Bulk hydrogen stable isotope composition of seaweeds: Clear separation between Ulvophyceae and other classes.

Little is known about the bulk hydrogen stable isotope composition (δ H) of seaweeds. This study investigated the bulk δ H in several different seaweed species collected from three different beaches in Brazil, Australia, and Argentina. Here, we show that Ulvophyceae (a group of green algae) had lower δ H values (between -94‰ and -130‰) than red algae (Florideophyceae), brown algae (Phaeophyceae), and species from the class Bryopsidophyceae (another group of green algae). Overall the latter three groups of seaweeds had δ H values between -50‰ and -90‰. These findings were similar at the three different geographic locations. Observed differences in δ H values were probably related to differences in hydrogen (H) metabolism among algal groups, also observed in the δ H values of their lipids. The marked difference between the δ H values of Ulvophyecae and those of the other groups could be useful to trace the food source of food webs in coastal rocky shores, to assess the impacts of green tides on coastal ecosystems, and to help clarify aspects of their phylogeny. However, reference materials for seaweed δ H are required before the full potential of using the δ H of seaweeds for ecological studies can be exploited.