Saturday, 26 March 2011

A life on the ocean waves

Fly to Brazil from Europe or Africa and you will pass over thousands of miles of ocean. As you look down on the endless waves you might reflect on life below - perhaps you imagine you see a whale spouting, or a fishing boat trawling for cod. If you've already experienced Brazil and it's teeming millions of insects, you might wonder if there are any of those down there too. In fact, in all the world there are only 5 species of ocean going insects, all from the same genus, Halobates, and only one of these H. micans, is found in the South Atlantic.

Dias & Lopes 2009. Occurrence, distribution and abundance of Halobates micans Eschscholtz, 1822 (Heteroptera, Gerridae) along the southeastern Brazilian coast. Braz. J. Biol. vol 69.

Halobates micans, the Sea Skater, is in the same family as the pond skaters, and you can see why, with it's long legs and antennae. They live in a purely 2 dimensional world, they can't fly and die if immersed under water for long, though they cover themselves with water repellent and are covered with tiny hairs which trap air, so they are very buoyant. Instead of flying or diving they skate across the sea surface at up to 1m per second, hunting for prey. Well, very small prey, as their bodies are only about 5mm long, so plankton, or perhaps fish larvae trapped on the water surface. The weak link is egg laying, for which they need a solid object. This can be hard to find in the open ocean and they will use anything, really anything, seaweed, dead jelly fish, lumps of petroleum. A plastic gallon jug was found to have 70,000 eggs attached!

Zoologische Staatssammlung München Halobates micans; Eschscholtz, 1822; Meerwasserläufer, Wikicommons

Sea skaters seems to be fairly common, though not near the coast, or too far south where the water is cold. But why does he have the whole south Atlantic to himself? After all there are plenty of insects living in fresh water. Well, salinity is a problem, although the salt marsh mosquito, for example, can tolerate 3x this level. Worse maybe is the problem of breathing. Insects need access to air, at least occasionally, and the rough and tumble of the ocean may drive their little bodies too deep into the ocean for them to return. This is maybe why the only insects there are restricted by super-buoyancy to the surface.

The ocean can, from above, appear like a desert, but for Halobates it's actually worse. Most desert animals can burrow into the sand to escape the heat of midday, or predators, but Sea Skaters are stuck on the surface with nowhere to hide. The sun burns down, with levels of UV that would fry most creatures, but Halobates is shielded by a layer of very dark UV protection in it's upper cuticle, which blocks pretty much all UV light. Then there are fish and sea birds attacking from below and above, which Sea Skaters avoid by jumping several centimetres into the air, away from the water surface.

Put all this together and you start to see why, of over 1,000,000 insect species, there is only one in the vastness of the South Atlantic, the little known Sea Skater, Halobates micans.

If you can lay your hands on Antenna, the journal of the Royal Entomological Society, there is an excellent article on Halobates there. Alternatively, there is a good web resource at

Saturday, 19 March 2011

Dinosaurs on the beach

The Ilha de Cajual, in the north of Brazil, is today a tranquil, restful, place. 95 million years ago it was a little more, shall we say, lively, with pterosaurs, giant turtles, and a 14 meter long, 7 tonne crocodile running towards you on it's hind legs!

Just recently researchers at the Universidade Federal do Rio de Janeiro have been displaying fossils of Oxalaia quilombensis, the largest animal of it's type ever found in Brazil. Actually, it wasn't really a crocodile, but a spinosaurid, a type of reptile with a huge crocodile like head that could walk on it's hind legs with a distinctive "sail" on it's back.

So what was life like for Sr. Oxalaia? Well, like most spinosaurids he probably spent most of his time in water - believe it or you can tell this by oxygen isotope analysis of their bones. His skull is characteristic of a predator of fish and small animals, not large prey, and in fact most Spinosaurids tend to be found with fish fossils The need for lots of small meals suggests he was probably quite an active hunter. The sail is a bit of a mystery though, some people say it helped spinosaurids control their temperature, some say it was for display, like a peacocks tail. Could be both of course.

