Combined Effects of Temperature and Nutrient Enrichment on Palatability of the Brown Alga Sargassum yezoense (Yamada) Yoshida & T. Konno

Abstract

Global warming is predicted to strengthen marine plant-herbivore interactions. However, little is known about the effect of temperature on palatability and the associated chemical composition of marine macroalgae. To study the effects of physiological stress caused by the warm water tem-peratures and nutrient-poor conditions that occur during summer, we cultured the brown alga Sargassum yezoense at three different temperatures (16˚C, 22˚C, and 28˚C) in both nutrient-enri-ched and non-enriched media. We then compared phlorotannin (i.e., defensive compounds) and nitrogen concentrations of S. yezoense as well as consumption rate by the sea urchin Hemicetrotus pulcherrimus among the treatment groups. No effect of culture temperature on phlorotannin and nitrogen concentrations or consumption rate was detected. Nutrient enrichment resulted in de-creased phlorotannin concentration and increased nitrogen concentration. Although nutrient en-richment did not affect consumption rate, a positive correlation between nitrogen concentration and consumption rate was detected. In contrast, there was no correlation between phlorotannin concentration and consumption rate. These results suggested that palatability of S. yezoense to H. pulcherrimus might not be affected by elevated temperature but that it could increase with nutri-ent enrichment.