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<p>Despite the widely recognized impact of fish herbivory on macroalgae, few studies have quantified the specific contributions of individual species in Japan. We used visual censuses along belt transects to investigate the abundance of herbivorous fishes, and measured fish feeding intensity on deployed native brown seaweed <i>Sargassum piluliferum</i> from underwater videos, at two coastal sites off Nagasaki Prefecture, southwestern Japan, in 2016 and 2018. A total of eight herbivorous species were observed, with <i>Girella</i> spp. and/or <i>Prionurus scalprum</i> comprising the majority of roving herbivorous fish at both sites. However, herbivory was driven by only three species: <i>Calotomus japonicus</i>, <i>Kyphosus bigibbus</i>, and <i>Siganus fuscescens</i>. At Nomo, <i>C. japonicus</i> was the principal species responsible for removal of <i>S. piluliferum</i>. At Mie, <i>S. fuscescens</i> was the most dominant in herbivory in 2016, but its contribution declined markedly in 2018, leading to <i>C. japonicus</i> becoming the principal species responsible for the removal. These findings indicate that only a subset of herbivorous fishes, even at low abundances, significantly reduces <i>Sargassum</i> biomass, and that the key herbivores may vary between reef sites. Identifying these key species using algal assays is an important step toward targeted management of herbivorous fish to support seaweed bed conservation and restoration.</p>

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Identity of herbivorous fishes preventing the restoration of Sargassum beds in Nagasaki Prefecture, southwestern Japan

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年8月4日

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  • Tatsuru Kadota,
  • Tsutomu Noda

摘要

Despite the widely recognized impact of fish herbivory on macroalgae, few studies have quantified the specific contributions of individual species in Japan. We used visual censuses along belt transects to investigate the abundance of herbivorous fishes, and measured fish feeding intensity on deployed native brown seaweed Sargassum piluliferum from underwater videos, at two coastal sites off Nagasaki Prefecture, southwestern Japan, in 2016 and 2018. A total of eight herbivorous species were observed, with Girella spp. and/or Prionurus scalprum comprising the majority of roving herbivorous fish at both sites. However, herbivory was driven by only three species: Calotomus japonicus, Kyphosus bigibbus, and Siganus fuscescens. At Nomo, C. japonicus was the principal species responsible for removal of S. piluliferum. At Mie, S. fuscescens was the most dominant in herbivory in 2016, but its contribution declined markedly in 2018, leading to C. japonicus becoming the principal species responsible for the removal. These findings indicate that only a subset of herbivorous fishes, even at low abundances, significantly reduces Sargassum biomass, and that the key herbivores may vary between reef sites. Identifying these key species using algal assays is an important step toward targeted management of herbivorous fish to support seaweed bed conservation and restoration.