Yes, that’s a bonnethead shark (Sphyrna tiburo) … and yes, that’s the Detroit River.

The photo was taken on July 21, 2006, by area resident Richard Kik IV (aka “Brooklamprey”) and posted to the forum of the North American Native Fishes Association.

Reaching a maximum length of 150 cm (Compagno, 1984), bonnetheads are relatively small and inoffensive congeners of the better-known hammerheads.  S. tiburo are common inhabitants of both estuaries and shallow coastal waters in the tropical and subtropical Western Atlantic and Eastern Pacific (ibid.), but monitoring of specimens along Florida’s Gulf of Mexico coast suggests that they’re unable to tolerate salinities lower than 15 ppt (Ubeda et al., 2009).  No bull shark, the little fellow clearly never had a chance.

So how this? Richard elaborates:

It was clearly a pet release in part and a prank second. The fish was found off of the public beach on Belle Isle in Detroit Michigan on the Detroit river. I have no idea how one managed to keep a 3 foot bonnethead alive to do this but it certainly was never swimming around for long. Stomach content check showed it empty.

I got a call early in the day that the staff there found a shark on the shoreline and it was very much alive. Personally I suspected just another Sturgeon but the lady on the phone was telling me NO it was an actual shark. I told them to corral it and I’d be by. Sure enough when I arrived it was an honest to goodness bonnethead shark. It was pretty much dead but still slightly breathing.

Fish is currently in my freezer… I plan to have it mounted and displayed at the Belle Isle Nature zoo as an example of the stupid things people try to release.

Deliberate release — as anyone familiar with irresponsible aquarists, game-fish stockers, and fang sheng practitioners can attest — is a major vector for aquatic invasive species.  Even the dumping of marine critters into decidedly non-briny waterways, bizarre though it might sound, is not without precedent; look to this report (with photo), of a 6-foot octopus pulled up from the Ohio River by an Indiana fisherman.

Some more photos of the expired elasmobranch:

Resources:

Before finding the right building, I wandered through the MCZ and a few exhibits of the Harvard Museum of Natural History.  Along the way, I couldn’t help but notice the unidentified swimming objects (USOs) gracing two of the jars.

These shrimp were in a glass case highlighting Louis Agassiz’s explorations in Brazil.  “Caridea” they are — to be more specific, they represent at least one (probably multiple) species of Palaemonid shrimp in the genus Macrobrachium.

Immediately behind their jar was a red-tailed boa (Boa constrictor constrictor), and to the right of that a peacock bass (Cichla ocellaris), a native of the Amazon, Orinoco, and La Plata basins (Schroder & Zaret, 1979) that has also become established in the Panama Canal Zone (Zaret & Paine, 1973) and in southern Florida (Schafland, 1996).

Though the orientation of the container made it difficult to read the locality description, these coordinates place it in the present-day state of Ceará, Brazil.

A closer look at the shrimp themselves.

Further along were yet more preserved organisms in an exhibit exploring the breadth of invertebrate diversity.  Beside a Panulirid spiny lobster and a Brachyuran crab was an admittedly lobster-like shrimp.

The locality left no doubt as to the identity of this “Macrobrachium sp.” — M. carcinus.

The doorway of the MCZ proper, to the left of the HMNH entrance.

Prior to my departure, Dr. Giribet and I also made the rounds of the MCZ’s crustacean collections and the Ernst Mayr Library, where we hunted down an early copy of Huxley’s Crayfish and saw a “secret room” filled with pre-1850 books, artworks, and field journals by the likes of Linnaeus, Buffon, Cuvier, and Darwin.

A parting shot of the museum itself.

All in all, a very worthwhile trip.

Resources

Shafland, P. L. (1996). Exotic Fishes of Florida-1994. Reviews in Fisheries Science 4(2):101-122.

Schroder, S.L., & T.M. Zaret. (1979). The adaptive significance of color patterns in Cichla ocellaris. Copeia 1979(1):43-47.

Zaret, T. M., & Paine, R. T. (1973). Species Introduction in a Tropical Lake: A newly introduced piscivore can produce population changes in a wide range of trophic levels. Science, 182(4111), 449-455.

The freshwater pond display — typically home to a range of aquatic beetles, Odonate larvae (dragonfly and damselfly nymphs), and assorted Hemiptera (water boatmen, backswimmers, water striders, and Belostomatid water bugs) — instead housed just a handful of Hydrophilid beetles alongside a dozen-odd freshwater prawns (most likely Macrobrachium lanchesteri).

