Permalink : http://hdl.handle.net/2115/68161

JaLCDOI : 10.14943/bull.fish.67.3.57

KEYWORDS : Diatoms;Resting stage cells;Red tides;Chattonella;Bottom sediment;Sediment perturbation;HAB control

Diatoms are the most predominant phytoplankton group in the coastal sea and many planktonic diatom species produce resting stage cells in their life cycle to endure unfavorable conditions. These diatom resting stage cells play an important role in initiating the blooms. It is empirically known that diatom cells are sparse in water during the course of red tides of harmful flagellates such as dinoflagellates and raphidophytes. A promising strategy to control the occurrences of red tides by harmful flagellates is to artificially induce diatom blooms just before the development of red tides of harmful flagellates. There usually exist more than 10⁵ cells of diatom resting stage cells or more in 1-g bottom sediments of coastal water areas, but they need light for germination and rejuvenation to become planktonic form. Sediment perturbation was carried out to transfer diatom resting stage cells in bottom sediments to euphotic zone and to induce germination and rejuvenation. This trial was made using dragnet fishing boats in coastal sea area of Tomonoura, Fukuyama City, Hiroshima Prefecture, in July 2016. The densities of diatom resting stage cells were 2.8×10⁵g-1 wet sediment at the site(Stn. A, 4m depth) outside of the dragnet-trawling zone and 1.2×10⁵g-1 wet sediment at the site(Stn. B, 4m depth) in the trawling zone. The densities of planktonic diatoms increased in the water column at Stn. B just after the trawling, but not at Stn, A, and totally increased thereafter(maximum value of 1,383 cells mL-1). The cell densities of the raphidophyte Chattonella spp. decreased at Stns. A and B. The water sample after sediment perturbation was collected at 2 m deep at Stn. B, and incubation experiments were conducted for the bottles in combination with the inoculation of Chattonella antiqua(200 cells mL-1) and the strengthening of SWM-3 culture medium(1/100). Diatoms always increased and Chattonella cells decreased in all the experimental bottles. The present study demonstrated a possible feasibility of sediment perturbation as a environment-frendly control strategy for Chattonella red tides in coastal sea area with artificial induction of phytoplankton flora to diatom dominant communities.