The Sea Hare Cometh

I pick my way along the beach

The sky is blue, the tide is out,

Exposed pools glitter; down I reach

To touch a sea hare on the snout.*

–

*(Perhaps it’s not quite etiquette

To poke all creatures, come what may,

The venomous, the delicate,

I’m like a little kid that way.)

The sea hare is a noble beast,

With body plump and soft and flaccid

On vegetation sea hares feast,

Or will, ’til oceans turn to acid.

–

Two adaptations well worth noting

For those who’d study the hare of the sea:

(And many more paragraphs I’ll be devoting

To this humble invert, so bear with me.)

–

First, we have the rhinophores

Which jut out oddly from the head

They’re used to smell the rocky shores

In search of food to stay well-fed.

–

(They’re also how our friend the hare

Received its name, although I pose

Why “marine koala bear”

Isn’t the handle taxonomists chose.)

Second, for robust self-protection

The sea hare can let loose a dye

An inky blast to escape detection

Just like immobile octopi.

–

Alas, the sea hare does not squirt

When I give it a gentle prod

It lies unmoved, blase, inert

A fleshy, nonplussed, oozy wad.

–

So I leave my spineless friend,

And continue with my quest

Which never will draw to an end:

To hunt down creatures to molest.

The tide pools of Playa Gigante, brimming with marine invertebrates just begging to be poked, prodded, examined, inspected, and otherwise harassed.

One Invasive Lionfish Down, A Hundred Thousand to Go

The Caribbean lionfish epidemic has been covered in FishiLeaks before, so all three of my devoted readers should be well aware of this pernicious menace. Lionfish can devour up to 80% of native fish larvae on a given patch of reef and, according to one NOAA marine biologist, could be the worst (ie, most rapacious and unstoppable) marine invaders ever. They make lake trout look downright inconsequential.

A juvenile lionfish looking less insidious in its natural habitat: Sipadan Island, Malaysia.

Still, I was taken aback to see a common lionfish, Pterois miles, lounging beneath a rock within fifteen minutes of my entering Utila’s waters on my first day in the Caribbean. I felt like I’d stumbled upon an infamous criminal, his face recognizable from Wanted posters, nonchalantly drinking a cup of coffee in a diner booth. Gaudy pectoral and dorsal fins betrayed the lionfish’s presence; I imagined its poisonous spines safeguarded a belly full of innocent juvenile parrotfish.

I swam back to the dock from which I’d been snorkeling and got the attention of a divemaster. I told him I’d seen a lionfish, and I told him I needed to kill it. He disappeared into the office and returned with a sort of trident, three sharp metal prongs at the end of an aluminum shaft. A long rubber strap dangled from the shaft’s other end. A small crowd gathered as he demonstrated the trident’s use: you hold the rubber strap like this, see, and pull the spear back against your forearm, stretching the strap tight. Then you just let go.

I tried it. The spear rocketed forward, propelled by the release of tension in the rubber sling. Wish me luck, I said.

I swam back to the rock wall and there was the lionfish, insouciant as ever, emboldened by the lack of predators in its non-native hemisphere. I cocked the spear and let fly from a distance, cautious of both frightening the malignant fish away and contacting its spines. The spear clattered ineffectually against the rocks; the lionfish darted several feet but, incredibly, did not flee. I fired again, missed again, and the fugitive retreated further into its rocky stronghold.

Did I hesitate, feel remorse, or dwell on the moral complexity of slaughtering an essentially blameless living thing as I pulled my spear back for my third shot? I did not.

The justly impaled invader wriggled for a moment on the tines of the trident and went still. I swam back to the dock and pulled myself aboard, cognizant that my grin was, perhaps, slightly more fierce and triumphant than was warranted by murdering a beautiful tropical fish no larger than my fist. No matter.

I got one, I said.

It’s Raining Fish. Hallelujah?

With no warning whatsoever some two thousand sardines and mackerel plunged to earth from the clouds… The fish were fresh, still with a smell of the sea about them. The fish struck people, cars, and roofs, but not, apparently, from a great height, so no serious injuries resulted. It was more shocking than anything else. A huge number of fish falling like hail from the sky – it was positively apocalyptic.

–Haruki Murakami, Kafka on the Shore

I thought of that passage this during the (now mercifully subsiding) furor over the Great Arkansan Birds Incident. Despite the maelstrom of implausible theories – fireworks, atmospheric contaminant, portent of The End of Days – nobody thought to propose that an elderly, mentally-challenged Japanese man with paranormal psychic abilities might be wandering around Arkansas conjuring plummeting animals, which honestly makes about as much sense as most of the explanations.

Sign of the Apocalypse, or the work of Nakata? Very probably neither. Courtesy of Stephen B. Thornton.

I agree with the Smithsonian bird curator who thinks that the bird kill is an arbitrary event, and not even an uncommon one, that’s become an infectious meme thanks to our innate propensity to spot patterns and events of great significance where none exist*. After the first bird kill was reported, news editors got it into their head that this was a Story, and began reporting mass animal deaths that ordinarily go undocumented.  Large-scale animal kills happen, and, while I’d be the last guy to dismiss the possibility of the bird kill being anthropogenic in nature, they do happen naturally – every other day, according to federal records.

