Limpets on Atlantic Shores: Bermuda

In rocky intertidal zones grazing by herbivores controls the abundance and biomass of primary producers (Coleman et al., 2006).  Grazing intensity therefore determines the net productivity of a given system (Coleman et al., 2006). Prominent grazing mollusks include limpets, pulmonate limpets, chitons, and multiple families of snails (littorinids, trochids, neritids, and hydrobiids) (Little 1989).  On many rocky shores limpets are the dominant grazers and have considerable ecological importance (Davies et al., 2006).  On European coasts limpets from the genus Patella are shown to control algal assemblages (Coleman et al., 2006), which indirectly controls productivity.  Johnson et al. (1998) determined that limpet grazing on Fucus establishment affected algal abundance and distribution patterns.

Understanding the underlying mechanism of grazing control requires studying foraging patterns and preferences of limpets.  Extensive studies have tracked the activity of species in diverse areas of the world (Branch 1981; Hartnoll and Wright 1977; Williams et al., 1999; Garrity and Levings 1983; Gray and Hodgson 1998; Davies et al., 2006) and have found some widespread patterns. Homing, a behavior in which limpets inhabit a home scar that they return to after foraging excursions, occurs in many siphonarian and prosobranch limpets (Hartnoll and Wright, 1977).  Home scars are typically a small indentation in rocks where the limpet shell grows to precisely match the rock shape (Cook 1971; Hartnoll and Wright, 1977).  Homing serves three functions, varying in importance between species: (1) protection against dessication and other abiotic factors, (2) protection from predators, and (3) advantage in competition due to their familiarity with the surrounding landscape (Garrity and Levings, 1983). 

Multiple methods for homing have been hypothesized and studied, including: landmark orientation, reverse-something, something, and following cues laid down by travelling limpets (cite siphonaria).  The general consensus is that a type of chemical trail, typically mucous, is laid down for limpet navigation, though this hypothesis has not been conclusively tested (Hartnoll and Wright, 1977; Cook 1971; Mackay and Underwood 1977).

Although much work has gone into understanding both the factors that control foraging patterns as well as the mechanism limpets use to home, the home scars themselves are rarely studied beyond their adaptive functions.  The process of home scar selection has not been investigated, leaving such questions as what factors make good home scars, how quickly a limpet establishes its home scar, and how conspecifics compete for prime home scar space, unanswered.  This study seeks to track the movements of limpets in the species Patella vulgata when displaced from their home scar and transferred to an unknown and uninhabited tide pool. It follows the tendency of limpets to occupy the same space after multiple days, as well as interspecific competition.