Seagrass Zostera Noltii Research Articles

A facultative mutualism facilitates European seagrass meadows

Coastal ecosystem functioning often hinges on habitat‐forming foundation species that engage in positive interactions (e.g. facilitation and mutualism) to reduce environmental stress. Seagrasses are important foundation species in coastal zones but are rapidly declining with losses typically linked to intensifying global change‐related environmental stress. There is growing evidence that loss or disruption of positive interactions can amplify coastal ecosystem degradation as it compromises its stress mitigating capacity. Multiple recent studies highlight that seagrass can engage in a facultative mutualistic relationship with lucinid bivalves that alleviate sulphide toxicity. So far, however, the generality of this mutualism, and how its strength and relative importance depend on environmental conditions, remains to be investigated. Here we study the importance of the seagrass‐lucinid mutualistic interaction on a continental‐scale using a field survey across Europe. We found that the lucinid bivalve Loripes orbiculatus is associated with the seagrasses Zostera noltii and Zostera marina across a large latitudinal range. At locations where the average minimum temperature was above 1 °C, L. orbiculatus was present in 79% of the Zostera meadows; whereas, it was absent below this temperature. At locations above this minimum temperature threshold, mud content was the second most important determinant explaining the presence or absence of L. orbiculatus. Further analyses suggest that the presence of the lucinids have a positive effect on seagrass biomass by mitigating sulphide stress. Finally, results of a structural equation model (SEM) support the existence of a mutualistic feedback between L. orbiculatus and Z. noltii. We argue that this seagrass‐lucinid mutualism should be more solidly integrated into management practices to improve seagrass ecosystem resilience to global change as well as the success of restoration efforts.

Increased temperature reduces the positive effect of sulfide-detoxification mutualism on Zostera noltii nutrient uptake and growth

Seagrass meadows form essential ecological components in coastal zones but are rapidly declining worldwide due to anthropogenic impacts, including eutrophication and climate change-related heat waves. An important consequence of increased eutrophication is organic matter input in the sediment, which, together with raised temperatures, stimulates the production of toxic sulfide. Although multiple recent studies have highlighted that seagrass can engage in a mutualistic relationship with lucinid bivalves alleviating sulfide toxicity in the rhizosphere, it remains unclear how this mutualism is affected by temperature and eutrophication. To unravel this relation, we investigated the response of the seagrass Zostera noltii to contrasting sediment organic matter conditions, temperatures and presence/absence of the lucinid clam Loripes orbiculatus in a full-factorial mesocosm experiment. Results demonstrate that temperature increased porewater sulfide and nutrient levels, particularly in treatments with high sediment organic matter content. Interestingly, L. orbiculatus reduced not only sulfide levels, but also porewater nutrients. The removal of sulfide in turn stimulated Z. noltii growth, despite lower nutrient availability. Finally, increased temperature suppressed the mutualistic benefit for Z. noltii as sulfide detoxification became hampered. We conclude that, as eutrophication remains an issue in the coastal zone and temperature extremes will likely become more common in the future, seagrass meadows where lucinids occur may need to increasingly rely on this mutualism. At the same time, however, this interaction will become more strained, with an inherent increasing risk of mutualism breakdown.

Finding some seagrass optimism in Wales, the case of Zostera noltii

There exists limited understanding of the long-term dynamics of the seagrass Zostera noltii and how this is influenced by anthropogenic pressures. Milford Haven is a heavily industrialised estuary and also one of the important sites for Zostera sp. in the UK. In this study we examine all available long-term spatial variability and abundance data of Zostera noltii within Milford Haven using historic datasets. Results show that Z. noltii in all sites have shown meadow expansion when compared to the first obtainable records. Little change in abundance over the past 10–15years for the two sites confirms certain seagrass populations to be robust and thriving. We hypothesise that these populations are showing a level of resilience to the high nutrient levels, disturbance and high turbidity present within the water column of the Haven.

