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Waterbirds disperse plant seeds within and between aquatic and terrestrial ecosystems in their faeces. However, seed dispersal distances, connectivity among habitat types, and implications for dispersal of weeds remain unquantified in agricultural landscapes. Therefore, we GPS-tagged 31 greylag geese Anser anser and collected 300 faecal samples from feeding flocks in seven agricultural habitats (four cereals, hayfields, pasture, and strawberries) across two landscapes in southern Sweden. We identified intact seeds, determined key plant traits, and tested three hypotheses: (1) geese ingest, transport, and egest seeds from a wide range of terrestrial and aquatic plants, including weeds and alien species; (2) the community and trait composition of plant seeds in faeces vary between habitat types; and (3) seed dispersal by geese is a directional dispersal mechanism that connects some habitat types more than others. We recovered 131 seeds from 41 plant species (19 families), including nine agricultural weeds and one alien species. Many seeds were from aquatic plants (45%), dispersed into terrestrial habitats. A connectivity network formed between habitat types (as nodes) and direct flights (as links) revealed that all agricultural habitats were directly connected with each other, although 66% of flights were between aquatic and agricultural habitats. Geese spent most time at lakes (34%), pastures (14%), barley (10%) and wheat (8%) fields, which were also the most interconnected habitats, with high seed species richness and seed abundance in faecal samples. Combining waterfowl movement data with faecal analysis provided support for all three hypotheses. Geese may contribute to previously overlooked agricultural conflicts through weed dispersal. Proximity to aquatic habitats suitable for roosting may increases the use of agricultural habitats, and potentially the seed dispersal into them.

Soft shoreline engineering is increasingly used to combine shoreline fortification with the enhancement of biodiversity and biological production of land–water transitions. From 2016 to 2021, the large-scale ecosystem restoration project Marker Wadden has created new multiple wetland islands from local sediments in the highly modified Lake Markermeer, the Netherlands. Instead of replacing steep rip-rap shorelines with soft shorelines, new islands with soft land–water transitions were engineered to offset the marked declines in bird and fish populations in this Natura 2000 area, protected under the European Union Birds and Habitats Directives.This new approach was evaluated by assessing the added value of the newly created wetland islands with soft shorelines to the existing steep rip-rap fortified shores of the lake, for the enhancement of fish spawning and nursery habitat.Young-of-the-year fish densities at the Marker Wadden islands were highest in sheltered bays and wetlands with nutrient-rich silt sediments, and lowest at wind-exposed sandy beaches. Both newly engineered soft shorelines and existing rip-rap shorelines contributed to habitat diversity, although fish densities declined considerably with increasing exposure to wind-induced wave power.Building soft shorelines as a new archipelago instead of replacing existing shoreline habitats increased the total length of the land–water transitions in the lake. The 800 ha Marker Wadden archipelago covers only 1% of the 70,000 ha lake surface area, but provides a 16% increase in shoreline habitat and a fivefold increase in soft shoreline for the lake.We conclude that designing wetland islands as a means of lake restoration can contribute effectively to sheltered habitat enhancement for fish spawning and nurseries, and thereby to the potential conservation of fish communities. The approach of building islands achieves this without compromising the complementary functionality of the original, more mature, shorelines o

Waterbirds disperse plant species via ingestion and egestion of seeds (endozoochory). However, our understanding about the regulating effects of seed traits, underlying mechanisms and possible (co)evolutionary processes is limited by our traditional reliance on data from feeding experiments with living waterbirds. Here, we overcome these limitations by developing and applying a new bioassay that realistically simulates digestive processes for Anseriformes waterbirds. We test three hypotheses: 1) seed survival and germination are most affected by mechanical digestion in the waterbird gizzard; 2) seed size, hardness, imbibition and shape regulate seed survival; and 3) plants growing in aquatic habitats benefit most from endozoochory by waterbirds. Experiments with 28 200 seeds of 48 plant species demonstrated species-specific seed survival that was entirely determined by digestion in the avian gizzard. Intestinal digestion did not affect seed survival but affected seed establishment (germinability and germination time) for 21% of the species. Large, hard seeds survived the simulations the best, in contrast to generally higher seed survival for smaller seeds during in vivo experiments. This mechanistically explains that small seeds escape digestive processes rather than being inherently more resistant (the ‘escape mechanism'), while large seeds are retained until fully digested or regurgitated (the ‘resistance and regurgitation mechanism'). Plants growing in wetter habitats had similar seed survival, but digestive processes stimulated their germinability and accelerated their germination more than for terrestrial plants. This indicates a relative advantage of endozoochory for plant species growing in wet habitats, possibly reflecting a co-evolutionary response related to dormancy breaking by gut passage. Simulating seed gut passage using a bioassay allowed establishing mechanisms and identifying relevant seed traits involved in seed dispersal by waterbirds. This inf

Soft shoreline engineering is increasingly used to combine shoreline fortification with the enhancement of biodiversity and biological production of land–water transitions. From 2016 to 2021, the large-scale ecosystem restoration project Marker Wadden has created new multiple wetland islands from local sediments in the highly modified Lake Markermeer, the Netherlands. Instead of replacing steep rip-rap shorelines with soft shorelines, new islands with soft land–water transitions were engineered to offset the marked declines in bird and fish populations in this Natura 2000 area, protected under the European Union Birds and Habitats Directives. This new approach was evaluated by assessing the added value of the newly created wetland islands with soft shorelines to the existing steep rip-rap fortified shores of the lake, for the enhancement of fish spawning and nursery habitat. Young-of-the-year fish densities at the Marker Wadden islands were highest in sheltered bays and wetlands with nutrient-rich silt sediments, and lowest at wind-exposed sandy beaches. Both newly engineered soft shorelines and existing rip-rap shorelines contributed to habitat diversity, although fish densities declined considerably with increasing exposure to wind-induced wave power. Building soft shorelines as a new archipelago instead of replacing existing shoreline habitats increased the total length of the land–water transitions in the lake. The 800 ha Marker Wadden archipelago covers only 1% of the 70,000 ha lake surface area, but provides a 16% increase in shoreline habitat and a fivefold increase in soft shoreline for the lake. We conclude that designing wetland islands as a means of lake restoration can contribute effectively to sheltered habitat enhancement for fish spawning and nurseries, and thereby to the potential conservation of fish communities. The approach of building islands achieves this without compromising the complementary functionality of the original, more mature, shore

