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Monday
Dec202010

How about an albino whale shark?

Or at least leucistic, based on what appears to be a bit of pigment at the base of the pectoral fin and, possibly, in the mouth (though those could be small remoras).  This was shot by a tour boat guide in the Galapagos and appears to show a female whale shark with no spots because she’s pure white.  I even hazard that she might be pregnant, given the slight bluge in the area above her pelvic fins.  Very cool

 

Sunday
Dec192010

Merry Christmas from Vancouver Aquarium

Our colleagues at the Vancouver Aquarium have an unbearably cute Christmas video for you.  I especially love the garden eels with little beanies on. Tip of the Santa hat to Akira Kanezaki for the link.

 

Saturday
Dec182010

DTF's Christmas Research Redux

In this peri-celebratory season things will be a little quiet here due to other commitments, so I thought I would bring back a few of my favourite research posts from the year.  Since this blog was effectively launched early in 2010, you might not have seen some of the earlier ones.  So here they are, I hope you enjoy them:

What’s a manta do?  A discussion of the surprising discovery that one of the worlds largest ocean-dwelling species is not “one” after all, but “three” (species, that is)

Slow down = Mow down?  The most viewed post of the year on DeepTypeFlow (>30K hits); a discussion of Ed Gerstein’s research on hearing abilities of manatees and the implications for boating in Florida

Your calamari wants a flat screen. A startling discovery that octopus can see hi-def TV, but not regular TV.  Bloody techno-snobs…

The Ocean conveyor running AMOC.  Two contradictory studies show the complexity of the global climate system and the role that the ocean plays therein.

When can we stop sampling and have a beer?  (Predictably?) one of my favourite topics - species accumulation curves and what they tell us about biology and about how to sample it.

When errors detract from the message, who is to blame?  A cranky rant about an especially shoddy bit of scientific editing.

To see the world in a grain of sand: movement from a turtle hatchling’s perspective.  An exploration of work out of Daniel Goldman’s lab at Georgia Tech regarding the suprisingly versatile turtle hatchling

Sunday
Dec122010

The World's Resilient Reefs

There’s no doubt about it, coral reefs face a lot of threats.  If you watch the news, read the paper or follow online, you might be familiar with many of these: overfishing, nutrient pollution, physical damage from tourists and of course the biggies - diseases, bleaching and ocean acidification.  If you have no idea what I am talking about, read J.E.N. Veron’s piece in Yale Environment 360 for a good introduction, and a thorough demoralisation!  The TL;DR of that article is that bleaching comes from heat stress that causes corals to expel their mutualistic algae, while all that atmospheric carbon dioxide we’re putting up in the air is leading to more acidic oceans that are ever more hostile to corals and other animals that want to deposit a calcium skeleton.  Together, these threats may spell the end of coral reefs as we know them within a generation.  That’s the idea anyway, but to the contrary, I want to make a case here that all is not lost and that efforts to restore reefs are not futile.  I will present two pieces of work that suggest that recovery is possible and can be enhanced if we make a decent effort to help the reef do what it does best - recover - and I want to offer another thought that is very relevant to reef recovery, concerning heterogeneity. 

Black band disease in a massive coralLets start with Caribbean reefs.  What a mess!  All over the Caribbean, reefs have been subjected to widespread damage, especially overharvesting and nutrient pollution, stressors which in turn have been associated with extensive outbreaks of previously unknown diseases.  Why does the Caribbean get it so bad?  Well, there aren’t nearly as many coral species in the West Atlantic as there are in the Indo-West Pacific to start with, i.e. diversity is much lower and so is the percentage of space occupied by corals, or “coral cover”.  So if the key coral species - staghorn Acropora cervicornis and elkhorn A. palmata in particular  - are wiped out, then a lot of the reef forming ability is lost.  With such low diversity, it isn’t far to fall, so to speak.  And that’s exactly what happened.  In some places it was the result of diseases that wiped out sea urchins that would normally graze down algae that would outcompete the corals.  In other places it was overharvesting of herbivorous fishes.  Take away the urchins/fish and the algae runs rampant and overgrows the corals and the reef dies.  To make it worse, we insist on tipping the balance further in favour of algae by adding nutrients in the form of sewage effluent.  A lot of diseases have also taken their toll on Caribbean corals.  Many of these have descriptive names like “brown band”, “black band” and “white pox” that evince the nature of the lesion (say, a discoloured stripe, slowly spreading across the colony); these simplistic descriptions also highlight that their causes are often poorly understood.

