Limpets on Atlantic Shores |
| Home | Background | Tectura testudinalis | Patella vulgata |
| What is a limpet? Limpets are herbivores that graze on algae in the rocky intertidal zone. They are often the dominant grazer in a system and play an important role in determining both the algae-species mosaic and net productivity. Many marine limpets are reliant on cold water temperatures and so are threatened by global warming. The MarClim project of the United Kingdom has identified 57 species of cold-water gastropods, including limpets, that are changing their home ranges due to rising ocean temperatures (Murphy 2006). Limpets are gastropods, a group of organisms that move with a single muscular foot which they ripple in a series of waves. Limpets feed on both micro and macroalgae in rocky intertidal zones, scraping algae off of rocks using a tooth-tongue appendage called a radula (Figure 1). Radula have different morphological characteristics depending on the they of vegetation a limpet species specializes in. The common limpet (Patella vulgata) is a generalist with a six-toothed radula, whereas the tortoiseshell limpet (Tectura testudinalis) specializes on coralline algae with its four-toothed and iron-silica tooth surface (Steneck 1982). Unlike most other marine gastropods limpets have no operculum. The operculum is a calcareous structure that grows on part of the muscular foot and is used to effectively seal the shell aperture off from external elements (Figure 2). In intertidal snails, the operculum principally prevents dessication. Limpets do not rely on an operculum, but rather suction against a substrate when emersed. They are reliant on how snugly their shells fit to the substrate to protect them from both predation and abiotic dangers such as dessication. Limpets must alternate between foraging and sealing themselves against the substrate. Most species exhibit triphasic movement, where an individual moves rapidly in one direction away from a resting site, then moves slowly and randomly for a period while foraging, and finally moves rapidly back to a home scar or a new resting site. A home scar is used only by limpets that 'home.' Homing is a behavior in which an individual inhabits a small indentation in the rocks around which it bases its foraging. Background of the Bermuda study describes homing in more detail. Here, ‘home site’ is distinguished from ‘home scar.’ A home scar is an indentation in the rock that an individual limpet returns to after foraging excursions with some fidelity. It offers protection for the limpet as the limpets shell grows to match the shape of the indentation precisely. A home site is an area (not an indentation) a limpet selects for its not-foraging period of a single day, so as to protect itself from predation and abiotic factors. A limpet does not move much from its home site until its next foraging excursion and shows no fidelity to it. Non-homing limpets change home sites after the majority of foraging excursions. Sources: Murphy 2006; Steneck 1982. |  Figure 1. Radula scrape marks from the limpet Patella vulgata  Figure 2. Snails have an operculum, a 'shield' that can seal their shell off. Copyright  Figure 3. An upturned limpet with no operculum: notice the antennae and visceral mass.. |