Abstract
The objective of this study was to determine the characteristics of seaweed attachment on floating structures constructed with the drifted pumice. Blast furnace cement, tap water, and drifted pumice were mixed in a weight ratio of 1:0.5:2.2 to produce the pumice blocks (15 × 15 × 5 cm). The field experiments were conducted in Nagashima-cho, Kagoshima Prefecture. 60 pumice blocks were placed on Nov 4, 2022 on the sea surface and seafloor, respectively. After 13, 27, 39, 67, 88, and 109 days of installation, 10 pumice blocks were collected from sea surface and seafloor, respectively. Wet weight of seaweed adhering to the top, side, and bottom of the pumice blocks was measured. The average amounts of seaweed attached to the pumice blocks placed on the sea surface were significantly higher than those placed on the sea floor. After 13 to 39 days, Enteromorpha sp. was observed on the top surfaces of the pumice blocks. Attachment of Ulva sp. was observed on the pumice blocks after 67, 88 and 109 days. The highest amounts of Ulva sp. were observed on the sides of the the pumice blocks placed on the sea surface. Installing the pumice blocks on the sea surface was expected to promote seaweed growth, which receives more solar radiation than the seafloor, and avoid covering by the sand after placing in the sea.