So, low diversity, excess nutrients, overharvesting, diseases, pretty hopeless right?  Well, yes, you might think so.  In many parts of the Caribbean, staghorn and elkhorn populations are down >95%.  Let me stress that: coral populations are down by ninety-five percent or more.  How grim is that?  There’s no coming back from that, right?  I mean, that’s too small a population to repopulate, right?  Well, we’ll see in a minute.

A bleached acroporid reefOK, now to the Pacific.  Pacific reefs are like a Rolls Royce to the Caribbean Toyota (see how I did that?  I offended millions of Toyota drivers and all the Caribbean reef fans at the same time - pretty nifty, huh?).  Its undeniable though: on the whole, Pacific reefs have higher diversity, higher coral cover and are just flat out better reefs.  Or rather, they were until the disastrous bleaching event of 1998/99 and those that have occured since.  In addition, with so many more “stony” corals (the reef-forming or scleractinian types), Pacific reefs may be especially susceptible to ocean acidification.  Various folks have tried to predict how the combination of heat/bleaching stress and acidification might affect Pacific reefs; I mentioned Veron’s article earlier, but you could also look at David Bellwoods paper from a couple of years back in Nature.

During the 1998/1999 El Nino event, vast tracts of Pacific reefs were bleached to death.  Areas that had previously had 100% live coral cover now had none, and were soon covered in a veneer of turf algae.  Much like the Caribbean situation, you have to wonder how a reef could possibly recover from that.

Yet - and this is where it gets good - recovery is possible.  Perhaps we shouldn’t be surprised; reefs have had to recover from cyclones, climate changes, diseases and pests since time immemorial.  But, can they recover from the man-made threats we’ve thrown at them lately?  Two people at least say yes.

Ken Nedimyer is an unlikely hero for coral reefs.  A former tropical fish and coral collector for the auqarium biz, he one day realised the threats to both his livelihood and his favourite places, and so he started and now runs runs the Coral Restoration Foundation, a non-profit reef restoration effort based in the Florida Keys.  It seems  like tilting at windmills, but no.  Ken visited Georgia Aquarium recently and explained the foundation’s activities and, crazy as they might seem, it just might work.  Ken and his team have a coral nursery off the coast of Key Largo, where they propagate corals to restore Florida reefs.  How is this possible?  Partly its the power of geometric increase.  If Ken takes a colony of coral and breaks it into 25 pieces, each of those can grow a new colony that within a year or two can be broken into another 25 pieces, or 625 pieces total.  Pretty soon you have enough “frags” or “nubs” to replant a decimated reef.  Ken has done just that and the reefs have shown phenomenal growth since then.  I asked him “What’s the point in replanting a reef if the original insult that killed the reef is still around?”  I thought it was a fair question, but so was his answer, that its like a rainforest thats been clearfelled: the cutting crew is actually long gone but the thing preventing the forest from regrowing is that there aren’t enough seeds left to repopulate.  But, if you plant some new colonies, you can recover the reef and do so suprisingly quickly.  He showed photographic evidence of the reocvery of replanted reefs in just a few short years and by the end, he’d made a believer out of me.  There IS potential for coral propagation as a meaningful way to rehab the reefs of Floirida and the Caribbean.

CRF Coral nursery. Image copyright: Carey Wagner, South Florida Sun Sentinel

What about the vast, vast Pacific though?  How can we possibly restore those reefs?  Enter our second reef scientist, Dr. Bruce Carlson.  Bruce has been a leading figure in coral aquariculture for decades since his seminal works at the Waikiki Aquarium, but he’s also a passionate conservationist, diver and photographer, all of which combined to help him study natural resilience of Pacific reefs.  After the 1998 bleaching event, Bruce had a chance to study the recovery of a number of reefs in Fiji, which he did in collaboration with his wife Marj Awai for the next decade, often on their own dime.  Together they showed that the reef could crash from 100% live cover to just 3% and back to >95% in less than ten years.  In the geological timescale (hell, even the biological), ten years is a fleeting instant.  Thus they showed that reefs can and will recover from disastrous bleaching , naturally.

Bruce Carlson on one of his transects in Fiji. Photo by Marj Awai

The reefs of the world are incredibly special places and we should all be concerned about the threats that they face, but we can’t succumb to fatalism, because if we think that there is no hope, then we will take no action.  To do so would be a terrible mistake because, as Ken Nedimyer and Bruce Carlson show us, passionate and committed people can make a big difference and reefs can heal naturally and do so even better with our help.

