Explosive radiation (in) rocks!

Much like internal waves, I always loved the idea of explosive radiation.  Not the nasty, pernicious Chernobyl kind; I mean the rapid evolution of a whole bunch of species from a common ancestor, over a relatively short period of time.   There's a few textbook examples of explosive radiations, but none so well-worn (possibly even hackneyed) as that of the cichlid fishes in the rift lakes of eastern Africa.  The startling diversity of these little fishes in lakes Tanganyika, Malawi and Victoria has kept evolutionary biologists busy (and Africans fed) for years.  See for example, the paper by Elmer and colleagues cited below, which points out that due to the drying-out of Lake Victoria 15-18,000 years ago, either all the cichlids there evolved since then based on stock that re-colonised from Lake Tanganyika, or they sought refuge elsewhere during the dry spell and returned when the lake refilled.

Cichlids are nice and all, but if you look around, you start to see radiations all over the place.  Turtles, bivalves and salamanders in the US south-east; tetras in the Amazon, eleotrid gudgeons in Australia, and gobies on coral reefs are just a handful of aquatic examples that are still with us, but there are many others in the fossil record too (hence my title) including trilobites and ammonoids and lots more.  Presumably these are the sorts of patterns that led Stephen Jay Gould and Niles Eldredge to develop the concept of punctuated equilibrium back in the 70's: theirs was the idea that evolution proceeds not gradually, but in fits and starts, in response to dramatic environmental changes and chance events.  The way I see this idea, most of the species we observe around us are the dregs of explosive radiations past, whittled away by extinctions to just the most successful few, either gradually or equally punctuated.  Cases like the rift-lake cichlids are just ones in which relatively few have gone extinct yet (but see the effects of the introduced Nile perch!)

All of this was just a preamble for what I really wanted to post about, which was about a radiation I only heard about recently.  Late last year I was at a scientific exchange  of US and Russian fish health researchers organised by the National Fish Health Research Laboratories and sponsored by the Living Oceans Foundation, at which one of the Russian speakers  Maxim Timofeev introduced us the radiation of several groups, including amphipods, in Russia.  Amphipods are (usually) tiny shrimp-like animals that live on the bottom or among dense plants or algae; read more about them in the Väinölä paper cited below.  Well, in Siberia's Lake Baikal, the worlds oldest, largest and deepest freshwater lake, they underwent a remarkable radiation, to produce over 300 species (a third of the worlds entire fauna), including spectacular beasts such as the fish predator (!) shown here. I mean, HOW AWESOME IS THAT THING?  Freaks me almost as much as giant wetas used to do, when I was younger (if you don't dig on bugs, I recommend not clicking that link...).  Anyway, I had no idea these things existed until Maxim gave his talk.  Don't you just love discovering new critters you never knew about before?  And not just one, but hundreds.

(Check out this link about Baikal fauna too; the language is just terrific.  Try this turn of phrase on for size: "When it comes to tenderness and gustatory qualities of meat, the omul knows no rivals")

Elmer, K., Reggio, C., Wirth, T., Verheyen, E., Salzburger, W., & Meyer, A. (2009). Pleistocene desiccation in East Africa bottlenecked but did not extirpate the adaptive radiation of Lake Victoria haplochromine cichlid fishes Proceedings of the National Academy of Sciences, 106 (32), 13404-13409 DOI: 10.1073/pnas.0902299106

Väinölä, R., Witt, J., Grabowski, M., Bradbury, J., Jazdzewski, K., & Sket, B. (2007). Global diversity of amphipods (Amphipoda; Crustacea) in freshwater Hydrobiologia, 595 (1), 241-255 DOI: 10.1007/s10750-007-9020-6

When can we stop sampling and have a beer?

Yesterday I got a very kind email from a fellow scientist, Eric Seabloom at Oregon State University, letting me know that a paper I wrote with my PhD advisor Tom Cribb (University of Queensland) a few years ago had influenced a recent publication of his.  My paper was about one of those patterns in nature that just seem to be universal.  They're called species accumulation curves and, at the heart of it, they represent the "law of diminishing returns"* as it applies to sampling animals in nature. Basically, they show that when you first start looking for animals - maybe in a net, a trap or a quadrat - pretty much everything you find is new to you, but as you go along, you find fewer and fewer new species, until eventually you don't find any more new species.  Simple, maybe even obvious, right?  Well it turns out that that simple observation has embedded within it all sorts of useful information about the way animal diversity is spread around, and even about how animals interact with each other in nature.  Consider the figure on the above right, which represents two sets of 5 samples (the tall boxes), containing different animal species (the smaller coloured boxes).  The first thing to note is that both set (a) and set (b) consist of 5 samples, and both have a total diversity of 5 species (i.e. 5 different colours).  In set (a), all the diversity is present in every sample, but in set (b) there's only one species per sample, so you have to look at all 5 samples before you find all 5 species.  If you were to plot a graph of these findings, you'd get very different species accumulation curves; they would both end at 5 species, but they would be shaped differently.  They'd look much like what you see below:

 Set (a) would be more like the curve on the left (in fact, it would be a perfect right angle), while set (b) would be more like the curve on the right (in fact, it would be a straight diagonal line).  You can see some other properties on the two types of curves above also, for the more ecologically inclined, but the gist is, the shape of the curves means something about the communities they describe.

