Dispersal mechanisms in amphipods: a case study of Jassa herdmani (Crustacea, Amphipoda) in the North Sea
Jassa herdmani (Walker 1893), a tube-building amphipod typical of hard substrates, was found in large densities on shipwrecks from the Belgian part of the North Sea, in association with the hydrozoan Tubularia indivisa. In this area, shipwrecks only represent the source of hard substrates in an environment dominated by soft sediments. Nevertheless, the long-distance dispersal of Jassa species has never been investigated. Therefore, we tested the hypothesis of dispersal with currents, by investigating the behaviour of J. herdmani in the laboratory. Size distribution revealed that newly released juveniles (<1 mm) predominated throughout the year and the lower frequency of the size class 1–3 mm indicates a high mortality or a dispersal at this life stage. Individuals of J. herdmani may initiate actively the transport by tidal or surface currents by swimming to the surface of the water or by floating at the surface, as suggested by behaviours noted in the laboratory. The reaction of the amphipods to a current was investigated in the laboratory. We could not detect any sexual function associated with drifting and there was also no preponderance of a size class in the drifting individuals. When testing different substrates, we observed a significant influence of the substrate type on the frequency at which drifting occurred: J. herdmani showed a better adherence on T. indivisa compared to other substrates. Finally, the amphipod showed also a preference for its host compared to other substrates, which suggests a possible detection mechanism.
KeywordsSubstrate Type Hydroid Artificial Substrate Gravid Female Brush Hair
This study has been financially supported by a ‘plan Action II’ grant (contract number WI/36/C04) from the Belgian Science Policy and by the BEWREMABI project (Belgian Science Policy). J. Mallepet is a research associate of the FNRS. The present study has been performed in agreement with the current Belgian laws. The authors wish also to thank the crew of the RV Zeeleeuw and RV Belgica for their help during the sampling campaigns. It’s also our pleasure to thank all the people who helped collecting the samples: Dr. A. Norro, Dr. Y. Laitat, A. Simon, D. Delbare, E. Vanden Bergh, T. Schils, Mss C. Delforge and R. Gyssens and Mrs P.B. Demoulin, G. Rooms, D. Marsham, F. Cray, M. Van Espen, Y. Verkemping, M. Backx, J. Haelters, F. Hernandez, F. Darchambeau, G. Van Hoydonck, A. Vanhaelen, R. Knuts & P. Van de Steen.
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