It’s ironic that the Beebe incident has us all so riled up, because things occur in nature that are a lot weirder than the so-called Aflockalypse. Even Murakami’s vision – fish falling like rain – has a basis in reality. In Honduras, in fact, it’s a regular occurrence.

Nearly every year, between May and July, the Departamento de Yoro (Honduras is divided into eighteen departments) experiences La Lluvia de Peces – the Rain of Fish.

La Lluvia begins with an intense storm: wind, torrential rain, thunder, the works. Except that after the storm clears, instead of merely puddles and rivulets, the ground is strewn with hundreds of writhing, silver fish, deposited as if by divine intervention. Joyful villagers from the town of Yoro swarm the sopping fields and collect the flopping fish in baskets. It’s apparently quite a spectacle, and so predictable that there’s even a festival organized around it.

Where my ichthyologists at? Courtesy of Atlas Obscura.

 

A lot weirder than the Arkansas bird kill, right? But, although there’s plenty of head-scratching and Praise-the-Lord-ing during La Lluvia de Peces (a Spanish priest claimed that he induced the fishfall by praying to god for sustenance), there are also credible scientific hypotheses that attempt to explain the piscine apparition.

First, the prevailing wisdom: the fish are sardines from the Atlantic Ocean, sucked up and deposited by a waterspout. This is the most common explanation, the one favored by the people of Yoro; and such ‘animal rain’ is actually not without precedent. But the waterspout hypothesis relies a little too heavily on coincidence: are we meant to believe that during the same months every year, a waterspout encounters and scoops up a school of sardines, and then unerringly transports it to the exact same tiny village? And that the waterspout lays down the fish so delicately that they’re evidently uninjured by the ordeal?! Impossible, maybe not; but far-fetched? Extremely.

Mmmmm... I'm skeptical. Courtesy of the Many Faces of Spaces.

 

The alternative explanation holds a little more water. According to a team of National Geographic researchers who visited Yoro in the 1970s, the fish are blind. This fact suggests that the fish are subterranean in origin, since by and large troglodyte species have lost the use of their eyes. The hypothesis, then, is that the heavy rains flood underground rivers and force the fish into the open through crevices in the fields. The rains occur at the end of prolonged dry seasons; so perhaps the fish, with their underground rivers drying up, are actually drawn to the surface by the sudden precipitation. This, to me, sounds a lot more plausible than a literal Fish Rain.

The strangest aspect is how little we know about the fish themselves. You would think that a high-profile biological mystery would be the subject of much scientific inquiry, yet La Lluvia is weirdly understudied. A National Geographic team went down to Honduras in the 70’s, yet their expedition raised more questions than it answered. No footage or photography survives (not on the Internet, anyway), and no article about the phenomenon ever appeared in the magazine. The NG team claimed that the fish were blind, thus originating the subterranean stream hypothesis; but townsfolk say that the fish have functional eyes. The NGers said the fish were a unique species previously unknown to science; the townsfolk descibre them as common, with one faction calling them sardines and another declaring them a freshwater fish.

Fish out of water. BUT HOW DID THEY GET THERE? Courtesy of The Many Faces of Spaces

About all anybody can agree on is that fish that fall (or ascend) during La Lluvia are silver, 12 to 15 cm long, and taste perceptibly different than fish procured from other sources. If they really do arise from caves, let’s hope the flavor discrepancies aren’t due to heavy metal contamination or agricultural runoff in the groundwater.

Well, so, the takeaway from all this? Nature does weird stuff all the time – stuff that’s a hell of a lot less explicable, and more fascinating, and more quasi-religious if you’re inclined in that direction, than a few birds falling out of the sky. These are dark times in many respects, and apocalypse seekers can find harbingers much more ominous than a few, quite possibly perfectly natural, fish and bird kills.

Harbingers like, say, the literally hundreds of species that go extinct every week. It’s possible that over a thousand unique species have vanished from existence since this whole Aflockalypse began. As long as we’re in the mood to wring our hands over animal deaths, let’s wring them over reefs and rainforests too, shall we? I have hope that the Aflockalypse’s impact will ultimately be positive, insofar as it forces people to confront the possibility of anthropogenic environmental destruction (an especially ironic outcome if the deaths turn out to be natural in cause).

*Footnote: The anthropologist Pascal Boyer has one of those evolutionary theories that sounds like a concocted just-so story but is pretty cool anyway: that ascribing significance in random happenstance is an evolutionary adaptation, and also the reason people believe in God. Early humans found it advantageous to overzealously detect agency – imagine, if you will, two cavemen, each of whom hears a rustle in the branches overhead. The first caveman assumes that he’s merely hearing the wind and blithely goes on foraging, but wouldn’tcha know, the rustle actually represents the stalking maneuvers of a leopard, who promptly devours the caveman, leaving behind only a stone adz for later anthropological discovery.

In such a perilous climate, Boyer theorizes, it was advantageous to spot an agent behind stimuli – the caveman who assumes that the rustle is a leopard, of course, is the one who survives. (Within reason – if you drop your basket of berries and flee every time a twig snaps, you’re at a pretty serious disadvantage, too.) That explains our contemporary reliance on religious and paranormal explanations to random events: the cognitive structures in our brains that detect agency are set to Hyperactive. Again, it’s a neat idea, but one that I’m not sure is backed by much science.

