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  • Carbon density in boreal forests responds non-linearly to temperature: an example from the Greater Khingan Mountains, northeast China
    Publication . Liu, Yang; Trancoso, Ralph; Ma, Qin; Ciais, Philippe; Gouvêa, Lidiane; Yue, Chaofang; Assis, Jorge; Blanco, Juan A.
    Boreal forests play a crucial role in the global carbon (C) cycle and in climate stabilization. To better predict global C budgets, it is important to accurately estimate the size of forest C pools, and to identify the factors affecting them. We used national forest inventory data for the Greater Khingan Mountains, northeast China from 1999 to 2018 and 149 additional field plots to estimate C storage and its changes in forest vegetation, excluding C stored in soils, and to calculate the total C density in forest ecosystems. From 1999 to 2018, the vegetation C storage and density increased by 92.22 Tg and 4.30 Mg C ha-1, respectively, while the mean C sink was 4.61 Tg C yr-1. Carbon storage and density showed the same pattern, with the largest stocks in trees, followed by herbs, shrubs, and then litter. Mean C density was higher in mature forests than in young forests. The maximum C density was recorded in Populus davidiana forests, and was 2.2-times larger than in Betula davurica forests (the minimum). The mean (& PLUSMN; standard error) total C density of forest ecosystems was 111.3 & PLUSMN; 2.9 Mg C ha-1, including C stored in soils. Mean annual temperature (MAT) controlled total C density, as MAT had positive effects when it was lower than the temperature of the inflection point (-2.1 to -4.6 degrees C) and negative effects when it was above the inflection point. The rate of change in the total C density depended on the quantile points of the conditional distribution of total C density. Natural and anthropogenic disturbances had weaker effects on C density than temperature and precipitation. In conclusion, our results indicate that there might be a temperatureinduced pervasive decrease in C storage and an increase in tree mortality across Eastern Asian boreal forests with future climate warming.
  • Habitat continuity and stepping-stone oceanographic distances explain population genetic connectivity of the brown alga Cystoseira amentacea
    Publication . Buonomo, Roberto; Assis, J.; Fernandes, Francisco; Engelen, Aschwin H.; Airoldi, Laura; Serrao, Ester A.
    Effective predictive and management approaches for species occurring in a metapopulation structure require good understanding of interpopulation connectivity. In this study, we ask whether population genetic structure of marine species with fragmented distributions can be predicted by stepping-stone oceanographic transport and habitat continuity, using as model an ecosystem-structuring brown alga, Cystoseira amentacea var. stricta. To answer this question, we analysed the genetic structure and estimated the connectivity of populations along discontinuous rocky habitat patches in southern Italy, using microsatellite markers at multiple scales. In addition, we modelled the effect of rocky habitat continuity and ocean circulation on gene flow by simulating Lagrangian particle dispersal based on ocean surface currents allowing multigenerational stepping-stone dynamics. Populations were highly differentiated, at scales from few metres up to thousands of kilometres. The best possible model fit to explain the genetic results combined current direction, rocky habitat extension and distance along the coast among rocky sites. We conclude that a combination of variable suitable habitat and oceanographic transport is a useful predictor of genetic structure. This relationship provides insight into the mechanisms of dispersal and the role of life-history traits. Our results highlight the importance of spatially explicit modelling of stepping-stone dynamics and oceanographic directional transport coupled with habitat suitability, to better describe and predict marine population structure and differentiation. This study also suggests the appropriate spatial scales for the conservation, restoration and management of species that are increasingly affected by habitat modifications.
  • High and distinct range-edge genetic diversity despite local bottlenecks
    Publication . Assis, J.; Castilho Coelho, N.; Alberto, F.; Valero, Myriam; Raimondi, P. T.; Reed, D. C.; Serrão, Ester
    The genetic consequences of living on the edge of distributional ranges have been the subject of a largely unresolved debate. Populations occurring along persistent low latitude ranges (rear-edge) are expected to retain high and unique genetic diversity. In contrast, currently less favourable environmental conditions limiting population size at such range-edges may have caused genetic erosion that prevails over past historical effects, with potential consequences on reducing future adaptive capacity. The present study provides an empirical test of whether population declines towards a peripheral range might be reflected on decreasing diversity and increasing population isolation and differentiation. We compare population genetic differentiation and diversity with trends in abundance along a latitudinal gradient towards the peripheral distribution range of Saccorhiza polyschides, a large brown seaweed that is the main structural species of kelp forests in SW Europe. Signatures of recent bottleneck events were also evaluated to determine whether the recently recorded distributional shifts had a negative influence on effective population size. Our findings show decreasing population density and increasing spatial fragmentation and local extinctions towards the southern edge. Genetic data revealed two well supported groups with a central contact zone. As predicted, higher differentiation and signs of bottlenecks were found at the southern edge region. However, a decrease in genetic diversity associated with this pattern was not verified. Surprisingly, genetic diversity increased towards the edge despite bottlenecks and much lower densities, suggesting that extinctions and recolonizations have not strongly reduced diversity or that diversity might have been even higher there in the past, a process of shifting genetic baselines.
