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Seagrass meadows are declining at alarming rates globally due to both anthropogenic activities and natural threats. Seagrasses play key ecological roles in coastal ecosystems as primary producers and providers of habitat and environmental structure. Therefore, mapping seagrass beds is indispensable for the effective monitoring and management of coastal vegetated habitats. In contrast to direct sampling techniques and optical remote sensing, active hydroacoustic techniques are relatively inexpensive and efficient for the detection of seagrass. We used a single beam echosounder to detect the spatial and temporal distribution characteristics of the eelgrass Zostera marina L. in an important overwintering habitat for the whooper swan Cygnus cygnus (Swan-Lake lagoon), northern China. We also distinguished echograms of the macroalgae Chaetomorpha linum K. and outlined its threat to seagrass. We also propose a method for calculating the accuracy of interpolation analyses. Results showed that: (1) The distribution of seagrass in Swan Lake varies with seasons, with maximum distribution area in summer. The maximum distribution area of seagrass beds in Swan Lake was 199.09 ha–231.67 ha, accounting for 41.48%–48.26% of the area of Swan Lake; (2) C. linum is a growing threat for seagrass beds of Swan-lake, with distribution area as high as 129.28 ha in May 2018. The invasion and competition by C. linum against seagrass beds could be one of the reasons for the decline in seagrass beds in Swan-Lake; (3) Topo to Raster has the highest interpolation accuracy and is the most conservative among three interpolation methods. Topo to Raster was the most suitable interpolation method for the sonar detection of seagrass beds. The findings may facilitate the application of sonar technology in seagrass monitoring and provide data for the formulation of appropriate seagrass bed management and restoration strategies and policies.

The studies on novel and efficient biosorbent materials for the promotion of environmental and economic sustainability have been become an up-to-date attempt by scientists for the removal of synthetic dyes from industrial effluents. The biosorbents prepared from biomass based resources are emerging as an alternative promising material for the environmental clean-up because of their low-cost, renewability, eco-friendly, easy availability and so forth characteristics. Hence, for the first time, the biosorption performance of abundantly available natural biowastes originating from coastal Zostera marina L. meadows was explored for the biotreatment of colored industrial effluents in the present study. The biosorption properties of biosorbent for methylene blue as a representative synthetic industrial dye were investigated by means of the operational parameters optimization, kinetic, isotherm, thermodynamic and characterization studies. The operating conditions significantly affected the biosorption process and the optimal values were determined as pH of 8, biosorbent dosage of 10 mg, dye concentration of 15 mg L−1 and contact time of 120 min. Elovich and Freundlich models provided the best fit to the kinetic and isotherm data compared with other applied models, respectively. The negative change in free energy (−10.682 to −8.466 kJ mol−1) indicated a thermodynamically feasible and spontaneous process. The characterization analysis showed that the biosorbent has appropriate chemical and physical properties for the dye biosorption. Thus, the present study displayed that the waste materials originating from coastal Z. marina L. meadows can be applied as a highly efficient as well as cost-effective green generation biosorbent for the clean-up of colored aquatic media.

Structure provided by temperate seagrasses is expected to reduce encounter rates with predators and therefore benefit small nekton most in summer, when predation is intense and seagrass reaches peak biomass, and in the day relative to night, when darkness limits visually-oriented predators regardless of habitat. Based on seines in eelgrass ( Zostera marina ), unvegetated habitat, and edges in Willapa Bay, Washington, USA, nekton abundances varied across habitats and on both diel and seasonal time scales, yet only a few time-by-habitat interactions were observed, in which habitat distinctions were most pronounced at certain times. One explanation is that four of the six most abundant species disproportionately occupied unvegetated habitat or were habitat generalists , but our expectations were based on eelgrass-associated taxa. Multivariate community structure responded separately to season, habitat, and diel period, in order of importance. Total abundance showed a significant season-by-habitat interaction. A summer peak in vegetated habitats was largely driven by shiner perch and sticklebacks , two eelgrass-associated fishes, while unvegetated habitat showed year-round uniform abundances due to taxa like English sole and sand shrimp with winter and spring peaks, and no strong habitat associations or association with unvegetated habitat, respectively. In a single diel-by-habitat interaction, shiner perch were eelgrass-associated during the day but not at night. No evidence emerged of differences in body size across habitats for any species measured, but many taxa grew seasonally, likely as cohorts migrating out of the estuary . Seasonality was thus the strongest signal governing patterns of community structure, abundance, and body size across time and space, while habitat structure and diel period were less important. Our results are largely consistent with the other studies showing the primacy of seasonality in structuring estuarine nekton communities, but also show that this pattern is highly dependent on the seasonal recruitment patterns and habitat associations of abundant nekton.

The present study aimed to assess the utilization of three seagrasses (Zostera marina, Z. japonica, and Z. caespitosa) along the eastern coast of the Shandong Peninsula as bioindicators of heavy metal pollution. Heavy metal concentrations (Cd, Cr, Cu, Pb and Zn) were investigated in the sediments and in the aboveground and belowground tissues of seagrasses. The results show that the aboveground tissues of seagrasses accumulated higher levels of Cd and Cu (excluding Z. caespitosa), whereas other metals, such as Cr, Pb and Zn, were mainly restricted to the belowground tissues. Compared to Z. japonica and Z. caespitosa, Z. marina had a higher enrichment capacity for heavy metals. Overall, the seagrasses can reflect the levels of metals in the sediments, especially Z. marina, whose heavy metal tissue levels were significantly and positively correlated with the levels of all metals in the sediments. This study showed that Z. marina could be used as an effective bioindicator for heavy metal pollution of sediments in ecological quality monitoring programs in the future, at least in the temperate waters of China.

The influence of algicidal and growth-inhibiting bacteria in a seagrass (Zostera marina) bed, and their capability of controlling blooms of the fish-killing raphidophyte flagellate, Chattonella antiqua, were examined in laboratory microcosm experiments. Bacterial communities in seawater collected from the seagrass bed and Z. marina biofilm suppressed artificial Chattonella blooms in the presence of their natural competitors and predators. Phylogenetic analysis suggest that considerable numbers of bacteria that suppress Chattonella, including algicidal or growth-inhibiting bacteria isolated from seagrass biofilm and seawater from the seagrass bed, are members of Proteobacteria that can decompose lignocellulosic compounds. A direct comparison of partial 16S rRNA gene sequences (500 bp) revealed that the growth-limiting bacterium (strain ZM101) isolated from Z. marina biofilm belonged to the genus Phaeobacter (Alphaproteobacteria) showed 100% similarity with strains of growth-limiting bacteria isolated from seawater of both the seagrass bed and nearshore region, suggesting that the origin of these growth-limiting bacteria are the seagrass biofilm or seawater surrounding the seagrass bed. This study demonstrates that Chattonella growth-limiting bacteria living on seagrass biofilm and in the adjacent seawater can suppress Chattonella blooms, suggesting the possibility of Chattonella bloom prevention through restoration, protection, or introduction of seagrass in coastal areas.

This study tested the responses of leaves and root-rhizomes of eelgrass Zostera marina plants to iron additions in a two-compartment system which allowed the separation of the root-rhizome portion from the stems and leaves. We subjected whole Z. marina plants to seawater containing 500 μg l−1 Fe (reference seawater) and 700 μg l−1 Fe in the leaf and/or root-rhizome compartments for over 30 days under controlled laboratory conditions. We measured plant response in terms of survivorship, morphology, growth and leaf pigment content. The results showed that adding Fe to the leaf compartment resulted in higher survival and stimulated both leaf and root-rhizome growth of the Z. marina plants. However, Fe addition to root-rhizome compartment only obtained higher survival and greater internode diameter and root elongation rate. Survival analysis combined with morphological and dynamic assessment suggested that both the leaves and the root-rhizome system of Z. marina have the ability to absorb iron from their environment but uptake occurs mainly in the leaves from the surrounding water. And the result also suggested that iron is mainly translocated from leaves to root-rhizomes. Furthermore, adding Fe to the leaf compartment stimulated significant increases in leaf chlorophyll contents of the Z. marina plants, is similar to those reported for other seagrass species. This study will further develop our understanding of the physiological ecology of this species and provides data that could prove helpful in the development of successful establishment of Z. marina plants.