Genetic Description and Remote Sensing Techniques as Management Tools for Zostera noltii Seagrass Populations along the Atlantic Moroccan Coast

ABSTRACT Zarranz Elso, M.; Manent, P.; Luque, A.; Ramdani, M., and Robaina, R.R., 2017. Genetic description and remote sensing techniques as management tools for Zostera noltii seagrass populations along the Atlantic Moroccan coast. Seagrass meadows provide an essential ecological service in coastal ecosystems worldwide, although they are sensitive to many human factors, as a serious global regression has been documented. During sampling along the Atlantic Moroccan coast, five coastal lagoons were found characterized by the presence of intertidal monospecific seagrass Zostera noltii meadows (from south to north, Nayla, Oualidia, Sidi Moussa, Moulay Bousselham, and Larache). Two descriptive methods used to characterize Z. noltii populations could be used as management tools for future monitoring implementations: (1) the estimation of surface area covered by Z. noltii meadows using remote sensing techniques and in situ field surveys, and (2) the genetic characterisation of Z. noltii populations using simple...

Zostera noltiiin the Canary Islands: A Genetic Description for Conservation Purposes

ABSTRACT Zarranz Elso, M.; Manent, P., and Robaina, R.R., 2018. Zostera noltii in the Canary Islands: A genetic description for conservation purposes. The extremely delicate situation affecting the seagrass Zostera noltii in the Canary Islands (listed as ‘threatened with extinction') requires urgent measures to ensure its preservation. The genetic or genotypic description of populations and knowledge about their connectivity are important genetic issues that should be taken into account to accomplish appropriate conservation and restoration programmes, particularly for threatened habitats or species. Therefore, a genetic characterisation of the single remaining meadow located on the coast of Lanzarote was conducted using nine microsatellite loci, and its genetic relationship with the geographically closest Moroccan populations was studied for restoration purposes. Results showed that the Lanzarote population has recently suffered a significant reduction in effective population size and presents low levels...

Macrophytobenthos of the Caspian Sea: Diversity, distribution, and productivity

In the Russian sector of the northern and middle Caspian Sea, 36 species of macroalgae have been identified. The green and red algae from the mesosaprobic group are dominant. An increase in the number of green algae species is revealed. The distribution of macroalgae is inhomogeneous. It is confined to the solid substrate and epiphyton. The biomass of seaweeds reaches 1.5 kg/m2. Climate change has little influence on the appearance of new species in the northern Caspian Sea, but new invaders can appear in the Middle and Southern Caspian. The distribution of aquatic and coastal hygrophytic vegetation shows considerable spatial dynamics due to fluctuations in the level and salinity of the Caspian Sea. The biomass of aquatic vegetation varies in a wide range from 0.5 to 10.0 kg/m2. Spatially detailed mathematical models adequately reflect the changes in key species of aquatic plants in space and time. It is shown that expansion of the zone of the seagrass Zostera noltii to shallow water areas is occurring at present, as well as shrinkage of the range of the dominant littoral aquatic plant Phragmites australis.

Toxic effects of increased sediment nutrient and organic matter loading on the seagrass Zostera noltii

As a result of anthropogenic disturbances and natural stressors, seagrass beds are often patchy and heterogeneous. The effects of high loads of nutrients and organic matter in patch development and expansion in heterogeneous seagrass beds have, however, poorly been studied. We experimentally assessed the in situ effects of sediment quality on seagrass (Zostera noltii) patch dynamics by studying patch (0.35m diameter) development and expansion for 4 sediment treatments: control, nutrient addition (NPK), organic matter addition (OM) and a combination (NPK+OM). OM addition strongly increased porewater sulfide concentrations whereas NPK increased porewater ammonium, nitrate and phosphate concentrations. As high nitrate concentrations suppressed sulfide production in NPK+OM, this treatment was biogeochemically comparable to NPK. Sulfide and ammonium concentrations differed within treatments, but over a 77 days period, seagrass patch survival and expansion were impaired by all additions compared to the control treatment. Expansion decreased at porewater ammonium concentrations >2000μmolL−1. Mother patch biomass was not affected by high porewater ammonium concentrations as a result of its detoxification by higher seagrass densities. Sulfide concentrations >1000μmolL−1 were toxic to both patch expansion and mother patch. We conclude that patch survival and expansion are constrained at high loads of nutrients or organic matter as a result of porewater ammonium or sulfide toxicity.