Background: Freshwater fish communities typically thrive in heterogenous ecosystems that offer various abiotic conditions. However, human impact increasingly leads to loss of this natural heterogeneity and its associated rich fish communities. To reverse this trend, we need guidelines on how to effectively restore or recreate habitats for multiple fish species. Lake Markermeer in the Netherlands is a human-created 70,000-ha lake with a uniform 4 m-water depth, steep shorelines, high wind-induced turbidity, and a declining fish community. In 2016, a forward-looking restoration project newly created a 1000-ha five-island archipelago in this degrading lake, which offered new sheltered shallow waters and deep sand excavations to the fish community. Methods: In 2020, we assessed how omnivorous and piscivorous fish species used these new habitats by tracking 78 adult fish of five key species across local and lake-scales. We monitored spring arrival of adult fish and assessed local macro-invertebrate and young-of-the-year fish densities. Results: Adult omnivorous Cyprinidae and piscivorous Percidae arrived at the archipelago in early spring, corresponding with expected spawning movements. During the productive summer season, 12 species of young-of-the-year fish appeared along the sheltered shorelines, with particularly high densities of common roach (Rutilus rutilus) and European perch (Perca fluviatilis). This suggests the sheltered, shallow, vegetated waters formed new suitable spawning and recruitment habitat for the fish community. Despite highest food densities for adult fish in the shallowest habitats (< 2-m), adult fish preferred minimally 2-m deep water. After spawning most Cyprinidae left the archipelago and moved long distances through the lake system, while most Percidae remained resident. This may be related to (1) high densities of young-of-the-year fish as food for piscivores, (2) medium food densities for omnivores compared to elsewhere in the lake-system, o

Land-water transition areas play a significant role in the functioning of aquatic ecosystems. However, anthropogenic pressures are posing severe threats on land-water transition areas, which leads to degradation of the ecological integrity of many lakes worldwide. Enhancing habitat complexity and heterogeneity by restoring land-water transition areas in lake systems is deemed a suitable method to restore lakes bottom-up by stimulating lower trophic levels. Stimulating productivity of lower trophic levels (phytoplankton, zooplankton) generates important food sources for declining higher trophic levels (fish, birds). Here, we study ecosystem restoration project Marker Wadden in Lake Markermeer, The Netherlands. This project involved the construction of a 700-ha archipelago of five islands in a degrading shallow lake, aiming to create additional sheltered land-water transition areas to stimulate food web development from its base by improving phytoplankton quantity and quality. We found that phytoplankton quantity (chlorophyll-a concentration) and quality (inversed carbon:nutrient ratio) in the shallow waters inside the Marker Wadden archipelago were significantly improved, likely due to higher nutrient availabilities, while light availability remained sufficient, compared to the surrounding lake. Higher phytoplankton quantity and quality was positively correlated with zooplankton biomass, which was higher inside the archipelago than in the surrounding lake due to improved trophic transfer efficiency between phytoplankton and zooplankton. We conclude that creating new land-water transition areas can be used to increase light and nutrient availabilities and thereby enhancing primary productivity, which in turn can stimulate higher trophic levels in degrading aquatic ecosystems.

Land-water transition areas play a significant role in the functioning of aquatic ecosystems. However, anthropogenic pressures are posing severe threats on land-water transition areas, which leads to degradation of the ecological integrity of many lakes worldwide. Enhancing habitat complexity and heterogeneity by restoring land-water transition areas in lake systems is deemed a suitable method to restore lakes bottom-up by stimulating lower trophic levels. Stimulating productivity of lower trophic levels (phytoplankton, zooplankton) generates important food sources for declining higher trophic levels (fish, birds). Here, we study ecosystem restoration project Marker Wadden in Lake Markermeer, The Netherlands. This project involved the construction of a 700-ha archipelago of five islands in a degrading shallow lake, aiming to create additional sheltered land-water transition areas to stimulate food web development from its base by improving phytoplankton quantity and quality. We found that phytoplankton quantity (chlorophyll-a concentration) and quality (inversed carbon:nutrient ratio) in the shallow waters inside the Marker Wadden archipelago were significantly improved, likely due to higher nutrient availabilities, while light availability remained sufficient, compared to the surrounding lake. Higher phytoplankton quantity and quality was positively correlated with zooplankton biomass, which was higher inside the archipelago than in the surrounding lake due to improved trophic transfer efficiency between phytoplankton and zooplankton. We conclude that creating new land-water transition areas can be used to increase light and nutrient availabilities and thereby enhancing primary productivity, which in turn can stimulate higher trophic levels in degrading aquatic ecosystems.

Waterbirds disperse plant species via ingestion and egestion of seeds (endozoochory). However, our understanding about the regulating effects of seed traits, underlying mechanisms and possible (co)evolutionary processes is limited by our traditional reliance on data from feeding experiments with living waterbirds. Here, we overcome these limitations by developing and applying a new bioassay that realistically simulates digestive processes for Anseriformes waterbirds. We test three hypotheses: 1) seed survival and germination are most affected by mechanical digestion in the waterbird gizzard; 2) seed size, hardness, imbibition and shape regulate seed survival; and 3) plants growing in aquatic habitats benefit most from endozoochory by waterbirds. Experiments with 28 200 seeds of 48 plant species demonstrated species-specific seed survival that was entirely determined by digestion in the avian gizzard. Intestinal digestion did not affect seed survival but affected seed establishment (germinability and germination time) for 21% of the species. Large, hard seeds survived the simulations the best, in contrast to generally higher seed survival for smaller seeds during in vivo experiments. This mechanistically explains that small seeds escape digestive processes rather than being inherently more resistant (the ‘escape mechanism'), while large seeds are retained until fully digested or regurgitated (the ‘resistance and regurgitation mechanism'). Plants growing in wetter habitats had similar seed survival, but digestive processes stimulated their germinability and accelerated their germination more than for terrestrial plants. This indicates a relative advantage of endozoochory for plant species growing in wet habitats, possibly reflecting a co-evolutionary response related to dormancy breaking by gut passage. Simulating seed gut passage using a bioassay allowed establishing mechanisms and identifying relevant seed traits involved in seed dispersal by waterbirds. This inform