***

Big hat tip to Cephalovefor featuring FishiLeaks in this month’s Circus of the Spineless, a blog carnival about the world of invertebrates. (He even called FishiLeaks “the cleverest blog title I’ve seen in a while.” I’m sticky!)

And lastly but not leastly, I’m finally making the move to Utila Island, Honduras this week! Expect FishiLeaks posts to become more frequent, briefer, and filled with pictures from my rockin’ new camera as I advance toward DiveMastery. Also, whale sharks. Just sayin’.

Turtle Crap: It’s What’s for Dinner (if you’re a batfish).

The batfish* is one of the most common reef denizens in Southeast Asia, and also one of the most pleasant. They’re large, triangular-bodied fish, and they move with the undisturbed placidity of organisms that are neither predator nor prey. They tend to congregate in schools of anywhere from 10 to 100 individuals, and resemble nothing so much as beautiful, silvery sheep.

*According to most guidebooks, “batfish” is synonymous with “spadefish.” But in reality the spadefish make up an entire family, Ephippidae, of which batfish (genus Platax) are merely the largest component. All batfishes are spadefishes; all spadefishes are not batfishes. Get it, got it, good. (The term “batfish” can also refer to a separate family of crazy-looking bottom dwellers, cousins of anglerfish, but that’s not what we’re talking about here.)

Batfish are often seen glued to the hips of green turtles, the awkward Sancho Panza to the reptile’s Don Quixote. But they’re not squiring the turtles – instead, batfish eat turtle feces, fresh from the source.

That just could not look any tastier than it does.

I haven’t been able to find much information about what, exactly, makes turtle droppings so scrumptious for batfish. Green turtles and batfish have similar diets, heavy on vegetation and small crustaceans, so it could be that batfish simply have an easier time breaking down food that’s been pre-digested; or perhaps the turtles actually produce and excrete some salutary nutrient. Whatever the case, nearly every swimming turtle is accompanied by a batfish escort.

Thanks to their compatible diets, batfish are capable of playing the same ecological role as turtles: top-level lawnmowers. This is important, because in areas that have been denuded of turtles, dugongs, and large fish, harmful seaweed frequently proliferates and chokes out coral. While other herbivorous fish are unwilling or unable to make a dent in the thick vegetative mats, batfish chow down on the seaweed and prevent it from becoming hopelessly overgrown. Without batfish, reefs would be far more vulnerable to weed invasion.

Batfish are also one of many fish varieties whose juveniles differ dramatically in appearance. Young batfish are vertically elongated, as though their entire bodies consist of magnificent tails. As batfish age, they slowly fill out horizontally; they transform from elegant juveniles into ungainly adults.

This youngster imitates an inedible flatworm, and does it well. Courtesy of http://www.seaphotos.com

The reason for their unusual juvenile morphs is mimicry. Although adult batfish are too large to be frequently preyed upon, the young make tasty morsels. Thus they’ve evolved unpalatable shapes to avoid predation. Fascinatingly, each species of batfish imitates something different – for example, young round batfish resemble floating leaves. Other species mimic crinoids (echinoderms known as feather-stars), clumps of seaweed, and poisonous flatworms. (No reports on whether batfish are yet evolving to mimic floating plastic bags, although I suspect it’ll be any day now.)

Apparently there are Ephippidae in Caribbean waters, so we’ll still get our spadefish fix in Honduras. The five species of the genus Platax, however, are endemic to Indo-Pacific waters, so I may have seen my last true batfish for quite a while*.

*In classic fashion, everybody agrees there are five species, but no one can agree about what they’re called. For example, the species that I refer to as the Pinnate Batfish is, according to the website What’s That Fish?, also called the Shaded Batfish, Red Rimmed Batfish, Red-stripe Batfish, Red-faced Batfish, Red-faced Orbic Batfish, Red-finned Batfish, Longfin Batfish, Long-finned Batfish, and Dusky Batfish. I mean, come on.

***

Finally, FishiLeaks is excited to announce the arrival of this month’s Carnival of the Blue, hosted by the estimable Beach Chair Scientist. CotB is a compilation of the month’s best ocean blogging, and my post about moray eel anatomy and behavior made the cut! There’s all kinds of cool stuff in this month’s edition; check it out.

I know hybridization is bad and everything, but is it really too much to ask one walrus and one orca to get it on?

According to mammalogists in Nature, loss of Arctic sea ice could lead to the hybridization of certain marine mammals.

Killer Whalerus, scourge of the polar seas.

Well, okay, not really. But holy crap would that be awesome. The animals that are actually in danger of hybridizing include several seal species, e.g. ribbon seals with harp seals; narwhals with belugas; and right whales with bowhead whales.

This is especially bad news for right whales, as the North Polar sub-population consists of fewer than 200 individuals. With sea ice diminishing, the barriers that separates right whales from bowheads will eventually vanish – potentially leading to the mixing and sublimation of the genes that make right whales unique. These unique genes are precisely adapted to the North Polar sub-population’s niche, and if they’re diluted the population may suffer a serious decline in fitness.

