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A life-cycle model describing the demographic stages (boxes) and transitions (arrows) Posidonia australis follows to adulthood and the months each transition spanned. The transitions included; Seed-dependency, when seedlings are highly dependent on seed reserves, Sd (Decemberyr1–Januaryyr1). Seedlings then undergo an extended period where they continue to draw nourishment from maternally-derived reserves but there is greater uptake and assimilation of resources from the environment due to production of photosynthetically active leaves and development of a small but functional root system; autonomous development, Ad (Januaryyr1–Aprilyr1). By the end of this period seedlings have exhausted the majority (~90%) of their seed reserves and are relatively independent of their seed. Seedlings then become fully integrated into their environment upon exhaustion of the seed reserves; seedling establishment, Es (Aprilyr1–Septemberyr1). Production of new shoots, Ns (Septemberyr1–year 2) typically occurs in the months following seedling establishment and seedlings become Juveniles. Juveniles transition into adults after plants undergo horizontal vegetative expansion, Ve (year 2–3). Adults typically become reproductively mature, f (fecundity), between years 3–5.
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Identifying early life-stage transitions limiting seagrass recruitment could improve our ability to target demographic processes most responsive to management. Here we determine the magnitude of life-stage transitions along gradients in physical disturbance limiting seedling establishment for the marine angiosperm, Posidonia australis. Transition m...
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Seagrass meadows are highly productive ecosystems that provide ecosystem services to the coastal zone but are declining globally, particularly due to anthropogenic activities that reduce the quantity of light reaching seagrasses, such as dredging, river discharge and eutrophication. Light quality (the spectral composition of the light) is also alte...
Citations
... flow-induced energy flux and mass transport) in such a way that ensures survival and promotes further proliferation. Preliminarily, this can be externally achieved through shelter provided by other structures 16 . Building on this, Carus et al. 17 proposed the use of biodegradable mats of artificial seagrass (ASG) to serve as shelter for real seagrass and thus promote growth. ...
Seagrass restoration can be promoted through the use of artificial seagrass (ASG). However, there is no guideline for ASG design, which requires a sound understanding of the inherent hydrodynamics in a submerged environment. Present know-how primarily stems from idealized ASG attached to a fixed bed. To develop accessible field deployment for restoration, anchored prototype scale ASG mats (coconut mesh) were proposed and tested under differing wave conditions. The aim of this study was then to: 1) analyze hydrodynamic interaction of ASG mats; and 2) assess the suitability of contemporary predictive hydrodynamic models. Velocity structure and wave propagation were measured around one and two ASG mats (separated by a 2-m gap). The mats reduced orbital velocities by up to 16% (2 mats), whereby the average reduction of all tested vegetated conditions was low ( < 10% ) compared to the non-vegetated conditions. Velocities increased above the ASG, with the gap enhancing velocity (up to 11%) instead of attenuating it. Wave decay followed an exponential decrease, further enhanced by the second mat. Current models did not capture the induced hydrodynamics for the full range of wave conditions tested, with the second mat increasing uncertainties. Wave decay models generally overestimated wave attenuation (up to 30%), except for longer wave periods. Nevertheless, for the full range of conditions, the models provide accurate insight into the expected magnitude of attenuation under field conditions. It is speculated that mat flexibility affects the surrounding hydrodynamics through inherent motion, with the gap contributing to the uncertainties.
... A surprising observation was that some seeds do not move far after settling on the sediment surface, remaining near the parent plant (Orth et al. 1994;Manley et al. 2015;Hosokawa et al. 2015;Li et al. 2018;Kendrick et al. 2019a). Bioturbation and physical processes appear to contribute to seed retention, rapid burial, or loss of settled seeds (Luckenbach and Orth 1999;Delefosse and Kristensen 2012;Blackburn and Orth 2013;Statton et al. 2017). Similar to the fate of seeds in the terrestrial environment (Janzen 1970), predation can result in significant loss of seagrass seeds (Fishman and Orth 1996;Orth et al. 2006c). ...
