Floating substances in the marine or freshwater environment often carry hitch hiking organisms. It is argued that many species may use this dispersal vector to reach new habitats, however to my knowledge there is no hard evidence / no documented case. This may be because of the difficulty to associate an established species with a certain vector of introduction.

By floating substances I refer to natural floating substances such as detached algae, trees or pumice and those of anthropogenic origin such as litter items, detached buoys, etc. (in whatever aquatic environment: sea, lakes, rivers)

Any help to find a reference / documented case study is very welcome!

  • $\begingroup$ But not including actual sea-going vessels? $\endgroup$
    – Alan Boyd
    Apr 4 '14 at 19:08
  • $\begingroup$ Right, no vessels. Their dispersal capacity, especially considering vessels with ballast tanks, is not readily comparable to other floating "substances" and IMHO better understood. $\endgroup$
    – Stockfisch
    Apr 4 '14 at 19:17
  • 1
    $\begingroup$ As far as I know, this is dicussed for the distribution of geckos through the pacific. They are common on quite a number of islands. $\endgroup$
    – Chris
    Apr 4 '14 at 20:59
  • $\begingroup$ im pretty sure it happens all the time - geologically speaking. @Chris could cite 'Voyage of the Beagle' for the galapagos chapters really $\endgroup$
    – shigeta
    Apr 7 '14 at 20:36

There is a number of reported cases of marine species reaching new locations through "hitchhiking" in recent times. However, it seems harder to find reports of species actually becoming established in a new location through this.

The following articles describe examples of species transported with ocean debris:

In an early study on the dispersal of plastic pellets (3), it was suggested that pellets encrusted with the bryozoan Membranipora tuberculata was transported to New Zealand across the Tasman Sea from Australia. Barring one exception, this was the first time the species was observed in New Zealand waters.

Appendix A of a later article by the same author (1) contains 13 examples of species transported by sea (not necessarily through debris, or invasive), including the previous example. Of it, the author writes that

Later, L. M. Stevens (1992, unpublished data) was to report that [Membranipora tuberculata] was abundant on both eastern and western shores around northernmost New Zealand.

Thus, this is possibly a case of a species transported on floating debris and subsequently becoming established in a new habitat.

Jose Derraik also deals with the topic in a review (4):

Plastics floating at sea may acquire a fauna of various encrusting organisms such as bacteria, diatoms, algae, barnacles, hydroids and tunicates (Carpenter et al., 1972; Carpenter and Smith, 1972; Minchin, 1996; Clark, 1997). The bryozoan Membranipora tuberculata, for instance, is believed to have crossed the Tasman Sea, from Australia to New Zealand, encrusted on plastic pellets (Gregory, 1978). The same species together with another bryozoan (Electra tenella) were found on plastics washed ashore on the Florida coast, USA, and they seem to be increasingtheir abundance in the region by driftingon plastic debris from the Caribbean area (Winston, 1982; Winston et al., 1997). Minchin (1996) also describes barnacles that crossed the North Atlantic Ocean attached to plastic debris. Drift plastics can therefore increase the range of certain marine organisms or introduce species into an environment where they were previously absent (Winston, 1982).

Finally, the book Marine Pollution: New Research (2) contains the following passage which ends with the observation that conclusive proof is difficult to obtain:

Drift plastics are known to have introduced exotic marine species to several areas (Winston et al., 1997; Deraik, 2002). Winston et al. (1997) reported that the non-indegenous oyster Lopha cristagalli was fond on plastics wshed ashore in southern New Zealand, and that the exotic bryozoan Thalamoperella evelinae was found on plastics washed ashore in Florida. Barnes and Milnder (2005) fond the exotic barnacle Elminius modestus on plastic debris in the Shetland Islands (Atlantic Ocean). The bryozoaen Membranipora tuberculate is believed to have crossed the Tasman Sea from Australia to New Zealand rafting on plastic pellets (Gregory, 1978). M Tuberculate and the bryozan Electra tenella seem to be increasing their abundance on the Florida coast by drifting on plastic debris from the Caribbean sea (Winston, 1982 Winston et al, 1997). Maso et al. (2003) (...) However, attributing a marine biological invasion to floating marine debris and not to other mechanisms is very difficult in most cases, and available data are generally insufficient.


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