M. lanchesteri gathering loose detritus from the substrate with its second pereiopods.

Though I couldn’t help but wonder whether the other tenants had been eaten by the new additions, they exhibited little aggression towards the remaining beetles … which is not to say that the tank was sedate — far from it.  The water column and substrate were a constant crustaceous blur of swimming and scurrying forms — as two prawns would squabble over tatters of shed exuvium under the watchful gaze of a dominant male at one end of the tank, an ovigerous female would be aerating the lime-green brood amidst its fluttering pleopods at the other.

Despite the shallowness and slack circulation of the water, the Zoo’s prawns seemed to be in good condition.  M. lanchesteri, unsuprisingly, tolerates a broad range of habitats throughout Thailand, Peninuslar Malaysia, Myanmar, southern China, and Java, including not only streams and rivers but also rice fields, ponds, and reservoirs (Cai et al., 2004).

Dominant male M. lanchesteri (~5 cm in rostrum-telson body length; note development of second pereiopods) lurking beneath a leaf.  If the silt and algae swaddling most of the plants were anything to go by, aufwuchs appear to make up only a small portion of these prawns’ diet.

Female M. lanchesteri with green ovary mass.

As Wong (1994) noted, M. lanchesteri produces large, floating larvae able to complete development in freshwater; berried females notwithstanding, I didn’t notice any juveniles.  If their parents weren’t just very recent additions, it may be that they’re being consumed by older tankmates for want of cover — or that they’re succumbing to that latterday Charybdis of the filter intake.

Resources

In addition to submitting an original research paper, initial entrants are also judged on essays, coursework, and test scores; it’s like a college application, but more intense. I was working frantically to complete my essays the very day of the deadline and ended up hand-carrying my envelopes into the DC office not too many minutes before the 8 PM cutoff. Given my last-minute rush — and the fact that animal science/zoology projects have usually met with little success in this competition — I didn’t get my hopes too high. Through who knows what kind of black magic, the STS reviewers whittled 1600 applicants down to 300 semifinalists, and then to 40 finalists. Astoundingly, I remained afloat.

From March 5-11, I underwent the single most grueling yet most elating week I’ve ever experienced — the final round of STS. No sooner had I arrived than I was subjected to two days of cross-examination by four panels of judges ensconced in separate interrogation chambers. Three judges per room, one question per judge, five minutes per answer … in every field from physics to medical science. (And not just any judges, mind you; we had, among others, the discoverer of dark matter, a nuclear physicist from Los Alamos, and leaders in cancer research.)

A good grasp of the fundamentals, logical rigor, and creativity of thought were key — no small feat when a single breath might take you from the molecular basis of mad cow disease to a pro-con analysis of the digital TV transition … and that’s before you’re judged on your own project. Three poster sessions later, I’d just about lost my voice, but the trial was over. Over the remaining few days, I shook hands with President Obama, dipped skewered fruit in chocolate fondue, debated transhumanism with Intel’s Justin Rattner, went bowling, had a minor planet named for me by MIT’s Lincoln Laboratory, talked geopolitics with Senator Inhofe, and — ushered past those poor saps in the security line by Capitol Hill staffers — got my photo taken with Congressmen Lieberman, Kerry, Coburn, and Connolly.

After all this, the awards ceremony felt almost like an afterthought. Well, almost — Colin Powell and Secretary of Energy Stephen Chu joined Intel Chairman Craig Barrett as that evening’s speakers.  I was honored to receive 7th place, but what I’ll treasure most are my memories of the 39 other finalists.  Congratulations to all of my fellow researchers, particularly classmate Naren Tallapragada (also in the top 10), and deepest thanks to my parents, to my teachers and mentors, and to Thomas Henry Huxley, for penning the 12 words that started it all.

Containing 20% of the world’s freshwater, reaching a depth of over 1600 meters, and having endured for 28 million years, Lake Baikal is the deepest, most voluminous, and most ancient of all freshwater lakes (Mats, 1992; Logatchev, 1993).  Situated north of Russia’s Mongolian border, the “Blue Eye of Siberia” is not wanting for motes; Baikal’s species assemblages include reefs of green, branching sponges, a landlocked seal (the nerpa, Pusa sibirica), and spectacular adaptive radiations of cottoid sculpins and gammaroid amphipods.  I could go on (and, in later posts, will), but let it suffice to say that the bed and waters of this lake are surreal beyond imagination.

