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Figure 1.

Significant pumice rafting events over the last 200 years.

Volcanic eruption locations, eruption dates and general trajectory paths of pumice rafts are shown illustrating the global scale and frequency of such events. To maintain figure clarity, only pumice raft-producing eruptions for the last 50 years from the Tonga-Kermadec arc, (southwest Pacific) are listed. Data sources are given in Supporting Information (Appendix S1) to this paper. Base map is from Amante and Eakins [14].

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Table 1.

Pumice strand sample sites, Eastern Australia.

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Figure 2.

Trajectory map of the 2006–2007 pumice rafts, based on the integrated surface velocity field.

Pumice strandings following the Home Reef (HR) eruption were reported at the following locations: Fiji (∼33 days); Vanuatu (VA, 88 days); New Caledonia (NC, ∼115 days); Willis Island (WI, ∼180 days); Lizard Island (LI, ∼200 days); Mackay (MA, ∼250 days); Broadbeach (BR, ∼250 days). Other abbreviations: LB, Lau Basin; NZ, New Zealand; PNG, Papua New Guinea; MR, Marion Reef; LM, Lady Musgrave Reef; WH, Whitsunday Island; BA, Ballina. Brown shaded region along northeastern Australia is the Great Barrier Reef World Heritage Area. Grey areas without bathymetric information represent continental shelves of <1000 m depth, where geostrophic ocean currents were not calculated. An animated version of the pumice raft trajectory is provided in Supporting Information (Figure S1) to this paper.

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Table 2.

Quantitative data for epibionts transported by the 2006–2007 pumice rafts.

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Table 3.

Quantitative data for colonial epibionts transported by the 2006–2007 pumice rafts.

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Table 4.

Temporal variation in total epibiont coverage.

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Table 5.

Summary of epibiont taxa, their designated feeding guild and their averaged frequency of occurrence.

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Figure 3.

Proportions of rafted epibionts along the trajectory.

Number refers to number of taxonomic units identified at each sample site. Marine invertebrates are grouped in terms of feeding behaviours. Suspension and filter feeders (e.g., cheilostome Bryozoa, goose barnacles, hydroids/scyphozoans, serpulids, corals, molluscs, and oysters) show significant early recruitment (Tonga) with epibiont diversity generally maintained along the raft trajectory. The numbers of plants (cyanobacteria, macroalgae and calcareous algae) increased with time and along the trajectory, particularly once pumice had arrived into eastern Australian waters. Overall, epibiont diversity increased with time. Bar graphs are colour-coded with respect to observation/collection timing: purple, February 2007; blue, April-May 2007 and; green, December 2007. N is total number of species/taxonomic units observed, and n is number of pumice clasts described from each location. Abbreviations: Ph, photosynthetic; S & FF, suspension & filter feeders; G & B, grazers & borers; P & S, predators and scavengers. Locations: MR, Marion Reef; MA, Mackay; LM, Lady Musgrave; BR, Broadbeach; BB, Byron Bay; BA, Ballina. Tonga sample site occurs ∼2900 km to the east. Base map from Google Earth.

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Figure 4.

Epibiont colonisation on Home Reef pumice.

(A) Pumice clast collected from Marion Reef on April 30, 2007 with a mature epibiont fauna attached. Based on compiled growth rates [23], the largest goose barnacles (Lepas anserifera; 23 mm length) have been attached to the pumice for a minimum of 60 days, while the size of the mollusc indicates up to 200 days of growth [33]. Note the rounded and abraded form of the pumice clast on to which the epibionts have attached. Coin is 2 cm diameter. (B) Heavily fouled pumice collected from a secondary stranding at Broadbeach, southeastern Queensland on December 27, 2007 (807 days after the eruption). Two pumice clasts are bound together by cyanobacteria (principally Rivularia sp.) and macroalgae (Caulerpa sp.) with two corals (Pocillopora sp.), a colonial scyphozoan (Order Coronatae), goose barnacles (Lepas anserifera) and mollusc (Pinctada sp.) also attached. Coin is 2.4 cm diameter.

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Figure 5.

Epibiont distribution on Home Reef pumice.

(A) Three pumice clasts collected from Broadbeach on December 27, 2007 with well-developed biological keels of the anemone Calliactus sp. with cheilostome Bryozoa (Jellyella sp.) along the waterline and Rivularia spp. occupying all of the dorsal surface with occasional goose barnacles (Lepas anserifera); pumice clast at left is 5 cm long. (B) Typical observed polarity in epibiont distribution on pumice with dorsal surfaces almost exclusively occupied by cyanobacteria (Rivularia sp.), and here, the ventral surface entirely covered by cheilostome Bryozoa (Jellyella sp.) colonies. Clast is 1.7 cm long, collected from Lamberts Beach, Mackay.

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Table 6.

ANOSIM results.

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Figure 6.

Biotic changes of the Home Reef pumice rafts during 2006 and 2007.

Frequency of occurrence (expressed as %) of biota on pumice clasts is shown relative to pumice raft arrival time, sample location (A) and approximate distance along the trajectory in kilometres (B), which correlates with floating time. Three general epibiont trends are observed with time: 1) rapid colonisation of all available pumice resulting in ubiquity (cyanobacteria) – a few sample sites showed slightly reduced occurrences of cyanobacteria on pumice (e.g., Lady Musgrave), but this resulted from clast abrasion across reefs, followed by some post-stranding desiccation and spalling; 2) a progressive increase in occurrence with time (e.g., cheilostome Bryozoa, gastropods and macroalgae) and; 3) stalled colonisation where some species were successfully recruited early on to pumice but underwent no further colonisation expansion due to insufficient time to reach sexual maturity (corals), or the epibionts continued to colonise the same clast (serpulids, hydrozoans/scyphozoans), increasing the numbers of conspecifics per clast; these taxa also had relatively low initial recruitment numbers.

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