Heterogeneity plays an important part in both the decline of reefs and our efforts to rehabilitate them.  In ecological parlance, heterogeneity means “patchiness” and it’s a pervasive feature of studies in biology.  Heterogeneity is important in the problems that reefs suffer: it’s not all reefs everywhere that are degraded, it’s some reefs in some places.  Similarly, our efforts to recover reefs will not occur everywhere reefs do; they will be highly focused in time and especially in space.  Heterogeneity is thus a critical feature of both the problem and the solution.  It means that we must always be mindful of where and when the problems occur, and that we must be equally strategic about applying solutions like Ken’s coral propagation programs.  Given the severity of the problem and the limited resources available to meet the challenge, we have few other choices but we can be confident in the success of our efforts  at preserveing or restoring reefs in at least some places, so that future generations can enjoy them as we have.

 

Saturday
Dec112010

A site visit to Harbor Branch

The submersible Johnson Sea Link aboard R/V Seward JohnsonOn Thursday morning Bruce Carlson and I rose early and headed out to visit Harbor Branch Oceanographic Institute in Fort Pierce Florida; the first visit for both of us.  I had long been aware of their marine engineering division and the important role of the R/V Seward Johnson and its attendant submersibles - the Clelia (which we had on display at Georgia Aquarium for a while) and the Johnson Sea Link - in NOAA’s UNOLS oceanographic fleet, but there was much more in awaiting us at that storied campus than I think either of us expected.

Harbor Branch was established in the early 70’s as a private non-profit ocean research center by J. Seward Johnson, the son of Johnson & Johnson founder Robert Wood Johnson.  More recently HBOI became a part of Florida Atlantic University, based a ways up the A1A in Boca Raton

As we toured the site with Assistant Executive Director Megan Davis on the first day, I was first surprised and eventually staggered at the scale of their aquaculture actvities.  Their experimental production facilities extend over several acres of spotless Quonset huts on the shores of the Indian River Lagoon and include programs on conch (queen and fighting), clams (hard and sunray venus) and marine snails, though some of their biggest efforts are currently directed towards Florida pompano.  Harbor Branch also has an extensive marine drug discovery program that searches for active compounds among the thousands of species in their collection, which might then be used to treat human diseases.  There’s a great synergy between that program and the ocean exploration group in that submersibles can bring back new candidate species (especially deep sea sponges) from research cruises around the world, which the clever biochemists and microbiologists can then go to work studying for their potential applications.  Its painstaking and tremendously challenging work, but they’ve had at least one anti-cancer drug through to Phase I clinical trials, so the potential is there.  Finally there’s a well-established marine mammal program at Harbor Branch, which includes studies on the health of dolphins and manatees in Indian River Lagoon and is responsible for responding to all strandings on that part of the Atlantic Florida coast and the pathology research on those unfortunate animals that don’t make it.  The aquarium is intimately involved in these studies because our Cheif Veterinary Officer Dr. Greg Bossart was based at HBOI for many years

On the second day we also toured Oceans, Reefs and Aquariums: a private ornamental fish and coral culture company that is co-located on the HBOI campus and breeds over 70 varieties of marine ornamental fishes.  Many people are surprised to learn that marine ornamentals like clownfish, dottybacks, cardinal fish, mandarin gobies and seahorses can be and are bred on commercial scales; there seems to be a well-entrenched dogma that marine species don’t breed in aquariums.  Of course, thats not true, they breed all the time.  But, as Bruce would say, its not the spawning thats the problem, its the early rearing and especially the need for speciality foods.  Why so hard?  Well, many species cultured for food have large yolky eggs and big larvae that can feed on common foods like brine shrimp nauplii straight out of their eggs, but reef fishes are different; they often have tiny eggs and larvae that are smaller than many of the food items they might otherwise be fed.  Perhaps not surprisingly, those marine ornamentals that have been bred so far have larger eggs than some of their relatives, but successfully rearing fishes like angels and butterfly fish is still proving to be a tremendous challenge.  Not so with corals.  ORA’s coral culture greenhouse is replete with relatively low-tech trough systems where technicians skillfully “frag” coral colonies (cut little bits off the branches) in exactly the same way as a horticulturist might take cuttings from a plant.  The end result is successful multiplication and large scale propagation of many branching, plating and massive corals.  This provides a premium marketable product while reducing impact on natural reef systems because no further extraction is needed after the earliest parent colonies.  In cheesy business-speak: it’s truly a win-win.

Happy acroporid coral frags at the ORA facility

While we were there, Bruce and I also gave seminars about our respective studies - his on resiliance of Fijian coral reefs to bleaching and mine on (what else?) whale sharks.  It was a lot to fit into two days, but I came away with a much deeper appreciation for the breadth and depth of programs at one of the world’s best-known marine science facilities.  I hope it was the first of many such visits because they’ve got a lot of great stuff going on there.