Uptake of nitrogen from compound pools by the seagrass Zostera noltii

In nature, seagrasses are confronted with a compound pool of low concentrations of inorganic and organic nitrogen-containing substances of varying bioavailability. Nevertheless, the majority of research on nitrogen acquisition by seagrasses has been largely limited to studies addressing a single nitrogen substrate at a time. Using a combination of one of 15N-labeled substrates and one 14N-labeled background substrate, we investigated how the rate of nitrogen uptake by the seagrass Zostera noltii varies with nitrogen background. Leaf and root mediated uptake were studied separately for different combinations of inorganic (ammonium and nitrate) and organic substrates (urea and glycine). Ammonium uptake rates were higher than for the other substrates. However, substrate uptake was not dependent on the background nutrient. Similar patterns and uptake rates were found for above- and belowground plant parts. The dependence of uptake rate on substrate type, combined with an independence of nutrient background is explained as difference in uptake capacity, rather than substrate preference. For the dual labeled (15N and 13C) urea and glycine, strong relationships existed between nitrogen and carbon uptake, but with deviations from expectations under complete uptake of the molecules. Overall, this study indicates that at realistically low ambient concentrations, seagrasses can simultaneously use inorganic and organic sources for their nitrogen needs, and do not distinguish between substrates. In other words, they take up whatever is available.

Primary Productivity Temporal Fluctuations in a Nutrient-Rich Estuary due to Climate-Driven Events

In estuaries, climate and nutrients are the major drivers of primary productivity, since light availability, water movements, nutrient supplies, and physical stability determine the ability of primary producers to photosynthesize, grow, and survive. Therefore, in nutrient-rich estuaries, climate is expected to be the driving force of primary productivity. As global climate changes may increase the probability of some local ordinary weather events reaching extreme levels, it becomes pertinent to understand whether climate influences estuarine primary productivity patterns over the years. By means of long-term time series of phytoplankton, seagrass (Zostera noltii), and macroalgae (Gracilaria gracilis and Ulva spp.) production measurements, the influence of local weather events upon primary productivity was investigated in a temperate nutrient-rich estuary. The hypothesis proposed that estuarine primary productivity would show temporal fluctuations linked to climate-driven events and to the mitigation measures used to combat local anthropogenic pressures. Results revealed that, in the Mondego estuary, the most primary productivity is carried out by phytoplankton and that Z. noltii leaves and G. gracilis contribute equally to the daily productivity of the estuary, followed by Z. noltii belowground and finally by Ulva spp. Phytoplankton productivity seems to reach its highest rates in dry years, whereas a considerable decrease occurred during rainy periods. Regarding Z. noltii leaves, the highest productivity rates were attained in cold years. Moreover, the results do not support any relation between macroalgae productivity and climate events, but it would appear that the absence of local anthropogenic pressures increased its production rates. In what concerns primary productivity in temperate regions, small estuaries seem to have the ability to recover from singular intense weather events occurring over the years. Since recent climate change projections point out that drought periods are expected to increase and precipitation is expected to decrease, it was possible to infer that phytoplankton, in temperate estuaries, is likely to play an important role in the fixation of carbon dioxide acting as a sink of carbon, which, in turn, may increase coastal productivity. This knowledge could contribute to reduce uncertainty in future climate change projections and to enhance management strategies at a regional level, which have important environmental and socioeconomic repercussions.

