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

Little is known about the bulk hydrogen stable isotope composition (δ² H) of seaweeds. This study investigated the bulk δ² 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 δ² 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 δ² H values between -50‰ and -90‰. These findings were similar at the three different geographic locations. Observed differences in δ² H values were probably related to differences in hydrogen (H) metabolism among algal groups, also observed in the δ² H values of their lipids. The marked difference between the δ² 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 δ² H are required before the full potential of using the δ² H of seaweeds for ecological studies can be exploited.