  • Oceanographic conditions limit the spread of a marine invader along Southern African shores
    Publication . Assis, J.; Zupan, Mirta; Nicastro, Katy; Zardi, Gerardo I.; McQuaid, Christopher D.; Serrao, Ester A.
    Invasive species can affect the function and structure of natural ecological communities, hence understanding and predicting their potential for spreading is a major ecological challenge. Once established in a new region, the spread of invasive species is largely controlled by their dispersal capacity, local environmental conditions and species interactions. The mussel Mytilus galloprovincialis is native to the Mediterranean and is the most successful marine invader in southern Africa. Its distribution there has expanded rapidly and extensively since the 1970s, however, over the last decade its spread has ceased. In this study, we coupled broad scale field surveys, Ecological Niche Modelling (ENM) and Lagrangian Particle Simulations (LPS) to assess the current invaded distribution of M. galloprovincialis in southern Africa and to evaluate what prevents further spread of this species. Results showed that all environmentally suitable habitats in southern Africa have been occupied by the species. This includes rocky shores between Rocky Point in Namibia and East London in South Africa (approx. 2800 km) and these limits coincide with the steep transitions between cool-temperate and subtropical-warmer climates, on both west and southeast African coasts. On the west coast, simulations of drifting larvae almost entirely followed the northward and offshore direction of the Benguela current, creating a clear dispersal barrier by advecting larvae away from the coast. On the southeast coast, nearshore currents give larvae the potential to move eastwards, against the prevalent Agulhas current and beyond the present distributional limit, however environmental conditions prevent the establishment of the species. The transition between the cooler and warmer water regimes is therefore the main factor limiting the northern spread on the southeast coast; however, biotic interactions with native fauna may also play an important role.
  • A global dataset of demosponge distribution records
    Publication . Vafeiadou, Ariadni; Fragkopoulou, Eliza; Assis, Jorge
    Biodiversity information in the form of species occurrence records is key for monitoring and predicting current and fu- ture biodiversity patterns, as well as for guiding conserva- tion and management strategies. However, the reliability and accuracy of this information are frequently undermined by taxonomic and spatial errors. Additionally, biodiversity in- formation facilities often share data in diverse incompatible formats, precluding seamless integration and interoperabil- ity. We provide a comprehensive quality-controlled dataset of occurrence records of the Class Demospongiae, which comprises 81% of the entire Porifera phylum. Demosponges are ecologically significant as they structure rich habitats and play a key role in nutrient cycling within marine ben- thic communities. The dataset aggregates occurrence records from multiple sources, employs dereplication and taxonomic curation techniques, and is flagged for potentially incorrect records based on expert knowledge regarding each species’ bathymetric and geographic distributions. It yields 417,626 records of 1,816 accepted demosponge species (of which 321,660 records of 1,495 species are flagged as potentially correct), which are provided under the FAIR principle of Find- ability, Accessibility, Interoperability and Reusability in the Darwin Core Standard. This dataset constitutes the most up- to-date baseline for studying demosponge diversity at the global scale, enabling researchers to examine biodiversity patterns (e.g., species richness and endemicity), and forecast
  • Comparison of small remotely operated vehicles and diver-operated video of circalittoral benthos
    Publication . Boavida, Joana; Assis, J.; Reed, John; Serrão, Ester; Gonçalves, Jorge Manuel Santos
    Underwater video transect methods using small remotely operated vehicles (ROVs) and diver-operated video (DOV) are commonly used in benthic biodiversity assessments. Constraints posed by deeper waters have made surveys of the circalittoral zone (> 30 m depth), a particularly challenging problem. Here we compare benthic diversity metrics and cluster analyses obtained with ROV and DOV between 45 and 65 m depth off southwest Iberia, across local (tens to hundreds of meters) and regional scales (tens of kilometers). Results showed no difference between methods in terms of the benthic species richness, taxonomic distinctness, and beta diversity, but only minor differences in the spatial structure depicted at the regional level. At the local scale, DOV performed better at discriminating patterns likely because of the divers visual acuity. We found that small ROV and DOV are reliable and comparable methods for the study of circalittoral benthic assemblages and can be used in a complimentary way to detect the greatest amount of variation in benthic ecosystems. Our study facilitates the understanding of capabilities and limitations of two underwater video methods and provides important insight into choice of the most appropriate technique.
