Depth moderates loss of marine foundation species after an extreme marine heatwave: could deep temperate reefs act as a refuge?

Abstract

Marine heatwaves (MHWs) have been documented around the world, causing widespread mortality of numerous benthic species on shallow reefs (less than 15 m depth). Deeper habitats are hypothesized to be a potential refuge from environmental extremes, though we have little understanding of the response of deeper benthic communities to MHWs. Here, we show how increasing depth moderates the response of seaweed- and coral-dominated benthic communities to an extreme MHW across a subtropical–temperate biogeographical transition zone. Benthic community composition and key habitat-building species were characterized across three depths (15, 25 and 40 m) before and several times after the 2011 Western Australian MHW to assess resistance during and recovery after the heatwave. We found high natural variability in benthic community composition along the biogeographic transition zone and across depths with a clear shift in the composition after the MHW in shallow (15 m) sites but a lot less in deeper communities (40 m). Most importantly, key habitat-building seaweeds such as Ecklonia radiata and Syctothalia dorycarpa which had catastrophic losses on shallow reefs, remained and were less affected in deeper communities. Evidently, deep reefs have the potential to act as a refuge during MHWs for the foundation species of shallow reefs in this region.

Species on the move around the Australian coastline: A continental‐scale review of climate‐driven species redistribution in marine systems

“…However, detecting the redistribution of species to greater depth can be challenging due to logistical constraints associated with recreational and scientific diving depth limitations (Fetterplace et al, 2018). Changes in sampling methodologies, such as the use of baited remote underwater monitoring systems (BRUVs) and other autonomous devices, offer the potential to facilitate monitoring of species ranges across a gradient of depth (Fetterplace et al, 2018; Giraldo‐Ospina et al, 2020). For example, BRUVs have already been applied to document species (within their latitudinal distribution) inhabiting waters deeper than previously known (Fetterplace et al, 2018).…”

“…For example, BRUVs have already been applied to document species (within their latitudinal distribution) inhabiting waters deeper than previously known (Fetterplace et al, 2018). Similarly, following the 2011 Western Australian marine heatwave event, autonomous underwater vehicles conducted benthic surveys on deeper reefs (>30 m deep), revealing a buffering effect of depth on species whose abundances had declined in shallow warmer waters (Giraldo‐Ospina et al, 2020). Emerging technologies for monitoring ecological assemblages at depths greater than ~20 m have the potential to disentangle latitudinal and vertical shifts in the distributions of Australian marine biota in response to climate warming.…”

Reproductive Output, Synchrony across Depth and Influence of Source Depth in the Development of Early Life stages of Kelp

“…The ability of this foundation species to reproduce across its depth range together with the resistance of deeper populations to biophysical disturbances (Giraldo‐Ospina et al. 2020) may enhance the natural resilience of temperate reefs, potentially reducing their vulnerability to the threats posed by future climate change.…”

“…2016, Giraldo‐Ospina et al. 2020). In late March 2019, when high reproductive outputs were expected at all depths, sporophytes were collected in the same sites, and zoospores were extracted and cultured, and their gametophyte morphological traits were measured to assess their development.…”

“…In marine systems, deep habitats that may be buffered from environmental disturbances (Giraldo‐Ospina et al. 2020) have been regarded as potential areas of refuge against extreme climatic events with potential to constitute refugia from future climate change (Smith et al. 2014, Assis et al.…”