Search publications of the members of the Royal Belgian institute of natural Sciences
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North Sea Hydrodynamics With Nested Models
- The North Sea is an epeiric sea on the European continental shelf, which connects to the Atlantic Ocean through the English Channel in the South and the Norwegian Sea in the North. It hosts key north European shipping lanes, and it is a major fishery and a rich source of energy resources, including wind, wave and solar power. Here we present a nested hydrodynamics model that is calibrated against in situ data for the year 2009, and validated for the years 2010, 2011 and 2015, which present a large range of contrasting North Atlantic Oscillation (NAO) indices. Our results are openly available and provide 10+ years of hydrodynamics data (sea surface elevation, sea water velocity, potential temperature and salinity) with a resolution of 30 arcseconds in the Southern Bight of the North Sea, and 2 arcminutes elsewhere. With our model and resulting dataset, we aim at supporting marine research and policy in a highly, anthropogenically impacted system, allowing stakeholders to take informed decisions to sustainably manage its valuable resources.
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Ecosystem Modeling in the North Sea
- The North Sea is an epeiric sea on the European continental shelf, which connects to the Atlantic Ocean through the English Channel in the South and the Norwegian Sea in the North. It hosts key north European shipping lanes, and it is a major fishery and a rich source of energy resources, including wind and wave power. Here we present a multi-year effort at developing a modeling infrastructure to support research in marine ecology and biogeochemistry in such highly, anthropogenically impacted system, and allow stakeholders taking informed decisions to sustainably manage its valuable resources. Our approach is fully open-source and mainly based on the numerical model COHERENS to simulate hydrodynamical and biogeochemical processes in three spatial dimensions and time. Our model is specifically validated against relevant in situ data in view of its main applications, for which it provides a large-scale virtual laboratory. For example, our model is used to investigate the impact of floating solar panel farms on primary production, but also to assess the efficiency of enhanced silicate weathering to serve as negative emission technology.
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Dense Vegetation Hinders Sediment Transport Towards Saltmarsh Interiors
- The resilience of saltmarshes mainly depends on their ability to gain elevation by sediment accretion to keep pace with sea level rise, and tidal channels play a crucial role in the supply of sediments towards their interiors. While feedbacks between vegetation and geomorphology are increasingly recognized as key drivers shaping a variety of tidal channel network structures, the resulting impact on long-term sediment accretion over the vegetated platforms remains poorly studied. At the plant-scale, vegetation facilitates sediment accretion by trapping mineral sediments and producing organic matter. At the landscape-scale, vegetation promotes the formation of dense, branching, and meandering tidal channel networks, which reduce the distance between saltmarsh interiors and their source of suspended sediments. In this presentation, we use a biogeomorphic model validated against data to reveal two mechanisms by which vegetation also hinders sediment transport towards saltmarsh interiors. First, vegetation concentrates tidal flow and sediment transport inside channels, which reduces sediment availability for deposition on saltmarsh platforms. Secondly, vegetation enhances sediment deposition close to channels, which deprives saltmarsh interiors of suspended sediments, creating levee-depression patterns and leading to pond formation. In the present context of accelerating sea level rise and human-induced decrease of sediment supply, our findings suggest that saltmarshes are more vulnerable than previously thought.
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How does landscape vegetation configuration regulate local channel initiation in rapidly expanding marsh?
- Biogeomorphic interactions between tidal channels and marsh plants play a crucial role in enhancing coastal resilience to climate change. Previous studies linking the channel formation with vegetation dynamics predominantly focused on the early initiation, characterized by local-scale plant-flow feedbacks. However, the influence of rapid changes in landscape-scale vegetation pattern on the channel initiation remains poorly understood, especially in micro-tidal system. In this study, we investigated this relationship through biogeomorphic modeling combined with the analysis of satellite images in a rapidly expanding marsh in China under Spartina alterniflora invasion. The satellite images demonstrated the increase in drainage density and the decrease in unchanneled path length following plant encroachment. Our modeling results showed that local flow acceleration between vegetation patches was insufficient to initiate channels rapidly before the merging of isolated patches under micro-tidal conditions. With plant expansion, the continuous marsh caused landscape flow diversion from homogenous platform flow to concentrated channel flow, which promoted evident tributary channel initiation in the landward marsh zone. The vegetation removal scenarios further highlighted that the flow divergence from adjacent platforms due to the spatial heterogeneity in plant configuration amplified the magnitude of local hydrodynamics and further channel incision. Our findings emphasize that the initiation of tidal channels not only depends on local plant-flow interaction but is largely driven by landscape vegetation configuration under micro-tidal conditions.
