Dominic Franco C. Belleza, Shin-ichiro Tanimae, Takeshi Urae, Hiroto Tateishi, Shigetaka Matsumuro, Makoto Kabeyama, Gregory N. Nishihara
Prolonging alarm cues in an area can potentially decrease foraging and increase the anti-predator behaviors in sea urchins. In this study we investigated a method of prolonging the alarm cues in the field by embedding fresh sea urchin extracts in food-grade agar. We conducted lab experiments to determine the effects of prolonged immersion on the physical properties of agar and also conducted experiments to test the effects of agar-embedded extracts on sea urchin foraging behaviors in the field. We found that agar discs containing high extract concentrations degraded faster in warmer incubation temperatures compared to those with lower concentrations incubated at low temperatures. This was due to increasing seawater penetration over time, and the rapid degradation of organic substances in the sea urchin extracts associated with higher temperatures. With regards to the anti-predator response experiment, the 20% homogenate treatment conducted during the season with high algal cover repelled about 23.1% of urchins after the 5–day observation period. However, the effects were less pronounced when conducted in the season with low algal cover (5.8% reduction). The 10% homogenate treatments were less effective than the 20% homogenate, repelling only 15.2% in the season with high algal cover and had almost no observable effect in the season with low algal cover. It appears that although the predation cues were prolonged in a small area for several days, the anti-predator behaviors in Heliocidaris crassispina was still constrained by the sea urchin's nutritional condition brought about by the seasonal availability of food. © 2025 The Author(s)
of Fisheries and Environmental Sciences, Nagasaki University, Nagasaki, Japan; Department of Biology, University of San Carlos, Talamban Campus, Cebu City, Philippines; Organization for Marine Science and Technology, Institute for East China Sea Research, Nagasaki University, Nagasaki, Japan