Transitions in sandflat biota since the 1930s: effects of sea-level rise, eutrophication and biological globalization in the tidal bay Königshafen, northern Wadden Sea

Conspicuous macrozoobenthos and vegetation of intertidal sandflats in Königshafen (Island of Sylt, SE North Sea) were mapped in 1932, 1988 and 2008. Higher water levels since the 1930s with a concomitant increase in tidal dynamics are assumed to have weakened sediment stability. This dissolved the distinctly banded macrobenthic zonation of the 1930s. Near high water level, cyanobacterial mats with associated beetles, belts of the mudshrimp Corophium volutator and the seagrass Zostera noltii have vanished, while the range of the lugworm Arenicola marina has extended towards the shore. Near low water level, sandy elevations have become permanently submerged because a tidal creek has widened its bed. In 1988, extensive green algal mats and the almost complete absence of seagrass are attributed to peak eutrophication. This partially reversed until 2008. The mussel Mytilus edulis had strongly extended its beds along the creek in 1988. These were taken over by introduced Pacific oysters Crassostrea gigas in 2008. Also in 2008, the cordgrass Spartina anglica, another introduced species, grew into large tussocks where cyanobacterial mats and a Corophium-belt had been mapped in the 1930s. Former benthic patterns may have little chance of resurrection by conventional nature protection because these small-scale shifts represent responses to regional and global change.

Seagrasses are negatively affected by organic matter loading and Arenicola marina activity in a laboratory experiment

When two ecosystem engineers share the same natural environment, the outcome of their interaction will be unclear if they have contrasting habitat-modifying effects (e.g., sediment stabilization vs. sediment destabilization). The outcome of the interaction may depend on local environmental conditions such as season or sediment type, which may affect the extent and type of habitat modification by the ecosystem engineers involved. We mechanistically studied the interaction between the sediment-stabilizing seagrass Zostera noltii and the bioturbating and sediment-destabilizing lugworm Arenicola marina, which sometimes co-occur for prolonged periods. We investigated (1) if the negative sediment destabilization effect of A. marina on Z. noltii might be counteracted by positive biogeochemical effects of bioirrigation (burrow flushing) by A. marina in sulfide-rich sediments, and (2) if previously observed nutrient release by A. marina bioirrigation could affect seagrasses. We tested the individual and combined effects of A. marina presence and high porewater sulfide concentrations (induced by organic matter addition) on seagrass biomass in a full factorial lab experiment. Contrary to our expectations, we did not find an effect of A. marina on porewater sulfide concentrations. A. marina activities affected the seagrass physically as well as by pumping nutrients, mainly ammonium and phosphate, from the porewater to the surface water, which promoted epiphyte growth on seagrass leaves in our experimental set-up. We conclude that A. marina bioirrigation did not alleviate sulfide stress to seagrasses. Instead, we found synergistic negative effects of the presence of A. marina and high sediment sulfide levels on seagrass biomass.

Projecting future distribution of the seagrass Zostera noltii under global warming and sea level rise

In future decades, coastal ecosystems are expected to be exposed to increased risk of experiencing adverse consequences related to climate change, exacerbated by human induced pressures. The seagrass Zostera noltii forms meadows mainly within the intertidal zone, leading it to be particularly vulnerable to seawater temperature increase and sea level rise (SLR). Considering the presently declining situation and the predicted scenarios of increasing seawater temperature and SLR by the end of the 21st century, we assessed the response of Z. noltii to climate change (i) accounting for changes in seawater temperature at its entire biogeographical range level; and (ii) under SLR scenarios at estuary level (Oka estuary, Basque Country, south-eastern Bay of Biscay). Objectives were addressed coupling habitat suitability models with climate change simulations. By the end of the 21st century, seawater temperature increase will trigger a northward distributional shift of 888km in the suitable habitat of the species, and a retreat of southernmost populations. The loss of southernmost populations due to climate change may imply future conservation problems. In contrast, SLR and derived changes in current velocities are expected to induce the landward migration of the species in the Oka estuary, increasing the available suitable intertidal areas (14–18%) to limits imposed by anthropogenic barriers. This modelling approach could lead to an advanced understanding of the species’ response to climate change effects; moreover, the information generated might support conservation actions towards the sites where the habitat would remain suitable for the species under climate change.

