Supplementary material from "Positive species interactions strengthen in a high-CO 2 ocean"

• Main Authors: Ferreira, Camilo M., Connell, Sean D., Goldenberg, Silvan U., Nagelkerken, Ivan
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: The Royal Society 2021
• Subjects: Ecology; FOS Biological sciences; 60801 Animal Behaviour; Parma; Ocean acidification
• Online Access: https://dx.doi.org/10.6084/m9.figshare.c.5479633.v1; https://rs.figshare.com/collections/Supplementary_material_from_Positive_species_interactions_strengthen_in_a_high-CO_sub_2_sub_ocean_/5479633/1

Negative interactions among species are a major force shaping natural communities and are predicted to strengthen as climate change intensifies. Similarly, positive interactions are anticipated to intensify, and could buffer the consequences of climate-driven disturbances. We used in situ experiments at volcanic CO 2 vents within a temperate rocky reef to show that ocean acidification can drive community reorganization through indirect and direct positive pathways. A keystone species, the algal-farming damselfish Parma alboscapularis, enhanced primary productivity through its weeding of algae whose productivity was also boosted by elevated CO 2 . The accelerated primary productivity was associated with increased densities of primary consumers (herbivorous invertebrates), which indirectly supported increased secondary consumers densities (predatory fish) (i.e. strengthening of bottom-up fuelling). However, this keystone species also reduced predatory fish densities through behavioural interference, releasing invertebrate prey from predation pressure and enabling a further boost in prey densities (i.e. weakening of top-down control). We uncover a novel mechanism where a keystone herbivore mediates bottom-up and top-down processes simultaneously to boost populations of a coexisting herbivore, resulting in altered food web interactions and predator populations under future ocean acidification.