Mammologists claim that there are three distinct subspecies of right whale, which haven't bred in bewteen 3 and 12 million years. Amazngly, they figured this out not only by testing the whales, but by running DNA tests on the separate species of lice that colonize each whale. Image courtesy of http://www.socalrangecomplexeis.com

Genetic diversity is what allows species to adapt and survive during periods of rapid and extreme change – like, say, the melting of all the sea ice. When genetically distinct populations interbreed, oftentimes the resultant chimera is less fit than its parents, and the entire gene pool grows more homogeneous, reducing adaptive potential. And, although whales haven’t yet begun to interbreed (the paper is merely speculative), polar and grizzly bears have, perhaps as a consequence of range shifts caused by climate change. Yikes.

A pizzly, aka grolar, bear. Nothing about this image really suggests that it's a hybrid; apparently there are some brown splotches on the flanks. These guys, meanwhile, look a little too pleased with themselves. Image courtesy of National Geographic.

On the other hand, mingling sub-populations isn’t always bad news. In fact, the study of island biogeography suggests that small, isolated populations are at greater risk of being wiped out by random fluctuations or freak tragedy (disease, famine, etc.). The elimination of sea ice barriers might therefore help sub-populations like the North Polar right whales, by providing them an important influx of new individuals to safeguard against sudden population crashes. And it’s possible that those bowhead whales possess some useful genes, too, that will actually bolster the right whales’ fitness.

There’s something psuedo-eugenic about rejecting hybridization in all cases, considering that many contemporary species are the byproducts of commingling. Species aren’t static; in fact, preventing hybridization may stifle evolution. The goal of conservation should be to maintain populations’ evolutionary potential, not to keep them preserved in glass.

Still, adaptive radiation – the evolution of species to fill every available niche – is what makes ecosystems resilient and productive, and hybridization negates adaptive radiation and its benefits. Environmental managers shouldn’t necessarily stamp out every hybrid, but have to consider culling ones that are the products of anthropogenic changes. In the case of salmon, for example, farmed fish have been escaping and mating with wild fish for many years, and there’s evidence that wild salmon are losing their migratory skills as a result.

All of that said, I think it’s pretty clear that a killer whalerus would dramatically enhance both species’ fitness, and oh by the way be totally effing awesome.

A Diver’s Guide to Sipadan Island (and a good excuse to post more great pictures).

Last week I posted a geological history of, and introduction to diving at, Sipadan Island, one of Jacques Cousteau’s favorite dive spots. Today I’d like to offer some advice to intrepid divers considering a journey to Sipadan.

A batfish photo-bombs a picture of a Sipadan coral reef.

In 2005 Sipadan was declared a national park, an enormous win for conservationists. The designation not only banned fishing* and development on the island, it also curtailed diving. Today, diving at Sipadan requires a permit, and only 120 permits are issued daily. Demand far outstrips supply, and, although it’s possible to sneak in off the waiting list, tourists should make reservations with a dive shop and secure their permits several months in advance. The waiting list is a dicey proposition: we saw many waitlisters  sitting glumly on the verandas of their bungalows, like grounded passengers in a snow-bound airport.

*Fishing at Sipadan is prohibited, but the no-take zone only extends for less than a kilometer around the island. Trawlers stalk the horizon, prowling for fish who stray from the protected area. Consequently, while divemasters claim that protection has helped those fish whose ecology keeps them close to the reef, the pelagic, or open-ocean, fish haven’t bounced back.

Thanks to the permitting system, most divers are only able to visit Sipadan for a day or two. Maximize your brief trip by making sure your shop takes you to the following three sites: 

Drop-Off / Turtle Cave

Geography: Back when resorts still held the island hostage, this was considered the best beach dive in the world. Now you start from a boat, but it’s still incredible – a precipitous plunge down to Turtle Cave, a maze of limestone caverns filled with the skeletons of turtles who got lost in the labyrinth and perished. Unfortunately you can’t enter the cave proper unless you have cave-diving certification (silly turtles), but all divers get to hang out in its mouth, which is still pitch-black and eerie and un-freaking-believably cool.

Trevally pour from the mouth of Turtle Cave. I may or may not have written this blog post as an excuse to post pictures.

What to Watch For: The mouth of the cave is home to a school of trevally, and seeing the fish gleam silver in the darkness is chilling and gorgeous. After emerging from the cave, we saw harlequin sweetlips and midnight snapper in large numbers. Watch out, too, for longnose hawkfish, pinkie-length orange fish which take up residence in Gorgonian sea fans. Despite their benign appearance, they’re fearsome predators, at least if you’re a larval crustacean.

Mild-mannered longnose hawkfish by day, cold-blooded devourer of all things swimming by night.

Barracuda Point

A black-tipped reef shark chillaxes in the currents of Barracuda Point.

Geography: The main draw at Barracuda Point is the famous “barracuda tornado,” a schooling vortex of thousands of great barracuda, and the dive begins wherever the tornado is. If the boat driver can’t find the tornado, as was the case during both of our dives there, you follow a rock wall for half an hour and then slowly make your up a broad, sandy-floored valley with steep coral embankments.

What to Watch For: The barracuda, dummy. (Check out this totally great barracuda ID guide for a good fish-related time, by the way.) We didn’t dive amongst the ‘cuda, but we did manage to snorkel with them. Barracuda detest divers, and it’s actually possible to get closer snorkeling than diving; so we didn’t get shafted by any means.