Accumulation of the Oil Hydrocarbons by the Marine Organisms of the Seaweed Zostera noltii Thickets in the Kazacha Bay (the Black Sea)

Paper deals with data on the contents of oil hydrocarbons in hydrobionts, inhabiting thickets of the sea grass Zostera noltii (Hornemann) in the relatively clean waters of the south-west coast of the Crimea. Average content of oil hydrocarbons in Z. noltii and microphytoperiphyton was very close − respectively 0.56 ± 0.12 and 0.62 ± 0.15 mg/100 mg. There was no significant difference between content of oil hydrocarbons in the plant-eating mollusks (Rissoa membranacea (J. Adams), Bittium reticulatum (da Costa), Tricolia pullus (L.)) and filterer mollusks (Mytilidae, Parvicardium exiguum (Gmelin)). The obtained data can be used for environmental monitoring and for the study of the coastal biofluxes of oil hydrocarbons.

Entangled effects of allelic and clonal (genotypic) richness in the resistance and resilience of experimental populations of the seagrass Zostera noltii to diatom invasion.

BackgroundThe relationship between species diversity and components of ecosystem stability has been extensively studied, whilst the influence of the genetic component of biodiversity remains poorly understood. Here we manipulated both genotypic and allelic richness of the seagrass Zostera noltii, in order to explore their respective influences on the resistance of the experimental population to stress. Thus far intra-specific diversity was seldom taken into account in management plans, and restoration actions showed very low success. Information is therefore needed to understand the factors affecting resistance and resilience of populations.ResultsOur results show a positive influence of both allelic and genotypic richness on the resistance of meadows to environmental perturbations. They also show that at the low genotypic (i.e. clonal) richness levels used in prior experimental approaches, the effects of genotypic and allelic richness could not be disentangled and allelic richness was a likely hidden treatment explaining at least part of the effects hitherto attributed to genotypic richness.ConclusionsAltogether, these results emphasize the need to acknowledge and take into account the interdependency of both genotypic and allelic richness in experimental designs attempting to estimate their importance alone or in combination. A positive influence of allelic richness on resistance to perturbations, and of allelic richness combined with genotypic richness on the recovery (resilience) of the experimental populations is supported by differential mortality. These results, on the key species structuring of one of the most threatened coastal ecosystem worldwide, seagrass meadows, support the need to better take into account the distinct compartments of clonal and genetic diversity in management strategies, and in possible restoration plans in the future.

Interaction between ammonium and phosphate uptake rates in the seagrass Zostera noltii

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 488:133-143 (2013) - DOI: https://doi.org/10.3354/meps10395 Interaction between ammonium and phosphate uptake rates in the seagrass Zostera noltii Beatriz Villazán*, Fernando G. Brun, Rocío Jiménez-Ramos, J. Lucas Pérez-Lloréns, Juan J. Vergara Departamento de Biología (Área de Ecología), Facultad de Ciencias del Mar y Ambientales, Universidad de Cádiz, Campus de Excelencia Internacional del Mar (CEIMAR), Puerto Real 11510, Cádiz, Spain *Email: beatriz.villazan@uca.es ABSTRACT: Foliar ammonium and phosphate uptake rates and their interactions were assessed in whole seagrass Zostera noltii plants incubated in 2-compartment transparent chambers. This method allowed the calculation of nutrient uptake rates by leaves and by roots and rhizomes independently, avoiding plant breakage. Overall, a direct linear relationship between foliar uptake rates and seawater nutrient concentrations (phosphate or ammonium) was found, with uptake rates much higher in the first 5 min (nutrient adsorption). This faster adsorption was followed by slower uptake rates (nutrient absorption) in the next time intervals. When both nutrients were supplied separately, foliar ammonium uptake rates were 3-fold higher than those of phosphate in the range of the nutrient concentrations assayed for the whole incubation interval (120 min). When both nutrients were added simultaneously (10 µM phosphate and 50 µM ammonium, final concentrations), ammonium uptake rates were similar to those values recorded when ammonium was provided alone, whereas phosphate uptake rates were about 55% lower than those measured when phosphate was added alone. This study reveals for the first time the inhibitory effect of ammonium on phosphate uptake in seagrasses. KEY WORDS: Ammonium toxicity · Phosphate uptake · Ammonium uptake · Zostera noltii · Eutrophication · Membrane potential · Seagrass Full text in pdf format PreviousNextCite this article as: Villazán B, Brun FG, Jiménez-Ramos R, Pérez-Lloréns JL, Vergara JJ (2013) Interaction between ammonium and phosphate uptake rates in the seagrass Zostera noltii. Mar Ecol Prog Ser 488:133-143. https://doi.org/10.3354/meps10395 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 488. Online publication date: August 15, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Multi-metric index based on the seagrass Zostera noltii (ZoNI) for ecological quality assessment of coastal and estuarine systems in SW Iberian Peninsula