These last, the gammaroids of Baikal, represent a burst of diversification without peer amongst contemporary freshwater invertebrates (Brooks, 1950; Kozhov, 1963).  Of some 800 gammaroid species known worldwide [EDIT: see comments for discussion], over one third are endemic to this lake (Kamaltynov, 2002; Vaïnölä et al., 2005).  While gammaroids elsewhere tend to be morphologically conservative and rather nondescript (if you’ve seen one scud, you’ve seen ‘em all), the Baikalian taxa are highly diverse in body form and ecological niche, ranging from “dwarfed herbivorous Micruropus to giant deepwater Abyssogammarus and Garjajewia” and “from the parasitic genera Pachyschesis and Spinacanthus to the pelagic Macrohectopus” (Sherbakov et al., 1998).

Some, in fact, bear spiny protrusions of varying form and position (termed “body teeth”), which presumably serve a defensive function.  The Baikal forms are close to unique in having these armaments (Barnard and Barnard, 1983) — as far as gammaroids go.  Aetosaurs are a different matter.

Darren Naish, at Tetrapod Zoology, presents a far better overview of these “omnivorous armoured crurotarsans of the Late Triassic” than I could hope to give — well worth a read even if you’re not a vertebrate person (i.e., a “spineless scalawag”).  Despite being 6 m long instead of 6 cm, having osteoderms in place of chitinous plates, and — let’s face it — being a Texan archosaur instead of a lacustrine crustacean from Siberia, Desmatosuchus haploceros bears a striking resemblance to the Acanthogammarus shown below.

I’ll concede that dorsal protrustions are more pronounced in our amphipod than in our aetosaur, but the shapes and relative lengths of the curved lateral spines are remarkably similar in both.

Acanthogammarus, Sherbakov et al. explain, are benthic, mostly carnivorous (though not above scavenging and detritivory), and represented in both shallow (<200 m) and deep water by large (20-50 mm) and giant (>50 mm) species. A. victorii is strikingly colored (those of you familiar with the BBC’s “Planet Earth: Freshwater” may recall the orange fellows beneath the ice) and I suspect this to be the true identity of the aetosaur-impersonators above.

[All photos of amphipods taken from this page; first aetosaur photo from here; second from here.]

Resources:

As someone interested in the evolutionary history of river prawns of the genus Macrobrachium, a crustacean taxon poorly reported from the fossil record despite a global distribution and reasonable antiquity (probably late Oligocene to early Miocene: Murphy & Austin, 2005), I know how frustrating an bad paleontological record can be.  Given the large size, wide range, and heavily calcified claws of the American M. carcinus (pictured in the title bar of this blog), I’ve often wondered why it’s never been documented — so far as I could tell — in fossil or subfossil deposits.  Middens might be a good place to search for more recent material (Losey et al., 2004), which could perhaps lend insight into historic prawn abundance and shifting patterns of exploitation.

It was with great interest, then, that I read “New Cretaceous and Cenozoic Decapoda (Crustacea: Thalassinidea, Brachyura) from Puerto Rico, United States Territory” (Schweitzer et al., 2008), a paper from the Bulletin of the Mizunami Fossil Museum.  Although the article is also notable for having the first records of [edit:] Cretaceous decapods from the island, I was most intrigued by its treatment of Pleistocene material — another novelty for Puerto Rico:

A crushed cheliped recovered from a cave was matched to the still-extant crab Cardisoma guanhumi (Brachyura: Grapsoidea: Gecarcinidae).  Fossil fragments identified with this species had heretofore only been known from the Pliocene of Panama, the Pliocene of Costa Rica, and the Pleistocene of Jamaica.  “The freshwater crab families,” the authors elaborate, “have a poor fossil record; thus, the occurrence is noteworthy and may document dispersal of the crab by humans.”

The male C. guanhumi shown above leaves no doubt as to the basis of its species’ common name, “blue land crab”.  In males, pronounced asymmetry of the claws is typical. (Image Source)

In females, by contrast, “even-handedness” seems to be the norm. (Image Source)

Now, when we think of anthropogenic transport of live animals — especially prior to the rise of the global seafood and pet trades — crabs like C. guanhumi don’t figure very large.  Do any aspects of C. guanhumi‘s distribution or biology suggest otherwise?  Schweitzer and colleagues continue:

Extant members of Cardisoma guanhumi are known from throughout the Caribbean region and along the coast of Brazil as far south as São Paulo (Rathbun, 1918b). Other extant species of the genus Cardisoma have been reported from the Caribbean, the west Atlantic Ocean, Brazil, and West Africa (Rathbun, 1935b; Türkay, 1973; Manning and Holthuis, 1981). Türkay (1974) and Davie (2002) document a circumtropical distribution for the genus based upon the occurrence of species in Australia and many Pacific islands. Türkay and Sakai (1976) documented the presence of Cardisoma carnifex in Japan.

