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Abstract

Kelp forests are extensive underwater habitats that range along 25% of the world’s coastlines, providing valuable resources, habitat, and services for coastal communities. They grow best in cold, nutrient-rich water, where they attain some of the highest rates of primary production of any natural ecosystem. Kelps exhibit a great diversity of growth forms and life strategies, with the largest individuals reaching lengths of more than 30 m and biomasses of 42 kg. In the past half century, threats to kelp forests have increased in number and severity, leading to a global decline of kelp abundances of ~2% per year. Trajectories of change vary considerable across regions and include range contractions, range expansions, species replacements, establishment of invasive kelps, replacement by turf algae reefs or regime shifts to sea urchin barrens. These changes will likely have significant impacts on marine biodiversity and ecosystem functioning because kelps are foundation species for a plethora of habitat-associated plants and animals, many of which are socio-economically important. Some forms of management have been effective in restoring kelp forests, however in many cases the threats facing kelp forests in the future greatly exceed local conservation strategies, necessitating novel conservation solutions to protect and conserve these ecosystems. Although the diversity of changes to kelp forest globally make it challenging to generalize about their future, it seems almost certain that many kelp forests a few decades from now will differ substantially from what they are today.
Authors note: Correction of error: Fig 3.1 B) is Nereocystis, C) is Saccharina,
D) is Ecklonia radiata, E) is Chorda, F) is Laminaria pallida,
G) is Laminaria hyperborea and H) is Alaria.
Authors note: Correction of error: Photo (A) was taken by Jenn Burt.
Authors note: Correction of error - first line in 3.4.4 should read "declines (61%) are observed
much more commonly than increases (5%)"
... The Seaweed Manifesto (Giercksky and Doumeizel, 2020) has highlighted the contribution of these organisms to several of the Sustainable Development Goals due to their contributions as a source of quality food for human populations (food security) and their role in carbon capture and the mitigation of the consequences of ocean acidification (climate change mitigation). They are key organisms for the maintenance of coastal marine ecosystems and biodiversity conservation and are a relevant factor for facilitating coastal community resilience (Wernberg et al., 2019;Morris et al., 2020;Hynes et al., 2021;Cai et al., 2021a;Cuba et al., 2022;Earp et al., 2022). ...
... The consequences of the abovementioned phenomena on seaweeds are already noticeable, with clear evidence of a global decrease in algal populations (Krumhansl et al., 2016). Worldwide changes in the distribution and abundance of important species such as kelps have been recorded in different ecosystems owing to the direct or indirect effects of anthropogenic activities (Wernberg et al., 2019;Oyarzo-Miranda et al., 2020;Jara-Yañez et al., 2021;Latorre-Padilla et al., 2021). However, the impact of these changes varies among geographical regions, indicating that local stressors and regional variations can modify the effects of global drivers of seaweed populations (Wernberg et al., 2019). ...
... Worldwide changes in the distribution and abundance of important species such as kelps have been recorded in different ecosystems owing to the direct or indirect effects of anthropogenic activities (Wernberg et al., 2019;Oyarzo-Miranda et al., 2020;Jara-Yañez et al., 2021;Latorre-Padilla et al., 2021). However, the impact of these changes varies among geographical regions, indicating that local stressors and regional variations can modify the effects of global drivers of seaweed populations (Wernberg et al., 2019). For example, no great changes attributable to global drivers have been reported for kelp forest ecosystems located off the South American coast (Perúand Chile), probably owing to the effects of the Humboldt Current, which has prevented water warming over recent decades (Seabra et al., 2019;Smale, 2020). ...