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Coastal marsh resilience: a study on the role of bio-geomorphic self-organization
- Tidal marshes are valuable coastal ecosystems that are threatened by global climate warming and the resulting sea level rise. Whether they drown or continue to exist, depends on the trapping of sediments that builds up the land surface. Tidal channel networks, which typically occur within tidal marshes, are the major supply routes for sediments towards the marshes and hence are expected to affect the capacity of marshes to keep up with sea level rise by sediment trapping. The development and evolution of tidal channel networks and the sediment trapping are locally determined by so-called bio-geomorphic interactions between plants, water flow and sediment transport. However, the effect of different environmental variables on channel network formation remains poorly understood. In this research, we investigated the impact of spatio-temporal plant colonization patterns by means of flume experiments. Four scaled landscape scale experiments were conducted in the Metronome tidal facility, a unique flume that tilts periodically to generate tidal currents. Two control experiments without vegetation, a third experiment with a channel-fringing vegetation colonization pattern, and a fourth with patchy vegetation colonization pattern. Seeds were distributed by water in the channel-fringing experiment, while a manual sowing method was used to obtain laterally expanding circular patches in the patchy experiment. Our results show that vegetation and their respective colonization pattern affect channel network formation both on a landscape scale and local scale. More extensive and effective channel networks are found in vegetation experiments. These results indicate that channel-fringing or patchy recruitment strategies might produce landscapes that are more resilient to sea level rise.
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Contrasting saltmarsh vegetation impacts under increasing sea level rise rates
- The resilience of saltmarshes mainly depends on their ability to gain elevation by sediment accretion to keep pace with sea level rise. While vegetation is known to facilitate sediment accretion at the plant scale by trapping mineral sediments and producing organic matter, the long-term impact at the landscape scale is still poorly understood. Here we use the biogeomorphic model Demeter to reveal contrasting vegetation impacts on spatial patterns of sediment accretion under different sea level rise regimes. Under contemporary sea level rise rates (2-10 mm/yr), vegetation inhibits sediment transport from tidal channels to platform interiors and creates levee-depression patterns. Hence, intertidal platforms accrete slower with vegetation than without, but this trend attenuates with increasing sea level rise rate, as water depth increases, and vegetation drag decreases. Under extreme sea level rise rate (20 mm/yr), platform interiors don’t keep up and turn into open water, while vegetation allows to preserve intertidal levees. Our results help to better understand some basic biophysical mechanisms that will control the fate of coastal wetlands under global climate change.
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Observations of tidal attenuation and amplification in a mangrove forest: channels as conduits
- Mangroves are increasingly recognized as an effective nature-based coastal defence strategy. Mangrove trees are proven to reduce the height of propagating long-period waves such as storm tides and extreme sea levels. Existing empirical studies, however, are limited to small scales (~10²-10³ m) or only cover continuous belts of mangroves. Here we present water level measurements along a 20 km channel and in the surrounding mangrove forests for regular neap- and spring tides in a natural mangrove forest in the Guayas Delta, Ecuador. For tides with peak water levels which are high enough to flood the surrounding mangroves, inundation levels reached 45 cm with attenuation rates up to 40 cm/km. Along the entire 20 km channel, however, no attenuation occurred. Instead, we measured amplification with rates varying between 4.3 and 4.6 cm/km. Amplification rates increased with peak water level until water levels were high enough to flood the surrounding mangroves, upon which amplification rates decreased with peak water level. The latter implies that with higher peak levels, such as during an extreme sea level event, the capacity of mangroves to dampen amplification or even attenuate increases.
