Description: Rafting of marine and terrestrial organisms has been reported from a variety of substrata and from all major oceans of the world. Herein we present information on common rafting organisms and on ecological interactions during rafting voyages. An extensive literature review revealed a total of 1206 organisms, for which rafting was confirmed or inferred based on distributional or genetic evidence. Rafting organisms comprised cyanobacteria, algae, protists, invertebrates from most marine but also terrestrial phyla, and even a few terrestrial vertebrates. Marine hydrozoans, bryozoans, crustaceans and gastropods were the most common taxa that had been observed rafting. All major feeding types were represented among rafters, being dominated by grazing/boring and suspension-feeding organisms, which occurred on all floating substrata. Besides these principal trophic groups, predators/scavengers and detritus-feeders were also reported. Motility of rafting organisms was highest on macroalgae and lowest on abiotic substrata such as plastics and volcanic pumice. Important trends were revealed for the reproductive biology of rafting organisms. A high proportion of clonal organisms (Cnidaria and Bryozoa) featured asexual reproduction, often in combination with sexual reproduction. Almost all rafting organisms have internal fertilisation, which may be due to the fact that gamete concentrations in the rafting environment are too low for successful fertilisation of external fertilisers. Following fertilisation, many rafting organisms incubate their offspring in/on their body or deposit embryos in egg masses on rafts. Local recruitment, where offspring settle in the immediate vicinity of parents, is considered an important advantage for establishing persistent local populations on a raft, or in new habitats. Some organisms are obligate rafters, spending their entire life cycle on a raft, but the large majority of reported rafters are considered facultative rafters. These organisms typically live in benthic (or terrestrial) habitats, but may become dispersed while being confined to a floating item. Substratum characteristics (complexity, surface, size) have important effects on the composition of the rafting community. While at sea, ecological interactions (facilitation, competition, predation) contribute to the community succession on rafts. Organisms capable to compete for and exploit resources on a raft (space and food) will be able to persist throughout community succession. The duration of rafting voyages is closely related to rafting distances, which may cover various geographical scales. In chronological order, three features of an organism gain in importance during rafting, these being ability to (1) hold onto floating items, (2) establish and compete successfully, and (3) develop persistent local populations during a long voyage. Small organisms that do not feed on their floating substratum and with asexual reproduction or direct development combine all these features, and appear to be most suited for long-distance dispersal on rafts and successful colonisation after reaching new habitats. All available evidence suggests that rafting is an important process for the population dynamics of many organisms and that it also has had and continues to have a strong influence on coastal biodiversity.

Description: The composition of macrozoobenthos was used as an indicator for the evaluation of the water quality around Helgoland (German Bight, North Sea) according to the European Union Water Framework Directive (EU-WFD). Changes in the species community over the past 150 years were assessed from an extensive literature survey for the island of Helgoland as well as the adjacent Tiefe Rinne - a depression of the seafloor down to 60 m depth. Water quality, as far as macrozoobenthos is concerned, was presently found to be moderate for both investigated areas.Within the time period reviewed, species richness was highest in the Crustacea, Mollusca and Polychaeta. Due to their conspicuousness these groups were considered robust towards methodical irregularities making them reliable indicators of long-term changes in faunal communities. Consequently, further analyses were performed exclusively on these groups. The results revealed major changes over time issuing from substantial loss in species richness as well as from substantial exchange of species. The Sørensen-Index revealed fairly low similarities ranging from about 30 to 55 % for Helgoland and from around 40 to 53 % for the Tiefe Rinne .Changes in abundance over time are very difficult to assess for various reasons. One major problem is that in most historical publications, quantitative information is described in words rather than numbers and therefore implies a high amount of subjectivity with regard to both the author and the reader. Yet, to make data comparable, all quantitative information available was ranked by common sense according to 6 different categories of abundance . Referring to the conspicuous taxa mentioned above, the results for both locations indicated a general trend of decrease in abundance over time in? 4.1 to 10.0 % of the species.To overcome the problem of missing quantitative data, the authors created a working basis leading to reasonable results, which could even be confirmed by some case studies, eg. the extinction of the European Oyster Ostrea edulis in the vicinity of Helgoland. The proposed method for a quantification of historical data was commonly accepted. It provides an efficient and fairly objective approach to assess changes in faunal associations. With respect to the difficulties mentioned above, further development and the reconfirmation of accuracy of the proposed method was recommended among the participants of the workshop. This was particularly emphasised in view of the urgent request of applying the proposed method not only to benthic data but also to the historical plankton data sets of Helgoland roads.

Description: 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.

Description: An extensive literature survey revealed that rafting on objects floating at the sea surface is a common dispersal mechanism in marine crustaceans. A great variety of objects including detached macroalgae, plastic items and wood have been found to serve as substrata for rafting organisms. A total of 365 crustacean species from all major taxonomic groups have been reported from floating objects. Amphipods (104 species) represent the most diverse group followed by brachyuran decapods (60 species). 296 species are facultative rafters. These animals usually have a benthic or pelagic life-style and inhabit floating items as a secondary habitat. However, 23 species, mainly represented by barnacles, have been identified as obligate rafters living exclusively on floating substrata. Most rafting crustaceans reproduce sexually, primarily featuring a gonochoric sexual system with few hermaphroditic species. Fertilization mode is internal in all species. Direct development of juveniles without pelagic larvae is the major developmental mode, facilitating the retention of juveniles close to the parental animals. Mobile species able to walk or crawl dominate on natural substrata that are exposed to biological degradation. Persistent substrata, however, are often colonized by sessile animals. Feeding mode of the animals also appears to depend on substratum characteristics. Many grazing species are found on floating macroalgae while suspension feeders and predators dominate on abiotic objects and wood. The high degree of functional and morphological diversity within the Crustacea allows these animals to colonize a great variety of floating substrata making rafting an efficient dispersal mechanism for this group.