A shift of tropical herbivores into temperate-tropical kelp forests can result in the loss of kelps, which provide habitat for hundreds of species, according to a study. Climate change can have direct physiological impacts on organisms and induce novel species interactions. Yet long-term changes in species interactions are difficult to track. To study the range expansion of tropical herbivorous fishes into a tropical-temperate kelp forest off eastern Australia, Adriana Vergés and colleagues recorded underwater video spanning a 10-year period during which the seawater warmed by 0.6 °C. At the study sites, the kelp forests disappeared, and fish communities became increasingly dominated by tropical herbivores over time. Two key topical-subtropical herbivores, the rabbitfish (Siganus fuscescens) and drummer (Kyphosus bigibbus), consumed transplanted kelp within hours. The number of fishes that consumed algae growing on rock surfaces also increased, and these fishes cleared algae from rocks more rapidly at sites without kelp than at near-shore sites where kelp still exists, suggesting that these fishes may help maintain a kelp-free zone by removing kelp recruits. Kelp decline was not directly related to seawater temperatures, storms, or nutrient concentrations. According to the authors, tropical and subtropical herbivores may increasingly alter temperate algal communities worldwide, posing a threat to the long-term stability of ecosystems. - Read at PNAS.org
Article #16-10725: “Long-term empirical evidence of ocean warming leading to tropicalization of fish communities, increased herbivory, and loss of kelp,” by Adriana Vergés et al.