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Several seaweed species are commercialized worldwide both due to high demand for food and feed and as a raw material for the extraction of phycocolloids such as agar, carrageenan, and alginates that are used broadly in the food, cosmetic, and pharmaceutical industries. Chile is the world’s leading marine seaweed biomass producer when it comes to the exploitation of natural kelp beds. This extraction pressure has persisted for decades and has resulted in a reduction in natural stocks along the benthic ecosystems of the Chilean coast. Over the last three decades, several strategies aimed at restoring seaweed stocks have been implemented (i.e., sexual and asexual reproduction, the use of spore-type propagules or fragments of thalli, and entire thallus transplants). Success rates have varied, but the biological feasibility of such strategies has been demonstrated for several species. However, technological improvements must be achieved to move from small-scale, pilot experiments to cost-effective restocking strategies that are easy to transfer to fisher communities and another end-users, scalable to marine field conditions, and socio-ecologically sustainable. Researchers in other geographic areas have explored similar pathways for developing kelp restocking strategies and have tackled the research gaps regarding its massification. This work summarizes the research activities carried out in recent decades in the search for sustainable strategies to restore algal stocks in Chile
... Mounting evidence suggests that changes in the physical ocean climate are precipitating declines in kelp forests at a global scale (Filbee-Dexter & Wernberg, 2018;Krumhansl et al., 2016;Wernberg et al., 2019). In particular, ocean warming and marine heatwave events are compromising the adaptability of many kelp species, causing direct physiological stress and mortality . ...
... Although this study is focussed on a region of southern Australia, the methods applied here can be applied to temperate areas around the world where kelp forests exist. Global studies have shown that kelp forests are at risk of decline in many regions (Krumhansl et al., 2016;Wernberg et al., 2019) and a better understanding of the multiple factors driving those declines and how these declines vary spatially can be analysed and applied to their management. As foundation species, kelps have a disproportionate impact on the ecosystems they support Steneck & Johnson, 2013;Wernberg et al., 2019) and continued monitoring and management are required to protect them into the future. ...
... Global studies have shown that kelp forests are at risk of decline in many regions (Krumhansl et al., 2016;Wernberg et al., 2019) and a better understanding of the multiple factors driving those declines and how these declines vary spatially can be analysed and applied to their management. As foundation species, kelps have a disproportionate impact on the ecosystems they support Steneck & Johnson, 2013;Wernberg et al., 2019) and continued monitoring and management are required to protect them into the future. Therefore, understanding the multiple stressors linked to their decline is imperative. ...
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Aim Kelp forests throughout temperate regions of the world serve as foundation species that play a critical role in sustaining the health and function of marine ecosystems but are experiencing declines in abundance due to a loss in resilience as the ocean climate changes. Ocean warming along southeast Australia has already been linked to dramatic losses of kelp species and is contributing to the range expansion and population increases of two species of sea urchin. This research attempts to understand the impact of multiple stressors on the decline in kelps in this region. Location Coastal Waters of Victoria, Southeast Australia. Methods In this study, we use long‐term (>20 years) datasets on biological observations across Victorian waters to determine trends in coverage and the impact of multiple environmental variables (oceanography, habitat, and urchin abundances) on two important kelps that serve as foundation species (Phyllospora comosa and Ecklonia radiata) using boosted regression trees. These models were then used to develop predictive distribution models for each species and also to project abundance distributions into the future. Results We found that both kelp species are decreasing in percent coverage over time with multiple environmental variables contributing to these declines, including increasing temperatures, intensifying wave energy, changes in currents and recruitment patterns, and increases in urchin populations. Additionally, future projections of temperature, wave energy, and urchin populations show that both species will continue to decrease across 62%–94% of their range by 2090. Main conclusions Long‐term biological datasets allowed us to develop maps of the past, current, and future distributions of these important foundation species, providing valuable information to managers for prioritization of areas for targeted urchin management and restoration of kelps. Understanding the environmental factors affecting their distribution helps guide manager restoration investments in regions where kelp populations are most likely to persist in the future.
... Opening the black box of kelps: Response of early life stages to anthropogenic stressors Kelps form marine forests along world's coastlines, providing valuable ecosystem goods and services, either directly as a source of food or medicinal products, or indirectly as biogenic habitats or carbon sink agents (Teagle et al., 2017;Wernberg et al., 2019). However, kelp forests are currently under threat due to anthropogenic climate change with latitudinal range shifts and large-scale declines at a global scale (Smale et al., 2019;Wernberg et al., 2019). ...