Well, what does this imply?

The extremely broad distribution of a terrestrial brachyuran species in remote, isolated locations introduces the possibility of dispersal by humans. Specimens of land crabs could have served as a food resource on oceanic voyages, providing a venue for introduction of the animals into otherwise inaccessible locales.

Cardisoma are still prized as edibles; no Bahamian gourmet worth his salt is anything less than familiar with “crab and rice”.  As shipboard companions-cum-rations go, their formidable claws and swift scuttling might have posed less of a problem than one might expect; Cardisoma seem to keep well even in trussed-up-bundles hawked on roadsides, and the occasional dip over the side would suffice to moisten their gills.

Ucides occidentalis wrapped in twine at Ecuador’s Latacunga market (Image Source)

But let’s not get too far into the realm of speculation — is  the claim of human introduction adequately warranted to start with?

In my view, no.  A likelier alternative seems to present itself in the very next paragraph (emphasis mine):

Rathbun (1918b) reported that the crabs live in a variety of terrestrial habitats ranging from swamps to forests, that they produce deep burrows, forage at night, and return to the sea to reproduce. The occurrence of the fossil specimen from Puerto Rico in a cave deposit and in association with fossils of terrestrial organisms is consistent with this interpretation. Their habit of returning to marine environments to reproduce is supported by the observation of Collins and Donovan (1997) that Cardisoma guanhumi has been collected from a marine unit, the Port Morant Formation in Jamaica.

It is a mistake to consider Cardisoma purely “freshwater” or “terrestrial” organisms when the entirety of their larval lives are spent amongst the plankton of warm coastal seas — floating … drifting … wafting from shore to shore with the currents.

Costlow & Bookhout (1968 b) raised C. guanhumi from newly hatched eggs to the first crab stage in 35 ppt saltwater, reporting there to be five zoeal stages and one megalopal stage.  The necessity of salt was affirmed in a series of epxeriments conducted by Kabler & Costlow (1968), whereby C. guanhumi were found to hyperregulate in 10 ppt seawater and hyporegulate at 40 ppt for the first third of their larvae life, with progressively less saline isosmotic points thereafter).   “From the time of hatching,” they conclude, “the osmoregulatory pattern of developing C. guanhumi fits them for deep penetration of estuaries and for crossing steep saline gradients.”

What implications could this life cycle have for genetic variation between far-flung populations of C. guanhumi?  De Oliveira-Neto et al. (2008), sampling across 5 Brazilian states, reported that “Populations of the blue land crab are characterized by a high level of genetic variability that is homogeneously distributed throughout the entire studied region along the Brazilian coast.  High genetic diversity is thought to result from a combination of high mutation rate in the study fragment and the large population size of the species.”  Do we  have to invoke ocean-going travellers with living larders to account for this?  Not at all.  “The dispersal capacity of their larvae is probably amplified through coastal currents, such that the genetic compositions of populations in different estuaries are homogenized” (ibid.).

Cardisoma armatum (Image Source)

In larval physiology — and thus dispersal potential — C. guanhumi seems to be rather typical for its genus, if geographic distributions are any indication.  Costlow & Bookhout (1968 a) report C. guanhumi larvae to survive to the first crab stage (i.e. complete larval development) “in salinities of 15–45 p.p.t., 25° and 30°C.”  Precise salinity, they suggest, is less crucial than temperature.  C. armatum of West Africa offers few surprises.   The first four zoeal stages tolerate salinities of 15–45‰, and 15–35‰ during later development, though 15‰ salinity “tended to cause higher mortality and a significantly delayed development in most stages, while 25‰ allowed for maximum survival through metamorphosis” (Cuesta & Anger, 2005).   For both species, larval euryhalinity makes both estuary-hopping and trans-oceanic dispersal theoretical possibilities.

Even beyond Cardisoma, we find indications aplenty that larval transport through ocean circulation can be a perfectly adequate explanation for wide distributions.  The mangrove crab Ucides cordatus cordatus (Ocypodidae) has a distribution nearly identical to that of C. guanhumi — “along the subtropical and tropical Atlantic coast of America from Florida to Uruguay, and on the Caribbean Islands” (Burggren and McMahon 1988).  As one might expect, its salinity tolerance is also quite similar: “larvae only survived to megalopa at salinities ≥15, with highest numbers at salinity 30 (72%) [the highest salinity treatment] and lowest at 15 (16%)” (Diele & Simith, 2006).