The goal of this perspective is to review how seagrass research has evolved over the past half century to our current state of knowledge. We review how our knowledge of seagrass ecosystems changed from the pre-1970s when so little was known about seagrasses and how it progressed during the next 5 decades when seagrass knowledge rapidly expanded. Here, we concentrate on accomplishments in the areas of reproductive biology and ecology, population biology, seagrass-animal relationships, conservation and restoration, and mapping and monitoring. We also look ahead and discuss some areas that are ripe for future research, especially those employing new mapping and monitoring technologies, improved restoration methods that include multiple genetic variants, rhizosphere studies that result in a deeper understanding of microbial effects on nitrogen availability, sulfide levels and carbon sequestration, and how changing climatic regimes and tropicalization will likely affect temperate and tropical seagrass-dominated ecosystems.
... Sinclair et al., 2016Sinclair et al., , 2018, and bottlenecks to seedling recruitment (e.g. Statton et al., 2017). However, there is no information on flowering, seed production, and long-term survival of seedlings to complete the cycle. ...
... Once seeds of P. australis dehisce from their floating fruit and settle onto suitable habitat, they undergo significant seed predation that can remove ≤80% of seeds daily in seagrass meadows, or 10% daily over bare sand suggesting seeds are more likely to recruit into gaps within existing meadows (Orth et al., 2006;Statton et al., 2017). ...
... Seagrass recruitment has been assessed for some seagrass species , but most studies have failed to quantify seedling recruitment and survival rates across multiple years. A recruiting seedling is considered to be the most sensitive stage of the plant life cycle (Eriksson & Ehrlén, 1992;Harper et al., 1977), is a bottleneck and therefore subject to the highest mortality rates (Orth et al., 2006;Statton et al., 2017). In the European seagrass, Zostera noltii, recruitment accounted for nearly 20% of the new shoots each spring and ~30% were traced to seeds from up to 3 years earlier, suggesting that the stability and genetic diversity of meadows is related to persistent seed banks (Zipperle et al., 2009). ...
Understanding sexual reproduction and recruitment in seagrasses is crucial to their conservation and restoration. Flowering, seed production, seed recruitment, and seedling establishment data for the seagrass Posidonia australis was collected annually between 2013 and 2018 in meadows at six locations around Rottnest Island, Western Australia. Variable annual rates of flowering and seed production were observed among meadows between northern and southern sides of the island and among years. Meadows on the northern shore consistently flowered more intensely and produced more seeds across the years of the survey. Inter‐site variation in clonal diversity and size of clones, seed production, wind and surface currents during pollen and seed release, and the large, but variable, impact of seed predation are likely the principal drivers of successful recruitment into established meadows and in colonizing unvegetated sands. The prolific but variable annual reproductive investment increases the probability of low levels of continuous recruitment from seed in this seagrass, despite high rates of abiotic and biotic disturbance at seedling, shoot, and patch scales. This strategy also imparts a level of ecological resilience to this long‐lived and persistent species.
... Key to the success of the DIS-method is the controlled storage of seeds during the winter prior to spring seeding. In the field, high winter seed losses may have resulted from bioturbation (Delfosse & Kristensen, 2012;Valdemarsen et al., 2011;Wang et al., 2016), seed predation , disease , high sediment mobility (Statton et al., 2017) and waves and currents moving seeds into unsuitable growth conditions (Kuusemäe et al., 2018). Winter storage has resulted in high seed viability rates (>75 %), successfully keeping seeds away from all bottlenecks listed above except for disease (i.e., Phytophthora spp. ...
... Seed-based restoration trials often suffer from low seed recruitment rates (e.g., Golden et al. 2010;Eriander et al. 2016), reducing the efficiency and reliability of many seed-based restoration methods. Low recruitment rates have been attributed to a number of site-specific reasons (e.g., bioturbation (Valdermansen et al. 2011), predation (Orth et al. 2006b), hydrodynamics (Statton et al. 2017) and disease ). In the intertidal Wadden Sea, the failure of previous seagrass restoration trials has been mainly attributed to the dislocation of seeds due to hydrodynamic forcing and seed mortality due to Phytophthora off between closeness to surface and increased chance for dislocation. ...
