Friday, August 8, 2008

Clod cards are what??


By Brittany Huntington, Doctoral Student, RMSAS Univ. of Miami and BREAM summer graduate intern, funded by ACP

What are these? Fossilized marshmallows? White chocolate petite fours? No no…this is real science people!

This abundance of ice cube shaped trapezoids are nicknamed “clod cards”: a simple yet effective way to measure water movement as a proxy for current and flow exposure at underwater sites (developed by Doty et al., 1971).

The mechanism is straight-forward. These plaster of paris ‘clods’ are all identical in composition, shape and size. Each clod should therefore dissolve slowly underwater at a constant rate.

By weighing the dry clod cards before deployment, leaving them underwater for a fixed time period (usually between 24-48 hours) and then collecting them and re-weighing each clod, we can determine the precise weight of plaster of paris lost from each card. Clods losing more weight were exposed to greater water flow than cards exposed to less water flow.

I am a visiting graduate student to Bermuda for the month, working with Thad on patch reef dynamics. By comparing the loss of clods at two depths (2m and 4m) on patch reefs across my study region, I can better understand the relative gradients of flow that may exist across the patch system, impacting connectivity and community of corals found on these reefs. These babies should be deployed in the next few days once they are done drying. Stay tuned for results…Brittany Huntington, Doctoral Student, RMSAS Univ. of Miami