This study aimed to elucidate the biological responses of eelgrass (Zostera marina) to artificially induced stresses such as herbicide (Irgarol 1051, Irg) exposure, insufficient light, and high water temperature (27 ± 1.0 °C) by evaluating growth inhibition, photosynthetic activity, and metabolomic profiles. After 14 days, all treatments inhibited growth, but photosynthetic activity was only reduced in the Irg-exposed group. In the Irg-exposed and insufficient light groups, the metabolomic profiles were characterized by decreased levels of sugar (sucrose) and increased levels of amino acids such as glutamine, glycine, and leucine. Biochemical and ultrastructural analyses revealed that the loss of sugar-derived metabolic energy was compensated for by energy generated during autophagic protein degradation. Furthermore, the level of myo-inositol, which has various biological roles and participates in several cellular processes such as cell wall synthesis, stress response, and mineral nutrient storage, was markedly increased in the Irg-exposed and insufficient light groups. A combination of metabolomic analysis with other analyses such as measurement of photosynthetic activity might further elucidate the response of eelgrass to ambient stresses in the natural environment.

The objective of this study was to identify the parasite causing the formation of root hair galls on eelgrass (Zostera marina) in Puget Sound, WA. Microscopic and molecular analyses revealed that a novel protist formed plasmodia that developed into sporangia in root hair tip galls and released biflagellate swimming zoospores. Root hair galls were also observed in the basal section of root hairs, and contained plasmodia or formed thick-walled structures filled with cells (resting spores). Phylogenetic analyses of 18S rDNA sequence data obtained from cells in sporangia indicated that the closest relative of the parasite with a known taxonomic identification was Plasmodiophora diplantherae (86.9% sequence similarity), a phagomyxid parasite that infects the seagrass Halodule spp. To determine the local geographic distribution of the parasite, root and soil samples were taken from four eelgrass populations in Puget Sound and analyzed for root hair galls and parasite DNA using a newly designed qPCR protocol. The percent of root hairs with galls and amount of parasite DNA in roots and sediment varied among the four eelgrass populations. Future studies are needed to establish the taxonomy of the parasite, its effects on Z. marina, and the factors that determine its distribution and abundance.

Photosystem II (PSII) herbicides are widely used and commonly detected in coastal environments and seagrass beds are often exposed to these herbicides. While acute inhibition of seagrass photosynthesis by PSII herbicides has been shown, there are few reports on the potential impacts of herbicide exposures on sexual reproduction and on metabolism. Seagrass Zostera marina L., which were in the process of sexual reproduction, were exposed to elevated atrazine concentrations (1, 3 and 10 μg l−1) for 30 days. Results showed that atrazine significantly inhibited photosynthetic efficiency (ΔF/F’m and Fv/Fm) and significant reduced levels of sugars in shoots. The decreased sugars and C:N ratio implied the long term atrazine exposure (10 μg l−1) decreased energy supply and changed carbon and nitrogen metabolism. Atrazine induced increases in γ-aminobutyric acid (GABA) and 1-aminocyclopropane carboxylic acid (ACC). GABA may be involved in C and N metabolism and in combination with ACC to participate in more complicated signal transduction processes. The effects of atrazine on eelgrass energy reserves and metabolism may lead to inhibition on plant growth. Though no significant decreased sexual reproduction effort was found, there may be potential effect of herbicide on eelgrass shoots, especially rhizome function of energy storage and thus on energy investment in flowering.

A restored Zostera marina population was established at Xiaoheishan Island in 2013 using seeds transplanted from a natural population in Lidao Bay (Shandong Provence, Northern China). To determine the factors influencing restoration outcomes and to evaluate restoration efficacy, growth characteristics of both natural and restored populations were monitored, and water column and sediment chemical parameters were examined by field investigation during 2014–2016. In addition, shoot density biomass were assessed alongside environmental variable measurements. The results showed that there were no significant differences in chemical oxygen demand, suspended solids, or NH4+, NO2−, and NO3− concentrations among sampling times, and there were no distinct seasonal trends. Mean (and range) heavy metal, sulfide, and total petroleum sediment concentrations were similar, and shoot height exhibited significant seasonal variations at both sites. Leaf N and P content, and N/P ratio were significantly varied among sampling times and between sites, respectively. In Lidao Bay, shoot density was significantly correlated with Cu2+ sediment concentration, whereas N/P ratio and root: shoot ratio were significantly correlated with As2+. At Xiaoheishan Island, shoot density and root: shoot ratio were significantly correlated with water column total petroleum and NH4+, respectively. This indicates that the restored population was similar to the natural population with regards to growth characteristics but differences between chemical parameters in the water column and sediment may affect longer term growth and restoration outcomes.

Macroalgae and seagrasses form the base of productive ecosystems in the Northeastern Pacific Ocean. Often, ecological research on macroalgae, seagrasses, and sea wrack requires the conversion of biomass from wet to dry to create consistency across investigations. This process, however, can be destructive, impractical, time consuming, and labour intensive. We collected samples of twelve common Northeastern Pacific Ocean seaweed species (Alaria marginata, Codium fragile, Egregia menziesii, Fucus distichus, Macrocystis pyrifera, Mazzaella spp., Nereocystis luetkeana, Pterygophora californica, Pyropia spp., Ulva spp., and the seagrasses Zostera marina and Phyllospadix spp.) in two states: wet and fresh, or aged and partially desiccated. We weighed, dried, and compared samples, finding that many species displayed a strong (R2 > 0.8) and predictable linear relationship between wet and dried conditions. In contrast, half the aged samples did not have a significant relationship between partially desiccated and dried conditions. Our results provide practical wet weight to dry weight ratios for many species, and with further research, a reliable set of species-specific wet to dry weight ratios for all species could be established. Wet to dry weight ratios are useful for macroalgae, seagrass, and sea wrack research or commercial applications and would reduce the need to conduct extensive wet-dry calibrations in each study.

Seagrass meadows ecosystem engineering effects are correlated to their density (which is in turn linked to seasonal cycles) and often cannot be perceived below a given threshold level of engineer density. The density and biomass of seagrass meadows ( Z. marina ) together with associated macrophytes undergo substantial seasonal changes, with clear declines in winter. The present study aims to test whether the seasonal changes in the density of recovering seagrass meadows affect the benthic food webs of the southern Baltic Sea (Puck Bay). It includes meiofauna , macrofauna and fish of vegetated and unvegetated habitats in summer and winter seasons. Two levels of organization have been tested – species-specific diet preferences using stable isotopes ( δ13C, δ15 N) in Bayesian mixing models (MixSIAR) and the community-scale food web characteristics by means of isotopic niches (SIBER). Between-habitat differences were observed for grazers, as a greater food source diversity in species from vegetated habitats was noted in both seasons. Larger between-habitat differences in winter were documented for suspension/detritus feeders. The community-wide approach showed that the differences between the habitats were greater in winter than in summer (as indicated by the lower overlap of the respective isotope niches). Overall, the presence of seagrass meadows increased ecological stability (in terms of the range of food sources utilized by consumers) in the faunal assemblage , while invertebrates from unvegetated areas shifted their diet to cope with winter conditions. Therefore, as a more complex system, not sensitive to seasonal changes, Z. marina meadows create a stable habitat with high resilience potential.