The Point is also home to enormous schools of jacks and innumerable black-tipped reef sharks. Strong currents whip through the valley, and the sharks lie contentedly on the sandy channel floor and enjoy the salutary effects of water rushing through their gills.

A lone chevron barracuda wonders how exactly he got separated from like 3000 of his friends.

Hanging Gardens:

Geography: Classic Sipadan drift dive, with some of the island’s fastest currents. The Conveyor Belt of Awesomeness is almost too fast on this dive, and at times it’s impossible to examine organisms along the coral wall without being whisked away by the inexorable currents. But the gorgeous, radiant garden at the dive’s conclusion more than makes up for being hustled along on the way there.

What to Watch For: Maybe we caught Hanging Gardens on a good day, but the quantity and diversity of life here surpassed any other site. Sightings included a school of bumphead parrotfish, enormous bucktoothed coral grazers that cruise reefs like marine bison, leaving contrails of crushed coral in their wake.

A zeppelin-sized parrotfish cruises the reef, looking, as always, for something crunchy to devour.

We also spotted a Napoleon (aka Maori) wrasse: a truly immense fish, pushing two meters long, that zoomed past us against the current. Napoleon wrasse are experiencing a precipitous decline – like another massive sea creature, the blue whale, the wrasse’s huge size engenders long lives, slow metabolisms, and, unfortunately, birth rates too low to rejuvenate depleted stocks. We were fortunate to see one.

A fish market in Sabah, Malaysia.

All Sipadan trips are based from nearby Mabul Island, itself a muck-diving haven. On Mabul, traditional fishing villages uneasily cohabit with a dozen or so dive shops – uneasily, because the villagers over-harvest species, practice shark-finning, don’t always respect no-take zones, and generally fish in ways that are inimical to a paradisaical diving atmosphere. Then again, if I were a Malaysian villager, I wouldn’t want to abdicate my family’s traditional grounds just so white people could spectate there, either. To both parties’ credit, it seems like the shops and the fisherpeople have taken steps to cooperate on conservation initiatives, and live more harmoniously now than they once did.

We dove with a shop called Scuba Junkie, which has one big thing going for it: it begins its Sipadan trips an hour earlier than any other shop, meaning that you can squeeze in four daily dives instead of three. That alone is enough to recommend SJ – which, for the record, has lots of other stuff going for it, including great equipment and amenities, a nerdily enthusiastic and knowledgeable staff, and glorious quantities of buffet food.

The takeaways from this post: dive with Scuba Junkie; visit Turtle Cave; develop a healthy fear of longnose hawkfish.  (That last point was really intended for all my larval crustacean readers.)

Moray Eels Do Things That Will Blow Your Mind

The moray eel thrusting its head from a crevice, jaws agape, is an iconic underwater tableau, recognizable even to those unfortunate souls who care nothing for marine life.

A fimbriated (aka spot-face) moray gives me the evil eye in the Perhentian Islands, Malaysia.

At least in Malaysia, where I’ve done most of my diving, morays are common, but never does the thrill diminish. I normally try to avoid anthropomorphizing animals, but with morays I can’t help it: the grin-like curvature of the jaws, and the apparent intelligence with which they regard passing divers, suggests an eerie sentience.

As it turns out, morays may be among the world’s smartest fish, exhibiting the kind of complex behavior we usually associate with chimpanzees. At the very least, they display hunting adaptations that strike fear in the hearts of every reef fish.

First, the way morays swallow their prey is unique in the animal kingdom, and very different from the way other fishes go about ingesting their prey. From the University of Washington’s Biology of Fishes:

Generally speaking, the vast majority of living fishes are gape and suck feeders. They feed by opening the mouth while simultaneously lowering the mouth and expanding the sides of the mouth cavity. This great and sudden increase in volume creates negative pressure (i.e., a vacuum), which, in turn, results in a sudden rush of water into the mouth. When directed adequately by the predator, it’s this sudden rush of water that carries or pulls prey into the mouth to be swallowed.

That’s an ingenious system, and incidentally describes how I eat most baked goods, but morays can’t use it. Owing to their long, serpentine bodies, their heads are simply too narrow to create enough negative pressure to feed by the gape/suck method. They can’t expand their mouth wide enough to induce the vacuum.

Despite being unable to gape/suck its prey, this moray won't go hungry.

But don’t feel too bad for morays, since they’ve evolved an incredible alternative to gaping and sucking: pharyngeal jaws.  These are a second pair of jaws deep in the moray’s throat, operated on a kind of a spring. The moray grips its prey in its primary jaws; then, when the eel is ready to swallow, it launches the pharyngeal jaws up into its mouth at high velocity, uses them to grab the prey, and drags the hapless fish into the esophagus. If you’ve ever seen the Alien movies, this slow-motion clip will look familiar (courtesy of YouTube user sciencetranslator). The white protrusion at the end isn’t the tongue, but those second jaws:

Crazy, right? Pharyngeal jaws are just bonkers. A few other fish possess them, but those fish’s pharyngeal jaws are stationary in the back of the throat, and merely used to grind or crush food. Morays’ pharyngeal jaws not only leap forward, they’re studded with long, curved teeth. Contemplating the evolution of pharyngeal jaws is mind-blowing. (So, too, is the fact that moray anatomy wasn’t explicated until 2007.)

