The ecology of rafting in the marine environment - Bedim

RAFTING OF BENTHIC MARINE ORGANISMS
Table 10 (continued) Mollusca reported or inferred as rafting
Species Region
Rafting
inference
Crepidula convexa, on tiles attached to mangrove roots. Possibly, recruits of these snails arrived
on floating substrata (see also Collin 2001). Small snails such as the mud snail Hydrobia ulvae can
also float by extending their foot, and utilising the surface tension of the sea surface they are
dispersed by tidal currents over variable distances (e.g., Armonies & Hartke 1995, Adachi & Wada
1999), thus being independent from rafting. However, larger individuals or species depend on
floating items to become dispersed via water currents.
Many prosobranch gastropods have been found on floating macroalgae. Three different gastropod
species were found on floating kelp off St. Helena (Arnaud et al. 1976). In particular, small
species and species with benthic egg masses are inferred to have been dispersed via rafting
(Johannesson 1988, Ingólfsson 1992, 1995, 1998, Davenport & Stevenson 1998, Hobday 2000a).
Large prosobranch species may not be able to hold on to floating items. Rafting for these species
may only be possible via rafting of egg masses. Leal & Bouchet (1991) suggested rafting as a
possible mechanism of dispersal for prosobranchs along the Vitória-Trinidade Seamount Chain
extending about 1100 km eastward from the Brazilian coast. The number of directly developing
species inhabiting the seamounts varied little with distance from the mainland coast, indicating that
dispersal via rafting is as efficient as larval dispersal over distances of about 100–250 km. Since
only the largest species of their study, Bullata sp., was restricted to only one locality, they inferred that
species with smaller eggs, juveniles and adults are probably better suited for rafting than larger ones.
Nudibranchs are among the most diverse representatives of the rafting fauna. Most species feed
on hydroids and bryozoans growing on floating items (Geiselmann 1983, Il’in & Roginskaya 1987,
Schrödl 1999b). They occur primarily on macroalgae (Butler et al. 1983, Bushing 1994). The
nudibranch Adalaria proxima has been observed on entangled macroalgae, and rafting may occur
under certain conditions (Todd et al. 1998). Nudibranchs have also been reported from floating
plastics in the Mediterranean (Aliani & Molcard 2003). However, the two species encountered
(Doto sp. and Fiona pinnata) were not very abundant and represented only a small fraction of the
total community of 14 species on floating abiotic objects. Many ophistobranch species also attach
their eggs to algae and seagrasses. Worcester (1994) found egg masses of Phyllaplysia taylori and
other opisthobranchs on floating seagrass in Tomales Bay, California.
333
Floating
substratum Reference
Cephalopoda
Argonauta sp. Panama R W Donlan & Nelson 2003
Idiosepius pygmaeus Sagami Bay, Japan R M Hirosaki 1964
Loligo sp. Sagami Bay, Japan R M Hirosaki 1964
Octopus bimaculatus California R M Bushing 1994
Octopus bimaculoides California R M Hobday 2000a
Octopus micropyrsus California R M Hobday 2000a
Octopus variabilis Sagami Bay, Japan R M Hirosaki 1964
Octopus vulgaris Sagami Bay, Japan R M Hirosaki 1964
Onychia caribaea Northwest Atlantic, R M Adams 1960, Coston-Clements
Sargasso Sea
et al. 1991
Sepiola birostrata Sagami Bay, Japan R M Hirosaki 1964
Sepioteuthis lessoniana Sagami Bay, Japan R M Hirosaki 1964
Notes: B = stranded floating item on beach; C = circumstantial; D = distributional inference; G = genetic inference; M
= macroalgae; n.i. = no information; O = other; P = plastics; R = rafting; V = volcanic pumice; W = wood.
* References refer to this species under a different name.