... Several previous studies (e.g., van Katwijk et al. 2016;Statton et al. 2017) have noted that suitable site selection is key for successful seagrass restoration. ...
In coastal waters around the globe, seagrasses form the basis of productive ecosystems. Unfortunately, these valuable ecosystems have suffered massive losses during the last century and are in dire need of effective conservation measures. In this thesis, we investigated if and how eelgrass (Zostera marina) can be restored in the intertidal Wadden Sea. Through an applied and adaptive approach we were able to develop and optimize a new restoration method (DIS-method), with which seagrass seeds are injected into the sediment with normal caulking guns. By sowing seagrass with the DIS-method in spatial designs that trigger beneficial intraspecific feedbacks we were able to restore very high seagrass densities (~60 plants/m²) with high efficiency. Our restoration efforts not only resulted in seagrass establishment, but also quickly increased the diversity of benthic animals to levels found in natural seagrass meadows. Additionally, we found that benthic animals can offer previously untapped information about seagrass habitat suitability, a discovery that can potentially help with the identification of suitable restoration sites. Our results show that seagrass restoration is not only possible in the intertidal Wadden Sea, but can in fact even be highly successful and effective. This is highlighted by the fact that our restoration efforts led to the establishment of the largest seagrass population in the Dutch Wadden Sea (1 million plants scattered over 650 hectares). In conclusion, the applied knowledge we have gathered can in the future be used to effectively restore these important plants and their associated ecosystems in coastal areas worldwide.
... flow-induced energy flux and mass transport) in such a way that ensures survival and promotes further proliferation. Preliminarily, this can be externally achieved through shelter provided by other structures 15 . Building on this, Carus et al. 16 proposed the use of biodegradable mats of artificial seagrass (ASG) to serve as shelter for real seagrass and thus promote growth. ...
This preprint has not undergone peer review or any post-submission improvements or corrections. The Version of Record of this article is published in Scientific Reports, and is available online at https://doi.org/10.1038/s41598-023-46612-z
Abstract:
Seagrass restoration requires a sound understanding of the hydrodynamics around established meadows. Present know-how primarily stems from idealized artificial seagrass (ASG) attached to a fixed bed. With the goal of accessible field deployment for restoration, anchored prototype scale ASG mats (coconut mesh) were tested under differing wave conditions to analyze hydrodynamic interaction and assess the suitability of contemporary predictive models. Velocity structure and wave propagation were measured around one and two ASG mats (separated by a 2-m gap). The mats reduced orbital velocities by up to 16% (2 mats), whereby the average reduction was low (< 10%) compared to the non-vegetated conditions. Velocities increased above the ASG, with the gap enhancing velocity (up to 11%) instead of attenuating it. Wave decay followed an exponential decrease, further enhanced by the second mat. Current models did not capture the induced hydrodynamics for the full range of wave conditions tested, with the second mat increasing uncertainties. Wave decay models generally overestimated wave attenuation (up to 30%), except for longer wave periods. Nevertheless, for the full range of conditions, the models provide accurate insight into the expected magnitude of attenuation under field conditions. It is speculated that mat flexibility affects the surrounding hydrodynamics through inherent motion, with the gap contributing to the uncertainties.
... To prevent and reverse further losses, seagrass restoration efforts, using sods and rhizome fragments, are being undertaken across the world (Valdez et al., 2020). Nonetheless, the success rates of these efforts remain generally low (Bayraktarov et al., 2015;Valdez et al., 2020;van der Heide et al., 2007) and are mostly focused on decreasing environmental (e.g., hydrodynamic forces) and physiological stressors (diseases) on seagrasses on a small spatial scale Marion et al., 2020;Statton et al., 2017). In contrast, biotic interactions, which could also affect restoration success, are less well studied (Gagnon et al., 2020;Statton et al., 2017;Valdez et al., 2020). ...
... Nonetheless, the success rates of these efforts remain generally low (Bayraktarov et al., 2015;Valdez et al., 2020;van der Heide et al., 2007) and are mostly focused on decreasing environmental (e.g., hydrodynamic forces) and physiological stressors (diseases) on seagrasses on a small spatial scale Marion et al., 2020;Statton et al., 2017). In contrast, biotic interactions, which could also affect restoration success, are less well studied (Gagnon et al., 2020;Statton et al., 2017;Valdez et al., 2020). ...