Freshwater fish communities typically thrive in heterogenous ecosystems that offer various abiotic conditions. However, human impact increasingly leads to loss of this natural heterogeneity and its associated rich fish communities. To reverse this trend, we need guidelines on how to effectively restore or recreate habitats for multiple fish species. Lake Markermeer in the Netherlands is a human-created 70,000-ha lake with a uniform 4 m-water depth, steep shorelines, high wind-induced turbidity, and a declining fish community. In 2016, a forward-looking restoration project newly created a 1000-ha five-island archipelago in this degrading lake, which offered new sheltered shallow waters and deep sand excavations to the fish community. In 2020, we assessed how omnivorous and piscivorous fish species used these new habitats by tracking 78 adult fish of five key species across local and lake scales. We monitored spring arrival of adult fish and assessed local macro-invertebrate and young-of-the-year fish densities. Adult omnivorous Cyprinidae and piscivorous Percidae arrived at the archipelago in early spring, corresponding with expected spawning movements. During the productive summer season, 12 species of young-of-the-year fish appeared along the sheltered shorelines, with particularly high densities of common roach (Rutilus rutilus) and European perch (Perca fluviatilis). This suggests the sheltered, shallow, vegetated waters formed new suitable spawning and recruitment habitat for the fish community. Despite the highest food densities for adult fish in the shallowest habitats (< 2-m), adult fish preferred minimally 2-m deep water. After spawning, most Cyprinidae left the archipelago and moved long distances through the lake system, while most Percidae remained resident. This may be related to (1) high densities of young-of-the-year fish as food for piscivores, (2) medium food densities for omnivores compared to elsewhere in the lake-system, or (3) the attractiveness

Wetlands provide vital services on which human societies depend. As they have been rapidly degrading due to anthropogenic impacts worldwide, wetland restoration is increasingly applied. When a return to the original state of a wetland is constrained, forward-looking restoration can provide a new way to enhance an ecosystem's ecological integrity. However, the direction in which new ecosystems will develop is strongly coupled to the initial environmental conditions and may benefit from active decisions on (future) management. To improve the natural values of a degrading freshwater lake in the Netherlands, a forward-looking restoration project was initiated in lake Markermeer in 2016, involving the construction of a 700-ha archipelago called the “Marker Wadden”. This archipelago should provide new habitat to higher trophic levels in the lake's food web through the development of currently missing Common reed (Phragmites australis) dominated marshlands with gradual land-water transitions. However, the restoration project faces strong grazing pressure by Greylag geese (Anser anser) that possibly inhibit reed establishment. Here, we aimed to unravel the effect of herbivory by Greylag geese (using exclosures) and the introduction of reed rhizomes on early vegetation development and carbon dynamics on the bare soils of this new ecosystem in a manipulative field experiment. Our results showed that excluding herbivores strongly increased reed-vegetation cover, density and maximum height, but only when reed rhizomes were actively introduced. Spontaneous vegetation development on bare soils was limited, and colonization by Broadleaf cattail (Typha latifolia) dominated over reed. Net ecosystem exchange of carbon and ecosystem respiration were strongly linked to vegetation development, with highest methane emissions in the most densely vegetated plots. We conclude that the establishment of reed marshes can strongly benefit from excluding herbivores and the introduction of reed

Wind-induced turbulence can strongly impact ecological processes in shallow lake ecosystems. The creation of shelter against wind can be expected to affect both primary producers and herbivores in aquatic food webs. Shelter may benefit particular primary producers more than others by changing relative resource availabilities for different primary producers. Herbivore community compositions may be affected either directly or indirectly as a consequence of changes in their food quantity and quality that, in turn, may affect the transfer efficiency between primary producers and herbivores. A reduction in trophic transfer efficiency resulting from wind-induced turbulence potentially can lead to declines of higher trophic levels, but is generally understudied. Here, we focus on the impact of wind on aquatic primary producers and trophic transfer efficiency. We hypothesised that reducing wind-induced turbulence will stimulate higher trophic production in shallow lakes. However, the multitude of impacts of wind-induced turbulence on aquatic food webs make it challenging to predict the direction of change when creating sheltered conditions. We tested our hypothesis in the shallow waters of a newly constructed archipelago named Marker Wadden in lake Markermeer in the Netherlands. Lake Markermeer has experienced declining numbers of birds and fish. These declines have been related to wind-induced sediment resuspension that potentially limits primary production and trophic transfer efficiency. Marker Wadden is a large-scale restoration project that aims to add sheltered and heterogeneous habitat to the otherwise mostly homogeneous lake, thus targeting the potential problems associated with wind-induced turbulence. We executed a 2-month manipulative field mesocosm experiment in the shallow waters of Marker Wadden to study the effect of reduced wind-induced turbulence (i.e., shelter) on aquatic food webs. Specifically, we studied the effects on primary producers, trophic tran

Omnivorous waterbirds play an important role in aquatic ecosystems as dispersal vectors via direct ingestion, transportation, and egestion of plant and invertebrate propagules (i.e. endozoochory). Predatory birds also have the potential to disperse plants and invertebrates that were first carried internally or externally by their prey animals. However, the potential contribution of predatory waterbird species to propagule dispersal in aquatic ecosystems remains understudied. We chose the grey heron Ardea cinerea (Ardeidae) to study the potential of predatory waterbirds to disperse propagules within and among aquatic ecosystems. We hypothesised that: (1) herons disperse a wide variety of plant and invertebrate propagules, from different habitats, with different morphologies (i.e. dispersal syndromes), and including both native and alien species; (2) propagules are ingested with prey species that are primary dispersal vectors (i.e., herons are secondary dispersers); (3) heron pellets show a similar abundance and richness of propagules across their widespread range. We collected 73 regurgitated heron pellets containing undigestible remains from 12 locations across the U.K. and The Netherlands, and examined the taxonomic diversity of plant seeds, invertebrates and prey remains. Pellets were dominated by mammal hairs (99% by volume), and bones confirmed the ingestion of small mammals (prevalence of 38%, e.g. water voles Arvicola amphibius), fish (14%), and birds or amphibians (6%). A total of 266 intact plant seeds were recovered from 71% of the pellets, representing 50 taxa from 17 plant families, including the alien Cotula coronopifolia. The cumulative number of plant species dispersed was lower at higher latitudes. Eight plant species recorded had not previously been recorded as dispersed via waterbirds, and only three species have an endozoochorous dispersal syndrome. Plant taxa were dominated by Caryophyllaceae, Cyperaceae, Juncaceae, and Poaceae, with 24 species

