Ocean currents and herbivory drive macroalgae-to-coral community shift under climate warming

Abstract

Coral and macroalgal communities are threatened by global stressors. However, recently reported community shifts from temperate macroalgae to tropical corals offer conservation potential for corals at the expense of macroalgae under climate warming. Although such community shifts are expanding geographically, our understanding of the driving processes is still limited. Here, we reconstruct long-term climate-driven range shifts in 45 species of macroalgae, corals, and herbivorous fishes from over 60 years of records (mainly 1950-2015), stretching across 3,000 km of the Japanese archipelago from tropical to subarctic zones. Based on a revised coastal version of climate velocity trajectories, we found that prediction models combining the effects of climate and ocean currents consistently explained observed community shifts significantly better than those relying on climate alone. Corals and herbivorous fishes performed better at exploiting opportunities offered by this interaction. The contrasting range dynamics for these taxa suggest that ocean warming is promoting macroalgal-to-coral shifts both directly by increased competition from the expansion of tropical corals into the contracting temperate macroalgae, and indirectly via deforestation by the expansion of tropical herbivorous fish. Beyond individual species' effects, our results provide evidence on the important role that the interaction between climate warming and external forces conditioning the dispersal of organisms, such as ocean currents, can have in shaping community-level responses, with concomitant changes to ecosystem structure and functioning. Furthermore, we found that community shifts from macroalgae to corals might accelerate with future climate warming, highlighting the complexity of managing these evolving communities under future climate change.

Tropicalisation of temperate reefs: Implications for ecosystem functions and management actions

“…Changes in biodiversity can also be strongly influenced by the range expansion of coral as alternative habitat formers, a process already occurring along the coasts of Japan (Kumagai et al, 2018;Yamano et al, 2011), Korea (Denis et al, 2014), the western Mediterranean (Serrano, Coma, & Ribes, 2012) and Australia (Baird, Sommer, & Madin, 2012;Tuckett et al, 2017). The range expansion of structurally complex corals is likely to result in increases in biodiversity as new ecological niches become available in temperate latitudes, and in some instances, the associated fauna are already expanding their range along with coral organisms (Yamano et al, 2012).…”

“…Rapid warming, such as during marine heatwaves, can also result in mass die‐offs of kelp (Wernberg et al, ). These phenomena have led to extensive losses of seaweed forests and the species they support over hundreds of kilometres of coastlines, with declines now documented from eastern and western Australia to Japan, Korea and the Mediterranean (Denis, Chen, Song, & Woo, ; Kumagai et al, ; Vergés, Tomas, et al, ; Wernberg et al, ).…”

Refugia under threat: Mass bleaching of coral assemblages in high‐latitude eastern Australia

“…While the tropicalisation of high‐latitude communities is primarily driven by the direct and indirect effects of progressive warming, acute thermal anomalies impose punctuated stress events that further alter the dynamics of resident high‐latitude species (Smale et al, ). A common trend observed among high‐latitude marine communities under progressive warming is a regime shift in foundation species from cold‐adapted macroalgae to scleractinian corals (Kumagai et al, ; Smale et al, ; Vergés et al, , ). Notwithstanding their increasing abundances, scleractinian corals at high‐latitudes are also vulnerable to acute heat stress.…”

“…Interestingly, the introduction of tropical species into highlatitude communities is not the only driver of contemporary changes in high-latitude community compositions. Climate-mediated changes in species interactions following the introduction of vagrant species into high-latitude communities (Kumagai et al, 2018;Smale et al, 2019;Vergés et al, 2019;Visser, 2008) and local rearrangements of species abundance (Tuckett, de Bettignies, Fromont, & Wernberg, 2017) can outweigh the direct influence of species range shifts on the changes in contemporary high-latitude community compositions. As such, understanding of the direct effects of progressive warming (e.g.…”

VoCC: An r package for calculating the velocity of climate change and related climatic metrics

“…Species distribution shifts are among the most frequent, ubiquitous responses to climate change observed in marine, freshwater and terrestrial biota (Parmesan & Yohe, ; Poloczanska et al, ). Several global (Brown et al, ; García Molinos, Burrows, & Poloczanska, ; Poloczanska et al, ) and regional (Comte & Grenouillet, ; Hiddink, Burrows, & García Molinos, ; Kumagai et al, ; VanDerWal et al, ) analyses have investigated whether patterns of species’ range shifts follow climate expectations using climate velocity. Here we reproduce a global meta‐analysis of observed distances of range shifts in marine species over given time periods (Poloczanska et al, ) using gradient‐based and distance‐based velocities.…”