  • Genetic diversity increases with depth in red gorgonian populations of the Mediterranean Sea and the Atlantic Ocean
    Publication . Pilczynska, Joanna; Cocito, Silvia; Boavida, Joana; Serrao, Ester; Assis, J.; Fragkopoulou, Eliza; Queiroga, Henrique
    In the ocean, the variability of environmental conditions found along depth gradients exposes populations to contrasting levels of perturbation, which can be reflected in the overall patterns of species genetic diversity. At shallow sites, resource availability may structure large, persistent and well-connected populations with higher levels of diversity. In contrast, the more extreme conditions, such as thermal stress during heat waves, can lead to population bottlenecks and genetic erosion, inverting the natural expectation. Here we examine how genetic diversity varies along depth for a long-lived, important ecosystem-structuring species, the red gorgonian, Paramuricea clavata.
  • Performing fish counts with a wide-angle camera, a promising approach reducing divers' limitations
    Publication . Assis, J.; Claro, B.; Ramos, Ana; Boavida, Joana; Serrão, Ester
    Visual standardised methods for census of reef fishes have long been used in fisheries management and biological surveys. However, these tools have inherent sources of bias and the SCUBA divers who perform them are highly constrained in terms of survey time,maximumdepth and frequency of sampling. Alternatives like underwater video are thus being recommended in a wide range of configurations. Yet, all these techniques are still limited in field of view, particularly when compared to the ability of a SCUBA diver performing censuses. In this scope, we evaluated the potential of an underwater wide-angle camera (UWC) to survey fish assemblages by testing it against instantaneous underwater visual census (UVC). Our results showed minimal yet significant differences between methods, mainly because of the camera's loss of resolution when under extreme visibility conditions. Both approaches had the same consistency and ability to detect changes in fish assemblages but, to estimate total species richness, the UWC needed less field effort. Moreover, a SCUBA diver performing census had an effect on fish assemblages which introduced differences of greater magnitude than those found between methods. The removal of the diver effect, the proven ability to detect changes in fish assemblages and the verified gain in field effort, pointed the wide-angle camera as a promising tool to perform census of reef fishes.
  • Corrigendum to “Golden carbon of Sargassum forests revealed as an opportunity for climate change mitigation” [Sci. Total Environ., 729 (2020) Start page – End page/ 138745]
    Publication . Gouvêa, Lidiane P.; Assis, J.; Gurgel, Carlos F.D.; Serrao, Ester; Silveira, Thiago C.L.; Santos, Rui; Duarte, Carlos M.; Peres, Leticia M.C.; Carvalho, Vanessa; Batista, Manuela; Bastos, Eduardo; Sissini, Marina N.; Horta, Paulo A.
  • The invasive alga Gracilaria vermiculophylla in the native northwest Pacific under ocean warming: Southern genetic consequence and northern range expansion
    Publication . Liu, Yi-Jia; Zhong, Kai-Le; Jueterbock, Alexander; Satoshi, Shimada; Choi, Han-Gil; Weinberger, Florian; Assis, Jorge; Hu, Zi-Min
    Ocean warming is one of the most important factors in shaping the spatial distribution and genetic biodiversity of marine organisms worldwide. The northwest Pacific has been broadly illustrated as an essential seaweed diversity hotspot. However, few studies have yet investigated in this region on whether and how past and ongoing climate warming impacted the distribution and genetic pools of coastal seaweeds. Here, we chose the invasive species Gracilaria vermiculophylla as a model, and identified multiple genetic lineages in the native range through genome-scale microsatellite genotyping. Subsequently, by reconstructing decadal trends of sea surface temperature (SST) change between 1978 and 2018, we found that SST in northern Japan and the East China Sea indeed increased broadly by 0.25-0.4 degrees C/decade. The projections of species distribution models (SDMs) under different future climate change scenarios (RCP 2.6, RCP 4.5, RCP 6.0 and RCP 8.5) indicated that a unique genetic pool of G. vermiculophylla at its current southern range limit (i.e. the South China Sea) is at high risk of disappearance, and that the populations at its current northern range limit (i.e. in Hokkaido region) will undergo poleward expansions, particularly by the year 2100. Such responses, along with this species' limited dispersal potential, may considerably alter the contemporary distribution and genetic composition of G. vermiculophylla in the northwest Pacific, and ultimately threaten ecological services provided by this habitat-forming species and other associated functional roles.