Wind-induced sediment resuspension in shallow lakes may enhance nutrient availability while reducing light availability for phytoplankton growth, thereby affecting the entire food-web. Lake restoration projects that reduce wind-induced resuspension are expected to enhance trophic transfer efficiencies, thereby improving food-web structure and functioning. Yet, reduced resuspension may also lead to lower nutrient concentrations in the water column, promote benthic algae development, reduce phytoplankton biomass production and thereby reduce secondary production by zooplankton. Lake Markermeer is a shallow delta lake in The Netherlands subject to wind-induced sediment resuspension. Restoration project Marker Wadden consists of newly built islands aiming to reduce sediment resuspension and promote higher trophic levels. Here, we tested the effects of reduced sediment resuspension on phytoplankton biomass build-up, benthic algae development, and zooplankton abundances at different temperatures in a 14-day indoor microcosm experiment. We used Marker Wadden sediment with three resuspension intensities combined with three temperatures, to also test effects of higher temperatures in shallow sheltered waters. Reduced sediment resuspension decreased nutrient concentrations and phytoplankton biomass build-up, while increasing light availability and enhancing benthic algae biomass development. Reduced sediment resuspension furthermore increased zooplankton biomass. Enhanced sediment resuspension and higher temperatures synergistically interacted, maintaining a high level of inorganic suspended solids. Our experimental results are in line with long-term seasonal observations from Lake Markermeer. Our findings demonstrate that for shallow lakes suffering from wind effects, measures such as Marker Wadden aimed at reducing sediment resuspension can be effective in restoring secondary production and supporting higher trophic levels.

Wetlands provide vital services on which human societies depend. As they have been rapidly degrading due to anthropogenic impacts worldwide, wetland restoration is increasingly applied. When a return to the original state of a wetland is constrained, forward-looking restoration can provide a new way to enhance an ecosystem's ecological integrity. However, the direction in which new ecosystems will develop is strongly coupled to the initial environmental conditions and may benefit from active decisions on (future) management. To improve the natural values of a degrading freshwater lake in the Netherlands, a forward-looking restoration project was initiated in lake Markermeer in 2016, involving the construction of a 700-ha archipelago called the “Marker Wadden”. This archipelago should provide new habitat to higher trophic levels in the lake's food web through the development of currently missing Common reed (Phragmites australis) dominated marshlands with gradual land-water transitions. However, the restoration project faces strong grazing pressure by Greylag geese (Anser anser) that possibly inhibit reed establishment. Here, we aimed to unravel the effect of herbivory by Greylag geese (using exclosures) and the introduction of reed rhizomes on early vegetation development and carbon dynamics on the bare soils of this new ecosystem in a manipulative field experiment. Our results showed that excluding herbivores strongly increased reed-vegetation cover, density and maximum height, but only when reed rhizomes were actively introduced. Spontaneous vegetation development on bare soils was limited, and colonization by Broadleaf cattail (Typha latifolia) dominated over reed. Net ecosystem exchange of carbon and ecosystem respiration were strongly linked to vegetation development, with highest methane emissions in the most densely vegetated plots. We conclude that the establishment of reed marshes can strongly benefit from excluding herbivores and the introduction of ree

De nieuwe eilandengroep Marker Wadden heeft een grote potentie als paai- en opgroeigebied voor vis, maar tegelijkertijd is de hoeveelheid jonge vis in het Markermeer de afgelopen jaren sterk gedaald. Opvallend is dat de snoekbaarsvangsten juist sterk toenemen. Hoe is dit te verklaren en wat betekent dat voor de toekomstige visstand in het Markermeer?

Many angiosperms rely on vertebrates for seed dispersal via gut passage, an interaction that has been traditionally classified as a mutualism. The seed dispersal effectiveness (SDE) framework provides a mechanistic approach to evaluate evolutionary and ecological characteristics of animal-mediated seed dispersal, by synthesising the quantity and the quality of the dispersal that a plant species receives from each of its animal dispersers. However, the application of the SDE framework has been largely restricted to plant–frugivore interactions, whereas animal-mediated seed dispersal results from plant–disperser interactions that cover a continuum from pure mutualisms to antagonisms. This biases ecological and evolutionary knowledge on plant–disperser interactions. Here, we propose an extended SDE framework (‘eSDE') that allows comparing plant–disperser interactions in the full mutualism–antagonism continuum ranging from pure mutualisms (frugivores) to conditional mutualisms (scatter-hoarding granivores and folivores) and antagonisms (pure granivores). We present the eSDE framework, and use examples to illustrate how it can be applied to compare effectiveness among plant–disperser interaction types. Our initial comparison based on available data suggests that vertebrate species differ more in the number of seeds they deposit away from the mother plant (quantity), than in the effects such dispersal processes have on seed fate (quality). Scatter-hoarding granivores provide the most effective dispersal due to high removal rates, closely followed by frugivores due to high deposition rates. Folivores and pure granivores provide low quantity dispersal, but of high and moderate quality, respectively. These early comparative insights illustrate the necessity and usefulness of more standardized data collection protocols, for which we provide recommendations. Applying the eSDE framework can reveal broad-scale patterns across and within plant–disperser interaction types, which w

Wind-induced turbulence can strongly impact ecological processes in shallow lake ecosystems. The creation of shelter against wind can be expected to affect both primary producers and herbivores in aquatic food webs. Shelter may benefit particular primary producers more than others by changing relative resource availabilities for different primary producers. Herbivore community compositions may be affected either directly or indirectly as a consequence of changes in their food quantity and quality that, in turn, may affect the transfer efficiency between primary producers and herbivores. A reduction in trophic transfer efficiency resulting from wind-induced turbulence potentially can lead to declines of higher trophic levels, but is generally understudied. Here, we focus on the impact of wind on aquatic primary producers and trophic transfer efficiency. We hypothesised that reducing wind-induced turbulence will stimulate higher trophic production in shallow lakes. However, the multitude of impacts of wind-induced turbulence on aquatic food webs make it challenging to predict the direction of change when creating sheltered conditions. We tested our hypothesis in the shallow waters of a newly constructed archipelago named Marker Wadden in lake Markermeer in the Netherlands. Lake Markermeer has experienced declining numbers of birds and fish. These declines have been related to wind-induced sediment resuspension that potentially limits primary production and trophic transfer efficiency. Marker Wadden is a large-scale restoration project that aims to add sheltered and heterogeneous habitat to the otherwise mostly homogeneous lake, thus targeting the potential problems associated with wind-induced turbulence. We executed a 2-month manipulative field mesocosm experiment in the shallow waters of Marker Wadden to study the effect of reduced wind-induced turbulence (i.e., shelter) on aquatic food webs. Specifically, we studied the effects on primary producers, trophic tran