Wednesday
Dec082010

Dr. Roy's Aquariumania

If you’re into podcasts, my colleage and good bud from the University of Florida, Dr. Roy Yanong, is doing a series called Aquariumania.  Check them out.  Roy is a veterinarian and fish health researcher and his latest podcast is an interview with fish curator at SeaWorld, Jim Kinsler.  He’s got other gems too, like this interview with Shedd Aquarium water quality expert Allen Lapointe and this one with Dr Helen Roberts, one of the few private veterinary practitioners for whom the bulk of their business is made up of fish patients.

Bear with some ads early on and you’ll be able to listen to some of the current luminaries in aquarium health, interviewed by one of their own.  Kudos to Roy for embracing the new media!  If you’re into aquariums and fish health at all, they’re well worth your time.

Wednesday
Dec082010

Where is your line?

I am pretty sure I’ve found mine.  A fellow student when I was at college was from Taiwan and used to tell me about a fish dish cooked in such a way that the fish was alive when it was brought to the table and that you ate it while it was still “gilling”.  I never believed him until now.  The following video may be disturbing to you, because it shows exactly the dish my colleague described.  It comes from Discovery News story (hat tip to @sharkb8t on Twitter) in reference to a new book from Penn State Researcher Victoria Braithwaite about whether or not fish can feel pain.  I am agnostic on the question - I just don’t feel I know enough to make a sound judgement - but in this case, doesn’t it seem best to err on the side of caution?  Does the culinary novelty, the ability to say thats really fresh, outweigh even a slim possibility that this fish could feel some part of the process and is, or was, suffering as a result?  I’m inclined to think not, but what do you think? 

Friday
Dec032010

Carnival of the Blue #43 - the seasonal arboreal phasianid edition

 

 

I’m delighted to host this month’s Carnival of the Blue; my thanks to Jason and Mark for letting me help.  If this is your first visit to Deep Type Flow, then welcome!  You’ll find here a lot about whale sharks, which is my main research thrust at Georgia Aquarium, but there’s a lot of other diverse stuff too, like ecology, oceanography, marine mammals, turtles, fish, parasites and more.  Basically anything about the diversity of ocean life or the science that flows from it.  If you’re a return visitor, thanks for participating.

Since it’s the season for it, I thought we would do the Carnival to the tune of “The Twelve Days of Christmas”.  SO, my horrible attempts to shoehorn too many syllables into that well-worn melody notwithstanding, please sing along with the following while you enjoy these excellent ocean-themed blog posts (this is best done with a glass of egg-nog by the fire on the iPad you got from santa). 

 

On the 12th day of Cot-B, the bloggers gave to me:

Oil Drums a-leaking  ♪  The DeepSeaNews crew continue their comprehensive coverage of the Deepwater Horizon oil spill and its ecological consequences.

A mantis nails a damsel  ♪  From Michael at Southern Fried Science/Arthropoda.  The story behind a remarkable photo capturing an impossibly fleeting predatory coup de grace.

10 New Jersey Shorebirds  ♪ From Alex at The Nemesis BirdBeautiful photographs of seabirds from down around Cap May in far southern New Jersey

Crabs eating cordgrass  ♪  From Sam at Oceanographer’s Choice.  Essential coastal salt marshes of Cape Cod are are being munched by tiny crabs freed of predation by declines in tautog abundance.

♫ Google’s acid oceans   ♪  From Emily at Oceana’s blog The Beacon. Google Earth has teamed up with Oceana to make a tour explaining the implications of an increasingly-acidic ocean

♫ Sustainable seafood  ♪  At Blogfish, Mark offes Powell’s Law and wonders whether self-righteous activism is getting in the way of people’s ability to enjoy seafood

♫ Fearless seals a-feeding  ♪  From Chuck at Southern Fried Science/Ya Like Dags? In another predator-release case, seals freed from fear of predation by sleeper sharks have bolder prey searching strategies

♫ FIVE! DI-A-GRAMS!  ♪  From David at Southern Fried Science/WhySharksMatter. An original post considering 5 drawings of experimental apparatus that, taken out of context, might look altogether different

Grey literature  ♪  From Andrew at Southern Fried Science. Thaler considers the perennial quandary of what to do about grey (i.e. not peer reviewed) literature, as it applies to urgent fishery management

♫ 3 Hermit crabs  ♪  From Susannah at Wandering Weeta.  Anecdote about antagonistic anomurans arguing about alternative accommodations

Two of Al Dove’s  ♪ (this one and this one). The dynamic movements of baby turtles and the  surprising impact that slowing a boat can have on manatees

And a Barnacle on an Oyster.  ♪  From Jessica at Oceanwood.  A photographic allegory about crustaceans and civilisation

There’s lots of other great blogs out there with marine content, too.  Here’s just some of the other 2010 Carnivals hosted at blogs not represented in the list above: SeaNotes (#32, Jan), Oh, for the love of Science! (#35, Apr), Observations of a Nerd (#36, May), Saipan blog (#40, Sep) and Jason’s own Cephalopodcast (#41, Oct). And with that:

A very happy <insert holiday of your choice here> to you all!