... Inclusion of these positive interactions between bivalves and seagrasses may thus increase seagrass restoration success (De Fouw et al., 2016;Gagnon et al., 2020;Peterson and Heck, 2001;Valdez et al., 2020;Van der Geest et al., 2020;. In contrast, species interactions may also form a bottleneck for seagrass restoration efforts (Statton et al., 2017). Sediment reworking by bioturbating species may negatively affect seagrass growth and may lead to seed loss, forming an early-life stage bottleneck for seagrasses (Marion et al., 2020;Statton et al., 2017;Valdemarsen et al., 2011). ...
Seagrasses are globally declining and multiple restoration efforts are undertaken to reverse these losses. However, these efforts have proven to be challenging, facing a variety of bottlenecks. We studied how predation by macroinvertebrates may form a potential bottleneck for seed-based seagrass restoration. Specifically, we questioned if the omnivorous common ragworm (Hediste diversicolor) may act as a predator on eelgrass (Zostera marina) seeds and whether that could affect seed-based eelgrass restoration trials. In a controlled lab experiment, we studied (1) how seedling establishment was affected by ragworm biomass (0, 2, 8 g DW m⁻²), (2) if the absence or presence of an additional or alternative high-protein food source (Sanikoi ® Gold Protein Plus, 52% protein) prevented potential seed predation by ragworms and (3) how ragworm size (small: 0.0029 g and 3.3× bigger: 0.0095 g DW ragworm⁻¹) affected eelgrass seedling establishment. Additionally, we questioned (4) if ragworms may provide a bottleneck for annual eelgrass restoration experiments in the Dutch Wadden Sea by combining data from a large-scale benthic survey (SIBES, Netherlands Institute for Sea Research (NIOZ), Texel) with an existing eelgrass habitat suitability map. We found that >2 g DW m⁻² ragworms completely hampered eelgrass seedling establishment, even when fed an additional, protein-rich, food source. Ragworms only seemed to target sprouted seeds rather than intact seeds. Additionally, sprouted seed consumption by ragworms was size-dependent: sprouted seeds escaped predation by smaller ragworms even when present in high biomass (2 g DW m⁻²). By extrapolating our findings to the field, we showed that 52.8% of the potential eelgrass growth sites in the Dutch Wadden Sea overlap with impeding ragworm biomass (≥2 g DW m⁻²). By consuming sprouted eelgrass seeds, ragworms may consequently strongly impede seed-based eelgrass restoration efforts, especially since both species have highly overlapping distributions. We thus provided novel insights into an unknown bottleneck for seed-based eelgrass establishment, which may have restoration implications. Especially for annual eelgrass that fully depends on successful seedling establishment for their persistence and survival.
... Further research is recommended on some specific variables that proved critical to the modelling but for which there was a lack of quantitative data, such as differences between modelling habitat suitability for stable populations (established meadows) versus conditions that facilitate colonisation and recovery by seeds and seedlings including supply, (micro) site habitat suitability and 'windows of opportunity' allowing successful establishment of new recruits (Inglis, 2000;Orth et al., 2006;Rivers et al., 2011;Cambridge et al., 2002;Balke et al., 2014;Statton et al., 2017). We also recommend further study to better parameterise the growth of opportunistic epiphytes on seagrass blades, the amount of light attenuation (shading) this causes, and how this affects different seagrass species. ...
Habitat suitability modelling was used to test the relationship between coastal discharges and seagrass occurrence based on data from Adelaide (South Australia). Seven variables (benthic light including epiphyte shading, temperature, salinity, substrate, wave exposure, currents and tidal exposure) were simulated using a coupled hydrodynamic-biogeochemical model and interrogated against literature-derived thresholds for nine local sea-grass species. Light availability was the most critical driver across the study area but wave exposure played a key role in shallow nearshore areas. Model validation against seagrass mapping data showed 86 % goodness-of-fit. Comparison against later mapping data suggested that modelling could predict ~745 ha of seagrass recovery in areas previously classified as 'false positives'. These results suggest that habitat suitability modelling is reliable to test scenarios and predict seagrass response to reduction of land-based loads, providing a useful tool to guide (investment) decisions to prevent loss and promote recovery of seagrasses.