... Opening the black box of kelps: Response of early life stages to anthropogenic stressors Kelps form marine forests along world's coastlines, providing valuable ecosystem goods and services, either directly as a source of food or medicinal products, or indirectly as biogenic habitats or carbon sink agents (Teagle et al., 2017;Wernberg et al., 2019). However, kelp forests are currently under threat due to anthropogenic climate change with latitudinal range shifts and large-scale declines at a global scale (Smale et al., 2019;Wernberg et al., 2019). Most studies on the impact of anthropogenic stressors on kelps have focused on the macroscopic sporophyte stage of the haploid-diploid life cycle (Schiel and Foster, 2006;Veenhof et al., 2022). ...
... Editor: Rui Rosa, MARE -Faculdade de Ciencias da Universidade de Lisboa, PORTUGAL kelp forest have been lost and many of the remaining systems show a declining trajectory [1,[7][8][9][10]. ...
... Kelp forests represent one of the most diverse and productive natural ecosystems on the planet [1]. Their temperate bi-hemispheric distribution means they support many of the world's large coastal fisheries through the provision of food and habitat [2][3][4] and through their physical presence they offer many ecosystem services [5,6]. ...
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Rising ocean temperature is a major driver of kelp forest decline worldwide and one that threatens to intensify over the coming decades. What is not particularly well understood are the mechanisms that drive loss and how they operate at differing life stages. This study aimed to establish an understanding of the effects of increasing temperature on the early developmental stages of the giant kelp, Macrocystis pyrifera . Sporulation was carried out across 10 temperature treatments from 9.5 to 26.2°C ± 0.2°C at approximately 2°C intervals. Spores were then incubated at these temperatures under a 20.3±1.7 μmol photons m ⁻² s ⁻¹ , 16L:8D photoperiod for 5 days. Results indicate that spore release was positively correlated with increasing temperature, whereas an inverse trend was observed between temperature and the growth of germ-tube. The thermal threshold for spore and germling development was determined to be between 21.7°C and 23.8°C. Spore settlement was the most drastically effected developmental phase by increasing temperature. This study highlights the vulnerability of early life stages of M . pyrifera development to rising ocean temperature and has implications for modelling future distribution of this valuable ecosystem engineer in a changing ocean.
... A better understanding of the distribution and abundance of these habitats is vital to quantify the function of marine ecosystems, the ecological drivers of change, and how to manage these ecosystems and associated resources sustainable way (Norderhaug et al., 2020a;Norderhaug et al., 2020b;St-Pierre and Gagnon, 2020). Kelp forests are the largest vegetated ecosystem in the world and are key drivers of productivity in shallow marine habitats (Pessarrodona et al., 2022), and large parts of their distribution are unmapped, or rely on coarse species distribution models using limited data (Wernberg et al., 2019;Assis et al., 2022). This is especially true for kelps that form subsurface canopies, which comprise about a third of all kelp species, and unlike surface canopy forming kelps cannot be reliably mapped across their depth range using satellites or drones (Mora-Soto et al., 2020;Cavanaugh et al., 2021). ...
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Kelp forests are the largest vegetated marine ecosystem on earth, but vast areas of their distribution remain unmapped and unmonitored. Efficient and cost-effective methods for measuring the standing biomass of these ecosystems are urgently needed for coastal mapping, ocean accounting and sustainable management of wild harvest. Here we show how widely available acoustic equipment on vessels can be used to perform robust and large-scale (kilometer) quantifications of kelp biomass which can be used in assessments and monitoring programs. We demonstrate how to interpret echograms from acoustic systems into point estimates of standing biomass in order to create spatial maps of biomass distribution. We also explore what environmental conditions are suitable for acoustic measures. This has direct application for blue carbon accounting, coastal monitoring, management of wild seaweed harvest and the protection and conservation of marine habitats supporting high biodiversity.
