Homogenization and miniaturization of habitat structure in temperate marine forests

Abstract

Humans are rapidly transforming the structural configuration of the planet's ecosystems, but these changes and their ecological consequences remain poorly quantified in underwater habitats. Here, we show that the loss of forest-forming seaweeds and the rise of ground-covering 'turfs' across four continents consistently resulted in the miniaturization of underwater habitat structure, with seascapes converging towards flattened habitats with smaller habitable spaces. Globally, turf seascapes occupied a smaller architectural trait space and were structurally more similar across regions than marine forests, evidencing habitat homogenization. Surprisingly, such habitat convergence occurred despite turf seascapes consisting of vastly different species richness and with different taxa providing habitat architecture, as well as across disparate drivers of marine forest decline. Turf seascapes contained high sediment loads, with the miniaturization of habitat across 100s of km in mid-Western Australia resulting in reefs retaining an additional ~242 million tons of sediment (four orders of magnitude more than the sediments delivered fluvially annually). Together, this work demonstrates that the replacement of marine forests by turfs is a generalizable phenomenon that has profound consequences for the ecology of temperate reefs. | 5263 PESSARRODONA Et Al.

Major Expansion of Marine Forests in a Warmer Arctic

“…Despite the hypothesized poleward expansion of marine macrophytes in the future, the Arctic has received less attention compared to other global oceans (Melo-Merino et al, 2020;Starko et al, 2021). At present, projections for macrophytes are only available for few species or at regional scales (Campana et al, 2009;Müller et al, 2009;Krause-Jensen and Duarte, 2014;Assis et al, 2017a;Krause-Jensen et al, 2020) and are mostly focused on the potential impacts at lower latitude ranges, or the replacement of coldadapted by warm-adapted taxa (Vergés et al, 2016;Filbee-Dexter et al, 2020;Pessarrodona et al, 2021). A comprehensive estimate of the expansion of macrophytes across the Arctic under contrasting scenarios of future climate change is still missing, precluding well-informed IPCC impact assessments, conservation, mitigation and management, by both international and national committees, organizations, and other stakeholders.…”

Tropicalization unlocks novel trophic pathways and enhances secondary productivity in temperate reefs

“…In coral reefs, the nutritional value of turfs and its yield to herbivorous fishes is influenced by sediment loads (Tebbett et al, 2018), with precipitous declines in the primary productivity of turfs and the relative value of its associated particulates beyond sediment loads of 0.1 kg/m 2 (Tebbett & Bellwood, 2020). Turfs in western Australia contained an average of 1.8 ± 0.25 kg/m 2 of inorganic sediment, seven times more than those on the east and one of the highest loads reported in the subtidal literature (Pessarrodona, Filbee-Dexter, et al, 2021;. This diluted their organic quality and likely their nutritional yield to herbivorous fishes in the region (scrapers and sediment suckers), which ingest sediment while feeding and are therefore likely susceptible to high sediment loads and reduced organic content (Gordon et al, 2016).…”

“…Samples were frozen within 6 hr of collection and transported to the laboratory and processed as per Pessarrodona, Filbee‐Dexter, et al. (2021). Briefly, we separated the benthic particulates and algal components which were grouped into algal functional groups (filamentous, foliose, corticated, leathery and articulated coralline algae) following Steneck and Dethier (1994).…”

Arctic marine forest distribution models showcase potentially severe habitat losses for cryophilic species under climate change

“…Thus, the combination of species making up marine forests has a large effect on associated communities, with different assemblages of marine forest species providing different biological characters to the overall ecosystem(s). Of concern, highly variable localized responses have amounted to a small global average decline in kelps (Krumhansl et al, 2016), and marine heatwaves threaten to extirpate cold‐adapted flora in favour of warm‐adapted turf‐forming species, with accompanying changes to ecosystem function (Filbee‐Dexter & Wernberg, 2019; Filbee‐Dexter et al, 2020; Pessarrodona et al, 2021; Vergés et al, 2016).…”

“…Of concern, highly variable localized responses have amounted to a small global average decline in kelps (Krumhansl et al, 2016), and marine heatwaves threaten to extirpate cold-adapted flora in favour of warm-adapted turf-forming species, with accompanying changes to ecosystem function Filbee-Dexter et al, 2020;Pessarrodona et al, 2021;Vergés et al, 2016).…”