An experimental study of the pattern and significance of the climbing behaviour of Hydrobia ulvae

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Abstract
The climbing behaviour of the gastropod Hydrobia ulvae (Pennant) and its relationship with flotation/dispersal were investigated by field observations and experiments in Norfolk, U.K. and by laboratory experiments. Field experiments of the type used by previous authors were discontinued when it was observed that counts at low tide of snails which had climbed objects the previous high tide did not reflect adequately climbing activity during that period of tidal cover. Both field and laboratory studies yielded five general results: (i) snails climbed only when covered by tidal water; (ii) climbing activity was not related to population density; (iii) climbing activity, under conditions of constant population density, varied markedly during the cycle of spring tidal cover, reaching a peak after the first few tides and declining rapidly thereafter; (iv) maximum numbers of snails were present on submerged structures relatively early in any given period of cover and declined (snails crawled downwards off the structure) as the period of cover continued; and (v) rarely were large proportions of climbed Hydrobia floated off their support by the incoming tide; this was associated only with conditions of extreme calm.