Lethal effects caused by suspended particles and sediment load on zoospores and gametophytes of the brown alga Eisenia bicyclis

Abstract

The effects caused by suspended particles in seawater and sediment cover of the substrate on the attachment to the substrate of zoospores, and on the subsequent growth and survival of gametophytes of the brown alga Eisenia bicyclis were examined in the laboratory. The attachment rate to the substrate of the zoospores was remarkably reduced by the sediment cover on the substrate, and it decreased to 3.8% of the no-sediment control by a slight sediment cover of 3.0 mg/cm2 (0.048 mm in thickness). The growth of gametophytes was not inhibited at 10 mg/cm2 or less of sediment cover, though it was stopped at 30 mg/cm2. The survival rate of gametophytes became 39.4% at 5 mg/cm2 on the substrate, and gametophytes were all blighted at 30 mg/cm2. The ratio of male of female of the surviving gametophytes became 81.5:18.5, when the sediment cover was 10 mg/cm2. The rate of total loss (TL [%]) of zoospores and gametophytes of Eisenia bicyclis was obtained from the following equation: TL=100 (1−exp[−0.0339 C] exp[−1.24 Q]), where, C(mg/L) and Q (mg/cm2) indicate the concentration of suspended particles in seawater and the sediment on the substrate, respectively.