The ecology of rafting in the marine environment - Bedim

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MARTIN THIEL & LARS GUTOW as suitable rafts for insects. Since large parts of the Bay of Fundy are surrounded by land masses, aerial introduction of insects is possible but rafting appears a reasonable explanation for the occurrence of numerous wingless insects or developmental stages (generally pupae) as well as spiders and mites in the central bay. Species from the genus Halobates have assumed a holopelagic lifestyle. They skate autonomously over the water surface, but are often associated with floating items and drift lines where they find food and attachment sites for their eggs (see Andersen & Cheng 2004 for further details). Arthropoda (Crustacea, Cladocera) In a compilation of animals commonly associated with Sargassum weed, Evadne spinifera is listed as the only cladoceran species (Adams 1960) (Table 8). However, it is doubtful whether this species can be considered as a rafter. Ingólfsson (1998) reported pelagic stages (larvae and adults) of several crustacean taxa such as cladocerans, calanoid copepods, cirripede larvae and decapod larvae. These taxa were not more common in samples of floating algae than in algal-free control hauls (see also Shaffer et al. 1995). Furthermore, unlike typical rafters no correlation was detected between the number of individuals and clump size. Hence, the author concluded that these taxa are not a priori associated with floating algae but were probably accidentally caught with seaweed. Arthropoda (Crustacea, Ostracoda) A few ostracod species have also been inferred to be dispersed via rafting (Peck 1994) (Table 8). The species Philomedes globosus has been found on floating macroalgae near Iceland (Ingólfsson 1995). Arthropoda (Crustacea, Copepoda) The lifestyle of most calanoid and cyclopoid copepods is planktonic. However, if copepods are found in clumps of floating seaweeds while they are missing from the surrounding plankton, as it was found for Microcalanus sp. (Shaffer et al. 1995), the animals might have used the substratum as a raft. Similar to calanoids, cyclopoid copepods, too, are incidentally found in floating seaweeds (e.g., Yeatman 1962, Hicks 1988). In contrast to the two former groups, harpacticoid copepods are common rafting organisms, in particular on floating macroalgae (Yeatman 1962, Shaffer et al. 1995, Ingólfsson & Ólafsson 1997, Ólafsson et al. 2001) (Table 8). From floating algae Ascophyllum nodosum and Fucus vesiculosus caught in coastal waters of Iceland, Ólafsson et al. (2001) reported 38 species of harpacticoid copepods, most of which usually inhabit benthic macroalgae. Some of the commonly encountered species are also found associated with sandy or muddy bottoms but none of these species is known to exclusively dwell in muddy or sandy habitats. As in other meiofaunal species such as nematodes, rafting of harpacticoid copepods might be the result of incidental encounter of the animals with floating structures during active or passive suspension in the water column. While active movements of copepods on algal rafts are mostly restricted to short-distance swimming from branch to branch within the algal patch, Yeatman (1962) considered it as quite probable that the animals could also swim short distances from clump to clump. This might have important effects on the dynamics, (genetic) structure and persistence of local populations on algal patches that are temporally connected by this mechanism. Harpacticoid copepods rapidly colonised macroalgae tethered in nearshore habitats (Ólafsson et al. 2001). Within 8 or 9 days, the density of harpacticoids increased significantly. After the same period the harpacticoid community was more diverse on floating algal clumps than on attached algae of the same species. The floating macroalgae are used as shelter, as feeding and also as a 310
RAFTING OF BENTHIC MARINE ORGANISMS Table 8 Arthropoda Branchiopoda and Maxillopoda reported or inferred as rafting Species Region Branchiopoda Evadne spinifera Northwest Atlantic, Sargasso Sea Rafting inference 311 Floating substratum Reference R M Adams 1960, Coston-Clements et al. 1991 Evadne sp. U.S. West Coast R M Shaffer et al. 1995 Podon sp. U.S. West Coast R M Shaffer et al. 1995 Ostracoda Anchistrocheles darwini Galapagos D n.i. Peck 1994 Occultocythereis augusta Galapagos D n.i. Peck 1994 Paracypris crispa Galapagos D n.i. Peck 1994 Philomedes globosus Iceland R M Ingólfsson 1995 Copepoda, Cyclopoida Copilia mediterranea Northwest Atlantic, Sargasso Sea R M Adams 1960, Coston-Clements et al. 1991 Corycaeus sp. U.S. West Coast R M Shaffer et al. 1995 Macrochiron sargassi Sargasso Sea, Gulf Stream R M Butler et al. 1983, Coston- Clements et al. 1991 Oithona sp. U.S. West Coast R M Shaffer et al. 1995 Oncaea sp. U.S. West Coast R M Shaffer et al. 1995 Pseudomacrochiron parvum Sargasso Sea R M Butler et al. 1983 Copepoda, Calanoida Acartia sp. U.S. West Coast R M Shaffer et al. 1995 Anomalocera patersoni Irish Sea R M Davenport & Rees 1993 Calanus sp. U.S. West Coast R M Shaffer et al. 1995 Centropages typicus Irish Sea R M Davenport & Rees 1993 Centropages sp. U.S. West Coast R M Shaffer et al. 1995 Microcalanus sp. U.S. West Coast R M Shaffer et al. 1995 Paracalanus sp. U.S. West Coast R M Shaffer et al. 1995 Pseudocalanus sp. U.S. West Coast R M Shaffer et al. 1995 Copepoda, Harpacticoida Ameira longipes Iceland R M Ólafsson et al. 2001 Amonardia arctica Iceland R M Ólafsson et al. 2001 Amonardia phyllopus Sargasso Sea, Gulf Stream R M Yeatman 1962, Butler et al. 1983, Coston-Clements et al. 1991 Amphiascoides debilis Iceland R M Ólafsson et al. 2001 Amphiascoides nanus Iceland R M Ólafsson et al. 2001 Amphiascus minutus Iceland R M Ólafsson et al. 2001 Brianola cf. pori New Zealand R O Hicks 1988 Dactylopodia tisboides Sargasso Sea, Gulf Stream, New Zealand R M Yeatman 1962, Hicks 1977, Butler et al. 1983, Coston-Clements et al. 1991 Dactylopodia sp. U.S. West Coast R M Shaffer et al. 1995 Dactylopusia vulgaris Iceland R M Ólafsson et al. 2001 Diarthrodes major Iceland R M Ólafsson et al. 2001 Diarthrodes nobilis Iceland R M Ólafsson et al. 2001
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RAFTING OF BENTHIC MARINE ORGANISMS
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Substratum selectivity Lepadidae RA
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B A Organic Matter Small Predators
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Abundance (number of individuals) 0
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Table 18 Comparison between benthic
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Proportion of Debris Items Colonize
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Fall off (scraped off) Clonal growt
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Species number Proportion Holding o
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The ecology of rafting in the marine environment - Bedim

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