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Effects of transparent exopolymer particles and muddy terrigenous sediments on the survival of hard coral recruits

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Fabricius, K. E. , Wild, C. , Wolanski, E. and Abele, D. (2003): Effects of transparent exopolymer particles and muddy terrigenous sediments on the survival of hard coral recruits , Estuar. Coast. Shelf. Sci., 57 , pp. 613-621 .
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Abstract:

Sedimentation is a major cause of mortality in scleractinian coral recruits.In this study, we compared the effects of muddy coastal sediments, withand without enrichment by "marine snow" on the survivorship of recruits ofthe hard coral Acropora willisae. Transparent exopolymer particles (TEP)were measured as characteristic components of marine snow using astaining method (Passow&Alldredge 1995). Four-week old recruits wereexposed to (i) muddy coastal sediments, (ii) TEP, (iii) TEP-enriched muddycoastal sediments, and (iv) unfiltered sea water, for 43 h in aerated flowchambers. Thirty-three percent (± 5 SE) of coral recruits died after 43-hexposure to TEP-enriched muddy coastal sediments (~14 mg cm-2sediments enriched with 3.8 ± 0.2 mg cm-2 gum xanthan equivalents [GX]TEP). In contrast, no or minimal mortality was observed in the other threetreatments. Mortality increased to >80% when the amount of deposited TEPwas almost tripled (10.9 ± 1.3 mg cm-2 GX) and sediment increased by50%. Thus, coral recruits survived short-term exposure to low levels of TEPand low levels of muddy sediments, but sediments enriched with TEP atconcentrations recorded at some of the inshore stations proved to bedetrimental. Concentrations of TEP were measured around and away fromreefs in inshore and shelf regions ???of the central Great Barrier Reef(latitude 16 ? 18° S) in summer, the season of coral spawning andrecruitment. Within <10 km off the coast, TEP concentrations were high(mean = 291 ± 49 SE mg GX L-1, range = 152 - 791 mg GX L-1).Concentrations declined with increasing distance from the coast, andaveraged 83 (± 26 SE) mg GX L-1 around oceanic reefs >40 km off thecoast. Our study suggests that both sediment composition and short-term(43 h) sediment deposition affect survivalof coral juveniles, which has implications for the capacity of inshore reefs to be recolonised by corals to recover from large-scale disturbance events.

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