Omnivorous waterbirds play an important role in aquatic ecosystems as dispersal vectors via direct ingestion, transportation, and egestion of plant and invertebrate propagules (i.e. endozoochory). Predatory birds also have the potential to disperse plants and invertebrates that were first carried internally or externally by their prey animals. However, the potential contribution of predatory waterbird species to propagule dispersal in aquatic ecosystems remains understudied. We chose the grey heron Ardea cinerea (Ardeidae) to study the potential of predatory waterbirds to disperse propagules within and among aquatic ecosystems. We hypothesised that: (1) herons disperse a wide variety of plant and invertebrate propagules, from different habitats, with different morphologies (i.e. dispersal syndromes), and including both native and alien species; (2) propagules are ingested with prey species that are primary dispersal vectors (i.e., herons are secondary dispersers); (3) heron pellets show a similar abundance and richness of propagules across their widespread range. We collected 73 regurgitated heron pellets containing undigestible remains from 12 locations across the U.K. and The Netherlands, and examined the taxonomic diversity of plant seeds, invertebrates and prey remains. Pellets were dominated by mammal hairs (99% by volume), and bones confirmed the ingestion of small mammals (prevalence of 38%, e.g. water voles Arvicola amphibius), fish (14%), and birds or amphibians (6%). A total of 266 intact plant seeds were recovered from 71% of the pellets, representing 50 taxa from 17 plant families, including the alien Cotula coronopifolia. The cumulative number of plant species dispersed was lower at higher latitudes. Eight plant species recorded had not previously been recorded as dispersed via waterbirds, and only three species have an endozoochorous dispersal syndrome. Plant taxa were dominated by Caryophyllaceae, Cyperaceae, Juncaceae, and Poaceae, with 24 species

Wind-induced sediment resuspension in shallow lakes may enhance nutrient availability while reducing light availability for phytoplankton growth, thereby affecting the entire food-web. Lake restoration projects that reduce wind-induced resuspension are expected to enhance trophic transfer efficiencies, thereby improving food-web structure and functioning. Yet, reduced resuspension may also lead to lower nutrient concentrations in the water column, promote benthic algae development, reduce phytoplankton biomass production and thereby reduce secondary production by zooplankton. Lake Markermeer is a shallow delta lake in The Netherlands subject to wind-induced sediment resuspension. Restoration project Marker Wadden consists of newly built islands aiming to reduce sediment resuspension and promote higher trophic levels. Here, we tested the effects of reduced sediment resuspension on phytoplankton biomass build-up, benthic algae development, and zooplankton abundances at different temperatures in a 14-day indoor microcosm experiment. We used Marker Wadden sediment with three resuspension intensities combined with three temperatures, to also test effects of higher temperatures in shallow sheltered waters. Reduced sediment resuspension decreased nutrient concentrations and phytoplankton biomass build-up, while increasing light availability and enhancing benthic algae biomass development. Reduced sediment resuspension furthermore increased zooplankton biomass. Enhanced sediment resuspension and higher temperatures synergistically interacted, maintaining a high level of inorganic suspended solids. Our experimental results are in line with long-term seasonal observations from Lake Markermeer. Our findings demonstrate that for shallow lakes suffering from wind effects, measures such as Marker Wadden aimed at reducing sediment resuspension can be effective in restoring secondary production and supporting higher trophic levels.

Wetlands provide vital services on which human societies depend. As they have been rapidly degrading due to anthropogenic impacts worldwide, wetland restoration is increasingly applied. When a return to the original state of a wetland is constrained, forward-looking restoration can provide a new way to enhance an ecosystem's ecological integrity. However, the direction in which new ecosystems will develop is strongly coupled to the initial environmental conditions and may benefit from active decisions on (future) management. To improve the natural values of a degrading freshwater lake in the Netherlands, a forward-looking restoration project was initiated in lake Markermeer in 2016, involving the construction of a 700-ha archipelago called the “Marker Wadden”. This archipelago should provide new habitat to higher trophic levels in the lake's food web through the development of currently missing Common reed (Phragmites australis) dominated marshlands with gradual land-water transitions. However, the restoration project faces strong grazing pressure by Greylag geese (Anser anser) that possibly inhibit reed establishment. Here, we aimed to unravel the effect of herbivory by Greylag geese (using exclosures) and the introduction of reed rhizomes on early vegetation development and carbon dynamics on the bare soils of this new ecosystem in a manipulative field experiment. Our results showed that excluding herbivores strongly increased reed-vegetation cover, density and maximum height, but only when reed rhizomes were actively introduced. Spontaneous vegetation development on bare soils was limited, and colonization by Broadleaf cattail (Typha latifolia) dominated over reed. Net ecosystem exchange of carbon and ecosystem respiration were strongly linked to vegetation development, with highest methane emissions in the most densely vegetated plots. We conclude that the establishment of reed marshes can strongly benefit from excluding herbivores and the introduction of ree