Mesopredators must contend with both top-down (predation pressure by top predators) and bottom-up (food availability) drivers when selecting habitat. We studied the distribution and trophic dynamics of an abundant mesopredator (the three-spined stickleback; Gasterosteus aculeatus) in three habitats of differing complexity: a macroalgal bed (Fucus vesiculosus), a seagrass meadow (Zostera marina), and a sand flat. We found that stickleback abundance and food availability were highest in the macroalgae, intermediate in the seagrass, and very low in the sand flat. We then tested in situ predation pressure on isopods and amphipods by tethering live prey in the three habitats. Predation on amphipods was very high in early summer, when it was highest in the sand flat, intermediate in the seagrass, and lowest in the macroalgae. However, small-scale within-habitat differences in physical complexity (shoot density) or location (interior vs. edge) did not affect predation rates. Predation rates on amphipods decreased with prey size, but predation on isopods was always low. Laboratory experiments using amphipod prey and stickleback predators supported the patterns observed in the field, where predation success was highest in the sand and lowest in the Fucus. Overall, sticklebacks were more abundant in, and preferentially chose, the two habitats with highest structural complexity (the macroalgae bed and seagrass meadow), potentially trading off low predation success for higher food availability and increased shelter from top predators. These results confirm the critical importance of these structured habitats for coastal trophic networks.

Seed dispersal plays an important role in the spread of eelgrass (Zostera marina). In order to study the temporal and spatial patterns of eelgrass seed dispersal in Moon Lake, Shandong, China, a continuous eelgrass meadow without outlying patches in a subtidal area was selected and assumed as the source of seed dispersal in the experiment. A square plot of 8 m by 8 m was set up inside the meadow and another two plots of the same size were also set up outside the meadow. Seed traps made of artificial turf were used to collect seeds transported by currents during the study period. Results showed that the potential seed production of the selected bed was 10,028 ± 4874 seeds m−2 and seed dispersal lasted from July to September. In all experimental plots, the highest densities of seed rain during a half-month period were observed in July. After two months, the average density of seed rain across all transects inside the meadow was 154 ± 27 seeds m-2, while outside the meadow, the density decreased nearly to zero. Over the entire study period, the average seed rain density across all transects inside the meadow was 1634 ± 94 seeds m−2, while at a distance of 8 m away from the meadow either downstream or perpendicular to the main tidal current direction, the average accumulated density of seed rain was 515 ± 80 and 203 ± 42seeds m−2, respectively. Our results indicate that though most of the seed rain falls within the parent bed in Moon Lake, tidal currents can disperse the seeds at a distance of 8 m, and besides tidal currents, seeds might also be dispersed in other ways, such as seed predators, wind-driven waves and other processes.

Seagrass meadows with more than two species co-occurring at a small scale are unusual in temperate regions, and such multispecies seagrass beds are undocumented in the Northeastern Pacific. Seagrasses in multispecies beds may coexist through trait differentiation in body size, life history types and phenology, especially when competitive exclusion is interrupted by environmental variability. Here, we survey and manipulate a multispecies seagrass meadow in Willapa Bay, Washington (USA), containing Zostera marina, Zostera japonica and Ruppia maritima; our 13-month survey is the first formal documentation of multispecies seagrass bed occurrence in the Northeastern Pacific. Z. japonica, a non-native species, reached an end-of-summer biomass that was an order of magnitude greater than either native seagrass. To test competition, we experimentally removed Z. japonica and found competition occurred disproportionately on the smaller R maritima relative to larger Z. marina. R. maritima germinated later and senesced earlier than the two Zostera species, and the removal of Z. japonica positively affected R. maritima biomass, supporting previous studies that R. maritima is an opportunistic species. In addition to species-specific phenology and body size, all species presented annual life histories and thus began each annual cycle under high resource availability, such as light, space and nutrients, which may contribute to coexistence.

Aquatic plant meadows are valuable components to the ‘coastal filter’ and it is important to understand the processes that drive their ability to cycle nutrients. However, at present, the field-based evidence for understanding the drivers of nutrient uptake by plants is lacking. This study aimed to investigate how well individual shoots of aquatic plants could meet their nitrogen demands using the sediment nutrient pool (porewater ammonium) and to explore which traits helped to facilitate such uptake. Several species were investigated in shallow, submerged (2–4 m) mixed-species communities in the northern Baltic Sea using incubation experiments with enriched ammonium. After a 3.5 h incubation time, individuals were collected and analysed for nitrogen (% DW) and 15N (at-%) concentrations. Uptake by plants was calculated per unit nitrogen in response to the 15 N-labelled source and to overall nitrogen availability. Background porewater ammonium availability was highly variable between individual plants. Species identity did not significantly affect uptake metrics and the effect of ambient porewater availability was weak. As biomass increased there were significant logarithmic declines in the 95th quantiles of nutrient uptake rates, ambient porewater nutrient availability and aboveground nitrogen tissue concentrations (% DW). Such findings suggested that uptake rates of plants were significantly demand-driven and the nutrient conditions of the porewater were significantly driven by the demands of the plant. Findings parameterised the unfulfilled potential for some aquatic plants to cycle nutrients more efficiently and highlighted the potential importance of access to new nutrient sources as a way of enhancing nutrient cycling by aquatic plants. Plant traits and community properties such as the activity of infauna could facilitate such an access and are likely important for nutrient uptake.

Seagrasses are major coastal primary producers and are widely distributed on coasts worldwide. Seagrasses show sensitivity to environmental stress due to their high phenotypic plasticity, and therefore, we evaluated the use of constituent elements in four dominant seagrass species as early warning indicators for nitrogen eutrophication of coastal regions. A meta-analysis was conducted with published data to develop a global benchmark for the selected indicator, which was used to evaluate nitrogen loading at a global scale. A case study at three bays was subsequently conducted to test for local-scale differences in leaf C/N ratios in four seagrasses. Additionally, morphological and physiological metrics of seagrasses were measured from the three locations under varied nitrogen levels to develop further assessment indexes. The benchmark and local study showed that leaf C/N ratios of Zostera marina were sensitive to nitrogen discharge, which could be a highly valuable early warning indicator on a global scale. Moreover, the threshold value of seagrass leaf C/N was determined according to the benchmark to differentiate eutrophic and low nitrogen levels at a local scale. Of the eight phenotypic metrics measured, leaf width, total chlorophyll ( a + b ), chlorophyll ratio ( a / b ), and starch in the rhizome were the most effective at discriminating between the three locations and could also be promising indicators for monitoring eutrophication.

Seagrass habitats are highly productive areas that support vegetative habitats and provide shelter for various marine animals. In seagrass beds, vegetation patterns are important factors that control faunal assemblage structure. In this study, we surveyed fish assemblage structures in Zostera marina beds and in adjacent unvegetated habitats to assess the influences of seagrass vegetation and biomass on fish assemblage structures. In total, fifty-four fish species belonging to 30 families were collected using a small beam trawl at both seagrass beds and unvegetated habitats from two different areas off the coast of Namhae Island, South Korea. The dominant fish species in seagrass beds were Sebastes inermis and Rudarius ercodes, whereas Acanthogobius flavimanus and Takifugu niphobles were the most abundant fish species in unvegetated habitats. The number of species, their abundance, and the diversity of fish assemblages varied greatly by habitat type, study site, and season. Abundance peaked in seagrass beds and during the spring, and were lowest catch rate in unvegetated habitats and during the winter months. Multivariate analyses revealed that habitat type, site, and season affected the structure of fish assemblages. Seagrass vegetation supported higher densities and greater fish species richness, but not species diversity. Among the dominant species, Lateolabrax japonicus, Sebastes schlegelii, Syngnathus schlegeli, and Rudarius ercodes characterized the fish assemblages in seagrass beds, with the former two more abundant under conditions of higher seagrass biomass. Gobiid species were significantly correlated with unvegetated habitats.