But that swallowing system isn’t the moray’s only amazing hunting adaptation. In fact, it might not even be the coolest.

Giant moray eels (Gymnothorax javanicus) in the Red Sea do something that, as far as humans know, no other fish does: they hunt cooperatively with another species.

In 2006, a team of marine biologists in the Red Sea observed a remarkable behavior: groupers, another big predatory fish, approaching giant morays in their crevices and making a strange, rapid head-shaking motion – a sort of summons:

…after which the morays would leave their holes and join the grouper in open water. Morays are nocturnal ambush feeders, so swimming freely in broad daylight is bizarre behavior for them – let alone in the company of another predator. (I’ve always found the sight of swimming morays, their exposed bodies wrinkled and writhing, a little illicit, like walking in on somebody changing.)

So: what’s the point of this partnership? The eel and grouper are hunting buddies. Groupers pursue reef fish in open water, while morays corner their prey in cracks and crevices. As the study’s authors put it,

The hunting strategies of the two predators are therefore complementary, and a coordinated hunt between individuals of the two species confronts prey with a multipredator attack that is difficult to avoid; prey are not safe in open water because of the grouper hunting strategy but cannot hide in crevices because of the moray’s mode of attack.

Sure enough, the study found that the groupers were substantially better at hunting when accompanied by the eels. (The eels also ate well with the groupers, but since it’s almost impossible to observe an ambushing moray in action, the authors couldn’t compare rates.) Additionally, the authors found that hungry groupers were far more likely than well-fed ones to make the head-shaking motions and ‘recruit’ the eels, supporting the notion of deliberate hunting coordination.

Before we hail the moray and grouper as a glorious example of bipartisanship, bear in mind that neither animal is sacrificing anything for the sake of the other. Both species are simply trying to maximize their own welfare; it just so happens that cooperation helps them do so. This sort of interspecies commensalism is almost undocumented in Kingdom Animalia. The study makes a fascinating point: the fact that groupers and eels swallow their prey whole, instead of gnawing, chewing, or tearing, may be critical to their cooperation. Perhaps, say, lions and leopards don’t hunt cooperatively because they’d wind up fighting over the carcasses.

I highly recommend that you read the discussion at the end of Interspecific Communicative and Coordinated Hunting between Groupers and Giant Moray Eels in the Red Sea. Suffice to say, it will make you reconsider the ostensible intelligence gap between primates and fish – either they’re smarter than we think they are, or our allegedly unique abilities to communicate and live mutualistically aren’t so unique. I’m sure that as our understanding of ecology deepens, we’ll find many more examples of creatures that rely on each other not only via unconscious food webs, but through deliberate cooperation.

Maybe I’m still wrong to anthropomorphize the moray, but I bet there’s more going on in that head than pharyngeal jaws.

Small Fish/Big Pond Sunday

In which we explore happenings in the hydro- and blogospheres.

1) Most ocean enthusiasts know all about the lionfish invasion that currently plagues America’s eastern seaboard and the Caribbean. Lionfish, introduced to the Eastern hemisphere by aquarium traders in the 1980’s, are voracious predators of juvenile fish and are fast becoming the dominant species on many Florida reefs, with predictably catastrophic ecological consequences.

Common lionfish I photographed in its natural habitat: Perhentian Islands, Malaysia. We're accustomed to associating invasiveness with ugliness (rats, pigeons, cane toads) but lionfish are a good reminder that beautiful animals can be insidious little bastards too.

So: how to get rid of ’em? Well, the New York Times has this entertaining video about lionfish tournaments, in which teams of divers compete for $1,000 by killing as many of the invaders as they can. (Or maybe it’s only entertaining to people who professionally killed invasive fish for a summer – I dunno.)

One of the many things I appreciate about the video is that it depicts divers as active managers of ecosystems, warriors on the front lines of reef degradation. The diving community represents a vast potential pool of environmental technicians, and aside from the occasional reef clean-up this potential goes largely untapped. The vast majority of the divers I’ve met would love to be more involved in reef protection.

2) In Japan, the black kokanee, a species of salmon that had been considered extinct for the last 70 years, was rediscovered in a lake near Mount Fuji. When its native lake was converted for hydroelectric use, 100,000 kokanee eggs were relocated to Lake Saiko, yet the transplant appeared to fail. As it turns out, the kokanee are alive and kicking. No doubt the Japanese fishing industry is salivating: a new species to eradicate!

If I were a previously unknown fish species, the absolute last place I'd want to be found is Japan.

3) One of the things I’ve enjoyed most about creating Thirty Below is that it’s given me an excuse to read many other cool marine blogs. There’s a cornucopia of great content out there – which is both inspiring and, for a neophyte blogger trying to carve out a niche, a little daunting. Anyway, among those sites is RTSea Blog, an ocean-news blog run by an undersea film company. This week they got their hands on a press release issued by the team of experts that the Egyptian government called in to analyze the causes of the recent Red Sea shark attacks.

Predictably, the experts concluded that illegal human activity – from fish poaching that reduced the sharks’ food supply to dive operators feeding the sharks themselves – were among the major causes. But the craziest factor?  “The illegal dumping of sheep carcasses by animal transport vessels within 1.2 miles of the shore.”  Uh, yeah, that’ll draw sharks.

Undersea Penis Fencing! (That got your attention.)

