1,721,042 research outputs found
Combined effects of climate change, offshore wind farms and aquaculture on marine ecosystem functioning
No full textDit onderzoek werd opgebouwd rond de meervoudige effecten van klimaatverandering, windmolenparken op zee en aquacultuur op het functioneren van het mariene ecosysteem in de Noordzee. Door de introductie van artificiële harde substraten in een omgeving gekenmerkt door een zanderige bodem vindt een lokale shift plaats naar een nieuwe soortengemeenschap. Deze shift brengt veranderingen teweeg in de functionaliteiten en de nutriëntenhuishouding van het lokale ecosysteem. Deze lokale verandering vinden echter plaats in het globale kader van klimaatverandering, waarbij opwarming en verzuring van het zeewater een grote impact hebben op de fysiologie van de gevestigde soorten. De combinatie van deze lokale en globale effecten heeft zijn weerslag op de ecosysteemdiensten gelinkt aan deze omgevingen. Vervolgens wordt ook meervoudig ruimtegebruik van mariene systemen onder de loep genoemen, in dit geval wanneer aquacultuur van mosselen wordt uitgeoefend binnen de grenzen van een windmolenpark op zee. Deze combinatie beïnvloedt niet enkel het lokale ecosysteem, maar effecten zijn ook merkbaar verderop. Experimentele resultaten werden gebundeld in een nieuw ecologisch model, waardoor voorspellingen rond de veelzijdige en cumulatieve impacten van klimaatverandering, windmolenparken en aquacultuur kunnen gekwantificeerd worden. Dit soort voorspellingen zijn noodzakelijk bij het monitoren en correct beheren van ons marien ecosysteem in een veranderend klimaat
Behavioural and ecophysiological responses of marine benthos to ocean acidification and warming
Get PDFThe atmospheric carbon dioxide concentrations (CO2) are projected to rise from 400 ppm to 1000 ppm by the end of 21st century. The increase in atmospheric CO2 has been absorbed by the ocean resulting in a process called ocean acidification. Concurrently, the increase of atmospheric CO2 also intensifies the greenhouse effect, resulting in an increase of ocean surface temperature. The progressive modification of ocean environment is expected to affect marine ecosystems via changes in species behaviour, physiology and survival that will determine population, interaction within the community, with implications for biodiversity-mediated ecosystem functioning. Therefore, studying the combined effects of both drivers is fundamental for our understanding of future ocean environments. This PhD thesis reveals the impacts of both acidification and warming on behavioural and physiological responses of estuarine intertidal key species (Cerastoderma edule and Scrobicularia plana) and community. The community response to stressors can be due to direct effects of climate change on individual species as well as indirect effects via alterations of trophic interactions. In summary, this PhD reveals the impacts of lowered pH and elevated temperature on estuarine intertidal sediments at different levels of biological organisation. The observed distinct sensitivity of marine intertidal species to these stressors highlights the importance of ecosystem-based approaches incorporating all interactions
Ecosystem functioning in offshore windfarms : integrating ocean warming and acidification effects on macrofauna ecophysiology, behavior and biogeochemistry
No full textFunctional roles of benthic macrofauna in sediment biogeochemistry across natural and anthropogenic gradients
No full textSeawater carbonate chemistry and the ecophysiology and ecological functioning of an offshore wind farm artificial hard substrate community
No full textIn the effort towards a decarbonised future, the local effects of a proliferating offshore wind farm (OWF) industry add to and interact with the global effects of marine climate change. This study aimed to quantify potential ecophysiological effects of ocean warming and acidification and to estimate and compare the cumulative clearance potential of suspended food items by OWF epifauna under current and future climate conditions. To this end, this study combined ecophysiological responses to ocean warming and acidification of three dominant colonising species on OWF artificial hard substrates (the blue mussel Mytilus edulis, the tube-building amphipod Jassa herdmani and the plumose anemone Metridium senile). In general, mortality, respiration rate and clearance rate increased during 3- to 6-week experimental exposures across all three species, except for M. senile, who exhibited a lower clearance rate in the warmed treatments (+3 °C) and an insensitivity to lowered pH (−0.3 pH units) in terms of survival and respiration rate. Ocean warming and acidification affected growth antagonistically, with elevated temperature being beneficial for M. edulis and lowered pH being beneficial for M. senile. The seawater volume potentially cleared from suspended food particles by this AHS colonising community increased significantly, extending the affected distance around an OWF foundation by 9.2% in a future climate scenario. By using an experimental multi-stressor approach, this study thus demonstrates how ecophysiology underpins functional responses to climate change in these environments, highlighting for the first time the integrated, cascading potential effects of OWFs and climate change on the marine ecosystem
