Extreme heatwave drives topography‐dependent patterns of mortality in a bed‐forming intertidal barnacle, with implications for associated community structure

Abstract

Heatwave frequency and intensity will increase as climate change progresses.Intertidal sessile invertebrates, which often form thermally benign microhabitats for associated species, are vulnerable to thermal stress because they have minimal ability to behaviourally thermoregulate. Understanding what factors influence the mortality of biogenic species and how heatwaves might impact their ability to provide habitat is critical. Here, we characterize the community associated with the thatched barnacle, Semibalanus cariosus (Pallass, 1788), in British Columbia (BC), Canada. Then, we investigate what site-level and plot-level environmental factors explained variations in barnacle mortality resulting from an unprecedented regional heatwave in BC, Canada. Furthermore, we used a manipulative shading experiment deployed prior to the heatwave to examine the effect of thermal stress on barnacle survival and recruitment and the barnacle-associated community. We identified 50 taxa inhabiting S. cariosus beds, with variations in community composition between sites. Site-scale variables and algal canopy cover did not predict S. cariosus mortality, but patch-scale variation in substratum orientation did, with more direct solar irradiance corresponding with higher barnacle mortality. The shading experiment demonstrated that S. cariosus survival, barnacle recruitment, and invertebrate community diversity were higher under shades where substratum temperatures were lower. Associated community composition also differed between shaded and non-shaded plots, suggesting S. cariosus was not able to fully buffer acute thermal stress for its associated community. While habitat provisioning by intertidal foundation species is an important source of biodiversity, these species alone may not be enough to prevent substantial community shifts following extreme heatwaves. As heatwaves become more frequent and severe, they may further reduce diversity via the loss of biogenic habitat, and spatial variation in these impacts may be substantial.

Behavioural thermoregulation and food availability drive fine‐scale seasonal habitat partitioning in limpets

“…This behavioural thermoregulation probably plays a significant role in the resilience of limpet populations against extreme heat events, which are becoming increasingly common in the intertidal zone (Harley, 2008;Hesketh & Harley, 2023;Jones et al, 2010;Raymond et al, 2022;Schiel et al, 2019).…”

Biotic interactions structure zooplankton metacommunity dynamics following a summer heatwave

“…As the climate changes, extreme weather events, such as heatwaves, droughts, and storms, are increasing in frequency and intensity (IPCC 2021), placing ecological communities under considerable stress (Hesketh & Harley 2023). To design strategies aimed at mitigating the impacts of climate change on natural ecosystems, we require a sound understanding of the processes that determine how species and ecological communities respond to environmental change.…”

Shoreline sentinels of global change show the consequences of extreme events

“…The direct effects of an extreme event on a foundation species and its community‐level consequences have been excellently explored by Hesketh and Harley ( 2022 ) in this issue. They report on rocky shore habitats exposed to a major heat anomaly—the 2021 Pacific Northwest Heat Dome.…”

“…Insights from experimental ecology can be invaluable in interpreting assemblage level responses, including unraveling the direct effects of climate from their indirect modulation by biological interactions (e.g., classic 1960s work by Connell informing time‐series analysis and modeling of warm‐water barnacles being released from competition from faster‐growing cold‐water species in warm springs by Poloczanska et al, 2008 ). Hesketh and Harley ( 2022 ) have amply demonstrated the melding of these twin traditions to better understand processes involved in climate change responses and their consequences at community level.…”

“…Hesketh and Harley ( 2022 ) also emphasize the importance of sustained observations or monitoring of both biota and environmental drivers in anticipation of extreme events which can cause much disturbance and mortality. Our work in the British Isles and Europe stretching back over four decades, overlapping with or re‐surveying work done by Crisp, Southward, and Lewis dating back to the 1950s, has shown gradual shifts in relative abundance of co‐existing sets of species from differing thermal evolutionary origins, with these increases in abundance driving poleward extensions of range edges (Hawkins et al, 2009 ).…”