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.