Clamples!

A thick, hearty slice of Tridacna maxima

During my time in Eilat and Aqaba, I have obtained many shell specimens. For my work, I only need a section of shell exposing the growth bands along the longest axis of growth within the shell. Whole shells would be impractical to take back to the US, and my permits here only allow me to take pieces of shell. Back at UCSC, we have a large radial sawblade specifically for cutting geological specimens to make thin sections. Unfortunately I do not have access to such a blade here, so we've had to think creatively!

Photos by Michele Markowitz.

The scientific technician here, Moty Ohevia, devised a setup for me using a 4-inch blade on a pneumatic cutter. Being powered by compressed air is safer than electricity because I can use water to cool off the blade and sample. The blade is dull and turns slowly, which means I'm not at risk of losing my finger for science. But it also makes a big mess and is noisy, so I am using eye protection, a mask to keep out dust, earplugs, and close-toed shoes for safety. Other members of our group including Noam, Adina and Michele (who took these pictures) have been helping me by holding the power trigger on the drill and spraying the sample with water as I direct the sample over the blade.

The slow spinning action also makes for a very smooth cut. When I return to UCSC, I will be sanding down the surface with sandpaper and fine grit on a rotating wheel, to make the surface smooth enough to see very fine growth increments. I believe some of these increments are formed over fortnightly (14-day) tidal periods! 

Acetate peel of a Tridacna maxima shell. To take a peel, the shell surface is sanded very finely, etched with a weak acid, splashed with acetone and stuck to a sheet of acetate. After applying pressure while drying, the shell is peeled off and a thin layer is stuck to the transparency, making fine growth bands more visible. I took this picture through a hand lens to show the fine growth bands that can be seen in the shell.

Counting these bands will allow me to measure the clam's rate of growth. I will then use a computer controlled micromill to sample from these bands. The micromill is basically a little robot that drills exactly where I tell it to with a dental drill bit, at sub-millimeter resolution. I will collect the powder from the drilling and use a mass spectrometer to create a very detailed record of carbon and oxygen isotopes. These isotopic records can be used to reconstruct the clam's environment and physiology during its life, including whether it had to regularly had to stop growth due to temperature and other sources of stress.