Hot, heatwaves and herbivores – drivers and feedbacks of changing species distributions and community reconfiguration

Thomas Wernberg (1)

(1) UWA Oceans Institute & School of Plant Biology, The University of Western Australia, WA 6009 Crawley, Perth.

Humans are driving the redistribution of species at a global scale, rapidly breaking down long-standing biogeographic boundaries, and paving the way for novel ecosystems where new species interact with unknown long-term ecological consequences. Decades of ocean warming and recent marine heatwaves have transformed temperate marine communities in southwestern Australia. As temperatures soared, a threshold was passed and kelp forests contracted >100 km poleward in less than two years. Temperate species vanished or declined, but were replaced by seaweeds, invertebrates, corals and fishes characteristic of warm and tropical waters. Turf forming seaweeds and herbivorous fishes have now established feedbacks providing resilience to the new tropicalized ecosystem state. This community-wide phase shift provides a powerful example of the potent consequences of interacting pulse and press perturbations. Early signs of similar changes are seen in temperate ecosystems worldwide, and the extensive degradation of an Australian kelp forests ecosystem is a strong warning of what might be in store for temperate marine ecosystems globally.