The relationship between seagrasses and pore-water hydrogen sulfide in the sediment is complex due to the opposing effects of the seagrass root system, which can reduce sulfide concentration by promoting its oxidation to sulfate, and the burial of organic matter from the plant itself, which can increase sulfide concentration by stimulating anaerobic sulfate reduction. Here, field samples of pore-water sulfide were collected in areas with and without Zostera marina shoots using Diffusive Gradients in Thin-Films (DGTs) to obtain two-dimensional visualizations of sulfide concentrations within the sediment in relation to location of eelgrass detritus and the rhizosphere. To decouple the effects of leaf detritus and the eelgrass rhizosphere on sulfide, manipulative laboratory studies were conducted over 4 weeks using 10 aquaria with or without eelgrass and different quantities of eelgrass detritus planted at 4 cm and 11 cm depths. Spatial distribution of pore-water sulfide was again measured via DGT. We found high spatial variation in pore-water sulfide concentration depending on the location analyzed relative to the rhizosphere or detritus. In the field study, pore-water sulfide concentration was greater in samples with eelgrass present, and the presence of leaf detritus accounted for higher than average sulfide concentrations in the sediment. In the laboratory experiment, sulfide concentrations localized around the leaf detritus increased with higher mass of added detritus, and sediment within the rhizosphere exhibited reduced sulfide concentrations. These results suggest that on the large scale the presence of eelgrass increases sulfide concentration, but on the smaller scale the pattern varies, with higher concentrations near buried detritus and lower concentrations near root tips.

Epiphytes on seagrass (Zostera marina) growing in the lower intertidal were examined along an estuarine gradient within Yaquina Bay, Oregon over a period of 4 years. The Yaquina Estuary receives high levels of nutrients from the watershed during the wet season and from the ocean during the dry season. Mean epiphyte biomass per unit seagrass leaf surface area (epiphyte load) peaked during the summer, and thus epiphyte load was higher during dry season than wet season in both marine and riverine dominated regions. Epiphyte load was greater in marine than in riverine dominated areas in both wet and dry seasons, although only dry season differences were significant. There was no evidence that grazers controlled epiphyte load differences. Annual DIN concentration was inversely related to epiphyte load, principally because of elevated wet season dissolved inorganic nitrogen from river inputs. While there was a positive annual relation of epiphyte load to PO(4) concentration, it is not clear that phosphorus becomes a limiting nutrient for epiphyte growth. Water column light attenuation tends to increase linearly with distance from the estuary mouth, while both epiphyte load and Z. marina biomass tend to decrease. Both seagrass and seagrass epiphytes may be increasingly light limited in the upper estuary, and thus, epiphyte loads may have proportionally more impact on seagrass occurrence in this estuarine region.

Seagrass meadows are among the most diverse and productive coastal ecosystems in the world. Currently, the accelerating loss of these habitats is recognized worldwide. In the southern Baltic Sea, a natural recovery of Zostera marina meadows has occurred after a dramatic reduction within the last century. The aim of this study is to understand if and how the recovering eelgrass meadows affect the functioning of benthic ecosystems. The trophic links within the benthic food webs in the seagrass meadows and bare sandy bottoms were depicted and compared. The trophic connections were examined by combining stable isotope (SI) composition (δ13C, δ15N) and fatty acid (FA) profiles of meio- and macrofauna consumers and of potential food sources (particulate organic matter, surface sediment organic matter, epiphytes, microphytobenthos/bacteria and macrophytes) in a Bayesian mixing model framework (MixSIAR). Significantly higher amounts of the FA bacterial marker (C18:1ɷ7) were observed in meiofauna (approximately 40%) than in the macrofauna (1% on average), suggesting that bacteria are an important part of the meiofauna diet. The mixing model results indicated that the benthic consumers in the vegetated habitat utilized more food sources (e.g., epiphytes in the diets of meiofauna and macrofaunal grazers) and thus had a more diverse diet. Macrofaunal omnivores relied to a larger degree on animal-derived organic matter in vegetated habitat, which could be linked to higher invertebrate prey availability. The results highlight the importance of recovering seagrass meadows in driving the mechanisms responsible for food web organization. Any type of change to the state of seagrass meadows is crucial to the functioning and stability of marine ecosystems.

Edge effects may be important drivers of community dynamics across marine habitat mosaics. Past research has consistently suggested that within temperate and sub-tropical seagrass habitats, organisms inhabiting meadow edges experience lower survivorship, presumably correlated with increased predation. However, these survivorship trends have not consistently translated to differences in faunal densities between edge and interior regions of seagrass meadows. We evaluated the evidence of edge effects on predation upon two dominant mesopredators within temperate eelgrass (Zostera marina) communities of the U.S. East Coast: blue crabs (Callinectes sapidus) and pinfish (Lagodon rhomboides). We considered three lines of data to arbitrate the null hypothesis that edge has no impact on distribution or predation on blue crabs or pinfish: (1) relative density as measured by catch-per-unit-effort (CPUE) of blue crabs and pinfish within edge ( 3 m from unstructured sandflat boundaries) regions of eelgrass meadows; (2) distribution of acoustically tagged red drum (Sciaenops ocellatus), a recognized predator of both blue crabs and pinfish, within eelgrass meadows (at 1-m bin resolution); and (3) relative mortality of tethered blue crabs and pinfish within edge versus interior regions of eelgrass meadows. Additionally, we manipulated seagrass shoot density to evaluate potential interactions between local habitat complexity and edge effects. We found no statistically detectable difference in catch rates of blue crabs or pinfish in edge versus interior habitats, and red drum detection frequencies were statistically indistinguishable moving from the seagrass-sandflat boundary toward the meadow interior. Despite these findings, we did record statistically and ecologically significant edge effects on predation rates of tethered blue crabs and pinfish. Counter to previous work, we found that blue crabs survived >2.5× longer, and pinfish survived >2× longer, along the meadow edge relative to interior. Furthermore, the strength of these predation-related edge effects was most notable for blue crabs within plots with higher shoot density, while the opposite pattern was true for pinfish. These findings are, in part, consistent with the dichotomy apparent in the seagrass literature with respect to edge effects on faunal density and survivorship. Additionally, our work provides new detail on how habitat edges may affect the population ecology of larger bodied, more mobile mesopredator species that have not received as much attention in previous studies (i.e., higher survivorship possible along edges).

This paper presents a model of the cross-shore beach profile taking into account the presence of the seagrass Posidonia oceanica whose ultimate objective is to reduce the volume of sand used in beach nourishment. The methodology describes the training, validation, testing and application of models of artificial neural networks (ANN) for computing the cross-shore beach profile of sandy beaches in the province of Murcia (Spain). Eighty ANN models were generated by modifying both the input variables and the number of neurons in the hidden layer. The input variables consist of wave and sediment data and data concerning the Posidonia oceanica. To select and evaluate the performance of the optimal model, the following parameters were used: R2, absolute error, mean absolute percentage error and percentage relative error. The results show a mean absolute error of 0.22 m (0.21 m in training and 0.28 m in test), representing an improvement of 85.1% compared to models that do not use the Posidonia oceanica and 69.8% against those that consider it. Although the ANN was developed for beaches with P.oceanica, it could be used in areas with other seagrass able to reduce wave energy and consolidate the sand such as Syringodium filiforme, Thaalassia testudinum, Laminaria hyperborea, Halodule wrightii and Zostera marina. This work was partially supported by the Universidad de Alicante through the project “Estudio sobre el perfil de equilibrio y la profundidad de cierre en playas de arena” (GRE15-02).

Seagrass meadows provide ecosystem services that contribute to climate mitigation and ecosystem resilience in coastal environments, being recognised among the most effective carbon sink ecosystems on Earth. Although seagrass meadows are declining worldwide at alarming rates, direct measurements of the consequences of habitat degradation on the sedimentary carbon stock remains still scarce. The aim of this study is to investigate the effects of the physical disturbance caused by clam harvesting on the capacity of a subtidal Zostera marina meadow to accumulate organic matter and sequester carbon. Biotic (seagrass cover, density and biomass) and abiotic factors (water depth and sediment grain size distribution) of the studied meadow were characterized and carbon stocks in control and impacted areas of vegetated and bare sand zones were compared. The physical disturbance resulted in a significant reduction in shoot density (63%) and biomass (64%) in the impacted area with respect to the adjacent zone not affected by the disturbance, whereas the sedimentary carbon stock was reduced by 50%, reaching similar levels to those recorded in un-vegetated areas. The meadow exposed to the harvesting activity showed a decreasing capacity to sequester carbon by reducing the seagrass standing stock and carbon preservation in the associated sediments. Thus, clam harvesting activity not only eroded the historical carbon stock accumulated over decades but also endangers further potential accumulation. Therefore, sustainable management of the exploited area should take into account not only the durability of clam stocks but also the resilience of the seagrass meadow and its capacity to provide critical ecosystem services.