Ucides cordatus (Image Source)

Not only have genetic studies of U. cordatus revealed a “very modest degree of differentiation over a wide geographical area”, suggesting “preponderance of the larval export strategy” throughout the species’ evolutionary history (Oliveira-Neto et al., 2007), researchers in the Furo Grande Region of Brazil’s northern State of Pará have actually observed “synchronized massive releases of larvae that were exported up to 200 km off the coast” (ibid.; Diele, 2000).

The parallels with the land crabs of Christmas Island (previously blogged about here) are obvious.  If the planktonic young of crabs on a tiny Indian Ocean island are able to satiate the largest fish in the sea, I can’t help but be astonished by the trophic implications of “massive release” along huge swaths of continental coast.

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A Red Lobster diner in Salt Lake City: Not a home-grown industry, I’m afraid.

(Photo Source)

In the truly excellent Tinkering with Eden: A Natural History of Exotics in America (pp. 107-108), Kim Todd writes:

With the transcontinental railroad cabling one coast to the other in 1869, and shipping methods improving all the time, fish could be carried farther and faster than before.  Ponds and lakes, rather than being viewed as complex ecosystems, were treated as outdoor aquariums waiting to be filled.  Once walled in by the boundaries of their pools or watersheds, now eastern fish traveled west, western fish journeyed east, English fish came to the United States, American fish swam through streams in Australia.  Leather carp were whisked from Washington, D.C., to Scotland; Lake Michigan whitefish found themselves in New Zealand.  German carp settled in Alabama, while Hawaiian mullet traveled to the mainland.  Between 1874 and 1880 the Fish Commission transported more than four million California salmon to foreign countries, including Canada, England, France, Holland, Germany, New Zealand, Australia, and the Sandwich Islands.

These early attempts … were a race against death.  On one shipment of live lobsters from Maine to California, the fish culturists juggled sponges, damp straw, salt water, and blocks of ice in an effort to keep their charges cool, damp, and alive.  Then the lid of one aquarium slid shut, suffocating all the crustaceans inside.  As the trip continued, still more died.  The fish culturists dropped off one of their few remaining pairs of lobsters in Utah to breed in the Great Salt Lake.  By the time the lobsters reached California, only four lingered to be released from a wharf in Oakland.

Emphasis mine.  Obviously, they didn’t take, but the odds were long to begin with.  According to Stephens, “During the late 1800′s, [Great Salt Lake] salinity ranged from about 13 to 23 percent.”  The American lobster (Homarus americanus, the species that was most likely ferried west on this fateful journey) is usually considered stenohaline and intolerant of salinities <25‰ (Dall).  It’s worth noting that estuarine Homarus populations may be subjected to considerably lower salinities in times of high freshwater input.  Research has established that 50 % lethal salinities (LS50 values) in Homarus range “from approximately 15-17‰ in larvae to approximately 12‰ in postlarvae and 10‰ in adults” (Charmantier et al.).  On the other hand, few researchers seem to have looked into salinity maxima.  I would hazard an upper tolerance not much higher than 37‰ or so.  Mind the units.

(Photo Source)

Had our lobsters come a century or so later, they might have had a more sporting chance.  A causeway completed in 1959 effectively divided the Lake into a southern half subject to the bulk of freshwater input (subsequent salinity from 6-28%), and a saltier northern half (16-29%) (Stephens).  In the mid-1980s, the Lake’s resident brine flies (Ephydra spp.) and brine shrimp (Artemia franciscana, actually Branchiopods and not Malacostracans like true shrimp) were joined for the first time by fish:

During 1986, the decreased salinity of the south part [to "about 6 percent"] allowed a breeding population of rainwater killifish, Lucania parva (Baird) to enter the lake near Stansbury Island. The 4-cm-long fish are members of the Cyprinodontidae family and are commonly found in brackish and slightly saline waters. This is the first documented report of fish living in Great Salt Lake in recorded history.

Even the New York Times took heed; an article from August of that year spoke of killifish frolicking in salinities “less than 4 percent”.  Alas, it was too good to last for long.  Stephens continues:

As the total precipitation during 1987 at Salt Lake City was about 80 percent of average and the salinity of the southern part had increased to 7.2 percent by March 1988, the future of fish in Great Salt Lake is tenuous.

By now, I suppose, the Great Salt Lake is back to its plain old hypersaline self again … bereft of fish — and lobsters.