Wageningen Marine Research rapport C058/21 | 5 van 66 Samenvatting Marker Wadden is een eilandengroep die sinds 2016 aangelegd wordt in het Markermeer. In het kader van het Kennis- en Innovatieprogramma Marker Wadden (KIMA) is onderzocht hoe de nieuw gevormde habitats op en rond Marker Wadden worden benut als paaigebieden en opgroeigebieden voor jonge vis en op die manier bijdragen aan de visproductie en voedselbasis voor visetende watervogels. Dit rapport vormt een achtergronddocument voor het KIMA-syntheserapport 2022 (KIMA, concept 2021) dat het onderzoek in de eerste 5 jaar van het ontstaan van de archipel samenvat. Voor het onderzoek naar paai- en opgroeigebieden voor vis zijn intensieve visstandbemonsteringen uitgevoerd naar het voorkomen en de abundantie van vislarven en jonge vis in het voorjaar en de zomer (april/mei-september) van 2019 (eerste eiland,) en 2020 en 2021 (alle eilanden). In juni 2020 is tevens eenmaal een bemonstering uitgevoerd in de nieuwe habitats van Trintelzand. Waar mogelijk werd wadend in ondiepe oeverzones bemonsterd met respectievelijk een larvennet, RAVON-net en een broedzegen. Bij instabiele bodems (met name in de eerste periode na aanleg) werd ook vanuit Canadese kano’s gevist. In 2020 en 2021 zijn de bemonsteringen in samenwerking met onderzoeksprogramma Natuur in Productie (Nederlands Instituut voor Ecologie, Rijksuniversiteit Groningen en Radboud Universiteit) uitgevoerd. Determinatie van jonge vis gebeurde grotendeels in het veld. Kleine larven werden verzameld op formol voor nadere identificatie in het lab (microscoop). In aanvulling op het onderzoek naar paai- en opgroeigebieden rond de eilanden van Marker Wadden zijn in 2018 in het westelijk Markermeer verschillende bemonsteringsmethoden getest voor het vaststellen van soortsamenstelling van vis in en tussen fonteinkruidvelden, een type habitat dat zich op grote schaal ontwikkelt tussen de eilanden van Marker Wadden en Trintelzand. In augustus 2019 is daarnaast nog het voor

Wind-induced turbulence can strongly impact ecological processes in shallow lake ecosystems. The creation of shelter against wind can be expected to affect both primary producers and herbivores in aquatic food webs. Shelter may benefit particular primary producers more than others by changing relative resource availabilities for different primary producers. Herbivore community compositions may be affected either directly or indirectly as a consequence of changes in their food quantity and quality that, in turn, may affect the transfer efficiency between primary producers and herbivores. A reduction in trophic transfer efficiency resulting from wind-induced turbulence potentially can lead to declines of higher trophic levels, but is generally understudied. Here, we focus on the impact of wind on aquatic primary producers and trophic transfer efficiency. We hypothesised that reducing wind-induced turbulence will stimulate higher trophic production in shallow lakes. However, the multitude of impacts of wind-induced turbulence on aquatic food webs make it challenging to predict the direction of change when creating sheltered conditions. We tested our hypothesis in the shallow waters of a newly constructed archipelago named Marker Wadden in lake Markermeer in the Netherlands. Lake Markermeer has experienced declining numbers of birds and fish. These declines have been related to wind-induced sediment resuspension that potentially limits primary production and trophic transfer efficiency. Marker Wadden is a large-scale restoration project that aims to add sheltered and heterogeneous habitat to the otherwise mostly homogeneous lake, thus targeting the potential problems associated with wind-induced turbulence. We executed a 2-month manipulative field mesocosm experiment in the shallow waters of Marker Wadden to study the effect of reduced wind-induced turbulence (i.e., shelter) on aquatic food webs. Specifically, we studied the effects on primary producers, trophic transfe

Many angiosperms rely on vertebrates for seed dispersal via gut passage, an interaction that has been traditionally classified as a mutualism. The seed dispersal effectiveness (SDE) framework provides a mechanistic approach to evaluate evolutionary and ecological characteristics of animal-mediated seed dispersal, by synthesising the quantity and the quality of the dispersal that a plant species receives from each of its animal dispersers. However, the application of the SDE framework has been largely restricted to plant–frugivore interactions, whereas animal-mediated seed dispersal results from plant–disperser interactions that cover a continuum from pure mutualisms to antagonisms. This biases ecological and evolutionary knowledge on plant–disperser interactions. Here, we propose an extended SDE framework (‘eSDE') that allows comparing plant–disperser interactions in the full mutualism–antagonism continuum ranging from pure mutualisms (frugivores) to conditional mutualisms (scatter-hoarding granivores and folivores) and antagonisms (pure granivores). We present the eSDE framework, and use examples to illustrate how it can be applied to compare effectiveness among plant–disperser interaction types. Our initial comparison based on available data suggests that vertebrate species differ more in the number of seeds they deposit away from the mother plant (quantity), than in the effects such dispersal processes have on seed fate (quality). Scatter-hoarding granivores provide the most effective dispersal due to high removal rates, closely followed by frugivores due to high deposition rates. Folivores and pure granivores provide low quantity dispersal, but of high and moderate quality, respectively. These early comparative insights illustrate the necessity and usefulness of more standardized data collection protocols, for which we provide recommendations. Applying the eSDE framework can reveal broad-scale patterns across and within plant–disperser interaction types, which w

Wetlands provide vital services on which human societies depend. As they have been rapidly degrading due to anthropogenic impacts worldwide, wetland restoration is increasingly applied. When a return to the original state of a wetland is constrained, forward-looking restoration can provide a new way to enhance an ecosystem's ecological integrity. However, the direction in which new ecosystems will develop is strongly coupled to the initial environmental conditions and may benefit from active decisions on (future) management. To improve the natural values of a degrading freshwater lake in the Netherlands, a forward-looking restoration project was initiated in lake Markermeer in 2016, involving the construction of a 700-ha archipelago called the “Marker Wadden”. This archipelago should provide new habitat to higher trophic levels in the lake's food web through the development of currently missing Common reed (Phragmites australis) dominated marshlands with gradual land-water transitions. However, the restoration project faces strong grazing pressure by Greylag geese (Anser anser) that possibly inhibit reed establishment. Here, we aimed to unravel the effect of herbivory by Greylag geese (using exclosures) and the introduction of reed rhizomes on early vegetation development and carbon dynamics on the bare soils of this new ecosystem in a manipulative field experiment. Our results showed that excluding herbivores strongly increased reed-vegetation cover, density and maximum height, but only when reed rhizomes were actively introduced. Spontaneous vegetation development on bare soils was limited, and colonization by Broadleaf cattail (Typha latifolia) dominated over reed. Net ecosystem exchange of carbon and ecosystem respiration were strongly linked to vegetation development, with highest methane emissions in the most densely vegetated plots. We conclude that the establishment of reed marshes can strongly benefit from excluding herbivores and the introduction of reed