Eelgrass (Zostera marina) differs in shoot size, growth rate, and life history investment along a 30-km estuarine gradient in Willapa Bay, Washington (USA). In this study, reciprocal transplants were carried out among four sites in the estuary to test the roles of source population and outplant site for summer-season performance, a method that distinguishes any advantage of locally-tuned phenotypes and whether such trait differences are fixed or phenotypically-plastic. Shoots were measured after 2–3 months for size, leaf emergence rate (productivity) and shoot emergence rate (fitness), as well as simply finding them again (retrieval). Results generally did not support that best performance came from local shoots (few source x outplant site interactions). However, at one site, local shoots had higher fitness than other sources, and for one source, local retrieval exceeded that at other sites. Across all outplants, retrieval improved with rhizome length, suggesting that longer rhizomes provided better anchors. Fitness and productivity were both reduced for transplants into eelgrass relative to those in nearby bare areas at most sites, likely reflecting strong intraspecific competition for transplanted shoots. At this within-estuary scale in summer, morphology appeared entirely plastic, given convergence to local size, but annual vs. perennial life history was strictly a function of source population regardless of outplant site. This reciprocal transplant study supports many of the best practices for restoration, which include effective anchoring of shoots into locations with suitable environmental conditions. Matching donor populations for life history may be more important than for size, given differential phenotypic plasticity in these traits.

We quantified the shallowing of the seafloor in five of six bays examined in the Chignik region of the Alaska Peninsula, confirming National Ocean Service observations that 1990s hydrographic surveys were shallower than previous surveys from the 1920s. Castle Bay, Chignik Lagoon, Hook Bay, Kujulik Bay and Mud Bay lost volume as calculated from Mean Lower Low Water (Chart Datum) to the deepest depths and four of these sites lost volume from Mean High Water to the deepest depths. Calculations relative to each datum were made because tidal datum records exhibited an increase in tidal range in this region from the 1920s to the 1990s. Our analysis showed that Mud Bay is quickly disappearing while Chignik Lagoon is being reduced to narrow channels. Anchorage Bay was the only site that increased in depth over time, perhaps due to erosion. Volcanoes dominate the landscape of the Chignik area. They have blanketed the region in deep ash deposits before the time frame of this study, and some have had smaller ash-producing eruptions during the time frame of this study. Remobilization of land-deposited ash and redeposition in marine areas - in some locations facilitated by extensive eelgrass (Zostera marina) beds (covering 54% of Chignik Lagoon and 68% of Mud Bay in 2010) - is the most likely cause of shallowing in the marine environment. Loss of shallow water marine habitat may alter future abundance and distribution of several fish, invertebrate and avian species.

A disjunct population of the annual form of the seagrass Zostera marina that occurred in the upper intertidal zone of Yaquina Bay, Oregon was sampled to determine whether there were differences in recruitment, growth, survivorship and morphology associated with microtopographic location on the sand flat. Population responses of seagrass found in areas differing by only a few cm in vertical elevation were compared. There was higher plant abundance and higher number of shoots per plant in microtopographic low areas. Plants in lower areas also had significantly longer shoots, greater total above ground biomass, greater biomass per shoot, and greater biomass of reproductive spathes than plants growing in immediately adjacent, microtopographic high areas. Cover of green macroalgae was higher and accumulated more rapidly in microtopographic high areas as compared to low areas, and both spatially and temporally was correlated with decreased recruitment and increased plant loss in these slightly elevated areas. While impacts of desiccation may have played some role in determining the influence of microtopographic variation on the annual Z. marina population, macroalgal effects appear to be predominant.

Eelgrass (Zostera marina) flowering development and seed production were assessed along a depth gradient at three sites during 2012 and 2013 to 1) describe the flowering seasonality in the Swedish west coast, and 2) evaluate methods using seeds for large-scale restoration, including harvesting, storage and separation of viable seeds using a vertical flume. Eelgrass flowering shoots were found in the field from June to October, reaching the highest densities in July and August (average 3.8 ± 0.5 shoots m−2). Flowering shoot densities decreased with depth, whereas shoot length, number of spathes, seeds/shoot and seed size increased with depth, resulting in the highest seed production at intermediate depths (2 m) in most bays and years. Because of low densities of flowering shoots, seed production in Sweden (on average 39–126 seeds m−2, Jul–Sep) was an order of magnitude lower than in other studied areas. Results showed that seed production differed 2.5–3.4 times between meadows and years, mainly driven by variation in seed production per shoot. This variation was only partly explained by temperature over the growing season, suggesting that other factors such as light and the amount of filamentous algal mats might also be important in flower development. Results suggest that flowering shoots should be harvested when >50% of the spathes have developing seeds, and that shoots should not be stored longer than 40 days in tanks to obtain an optimal release of viable seeds. A new mechanized method using a vertical flume to separate large amounts of viable seeds from the harvest is also presented.

One approach to identifying and mapping the state of marine biophysical conditions is the identification of large-scale ecological units for which conditions are similar and the strategies of management may also be similar. Because biological processes are difficult to directly record over large areas, abiotic characteristics are used as surrogate parameters. In this work, the Mediterranean Sea was classified into homogeneous spatial areas based on abiotic variables. Eight parameters were selected based on salinity, sea surface temperature, photosynthetically active radiation, sea-wave heights and depth variables. The parameters were gathered in grid points of 0.5° spatial resolution in the open sea and 0.125° in coastal areas. The typologies were obtained by data mining the eight parameters throughout the Mediterranean and combining two clustering techniques: self-organizing maps and the k-means algorithm. The result is a division of the Mediterranean Sea into seven typologies. For these typologies, the classification recognizes differences in temperature, salinity and radiation. In addition, it separates coastal from deep areas. The influence of river discharges and the entrance of water from other seas are also reflected. These results are consistent with the ecological requirements of the five studied seagrasses ( Posidonia oceanica , Zostera marina , Zostera noltei , Cymodocea nodosa , Halophila stipulacea ), supporting the suitability of the resulting classification and the proposed methodology. The approach thus provides a tool for the sustainable management of large marine areas and the ability to address not only present threats but also future conditions, such as climate change.

Documenting distribution patterns of juvenile Pacific herring (Clupea pallasii) can clarify habitat preferences and provide insight into ecological factors influencing early life survival. However, few analyses relating juvenile Pacific herring density to habitat characteristics have been conducted. We sampled age-0 Pacific herring in nine bays and fjords distributed throughout Alaska's Prince William Sound during November over a 3-year period (2013–2015) and investigated associations between catch rate and habitat covariates using generalized linear mixed models. Our results indicated that the night-time distribution of age-0 Pacific herring in the pelagic environment was influenced by proximity to eelgrass (Zostera marina) beds, salinity, and water depth. Age-0 Pacific herring catch rate was negatively associated with tow depth, with herring favoring shallower water across the range of depths sampled (7.2–35.4 m). In addition, Pacific herring distribution was positively associated with fresher water within the sampled salinity gradient (24.1–32.3 psu) and proximity to eelgrass beds. Seasonal changes in juvenile Pacific herring distribution were investigated by sampling one bay over a seven month period (October-April). Age-0 Pacific herring tended to remain in the inner bay region throughout the seven months, while age-1 Pacific herring had shifted from the inner to the outer bay by spring (March-April). Additionally, catch rate of age-0 Pacific herring in areas where ice breakup had just occurred was higher than in open water, suggesting that age-0 herring preferentially select ice-covered habitats when available. Based on our results we recommend that habitat preferences of age-0 Pacific herring should be considered in the development of Pacific herring year-class strength indices from catch data.

