Temperature-Dependent Food Consumption Rates of the Sea Urchin Mesocentrotus nudus and Top Shell Turbo sazae: Potential Impacts on Seaweed Beds

SIMPLE SUMMARY: Despite the expansion of barren grounds and a change in the habitats of macrograzers brought about by rising water temperatures linked to climate change, there is a lack of information regarding how this habitat alteration and grazing by macrograzers affect seaweed beds. This study assessed which species, sea urchin and top shell, would have a more significant influence on seaweed beds if the current trend of increasing water temperature continues. Our results suggest that top shell has a greater potential to cause barren ground and thus poses a greater threat than sea urchin. ABSTRACT: In Korea, the expansion of barren ground and a shift in macrograzer habitats due to increasing water temperatures associated with climate change are becoming increasingly problematic. This study assessed the potential effects of the sea urchin Mesocentrotus nudus and top shell Turbo sazae on seaweed beds by examining changes in their food consumption rates in response to changes in temperature. The food consumption rates of kelp (Saccharina japonica) for both species were estimated at 5 °C, 10 °C, 15 °C, 20 °C, and 25 °C in laboratory experiments. The rate for M. nudus increased with increasing water temperature, with the highest rate of 0.001 g g(−1) d(−1) at 15 °C and 20 °C, and the lowest at 25 °C, which killed some individual sea urchins. The rate for T. sazae also increased with increasing water temperature, with the highest being 0.087 g g(−1) d(−1) at 25 °C and the lowest being at 5 °C. T. sazae had a higher food consumption rate than M. nudus at all temperatures; as water temperature increased, the difference between species increased, with the largest difference occurring at 25 °C. These findings indicate that as water temperature increases, T. sazae places greater feeding pressure on macroalgae than M. nudus.