Browsing by Author "Wernberg, Thomas"
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- Herbivory drives kelp recruits into ‘hiding’ in a warm ocean climatePublication . Franco, João N.; Wernberg, Thomas; Bertocci, Iacopo; Duarte, Pedro; Jacinto, David; Tuya, Fernando; Vasco Rodrigues, NunoAssessing effects of herbivory across broad gradients of varying ocean climate conditions and over small spatial scales is crucial for understanding its influence on primary producers. Effects of herbivory on the distribution and abundance of kelp recruits were examined experimentally at two regions under contrasting ocean climate. Specifically, the abundance and survivorship of kelp recruits and the abundance of macro-herbivores were compared between a 'cool' and a 'warm' region in northern and central Portugal, respectively. In each region, the abundance of kelp recruits and the intensity of grazing were compared between habitats of different topography within reefs (open reef vs. crevices). Compared to the 'warm' region, the abundance of kelp recruits was 3.9 times greater in the 'cool' region, where 85% of recruits were found in open reef habitats. In contrast, 87% of recruits in the 'warm' region were restricted to crevices. The 'warm' region had 140 times greater abundances of sea urchins, 45 times more herbi vorous fish and 4.1 times more grazing marks on kelp recruits than the 'cool' region. Grazing assays showed ca. 50 times higher rates of kelp biomass consumption, mainly by fishes, and zero survivorship of kelp recruits in the 'warm' relative to the 'cool' region. This study suggests both temperature and herbivores affect abundances of kelp recruits across latitudes, and demonstrates how herbivores affect their distribution at local scales, driving kelp recruits into 'hiding' in crevices under intense herbivory. Consequently, where net recruitment success is compromised by herbivory, the persistence of kelps will be contingent on availability of topographical refuges.
- Kelp carbon sink potential decreases with warming due to accelerating decompositionPublication . Filbee-Dexter, Karen; Feehan, Colette J.; Smale, Dan A.; Krumhansi, Kira A.; Augustine, Skye; De Bettignies, Florian; Burrows, Michael T.; Byrnes, Jarrett E.K.; Campbell, Jillian; Davoult, Dominique; Dunton, Kenneth H.; Franco, Joao N.; Garrido, Ignacio; Grace, Sean P.; Hancke, Kasper; Johnson, Ladd E.; Konar, Brenda; Moore, Pippa J.; Norderhaug, Kjell Magnus; O'Dell, Alasdair; Pedersen, Morten F.; Salomon, Anne K.; Sousa-Pinto, Isabel; Tiegs, Scott; Yiu, Dara; Wernberg, ThomasCycling of organic carbon in the ocean has the potential to mitigate or exacerbate global climate change, but major questions remain about the environmental controls on organic carbon flux in the coastal zone. Here, we used a field experiment distributed across 28° of latitude, and the entire range of 2 dominant kelp species in the northern hemisphere, to measure decomposition rates of kelp detritus on the seafloor in relation to local environmental factors. Detritus decomposition in both species were strongly related to ocean temperature and initial carbon content, with higher rates of biomass loss at lower latitudes with warmer temperatures. Our experiment showed slow overall decomposition and turnover of kelp detritus and modeling of coastal residence times at our study sites revealed that a significant portion of this production can remain intact long enough to reach deep marine sinks. The results suggest that decomposition of these kelp species could accelerate with ocean warming and that low-latitude kelp forests could experience the greatest increase in remineralization with a 9% to 42% reduced potential for transport to long-term ocean sinks under short-term (RCP4.5) and long-term (RCP8.5) warming scenarios. However, slow decomposition at high latitudes, where kelp abundance is predicted to expand, indicates potential for increasing kelp-carbon sinks in cooler (northern) regions. Our findings reveal an important latitudinal gradient in coastal ecosystem function that provides an improved capacity to predict the implications of ocean warming on carbon cycling. Broad-scale patterns in organic carbon decomposition revealed here can be used to identify hotspots of carbon sequestration potential and resolve relationships between carbon cycling processes and ocean climate at a global scale.
- Leveraging the blue economy to transform marine forest restorationPublication . Filbee-Dexter, Karen; Wernberg, Thomas; Barreiro, Rodolfo; Coleman, Melinda A.; Bettignies, Thibaut de; Feehan, Colette J.; Franco, Joao N.; Hasler, Berit; Louro, Ines; Norderhaug, Kjell M.; Staehr, Perter A. U.; Tuya, Fernando; Verbeek, JanThe UN Decade of Ecosystem Restoration is a response to the urgent need to substantially accelerate and upscale ecological restoration to secure Earth’s sustainable future. Globally, restoration commitments have focused overwhelmingly on terrestrial forests. In contrast, despite a strong value proposition, efforts to restore seaweed forests lag far behind other major ecosystems and continue to be dominated by small-scale, short-term academic experiments. However, seaweed forest restoration can match the scale of damage and threat if moved from academia into the hands of community groups, industry, and restoration practitioners. Connecting two rapidly growing sectors in the Blue Economy—seaweed cultivation and the restoration industry—can transform marine forest restoration into a commercial-scale enterprise that can make a significant contribution to global restoration efforts.
