Attenborough and deep sea corals

There’s a new website up that talks about deep sea corals, including one of the species the science team has been studying here in Brazil - Lophelia.  Its even called Lophelia.org and was put together by some Scottish scientists who discovered Lophelia reefs off the coast of Scotland in 2003.  It’s very comprehensive and well worth a visit, and it’s recently earned an endorsement of the doyen of nature documentaries, Sir David Attenborough.  One of the weird things to think about when you click on over is that the same corals that form those reefs in Scotland are forming deep reefs here in Brazil.  How is that possible?  I mean, one is in the chilly North Atlantic, while the other is in the tripical south Atlantic.  Well, if you think about it, once you go deep, it doesn’t matter where you are, it’s always gloomy dark and cold!  For example, even though the surface temperature was in the high 20’s (low 80’s for the US readers) here in Brazil, the temperature down where the sub was going was 7-9 dgrees (around 45).

A Dendrophyllia alternata (originally mislabeled here as Lophelia) colony collected from the Abrolhos platform

The new website is a great resource for learning more about Lophelia and other deep coral reef species and just maybe it will help us all broaden our horizons to start considering coral reefs in a context broader than the insanely colourful shallow reefs that most easily comes to mind when you hear the phrase.

Dia 2 Campanha Seward Johnson - A guest post from Gustavo Duarte

Gustavo Duarte is a PhD student with the Abrolhos expedition.  Here, he describes for Portuguese readers, Day 2 of the research cruise.  Gustavo has a blog at IPAq; you can read more there.

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Ontem o que fizemos basicamente foi combinar toda a estratégia de coleta para hoje. O submersível estava agendado para descer as 8:00 da manhã com dois pesquisadores: Clovis Castro, meu orientador do Museu Nacional e Shirley Pomponi, do Harbor Branch, além do piloto e do co-piloto.

O mergulho foi um sucesso total. Foram trazidas várias espécies de mar profundo. O destaque foi uma belíssima estrala do mar, vários caranguejos bem diferentes, um lirio do mar e várias espécies de corais vivos.

A temperatura da água durante o mergulho foi de 6˚C aos 700 m subindo para 8˚C aos 450 m. Na verdade o submersível desce até a profundidade máxima do mergulho e vai junto ao fundo até a profundidade mínima e então sobe a superfície.

Os corais estão nos aquários que estão por sua vez dentro de uma câmara fria, a tal “environmental chamber”. Lá eu tenho água do mar corrente saindo de uma torneira. Montei os fragmentos num suporte usando superbonder gel e depois durepoxi. Se sobreviverem até amanhã vou alimentá-los com naupilios de artêmia e plancton coletado pelo navio.

Deu muito trabalho triar todo o material, veio muita coisa diferente. Mais a noite eu tento postar as fotos. Agora estamos fazendo coleta de água em várias profundidades para medir nutrientes, penetração da luz, níveis de clorofila, temperatura, tudo isso de acordo com a profundidade. Um pesquisador a bordo vai filtrar esta água e congelar o material a -80˚C para análise genética dos microorganismos presentes na coluna d’água. Para isso estão usando um CTD com uma rossette.

As 4 da tarde faremos um mergulho mais raso, que começará em 120 m e terminará em 70 m. Coletaremos amostras de corais com zooxantelas e eu medirei a resposta fotossintética destes organismos. Depois, usando uma serra copo, vou retirar uns plugs de cada coral e no laboratório do Rio iremos medir a clorofila das amostras, a microbiota associada bem como uma contagem de zooxantelas.

Com isso esperamos conhecer um pouco mais destes corais que conseguem fazer fotossíntese em regiões tão fundas.

Diving is like a box of chocolates...

…You never know what you’re going to get.  In this video, the Johnson Sea Link (JSL) is recovered after the first dive of the Abrolhos2011 Expedition.  Brazilian scientist Clovis Castro was aboard with HBOI scientist Shirley Pomponi. 

