Browsing by Author "Wernberg, Thomas"
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- A meta-analysis of seaweed impacts on seagrasses: generalities and knowledge gapsPublication . Thomsen, Mads S.; Wernberg, Thomas; Engelen, Aschwin; Tuya, Fernando; Vanderklift, Mat A.; Holmer, Marianne; McGlathery, Karen J.; Arenas, Francisco; Kotta, Jonne; Sillimann, Brian R.Seagrasses are important habitat-formers and ecosystem engineers that are under threat from bloom-forming seaweeds. These seaweeds have been suggested to outcompete the seagrasses, particularly when facilitated by eutrophication, causing regime shifts where green meadows and clear waters are replaced with unstable sediments, turbid waters, hypoxia, and poor habitat conditions for fishes and invertebrates. Understanding the situations under which seaweeds impact seagrasses on local patch scales can help proactive management and prevent losses at greater scales. Here, we provide a quantitative review of available published manipulative experiments (all conducted at the patch-scale), to test which attributes of seaweeds and seagrasses (e.g., their abundances, sizes, morphology, taxonomy, attachment type, or origin) influence impacts. Weighted and unweighted meta-analyses (Hedges d metric) of 59 experiments showed generally high variability in attribute-impact relationships. Our main significant findings were that (a) abundant seaweeds had stronger negative impacts on seagrasses than sparse seaweeds, (b) unattached and epiphytic seaweeds had stronger impacts than 'rooted' seaweeds, and (c) small seagrass species were more susceptible than larger species. Findings (a) and (c) were rather intuitive. It was more surprising that 'rooted' seaweeds had comparatively small impacts, particularly given that this category included the infamous invasive Caulerpa species. This result may reflect that seaweed biomass and/or shading and metabolic by-products like anoxia and sulphides could be lower for rooted seaweeds. In conclusion, our results represent simple and robust first-order generalities about seaweed impacts on seagrasses. This review also documented a limited number of primary studies. We therefore identified major knowledge gaps that need to be addressed before general predictive models on seaweed-seagrass interactions can be build, in order to effectively protect seagrass habitats from detrimental competition from seaweeds.
- Editorial: Opening the black box of kelps: Response of early life stages to anthropogenic stressorsPublication . Martins, Neusa; Coleman, Melinda A.; Wernberg, Thomas; Roleda, Michael Y.Kelps form marine forests along world’s coastlines, providing valuable ecosystem goods and services, either directly as a source offood 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). However, the microscopic stages considered as the “black box” of kelps due to the complexity of studying them in situ, have been suggested to play a crucial role in the persistence of populations that experience sporophyte mortality after large-scale disturbances (McConnico and Foster, 2005; Barradas et al., 2011) as they can persist as “seed bank” analogues under adverse conditions (Hoffmann and Santelices, 1991; Veenhof et al., 2022). This Research Topic is a collection of 8 articles contributing to opening the “black box” of kelps by providing greater insight into how microscopic life stages of kelps are affected by anthropogenic climate change, helping to predict the persistence of these foundation species and therefore the fate of ecosystems and coastal communities. These studies highlight that the response of kelp early life stages to stressors can be strongly dependent on the population and thermal history.
- Global estimates of the extent and production of macroalgal forestsPublication . Duarte, Carlos M.; Gattuso, Jean‐Pierre; Hancke, Kasper; Gundersen, Hege; Filbee‐Dexter, Karen; Pedersen, Morten F.; Middelburg, Jack J.; Burrows, Michael T.; Krumhansl, Kira A.; Wernberg, Thomas; Moore, Pippa; Pessarrodona, Albert; Ørberg, Sarah B.; Pinto, Isabel S.; Assis, Jorge; Queirós, Ana M.; Smale, Dan A.; Bekkby, Trine; Serrao, Ester; Krause‐Jensen, Dorte; Field, RichardAim Macroalgal habitats are believed to be the most extensive and productive of all coastal vegetated ecosystems. In stark contrast to the growing attention on their contribution to carbon export and sequestration, understanding of their global extent and production is limited and these have remained poorly assessed for decades. Here we report a first data-driven assessment of the global extent and production of macroalgal habitats based on modelled and observed distributions and net primary production (NPP) across habitat types. Location Global coastal ocean. Time period Contemporary. Major taxa studied Macroalgae. Methods Here we apply a comprehensive niche model to generate an improved global map of potential macroalgal distribution, constrained by incident light on the seafloor and substrate type. We compiled areal net primary production (NPP) rates across macroalgal habitats from the literature and combined this with our estimates of the global extent of these habitats to calculate global macroalgal NPP. Results We show that macroalgal forests are a major biome with a global area of 6.06-7.22 million km(2), dominated by red algae, and NPP of 1.32 Pg C/year, dominated by brown algae. Main conclusions The global macroalgal biome is comparable, in area and NPP, to the Amazon forest, but is globally distributed as a thin strip around shorelines. Macroalgae are expanding in polar, subpolar and tropical areas, where their potential extent is also largest, likely increasing the overall contribution of algal forests to global carbon sequestration.