Resources:

Why this is so, I can only speculate.

Note that changes in coloration can be quite dramatic in Atyopsis moluccensis and are so pronounced in C. serratirostris that it’s known to aquarists as the “ninja shrimp” — don’t come away thinking that the striping is an immutable characteristic of these two species.  From what I’ve seen in aquaria, the color-changing ability of Potimirim is more feeble (limited to stress-induced paling).  And while I don’t have any direct experience with Atya scabra, it — one way or another — seems to exhibit a fair amount of color variation between locales.

Though the first two species are similar in size (around 1-1.5 cm), the last are comparatively massive (Atyopsis moluccensis and Atya scabra may both exceed 10 cm).  This dichotomy is paralleled by functional morphology.  Potimirim feeds on algae and detritus, primarily by sweeping (Fryer); in this respect, it resembles many Caridina spp.  However, its bristle-bearing chelipeds can also be used (pers. obs.) for the kind of passive filtration that sees greatest development in Atyopsis and Atya.  In the absence of strong current (e.g., during drought conditions), shrimp from these two genera may resort to sweeping food from the substrate like their smaller relatives (Covich et al.).

Given the name of this blog, I’m obligated to point out that the four species shown above are all amphidromous; their larvae require saline water to develop and presumably waft downstream to estuaries or the ocean from the freshwater habitats occupied by adults (Page et al. & Yakushiko et al.).

Resources:

Shown here (photo courtesy of Jack Trout) is a Macrobrachium carcinus exuvium recovered from a cave in Belize.

Holthuis (1986) has the score, mostly — Belize is news to him:

Macrobrachium carcinus (Linnaeus, 1758). St. Augustine and Silver Springs, Florida, U.S.A. (in pools fed by subterranean water); Chiapas, Mexico; La Cueva Chica, San Luis Potosi, Mexico; Jamaica. Hobbs, Hobbs & Daniel, 1977: 148, 149, 150. — El Convento Cave, Puerto Rico. Nicholas, 1974, Int. Journ. Speleol, 6: 111.

Though it lacks explicit subterranean adaptations, M. carcinus is a well-known trogloxene (Hobbs incorrectly refers to it as a troglophile, but larval requirements for saltwater leave it unable to complete its life cycle in caves).

Now, the leap to cave-dwelling isn’t as daunting as you might think.  From what I’ve seen in El Verde, Puerto Rico, San Marcos, Texas, and the aquaria in my basement, this species is rather nocturnal to begin with … though captive specimens will quickly learn to associate your presence with food at any time of day.  Dr. Alan Covich (University of Georgia) describes going out at night to the mountain streams of El Yunque (formerly the Caribbean National Forest), where he observed Puerto Rican M. carcinus plucking smaller shrimp from the water column to pop into their mandibles like so many Fritos.  Illuminated in his flashlight beam, they’d continue grabbing at passers-by for several seconds before coming to their senses and darting out of sight with a flick of the tail.  Chemosensory antennae are clearly a good stand-in for eyes in near or total darkness.

Compared to surface water, caves also tend to have lower predation pressure, making them especially fine real estate for juveniles and adults preparing to molt.  Prior to shedding, shrimp actively seek out dark and cozy crevices in rock piles and undercut banks; it’s not unreasonable to think that our Belizean friend made his descent into darkness with a similar aim.  Then again, the specimen in question could just as well have been a long-term resident, its ink serenity broken only by glowworms and the fleeting glare of tourist headlamps.

M. carcinus is far from atypical.  Holthuis documented 12 species of Macrobrachium in subterranean waters, all of which were otherwise epigean forms.  However, several true stygobites have since been discovered, and many other species could easily be facultative cave-dwellers, the real number is probably much higher.

Macrobrachium poeti, from Java’s Gunung Sewu karst (photo by Cahyo Rahmadi).

Li et al., in their description of Macrobrachium lingyunense Li, 2006, from the Lingyun karst of Guangxi, China, summed things up pretty well:

Holthuis (1986) listed six troglobitic Macrobrachium species i.e., M. cavernicola (Kemp, 1924), M. villalobosi Hobbs, 1973, M. lucifugum Holthuis, 1974, M. acherontium Holthuis, 1977, M. microps Holthuis, 1978 and M. poeti Holthuis, 1984.  Chong (1989) described M. gua from Sabah, Malaysia, Hobbs & Hobbs (1995) described M. catonium from Middle America, and Komai & Fujita (2005) recently reported another new troglobitic species, M. miyakoense from the Ryukyu Islands, Japan, bringing to a total of nine troglobitic species.