Afterwards, the science team went to work processing invertebrate samples including gorgonians, the hard coral Lophelia, and a range of brittle stars, crinoids, urchins and miscellansous crustaceans

The Brazilian science team evaluates their first samples. L-R Gustavo Duarte, Clovis Castro, lead scientist Rodrigo Moura and Ronaldo Francini-Filho

Reporter Glenda Koslowski with Brazilian scientists (L-R) Gustavo Duarte, Clovis Castro, Rodrigo Moura and Ronaldo Francini-Filho

PhD student Gustavo Duarte takes Lophelia fragments for cultivation

 Alex Bastos with a fine carbonate mud sediment core from 600m

Which came first, the Abrolhos or the Abrolhos?

In just a couple of days I’ll join a group of scientists from Brazil, Australia and the US for an expedition to study the reefs of the Abrolhos platform, off Bahia state in Brazil.  When this trip was first mentioned I have to admit being confused.  That’s because, as a native Aussie, to me “the Abrolhos reefs” means a group of reefs and emergent islands off the remote Northwest coast of Western Australia.  So why are there two Abrolhos Reefs, and which came first?

My Brazilian friend and colleague Julia Todorov tells me that Abrolhos is a contraction of two Portuguese words, abro and olhos, meaning “open eyes” as in “Keep your eyes peeled, Marcos, lest you plough the ship into the reef!”.  That etymology is listed in several online sources.  The above Wikipedia link for the Aussie Abrolhos, however, says its not a true etymology, but I don’t see why not, since it applies just as well to reefs as it would to caltrops: basically, watch where you’re going!

Frederick de Houtman (Wikimedia commons)None of that explains why the Aussie reefs got the name, since the Portuguese did not explore Australia that we know of.  Nor does it explain which place name came first.  That’s a bit easier.  The Australian reefs are properly called the “Houtman Abrolhos” or “Frederick de Houtman’s Abrolhos” and were named by de Houtman, the captain of the Dutch East India Company ship Dordrecht in 1619.  He almost certainly named them after the Brazilian reefs, which he had previously sailed through in 1598.  The Brazilian reefs were already known and named at that time, so by name, the Brazilian Abrolhos came first.

Putting the trivialities of human history aside for a moment, we might ask a bigger question: which Abrolhos ultimately came first? Y’know, biologically.  Which reef grew up from the seafloor first?  In short, it was a tie.  Both reefs showed a major growth spurt around 8,000 years ago in the midst of the “last transgression”, when sea level started rising as the ice caps melted away from the last ice age.  This is a pretty common pattern everywhere.  In fact, there are pretty much no extant coral reefs anywhere older than about 12,000 years, since they were all high and dry back then (the reef organisms having receded into what are now much deeper areas).

OK then, if the current reef communities of the Abrolhoses (?) are both about the same age, then which reef came first geologically?  Which one has the longest geological history?  Chalk that one up as a win in the Houtman column.  The current  Houtman Abrolhos islands and reefs sit atop limestone bedrock that is the remnant of a coral reef that grew in the same location in the Quaternary period, before about 125,000 years ago.  The Brazilian Abrolhos, on the other hand, sit atop a layer of flood basalts (i.e. volcanic rocks, solidified lava) that spread out across the edge of the continental shelf during the Eocene (>30 million years ago).  When scientists core into the reef, the oldest reef they find before they hit the volcanic layer is a bit over 7,000 years; suggesting that the Brazilian reefs are relatively much younger (see Dillenburg & Hesp, 2009) 

The Houtman Abrolhos in Australia. (Wikimedia commons)Aside from the name and the similar recent growth spurt, the Abrolhos reefs have little in common; Houtman Abrolhos is a faily typical Indo-Pacific reef with high coral, invertebrate and fish diversity growing on a relict of an even older reef, whereas Brazilian Abrolhos is species poor and dominated by just a few coral and fish species growing on a volcanic base.  Could the short geological history of the Brazilian Abrolhos account for the biological differences?  Maybe, but biogeography probably has a lot to do with it too.  Houtman Abrolhos are not too far from the Indo-Pacific center of diversity, the highest tropical diversity there is and source of much species richness throughout the Indo-Pacific, whereas Brazilian Abrolhos are remote and cut-off from other major centers of reef diversity.  There will be a lot more to talk about regarding the diversity in Brazilian Abrolhos in future posts.

