The Ecology of Rafting in the Marine Environment. Ii. the Rafting Organisms and Community

Abstract

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 1205 species, 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 MARTIN THIEL & LARS GUTOW 280 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 appear to be mos...

Rapid changes in the epifaunal community after detachment of buoyant benthic macroalgae

“…Kingsford & Choat (1985) observed a similar loss of phytal amphipods from macroalgae immediately after detachment. This observation was surprising since peracarids are among the most common rafting invertebrate species in the world's oceans (Thiel & Gutow, 2005b) indicating their high potential for persistence on floating items. The number of peracarids decreased drastically after detachment of the algae despite their high capability of clinging efficiently to their algal host (Dommasnes, 1968).…”

“…Edgar (1987) expected that organisms on floating holdfasts of the giant kelp Macrocystis pyrifera experience greater water motion than on attached holdfasts. Accordingly, Thiel & Gutow (2005b) suggested that some of the original inhabitants of the algae are lost from the community immediately after detachment because of their incapability of holding onto floating items. The majority of the taxa found in our study, however, have been repeatedly recorded as rafting organisms on macroalgae in coastal and offshore waters around Iceland (Ingólfsson, 1995(Ingólfsson, , 1998, which confirms their general ability of clinging efficiently to floating algae.…”

“…Boring limnorid isopods quickly leave their holdfast burrows after experimental detachment of kelp holdfasts from the benthic substratum (Miranda & Thiel, 2008). Based on reports of low numbers of echinoderms, decapod crustaceans and gastropods on detached algae (Kingsford & Choat, 1985), Thiel & Gutow (2005b) suggested that particularly large organisms fall off quickly due to their incapability of holding onto floating objects. As a consequence, total densities of epifaunal invertebrates on macroalgae may significantly decrease during the first few minutes after detachment (Kingsford & Choat, 1985) resulting in substantial changes in the composition of the epifaunal community.…”

New Mediterranean Biodiversity Records (December 2012)

“…Furthermore, once arrived and established, the species widens local distribution through its ability in colonizing drifted plastics, a behaviour recorded by Winston (1982) and Thiel and Gutow (2005). Winston (1982) remarked the absence of E. tenella from floating natural substrata, and the opposite ability to exploit the particular niche offered by anthropogenic floating material.…”

Artisanal fishing net float loss and a proposal for a float design solution

“…Problems due to plastics in the marine environment have been summarized by COLE et al (2011). In addition to economic loss and chemical and physical pollution due to plastics, through rafting these plastics exert an important influence on coastal biodiversity (MASÓ et al, 2003;THIEL;GUTOW, 2005). Plastic fragments, regardless of origin, are ingested by marine animals, buried in sediments (COSTA et al, 2011) or washed up on beaches (ARAÚJO; COSTA, 2007).…”