Cheers!  Al

Wednesday
Dec012010

A new angle on diving in whale sharks

ResearchBlogging.org

Recently I featured a piece about how turtle hatchlings change their movement strategy several times in just the first few hours of life in order to suit their changing needs as they move across different types of sand.  Well, to go from the sublime to the ridiculous (or rather, just from the really small to the truly gargantuan) there’s a new paper out that shows that whale sharks, too, adjust the way they move according to their needs.  This new work follows nicely after Phil Motta’s paper earlier this year, also discussed here, which took a comprehensive look at how whale sharks feed.  Between them they make big strides in the autecologyof whale sharks.  The new paper, by Adrian Gleiss and Rory Wilson from Swansea University and Brad Norman from ECOCEAN, describes work they did at Ningaloo reef in Western Australia, perhaps the world’s best studied aggregation area for whale sharks.  They took a new type of accelerometer tag developed in Rory’s lab called a “daily diary” and deployed them on wild whale sharks to measure not only where they are (like traditional wildlife satellite tags) but also details about what the animals were doing: the beating of their tails and the rientation of their bodies in 3 dimensions.  From this information they could basically reconstruct the animal’s actions with computer game-like accuracy (indeed, the software looks a lot like something for the X-Box!).  The findings show Whale shark with accelerometer tag. Photo: Steve Lindfieldan animal with a surprising diversity of movement modes and a sophisticated approach to minimising the amount of energy they spend moving through the ocean.  They also help explain one of the most enduring mysteries of whale shark biology - a curious pattern of super-deep dives over the abyssal depths.

The first big observation is that whale sharks have 4 different types of dives and that these probably serve different purposes.  It was well known from traditional tagging studies (sat tags record depth data as well as location) that whale sharks dive quite a lot throughout the day, but the new daily diary tags showed that not all dives are the same and, in fact, they could be easily discriminated as one of four main types based on what the depth profile looks like: yo-yo (probably searching), V (horizontal movement), U (feeding at depth), and bottom bouncing (searching at depth).

Four dive types in whale sharks. (a) yo-yo, (b) V-shaped, (c) bottom bounce, (d) U-shaped

The second and a really key finding is that all the dive types feature a gliding descent and an active ascent.  In other words, they don’t beat their tails on the way down, but they do on the way up. Gliding converts their negative buoyancy (a sort of potential energy) into horizontal and vertical movement (kinetic energy).  The fact that their dive has both vertical (depth) and horizontal (forward motion) components, without active use of the tail, shows that their bodies are adapted to convert sinking to swimming.  Most of that effect comes from their pectoral fins, which serve as wings for gliding, but there is probably a big contribution from that incredibly broad head, which serves as a sort of lifting canard, a flat plane that creates lift at the front end. Gliding is an extremely efficient way to move; not only are they not spending energy operating their musculature to beat the tail through the water to create thrust, but the drag coefficient of water across their skin is a third as much when they glide as when they are actively beating their tails.

The third finding, which Gleiss and friends really go into in some, ahem, depth, is that angle of descent and ascent is consistently different for each type of dive and that they are optimal for whatever the purpose is.  For example, a V dive is meant to cover a great horizontal distance, so the gliding descent is at a shallow angle and the ascent angle is the one that minimizes the amount of energy spent to gain horizontal distance. In contrast, the angles of a yo-yo dive minimize the amount of energy spent to gain vertical distance.  The important point is that for any given purpose there is an optimal angle - one that uses the least energy for the most benefit - for both descent and ascent components.  Whale sharks adapt the geometry of their dives to stay in that optimum zone and minimize the amount of energy they spend on whatever they are doing.  Clever right?  Well, its probably not a conscious decision, but rather a state of tremendous efficiency towards which they have evolved: natural selection is a powerful tutor.

