Tuesday, July 9, 2013

Cris - Week 2

Botrylloides violaceus
This week Friday (7/5/13) I brought up four settlement plates from the inner basin that had been out for a week. They are attached to the PVC frame that was shown in my previous post and are 10cm x 10cm made of PVC sheeting. I put these four plates out and four more in the outer basin so that I had a chance to examine the plates and try to identify the various fouling species through a dissecting microscope. Upon examination I found many colonial ascidians - ascidians that colonize and are made of individuals called zooids - the most abundant of which were Botrylloides violaceus and Botryllus schlosseri. Among other organisms were barnacles, sponges, and spirorbid worms.

Shown to the left is a solitary tunicate, but the colonial tunicate has a similar structure with a shared excurrent canal (atriopore). These organisms filter feed using a pharyngeal basket, also known as an endostyle, by moving water through their incurrent canal (mouth) using cilia. The water is filtered through the endostyle and food is trapped in mucous. Tunicates are mobile in their larval stage and most are sessile as adults when they attach to a substrate.

A 9x9 grid simliar to the one produced
Using Microsoft Excel and Sigmaplot Systat we were able to produce a 9cm x 9cm grid to place on the 10cm x 10cm settlement plate when counting the fouling organisms under the dissecting scope. The purpose of the grid is to sample random squares, we picked 25, so that a representation of the entire plate is produced. Because of the hardware joining the plate to the frame, the 81 sq cm became 72 sq cm to compensate for the area occupied by the washers used. Our 25 random squares then gives us over a third of the total available area for subsampling. The random squares were acquired using a random number function in Excel.

This week Monday I will bring up my first set of 6 plates that have been out for a week and begin to examine and count the fouling organisms on them. I will switch them out with a second set of plates so that I can continue to leave them out for one week periods for the next 6 weeks, alternating between sets. The grid was printed on a clear plastic sheet so that it can be placed over the settlement plate and the appropriate squares examined. If there is minimal settling, sub-sampling will not suffice to give a general picture of the various species that have settled and the whole plate (minus the area covered by the hardware) will have to be examined. Once I have the plates out and begin to examine them I will have more pictures to post of the various species that I encounter. Until next week, cheers!

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