So the Aussie Abrolhos has probably been around quite a bit longer, but the Brazilian Abrolhos has been known to people (European at least) longer by about 100 years.  Despite this, the Brazilian reefs are still poorly known, having come to research and conservation attention only for the last two decades or so.  Its fantastic to think that on this expedition we will still have so much to learn about such a unique ecosystem.  I look forward to reporting  from onboard the R/V Seward Johnson some new biology in the Brazilian Abrolhos, starting later this week.  I hope you’ll stick around and join in the conversation.

Abrolhos, here we come!

Mussismilia braziliensis at the Abrolhos Reefs, BrazilThings have been a little quiet around here over the holiday break, but that’s about to change in a big way.  In just under a week’s time, I’ll be representing Georgia Aquarium in a new international consortium of scientists for an exciting expedition to explore the Abrolhos reef platform off the coast of Brazil from January 20-28.  The Abrolhos are completely unique reefs: they’re the largest and southernmost in the South Atlantic and biologically very different from perhaps more familiar Pacific or Caribbean Reefs.  You’d think they might show some similarity to Caribbean reefs, but not so, possibly because unfavourable currents and the influence of the Amazon pouring into the ocean between the two may serve as an important barrier to animal dispersal (more on that in future posts).  There’s tremendously high endemicity there, which is to say that many of the resident critters are found nowhere else in the world.  Of key importance is the main reef-forming coral Mussismilia braziliensis, a massive species that forms an unusual bommie-like reef structure called a mushroom reef; we’ll meet this species in more detail later too.

The main aim of the expedition is actually to go a bit deeper than the known parts of the Abrolhos, and look at the depths where light starts to get dim: the mesophotic zone.  These parts of many reef platforms are poorly known and nowhere moreso than at Abrolhos, where these areas are completely unexplored.  That’s because mesophotic reefs are beyond comfortable SCUBA diving range and therefore hard to get to.   To study them between 300 and 3,000ft in depth, we’ll be using the Johnson Sea Link, a submersible that operates from the R/V Seward Johnson, which is on a 5 year assignment from it’s home at Harbor Branch Oceanographic Insitute to CEPEMAR, a Brazilian environmental services company.

The Johnson Sea Link and R/V Seward Johnson

There’s much more to come in future blog posts here and in my tweet stream @para_sight or using the hashtag #Abrolhos2011.  We’ll discuss the Abrolhos reefs, mesophotic reefs, some geology and biology, as well as meeting the people and partners and exploring the logistic challenges of making a complex expedition like this happen.  So, I encourage you to follow along and also to share this information with colleagues and (especially) students of marine science so that they might also follow and share in the excitement of discovering new parts of the ocean floor, never seen before, in tropical Brazil.

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.

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.

Follow this NOAA expedition on a new "Deep Corals" blog

Lophelia, a deep sea coral.Fun news from colleague Andrew Shepard at Harbo Branch (Florida Atlantic U.), via Kim Morris-Zarneke:

“Tomorrow, Nov. 9, 2010, the NOAA ship Ron Brown departs Pensacola, FL, on the Extreme Corals 2010 Expedition. Chief scientists, Steve Ross, UNCW, and Sandra Brooke, Marine Conservation and Biology Institute, lead the effort to explore and characterize deep coral ecosystems from the West Florida Shelf to the northern Florida east coast using WHOI’s Jason ROV. We have set up a Web portal for the expedition at http://cioert.org/xcorals. The NC Museum of Natural Science is partnering on this web offering, providing access to daily blogs from sea, image gallery, education materials and more at http://deepcoral.wordpress.com”

