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Zum Phänomen der ortsunsteten Ruheversammlungen der Strandschnecke Planaxis sulcatus (Born) (Mollusca, Prosobranchia)
Magnus, D.B.E.; Haacker, U. (1968). Zum Phänomen der ortsunsteten Ruheversammlungen der Strandschnecke Planaxis sulcatus (Born) (Mollusca, Prosobranchia). Sarsia 34(1): 137-148.
In: Sarsia. University of Bergen. Universitetsforlaget: Bergen. ISSN 0036-4827; e-ISSN 1503-1128, more
Also appears in:
Brattström, H.; Matthews, J.B.L. (Ed.) (1968). The Importance of Water Movements for Biology and Distribution of Marine Organisms: 2nd European Symposium on Marine Biology, Bergen 24-28 August 1967. Sarsia, 34. Norwegian Universities Press: Bergen. 398 pp., more
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  • Magnus, D.B.E.
  • Haacker, U.

    Planaxis sulcatus snails make resting clusters at different levels on the beach on the rocky shore of the Red Sea during low tide. At the time of neap tides they are to be found on the seaward edge of the flat part of the beach, and at spring tides on the landward edge. An analysis of the causal factors showed that the clusters of P. sulcatus are not only due to the drying out of the habitat, but also to waves which break above the snails during high water. During neap tides the water rises at the same speed as the snails are able to crawl while grazing, so that they keep out of reach of the breakers. Only at high tide are they stopped by the breakers for a short time and make clusters. When the water falls they crawl back again to their former resting places behind the breakers. During spring tides the water rises too fast for the snails to keep ahead of the breakers, so they are forced to cluster when overtaken by the breakers and then crawl behind them towards the land. As the tide ebbs the breakers reach them again and stop them. The water continues to recede too fast for the snails to follow and the landward edge of the beach, where they are at that moment, dries out. For this reason the snails have to cluster there.

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