- Local flexibility in feeding behaviour and contrasting microhabitat use of an omnivore across latitudesPublication . Leclerc, Jean-Charles; Bettignies, Thibaut de; Bettignies, Florian de; Christie, Hartvig; Franco, João N.; Leroux, Cédric; Davoult, Dominique; Pedersen, Morten F.; Filbee‑Dexter, Karen; Wernberg, ThomasAs the environment is getting warmer and species are redistributed, consumers can be forced to adjust their interactions with available prey, and this could have cascading effects within food webs. To better understand the capacity for foraging flexibility, our study aimed to determine the diet variability of an ectotherm omnivore inhabiting kelp forests, the sea urchin Echinus esculentus, along its entire latitudinal distribution in the northeast Atlantic. Using a combination of gut content and stable isotope analyses, we determined the diet and trophic position of sea urchins at sites in Portugal (42° N), France (49° N), southern Norway (63° N), and northern Norway (70° N), and related these results to the local abundance and distribution of putative food items. With mean estimated trophic levels ranging from 2.4 to 4.6, omnivory and diet varied substantially within and between sites but not across latitudes. Diet composition generally reflected prey availability within epiphyte or understorey assemblages, with local affinities demonstrating that the sea urchin adjusts its foraging to match the small-scale distribution of food items. A net “preference” for epiphytic food sources was found in northern Norway, where understorey food was limited compared to other regions. We conclude that diet change may occur in response to food source redistribution at multiple spatial scales (microhabitats, sites, regions). Across these scales, the way that key consumers alter their foraging in response to food availability can have important implication for food web dynamics and ecosystem functions along current and future environmental gradients.
- Modulation of different kelp life stages by herbivory: compensatory growth versus population decimationPublication . Franco, Joao N; Wernberg, Thomas; Bertocci, Iacopo; Jacinto, David; Maranhão, Paulo; Pereira, Tânia; Martinez, Brezo; Arenas; Francisco; Sousa-Pinto, Isabel; Tuya, FernandoPartitioning the efects of herbivory on diferent life stages of primary producers is key to understanding the population-wide consequences of herbivory. We assessed the performance of microscopic (MiS <1 mm) juveniles, macroscopic (MaS) juveniles and adult kelp (Laminaria ochroleuca) under contrasting herbivory regimes through a herbivore exclusion feld experiment. The abundance of MiS and the survival of MaS decreased by 67 and 63%, respec tively, when herbivorous fshes and sea urchins were present. Blade growth (linear and area) of adult kelp displayed con trasting patterns under herbivore pressure: a 60% increase and a 46% decrease, respectively. These results indicate that while herbivory severely reduces juvenile survival, it may also induce compensatory growth (measured as linear growth) in adult kelp. In summary, we here demonstrate how herbivory afects all sporophyte life stages of the kelp L. ochroleuca. This is likely to have important implications for situations where historical patterns of herbivore presence and herbivory are changing, such as is increasingly the case in many temperate regions due to warming around the world.
- Niche and neutral assembly mechanisms contribute to latitudinal diversity gradients in reef fishesPublication . Bosch, Nestor E.; Wernberg, Thomas; Langlois, Tim J.; Smale, Dan A.; Moore, Pippa J.; Franco, João N.; Thiriet, Pierre; Feunteun, Eric; Ribeiro, Cláudia; Neves, Pedro; Freitas, Rui; Filbee-Dexter, Karen; Norderhaug, Kjell Magnus; Garcia, Alvaro; Otero-Ferrer, Francisco; Espino, Fernando; Haroun, Ricardo; Lazzari, Natali; Tuya, FernandoAim: The influence of niche and neutral mechanisms on the assembly of ecological communities have long been debated. However, we still have a limited knowledge on their relative importance to explain patterns of diversity across latitudinal gradients (LDG). Here, we investigate the extent to which these ecological mechanisms contribute to the LDG of reef fishes. Location: Eastern Atlantic Ocean. Taxon: Reef-associated ray-finned fishes. Methods: We combined abundance data across ~60° of latitude with functional trait data and phylogenetic trees. A null model approach was used to decouple the influence of taxonomic diversity (TD) on functional (FD) and phylogenetic (PD) diversity. Standardized effect sizes (SES FD and SES PD) were used to explore patterns of overdispersion, clustering and randomness. Information theoretic approaches were used to investigate the role of large-(temperature, geographic isolation, nitrate and net primary productivity) and local-scale (human population and depth) drivers. We further assessed the role of demographic stochasticity and its interaction with species trophic identity and dispersal capacity. Results: Taxonomic diversity peaked at ~15°–20° N, with a second mode of lower magnitude at ~45°N; a pattern that was predicted by temperature, geographic isolation and productivity. Tropical regions displayed a higher proportion of overdispersed assemblages, whilst clustering increased towards temperate regions. Phylogenetic and functional overdispersion were associated with warmer, productive and isolated regions. Demographic stochasticity also contributed largely to community assembly, independently of ecoregions, although variation was dependent on the trophic identity and body size of species. Main conclusions: Niche-based processes linking thermal and resource constraints to local coexistence mechanisms have contributed to the LDG in reef fishes. These processes do not act in isolation, stressing the importance of understanding interactions between deterministic and stochastic factors driving community structure in the face of rapid biodiversity change.