[genghisprawn: eleven with M. lingyunense Li, 2006, and M. sbordonii Mejía-Ortíz, described in 2006 from Chiapas, Mexico]

Macrobrachium lingyunense, from the Lingyun karst of Guangxi, China, caught and photographed by Arthur Clark.

In total, Hobbs documented 81 decapod crustacean troglobites and 58 other cavernicoles in subterranean waters ranging from springs to anchialine caves and blue holes in North and Central America, the Caribbean, and North Atlantic islands.  Of these, 36 were shrimps “(1 procarid, 11 atyids, 2 agostocarids, 15 palaemonids, 2 alpheids, 5 hippolytids),” 35 were cambarid crayfishes, and 10 were crabs “(1 grapsid, 7 pseudothelphusids, 2 trichodactylids)”.

Resources:

Chong, S.S.C. (1989). A new species of freshwater prawn, Macrobrachium gua sp. nov. (Decapoda, Caridea, Palaemonidae) from Sabah, East Malaysia, Borneo. Crustaceana, 56(1): 31-38, Figs. 1, 2.

Hobbs, H.H. (1973). Two new troglobitic shrimps (Decapoda: Alpheidae and Palaemonidae) from Oaxaca, Mexico. Association of Mexican Cave Studies, Bulletin 5: 73-80, Figs. 1-3.

Hobbs, H.H. III (1994). Biogeography of subterranean decapods in North and Central America and the Caribbean region (Caridea, Astacidea, Brachyura). Hydrobiologia 287: 95-104.

Hobbs, H.H. III & H.H. Hobbs, Jr. (1995). Macrobrachium catonium, a new species of troglobitic shrimp from the Cayo Dstrict of Belize (Crustaceana: Decapoda: Palaemonidae). Proceedings of the Biological Society of Washington, 108(1): 50-53, Fig. 1.

Holthuis, L.B. (1974). Subterranean Crustacea Decapoda Macrura collected by Mr. L. Botosaneanu during the 1973 Cuban-Rumanian Biospeleological Expedition to Cuba. International Journal of Speleology, 6: 231-242, Figs. 1-3.

Holthuis, L.B. (1977). Cave shrimps (Crustacea, Decapoda, Natantia) from Mexico—Subterranean fauna of Mexico. Part III. Futher results Italian zoological mission to Mexico, sponsored by the National Academy of Lincei (1973 and 1975). Problemi attuali di Scienze e di Cultura, Accademia nazionale dei Lincei, 171(3) : 173-195, Figs. 1-8.

Holthuis, L.B., 1978. Zoological results of the British speleological expedition to Papua new Guinea 1975. 7. Cavernicolous shrimps (Crustacea, Decapoda, Natantia) from New Ireland and the Philippines. Zoologische Mededelingen, 53(19): 209-224, Figs. 1-6.

Holthuis, L.B. (1986). Decapoda. In: Botosaneanu, L. (ed.) Stygofauna Mundi. A faunistic, distributional and ecological synthesis of the world fauna inhabiting subterranean waters (including the marine interstitial). Leiden: E.J. Brill. Pp. 589-615.

Kemp, S., 1924. Crustacea Decapoda of the Siju Cave, Garo Hills, Assam. Records of Indian Museum, 26: 42-48, Figs. 1-5.

Komai, T. & Y. Fujita (2005). A new stygiobiont species of Macrobrachium (Crustacea: Decapoda: Caridea: Palaemonidae) from an anchialine cave on Miyako Island, Ryukyu Islands, Zootaxa, 1021: 13-27.

Li, J., Cai, Y., Clarke, A. (2006). A new species of troglobitic freshwater prawn of the genus Macrobrachium from Southern China (Crustacea: Decapoda: Palaemonidae). Raffles Bulletin of Biology 54(2): 277-282.

Mejía-Ortíz, L., Baldari, F., & López-Mejía, M. (2006). Macrobrachium sbordonii (Decapoda: Palaemonidae), a new stygobitic species of freshwater prawn from Chiapas Mexico. Zootaxa 1814: 49-57.