Tom and I wrote our paper after many nights in the field spent dissecting coral reef fishes to recover new species of parasitic worms - a time consuming and sometimes tedious process (sometimes thrilling too, depending on what you do or don't find).  We were often motivated by another far more important factor too - when can we stop all this bloody sampling so that we can go and have a beer on the beach?!?   Species accumulation curves therefore have a very practical aspect to them - they tell you when its OK to stop sampling because you've either sampled all the available species, OR, you've sampled enough to extrapolate a good estimate of how many species there might be.

Back to Eric Seabloom.  He and his colleagues wrote a paper about the diversity of aphid-borne viruses infecting grasses of the US Pacific northwest and Canada.  While the environment that they sampled was about as far away as its possible to be from the coral reefs that Tom and I looked at, the patterns of saturated and unsaturated communities they observed were the same. I get a huge buzz out of that, and that out of the morass of published science out there, Dr. Seabloom found a scientific kindred spirit who had had the same thoughts and ideas about nature, however different the specific areas of study.  While Tom and I sipped beers on the beach and watched the sunset over the reef, I wonder if Eric and his colleagues blew the froth off a few while they watched the wind waves spread across the grasslands.  There's something so unifying about science; it can give you common ground with someone you never would have otherwise known, and that's just one reason why I love it so much.

*The tendency for a continuing application of effort or skill toward a particular project or goal to decline in effectiveness after a certain level of result has been achieved. Answers.com 

DOVE, A., & CRIBB, T. (2006). Species accumulation curves and their applications in parasite ecology Trends in Parasitology, 22 (12), 568-574 DOI: 10.1016/j.pt.2006.09.008

ERIC W. SEABLOOM, ELIZABETH T. BORER, CHARLES E. MITCHELL, & ALISON G. POWER (2010). Viral diversity and prevalence gradients in North American Pacific Coast grasslands Ecology, 91 (3), 721-732 (doi:10.1890/08-2170.1)

CITES epic fail?

David Helvarg has a scathing OpEd piece in the Huffington Post yesterday, and rightfully so.  CITES, the Council for International Trade in Endangered Species recently failed to give proposed protections to the northern bluefin tuna and several species of threatened sharks, apparently caving to the desires of Japan and other nations with similar pro-harvest agendas.  I dont know how much data you need to be convinced that these populations are threatened to the point of collapse, but even if if there were equivocation on the science (and there's not), why not err on the side of safety?  Just as line calls in baseball go to the batter, decisions regarding endangerment should always go to the organism.

The way I see it, bluefin are stuck in a positive feedback loop of ever increasing commodity value, feeding more intense searching/fishing efforts, further reducing the population and thereby driving the value yet higher.  Its a trajectory that only ends one way, and it ain't a good one.

Oh, and if what Helvarg says is true about the Japanese embassy serving bluefin sashimi at a reception for the CITES delegates, then wow. Just, wow.  I sincerely hope those were artificially reared and not ranched or wild-caught...

The ghost of fishers past

The folks you see out on their boats on the bay are not the only ones fishing; those who came before them still get a slice of the action, as this recent article about the retrieval of "ghost gear" from the Chesapeake Bay illustrates.  In many trap-based fishing industries, like lobsters and crabs, a significant number of traps are lost during the course of regular fishing efforts.  In addition, when a fishery turns bad, as happened in the Long Island Sound lobster fishery in 1999, some fishers cut their losses, and their marker floats, quit the fishery and just leave their gear where it is on the bottom of the bay.

The problem is, ghost gear like this keeps on fishing, long after the fisher has moved on to other endeavours.  The design of the trap continues to attract animals, even without bait, because the trap is basically a refuge or cave.  Those that enter are unable to leave and as they die they may act as bait to attract yet more animals to feed on their body.  In this way, the trap becomes a sort of "biomass black hole", sucking in animals from all around, for as long as the trap holds together.  Nets can ghost fish too, especially gillnets or any kind of trawl that can trap fish or strangle a reef

We used to trawl up ghost lobster gear all the time when I was working in Long Island Sound.  Indeed, few days on the water went by without snagging someone's old gear at some point, which speaks to the density of gear that's out there in some inshore waters.  I'm glad the fishers and the resource management agencies are working together to address the problem, because its one of those awful chronic out-of-sight, out-of-mind issues that can erode a fishery despite everyone's best efforts to manage things properly.  If you find ghost gear, call your local DEP or DEC, even the EPA, and let them know so they can come and retrieve it.