- Global seaweed productivityPublication . Pessarrodona, Albert; Assis, Jorge; Filbee-Dexter, Karen; Burrows, Michael T.; Gattuso, Jean-Pierre; Duarte, Carlos M.; Krause-Jensen, Dorte; Moore, Pippa J.; Smale, Dan A.; Wernberg, ThomasThe magnitude and distribution of net primary production (NPP) in the coastal ocean remains poorly constrained, particularly for shallow marine vegetation. Here, using a compilation of in situ annual NPP measurements across >400 sites in 72 geographic ecoregions, we provide global predictions of the productivity of seaweed habitats, which form the largest vegetated coastal biome on the planet. We find that seaweed NPP is strongly coupled to climatic variables, peaks at temperate latitudes, and is dominated by forests of large brown seaweeds. Seaweed forests exhibit exceptionally high per-area production rates (a global average of 656 and 1711 gC m-2 year-1 in the subtidal and intertidal, respectively), being up to 10 times higher than coastal phytoplankton in temperate and polar seas. Our results show that seaweed NPP is a strong driver of production in the coastal ocean and call for its integration in the oceanic carbon cycle, where it has traditionally been overlooked.
- Marine biodiversity exposed to prolonged and intense subsurface heatwavesPublication . Fragkopoulou, Eliza; Sen Gupta, Alex; Costello, Mark John; Wernberg, Thomas; Araújo, Miguel B.; Serrao, Ester; De Clerck, Olivier; Assis, JorgeMarine heatwaves (MHWs) are becoming increasingly common, with devastating ecosystem impacts. However, MHW understanding has almost exclusively relied on sea surface temperature with limited knowledge about their subsurface characteristics. Here we estimate global MHWs from the surface to 2,000 m depth, covering the period 1993-2019, and explore biodiversity exposure to their effects. We find that MHWs are typically more intense in the subsurface at 50-200 m and their duration increases up to twofold with depth, although with large spatial variability linked to different oceanographic conditions. Cumulative intensity (a thermal stress proxy) was highest in the upper 250 m, exposing subsurface biodiversity to MHW effects. This can be particularly concerning for up to 22% of the ocean, where high cumulative intensity overlapped the warm range edge of species distributions, thus being more sensitive to thermal stress. Subsurface MHWs can hence drive biodiversity patterns, with consequent effects on ecological interactions and ecosystem processes. The authors estimate the intensity, duration and number of global marine heatwaves from 1993 to 2019, from the surface to 2,000 m. They show generally higher intensity of marine heatwaves at 50-200 m, but increased duration with depth, and predict ocean regions of higher biodiversity exposure.
- Toward a coordinated global observing system for seagrasses and marine macroalgaePublication . Duffy, J. Emmett; Benedetti-Cecchi, Lisandro; Trinanes, Joaquin; Muller-Karger, Frank E.; Ambo-Rappe, Rohani; Boström, Christoffer; Buschmann, Alejandro H.; Byrnes, Jarrett; Coles, Robert G.; Creed, Joel; Cullen-Unsworth, Leanne C.; Diaz-Pulido, Guillermo; Duarte, Carlos M.; Edgar, Graham J.; Fortes, Miguel; Goni, Gustavo; Hu, Chuanmin; Huang, Xiaoping; Hurd, Catriona L.; Johnson, Craig; Konar, Brenda; Krause-Jensen, Dorte; Krumhansl, Kira; Macreadie, Peter; Marsh, Helene; McKenzie, Len J.; Mieszkowska, Nova; Miloslavich, Patricia; Montes, Enrique; Nakaoka, Masahiro; Norderhaug, Kjell Magnus; Norlund, Lina M.; Orth, Robert J.; Prathep, Anchana; Putman, Nathan F.; Samper-Villarreal, Jimena; Serrao, Ester; Short, Frederick; Pinto, Isabel Sousa; Steinberg, Peter; Stuart-Smith, Rick; Unsworth, Richard K. F.; van Keulen, Mike; van Tussenbroek, Brigitta I.; Wang, Mengqiu; Waycott, Michelle; Weatherdon, Lauren V.; Wernberg, Thomas; Yaakub, Siti MaryamIn coastal waters around the world, the dominant primary producers are benthic macrophytes, including seagrasses and macroalgae, that provide habitat structure and food for diverse and abundant biological communities and drive ecosystem processes. Seagrass meadows and macroalgal forests play key roles for coastal societies, contributing to fishery yields, storm protection, biogeochemical cycling and storage, and important cultural values. These socio-economically valuable services are threatened worldwide by human activities, with substantial areas of seagrass and macroalgal forests lost over the last half-century. Tracking the status and trends in marine macrophyte cover and quality is an emerging priority for ocean and coastal management, but doing so has been challenged by limited coordination across the numerous efforts to monitor macrophytes, which vary widely in goals, methodologies, scales, capacity, governance approaches, and data availability. Here, we present a consensus assessment and recommendations on the current state of and opportunities for advancing global marine macrophyte observations, integrating contributions from a community of researchers with broad geographic and disciplinary expertise. With the increasing scale of human impacts, the time is ripe to harmonize marine macrophyte observations by building on existing networks and identifying a core set of common metrics and approaches in sampling design, field measurements, governance, capacity building, and data management. We recommend a tiered observation system, with improvement of remote sensing and remote underwater imaging to expand capacity to capture broad-scale extent at intervals of several years, coordinated with strati fied in situ sampling annually to characterize the key variables of cover and taxonomic or functional group composition, and to provide ground-truth. A robust networked system of macrophyte observations will be facilitated by establishing best practices, including standard protocols, documentation, and sharing of resources at all stages of work flow, and secure archiving of open-access data. Because such a network is necessarily distributed, sustaining it depends on close engagement of local stakeholders and focusing on building and long-term maintenance of local capacity, particularly in the developing world. Realizing these recommendations will producemore effective, efficient, and responsive observing, a more accurate global picture of change in vegetated coastal systems, and stronger international capacity for sustaining observations.