This holiday season, millions of Americans will gush over freshly unwrapped Playstations and electric beard trimmers and other ribbon-festooned bits of electronic junk that will probably end up forgotten in a drawer by March. In all that exulting, one phrase that I doubt will be heard very often is: “Marine flatworms! No way! Oh boy oh boy oh boy oh boy!”

Yet those were the words I gleefully exclaimed last week when Elise’s mother presented me with Marine Flatworms: The World of Polyclads, a lushly pictorialized guidebook to some of my favorite invertebrates. I leafed through the sections on flatworm biology in a state of rapture. My girlfriend’s family looked on dubiously, no doubt wondering what kind of social deviant could possibly get so aroused by amorphous undersea blobs. I tried to persuade them of flatworms’ virtues, pointing fervently to the book’s most spectacular photographs: Check out this beauty, and this one, and this…

Marine flatworm, Thysanozoon sp. How is it that I have a million nudibranch pictures, but no flatties? Copyright Wolfgang Seifarth.

But convincing non-divers of flatworms’ merits isn’t easy. Sure, they’re colorful, but so are M&M’s. They may look pretty in the guidebook, but the page also renders them static, removes them from the context that makes them so spectacular: the reef.  It’s hard to explain how the vibrancy of the reef accentuates the worms’ gorgeous markings, how thrilling it is to find a species you’ve never before seen, how every dive becomes a joyful scavenger hunt for these brilliant invertebrates once you’re in the throes of flatworm mania. (I have equal love for the nudibranch, colloquially ‘sea slug,’ which looks quite similar to the flatworm but is taxonomically very different.)

Phrikoceros sp., copyright Michael D. Miller.

Only once have I seen a flatworm swimming, but I’ll never forget its supple grace, the way the margins of its body fluttered and undulated with heart-wrenching vulnerability: a soft-bodied little thing, detached from the reef that sheltered it, striking out in a vast predatory ocean, with only a thin coat of toxic mucus as protection.

Watch this video (flatworm begins swimming at 0:13) and tell me you’re not enthralled. Video courtesy of Youtube user memutic.

Anyway, I had to convince Elise’s family that flatworms are truly worthy of adulation. I flipped pages desperately, searching for the phrase that would catch their attention, and suddenly there it was – it might as well have been written in neon:

PENIS FENCING.

Say the book’s authors, Leslie Newman and Lester Cannon:

When two sexually aroused flatworms approach one another they slowly glide and touch, and then rear up, raising the front half of their body. The muscles around the copulatory structures are tensed and the penis, armed with a fine hypodermic-like hard stylet, is thrust out of the underside of the body and directed towards the partner. Then with deliberate motions each tries to stab its penis into the body of the partner – any part of the body. With short, stabbing motions each worm thrusts its penis stylet through the soft epidermis of its partner and injects a white bundle of sperm. They may do this repeatedly, until each bears multiple stab wounds and white blisters of foreign sperm. Then they lower their penis stylets and glide apart.

I nearly read this paragraph aloud, then realized that a description of a bizarre, rape-like sexual ritual was not the best excerpt to read to the family of one’s significant other. Good thinking, me.

Why do some flatworms engage in this strange behavior? (Only two groups actually penis fence; most flatworms care at least a little about consent.)  Worms are hermaphroditic, capable of being either father or mother, inseminator or inseminatee; so why would they rather impregnate than be pregnant?  The standard explanation is that becoming the mother is more energetically expensive – producing and carrying around a bundle of eggs is a serious drain on a flatworm’s resources. Although the eggs hatch after only a week, that week is still an exhausting and perilous one.

Video created by Leslie Newman – the very same Newman who wrote my guidebook. A strangely intense clip, complete with bombastic orchestral music and inane narration. Courtesy of http://www.theAwk.com

Also, fatherhood has an adaptive advantage: victorious father worms, which aren’t saddled with the egg burden, have the potential to inseminate other flatworms in battle and thereby spread their genes even further. Consequently, one would imagine, the entire flatworm population is steadily improving at penis fencing as good swordsmen propagate their genetic material. This strange mating behavior may well be producing a race of invertebrate Inigo Montoyas.

Finally, penis facing is also helpful in telling flatworms from their lookalikes, nudibranchs:

	Nudibranchs	Flatworms
Taxonomic Class	Gastropoda	Turbellaria
Breathing apparatus	External Gills	Respires through skin
Preferred Food	Sea Pens	Sea Squirts
Mode of Locomotion	Crawls with muscular foot	Undulates body to swim
Stance on penis fencing	No, does not engage in penis fencing	Yes, most definitely engages in penis fencing

Why Do Humans Eat So Many Sea Bass?

“Wild fish did not come into this world just to be our food,” Paul Greenberg writes toward the end of his book Four Fish.  “They came into this world to pursue their own individual destinies.”

Yet the way in which different fish species pursue those destinies – or, if you don’t like that quasi-mystical word, behave as their genes dictate – goes a long way in determining how likely a fish is to wind up pan-seared in butter and lemon juice.

Accordingly, one of Four Fish’s big questions is: Why do we eat certain species?  Well, you might answer, because they’re delicious, or plentiful, or good for you.  But what, specifically, about a fish’s anatomy makes it tasty?  What specific behaviors make it easy to catch?

