Bermuda: Experimental Design

An optimal tide pool was located in the rocky inter-tidal behind Tobacco Bay as described in the Location page.  This tide pool was on a nearly horizontal surface and contained no limpets on October 8.  Ten limpets from >1m away were removed from their scars and labeled from 1 to 10 with bee tags so that the smallest limpet was numbered 1 and the largest number 10 (Figure 1).  The labeled limpets were placed in the center of the tide pool (Figure 2) and two photographs, one of the entire tide pool and one a zoom on the limpets (so as to aide in their identification), were taken from two different angles.  Photographs were taken every 20 minutes for two hours during low tide.

On October 9 the 10 limpets were removed from their current locations and placed in the center of the tide pool.  The process above was repeated, taking photographs every 20 minutes for two hours to track the limpet movement.  Limpets were removed, replaced, and tracked for two more replicates on October 10 and 11.  All replicates occurred at low tide, when the tide pool was discernable from the ocean (i.e., above wave height) and accessible by foot.

The photographs were resized and rotated to align using three indicator features present in all of the photographs with the programs Microsoft Picture It! and Microsoft Powerpoint.  A 6x4 grid (4x4cm cells) was layered onto each photograph.  Limpet movement was tracked by recording which cell a limpet was present in at each time.  For each day, both average movement and the ratio of the total number of cells occupied to the total number of movements a limpet made was determined.  These were tested to determine whether limpets had a tendency to occupy a smaller set of cells than expected by the total movement.  Individual limpets were tested against each other to determine if some are ‘movers’ and some are ‘sitters.’  Movements patterns were compared to relative body size, and movement pattern across the two hour time period was determined.