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Revision of the Eurybrachidae (XV). The Oriental genus Purusha Distant, 1906 with two new species and a key to the genera of Eurybrachini (Hemiptera: Fulgoromorpha: Eurybrachidae)
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Grasping ecological opportunities: not one but five paedophagous species of Haplochromis (Teleostei: Cichlidae) in the Lake Edward system
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Paropeas achatinaceum (Pfeiffer, 1846) and other alien Subuline and Opeatine land snails in European greenhouses (Gastropoda, Achatinidae)
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Extension of the phasmid genus Presbistus to Cambodia with a new species and notes on genitalia and captive breeding (Phasmida, Aschiphasmatidae, Aschiphasmatinae)
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Brain evolution of early placental mammals: the impact of the end-Cretaceous mass extinction on the the neurosensory system of our distant relatives
- The end-Cretaceous mass extinction, 66 million years ago, profoundly reshaped the biodiversity of our planet. After likely originating in the Cretaceous, placental mammals (species giving live birth to well-developed young) survived the extinction and quickly diversified in the ensuing Paleocene. Compared to Mesozoic species, extant placentals have advanced neurosensory abilities, enabled by a proportionally large brain with an expanded neocortex. This brain construction was acquired by the Eocene, but its origins, and how its evolution relates to extinction survivorship and recovery, are unclear, because little is known about the neurosensory systems of Paleocene species. We used high-resolution computed tomography (CT) scanning to build digital brain models in 29 extinct placentals (including 23 from the Paleocene). We added these to data from the literature to construct a database of 98 taxa, from the Jurassic to the Eocene, which we assessed in a phylogenetic context. We find that the Phylogenetic Encephalization Quotient (PEQ), a measure of relative brain size, increased in the Cretaceous along branches leading to Placentalia, but then decreased in Paleocene clades (taeniodonts, phenacodontids, pantodonts, periptychids, and arctocyonids). Later, during the Eocene, the PEQ increased independently in all crown groups (e.g., euarchontoglirans and laurasiatherians). The Paleocene decline in PEQ was driven by body mass increasing much more rapidly after the extinction than brain volume. The neocortex remained small, relative to the rest of the brain, in Paleocene taxa and expanded independently in Eocene crown groups. The relative size of the olfactory bulbs, however, remained relatively stable over time, except for a major decrease in Euarchontoglires and some Eocene artiodactyls, while the petrosal lobules (associated with eye movement coordination) decreased in size in Laurasiatheria but increased in Euarchontoglires. Our results indicate that an enlarged, modern-style brain was not instrumental to the survival of placental mammal ancestors at the end-Cretaceous, nor to their radiation in the Paleocene. Instead, opening of new ecological niches post-extinction promoted the diversification of larger body sizes, while brain and neocortex sizes lagged behind. The independent increase in PEQ in Eocene crown groups is related to the expansion of the neocortex, possibly a response to ecological specialization as environments changed, long after the extinction. Funding Sources Marie Sklodowska-Curie Actions, European Research Council Starting Grant, National Science Foundation, Belgian Science Policy Office, DMNS No Walls Community Initiative.
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Phylogenetic position of Olbitherium (Mammalia, Perissodactyla) based on new material from the early Eocene Wutu Formation
- The genus Olbitherium was originally described in 2004 from the early Eocene of the Wutu Formation in China as a ‘perissodactyl-like’ archaic ungulate. Described material of Olbitherium consists of partial dentaries with lower cheek teeth, isolated upper molars, and an isolated upper premolar. Subsequent collaborative fieldwork by Belgian and Chinese researchers discovered new material including a partial skull, the anterior portion of the dentary, and associated postcrania. In their general form, the skull and postcrania are similar to those of early perissodactyls. The new material provides a more complete picture of the upper dentition, and the anterior dentary demonstrates the presence of three lower incisors and a large canine, both ancestral features for perissodactyls. A phylogenetic analysis was conducted to test the affinities of Olbitherium, using a matrix of 321 characters and 72 taxa of placental mammals emphasizing perissodactyls and other ungulates. The results produced four shortest trees of 1981 steps. In all four trees, Olbitherium is the sister-taxon to all perissodactyls except Ghazijhippus. In contrast, when scoring was restricted to the originally described material, the results produced 16 shortest trees of 1970 steps, and Olbitherium nests well within Perissodactyla as sister-taxon to a clade including Lambdotherium and the brontotheriids Eotitanops and Palaeosyops. The new material not only supports the identification of Olbitherium as a perissodactyl, but it also suggests that it is significant for understanding the ancestral perissodactyl morphotype. Funding Sources U.S. National Science Foundation (DEB1456826), Chinese Ministry of Science and Technology (2009DFA32210), and Belgian Science Policy Office (BL/36/C54).