WOS:000419410100010; The importance of seagrass habitat for the diversity of benthic fauna has been extensively studied worldwide. Most of the information available is, however, about a diversity while little consideration has been given to 13 diversity. To fill the knowledge gaps regarding the variability of epifaunal and infaunal seagrass assemblages at large spatial and temporal scales, we scrutinized an extensive dataset covering five years of monitoring of eight intertidal Zostera marina meadows around Brittany (France). High species richness arose at the regional scale from the combination of high local diversity of the meadows and substantial among-meadows 13 diversity. Epifauna and infauna appeared as distinct self-communities as they displayed different spatial and temporal patterns and varied in their responses to local hydrological conditions. Infauna had higher total 13 diversity than epifauna due to a tighter link to the great variability of local environmental conditions in the region. Both exhibited substantial variations in species composition and community structure with variations of dominant species that were accompanied by extensive change in numerous rare species. The dominant epifaunal species were all grazers. Changes in species composition were induced mostly by species replacement and rarely by richness differences between meadows. Indeed, species richness remained within a narrow range for all seagrass beds, suggesting a potential carrying capacity for species richness of the meadows. Overall, all meadows contributed equally to the regional turnover of seagrass macrofauna, emphasizing high variability and complementarity among beds at the regional scale. The implications of this substantial within-seagrass variability for the functioning of benthic ecosystems at broad scale and for conservation purposes in habitat mosaics warrant further investigations but our results clearly advocate taking into account within-habitat variation when evaluating the diversity of benthic habitats and the potential effect of habitat loss.

For the first time, this paper proposes natural seagrass based prominent ocean flowering and bio-friendly material for triboelectric nanogenerator (TENG) through a simple spray coating technique. Herein, two different seagrass species (Zostera marina and Phyllospadix japonicus) are effectively applied as a tribopositive material. Furthermore, spray coatable Phyllospadix japonicus seagrass film/PET TENG yields a higher power density of 70.42 μW/cm2 compared to Zostera marina seagrass film/PET TENG of 50.42 μW/cm2 because of the higher oxygen functional groups, which enables the device to offer increased electron-donating capability. Moreover, the output performance of the proposed spray coatable TENG device improved by about 31% compared to powder-based seagrass film. Furthermore, the Phyllospadix japonicus based TENG presents the extraordinary working stability up to 72,000 cycles (2 h), which confirms the excellent robustness of the fabricated device. It is further demonstrated that the proposed Phyllospadix japonicus based TENG can easily charge various commercial capacitors and capable of driving about 150 light-emitting diodes (LEDs), and other microelectronic devices. We anticipate that by applying seagrass as a tribopositive layer, the proposed spray coatable TENG device will serve its promising role for energy generation with extremely low fabrication cost. Furthermore, in addition to the economic use of seagrass as a TENG, this work can favorably contribute to sustainable seagrass management.

Coastal eutrophication has resulted in the rapid loss and deterioration of seagrass beds worldwide. The high concentration of ammonium in eutrophic aquatic environments has been invoked as the main cause. In this study, leaves and roots of the seagrass Zostera marina were treated with simulated eutrophic seawater with elevated ammonium concentrations. The tolerance to ammonium stress and mechanism of nitrogen metabolism detoxification in different tissues were investigated. The results showed that high ammonium stress significantly affected the growth of leaves and had a negative effect on photosynthesis. The root activity of Z. marina was not inhibited at ammonium concentrations of ≤100 mg/L, indicating that the roots exhibited tolerance to ammonium stress. Increasing ammonium concentrations led to a higher increase of ammonium and free amino acid (FAA) contents in leaves than in roots. However, nitrogen storage decreased in Z. marina leaves after high ammonium treatments. The enzyme activity and gene expression of glutamine synthetase (GS) in roots were significantly higher than in the leaves even under ammonium stress. Meanwhile, ammonium stress increased the enzyme activities and gene expression of glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH) in roots, which suggested that the roots had a strong ability to assimilate ammonium under ammonium stress. In contrast, although the GOGAT and GDH activity and gene expression in the leaves were initially increased, they significantly decreased when the ammonium concentration exceeded 100 mg/L. These results indicated that the concentration of 100 mg/L might be a threshold marking a transition from tolerance to toxicity for the leaves. Our study demonstrates that Z. marina leaves could be prone to higher damage than roots because the mechanism of ammonium assimilation in leaves is more susceptible to ammonium toxicity.

Sexual reproduction is critical to the resilience of seagrass beds impacted by habitat degradation or environmental changes, as robust seed banks allow new shoots to establish each year. Reproductive strategies of seagrass beds range on a continuum from strictly annual to perennial, driven by local environmental conditions. We examined the reproductive dynamics of Zostera marina beds at six sites on the Atlantic coast of Canada to characterize how life history strategies are shaped by the surrounding environment. Sites were categorized as wave protected and wave exposed, where protected sites were warm, shallow, with little water movement and muddy sediments, and exposed sites were either shallow or deep, with cooler water and sandy sediments. While mixed life history strategies were evident at all sites, protected eelgrass beds exhibited both the highest and lowest sexual reproductive effort relative to exposed beds. These beds regularly experienced thermal stress, with higher temperature range and extended warm water events relative to exposed beds. The development of reproductive shoots were similar across sites with comparable Growing Degree-days at the beginning and end of anthesis, but the First Flowering Date was earlier at the protected warmer sites relative to exposed sites. With different reproductive shoot density among sites, seed production, seed retention, and seedling recruitment also varied strongly. Only one site, located in a warm, shallow and protected lagoon, contained a mixed life history population with a high reproductive effort (33.7%), strong seed bank, and high seedling establishment. However, a primarily perennial population with the lowest reproductive effort (0.5%) was identified at the warmest site, suggesting that conditions here could not support high sexual reproduction. Robustness of seed banks was strongly linked to reproductive shoot density, although the role of seed retention, germination and seedling survival require further investigation. Our study provides insights into one key aspect of seagrass resilience, and suggests that resilience assessments should include reproductive shoot density to inform their management and conservation.

The aim of this study was to assess the relative importance of phytomer organogenesis, mortality, and elongation rates on the rhizome length of Eelgrass (Zostera marina). Rhizome length has both a discrete and a continuous component, which are the number of internodes and their lengths, respectively. We hypothesize that rhizome length would be more correlated with elongation rates than either phytomer organogenesis or mortality. An individual-based model was used to simulate the growth of Z. marina individuals in the Punta Banda estuary in Baja California, a low-latitude Eelgrass population. Individuals of the model were composed of a rhizome and lateral branches, both of which were composed of phytomers. The individuals changed by presenting horizontal growth, clonal reproduction, aging, and age-related mortality. Some growth rates were modeled with respect to environmental conditions. The model was validated by comparing the rhizome length of simulated and observed plants. A sensitivity analysis suggested that simulated rhizome length is most correlated to elongation rates, which are mainly affected by water temperature and irradiance.

Seagrasses are highly productive ecosystems and hotspots for biodiversity, providing a plethora of benefits to the environment and to people. Their value in sequestering and storing carbon is increasingly being recognised, as the world searches for ways to mitigate the effects and slow the pace of climate change. However, many uncertainties remain, with basic information such as average carbon stocks, variability and species-specific differences missing for many regions. This study evaluates, for the first time, the carbon storage capacity of Zostera noltii and Zostera marina from intertidal seagrass meadows in Scotland. Sediment carbon stocks in the top 50 cm from vegetated and reference unvegetated plots were quantified at 10 estuaries distributed along the Scottish east and west coasts. The organic carbon stocks in the top 50 cm of the seagrass sediment ranged from a minimum of 14.94 Mg C ha−1 at the Moray Firth to a maximum of 105.72 Mg C ha−1 at the Firth of Forth, with a mean (±SD) of 54.79 ± 35.02 Mg C ha−1 across the 10 estuaries sampled. Moreover, seagrass areas showed enhanced carbon storage compared to reference unvegetated ones, however this was highly variable across depth, and among sites and estuaries. This paper addresses key gaps in knowledge concerning the role of intertidal Scottish seagrass meadows as carbon sinks and discusses the implication of this emerging information for their effective management and conservation.

