Climate‐driven substitution of foundation species causes breakdown of a facilitation cascade with potential implications for higher trophic levels

Abstract

1. Climate change can alter ecological communities both directly, by driving shifts in species distributions and abundances, and indirectly by influencing the strength and direction of species interactions. Within benthic marine ecosystems, foundation species such as canopy-forming macro-algae often underpin important cascades of facilitative interactions.2. We examined the wider impacts of climate-driven shifts in the relative abundances of foundation species within a temperate reef system, with particular focus on a habitat cascade whereby kelp facilitate epiphytic algae that, in turn, facilitate mobile invertebrates. Specifically, we tested whether the warm-water kelp Laminaria ochroleuca, which has proliferated in response to recent warming trends, facilitated a secondary habitat-former (epiphytic algae on stipes) and associated mobile invertebrates, to the same degree as the cold-water kelp Laminaria hyperborea.3. The facilitative interaction between kelp and stipe-associated epiphytic algae was dramatically weaker for the warm-water foundation species, leading to breakdown of a habitat cascade and impoverished associated faunal assemblages. On average, the warm-water kelp supported >250 times less epiphytic algae (by biomass) and >50 times fewer mobile invertebrates (by abundance) than the cold-water kelp. Moreover, by comparing regions of pre-and postrange expansion by L. ochroleuca, we found that warming-impacted kelp forests supported around half the biomass of epiphytic algae and one-fifth of the abundance of mobile invertebrates, per unit area, compared with unimpacted forests. We suggest that disruption to this facilitation cascade has the potential to

Marine heatwaves and decreased light availability interact to erode the ecophysiological performance of habitat‐forming kelp species

“…warm-adapted species, Laminaria ochroleuca, was largely resistant to MHW activity occurring both spring and summer and under high-and low-light conditions. With increasing MHW activity, this species may continue to proliferate in the study region, partially replacing cool-adapted kelp species, with implications for ecological structure and functioning (Pessarrodona et al, 2019;Smale et al, 2015Smale et al, , 2022. Clearly, reducing local stressors, maintaining favorable environmental conditions, and prioritizing areas of cooler, clearer water for biodiversity conservation may be useful management approaches.…”

Climate change and species facilitation affect the recruitment of macroalgal marine forests

“…This could be (1) because of the lower recruitment in the presence of coralline algae or (2) because the effects of OW and OA on coralline algae exacerbate, in turn, its inhibiting effect on C. compressa 48,53 . Our experiment shows that complex interactions of biotic and abiotic factors could affect the key species that shape marine forest communities, with an ultimate effect at the ecosystem level 24 . As most experimental studies performed in controlled conditions, some limitations have to be highlighted.…”

“…However, marine forests are shrinking globally 17,18 due to several impacts such as urbanisation, marine farming, local pollution and herbivory 11,19,20 ; making these habitats more sensitive to global change 5,21 . The structure and productivity of marine forests are influenced by many environmental factors that drive the growth, survival, reproduction and metabolism of the organisms, which in turn affect the whole habitat or ecosystem [22][23][24] . Global change effects on marine forests can vary according to the location, the population characteristics and the species 20,25,26 .…”

“…Recently, new restoration techniques opened the door to the possibility of restoring these ecosystems, still, marine forests will be increasingly impacted by global change 1 and it has to be considered to achieve long-term population sustainability and/or successful restoration actions. The next step for the protection of these key ecosystems is to understand how climate change and other drivers acting at the local scale can interact, eventually providing additive or synergetic effects 98 , likely causing the restructure and redistribution of marine forests and affecting their ability to resist and recover under extreme conditions 24,26,28…”

Facilitation cascades across space: Monitoring estuarine foundation species from satellites to the microscope

“…Here we extend and build on this study by: (1) analyzing community structures and diversity in the facilitation cascade (including microscopic animals); (2) analyzing photos, drones, and satellite images to detect and quantify Ulva abundance across spatiotemporal scales and environmental gradients; (3) examining spatiotemporal patterns in the use of Austrovenus as attachment substrate by Ulva ; and (4) linking the results across methods to identify and propose scale‐dependent mechanistic drivers (e.g., light availability, nutrient concentration, sediment characteristics, hydrodynamics) of foundation species abundance and their associated biodiversity (Gribben et al, 2019). We hope this approach can provide a more comprehensive overview of how foundation species affect estuarine biodiversity, as well as a guideline to efficiently monitor their responses to disturbances and extreme environmental events, such as storms or marine heatwaves (Castorani et al, 2018; Montie & Thomsen, 2023b; Smale et al, 2022). We hypothesized that the abundance of Ulva and Austrovenus varied with season, site, and tidal elevation, being more abundant in the warmer season, at an “oceanic” site, and at lower elevation, due to higher metabolic rates, lower salinity stress, and lower desiccation stress, respectively (Adkins et al, 2016; Clemente & Thomsen, 2023).…”