Eelgrass Growth Research Articles

Insights into response of seagrass (Zostera marina) to sulfide exposure at morphological, physiochemical and molecular levels in context of coastal eutrophication and warming.

Sulfide in sediment porewaters, is toxic to rooted macrophytes in both marine and freshwater environments. Current research on sulfide stress in seagrasses primarily focuses on morphological and physiological aspects, with little known about the molecular response and resistance mechanisms. This study first investigated the damage caused by sulfide to eelgrass (Zostera marina L.) using transcriptomic, metabolomic, and other physiological and biochemical indicators and explored the potential resistance of eelgrass at molecular level through laboratory simulated and in-situ sulfide stress experiments. Comprehensive results showed that sulfide stress severely inhibited the growth, photosynthesis, and antioxidant enzyme activities of eelgrass. Importantly, transcriptome analysis revealed significant activation of pathways related to carbohydrate and sulfur metabolism. This activation served a dual purpose: providing an energy source for eelgrass stress response and achieving detoxification through accelerated sulfur metabolism-a potential resistance mechanism. The toxicity of sulfide increased with rising temperature as evidenced by a decrease in EC50. Results from recovery experiments indicated that when Fv/Fm reduced to about 0 under sulfide stress, the growth and photosynthesis of eelgrass recovered to normal level after timely removal of sulfide. However, prolonged exposure to sulfide resulted in failure to recover, leading ultimately to plant death. This study not only enhances our understanding of the molecular-level impacts of sulfide on seagrasses but also provides guidance for the management and ecological restoration of seagrass meadows under sulfide stress.

Microbial communities around seeds promote Zostera marina germination

Eelgrass meadows are vital not only for sustaining marine biodiversity as marine ecosystems but also for carbon fixation as blue carbon. However, the national decline in eelgrass meadows in Japan, which was initiated by economic growth in the 1980s, prompted the implementation of conservation measures. This study explored the fundamental techniques of the sediment environment to enhance Zostera marina seed germination rates. We investigated the microbial origin of Zostera marina seeds under anaerobic conditions and assessed their germination efficiency. Anaerobic sediments in the eelgrass meadows were found to increase eelgrass germination rate by 6% more than aerobic sediments. And interestingly, the sulfate-reducing bacteria Desulfovibrionaceae and Sulfurospirillaceae were detected mainly on eelgrass seeds. Our result clearly indicated that the sulfate-reducing bacteria around Zostera marina seeds create anaerobic conditions that promote germination through their sulfate-reducing function. Therefore, when developing new eelgrass meadows, it can be expected to improve germination rates by preparing the sediment environment to facilitate the increase of SRB coexisting with seeds. However, the difference in bottom sediment conditions varies by region, so it is necessary to be careful when adding or removing something. In addition, germination and growth of eelgrass must be considered separately, and factors that promote growth are not described in this work. The result of this study was an important finding for the implementation of Blue Carbon activities to improve sediment quality prior to the creation of eelgrass meadows and can also support eelgrass meadows maintenance after establishment.

Innovative multi-layered biocement development and marine implementation research that contributes to the creation of resilient eelgrass beds

Eelgrass (Zostera marina) beds are important sites of marine biodiversity. Professor Masataka Kusube, National Institute of Technology, Wakayama College, Japan, has extensive experience in this area of research. He focuses on the development of bio-cements created from locally sourced sea sand and bacteria and collaborates with chemicals and plastics manufacturers and local governments in his research on eelgrass meadows. Hydrogen sulfide interferes with cellular respiration and is therefore toxic to humans and animals. Recent research has suggested toxicity to plants, and it could be linked with a recent widespread decline in eelgrass meadows. Kusube has been developing bio-cements and utilises scanning electron microscopy (SEM) to visually examine its surface structure, as well as using PCR (polymerase chain reaction), 16S multigenomic sequencing, SYBR green staining and cell counts to further investigate and gather data on the growth and germination rates of eelgrass with and without his interventions. In the creation of bio-cements, Kusube and his team used urea-degrading bacteria isolating strains of bacteria that were able to provide the functions required. Using urea-degrading bacteria meant that the researchers could easily isolate them with phenol red staining as these colonies break down urea to produce ammonia, generating a distinct red colouration around colonies when using this indicator. So far, the team has found that water temperature and oxygen concentration can significantly affect germination rates, while Eelgrass growth can be promoted in the presence of organic matter and iron. This suggests the potential to enhance growth by manipulating these elements.