... In particular, it is considered that the Ecklonia complex can be sufficiently applied to Ecklonia spp. and Eisenia spp., which are kelp that are globally distributed and have high productivity and are very similar in shape [15,35,52]. If the results of this study are widely used in similar studies such as biomass estimation, calculation, and securing a blue carbon sink, more valuable results can be derived if more accurate estimation formulas are developed for more diverse species through additional research. ...
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This study was conducted to assess the feasibility of biomass estimation by non-destructive sampling, determine whether the results derived from various types of marine macroalgae are reliable, and a newly proposed method. A quantitative survey was conducted on marine macroalgae communities distributed in the subtidal zone in 67 coastal regions in Korea. Regression analyses were conducted on 11,642 fresh weight datasets covering of 135 species of marine macroalgae. The linear function was FW = 17.721C (adj r2 = 0.745, p < 0.001) and the power function was FW = 4.48C1.251 (adj r2 = 0.891, p < 0.001). Our analysis accounted for the fact that there were three vertically distributed layers of a marine macroalgal assemblages with various shapes (i.e., the Ecklonia complex, the Sargassum and Undaria complex, and the understory complex). For the Ecklonia complex, the linear function was FW = 27.360C (adj r2 = 0.886, p < 0.001) and the power function was FW = 9.626C1.223 (adj r2 = 0.909, p < 0.001). For the Sargassum and Undaria complex, the linear function was FW = 18.389C (adj r2 = 0.916, p < 0.001) and the power function was FW = 6.567C1.255 (adj r2 = 0.942, p < 0.001). For the understory complex, the linear function was FW = 10.419C (adj r2 = 0.737, p < 0.001) and the power function was FW = 4.377C1.182 (adj r2 = 0.871, p < 0.001). Our findings demonstrated that the proposed method can accurately estimate the primary productivity of a wide range of coastal ecosystems based on remote sensing and non-destructive surveys of small-scale marine macroalgal communities.
... In contrast, coral reefs have lost about half of their coral cover since the 1870s with losses accelerating in the last two to three decades and projected to accelerate event further in the future, as a direct result of ocean warming (IPCC, 2019; Wilkinson et al., 2016a). Trends for macroalgal forests are more difficult to ascertain because they are highly dynamic ecosystems (Krumhansl et al., 2016;Wernberg et al., 2019). Rogers et al. (2020). ...
Chapter
We review the current knowledge of the biodiversity of the ocean as well as the levels of decline and threat for species and habitats. The lack of understanding of the distribution of life in the ocean is identified as a significant barrier to restoring its biodiversity and health. We explore why the science of taxonomy has failed to deliver knowledge of what species are present in the ocean, how they are distributed and how they are responding to global and regional to local anthropogenic pressures. This failure prevents nations from meeting their international commitments to conserve marine biodiversity with the results that investment in taxonomy has declined in many countries. We explore a range of new technologies and approaches for discovery of marine species and their detection and monitoring. These include: imaging methods, molecular approaches, active and passive acoustics, the use of interconnected databases and citizen science. Whilst no one method is suitable for discovering or detecting all groups of organisms many are complementary and have been combined to give a more complete picture of biodiversity in marine ecosystems. We conclude that integrated approaches represent the best way forwards for accelerating species discovery, description and biodiversity assessment. Examples of integrated taxonomic approaches are identified from terrestrial ecosystems. Such integrated taxonomic approaches require the adoption of cybertaxonomy approaches and will be boosted by new autonomous sampling platforms and development of machine-speed exchange of digital information between databases.