Zostera marina, a widespread seagrass, evolved from a freshwater ancestor of terrestrial monocots and successfully transitioned into a completely submerged seagrass. We found that its oxygen-evolving complex (OEC) was partially inactivated in response to light exposure, as evidenced by both the increment of the relative variable fluorescence at the K-step and the downregulation of the OEC genes and proteins. This photosynthetic regulation was further addressed at both proteome and physiology levels by an in vivo study. The unchanged content of the ΔpH sensor PsbS protein and the non-photochemical quenching induction dynamics, described by a single exponential function, verified the absence of the fast qE component. Contents and activities of chlororespiration, Mehler reaction, malic acid synthesis, and photorespiration key enzymes were not upregulated, suggesting that alternative electron flows remained unactivated. Furthermore, neither significant production of singlet oxygen nor increment of total antioxidative capacity indicated that reactive oxygen species were not produced during light exposure. In summary, these low electron consumptions may allow Z. marina to efficiently use the limited electrons caused by partial OEC photoinactivation to maintain a normal carbon assimilation level.

Ecotones are ecological boundaries or areas of transition between ecosystems. They are sensitive indicators of global change, and studying their dynamics can be useful to predict habitat shifts and landscape transformation. The Ulva-Zostera ecotone in Elkhorn Slough (California, United States) is a good example of a transitional area between habitat-forming macrophytes in a highly eutrophic coastal system. This study focused on understanding its driving factors, spatiotemporal trends, and overall ecological implications. A combination of habitat monitoring, recruitment and transplant experiments, and sediment analysis were used to describe the ecological characteristics of the system. Ecotone dynamics were driven by seasonality of Ulva spp., its distribution across the ecotone delimited by processes affecting its early developmental stages. While water quality and light availability were not linked to abundance and distribution of Ulva spp., sediment composition likely affected macrophyte distribution and overall ecosystem structure. Remarkably, physico-chemical conditions that hinder growth and expansion of Ulva spp. occur where eelgrass (Zostera marina) is present. Understanding the processes involved in habitat boundary dynamics is important to identify stressors and anticipate change at larger scales.

A major highlight of restoration efforts is to improve the ecological structure and function of the natural ecosystem in the restored habitat. Assessment of restoration success is a crucial component of an optimal ecological management strategy. In studies to determine the restoration success of a transplanted seagrass habitat by assessing trophic recovery, we examined carbon and nitrogen stable isotope ratios of organic matter sources and macrobenthic assemblages in a transplanted eelgrass Zostera marina bed. The eelgrass bed was restored about 2 years after transplantation in a southern coastal bay of Korea, and consequently, the food web structure in the bed was compared with that in a natural reference site. Our results revealed no significant differences in isotopic values of both macrobenthic consumers and their putative food sources between the transplanted and natural seagrass beds. These isotopic similarities in florae and faunae in the two beds suggest a uniformity in food web structure formed by the diversity and availability of resources, and thereby suggest similarities in the resource–consumer relationship. Isotopic niche indices and high dietary overlaps of feeding guilds in the transplanted and natural beds further suggest the transplanted habitat provides similar ecological functions and ecosystem services to its natural counterpart. Collectively, our results suggest the eelgrass transplantation led to successful restoration of a common seagrass bed, with recovery of the functional properties of the food web structure. Finally, our findings support the idea that stable isotope measures can provide a better understanding of the functioning of restored ecosystems, and improve post-transplantation monitoring efforts for the future planning and managing of successful habitat restoration.

Microplastic (MPL) contamination in the marine environment is extensively studied yet little is known about the extent of MPL abundance in seagrass beds. The aim of this study was to evaluate MPL accumulation in coastal seagrass (Zostera marina) beds in the Baltic Sea, Estonia. Surface water was sampled by pumping using 40 μm plankton net, and sediments by trowel. MPL was extracted with NaCl, identified by microscopy and ATR-FTIR on selected samples. Surface water in the seagrass beds had 0.04–1.2 (median 0.14) MPL/L, similar to other areas of the Baltic Sea. Sediments had 0–1817 (median 208) MPL/kg (dwt), much higher than previously recorded from adjacent unvegetated and offshore sediments, thereby suggesting a strong ability of the sediments in seagrass beds to retain MPL. Of identified MPL, blue fibres were dominant in both the sampled media. Sediment characterization showed a correlation between MPL counts with poorly sorted sediments.

Seagrass beds are highly productive coastal ecosystems that are widely distributed along temperate and tropical coastlines globally. Although seagrass distribution and diversity have been widely reported on a global scale, there have been few reports on seagrass distribution and diversity in northern China, especially for coastal waters of the Liaodong Peninsula in the North Yellow Sea. In the present study, we investigated the distribution and diversity of seagrass in coastal waters of the Liaodong Peninsula in the North Yellow Sea, northern China. Field surveys of seagrass wrack were conducted along shorelines, to identify whether seagrass beds occurred in nearby waters, and sonar methods were then used to collect data relating to seagrass bed extent. Also, we analyzed the major threats facing seagrass beds. The results of the study revealed that four species (Zostera marina L., Z. japonica Aschers. & Graebn., Z. caespitosa M., and Phyllospadix iwatensis M.) were found in study area, covering a total area of 1253.47 ha. Seagrass bed area significantly decreased with increasing water depth, and most seagrass was recorded at depths of 2–5 m. Due to the steep slope of the seabed, seagrass beds exhibited a zonal distribution in most of the study areas. In addition, the amount of seagrass wrack along shorelines could be used to infer the size and distance of seagrass beds. Human activities, such as clam harvesting, land reclamation, coastal aquaculture pose a threat to the seagrass beds. This study provides new information to fill knowledge gaps regarding seagrass distribution in northern China and it provides a baseline for further monitoring of these seagrass beds.

Anthropogenic impacts on coastal areas have led to an increased degradation of marine environments globally. Eelgrass ecosystems are particularly susceptible to human induced stressors as they are sensitive to low light conditions and usually grow in shallow protected areas where pressure from coastal development is high. The extensive decline in coverage of eelgrass along the Swedish Northwest coast since the 1980s has largely been attributed to the effects of coastal eutrophication and overfishing. However, the impact on eelgrass from small-scale coastal development (docks and marinas) has never been investigated in this area. The aim of this study was to assess the local and large-scale effect of shading by docks and marinas on eelgrass habitats along the Swedish NW coast and to investigate the decision process behind small-scale exploitation to identify problems with the current legislation, which allows for continued exploitation of eelgrass. Through field assessments of eelgrass around docks and analysis of available data on eelgrass and dock distribution along the coast, the present study demonstrates that shading from docks reduced eelgrass coverage with on average 42–64% under and adjacent to the docks, and that floating docks affected larger areas and caused a much stronger reduction in eelgrass coverage (up to 100% loss) compared to docks elevated on poles (up to 70% reduction in coverage). The total eelgrass area negatively affected by docks and marinas along the NW coast was estimated to approximately 480 ha, an area corresponding to over 7% of the present areal coverage of eelgrass in the region. The analysis of decisions for dock construction showed that eelgrass was generally not assessed or considered in the decision process and that 69–88% of the applications were approved also in areas where eelgrass was present. Furthermore, marine protected areas only marginally reduced the approval of applications in eelgrass habitats. The continued small-scale development along the Swedish NW coast constitutes a significant threat to the already decimated coverage of eelgrass along the coast and changes in the management practices are needed in order to achieve both national and international goals on environmental status.