... attempts are generally low (<40%) (Bayraktarov et al. 2016;, with early plant establishment and survival being major hurdles hindering successful seagrass restoration. Fortunately, once successfully established, restored seagrass have in several areas been found to have very high long-term persistence rates (Statton et al. 2017;Rezek et al. 2019), highlighting the need for more effective restoration methods and strategies that can reduce bottlenecks hampering seedling establishment and survival. ...
... Several previous studies (e.g. Statton et al. 2017) have noted that suitable site selection is key for successful seagrass restoration. The failure of two consecutive restoration trials at Uithuizen reflects poor site selection, but also demonstrates the limits of the DIS method. ...
Due to the major declines of seagrasses worldwide, there is an urgent need for effective restoration methods and strategies. In the Dutch Wadden Sea, intertidal seagrass restoration has proven very challenging, despite numerous restoration trials with different restoration methods. Recently, however, the first field-trial performed with a newly developed ‘Dispenser Injection Seeding’-method (DIS) resulted in record-high plant densities and seed recruitment. Here, we present the further development of the methodology and consequently improved restoration results. During two consecutive growing seasons, we honed the seeding technique and experimentally investigated how seeding depth (2/4 cm), injection density (25/100 injects m⁻²) and seed amount (2/20 seeds inject⁻¹) affected restoration of intertidal annual Zostera marina. We found that all variables had a significant impact on plant establishment. Seeding deeper (4 cm) had the largest positive effect on restored plant densities, while lowered seed densities (2 seeds inject⁻¹) had the largest positive impact on seed recruitment. The optimized DIS-method, combined with an altered placement of the seeding-hole, resulted in a 50-fold increase in restored plant densities (from ~1 plant/m² to 57 plants/m²) and a simultaneous increase in seed recruitment (from 0.3% to 11.4%). These improvements stem from the method's ability to counteract a recruitment-bottleneck, where seeds are lost through hydrodynamic forcing. The methodological improvements described here are important steps towards restoring self-sustaining seagrass populations in the future and our study demonstrates the high potential of the seed-based DIS-method for seagrass restoration.
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... In some species, seeds produced from sexual reproduction undergo a period of dormancy which provides a buffer against times of reduced reproductive output, thereby increasing the resilience of local populations to disturbance (Smith et al., 2016). However, previous research on recruitment from seed in seagrasses have found high mortalities in seed settlement, with the probability of surviving at a density of 100 seeds·m -2 was expected to be around 0.1% (Orth et al., 2006b;Statton et al., 2017a). That phenomenon might be caused by the failure of seedling establishment or the loss of seed viability before the germination or seedings. ...
... That phenomenon might be caused by the failure of seedling establishment or the loss of seed viability before the germination or seedings. There have been numerous studies focusing on the relationships between seeding density and seedling establishment, and the seedling establishment process was considered as the most vulnerable step limiting restoration success (Marion and Orth, 2010;Statton et al., 2017a). However, few studies focused on the changes of seed abundance and viability, which is also a critical process in seed banks. ...
... Low salinity and relative high temperature could promote seagrass seed germination (Orth et al., 2000;Xu et al., 2016;Gu et al., 2017;Yue et al., 2019). In such conditions, H. ovalis seeds in the sediment quickly germinate, while the environmental conditions are not suitable for seedling establishment, resulting in losses to the seed bank and less effective recruitment the following spring (Statton et al., 2017a;Waite et al., 2021;Webster et al., 2021). Also, it was here demonstrated in an experiment that freshwater inputs over short-time periods contribute to Non-viable seed rate after exposing to different salinity (mean ± SE). (A) non-viable seeds after culturing for 7days (n=18); (B) non-viable seeds after culturing for 14 days(n=18). ...
