RESPONSES TO DISTURBANCE OF THE PERIWINKLE LITTORINA PUNCTATA (GMELIN) ON A SHORE IN GHANA

Authors


  • *Dove Marine Laboratory, Cullercoats, Northumberland.

Abstract

Specimens of Littorina punctata (Gmelin), the common periwinkle of Ghana, were subjected to a series of simple tests to see how they behaved when disturbed. The results suggested the initial tracks of freshly displaced winkles are compounded of two components, one directed up or down the shore, the other directed up or down a slope. In winkles collected from a vertical surface the upshore component is dominant on slopes below 90°; above 90° (reverse slope) it is the up slope component. In those collected from the flat floor of a rock pool the down slope component is dominant on slopes of 30° or more; on a flat surface the upshore component is revealed. The upshore component is related to a visual response, the slope component is not.

Results on a dark night with no moon do not differ from those in full sunlight. Visual responses depend on the use of terrestrial rather than astronomical beacons for at least part of the time. If winkles ever use the sun as a directional guide they allow for ephemeral changes in azimuth and also for change of transit bearing from north to south. A heavy swell can quickly alter the level at which the winkles are found and can temporarily affect some of their responses to disturbance.

Ancillary