The aim of this study was to develop an ecological quality index based on the seagrass Zostera noltii (ZoNI) according to the WFD requirements. Eleven Z. noltii meadows of SW Iberian Peninsula under contrasting levels of anthropogenic disturbance were considered: 5 sites in Ria Formosa (Portugal), and 6 sites in Spain (Huelva and Cadiz). Environmental quality was assessed through nutrients of the water column and seagrass variables from different organization levels; those variables were analyzed using PCA (47% of explained variance on the first component) to calculate the ecological quality ratio (that was significantly correlated to the environmental variables, R2=0.51, p<0.01) and the ecological quality status of the sites. As a result, 4 sites were classified as good, 6 sites as moderate and 3 sites as poor ecological status. The developed index ZoNI showed to be suitable to assess the ecological status of estuarine and coastal systems in SW Iberian Peninsula reflecting their water quality.

Spatio-Temporal Patterns of Submerged Macrophytes in Three Hydrologically Altered Mediterranean Coastal Lagoons

Rice cultivation in the Ebro Delta (Catalonia, Spain) has inverted the natural hydrological cycles of coastal lagoons and decreased water salinities for over 150 years. Adjustments in the water management practices—in terms of source and amount of freshwater inputs—have resulted in changes in the diversity, distribution and productivity of submerged angiosperms. Between the 1970s and late 1980s, a massive decline of the aquatic vegetation occurred in the Encanyissada–Clot and Tancada lagoons, but little information on the status is available after the recovery of macrophytes in the 1990s. Here, we evaluate the influence of salinity regimes resulting from current water management practices on the composition, distribution, seasonal abundance and flowering rates of submersed macrophytes, as well as on the occurrence of epiphyte and drift macroalgae blooms in three coastal lagoons. Our results show that Ruppia cirrhosa is the dominant species in the Encanyissada lagoon (185.97 ± 29.74 g DW m−2 year−1; 12–27 ‰ salinity) and the only plant species found in the Tancada lagoon (53.26 ± 10.94 g DW m2 year−1; 16–28 ‰ salinity). Flowering of R. cirrhosa (up to 1,011 ± 121 flowers m−2) was only observed within the Encanyissada and suggests that mesohaline summer conditions may favor these events. In contrast, low salinities in Clot lagoon (∼3–12 ‰) favor the development of Potamogeton pectinatus (130.53 ± 13.79 g DW m2 year−1) with intersperse R. cirrhosa (8.58 ± 1.71 g DW m−2) and mixed stands of P. pectinatus and Najas marina (up to ∼57 g DW m−2 year−1) in some reduced areas. The peak biomasses observed during the study are 88 to 95 % lower than maximum values reported in the literature at similar salinities, and there is also little or no recovery in some areas compared to last reports more than 20 years ago. The main management actions to restore the natural diversity and productivity of submersed angiosperms, such as the recovering of the seagrass Zostera noltii, should be the increase of salinity during the period of rice cultivation, by reducing freshwater inputs and increasing flushing connections with the bays.

Effects of CO(2) enrichment on photosynthesis, growth, and nitrogen metabolism of the seagrass Zostera noltii.