Adaptive responses of eelgrass (Zostera marina L.) to ocean warming and acidification

Ocean warming (OW) and ocean acidification (OA), driven by rapid global warming accelerating at unprecedented rates, are profoundly impacting the stability of seagrass ecosystems. Yet, our current understanding of the effects of OW and OA on seagrass remains constrained. Herein, we investigated the response of eelgrass (Zostera marina L.), a representative seagrass species, to OW and OA through comprehensive transcriptomic and metabolomic analyses. The results showed notable variations in plant performance under varying conditions: OW, OA, and OWA (a combination of both conditions). Specifically, under average oceanic temperature conditions for eelgrass growth over the past 20 years —from May to November—OA promoted the production of differentially expressed genes and metabolites associated with alanine, aspartate, and glutamate metabolism, as well as starch and sucrose metabolism. Under warming condition, eelgrass was resistant to OA by accelerating galactose metabolism, along with glycine, serine, and threonine metabolism, as well as the tricarboxylic acid (TCA) cycle. Under the combined OW and OA condition, eelgrass stimulated fructose and mannose metabolism, glycolysis, and carbon fixation, in addition to galactose metabolism and the TCA cycle to face the interplay. Our findings suggest that eelgrass exhibits adaptive capacity by inducing different metabolites and associated genes, primarily connected with carbon and nitrogen metabolism, in response to varying degrees of OW and OA. The data generated here support the exploration of mechanisms underlying seagrass responses to environmental fluctuations, which hold critical significance for the future conservation and management of these ecosystems.

The combined effect of seawater salinity and duration on the survival and growth of eelgrass Zostera marina

Abrupt changes in salinity are considered a key cause of seagrass bed degradation. In the study, we first quantified the effects of different combinations of salinity and duration on the responses of Zostera marina shoots in terms of survivorship, morphology, growth and physiology. The recovery potential (recovery of shoots from salinity stress to be returned to original salinity level) of Z. marina shoots was assessed. The LT50 (lethal time that caused an increase in mortality to 50 % of that of the control) and EC50 (effect concentration, i.e., salinity level that caused a decrease in growth to 50 % of that of the control) were calculated to reveal the quantitative relationship between salinity and duration that resulted in limiting effects on the survival and growth of Z. marina shoots. Z. marina shoots were exposed to different combinations of water salinity [20, 25, 30 (control), 35, 40, and 45 PSU] and duration (5, 10, 15 and 20 days), and then the shoots were transferred to the control condition for 30 days under laboratory conditions. The results showed that the survival rate of shoots at the end of recovery was significantly lower than those of shoots at the end of direct salinity stress at the hypersalinity levels of 40 and 45 PSU, indicating that short-term periods of increase in water salinity would lead to long-term effects on the survival of Z. marina shoots. The total leaf area of shoots at the end of recovery was significantly higher than those of shoots at the end of direct salinity stress at salinity levels of 25–35 PSU, indicating a significant recovery potential following the salinity stress. However, a poor recovery potential was found under combinations of hypersalinity (40–45 PSU) and duration of 20 days. Regression analysis revealed that the relationship between salinity and duration was a strong power function that could limit the growth of Z. marina. Pearson correlation analysis showed that the survival and growth of Z. marina shoots exposed to different salinity levels were significantly correlated with leaf soluble sugar contents when the duration was higher than 5 days. This study will further enhance our understanding of seagrass bed degeneration induced by abrupt changes in salinity.

Ragworms (Hediste diversicolor) limit eelgrass (Zostera marina) seedling settlement: Implications for seed-based restoration

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.

The combined effect of planting density and sediment fertilization on survival, growth and physiology of eelgrass Zostera marina.