Diving geomtry in whale sharks. The angles of descent and ascent (the two thetas) are optimised for minimum energy expenditureIn the course of their study, the researchers solved one of the great mysteries of whale shark biology: the extraordinary deep dives whale sharks do when they are over abyssal depths (see the Brunnschweiler reference).  These dives tend to happen around dawn and dusk and may exceed 1600m or more in depth; in fact, we don’t know just how far down they go, because most tags have a self-preservation device that cuts them free of the animal at 1600m, lest the tag be crushed by the immense pressure of the overlying water.  We’re talking depths enough to turn a Styrofoam coffee cup into a shrinky-dink thimble, as well as changing enzyme kinetics and making the urea in their blood greatly more toxic, so the motivation to dive so deep must be compelling. There had been suggestions that they go down to rid themselves of parasites (as a parasitologist, I never bought that: parasites would easily co-evolve to tolerate such a strategy), or to clean their filter plates (at those depths particulate organic matter redissolves!) or even to “sleep”, although there is no evidence that sharks do so.    Well, it turns out that they are dives of the V type, optimised to spend the least amount of energy while achieveing maximum horizontal movement (HD in the figure above).  In other words, to travel far, they glide deep, and then gently beat their tails and ascend at a very shallow angle (steeper angles costing more energy and achieving less horizontal distance).  This is a strategy best used during migratory phases when travelling, not feeding, is your number one priority. 

To recap then, whale sharks turn out to have at least 4 main types of dives, each serving a different purpose from feeding to horizontal travel, and the geometry of each type of dive is optimised to achieve the goal while minimising the energy cost.  Overall, it paints a picture of an animal that is a paragon of efficiency, which is understandable given that they dwell in the nutrient-poor surface waters of the tropics, which are typically much less productive than the rich cold temperate and Arctic seas frequented by their fellow filter feeders: basking sharks and baleen whales.  I suspect that future studies will show that whale sharks deploy these movement strategies to travel efficiently between hotspots of tropical productivity, be they fish spawning events or patches of seasonal tropical upwelling, and that they are therefore extremely strategic masters of the feeding/travelling trade-off.

Gleiss, A., Norman, B., & Wilson, R. (2010). Moved by that sinking feeling: variable diving geometry underlies movement strategies in whale sharks Functional EcologyDOI: 10.1111/j.1365-2435.2010.01801.x

Brunnschweiler, J., Baensch, H., Pierce, S., & Sims, D. (2009). Deep-diving behaviour of a whale shark during long-distance movement in the western Indian OceanJournal of Fish Biology, 74(3), 706-714 DOI: 10.1111/j.1095-8649.2008.02155.x

Monday
Nov292010

Carnival of the Blue is coming to Deep Type Flow

The 43rd Carnival of the Blue, bringing together the best of ocean blogging from around teh interwebz, will be right here at Deep Type Flow in the first week of December.  If you’re an ocean blogger, get your submission in now.  If you’re a reader, watch this space.  It’ll be oceany, it’ll be bloggy, it’ll be Christmahannukwanziky…you’ll love it.

 

Tuesday
Nov232010

From blue to black - diving in a cenote

If the idea of swimming through narrow stone tunnels with no access to overhead air scares you, then you and I have something in common.  SCUBA is great - the 3D freedom can’t be beaten - but the idea of SCUBA in caves has always carried with it a special kind of terror.  I mean, caving on foot is scary enough, but to do it in a suffocating medium, into the darkness, carrying all your air in a bottle on your back is freaky indeed.  So when the opportunity arose on a recent research trip to Mexico to do a “cavern dive” in a cenote, or sinkhole, I approached the idea with a mix of adolescent excitement and centenarian incontinence.

Luckily, my travelling partners were all experienced divers.  Oh, sorry, I should say Experienced Divers.  Two of them - Marj Awai and Dr. Bruce Carlson - are lifelong SCUBA scientists with thousands of dives in service of ichthyology and aquarium collections.  The other two - Elliott Jessup and Jeff Reid - are dive safety officers and experienced cave divers.  I am comfortable in the water, but admit being a little uncomfortable with my newbie status, especially with respect to diving in caves. Their experience is a source of some comfort. What could go wrong, right? Right??

Purist cavers will note that I earlier said “cavern” dive, which technically is not a cave dive, because if you extinguish artificial light you can always see some natural light to navigate your way back to the opening.  But, let me tell you, having done it, that that is as far underground as I have ever been and it was, in all practical respects a Cave as far as I was concerned; certainly enough so for a first timer.