Seagrass ecosystems are expected to benefit from the global increase in CO2 in the ocean because the photosynthetic rate of these plants may be Ci-limited at the current CO2 level. As well, it is expected that lower external pH will facilitate the nitrate uptake of seagrasses if nitrate is cotransported with H+ across the membrane as in terrestrial plants. Here, we investigate the effects of CO2 enrichment on both carbon and nitrogen metabolism of the seagrass Zostera noltii in a mesocosm experiment where plants were exposed for 5 months to two experimental CO2 concentrations (360 and 700 ppm). Both the maximum photosynthetic rate (Pm) and photosynthetic efficiency (α) were higher (1.3- and 4.1-fold, respectively) in plants exposed to CO2-enriched conditions. On the other hand, no significant effects of CO2 enrichment on leaf growth rates were observed, probably due to nitrogen limitation as revealed by the low nitrogen content of leaves. The leaf ammonium uptake rate and glutamine synthetase activity were not significantly affected by increased CO2 concentrations. On the other hand, the leaf nitrate uptake rate of plants exposed to CO2-enriched conditions was fourfold lower than the uptake of plants exposed to current CO2 level, suggesting that in the seagrass Z. noltii nitrate is not cotransported with H+ as in terrestrial plants. In contrast, the activity of nitrate reductase was threefold higher in plant leaves grown at high-CO2 concentrations. Our results suggest that the global effects of CO2 on seagrass production may be spatially heterogeneous and depend on the specific nitrogen availability of each system. Under a CO2 increase scenario, the natural levels of nutrients will probably become limiting for Z. noltii. This potential limitation becomes more relevant because the expected positive effect of CO2 increase on nitrate uptake rate was not confirmed.

Ecosystem engineering by seagrasses interacts with grazing to shape an intertidal landscape.

Self-facilitation through ecosystem engineering (i.e., organism modification of the abiotic environment) and consumer-resource interactions are both major determinants of spatial patchiness in ecosystems. However, interactive effects of these two mechanisms on spatial complexity have not been extensively studied. We investigated the mechanisms underlying a spatial mosaic of low-tide exposed hummocks and waterlogged hollows on an intertidal mudflat in the Wadden Sea dominated by the seagrass Zostera noltii. A combination of field measurements, an experiment and a spatially explicit model indicated that the mosaic resulted from localized sediment accretion by seagrass followed by selective waterfowl grazing. Hollows were bare in winter, but were rapidly colonized by seagrass during the growth season. Colonized hollows were heavily grazed by brent geese and widgeon in autumn, converting these patches to a bare state again and disrupting sediment accretion by seagrass. In contrast, hummocks were covered by seagrass throughout the year and were rarely grazed, most likely because the waterfowl were not able to employ their preferred but water requiring feeding strategy (‘dabbling’) here. Our study exemplifies that interactions between ecosystem engineering by a foundation species (seagrass) and consumption (waterfowl grazing) can increase spatial complexity at the landscape level.

Suppressing antagonistic bioengineering feedbacks doubles restoration success

In a seagrass restoration project, we explored the potential for enhancing the restoration process by excluding antagonistic engineering interactions (i.e., biomechanical warfare) between two ecosystem engineers: the bioturbating lugworm Arenicola marina and the sediment-stabilizing seagrass Zostera noltii Hornem. Applying a shell layer underneath half of our seagrass transplants successfully reduced adult lugworm density by over 80% and reduced lugworm-induced microtopography (a proxy for lugworm disturbance) at the wave-sheltered site. At the wave-exposed site adult lugworm densities and microtopography were already lower than at the sheltered site but were further reduced in the shell-treated units. Excluding lugworms and their bioengineering effects corresponded well with a strongly enhanced seagrass growth at the wave-sheltered site, which was absent at the exposed site. Enhanced seagrass growth in the present study was fully assigned to the removal of lugworms' negative engineering effects and not to any (indirect) evolving effects such as an altered biogeochemistry or sediment-stabilizing effects by the shell layer. The context-dependency implies that seagrass establishment at the exposed site is not constrained by negative ecosystem-engineering interactions only, but also by overriding physical stresses causing poor growth conditions. Present findings underline that, in addition to recent emphasis on considering positive (facilitating) interactions in ecological theory and practice, it is equally important to consider negative engineering interactions between ecosystem-engineering species. Removal of such negative interactions between ecosystem-engineering species can give a head start to the target species at the initial establishment phase, when positive engineering feedbacks by the target species on itself are still lacking. Though our study was carried out in a marine environment with variable levels of wave disturbance, similar principles may be expected to apply to other ecosystems that are inhabited by ecosystem engineers.