The ecology of rafting in the marine environment - Bedim

RAFTING OF BENTHIC MARINE ORGANISMS
Table 11 (continued) Echinodermata reported or inferred as rafting
Species Region
Ectoprocta (= Bryozoa)
Some of the most ubiquitous organisms on floating plastic items are bryozoans (Winston 1982,
Stevens et al. 1996, Winston et al. 1997, Barnes & Sanderson 2000). Barnes (2002) ranked the
bryozoa as the most abundant faunal group on marine debris. Bryozoans have been found on a
variety of different floating substrata including macroalgae (Arnaud et al. 1976, Niermann 1986,
Bushing 1994), seagrass blades (Keough & Chernoff 1987, Worcester 1994), seeds (Mason 1961),
Nautilus shells (Hamada 1964, Chirat 2000), floating corals (DeVantier 1992), plastic items (Gregory
1978, Winston 1982, Stevens et al. 1996, Winston et al. 1997, Barnes & Sanderson 2000,
Donlan & Nelson 2003) and tar balls (Shaw & Mapes 1979) (Table 12). Gregory (1978) suggested
that the cosmopolitan bryozoan Membranipora tuberculata, which is also very common on floating
Sargassum in the Sargasso Sea (Smith et al. 1973, Ryland 1974), may have crossed the Tasman
Sea from Australia to New Zealand via rafting on plastic pellets. Winston (1982) found Electra
tenella to be the dominating and often only bryozoan species on plastic debris cast up on beaches
along the Atlantic coast of Florida. In benthic habitats, however, this species occurs only sparsely
in that region. Winston (1982) predicted the niche of this species to expand spatially because of
the capability of the animals to utilise an increasing amount of anthropogenic debris floating in the
world’s oceans as a habitat. On natural substrata such as floating Sargassum, Electra tenella is
lacking, which could either be due to settlement preferences of this species or due to its competitive
inferiority to the dominating species on floating Sargassum in the North Atlantic, Membranipora
tuberculata. Similar as M. tuberculata, the erect bryozoan Bugula neritina can be found on a wide
variety of different substrata including seagrass blades (Keough & Chernoff 1987) and plastic
surfaces (Thiel et al. 2003).
In the western Mediterranean, Aliani & Molcard (2003) found four species of Bryozoa on
floating debris. While colonisation frequency decreased towards higher latitudes (Winston et al.
1997, Barnes & Sanderson 2000), bryozoans were still the most common sessile organisms reported
from floating plastics in the Southern Ocean (Barnes & Fraser 2003). Based on geographic evidence
and a meta-analysis of British bryozoans, Watts et al. (1998) suggested that rafting played an
important role in evolution and biogeography of cheilostome bryozoans (albeit in present-day
oceans transport via ships may overshadow rafting dispersal).
337
Rafting
inference
Floating
substratum Reference
Amphiura magellanica Southern Ocean R M Fell 1953, cited in Hendler
1991
Amphiura sp. Tasmania R M Edgar 1987
Ophiactis carnea St. Helena R M Arnaud et al. 1976
Ophiactis simplex California R M Hobday 2000a
Ophioplocus esmarki California R M Bushing 1994
Ophiothrix caespitosa Tasmania R M Edgar 1987
Ophiothrix spiculata California R M Hobday 2000a
Ophiothrix triglochis St. Helena R M Arnaud et al. 1976
Notes: D = distributional inference; G = genetic inference; M = macroalgae; n.i. = no information; R = rafting.
* References refer to this species under a different name.