Take, for example, the European sea bass.  Bass, according to Greenberg, owe their culinary popularity to one organ: their highly evolved swim bladder.  (In Thailand, I discovered, bladder is often served in a dubious dish called “fish maw soup,” which even Thais don’t even seem to like very much.) Greenberg doesn’t go in-depth about what traits make bass’ swim bladders so evolutionarily excellent, so I’ll try to fill in what he leaves out.

 

A fish’s swim bladder has a basic function: it keeps the fish from sinking.  Without the bladder, the fish would be heavier than its watery milieu, and would have to work very hard to stay afloat.  (Some fish, including sharks and coelacanths, manage this trick.  That’s why sharks have tails with longer upper lobes than bottom – heterocercal tails provide better lift).

A long upper tail lobe provides lift to help compensate for the shark's lack of swim bladder. Picture courtesy of hookedondestin.com

By filling their bladders with air, fish remain neutrally buoyant – ie, they weigh as much as the water around them – and expend far less energy than they would otherwise.  As fish move up and down, and the water pressure around them changes, they inflate and deflate their swim bladders correspondingly. Anybody who has ever dived has used a Buoyancy Control Device, and understands this intuitively.

Would you eat a soup made of that organ? Ummm... Courtesy of http://www.earthlife.net.

Now for the cool stuff – how do fish inflate their swim bladders?

There are two kinds of swim bladder: physostomous, or open, bladders; and physoclistous, or closed, bladders.

Human lungs and swim bladders share an ancestral organ, and that homology is very apparent when you look at an open bladder: a duct, like our windpipe, connects the fish’s mouth to its bladder.  The fish simply sticks its head out of the water and gulps some air when it wants to inflate and gain buoyancy; and burps when it wants to deflate.  (Think about Charlie and his grandpa in the original Charlie and the Chocolate Factory.)  Salmon, pike, goldfish, and many other species use this primitive system.

A Yellowstone cutthroat trout with its swim bladder fully inflated. Always nice to be able to use a photo that I took.

But sea bass, like all perciforms (perch-shaped fish), evolved the second, advanced kind of bladder: the closed bladder.  Closed bladders are so-called because they have no duct connecting to the mouth, or to any outside sources of air*.  Instead, perciforms regulate buoyancy by absorbing gas, usually oxygen, from the bloodstream into the bladder; and releasing that gas, when necessary, back into the blood.  To accomplish this, closed-bladder fish have an organ called the gas gland which secretes lactic acid, causing the eventual diffusion of oxygen from the blood into the bladder.  If you’re interested in exactly how this complicated process works, I suggest you consult either this Wikipedia page or a nephrologist.

*Closed-bladder fish have temporarily open bladders during their larval stage (approximately the first two weeks of their lives). A common cause of mortality among farmed fish is closed, or oil-covered, tanks, which prevent the larvae from taking gulps of air. The swim bladder forms around the first bubble of air that a fish swallows; without this bubble, larvae die, sink, or grow up deformed.

The upshot is that fish like sea bass have two big advantages over fish with open bladders: they don’t have to swim to the surface to freshen up their air bladders; and their buoyancy system is simply more efficient – they’re better at staying neutral.  This means they expend less energy than other fish, and, says Greenberg, is why they’re so delicious:

“Without a need to fight gravity all the time, perciforms became more efficient swimmers and were able to trade in their heavy, energy-demanding “red muscle” tissue for lighter, more delicate flesh.  Hence the white, light meat of many perciforms.  Perciforms also evolved an efficient muscle structure that is principally attached only to the central spine column.  The result: a smooth, mostly boneless fillet, very pleasant to eat.”

This unfortunate but delectable sea bass will never again diffuse internal gases across a chemical gradient. Courtesy of SFgate.com

Not only is smooth, delicate, boneless bass flesh tasty to eat, it was once easy to obtain.  Although a closed swim bladder allows its owner to remain below the surface, it also limits the depth to which the fish can dive – go too deep and the bladder may implode.  In general, the fish that can go the deepest, and can change depths most rapidly, are the fish that have no swim bladders at all, like mackerel, sharks, and flounder.  Because coastal sea bass are confined to shallow water by their large bladders, they’re much easier to spear and catch on a line than fish that lack bladders, or have small ones*.

*There are some perciforms, like the Patagonian toothfish (rebranded the Chilean sea bass, in a stroke of marketing genius) which live at great depths. The toothfish’s bladder has been replaced by glands which secrete lighter-than-water fat into the fish’s skin and allow it to maintain buoyancy effortlessly. The toothfish’s high fat content, incidentally, is what makes it so delicious, and thus so over-fished.

The author's brother gets his hands on a sea robin, a bottom-dwelling fish that uses its swim bladder to make drumming noises.

Europeans’ taste for sea bass, then, is the product of fish morphology and centuries of consequent exploitation.  Humans developed and maintained a taste for sea bass centuries ago; began to farm them intensively in the 1980’s; and eat them ravenously today.  All thanks to their remarkable closed-bladder buoyancy system that improves their energy efficiency and, in turn, makes them tastier, less bony, and comparatively easy to catch.  

I’m sure I’ll return to both swim bladders and Paul Greenberg’s great book in future posts, but enough for now. Big hat tip to Davidson Biology for a great site on this subject.