Subcontinental heat wave triggers terrestrial and marine, multi-taxa responses

Abstract

Heat waves have profoundly impacted biota globally over the past decade, especially where their ecological impacts are rapid, diverse, and broad-scale. Although usually considered in isolation for either terrestrial or marine ecosystems, heat waves can straddle ecosystems of both types at subcontinental scales, potentially impacting larger areas and taxonomic breadth than previously envisioned. Using climatic and multi-species demographic data collected in Western Australia, we show that a massive heat wave event straddling terrestrial and maritime ecosystems triggered abrupt, synchronous, and multi-trophic ecological disruptions, including mortality, demographic shifts and altered species distributions. Tree die-off and coral bleaching occurred concurrently in response to the heat wave, and were accompanied by terrestrial plant mortality, seagrass and kelp loss, population crash of an endangered terrestrial bird species, plummeting breeding success in marine penguins, and outbreaks of terrestrial wood-boring insects. These multiple taxa and trophic-level impacts spanned >300,000 km2—comparable to the size of California—encompassing one terrestrial Global Biodiversity Hotspot and two marine World Heritage Areas. The subcontinental multi-taxa context documented here reveals that terrestrial and marine biotic responses to heat waves do not occur in isolation, implying that the extent of ecological vulnerability to projected increases in heat waves is underestimated.

Spatio‐temporal dynamics of multi‐trophic communities reveal ecosystem‐wide functional reorganization

“…Yet, organisms across groups are connected through biotic interactions and shared environmental conditions (Fig. Multi-trophic community reorganization has also been linked to environmental change, such as shifts in large-scale hydro-meteorological forcing (Anderson and Piatt 1999, Beaugrand 2004, Lindegren et al 2018 or heatwaves (Ruthrof et al 2018). The importance of interactions across trophic levels can be illustrated through documented regime shifts and trophic cascades (DeYoung et al 2008), for instance the cascading effects of the loss of marine top predators on the abundances of the lower trophic levels (Baum andWorm 2009, Casini et al 2012).…”

Carbon consequences of drought differ in forests that resprout

“…In addition, the number of heatwave days in 2011 was the highest on record since 1960 (BOM, ). Prolonged reduction in rainfall, coupled with a heatwave, triggered significant, abrupt biotic disruptions across the region spanning both terrestrial and marine ecosystems, which included mortality as well as demographic shifts and altered species distributions (Ruthrof et al, ). During this event, it was estimated that approximately 16,000 ha of the NJF suffered severe canopy die‐off (Brouwers, Matusick, Ruthrof, Lyons, & Hardy, ; Matusick et al, ).…”

“…The Mediterranean climate‐type forest of southwestern Australia is a region dominated by resprouting canopy species (predominantly Eucalyptus and Corymbia spp.) and has experienced intermittent droughts since the mid 1970s, an acute drought in 2010, and multiple heatwave events in 2011 (Bates, Hope, Ryan, Smith, & Charles, ; Matusick et al, ; Petrone, Hughes, Niel, & Silberstein, ; Ruthrof et al, ). Mediterranean climate‐type ecosystems are considered highly vulnerable to climate change (Klausmeyer & Shaw, ) because of a retraction in the Mediterranean climate extent and increase in the prevalence of disturbances in these systems (e.g., fire, drought, temperature increase, invasive species; Cheddadi, Guiot, & Jolly, , Lenihan, Drapek, Bachelet, & Neilson, , Fried, Torn, & Mills, , Parry et al, , Enright, Fontaine, Lamont, Miller, & Westcott, , Enright, Fontaine, Bowman, Bradstock, & Williams, ).…”

“…Mediterranean climate‐type ecosystems are considered highly vulnerable to climate change (Klausmeyer & Shaw, ) because of a retraction in the Mediterranean climate extent and increase in the prevalence of disturbances in these systems (e.g., fire, drought, temperature increase, invasive species; Cheddadi, Guiot, & Jolly, , Lenihan, Drapek, Bachelet, & Neilson, , Fried, Torn, & Mills, , Parry et al, , Enright, Fontaine, Lamont, Miller, & Westcott, , Enright, Fontaine, Bowman, Bradstock, & Williams, ). Drought and heat events in 2010/2011 impacted multiple forest types in southwestern Australia, driving canopy die‐off and tree mortality across at least three forest types (Ruthrof et al, ); Tuart ( Eucalyptus gomphocephala ) woodlands (Matusick, Ruthrof, & Hardy, ), the Northern Jarrah ( Eucalyptus marginata ) Forest (Matusick, Ruthrof, Brouwers, Dell, & Hardy, ), and Banksia woodland (Bader et al ., ; Challis, Stevens, Mcgrath, & Miller, ). Although we are beginning to understand the ecological implications of drought to such forest and woodland systems, we do not yet know the magnitude of live carbon loss, or the effects on live and dead carbon pools within forest stands.…”

“…The Mediterranean climate-type forest of southwestern Australia is a region dominated by resprouting canopy species (predominantly Eucalyptus and Corymbia spp.) and has experienced intermittent droughts since the mid 1970s, an acute drought in 2010, and multiple heatwave events in 2011 (Bates, Hope, Ryan, Smith, & Charles, 2008;Matusick et al, 2018;Petrone, Hughes, Niel, & Silberstein, 2010;Ruthrof et al, 2018).…”