Bermuda: Analysis

Except for one limpet on October 15, no limpet moved more than one cell (4-8cm) from their location of origin.  Limpets only used 50% of the available space in the tide pool: 12 cells of the grid were never occupied (Figure 1).  Each day the number of limpets moving one cell away from their original location decreased, with the most limpets moving on October 15 and the fewest on October 18 (Figure 2).  The total number of moves (where one move = one limpet switching cells between two 20 minute time periods) decreased over the four days (Table 1).  Only one limpet on October 18 moved in a western direction, and only two limpets moved in a northern direction; 91.9% of movements were between south and east.  There were no differences between the number of moves between individuals (ANOVA p=0.500).  Surprisingly, >50% of the movement occurred in the first 40 minutes after displacement.  The hour after those 40 minutes was relatively uneventful, and then there was a second peak in activity during the last 20 minutes (17.5% of movement occurred here) (Figure 3).

Limpets of the species Patella vulgata do not move more than 10 cm outside of foraging times, even when dislodged from home scars and placed underwater in a tide pool.  It is unlikely that individuals attempt to locate new areas for home scars until their next nocturnal submersion.  Results indicate that movement decreases with increasing familiarity with an area over a period of four days.  Movement immediately after displacement could reflect the individual’s need for space.  The 10 limpets were placed with their shell edges touching each day, a situation which is unusual for non-grouping limpet species.

Other factors may also be influencing the experimental results, including the overall fitness effects of forcing a high density of limpets to live in a relatively small tide pool.  It was necessary to select an empty tide pool >1m away from other limpets so as to prevent the presence of mucous trails in the study site.  An empty tide pool could indicate marginal or uninhabitable space, meaning the displaced limpets were forced to live in poor conditions for four days.  Lack of food could also explain the decrease in movement over the four day period, for moving during non-foraging periods would waste energy.  Sampling for algal species and quantities in various sections of the tide pool before limpet transfer and after each of the two hour time periods could shed light on how individuals made movement decisions.