Temporal variability of algicidal and growth-inhibiting bacteria at an eelgrass bed in the Ariake Sea, Japan

Abstract

Temporal changes of algicidal and growth-inhibiting bacteria on the fish-killing raphidophyte flagellate, Chattonella antiqua, at an eelgrass (Zostera marina) bed in southern Ariake Sea, Japan in 2011 was investigated. The maximum value (5.1 × 10⁷ CFU g⁻¹ wet leaf) of algicidal bacteria (AB) was detected from a biofilm formed on Z. marina on August 1 when AB in the adjacent seawater had also peaked (1.2 × 10⁴ CFU mL⁻¹). Two causative bacteria isolated from the biofilm and seawater on August 1 were both identified to be of the genus Alteromonas (γ-proteobacteria). AB and growth-inhibiting bacteria (GIB) were present from the beginning of sampling (May 20) to August 26, fluctuating between 8.6 × 10² and 1.2 × 10⁴, 1.2 × 10³ and 9.3 × 10³ CFU mL⁻¹, respectively. The highest phytoplankton density observed was 6423 cells mL⁻¹ on September 29 and was comprised of centric diatoms such as Chaetoceros, Skeletonema, and Thalassiosira and coincided with the absence of AB and GIB where the decline of Z. marina was also observed. These findings provide a new ecological insight on AB and GIB associated with Z. marina beds, indicating eelgrass beds have the important role as the nursery of those bacteria that can be utilized as mitigation measures of harmful algal blooms (HABs) in the future.

Keywords:

• Algicidal bacteria
• Chattonella
• eelgrass bed
• growth-inhibiting bacteria
• HABs
• harmful algae
• mitigation
• restoration
• Zostera marina

Acknowledgments

We express sincere thanks to Dr Ken-Ichiro Ishii from SeedBank Inc. Co., Ltd, Dr Vera L. Trainer and Brian D. Bill from Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration (NOAA) for critical advice during sampling and manuscript editing. We also like to show our gratitude to Dr Sandy Wyllie-Echeverria from College of the environment, University of Washington for insightful comments and suggestions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was supported financially by the Agriculture, Forestry, and Fisheries Research Council of Japan (grant number 0319 B).