Tuesday, August 10, 2010

Collecting Spat

Two days without having to be rescued!! Yay! Miller seems to have fixed our boat problem, for which we are very grateful!

Yesterday and today, Anne and I worked on my pearl oyster recruitment experiment. My own Ph.D. research focuses on the population dynamics and restoration of black-lipped pearl oysters, Pinctada margaritifera, at Midway Atoll. This species is the same one that makes black pearls throughout the tropical Pacific (think Tahiti!), but in the Northwestern Hawaiian Islands, it was heavily harvested in the 1920s for the shell and has not recovered since then.

We’ve put a lot of effort into determining the temporal and spatial patterns of recruitment (= settling from planktonic larvae in the water column to a specific place on the seafloor). Since pearl oyster juveniles (see photo above) prefer dark crevices, I modeled my recruitment devices, or “spat collectors”, after what pearl farmers use. They’re essentially black shadecloth folded like an accordion attached to a buoy (see photo at right). We’ve deployed 10 at each of 9 sites throughout the atoll, and we measure and mark every pearl oyster juvenile on each spat collector every two weeks during our field season.

Today we went to sites 187 and 172, which are on the eastern side of the atoll. We tried to go there last week, but it was too rough to really accomplish something (the tradewinds from the east generally dominate this time of year), so we appreciated the calm today. Particularly since Anne’s stomach does NOT like measuring tiny things on a rocking boat! We got a lot done, but didn’t see anything particularly fascinating.

However, I did enjoy playing with an albatross chick that swam up to investigate us. Here’s above and below the water. We’ve learned to be careful with them in the water because they like to peck anything they can get, and the top of your head is right at their level!

We also observed a small patch reef with many solitary mushroom corals (Fungia scutaria). Each oval-shaped coral in the photo is one individual, as opposed to most corals where many individual polyps live in a colony. Corals in this family are called “mushroom corals” because they grow on a stalk or stem as juveniles and then break off, so they look like the cap of a mushroom. We often see clusters of them like this, which our coral book informs me is because a small attached stem repeatedly buds off new corals.

Our Mitsubishi volunteers arrive Thursday (2 days!), so probably no more posts until then. We’re looking forward to showing this wonderful place and our work to Bret, Crystal, Michael, and Seiji.

If you’re interested in learning more about Midway, a FWS volunteer, Barb Mayer, has been documenting her time here at Midway. She has a lot of great information about the land organisms and even fun activities. However, Barb leaves on the plane this Thursday, so I imagine it will be ending soon. It’s at: foam-friends-of-albatross-on-midway.blogspot.com/.

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