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Suspended sediments limit coral sperm availability
Ricardo, G.F.; Jones, R.J.; Clode, P.L.; Humanes, A.; Negri, A.P. (2015). Suspended sediments limit coral sperm availability. NPG Scientific Reports 5(18084): 12 pp. hdl.handle.net/10.1038/srep18084
In: Scientific Reports (Nature Publishing Group). Nature Publishing Group: London. ISSN 2045-2322, more
Peer reviewed article  

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Keyword
    Marine

Authors  Top 
  • Ricardo, G.F.
  • Jones, R.J.
  • Clode, P.L.
  • Humanes, A.
  • Negri, A.P.

Abstract
    Suspended sediment from dredging activities and natural resuspension events represent a risk to the reproductive processes of coral, and therefore the ongoing maintenance of reefal populations. To investigate the underlying mechanisms that could reduce the fertilisation success in turbid water, we conducted several experiments exposing gametes of the corals Acropora tenuis and A. millepora to two sediment types. Sperm limitation was identified in the presence of siliciclastic sediment (230 and ~700?mg L-1), with 2–37 fold more sperm required to achieve maximum fertilisation rates, when compared with sediment-free treatments. This effect was more pronounced at sub-optimum sperm concentrations. Considerable (>45%) decreases in sperm concentration at the water’s surface was recorded in the presence of siliciclastic sediment and a >20% decrease for carbonate sediment. Electron microscopy then confirmed sediment entangled sperm and we propose entrapment and sinking is the primary mechanism reducing sperm available to the egg. Longer exposure to suspended sediments and gamete aging further decreased fertilisation success when compared with a shorter exposure. Collectively, these findings demonstrate that high concentrations of suspended sediments effectively remove sperm from the water’s surface during coral spawning events, reducing the window for fertilisation with potential subsequent flow-on effects for recruitment.

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