Standard Presentation Australian Marine Sciences Association Annual Meeting 2023

Relationship between the distribution of microalgae and growth-limiting bacteria against HAB species in eelgrass beds and tides (#266)

Nobuharu Inaba 1 , Senri Kojima 2 , Satoshi Nagai 3 , Shuzo Takagi 4 , Ichiro Imai 2
  1. Civil Engineering Research Institute for Cold Region, Public Works Research Institute, Sapporo, Hokkaido, Japan
  2. Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido, Japan
  3. Japan Fisheries Research and Education Agency, Yokohama, Kanagawa, Japan
  4. Research Institute for Fisheries Science, Okayama Prefectural Technology Center for Agriculture, Forestry and Fisheries, Setouchi, Okayama, Japan

Growth-limiting bacteria (GLB) against harmful algal bloom (HAB) species have been reported to densely inhabit seagrass biofilms, implying that these bacteria are provided to surrounding environments and transported by tidal currents. However, no studies have shown the relationship between the distribution of GLBs in seagrass beds and tides. In this study, we evaluated the distribution of GLBs and microalgae in the Zostera marina bed and the surroundings concerning tidal currents on the coast of Okayama Prefecture, the Seto Inland Sea, Japan.

The densities of GLBs affecting tested algal species were detected between 105 and 107 CFU g-1 wet leaf from Z. marina biofilms. Although GLBs were constantly detected in the water at the Z. marina bed, the densities and frequency of GLBs were observed to be relatively higher at low tide in the offshore water. The percentage of pennate diatoms also increased outside of the eelgrass bed at low tide, suggesting that these microbes, including GLBs, were supplied from the eelgrass bed to the surrounding waters by tidal currents.

This study provided new insights into the ecological role of the eelgrass bed and its future application to mitigate HABs, highlighting the importance of restoring seagrass beds in the coastal environment.