Seaweeds and corals go through the media meat-grinder

“If it bleeds it leads” is a common meme in the journalism field, but when it becomes the mantra of science reporting, sometimes the real message gets lost in translation. Unfortunately, so it is with a new paper from Doug Rasher and Mark Hay down the road at Georgia Tech. In their work, published in PNAS this week, they show that algae from coral reefs can have toxic effects on adjacent corals including bleaching (expulsion of the symbiotic algae that are responsible for much of the corals success) and even death. They provide evidence that these effects are mediated by lipid soluble compounds and that they are much reduced on reefs that have healthy herbivorous fish populations to keep the algae in check. There, I summarized their work in 2 sentences. It’s disappointing, then, that the NSF (NSF for goodness sake!) turned that into “Killer Seaweed: Scientists Find First Proof that Chemicals from Seaweeds Damage Coral on Contact”. Unfortunately, that kind of catch-phrase gets picked up all over, so that MSNBC ran with “Killer seaweed threatens corals: Innocent-looking species turns into an assassin of nearby reefs” (assassin? Really?!). The Georgia Tech website went with “Research shows that chemicals from seaweed kills corals on contact”. Not as dramatic perhaps, but more reasonable. Ed Yong at Discover Blogs chose to emphasise the fish side of the story: “Overfishing gives toxic seaweeds an edge in their competition with corals”; both these seem fine to me, but honestly, I don’t know what’s wrong with using the title of the paper “Chemically rich seaweeds poison corals when not controlled by herbivores”. I think Rasher and Hay did a good job distilling the essence of the paper into a punchy and information-dense title. In any case, its frustrating to see crux of a paper lost in attempts to sensationalise the story, as did all the outlets who went with the “killer seaweed” theme.

Putting aside the press treatment, I think there’s an important part of the story missing from this paper. In it, Rasher and Hay report that in the absence of herbivores, 40-70% of common seaweeds cause bleaching of a model coral species (Porites), depending on where you are. If you average that – 55% - then roughly half of seaweeds were toxic to their model coral. On this proportion and their comparison of overfished and non-overfished reefs, they base the conclusion that these algae are bad for corals, that herbivores suppress the algae and, therefore, that overfishing will increase coral declines by allowing toxic algae to proliferate. All of these seem reasonable ideas, but I kept asking myself: what about the reciprocal effect? What percentage of corals are antagonistic to algae? If, say, half of all corals can damage adjacent algae, then the net effect of all this antagonism at the largest scale is zero. If half of algae kill corals and half of corals kill algae, it could be zero sum. This seems important to me, because it would undermine the conclusion that overfishing of herbivores will necessarily lead to declines in reef corals. Indeed, I could make the reverse argument that overfishing of corallivores (fish that eat corals) might lead to proliferation of corals and therefore the decline of reef algae. We just don't know because that work hasnt been done. 

Of course, you can’t include everything in a single paper and I would expect the authors to respond to my point by saying that the experiments I describe were beyond the scope of their project. But I think it could have been a better paper if they acknowledged that there’s another possibility that cannot be excluded, based on work that’s yet to be done.

Rasher, D., & Hay, M. (2010). Chemically rich seaweeds poison corals when not controlled by herbivores Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0912095107

Calling the corals home

Ed Yong at Discover Blogs has a great post up about a PLoS One paper describing how coral larvae find their way back to the reef from the plankton, using sound.  This is a remarkable ability for a tiny ciliated ball of cells, demonstrated through a nifty experiment where the scientists played sound from different directions into a dish of tubes containing coral larvae and showed that they moved towards the speaker playing sounds from a reef.

Putting aside the remarkable little larvae, maybe we shouldn't be surprised. Anyone who has ever put their head underwater on a reef, especially a Pacific reef, can tell you they are noisy places.  I always thought it sounded like frying bacon - a sizzling crackle of clicks, pops, scrapes and cracks, courtesy of snapping shrimps, parrotfish and a myriad other beasts.  The first time I heard that sound I remember being startled, and then amazed.  Serene underwater scenes?  Serene, my butt!