Seawater carbonate chemistry and respiration, clearance and calcification rates of the common cockle Cerastoderma edule
No full textThe combined effect of ocean acidification and warming on the common cockle Cerastoderma edule was investigated in a fully crossed laboratory experiment. Survival of the examined adult organisms remained high and was not affected by elevated temperature (+3 °C) or lowered pH (-0.3 units). However, the morphometric condition index of the cockles incubated under high pCO2 conditions (i.e. combined warming and acidification) was significantly reduced after six weeks of incubation. Respiration rates increased significantly under low pH, with highest rates measured under combined warm and low pH conditions. Calcification decreased significantly under low pH while clearance rates increased significantly under warm conditions and were generally lower in low pH treatments. The observed physiological responses suggest that the reduced food intake under hypercapnia is insufficient to support the higher energy requirements to compensate for the higher costs for basal maintenance and growth in future high pCO2waters
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Seawater carbonate chemistry and hatching success and size of the marine clam Limecola balthica
No full textAnthropogenic CO2 emissions are rapidly changing seawater temperature, pH and carbonate chemistry. This study compares the embryonic development under high pCO2conditions across the south-north distribution range of the marine clam Limecola balthicain NW Europe. The combined effects of elevated temperature and reduced pH on hatching success and size varied strongly between the three studied populations, with the Gulf of Finland population appearing most endangered under the conditions predicted to occur by 2100. These results demonstrate that the assessment of marine faunal population persistence to future climatic conditions needs to consider the interactive effects of co-occurring physico-chemical alterations in seawater within the local context that determines population fitness, adaptation potential and the system resilience to environmental change
Bioturbation in estuarine sediments : modelling macrofauna-mediated oxygen dynamics
Get PDFThe aim of this thesis was to provide a comprehensive examination of the roles of macrofauna in estuarine biogeochemistry by adopting a multidisciplinary field and laboratory-based approach and integrating species distribution modelling with biomass-dependent ecosystem function relationships. Eventually, an ecosystem management tool to provide insights into the ecological consequences of anthropogenic disturbance in estuaries was developed using the Western Scheldt as a model system. To establish a baseline understanding of the spatio-temporal patterns of macrobenthos (activities) and ecosystem functioning in the Scheldt estuary, a seasonal survey was carried out during four consecutive seasons in 2015 and 2016, sampling three habitats with different hydrodynamic regimes (low-dynamic intertidal, high-dynamic intertidal, subtidal) in each of the three main salinity zones (polyhaline, mesohaline, oligohaline). Fluxes of dissolved oxygen, nitrate, nitrite, ammonium and phosphate were measured, as well as environmental properties of the sediment and water, macrofaunal activity (bioturbation and bio-irrigation rates) and macrofauna trait composition with respect to sediment reworking. Luminophores were applied on top of the sediment to measure sediment particle mixing modes and rates. The decline in the concentration of the added inert tracer sodium bromide in the water column was used to estimate pore water exchange rate as a proxy for bio-irrigation. Data and insights obtained from this field survey are presented in Chapter 2 and Chapter 3. Chapter 2 assesses the spatial and temporal variability of these benthic ecosystem processes (i.e. particle mixing and bio-irrigation) in the Scheldt estuary. Luminophore profiles showed that biodiffusion was the dominant particle reworking mode. Rates of both particle reworking and bio-irrigation were highly variable among seasons and habitats, and different species were found to contribute unevenly to both processes, and between habitats and seasons. Habitat