Ecosystems are increasingly managed to provide multiple benefits to humans, which often degrades their ecological integrity. This strongly applies to aquatic ecosystems, in which engineering can enhance flood protection, drinking water supply, fisheries and recreation. Although these activities typically increase ecosystem functionality to humans, they often impair key aspects of biodiversity and natural functioning.Classical restoration of such degrading freshwater ecosystems can lead to societal opposition, if returning to a former ecosystem state affects previously acquired ecosystem services. Innovative nature-based solutions are therefore needed that enhance natural values in ecosystems, without affecting existing services.We present a large-scale project aiming to increase the ecological integrity of a human-modified freshwater lake while maintaining its services to humans. The freshwater lake Markermeer in the Netherlands was formed by closing off an estuary for flood protection. The ecological integrity of this lake diminished over time, likely because a declining primary productivity impaired biodiversity at higher trophic levels. This decline is associated with a lack of gradual land–water transitions, strong resuspension of fine sediments, low nutrient availability and lack of dynamics typically to be expected in a natural temperate freshwater lake. Restoring the lake to its former marine state would conflict with current ecosystem services.A nature-based solution was initiated in 2016, consisting of constructing a five-island archipelago from the lake's own soft-sediments called the ‘Marker Wadden’. The project aims to increase the lake's primary production by creating gradual land–water transitions, more heterogeneity in water depths and decreasing turbidity by creating shelter and deep sinks reducing fine-sediment resuspension by the wind – thus introducing currently missing elements that are typical for natural lakes. We present the underlying ecologi

Biotic resistance to alien plant invasions is mainly determined by ecological interactions in two layers of the food web: competition with native plant species and herbivory by native herbivores. While the direct effect of native plants on alien plant performance via competition has been well documented across ecosystems, less is known about the direct and indirect effects of herbivores in providing biotic resistance. Our main aims were to determine whether temperate native aquatic plants and herbivores can provide biotic resistance to plant invasions, understand the underlying mechanisms and search for potential interactive effects of competition and herbivory on invader performance (i.e. growth). We mimicked natural temperate mesotrophic and eutrophic freshwater lakes in mesoscosms, by growing three native submerged plant species in monocultures (Ceratophyllum demersum, Myriophyllum spicatum and Potamogeton perfoliatus) at three competition levels (no, low and high) without and with the native aquatic generalist snail Lymnaea stagnalis. We subsequently simulated an early stage of establishment of the South American highly invasive alien plant species Egeria densa. We found that competition by native plant biomass significantly reduced invader performance but depended on native species identity. Herbivory had no direct negative effect on invader performance as the snails fed mainly on the available filamentous algae, which are commonly found in meso- and eutrophic systems, instead of on the plants. However, the consumption of filamentous algae by herbivores indirectly had positive effects on the invader total biomass, thus facilitating the invasion by E. densa. Nonetheless, these indirect effects worked through different pathways depending on the native plant identity. Synthesis. We found evidence for biotic resistance through competition by native plant species. However, we show that herbivores can indirectly facilitate South American plant E. densa invasion pr

Peat-forming wetlands, particularly floating fens that form the initial stages of these ecosystems, are declining globally due to excavation, dehydration and eutrophication. Restoration typically involves reestablishment of early-successional open-water stages, with oligotrophic conditions that are characteristic for these systems. However, restoration success is notoriously limited. A potential improvement may be to initiate succession by reintroducing of target plant species. Knowledge is therefore needed on (a) which plant functional groups should be re-introduced to stimulate fen formation; and (b) how to manage nutrient levels during restoration, considering that plant growth may be slow in oligotrophic conditions. We hypothesized that increasing functional diversity of introduced species would stimulate the formation of peat-forming target communities, their biomass accumulation and expansion onto open water. We also hypothesized that nutrient availability would mediate the relative contribution of specific functional groups to these effects. We investigated this in 36 artificial outdoor ponds by manipulating plant functional diversity (clonal dominants, clonal stress-tolerators and interstitials) on constructed rafts with fen-forming communities, and subjected these to a range of nutrient loadings over 2 years. Increasing functional diversity as well as increasing nutrient loadings had stimulating effects on plant biomass accumulation, cover formation and rhizome growth onto open water. Both complementarity (due to niche partitioning or facilitation) and selection effects were mechanisms underlying the diversity effect, with a constant relative importance over the entire range of nutrient availabilities. Different functional groups were important for biomass production at different nutrient availabilities. Rhizome formation by clonal stress-tolerators contributed disproportionately to open water colonization, identifying this functional group as key across

Peat-forming wetlands, particularly floating fens that form the initial stages of these ecosystems, are declining globally due to excavation, dehydration and eutrophication. Restoration typically involves reestablishment of early-successional open-water stages, with oligotrophic conditions that are characteristic for these systems. However, restoration success is notoriously limited. A potential improvement may be to initiate succession by reintroducing of target plant species. Knowledge is therefore needed on (a) which plant functional groups should be re-introduced to stimulate fen formation; and (b) how to manage nutrient levels during restoration, considering that plant growth may be slow in oligotrophic conditions. We hypothesized that increasing functional diversity of introduced species would stimulate the formation of peat-forming target communities, their biomass accumulation and expansion onto open water. We also hypothesized that nutrient availability would mediate the relative contribution of specific functional groups to these effects. We investigated this in 36 artificial outdoor ponds by manipulating plant functional diversity (clonal dominants, clonal stress-tolerators and interstitials) on constructed rafts with fen-forming communities, and subjected these to a range of nutrient loadings over 2 years. Increasing functional diversity as well as increasing nutrient loadings had stimulating effects on plant biomass accumulation, cover formation and rhizome growth onto open water. Both complementarity (due to niche partitioning or facilitation) and selection effects were mechanisms underlying the diversity effect, with a constant relative importance over the entire range of nutrient availabilities. Different functional groups were important for biomass production at different nutrient availabilities. Rhizome formation by clonal stress-tolerators contributed disproportionately to open water colonization, identifying this functional group as key across al

Peat-forming wetlands, and particularly floating fens forming the initial stages of these ecosystems, are globally declining due to excavation, dehydration and eutrophication. Restoration of these valuable ecosystems typically involves re-establishment of early-successional open-water stages with oligotrophic conditions that are characteristic for these systems. However, restoration success is notoriously limited and a potential solution may be to initiate succession by re-introduction of target plant species. Knowledge is needed on (a) which plant functional groups should be re-introduced to stimulate fen formation; and (b) how to manage nutrient levels during restoration, considering that plant growth may be slow in oligotrophic conditions. 2. We hypothesized that (1) increasing functional diversity of introduced species would stimulate the formation of peat-forming target communities, their biomass accumulation and expansion onto open water; and that (2) nutrient availability would mediate the relative contribution of specific functional groups to these effects. We experimentally investigated this in 36 artificial outdoor ponds by manipulating plant functional diversity (clonal dominants, clonal stress-tolerators and interstitials) on constructed rafts with fen-forming communities and subjected these to a range of nutrient loadings over two years. 3. Increasing functional diversity as well as increasing nutrient loadings had stimulating effects on plant biomass accumulation, cover formation and rhizome growth onto open water. Both complementarity (due to niche partitioning or facilitation) and selection effects were mechanisms underlying the diversity effect, with a constant relative importance over the entire range of nutrient availabilities. Different functional groups were important for biomass production at different nutrient availabilities. Rhizome formation by clonal stress-tolerators contributed disproportionately to open water colonisation, identifying th