Shortly before I left for Georgia, I happened on an article by the BBC, Shark-cam captures ocean motion (Nov. 17). A team of researchers headed by Dr. Mike Meekan (Australian Institute of Marine Science), the BBC reports, struck “scientific gold” by collecting fecal material from a whale shark (Rhincodon typus), the largest fish in the sea. This act, what’s more, was caught on film and will see inclusion in a BBC Natural World documentary, Whale Shark.  Unimpressed? Consider this:

Short of splitting open multi-tonne fish to sort through their stomach contents, biologists face considerable challenges in determining what, exactly, these pelagic filter-feeders eat. The idea of examining R. typus fecal samples is not new, but digestive degradation often precludes morphological identification of prey species (Wilson & Newbound, 2001). More recently, researchers have used genetic analysis as a diagnostic tool for identifying prey species from feces, isolating a region of the nuclear large subunit (LSU) ribosomal RNA gene present in krill but not in other malacostracan crustaceans. This technique was pioneered with Adelie penguins, Pygoscelis adeliae, and pygmy blue whales Balaenoptera musculus brevicauda (Jarman et al., 2002), and was subsequently extended to whale sharks (Jarman & Wilson, 2004). Meekam’s team — though probably with a different gene region — seems to have done much the same.

So what’s so novel about Meekam’s work, you ask? Well, as Colman (1997) relates, migratory movement of whale sharks seems to correspond to peaks in prey density (like plankton blooms or mass-spawning events in fish). One such trackway brings significant numbers of whale sharks to the Indian Ocean’s Christmas Island during December and January — an aggregation that tellingly coincides with the seaward run of the world’s most famous land crab, Gecarcoidea natalis.  Meekam’s genetic study confirmed this hunch — the most massive of fish glut themselves on the young of these nearly-terrestrial crustaceans.

Commonly known as the Christmas Island red crab, G. natalis is the most abundant terrestrial Brachyuran on Christmas Island — population estimates range as high as 100 million individuals — and the dominant consumer of the forest floor, feeding on fallen leaves, seeds, and fruit as well as small animals (Green, 1997).  On this hearty diet, these burrow-dwelling, diurnal crabs can reach a carapace length of 120 mm and a weight of half a kilogram.  Impressive though these stats might be, it is their mode of reproduction that is the red crab’s claim to fame.  In a truly awe-inspiring series of overland migrations, G. natalensis march from the interior to the coast to mate and then release their eggs.  These eggs, as many as 100,000 per individual, are retained beneath the female’s abdomen like a fistful of caviar until they’re brought to the ocean’s edge “at night on the turn of the high tide between the last quarter of the moon and the new moon, sometimes from cliff faces” (Hicks, 1997). The larvae hatch on contact with seawater, spending 3 to 4 weeks as plankton before taking on a terrestrial body form and scuttling up from the beaches to the interior plateau.

I’ll let the photos speak for themselves:

But all is not well on Christmas Island.  Populations of the yellow crazy ant (Anoplolepis gracilipes), an invasive species likely introduced with timber, exploded in the 1990s; today, supercolonies occupy over 30% of Christmas Island’s rainforest (Abbott, 2006).  These voracious creatures have found in Christmas Island red crabs a fine solution for their caloric demand, effectively eliminating G. natalis from occupied areas and taking up residence in their burrows.  It is likely that several dozen millions of red crab have already perished, and as this keystone species continues to decline, massive disjunctions in seedling recruitment and leaf-litter processing are likely to ensue (O’Dowd et al., 2003).  In brief: invasional meltdown.

Above, yellow crazy ants swarm a crab (albeit what looks like a Sesarmid).

Could the ravages of A. gracilipes be felt as far away as whale shark bellies?  Perhaps so.

Resources:

Colman, J. G. (1997). A review of the biology and ecology of the whale shark. Journal of Fish Biology, 51(6), 1219-1234.

Green, P. T. (1997). Red Crabs in Rain Forest on Christmas Island, Indian Ocean: Activity Patterns, Density and Biomass. Journal of Tropical Ecology, 13(1), 17-38.

Hicks, J. (1985). The Breeding Behaviour and Migrations of the Terrestrial Crab Gecarcoidea natalis (Decapoda: Brachyura). Aust. J. Zool., 33(2), 127-142.

Jarman, S. N., Gales, N. J., Tierney, M., Gill, P. C., & Elliott, N. G. (2002). A DNA-based method for identification of krill species and its application to analysing the diet of marine vertebrate predators. Molecular Ecology, 11(12), 2679-2690.

Jarman, S. N., & Wilson, S. G. (2004). DNA-based species identification of krill consumed by whale sharks. Journal of Fish Biology, 65(2), 586-591.

Wilson S., & Newbound D. R. (2001) Two whale shark faecal samples from Ningaloo Reef, Western Australia. Bulletin of Marine Science, 68, 361-362.