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<p>Jellyfish have become a crucial functional group in marine and freshwater pelagic ecosystems in recent decades. The freshwater jellyfish <i>Craspedacusta sowerbii</i> has also been observed more frequently globally. Mechanisms affecting its positioning in the water column, and therefore, its observation and impact on the overall pelagic community, have not systematically been studied. Factors potentially affecting the vertical movement of the species have remained in question. Here, we tested how 1) the presence of light and 2) light intensities affected the vertical positioning of <i>C. sowerbii</i> medusae in a controlled laboratory experiment. Our results show that light triggered a vertical position change of jellyfish towards the water surface, suggesting positive phototaxis. Moreover, a high light intensity also helped direct jellyfish specimens towards the water surface. Our results suggest a fundamental role of light intensity affecting the observation of <i>C. sowerbii</i> medusae in freshwater ecosystems, as well as the pelagic food web harbouring the species. Our findings are in line with the majority of previous laboratory and in situ observations.</p>

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Light increases surface occurrence of the freshwater jellyfish Craspedacusta sowerbii via positive phototaxis

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年8月7日

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  • Florian Lüskow,
  • Botond Polgári,
  • Herwig Stibor,
  • Katrin Schachtl,
  • András Abonyi

摘要

Jellyfish have become a crucial functional group in marine and freshwater pelagic ecosystems in recent decades. The freshwater jellyfish Craspedacusta sowerbii has also been observed more frequently globally. Mechanisms affecting its positioning in the water column, and therefore, its observation and impact on the overall pelagic community, have not systematically been studied. Factors potentially affecting the vertical movement of the species have remained in question. Here, we tested how 1) the presence of light and 2) light intensities affected the vertical positioning of C. sowerbii medusae in a controlled laboratory experiment. Our results show that light triggered a vertical position change of jellyfish towards the water surface, suggesting positive phototaxis. Moreover, a high light intensity also helped direct jellyfish specimens towards the water surface. Our results suggest a fundamental role of light intensity affecting the observation of C. sowerbii medusae in freshwater ecosystems, as well as the pelagic food web harbouring the species. Our findings are in line with the majority of previous laboratory and in situ observations.