Thursday, September 17, 2009

Looking for plankton in PIPA

Kate Madin, Writer, Woods Hole Oceanographic Institution
Today was blue water dive day. Larry, Greg, Craig, Sam (one of Nai’a’s divemasters) and I dove off Kanton Island to find animal plankton. Naia’s skiff driver, Koroi, took us into the ocean where the bottom is thousands of feet down, and tied the skiff to the dive float.

Greg acted as the safety diver and went in first, then Craig and Sam – but before I got in the water, Greg stuck his head up and said, “You might want to hold up a while.”

A sizeable (6 ft.) shark had appeared as soon as the first divers splashed in, and was acting aggressively, coming at Greg twice. He fended it off with the shark stick, and it seemed to leave. Larry went in, I waited another 10 minutes or so – it didn’t return, so in I went.

Tumbling out of the skiff backward with scuba gear on feels like being in the wash cycle. Bubbles are everywhere, and it’s hard to tell at first which way is up. Then I check my buoyancy, and descend. Blue closes over me and deepens as I work my way down, holding the “down line” –a line tied to the float on one end and weighted on the other. Thirty feet down the line is the triangle-shaped metal “trapeze.” The divers clip 30-foot tether lines from the trapeze to their vests (“buoyancy compensators,” or BCs), so no one can drift away. The only visual points of reference are the lines, other divers, and ascending bubbles that reveal which way is up.

This kind of diving is like shopping. You are often in a vertical position, just “standing” there looking around for choice items to select. You’ve got a shopping bag – a blue mesh bag containing plastic jars to hold your catch. Divers might also have a camera or a shark stick clipped on the BC. Bag and stick and camera and tether line dangle between your legs or float over your head and generally get in your way, so you have keep them arranged during the dive. You scan the blue, not knowing exactly what distance you are focused on, looking for mostly transparent animals such as jellyfish.

If you see something you want, you swim over near it, being careful not to catch it in your bubble stream. Then fumble for a jar in your bag, gently guide the jar around it and replace the lid. This sounds easier than it is in practice, because gelatinous plankton are slippery and insubstantial, and flow right out of your jar if you aren’t careful.

This was a good dive. We saw different plankton here than at Nikumaroro, and every diver collected animals, including three kinds of jellyfish – one a box jellyfish (or cubozoan) that we will work to identify tonight; several siphonophores (relatives of the man-o’-war); and a beautiful transparent swimming snail (called Corolla) that looks like a butterfly (see image on bottom right).