Effects of ocean warming and lowered pH on algal growth and palatability to a grazing gastropod

Macroalgae support productive and diverse communities in marine habitats worldwide, but are threatened by changes to ocean conditions and altered interactions with marine herbivores. To better understand how non-calcifying macroalgae can persist in a changing ocean, we investigated the effects of co-occurring warming and ocean acidification on six species of temperate macroalgae, and subsequent change in palatability to a common gastropod herbivore. Algal growth was unaffected by moderate temperate increases of 2 °C, but five of the six species displayed reduced growth at increases of 4 °C. Lowered pH affected the growth of two species, with no interactions between temperature and pH evident. Changes to temperature and pH environment had little effect on the palatability of these algae to the gastropod Phasianotrochus eximius, with lowered pH increasing subsequent palatability for only one species of macroalgae. These results highlight the variation among algal species in their responses to changed ocean conditions and likely interactions with their consumers.