The assessment of the risk posed by invasive alien species (IAS) to the environment is a component of increasing importance for Pest Risk Analysis. Standardized and comprehensive procedures to assess their impacts on ecosystem services have been developed only recently. The invasive apple snails (Pomacea canaliculata and P. maculata) are used as a case study to demonstrate the application of an innovative procedure assessing the potential impact of these species on shallow freshwater ecosystems with aquatic macrophytes in Europe. The apple snail, Pomacea maculata, recently established in the Ebro delta in Spain resulting in a serious threat to rice production and wetlands, having also a high risk to spread to other European wetlands. Here, the population abundance of apple snails is regarded as the main driver of ecosystem change. The effects of ecosystem resistance, resilience and pest management on snail population abundance are estimated for the short (5 years) and the long (30 years) term. Expert judgment was used to evaluate the impacts on selected ecosystem services in a worst-case scenario. Our study shows that the combined effects of apple snails are estimated to have profound effects on the ecosystem services provided by shallow, macrophyte-dominated ecosystems in Europe. This case study illustrates that quantitative estimates of environmental impacts from different IAS are feasible and useful for decision-makers and invasive species managers that have to balance costs of control efforts against environmental and economic impacts of invasive species.

The assessment of the risk posed by invasive alien species (IAS) to the environment is a component of increasing importance for Pest Risk Analysis. Standardized and comprehensive procedures to assess their impacts on ecosystem services have been developed only recently. The invasive apple snails (Pomacea canaliculata and P. maculata) are used as a case study to demonstrate the application of an innovative procedure assessing the potential impact of these species on shallow freshwater ecosystems with aquatic macrophytes in Europe. The apple snail, Pomacea maculata, recently established in the Ebro delta in Spain resulting in a serious threat to rice production and wetlands, having also a high risk to spread to other European wetlands. Here, the population abundance of apple snails is regarded as the main driver of ecosystem change. The effects of ecosystem resistance, resilience and pest management on snail population abundance are estimated for the short (5 years) and the long (30 years) term. Expert judgment was used to evaluate the impacts on selected ecosystem services in a worst-case scenario. Our study shows that the combined effects of apple snails are estimated to have profound effects on the ecosystem services provided by shallow, macrophyte-dominated ecosystems in Europe. This case study illustrates that quantitative estimates of environmental impacts from different IAS are feasible and useful for decision-makers and invasive species managers that have to balance costs of control efforts against environmental and economic impacts of invasive species.

Dispersal of seeds by animals is an important mechanism regulating plant diversity, range expansions and invasions. Many birds, mammals, fish, and reptiles regularly ingest, transport and excrete viable seeds (known as endozoochory). The effectiveness of endozoochory is modelled in dispersal kernels: functions that describe seed shadows in the landscape by combining movement of animals with experimentally obtained seed retention times and survival. Currently, dispersal kernels use experimental data from resting animals, yet only moving animals disperse seeds. Although physical activity is known to affect digestive processes, little is known on how and to what extent this may influence current estimates of endozoochory. Activity may either prolong seed retention in the animal's gut (locomotion-priority mode hypothesis) or may not affect seed excretion rate (digestion-priority mode hypothesis), and may affect seed survival and germination positively or negatively. We tested how activity alters dispersal estimates in fish. We compared the seed dispersal potential of two riparian plant species (Carex acuta and C. riparia) by the common carp (Cyprinus carpio) subjected to three different activity levels: low (basal metabolic rate, BMR), medium (2×BMR), or high activity (3×BMR). Physical activity of the fish did not affect the number of intact retrieved seeds over 15 h of activity, but significantly affected seed retrieval patterns over time for both seed species. More active fish started seed excretion about 1 h later and kept excreting seeds at least 2 h longer. Effects of gut passage on germination could only be tested for C. acuta, where it reduced the percentage of germinating seeds by 22%, independent of the activity level. Seeds ingested by the fish germinated on average 3.5 days later than non-ingested control seeds. Seed retention times did not affect the timing of germination. Our results support the locomotion-priority mode hypothesis, and show that modelling d

Dispersal of seeds by animals is an important mechanism regulating plant diversity, range expansions and invasions. Many birds, mammals, fish, and reptiles regularly ingest, transport and excrete viable seeds (known as endozoochory). The effectiveness of endozoochory is modelled in dispersal kernels: functions that describe seed shadows in the landscape by combining movement of animals with experimentally obtained seed retention times and survival. Currently, dispersal kernels use experimental data from resting animals, yet only moving animals disperse seeds. Although physical activity is known to affect digestive processes, little is known on how and to what extent this may influence current estimates of endozoochory. Activity may either prolong seed retention in the animal's gut (locomotion-priority mode hypothesis) or may not affect seed excretion rate (digestion-priority mode hypothesis), and may affect seed survival and germination positively or negatively. We tested how activity alters dispersal estimates in fish. We compared the seed dispersal potential of two riparian plant species (Carex acuta and C. riparia) by the common carp (Cyprinus carpio) subjected to three different activity levels: low (basal metabolic rate, BMR), medium (2×BMR), or high activity (3×BMR). Physical activity of the fish did not affect the number of intact retrieved seeds over 15 h of activity, but significantly affected seed retrieval patterns over time for both seed species. More active fish started seed excretion about 1 h later and kept excreting seeds at least 2 h longer. Effects of gut passage on germination could only be tested for C. acuta, where it reduced the percentage of germinating seeds by 22%, independent of the activity level. Seeds ingested by the fish germinated on average 3.5 days later than non-ingested control seeds. Seed retention times did not affect the timing of germination. Our results support the locomotion-priority mode hypothesis, and show that modelling d