Title Restoration of kelp beds on an urchin barren : Removal of sea urchins by citizen divers in southwestern Hokkaido
Authers Akira WATANUKI, Toru AOTA, Eiji OTSUKA, Tadashi KAWAI, Yoshitoshi IWAHASHI, Hisami KUWAHARA and Daisuke FUJITA
Keywords grazing, Saccharina japonica var. religiosa, sea urchins, Strongylocentrotus nudus, kelp beds, monitoring, removal
Citation Bull. Fish. Res. Agen. No.32, 83-87, 2010
Along the southwestern coast of Hokkaido, urchin barren dominated by a sea urchin Strongylocentrotus nudus and nongeniculate coralline algae has persisted for a long time (locally > 80 years) while kelp beds comprised of Saccharina japonica var. religiosa and Undaria pinnatifida has been restricted in shallow waters largely less than 2m in depth. Although previous studies have revealed that S. nudus is the causative grazer of the barren state by removal of and/or defense from the sea urchin, no practical efforts have been done for the improvement of fisheries ground. As the fishermen on the coast are aged and depopulated, the authors introduced citizen volunteer divers (CVD) for the removal of the sea urchin. The attempt was practiced on an urchin barren near Kamoenai Fishing Port on the southern coast of Shakotan Peninsula in September 2005. Twenty CVD (including a few instructors and staffs) removed sea urchins from two blocks (50 x 50 m, 4-8m in depth) during two dives (ca. 1 hr/dive) beside the control block; subsequent monthly removal by monitors (i.e., researchers) was done in one of the two blocks. In May 2006, the average standing crops of the seaweed (largely kelp) were 865g/m2 (monthly removed after the CVD activity) and 150g/m2 (removed once by CVD) but 0g/m2 in control, while the density of sea urchin were 0.1, 3.5 and 4.2/m2 , respectively. The results show that the introduction of CVD can aid the restoration of kelp beds.
URI http://www.fra.affrc.go.jp/bulletin/bull/bull32/83-87.pdf