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A new genus and species of Cicada from Vietnam: Cochloeopsaltria duffelsi gen. et. sp. nov. (Hemiptera: Cicadomorpha: Cicadidae)
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Is the vertical distribution of meiofauna similar in two contrasting microhabitats? A case study of a macrotidal sandy beach
- Tides are an important forcing factor of macrotidal sandy beaches because they are directly responsible for the local morphodynamic conditions. Macrotidal beaches may harbor different microhabitats such as sandbars and runnels. We evaluated the influence of tides on the vertical distribution of meiofaunal organisms, particularly nematodes, in these two microhabitats at De Panne Beach, on the North Sea coast of Belgium. The 11 meiofaunal groups found were Acari, Amphipoda, Copepoda, Gastrotricha, Nematoda, Oligochaeta, Ostracoda, Polychaeta, Rotifera, Tardigrada and Turbellaria. The nematodes were identified to species level; the 147 species found included 112 in the sandbar and 117 in the runnel. Only turbellarians and nematodes migrated upward during low tide in the sandbar. The response of the nematodes was species-specific; during low tide, they migrated upward in the sandbar and downward toward deeper layers of the sediment in the runnel. These migration patterns were attributed to the feeding strategies in the sandbar (i.e. possible increase of diatom biomass in the surface layer due to high solar incidence), while environmental variables best explained the migration patterns in the runnel (i.e. preferred grain size and amount of total organic carbon). These results suggest a dissimilar vertical migration of the meiofauna over the tidal cycle in the two microhabitats. We attribute the vertical distribution of nematode species and some other meiofaunal groups to active migration toward preferred sites with more food or better environmental conditions. This study also indicated that other variables such as predation and competition, rather than the commonly studied physical variables should be included in future sampling designs of sandy-beach meiofauna assessments, since the environmental variables measured here could not fully explain the vertical distributions of the major meiofaunal groups or the community as a whole.
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Preface. in: Degraer, S. et al. (Eds.) (2017). Environmental impacts of offshore wind farms in the Belgian part of the North Sea: A continued move towards integration and quantification.
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Executive summary. in: Degraer, S. et al. (Eds.) (2017). Environmental impacts of offshore wind farms in the Belgian part of the North Sea: A continued move towards integration and quantification.
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Effects of pile driving on harbour porpoises in the Belgian part of the North Sea
- The harbour porpoise (Phocoena phocoena) is the most common marine mammal in the Belgian part of the North Sea and is protected by both national and EU law. In the North Sea, the harbour porpoise is considered under threat because of high bycatch levels and increasing noise pollution. Impulsive pile driving noise originating from the construction of offshore wind farms has been shown to affect porpoises up to distances of more than 20 km from the noise source. Driven by high porpoise densities in Belgian waters, a pile driving ban is in force from the start of January up to the end of April. However, The Netherlands do not enforce such an embargo for the Borssele offshore wind farm, which is only one kilometer away from Belgian waters. Considering the high mobility of harbour porpoises, there is a need for improved insights into the impact of pile driving noise on porpoises which can serve as a basis for an objective evaluation of the respective legal regimes. From May to September 2016 pile driving was taking place at the Nobelwind wind farm located on the Bligh Bank in Belgium. In this period, porpoise activity was recorded using passive acoustic monitoring (C-PODs), at various distances from the construction site (1 to 45 km). In this study we compare porpoise detections before, during and after pile driving with the focus on the influence of repeated pile driving events. In addition to porpoise monitoring data, noise measurements and noise levels are extrapolated for the different locations. The data for this study were obtained from the RBINS wind farm monitoring programme and the VLIZ Lifewatch observatory.
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The influence of pile driving noise on harbour porpoises
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Effects of Offshore Wind Farms on the Early Life Stages of Dicentrarchus labrax
- Anthropogenically generated underwater noise in the marine environment is ubiquitous, comprising both intense impulse and continuous noise. The installation of offshore wind farms across the North Sea has triggered a range of ecological questions regarding the impact of anthropogenically produced underwater noise on marine wildlife. Our interest is on the impact on the "passive drifters," i.e., the early life stages of fish that form the basis of fish populations and are an important prey for pelagic predators. This study deals with the impact of pile driving and operational noise generated at offshore wind farms on Dicentrarchus labrax (sea bass) larvae.