structuring effects on populations, density-dependent interactions with the habitat, and temperature-driven variability in macrobenthos activity and living position in the sediment are suggested to explain the observed spatial and temporal differences. In Chapter 3, the relative contributions of macrofauna and the environment to the spatial and temporal variability in benthic biogeochemistry were investigated. Using distance-based redundancy analysis, we found total density, bio-irrigation and temperature to be the main contributors to biogeochemical variability, but this model explained only 23 % of the total variation. Variation partitioning and analyses of subsets of the data in the different seasons, showed that processes linked to the biota were lowest and overruled by environmental steering in the coldest period of the year, while processes related the burrowing behaviour of macrofauna, or densities and biomasses of specific sediment reworking functional groups, predominantly determined biogeochemical variability from June onwards. Macrofaunal contribution to biogeochemistry was highest in low-dynamic intertidal habitats that are densely inhabited by biodiffusing and bio-irrigating fauna. We conclude that the impacts of macrofaunal and environmental factors on the biogeochemical fluxes in the Scheldt estuary vary along the estuarine gradients and with season and are thus highly context-dependent. This spatial and temporal variability should therefore be considered to extrapolate biogeochemical fluxes to entire ecosystems. The impact of two bioturbating benthic invertebrates, Limecola balthica and Hediste diversicolor, on sediment community oxygen uptake in the Scheldt Estuary was examined in Chapter 4. Both H. diversicolor and L. balthica irrigate the sediment, the former by ventilating their burrows and the latter by siphoning water. Laboratory-controlled microcosms containing defaunated sediment amended with artificially composed faunal densities of different body sizes were used to test how species identity, habitat, and population density influence O2 uptake in different habitats (muddy and sandy sediments) in monoculture. Both L. balthica and H. diversicolor facilitated O2 fluxes between the sediment and the overlaying water, and a major portion of the variance in sediment metabolism and bio-irrigation could be explained by the per capita body size and density, or by the total biomass of the inhabiting bioturbators. H. diversicolor showed a more pronounced relationship between biomass/density and faunal-mediated O2 consumption than L. balthica. Respiration was significant in predicting faunal-mediated O2 uptake among different species (H. diversicolor and L. balthica) across different habitats (sandy and muddy sediments); whilst the relationship between bio-irrigation and faunal-mediated O2 uptake was significant for H. diversicolor in both sediment types and and for L. balthica in sandy sediments only, with a lower predictive power of bio-irrigation compared to respiration as the predictor. Analysis of covariance demonstrated significant habitat effects in biomass-dependent bio-irrigation, which might be attributed to different physical constraints (e.g. O2 availability) in sandy and muddy sediments. In summary, we demonstrated that the faunal-mediated O2 consumption by macrobenthos is density- and biomass-dependent, but the extent to which the variance of faunal-mediated O2 uptake can be explained is also conditioned by the interplay between the abiotic environment and the biological traits of the species, which is in support of our hypothesis that biological traits (e.g. bio-irrigation) and sediment physico-chemical properties significantly affect faunal-mediated O2 consumption. The specific example of using macrobenthos for ecology conservation and estuarine ecosystem management is explored in Chapter 5, with H. diversicolor as the model species, since this species was found to be the dominant contributor to biogeochemical fluxes in the Scheldt estuary (Chapter 2-3). We quantified the contribution of H. diversicolor across a range of biomasses in sediment metabolism and extrapolated the spatial variability of the faunal-mediated O2 consumption based on its biomass and distribution within its natural habitats in the Western Scheldt. Biomass-scaling of faunal-mediated O2 uptake by H. diversicolor was quantified from laboratory-controlled microcosms containing defaunated sediment with artificially composed faunal densities and body sizes in its habitats (polyhaline sandy sediment, polyhaline muddy sediment and mesohaline muddy sediment) along the estuarine gradients of the Western Scheldt; and the spatial variability of the fauna-mediated O2 consumption was extrapolated at the landscape scale by combining spatial mapping of H. diversicolor