Intertidal seagrass has been selected as a Biological Quality Element for the assessment of ecological status under the Water Framework Directive. In Ireland, two species of seagrass, Zostera marina and Z. noltei occur in intertidal habitats. This study presents the first comprehensive assessment of the distribution and Water Framework Directive status of intertidal seagrass in the Republic of Ireland and Northern Ireland. Most of the areas assessed, using the Water Framework Directive-compliant assessment tool, have a status of HIGH or GOOD. Only two areas were found to have a status less than GOOD and in both, the cause for the decline was smothering by opportunistic foliose green macroalgae. Linear regression showed a relationship between pressure index scores and Ecological Quality Ratio, showing the relevance of the index as a metric of anthropogenic pressure. Trace element concentrations were examined in Z. noltei tissues and Trace Element Pollution Index values were calculated. The relationship between Trace Element contamination and Water Framework Directive status was examined but the results showed little correlation. However, a relationship between the pressure index and trace element contamination was obtained. This assessment provides the most comprehensive overview of intertidal seagrass beds in Ireland and establishes a strong baseline for ongoing monitoring and assessment under the Water Framework Directive. The data provide key information on the pressures affecting these valuable habitats which will assist in the development of measures to improve and protect our transitional and coastal waters.

Seagrass meadows are important sites of nitrogen (N) transformations in estuaries, however, the role of N loading in driving relative rates of N fixation and denitrification in seagrass habitats is unclear. The current study quantified N fluxes in eelgrass meadows (Zostera marina (L.)) and nearby unvegetated sand in trials representing in situ and N enriched conditions. Net N2 fluxes were low or negative under in situ conditions in both eelgrass and sand. Under N enriched conditions, denitrification was higher than N-fixation, and denitrification in eelgrass was significantly higher than sand. Denitrification of water column NO3- was more significant than coupled nitrification-denitrification in the eelgrass. Denitrification was likely supported by greater organic carbon and N within the eelgrass sediment compared to sand. Eelgrass meadows in Shinnecock Bay may facilitate the ecosystem service of N removal and retention during short-term nutrient pulses that can originate from groundwater discharge and stormwater runoff.

Seagrass meadows perform several important ecological roles in coastal areas. However, with multiple stressors threatening these aquatic plants, their current rate of decline is likely to increase, so understanding their ability to acclimate to a range of environments may be key to their survival. Light availability is critical for seagrass health, with loss of water clarity likely to cause decline. This study assessed the ability of the temperate intertidal species, Zostera muelleri , to compensate for variations in light in its natural environment. The impacts of light during inundation (high tide) and exposure (low tide) were examined along a vertical gradient from the high to low intertidal at two sites with differing light histories. Photo-acclimation was evaluated through morphological and physiological characteristics over two tidal cycles. Results were consistent with seagrasses having optimized their photosynthetic capacity, with physiological acclimations being site specific. Longer-term morphological changes were also noted, suggesting a dissimilar light history between sites for an extensive period. Interestingly, at the site with the greatest light range, but the lowest light penetration at depth, a significant reduction in photosynthetic activity during air exposure was observed. This suggests that Z. muelleri is capable of tolerating light stress through photo-acclimation, allowing for the more efficient harvesting of light at low levels. Overall, this study demonstrates that Z. muelleri has the ability to adjust both physiologically and morphologically to changing environmental conditions, a key aspect to survival and persistence in temperate intertidal zones.

The flavonoid content in leaves of Zostera marina and the endangered Zostera noltii, including mono- and disulphated flavonoids, from different sample localities were characterized. Seasonal variation of both individual and total flavonoid, as well as rosmarinic acid concentration were revealed. Minor amounts of luteolin 7-(6″-malonyl)glucoside ( 6 ) and apigenin7-(6″-malonyl)glucoside ( 11 ) were identified in Z. noltii for the first time. The total flavonoid content was found to be higher in Z. noltii than in Z. marina at most of the examined localities, and the qualitative flavonoid content was somewhat different in the two species. The quantitative variation of flavonoids and rosmarinic acid was found to be relatively consistent from year to year in Z. marina during a period of three years. The two species appeared though to have a different flavonoid production in the various seasons at the West coast. While Z. marina had the highest content in young leaves in May or June, with a markedly decrease from June to September and the lowest measured content in February, Z. noltii had the lowest measured flavonoid content in May/June followed by an increase from June to September and the highest measured content during wintertime in February. The observed seasonal differences may be related to the fact that Z. noltii is considered a perennial, thermophilous species, and the increasing flavonoid production during the colder seasons from September to March/April in Norway may serve as a protective function.

High temperatures, especially in the summer or during local heat waves, often coincide with high concentrations of herbicides in some estuarine areas during flood plumes. The combined effects of thermal stress (at 26–32 °C) and the herbicide atrazine (at concentrations of 0, 3 and 10 μg L−1) on eelgrass (Zostera marina L.) were studied in a 7-day exposure experiment. The results showed that both atrazine and temperatures above 30 °C inhibited the photosynthetic efficiency and energy conversion potential of the photosystem II (PsiI) as indicated by the effective quantum yield (ΔF/F’m) and the maximum yield (Fv/Fm), respectively. High temperatures (31 °C and 32 °C) decreased the Chl a content and stopped the leaf growth of eelgrass. Atrazine concentration had no effect on the photosynthetic pigments at all temperatures; however, decreased leaf growth rate was detected at 30 °C. A high level of agreement between the observed and predicted inhibition of photosynthesis by an Independent Action (IA) model demonstrates that the combined effects of high temperature and atrazine are more harmful to eelgrass than is a single pressure. The present study adds further evidence for seagrass protection and environmental management under the hypothesis that thermal stress combined with herbicides pose a greater threat to seagrasses.

Trace element poisoning remains a great threat to various waterfowl and waterbirds throughout the world. In this study, we determined the trace element exposure of herbivorous whooper swans (Cygnus cygnus) wintering in Swan Lake (Rongcheng), an important swan protection area in northern China. A total of 70 samples including abiotic factors (seawater, sediments), food sources (seagrass, macroalgae), feathers and feces of whooper swans were collected from the marine lagoon during the winters of 2014/2015 and 2015/2016. Concentrations of Cu, Zn, Pb, Cr, Cd, Hg and As were determined to investigate the trace element exposure of whooper swans wintering in the area. Results showed that there was an increasing trend in sediment trace element concentrations, compared with historical data. The trace element concentrations in swan feces most closely resembled those of Zostera marina leaves, especially for Cd and Cr. The Zn and Hg concentrations in the swan feces (49.57 and 0.01 mg/kg, respectively) were lower than the minimum values reported in the literature for other waterfowls, waterbirds and terrestrial birds. However, the concentrations of the other five trace elements fell within the lower and mediate range of values reported for birds across the world. These results suggest that the whooper swans wintering in Swan Lake, Rongcheng are not suffering severe trace element exposure; however, with the increasing input of trace elements to the lagoon, severe adverse impacts may occur in the future, and we therefore suggest that the input of trace elements to this area should be curbed.

Since dredged sea bottom sediments normally give off a horrible smell, the limitation of disposal places has become a serious problem in Japan. Hence, development of an alternative system to readily treat dredged sea bottom sediments is therefore needed. The development of “value-added” reused products from these sediments offers particular benefits both in terms of resource recovery and protection of the environment. We developed an in situ solidification system for the treatment of sea bottom sediments, the “ Hi-Biah-System (HBS)”. Firstly, this review deals with solidified sea bottom sediments for the construction of an artificial tidal flat in Ago Bay, Japan. The environmental conditions (pH, oxidation–reduction potential (ORP), acid volatile sulphide (AVS), loss on ignition (LOI), water content (WC), chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen (T-N), chlorophyll a and particle size) were then monitored in the constructed tidal flat. The number of benthos individuals and growth of short-necked clams ( Ruditapes philippinarum ) in the artificial tidal flat were also evaluated. The environmental conditions, number of benthos individuals and growth of short-necked clams in the artificial tidal flat were shown to be similar to those observed in a natural tidal flat. Next, the potential use of solidified sea bottom sediments as soil parent material in the germination/growth of seagrass is presented. The soil parent material consisting of solidified sediments obtained using HBS plus soil conditioner and hardener seems to be effective for the germination of Zostera marina . The best growth after six months was observed in plants grown in soil parent material consisting of a mixture of solidified sediments and the sand by weight ration 70:30. The present study may suggest the possible application of solidified sea bottom sediments into growth of other plants.