Epi-pelagic invasions - the drift vector

lgutow [ at ] awi-bremerhaven.de


Epipelagic transport (or rafting) was introduced as a dispersal mechanism for marine species. Rafting is the passive dispersal of organisms on objects floating at the sea surface. It is particularly important for species that lack a natural capacity for efficient dispersal such as species without extended planktonic larval development. The requirements rafting organisms have to cope with during their epipelagic journey were briefly discussed. The capabilities of holding on to a floating object, obtaining food, reproducing during the journey, and persisting in competition with other rafting species are decisive for the success of an organism in being dispersed via rafting.Historical changes in rafting opportunities have increased the importance of rafting as dispersal mechanism significantly. Naturally occurring rafts such as floating macroalgae, wood and pumice have become supplemented over the last decades by a dramatically increasing abundance of anthropogenic objects such as plastics and floating tar balls. Especially the advent of plastics in the marine environment was revolutionary for the efficiency of rafting. High densities of plastic objects in the worlds oceans have increased the frequency of rafting events. Due to their high resistance against natural degradation these objects allow for a transport of associated rafters over large distances. Consequently, the probability of introductions of non-indigenous species via rafting has increased significantly.The potential of rafting to introduce alien species has been demonstrated by examples of several non-indigenous peracarid species that were collected from floating objects in the North Sea. These species were of southern origin indicating that the severe temperature regime of the North Sea was responsible for their former absence from that region. However, a substantial increase in mean winter water temperatures observed since the 1990s probably allowed for a successful colonization. Furthermore, strong westerly winds in the North Atlantic region as a consequence of a consistently positive North Atlantic Oscillation Index probably favored the introduction of rafting species into the North Sea.These examples demonstrate that increasing rafting opportunities together with changing environmental conditions as they are expected from global climate change provide a powerful combination that potentially leads to range expansions of marine species.The North Sea is considered to be one of the best investigated marine areas in the world. However, in contrast to other regions such as the Mediterranean no information exist about the amount of flotsam of both natural and anthropogenic origin in that region. The monitoring of floating objects and associated rafters is highly recommended. Early observations of species introductions might help to evaluate and forecast consequences for native communities and to develop efficient management strategies.

Item Type
Conference (Talk)
Publication Status
Event Details
MarBEF and LargeNet Workshop on Long Term Data Set Networking, 3-4 March 2005, Helgoland, Germany..
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Cite as
Gutow, L. , Thiel, M. and Franke, H. D. (2005): Epi-pelagic invasions - the drift vector , MarBEF and LargeNet Workshop on Long Term Data Set Networking, 3-4 March 2005, Helgoland, Germany. .

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