developed from multi-quantile regression modelling. Furthermore, the years 1955 and 2010 were compared to investigate changes in H. diversicolor-mediated O2 consumption in relation to the anthropogenic modifications of the estuary between both years. By tuning the quantile of the responses (upper quantile and full quantile), two species distribution scenarios were developed to describe organisms’ responses to different environmental constraints. Biomass of H. diversicolor was a highly significant (R2 = 0.9) determinant of fauna-mediated O2 uptake (F1,26 = 119.6, p \u3c 0.001) that was unaffected by habitat type (F2, 26 = 3.12, p = 0.06). Therefore, the governing function of biomass scaling can be used to scale the biomass-dependent fauna-mediated O2 uptake to each of three different habitat types. In the intertidal region, maximal fauna-mediated O2 uptake estimated from the upper quantile regression (tau=0.95) was 8772 and 6201 mol d-1 in 1955 and 2010, respectively, corresponding to respective total biomasses of 4407.12 kg and 2915.03 kg H. diversicolor for the entire Western Scheldt. The full quantile regression model revealed a decline in total biomass of H. diversicolor to 34% of its 1955 level by 2010 (from 3044.71 kg to 1040.03 kg) in the intertidal region of the Western Scheldt, which corresponded with a reduction in the faunal-mediated O2 consumption by H. diversicolor in the intertidal area to 39.7% of the 1955 value by 2010, i.e. a decline from 5401.31 to 2145.93 mol d-1. Overall, variabilities in maximum current velocity induced by dredging activities most likely affected the spatial distribution and biomass of H. diversicolor. In Chapter 6, the key findings from data chapters Chapter 2-4 are combined to constitute a synthetic discussion about benthos contribution to ecosystem functioning across space and time, along with implications of the modelling methodology applied in Chapter 5 for the use of macrobenthos for estuarine ecosystem management. The approach adopted in this thesis, which combines small-scale experiments (Chapter 2-4) with broad-scale modelling (Chapter 5), could be used to predict faunal-mediated O2 consumption at an estuarine landscape level. The integration of species distribution and biomass-dependent ecosystem functioning models allows quantification and upscaling of variation in oxygen dynamics induced by bioturbators at high spatial resolution over a large temporal scale. Additionally, reflections of this study and an outlook for future research are presented. This thesis bridges small-scale experimental studies with the broad-scale mapping needs of society and managers, developing a predictive framework that can inform policy makers and conservation practitioners for sustainable management of estuaries. This approach is expected to have direct applications for society through the identification of risks to ecosystem functioning and through the generation of advice on species management in view of the provisioning of ecosystem services. It is clear from the work presented in this thesis that macrobenthic bioturbators play an important role in regulating oxygen dynamics in the Scheldt estuary, therefore conservation of specific species (e.g. H. diversicolor and L. balthica) should be a key priority. These commonly occurring species should be properly monitored and preserved to ensure that their population biomass remains sufficiently high to secure the delivery of ecosystem services. Human activities such as dredging can yield important direct and indirect negative impacts on habitats for macrobenthos, so the natural habitats of key bioturbators should be protected from human impacts through environmental legislation and management (e.g. European Habitats Directive and the EU Marine Strategy Framework Directive). In a wider context, species and ecosystem conservation and management need to integrate the vulnerability of key species to climate change (e.g. temperature and ocean acidification) and the predicted changes to the provisioning of ecosystem services. Additionally, the potential habitat loss caused by sea level rise and coastal squeeze are major challenges for coastal management in the Scheldt estuary. There is no place for intertidal habitats to migrate along with sea level rise since the estuary is heavily confined by dikes. On the one hand, sea level rise may pump saltwater further upstream; on the other hand, the changes in rainfall may affect freshwater intrusion. Even though more research is needed, the results in this study can act as a baseline for future studies, and the proposed predictive framework is expected to be more broadly applicable to quantify the bioturbation impact of other key species on landscape evolution and ecosystem functionality
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