Projected 21st‐century distribution of canopy‐forming seaweeds in the Northwest Atlantic with climate change

Abstract

Aim Climate change is predicted to alter the distribution and abundance of marine species, including canopy‐forming seaweeds which provide important ecosystem functions and services. We asked whether continued warming will affect the distribution of six common canopy‐forming species: mid‐intertidal fucoids (Ascophyllum nodosum, Fucus vesiculosus), low‐intertidal Irish moss (Chondrus crispus), subtidal laminarian kelps (Saccharina latissima, Laminaria digitata) and the invasive Codium fragile. Location Northwest Atlantic. Methods We used occurrence records and the correlative presence‐only species distribution model Maxent to determine present‐day distribution. This distribution was compared to each species’ warm‐water physiological thresholds indicating areas of stable or reduced growth and mortality. Present‐day models were then projected to mid‐century (2040–2050) and end‐century (2090–2100) using two contrasting carbon emission scenarios (RCP2.6 and 8.5) and two global climate models from CMIP5 based on changes in ocean temperatures. Results Projected range shifts were minimal under low emissions (RCP2.6), but substantial species‐specific range shifts were projected under high emissions (RCP8.5), with all species except C. fragile predicted to experience a northward shift in their southern (warm) edge of ≤406 km by the year 2100. Northward expansions outweighed southern extirpations for fucoids and C. crispus leading to overall range expansions, while range contractions were projected for kelps and C. fragile. Model projections generally agreed with physiological thresholds but were more conservative suggesting that range shifts for kelps may be underpredicted. Main conclusions Our results highlight the benefits to be gained from strong climate change mitigation (RCP2.6), which would limit changes in rocky shore community distribution and composition. The business‐as‐usual RCP8.5 scenario projected major range shifts, seaweed community reorganization and transitions in dominant species south of Newfoundland by 2100 (~47°N). As canopy‐forming seaweeds provide essential habitat, carbon storage, nutrient cycling and commercial value, understanding their response to continued climate warming is critical to inform coastal management and conservation planning.

Population Genetics of Sugar Kelp Throughout the Northeastern United States Using Genome-Wide Markers

“…In the future, genomewide SNP data should be applied to sugar kelp genetic diversity globally to help infer demographic histories as a context within which the role of selection can be inferred. Understanding the mechanisms generating variation in effective population size will be important for predicting adaptive capacity of sugar kelp in response to predict climate change (Hoffmann and Sgrò, 2011;Wilson et al, 2019).…”

“…This study is fundamental to understanding the patterns of genetic diversity of sugar kelp in Northeastern United States and can guide future conservation efforts such as germplasm banking. This is especially important as future climate change is expected to produce significant range contractions at low-latitude ranges for several kelps including S. latissima and Laminaria digitata (Wilson et al, 2019;Neiva et al, 2020). Furthermore, our work has the potential to inform recommendations for protecting coastal marine ecosystems by identifying population structure and guiding future kelp breeding and cultivation efforts by building a baseline of knowledge about kelp population diversity and connectivity.…”

Decadal losses of canopy‐forming algae along the warm temperate coastline of Brazil

“…All around the world canopy‐forming kelp and fucoid species are being impacted by warming waters (e.g. Australia: Phillips & Blackshaw, , Smale & Wernberg, , Japan: Tanaka, Taino, Haraguchi, Prendergast, & Hiraoka, , Mediterranean: Thibaut, Blanfune, Boudouresque, & Verlaque, ) and further massive changes to the distribution and composition of coastal seaweed communities are expected (Martinez et al, ; Wilson, Skinner, & Lotze, ). Along the Atlantic coast of South America, warming of western boundary currents and their extensions such as the Brazilian current (+1.93°C per century between 1950 and 2008) have been associated with greater poleward penetration of warm water (Wu et al, ).…”

Climate-Driven Range Shifts of Brown Seaweed Sargassum horneri in the Northwest Pacific

“…Most temperate seaweeds at the rear edge often suffer from summer isotherms above their maximum thermal thresholds (Eggert, 2012), causing their local extirpations. Summer temperature was deemed the dominant factor affecting the projected distribution boundaries of most canopy-forming seaweed in the Northwest Atlantic (Wilson et al, 2019), northern Japan (Sudo et al, 2020), and Australia (Martínez et al, 2018). The thermal thresholds of species are related to their life stages, thus integrating phenological trends should improve our ability to predict future distributional shifts at both regional and global scales.…”