Positive species interactions strengthen in a high-CO(2) ocean

• Published in: Proceedings of the Royal Society B: Biological Sciences
• Main Authors: Ferreira, Camilo M., Connell, Sean D., Goldenberg, Silvan U., Nagelkerken, Ivan
• Format: Text
• Language: English
• Published: The Royal Society 2021
• Subjects: Global Change and Conservation; Parma; Ocean acidification
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8261209/; http://www.ncbi.nlm.nih.gov/pubmed/34229493; https://doi.org/10.1098/rspb.2021.0475

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.