title for limpet section of the Odyssey
  Habitats & ecology
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Seasonal movements

  Topics on habitats & ecology of limpets include seasonal movements, considered here, and COMPETITION, POPULATION & COMMUNITY DYNAMICS, HOMING & TERRITORIALITY, SHELL GROWTH (SHAPE) & COLOUR, and LIFE IN THE INTERTIDAL ZONE presented in other sections.
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Research study 1

photograph of a cluster of Lottia digitalis on sandstone at Botanical  Beach, near Port Renfrew, British ColumbiaStudies in both Coos Bay, Oregon and Port Renfrew, British Columbia show that ribbed limpets Lottia digitalis undertake seasonal migrations – upward in autumn /winter, and downward in springtime.  In Oregon the upward movement is slightly greater than the downward, leading to a differential distribution of size classes, with the oldest and largest individuals being found highest in the intertidal zone.  These older animals presumably reach a compromise position between desiccatory stress at the upper levels and possibly increasing intraspecific competition from survival of recruits at lower levels.  The seasonal movement is about 0.5m and may allow access to high-level growth of diatoms for food in winter, and lessen the risk of drying in summer.   Frank 1965 Ecology 46: 831; Breen 1972 Veliger 15: 133.

Cluster of Lottia digitalis on sandstone at Botanical
Beach, near Port Renfrew, British Columbia 0.3X

Research study 2

How do limpets know up from down? Gravity sensors in gastropods, including limpets, are spherical organs called statocysts.  The statocysts are 100-200µm in diameter, are paired, and are located on the circumesophageal nerve ring.  The statocyst wall contains mechanosensory cells lined with sensory cilia.  The lumen is filled with fluid and contains one or many stones, or statoliths, which sink by gravity to stimulate cilia on the cells being loaded.  The stones are made principally of calcium carbonate.  Wiederhold et al. 1990 p. 393 In, Origin, evolution, and modern aspects of biomineralization in plants and animals (Crick, ed.) Plenum Press, NY.

NOTE  lit.  “standing stone” G.   Multiple stones are usually termed statoconia, and this condition seems to be a common feature of molluscs.  Exceptions are bivalves, which mostly have statoliths made up either of single crystals or of concretions of statoconia, and most cephalopods, which have statoliths, but of complex structure