sea life.
Ancient Roman Mosaic Prtraying Sealife from the British Museum
Triton with an octopus and squid (Forum Baths, Herculaneum)
Roman Mosaic of an Octopus
Modern mosaic makers were inspired by the Roman example and flamboyant cephalopods are a major theme of contemporary mosaics as well as ancient ones. Here are some modern octopus and squid mosaics for millionaires’ swimming pools, elementary schools, or even everyday bathrooms. Enjoy!
Modern copy of a Roman era mosaic from Milreu, Portugal
A Kraken for the bottom of a swimming pool (by Laurel Studios)
Octopus Mosaic for a public school
Contemporary Octopus Mosaic
A squid mosaic in downtown Pittsburgh, Pennsylvania
Octopus Mosaic from Seattle Country Day School
Navigation Mosaic by Mia Tavonatti