A typical spinosaurid skull

Why "Oxalaia quilombensis"? Well, quilombensis refers to the quilombo, a group of runaway African slaves who were once established on the Isha de Cajual. And Oxalaia is named after Oxalá , one of the highest gods of the Yoruba religion, which started in Africa and spread to the Americas. This African motif is actually very appropriate as the spinosaurids originated there - north Africa and Brazil have so many reptile and fresh water fish fossils in common from this period that there must once have been a land bridge between the two. Oxalaia had plenty of cousins in Africa.

If you would like to know more,
Oxalaia quilombensis is properly described in...

Kellner, Alexander W.A.; Sergio A.K. Azevedeo, Elaine B. Machado, Luciana B. Carvalho and Deise D.R. Henriques (2011). "A new dinosaur (Theropoda, Spinosauridae) from the Cretaceous (Cenomanian) Alcântara Formation, Cajual Island, Brazil". Anais da Academia Brasileira de Ciências 83 (1): 99-108.

Tuesday, 8 March 2011

Darwin's Carnival

It's Carnival time in Brazil. Thousands of people have been working all year on wonderful costumes and floats for this moment, and so it is especially gratifying for this blog that one of the winners, Uniao de Ilha, chose as their theme the English biologist Charles Darwin.

Darwin and his manuscripts

Although most people know of Darwin's voyage to the Galapgos on HMS Beagle, not many know that he stopped off on the way in Brazil. Fortunately, a friend has been kind enough to give me a copy of his diaries.
"It was impossible to wish for anything more delightful than thus to spend some weeks in so magnificent a country. In England any person fond of natural history enjoys in his walks a great advantage, by always having something to attract his attention; but in these fertile climates, teeming with life, the attractions are so numerous, that he is scarcely able to walk at all." he wrote in his journal.

After a quick stop at the volcanic island of Fernando de Noronha the Beagle next made landfall at Salvador in Bahia, where Darwin took the opportunity to explore inland.
"The day has passed delightfully. Delight itself, however, is a weak term to express the feelings of a naturalist who, for the first time, has wandered by himself in a Brazilian forest. The elegance of the grasses, the novelty of the parasitical plants, the beauty of the flowers, the glossy green of the foliage, but above all the general luxuriance of the vegetation, filled me with admiration. A most paradoxical mixture of sound and silence pervades the shady parts of the wood. The noise from the insects is so loud, that it may be heard even in a vessel anchored several hundred yards from the shore; yet within the recesses of the forest a universal silence appears to reign."

Next stop was Rio. Here an Englishman, Patrick Lennon, offered to take Darwin on a trek inland...
"Leaving the coast for a time, we again entered the forest. The trees were very lofty, and remarkable, compared with those of Europe, from the whiteness of their trunks. I see by my note-book, "wonderful and beautiful, flowering parasites," invariably struck me as the most novel object in these grand scenes. Travelling onwards we passed through tracts of pasturage, much injured by the enormous conical ants' nests, which were nearly twelve feet high."

The tree of life

There is material for a 100 blogs in Darwin's journals, which can be found online at

For now I will only add a passage from the journey after Rio, down to Montevideo
"In our passage to the Plata, we saw nothing particular, excepting on one day a great shoal of porpoises, many hundreds in number. The whole sea was in places furrowed by them; and a most extraordinary spectacle was presented, as hundreds, proceeding together by jumps, in which their whole bodies were exposed, thus cut the water. When the ship was running nine knots an hour, these animals could cross and recross the bows with the greatest of ease, and then dash away right ahead. As soon as we entered the estuary of the Plata, the weather was very unsettled. One dark night we were surrounded by numerous seals and penguins, which made such strange noises, that the officer on watch reported he could hear the cattle bellowing on shore. On a second night we witnessed a splendid scene of natural fireworks; the mast-head and yard-arm-ends shone with St. Elmo's light; and the form of the vane could almost be traced, as if it had been rubbed with phosphorus. The sea was so highly luminous, that the tracks of the penguins were marked by a fiery wake, and the darkness of the sky was momentarily illuminated by the most vivid lightning."