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Kelp forests are regarded as important nursery and foraging habitats for commercially important species of finfish and shellfish despite an absence of fishery-independent data in many regions. Here, we conducted targeted surveys at 12 subtidal reefs, distributed across 9° of latitude in the UK, using three complementary techniques (Underwater Visual Census (UVC), Baited Remote Underwater Video (BRUV) and deployment of prawn pots) to quantify the abundance of crustaceans within kelp forests. Commercially important species were recorded at all sites; Cancer pagurus (brown/edible crab) and Necora puber (velvet swimming crab) were the most abundant and commonly observed, although Maja brachydactyla (spider crab), Homarus gammarus (European lobster) and Palaemon serratus (common prawn) were also recorded. The abundance of some species exhibited pronounced regional variability, with higher abundances of C. pagurus within northern regions and, conversely, higher abundances of M. brachydactyla and P. serratus within southern regions. Each sampling technique yielded similar spatial patterns for the most abundant species but had varying sensitivity to some species. Most individuals observed were juvenile or sub-adults, suggesting kelp forests serve as important nursery grounds for commercially and ecologically important crustaceans. Further monitoring efforts, conducted across greater spatiotemporal scales and in different habitat types, are needed to provide a robust baseline against which to detect changes and to inform management and conservation actions.
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Canopy-forming kelps are foundation species in many coastal ecosystems, but kelp-forest communities are subject to abrupt state changes caused by environmental drivers and trophic dynamics. We examined changes in kelp communities at 5 sites along the Olympic Coast of Washington State, USA, during and following the recent perturbations of anomalous warm-water events and sea star wasting syndrome (SSWS). Anomalously warm water in 2013 and 2014 corresponded with a loss of approximately 50% of Macrocystis pyrifera and Nereocystis luetkeana canopy. However, the canopy quickly recovered, and stipe density increased after 2015. Purple sea urchins Strongylocentrotus purpuratus increased in density 164-fold, largely at one site, but this increase was first observed in 2017 and peaked in 2019, after the warm period. Sea stars did not show recovery from SSWS, with several species including Pycnopodia helianthoides continuing to decline. The majority of variation in assemblage structure occurred at the site level for kelps, macroinvertebrates, and fishes, while year explained most of the variability for juvenile rockfishes Sebastes spp. We did not see strong top-down effects of urchins on kelp, suggesting that top-down impacts were not dominant regionally during this period. In contrast, we found evidence for a bottom-up influence of kelp habitat on juvenile rockfishes, as rockfish recruits occurred with higher probability where kelp stipe density was higher. Our analyses highlight the importance of spatial variation in structuring changes in kelp forest communities associated with disturbance and suggest that it is essential to ensure the protection of a diversity of kelp forests.
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The genus Laminaria has a wide distribution range compared with other kelp genera because it is found in both the North and the South Atlantic, on both sides of the North Pacific, as well as in the Mediterranean. Hypotheses behind this biogeographical pattern have been discussed by several authors but have not yet been fully evaluated with time-calibrated phylogenies. Based on the analysis of four molecular markers (ITS2, rbcL, atp8 and trnWI), our goal was to reassess the Laminaria species diversity in South Africa, assess its relationship to the other species distributed in the South Atlantic and reconstruct the historical biogeography of the genus. Our results confirm the occurrence of a single species, L. pallida, in southern Africa, and its sister relationship to the North Atlantic L. ochroleuca. Both species belonged to a clade containing the other South Atlantic species: L. abyssalis from Brazil, and the Mediterranean L. rodriguezii. Our time-calibrated phylogenies suggest that Laminaria originated in the northern Pacific around 25 mya, followed by at least two migration events through the Bering Strait after its opening (ca. 5.32 mya). Today, the first is represented by L. solidungula in the Arctic, while the second gave rise to the rest of the Atlantic species. The colonisation of the North Atlantic was followed by a gradual colonization southward along the west coast of Europe, into the Mediterranean (ca. 2.07 mya) and two recent, but disconnected, migrations (ca. 1.34 and 0.87 mya) across the equator, giving rise to L. abyssalis in Brazil and L. pallida in southern Africa, respectively. This article is protected by copyright. All rights reserved.