Picture of ghost gear on a coral reef from NOAA

Lionfish - more spectacular than your average invasive, but still a right pest.

When we think of invasive species, flamboyant fish from coral reefs are not usually the first thing that comes to mind.  Indeed, if you put together a list of characteristics of successful invasive species (like this one), "boring" would probably be close to the top, along with being quick to reproduce, not fussy about what you eat, having a large natural range, a great tolerance for extremes in the environment, and lacking natural enemies such as predators or parasites.  Think of some of the most successful invaders and decide for yourself if these predictions hold true: carp, starlings, mosquitofish, rats, sparrows, mice, rabbits, dogs, cane toads, cats, foxes, kudzu, chickweed... 

All this makes the invasion of the Atlantic seaboard by the Pacific lionfish, Pterois volitans, all the more remarkable.  Lionfish are flat-out spectacular!  Long prized as an aquarium specimen, they have bold stripes that spill over onto their fantastically long and showy fins; their scientific name even means "fluttering wings".  The sheer beauty of lionfish doubtless plays a role in how they came to invade the Atlantic in the first place; most likely they were an escaped or released aquarium species that found itself able to survive quite nicely in the conditions of the coastal Atlantic.  The beauty of lionfish conceals a dangerous secret - venomous spines on their dorsal (back) and pelvic (bottom) fins.  While they won't kill a person; they cause excruciating pain.  I've never been stung by one, but I have been stung by related scorpionfish (most recently the short-spined wasp fish) and the feeling is not one I'd care to go through again!

Over the course of just a few years, mostly since 2000, lionfish have spread dramatically along the coast of the Atlantic, from North Carolina down to the southern Caribbean and Mexico's beautiful Yucatan peninsula.  Typically considered to be a rocky or coral reef species, they've now been found swimming in the intracoastal waterway; that labyrinth of salt-marshes, channels and estuaries, engineered to allow safe passage of boats along the US coast in wartime.  This is sort of an unusual location, but it speaks to the adaptability of this remarkable fish.

So, what to do about such an animal??  Well, that's a tough one.  Invasive species (or more accurately, moving species around) are one of the greatest impacts humanity has had on natural environments, and there are very few cases where we have successfully eradicated or controlled an invasive (but see prickly pear in Australia), more often they just become part of the furniture and we get used to their impacts on the local ecosystem.  Introducing natural enemies (diseases, predators) like they did for prickly pear is a dangerous game; if you tried to get the Cactoblastus moth introduced to Australia in these days of stricter biosecurity, you'd almost certainly be denied.  You can easily get into a "spider to catch the fly" situation too; in fact that's how cane toads were introduced to many places - to control sugar cane beetles (which they suck at).  Perhaps the best approach is to do what we do best - create a market that will promote human efforts to exploit them, and then rely on the Tragedy of the Commons to do the work for you.  This has already been proposed with Asian carp.  Fortunately, it turns out that lionfish are not only spectacular aquarium fish, but also delicious in a white wine sauce.  I am sure that if we set our minds to it, we could do as good a job wiping out this species as we have with so many others.  So c'mon everyone and grab a fork; Save a reef - eat a lionfish, today!

(Photo and graphic from NOAA)

Fish as filters?

There's been a bit of press lately (see for example) surrounding a new paper from VIMS that concludes that the Atlantic menhaden or Bunker (Brevoortia tyrannus) is not very good at cleaning the Chesapeake Bay.  This seems an odd sort of paper but its actually not that crazy an idea.  Its turns out that lots of bivalve species like hard clams and soft clams actually pump enough water through their gills, sifting food as they go, that they can actually have a significant impact on the water clarity and nutrient content of the water.  Indeed, the zebra and quagga mussels that have invaded the Great Lakes have changed the entire ecosystem by doing exactly that.  With clearer water, there's less plankton productivity in the water column and more macrophytic plants and algae growing on the bottom.  Menhaden are filter feeders too, and they can occur in large schools, so perhaps its logical to think that they might be able to do the same sort of thing as the clams.  Alas, based on the VIMS experiments, it seems that they can't.

This is an interesting example of a negative result publication.  Often times you'll hear folks say we shouldn't publish negative results because, technically, you failed to prove that they clean the water, which is not the same as proving that they don't.  Well, as long as everybody is aware of that distinction, I still think negative results like that are useful to know, for two reasons.  One, its likely that they don't; if they do, then the effect is so minor that it was difficult to detect.  And two, it might save someone else from having the same idea and trying the same futile experiment.

The Chesapeake has some sporadic problems with hypoxia, which is ultimately a nutrient pollution issue, so I applaud the researchers for looking at a biological solution for what is otherwise a pretty intractable problem.