Dominic Franco C. Belleza1, Shin-ichiro Tanimae1, Takeshi Urae1, Shigetaka Matsumuro1, Makoto Kabeyama1, Hiroto Tateishi1, Gregory N. Nishihara2
1Graduate School of Fisheries and Environmental Sciences, Nagasaki University, Nagasaki, Japan
2Organization for Marine Science and Technology, Institute for East China Sea Research, Nagasaki University, Nagasaki, Japan
The capacity of urchins to overgraze algal beds is well documented. Currently, the most effective way to restore seaweed ecosystems is to reduce urchin populations by removal. However, these can be expensive and success can be limited. Here we evaluate an alternative method of reducing grazing pressure by inducing predator-avoidance behaviors in the urchin Heliocidaris crassispina. We used fresh H. crassispina extracts embedded in food-grade agar discs as a feeding deterrent in field conditions. We also investigated the physical properties of agar as a medium to deliver the urchin extracts in a controlled manner. We tested two concentrations (10% and 20%) against a control (0%, plain agar) and observed urchin behavior using a time-lapse camera for 5 days. The results suggests that higher concentrations are effective over lower concentrations as there was a progressive decrease in the number of urchins in-frame at 20% but not at 0% and 10%, over the observation period. Moreover, we also suggest strategies for applying this method in field conditions.