Thursday, May 14, 2009

Crazy About Pearl Oysters

Well, I've already gone longer than I intended between blog posts - not an auspicious beginning! I think the first few blogs will be long as I introduce our work.

Anyway, we've been really busy with long, exhausting days on the water. Sunday, we were able to go on a "sediment collection" dive with Keoki Stender at a site they used to take tourists to called Fish Hole. We had a big grouper that followed us around for the whole dive, and saw some other really cool fish and invertebrates (I'll have to let Kate tell you about algae - not really my thing!). It was a great dive and a great re-introduction to Midway! Check out our photos on Picasa for more info. That night, Keoki gave a great talk on underwater photography, which I look forward to applying! At left is a photo of Keoki with his great camera and the grouper.

The last few days, we've been collecting and deploying temperature loggers at various sites around the atoll, checking my bivalve recruitment sites (AKA "spat collectors"), collecting coral reproduction samples, preparing for other projects, and organizing things. We have 8 temperature loggers deployed around the atoll that record water temperature every 15 minutes, so we have to bring these back to land once or twice per year to download the data and re-launch them. We've also collected a few tiny samples of coral to preserve in formalin and ethanol to determine when corals here are reproducing - maybe we'll discover a mass spawning event like they have on the Great Barrier Reef! We're figuring out how to build cages for my juvenile growth and predation experiment on pearl oysters and building large calipers to measure adult bivalves (= 2-shelled mollusks like clams, oysters, mussels). We also collected a huge net on the reef yesterday that would be an entanglement hazard to endangered monk seals, dolphins, and turtles.

However, our main project this week is checking my spat collectors for my own research. Black-lipped pearl oysters were heavily overfished in the Northwestern Hawaiian Islands (NWHI) in the 1920s for the mother-of-pearl or nacre on the inside of the shell, which was used to make buttons. NOAA surveys in the last few years determined that the species has not recovered in the 80 or so years since then, so the Papahanaumokuakea Marine National Monument (AKA, the Monument or PMNM) and FWS are interested in a restoration. Before last year, we'd never seen an adult pearl oyster at Midway, but we were finding a lot of pearl oyster recruits on our cages and tiles, so I decided to study the ecology and population dynamics of this species and methods for restoration.

Last year, I started a major project on the recruitment of this species, which means the settling of larvae onto substrate. In August of 2008, I put sets of 10 spat collectors, which are pieces of black plastic shadecloth folded like an accordion, at 10 different sites throughout the atoll to evaluate when and where recruitment is highest. Apparently, pearl oyster larvae really like dark crevices, so these spat collectors are perfect substrate and are used in pearl farms in the south and western Pacific. I check them every two weeks when we're here and measure and count all the tiny pearl oyster juveniles. At right is a photo of one of my spat collectors.

This year, I'm also planning some major surveys, permanent transects for population dynamics, and a caging experiment to determine growth and mortality with and without predators. More on this later as we get it started. Check out my photos of pearl oysters here and of the bivalve recruitment study here.

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