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Monday
Jan172011

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.

Reader Comments (2)

Darwin was in Brazilian Abrilhos, that is an important keyfact: http://viajandocomlucianadias.blogspot.com/2009/04/charles-darwin-em-abrolhos.html
January 26, 2011 | Unregistered CommenterGustavo Duarte
Thanks Gustavo, I didn't know that. For those of us not lucky enough to read Portuguese, can you tell us about what he learned while he was there?
January 27, 2011 | Registered CommenterAl Dove

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