The particular cenote we dove was Dos Ojos, which is part of the longest mapped cave system yet discovered, incorporating hundreds of kilometers of anastomosing voids in the limestone slab that makes up the eastern Yucatan, not far from Mayan ruins and the town of Tulum.  Most of the system is flooded, meaning that the caves and their spectacular salactite and stalagmite formations formed in dryer times when the sea-level was lower and the caves were full of air, then later the systems filled with water as the sea level rose and freshwater percolated through the stone to fill the voids.  Many cenotes are thus connected by tunnels of water under the stone floor of the jungles of Quintana Roo, and both our dives that day involved descending into one cenote and traveling underground to surface in a second.  Although Dos Ojos itself is very well-known and receives dozens of tourists a day, the same cannot be said of the rest of the cave system.  There are many parts that have yet to be explored, including where the system meets the sea.  That’s right, this flooded freshwater system connects to the ocean, somewhere along the Rivera Maya, maybe somewhere near Xel-Ha. 

Click the map to see the REST of the cave system!

How is it that some parts are a tourist destination and some parts unexplored?  The answer lies in the technical nature of diving these sorts of systems.  What we did was a simple in and out in a very superficial part of the system - we figuratively dipped out toe in the bathtub - but to go to the far reaches of the cave system, especially the uncharted parts, is a huge technical challenge that only a select few experienced divers are able to do.  Such exploratory dives often involve multiple staged dives, with the earlier dives aimed at laying out a guide line to follow on future dives and clipping off SCUBA tanks at regular intervals so that bottom time can be extended and the final push can be a long and penetrating dive that pushes into new territory.

For our much more superficial tourist dive, I was more than happy to be on a single tank and within sight of the blue glow of daylight.  As a diving experience it was, in a word, exquisite.  From the first cooling dip into the water (Q.Roo in August is H.O.T.), to some of the best visibility I’ve seen, to the incredible rock formations and the inquisitive tetras and cave shrimp, it was quite the best dive I have ever done that wasn’t primarily about animals. And as for the terror about being underground and all that noise?  It melted away in the pure joy of the experience.  Nonetheless, it was exciting to think that you could just keep going through tunnel after chamber, for hundreds of kilometers, all underground and underwater and that you could easily discover new rooms and new paths never seen before.  Its a thrill that such opportunities for discovery still exist today; there’s no app for that!

Sunday
Nov212010

Do you fugu?

Apropos of nothing, colleague Dr. Bruce Carlson recently bequeathed to me a curiosity from his personal collection: a 20-odd-year-old can of fugu, that potentially deadly Japanese delicacy made from the flesh of any one of a group of toxic tetradontiform fishes that live both in Japanese waters and elsewhere in the tropical and warm temperate world.  The risk posed by eating fugu is apparently proportional to the skill of the preparer and, as such, fugu is often excedingly expensive and regarded as a luxury item.  In this case, though, the fish is in a can and apparently has some sort of self-heating device in the base.  The pictographic instructions suggest that you indent a button in the middle of the bottom of the can, then set it upright and pop the lid and wait until its heated through before, mmmmm, tucking in.

Let me go on the record as saying that if I am ever to eat fugu, it will not be out of a can, and nor will I trust its cooking to some pop-cap device in the bottom thereof!

Takifugu rubripes, the most well known of the tetrodotoxic puffers

Learn more about fugu and its history at this excellent blog post.

Thursday
Nov182010

Georgia Aquarium is Five Years Old today!

Today marks the 5th anniversary of the opening of Georgia Aquarium.  I’ve been along for most of the ride since consulting before the aquarium opened, and it’s been an amazing experience.  Starting in the crazy busy opening days, through some tough times in 2007, to the current scene, which is great, its been a spectacularly interesting, challenging and ultimately satisfying endeavour to be a part of.  We’ve been able to share the wonders of the ocean with over 10 million guests so far, and during that time we’ve generated new science about some of our flagship species such as whale sharks, manta rays, beluga whales, dolphins and penguins.  I’ve met and worked with some tremendously passionate and talented people and been introduced to new ways of thinking about biology, animal collections, management and what you might call “non-traditional” science.  I wouldn’t trade my time here for anything!

So HAPPY BIRTHDAY Georgia Aquarium! I am excited about what the future holds for us all. And to those of you who haven’t been yet, I invite you to come to downtown Atlanta and share in a collection the likes of which you won’t see anywhere else.  Dive in, the water’s fine!

