Yesterday’s fieldwork was weird, and epic. There was a huge bloom of Trichodesmium cyanobacteria off Mafia Island.
What is Trichodesmium? Well, I Googled it so you don’t have to.
Everybody knows that Trichodesmium is the only known diazotroph able to fix nitrogen in daylight under aerobic conditions without the use of heterocysts, right?
Thanks, Wikipedia. I totally understand those words. Yup.
Edge of the Trichodesmium slick – thanks Steve de Neef for the photo
Further internet research (and asking Chris Rohner, always helpful) revealed that Trichodesmium is a nitrogen-fixing bacteria that was originally described by Captain Cook, the famed British explorer. Charles Darwin also did some makeshift scientific work on these bacteria while voyaging around on the vessel Beagle.
It’s a common bacteria, living by itself or in colonies, with the Red Sea actually named for the colouration provided by a Trichodesmium species. Colonies can be so large they are easily visible from space.
Turns out Trichodesmium are a pretty amazing and useful group, likely to provide the majority of nitrogen to marine ecosystems – potentially even exceeding rivers as an input source.
The slick at Mafia smelt like watermelon, in case you were wondering.
Anyway, back to yesterday. Trichodesmium is generally found in nutrient-poor waters so, heading out, I assumed that the presence of this massive bacterial slick would be a bad sign for us.
As usual, the sharks didn’t care what I thought. We puttered along the edge of the slick, and quickly found our first whale sharks for the day.
Jumping in the water, the view blew me away. The bacterial mat was so thick that it was genuinely dark underneath. Light only filtered through occasional rifts in the grungy surface carpet.
On the edge of this mat, there was a thick swarm of the small sergestid shrimps that the sharks like to feed on at Mafia.
The sharks were absolutely feasting, up to three sharks at once feeding in the same area, switching rapidly from large underwater gulps to hanging vertically in the water to suck in shrimp at the surface. Total crustacean carnage.
I imaging there’ll be some good stuff coming to Instagram soon from my friends Chris Rohner, Steve de Neef and Alexandra Watts. Steve was shooting stills and video for National Geographic, so I’ll post that piece here on the blog when it comes out.
I’ve added some of my own photos from the day below… always something new here at Mafia!
Alex with playmate
Steve getting caught in traffic
Chris getting some video
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I write a few articles just for my mailing list. They normally focus on something interesting, and possibly hilarious, that I've learnt about sharks (or other random animals) that week. There may also be groan-inducing jokes.
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