The seed bank of Halophila ovalis is crucial for resilience to disturbance through re-establishment. Understanding seasonal changes in abundance and quality of seeds in natural seed banks is critical for seed-based restoration. We selected an estuary in southwestern Australia and investigated the seasonal changes of seed distribution and viability in H. ovalis seed banks. We also adapted an X-ray viability test used for terrestrial seeds to test the viability of H. ovalis seeds. We then simulated the effect of low salinity on seed viability through a short-term indoor experiment. Seed density was significantly different between sites and seasons (0 to 43590 seeds·m⁻²), and the highest seed density in the seed banks was found after the reproductive season (May). The proportion of viable seeds in the seed bank was less than 22%, and was not subjected to substantial seasonal variability. The density of seeds in the seed bank decreased in spring, which indicated winter conditions were not prompt seed loss. We also predicted that extreme rainfall events and the resulting extremely low salinity would significantly reduce seed viability, and could decrease in seed germination; limit population recruitment. As it rapidly colonizes marine sediments from seeds, H. ovalis was considered an ideal seagrass for restoration purposes. Our results provide physiological information for H. ovalis seed banks to support seed-based restoration plans. Such understanding would enable accurate predictions about seagrass population resilience to extreme climate events in estuaries, where variable and extremely low salinity may limit seagrass population recovery from seeds through decreasing their viability.
... Compared to terrestrial ecosystems, in coastal wetlands, seed fate postsowing might be more convoluted due to being subject to strong spatiotemporal heterogeneity of multiple disturbances (e.g. inundation and sheet erosion), with the relative importance of these disturbances varying with time as the seed transitions through its life course (Friess et al., 2012;Statton et al., 2017). Key life stage transitions include seed retention, seedling emergence and seedling establishment (Friess et al., 2012). ...
... Most experimental studies using seed addition have reported massive seed losses, while the remaining seeds may still fail to germinate due to unsuitable habitat conditions (Statton et al., 2017;van Regteren et al., 2019;Zhu et al., 2020). This suggests that seed-based restoration in coastal wetlands may encounter multiple recruitment bottlenecks nested in different life stages. ...
... Differences in environmental settings may drive recruitment bottlenecks formed in varied life stage transitions, causing the outcomes of similar restoration approaches to differ between sites (Larson et al., 2015;Statton et al., 2017). However, identifying specific bottleneck(s) that may occur at a targeted restoration site remains a formidable challenge , because we have a fragmented understanding of the underlying causes of variation in transitions across stages, particularly for stages before seedling establishment. ...
Attaining the goals of ‘The UN‐Decade on Ecosystem Restoration’ requires efficient methods for large‐scale restoration of degraded ecosystems. Seed‐based approaches may offer opportunities for massive recovery of native vegetation but are prone to failure when applied to highly valued coastal wetlands such as salt marshes. Pinpointing the impact of early life stage transitions on recruitment variation across species and contexts is a critical first step toward amplifying seed‐based restoration efficiency.
Large‐scale field experiments were conducted in 100 microhabitats across eight salt marshes to investigate root causes of variation in seed retention and seedling emergence, using four globally occurring salt marsh species as models. The resulting insights and dataset were then translated into predictors using machine learning, for targeted application in disentangling recruitment bottlenecks.
Seed retention, regardless of species, was identified as the principal bottleneck in recruitment with hydrodynamic intensity, bed‐level dynamics, and burial depth as critical governing factors. Seedling emergence was discerned as the critical bottleneck driving cross‐species recruitment variability and was pivotally influenced by soil salinity and burial depth.
Predictions using machine learning under different restoration scenarios indicated that simple management, such as seed burial or species selection, can create opportunities to bypass potential recruitment bottlenecks.
Synthesis and applications. Our results suggest that the failure of seed‐based coastal wetland restoration should be attributed to multiple recruitment bottlenecks that arise from different life stage transitions and are context/species dependent. In planning future seed‐based restoration practices, managers should assess the variability of life stage‐specific dominant factors at target sites to identify site‐specific recruitment bottleneck(s). Our work underscores the need for strategic management that buffers against recruitment bottlenecks to improve restoration efficiency and advances the application of data‐driven techniques to make seed‐based restoration predictive.
