Sediment tolerance of Sargassum algae inhabiting sediment-covered rocky reefs |
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Authors: | Shigeru Kawamata Satoshi Yoshimitsu Shigemitsu Tokunaga Satoshi Kubo Toshihiro Tanaka |
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Institution: | (1) National Research Institute of Fisheries Engineering, Fisheries Research Agency, 7620-7 Hasaki, Kamisu City, Ibaraki 314-0408, Japan;(2) Kagoshima Prefectural Fisheries Technology and Development Center, Iwamoto, Ibusuki City, Kagoshima 891-0315, Japan |
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Abstract: | Although sediment deposition has detrimental effects on macroalgal settlement and recruitment, fucoid algae (mainly Sargassum duplicatum) thrive on rocky reefs always overlaid with fine sediments in sheltered sites of Kagoshima, Japan. The aim of the present
study was to assess their ability to settle and recruit onto sediment-covered substrata. A transplant experiment using boulders
with Sargassum juveniles attached showed that the 30-day survival rate was as high as 50% even for the juvenile stage (<10 mm) on boulders
completely buried with sediment. In addition, an outdoor tank experiment testing the effects of different sediment thicknesses
(0–4 mm) on already settled 4-day old S. duplicatum germlings indicated significant reductions in growth by the presence of sediment cover even at 0.5 mm but no significant
increase in mortality up to 2 mm. Furthermore, an in situ experiment in which sterilized cobbles were placed at a sediment-covered
site to allow sediment to settle over them before the embryo release showed a uniformly high recruitment of Sargassum over the cobbles. This suggests the presence of unknown mechanisms to allow the settlement of propagules on substrata thinly
but completely covered by fine sediments. |
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