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The displacements and activity by post-larval stages and early juveniles of Eupolymnia nebulosa sampled from two sites on the French (Bay of Banyuls) and Spanish (Bay of Blanes) Catalan coast were analysed and compared. Actographic track analysis indicated recognition of sediments that had been previously reworked by adults. Exploration time and track width were significantly different when more than one individual had explored the same area, which suggested that juveniles can recognise the biologically modified sediment and change their behaviour accordingly. This reaction may be related to the mucus trail left behind on the sand grains during displacements. Possible olfactory recognition either alone, or in combination with detection of the mucus film remaining on the sediment grains is hypothesised. Individuals from the Blanes population, living 150 km south of the Banyuls population, had a different type of behaviour in the presence of sediment reworked by adults from Banyuls. In the presence of sediment marked by adults from Banyuls they showed no positive response. |
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