Wednesday
Nov172010

To see the world in a grain of sand - movement from a turtle hatchling's perspective

This post was chosen as an Editor's Selection for ResearchBlogging.org

ResearchBlogging.org

(with apologies to William Blake).  A grain of sand represents many things to a baby turtle.  While still within the egg, sand represents a roof over your head, protection from the desiccating sun and from predators, and a blanket to keep you warm and level until its your turn to break free of the nest and do that mad nocturnal dash down the beach to the safety (yeah, right!) of the sea.  From the moment of hatching, however, sand presents a range of obstacles to a baby turtle, and believe it or not, the way they overcome those obstacles tells scientists a lot about how things can and should move through and across granular substrates, and maybe offers a few solutions to human problems of this kind too.  That’s because, while they look like little clockwork toys ceaselessly flapping their way to some unseen destination, they’re actually engaging in several different types of locomotion, and adapting them on the fly to best suit the substrate they happen to be on.  Discovered by Nicole Mazouchova and Nick Gravish from Daniel Goldman’s biomechanics lab at Georgia Tech, these adaptations show us that baby turtles are much cleverer than perhaps we gave them credit for, and they may even explain to some degree why turtles nest on some beaches and not others.

Immediately after hatching a foot or more below the surface of the beach, a baby turtle must get to the surface to draw breath and begin its journey down to the water.  That high up a beach, the sand is usually dry and loosely packed.  Governed by the laws of physics, sand of this type can act either as a liquid or as a solid, depending on the force applied to it. (if you ever want to see what I mean, add a little water to some corn starch in the palm of your hand until its like whipping cream, and then rub the surface with your other finger.  If you rub slowly, your finger will wet, but if you rub fast, the surface will appear dry and your finger will slide right across).  To move across this kind of sand, the turtle reaches forward with its front flipper and places it flat on the sand, then digs the leading edge down until the flipper is perpendicular to the surface and mostly buried.  By pushing back with just the right amount of force, the sand behind the flipper doesn’t yield, but solidifies like the corn starch in your hand, providing a solid point of leverage against which the turtle can gain traction and push further forward.  It then repeats the process on the other side, lurching forward one push at a time with alternating strokes, rather like a rock climber makes progress up a wall.  The key thing is that if the turtle pushes too hard or fast, the sand will fluidise and the flipper will pass through it like a liquid, producing no traction; they have to push just the right amount for the physics of the sand to work in their favour.  Nick, Nicole and Dr. Goldman observed this in wild loggerhead hatchlings, then showed why this is mathematically, and then created robot turtles that recreated exactly the scenario in the lab to confirm their mathematical model (what, you mean you don’t have a robot turtle hatchling in your lab?).  You might think that this kind of motion is pretty inefficient since you effectively stop after each push, but it works well for the hatchlings; they can move three body-lengths per second or more across the sandy surface.  That’s the equivalent of a human running at a full sprint, and they’re doing it on dry sand.  Good luck matching that effort!

Farther down the beach, the turtle meets a different kind of sand.  Wetted and a sorted by the tide, this sand is flat and compacted and the hatchling would be unable to dig its flipper in, so it changes strategy.  Instead of digging in and pushing against a block of solidified sand, it jams just the claw on the leading edge of its flipper into the surface like a spike and (with some help from the back flippers) pushes off it, rotating around the point as a pivot, to jam the next point in a little further ahead, just like a skier planting their stocks in the snow as the pivot point for turns.

Farther still, the turtle meets the water.  At this critical point, the game changes completely.  Instead of moving across a granular surface, the hatchling is now supported by a liquid medium that will never solidify or allow them to gain traction like thy did on the beach.  That’s OK, though, because now the turtle gets the benefit of “inertial movement”.  That is, it can build up momentum from repeated strokes, unlike on the sand, where as soon as you stop pushing, you stop moving.  Movement through this sort of medium requires a totally different motion, so the turtle switches again, this time to the familiar symmetrical flapping that it will use for the rest of its life, creating lift and thrust with every stroke of the paired front flippers.

These biomechanical adaptations to different substrates may have a role to play in why turtles nest on some beaches and not others.  That’s because not every sand behaves so predictably.  Sands where all the grains are of similar size behave differently from those where the grains vary; and well sorted sands behave differently from poorly sorted sands.  You know this is you’ve ever walked on a “squeaky” beach - those sounds come from the friction of sand grains all being the same size (try squeezing a bag of marbles and you’ll see what I mean).  Taken together, these adaptations show a remarkable flexibility of locomotion for an animal just in its first hours of life.  It must be working well for them, though, because the sea turtle lineage has been doing just fine on this planet for over 200 million years.  To borrow from Blake once more:

Every night and every morn
Some to misery are born,
Every morn and every night
Some are born to sweet delight.

Mazouchova, N., Gravish, N., Savu, A., & Goldman, D. (2010). Utilization of granular solidification during terrestrial locomotion of hatchling sea turtles Biology Letters, 6 (3), 398-401 DOI: 10.1098/rsbl.2009.1041

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