We subjected shoots of eelgrass Zostera marina to different combinations of planting density [300 (control), 450, 600, 750, 900 shoots m-2] and sediment fertilization [0 (control), 35, 70, 105, 140gm-2] for 6weeks under controlled conditions. We measured eelgrass responses in terms of survivorship, growth, productivity, leaf pigmentation and carbohydrate concentrations. The ramet frequency of Z. marina reached 47.8% when exposed to the combination of 600 shoots m-2 and 70gm-2, which was 3.2 times higher than that of shoots under the control. Survival analysis combined with growth assessment suggested that the optimal ranges of planting density and sediment fertilization for the propagation of Z. marina shoots were 501 to 530 shoots m-2 and 51 to 60gm-2, respectively. The promotion of survival and propagation of Z. marina that stemmed from planting density and sediment fertilization mainly depended on the increase of chlorophyll content and accumulation of non-structural carbohydrate. The total chlorophyll content of Z. marina leaves exposed to the combination of 600 shoots m-2 and 70gm-2 was 2.1 times higher than that of shoots under the control. The results will provide data that could prove helpful in the development of efficient artificial propagation technology for Z. marina shoots.

The influence of decreased salinity levels on the survival, growth and physiology of eelgrass Zostera marina

Low salinity generally promotes the growth and propagation of temperate seagrasses, but the appropriate range is unclear. We subjected shoots of eelgrass Zostera marina to different salinity levels [10, 15, 20, 25, 30 PSU (control)] for 6 weeks under controlled laboratory conditions. We measured eelgrass responses in terms of survivorship, growth, productivity, leaf pigmentation and carbohydrate concentrations. Survival analysis combined with growth assessment suggested that the optimal salinity range for the propagation of Z. marina shoots was 18–21 PSU. Structural equation model (SEM) analysis indicated that the promotion effect of decreased salinity levels on the survival and growth of Z. marina shoots mainly depended on the increase in chlorophyll content and the accumulation and synthesis of nonstructural carbohydrates. The carotenoid content and soluble sugar content of the aboveground tissues of Z. marina shoots exposed to 20 PSU were 1.1 and 1.6 times higher than those of shoots under the control, respectively. The results will provide valuable data that could prove helpful in the development of efficient artificial propagation technology for Z. marina shoots.

The effect of abrupt increase in water temperature on the survival and growth of eelgrass Zostera marina

Increased water temperature is considered an important cause of the loss of seagrass beds. This paper quantified the interactive influence of different combinations of water temperature and duration on the responses of Zostera marina plants in terms of survivorship, morphology, growth and physiology. The LT50 (lethal temperature that caused an increase in mortality to 50% of that of the control) and ET50 (effect time that caused a decrease in growth to 50% of that of the control) were calculated to reveal the quantitative relationship between temperature and duration that resulted in limiting effects on the survival and growth of Z. marina plants. Z. marina plants were exposed to different combinations of water temperature [23 (control), 25, 27, 29, and 31 °C] and duration (5, 10, 15 and 20 days), and then the plants were transferred to the control condition for over 30 days under laboratory conditions. The results showed that the survival rate of plants at the end of recovery were significantly lower than those of plants at the end of direct impact under the temperature levels of 29 and 31 °C in each duration, indicating that short-term periods of obviously increased water temperature would lead to long-term effects on the survival of Z. marina plants. Regression analysis revealed that the relationship between water temperature and duration that resulted in limiting effects on the survival and growth of Z. marina could be described as a strong power function. Pearson correlation analysis showed that the survival and growth of Z. marina plants exposed to different temperature levels were significantly correlated with leaf soluble sugar contents. This study will further develop our understanding of the degradation and disappearance of seagrass beds induced by increased temperature.

Warming northward shifting southern limits of the iconic temperate seagrass (Zostera marina)

SummaryGlobal warming can shift the range edges of numerous species poleward. Here, eelgrass distribution was reinvestigated at its southern limits on the eastern coast of China, which indicated that there has been a northward shift in the southern limit of Z. marina. To determine if regional warming resulted in a northward shift in suitable eelgrass habitats, sixteen transplantations of adult eelgrass shoots and seeds at the historical southern distribution limit of eelgrass were conducted between 2016 and 2021. The results showed that high water temperatures in summer had negative effects on eelgrass growth, and directly triggered shoot mortality during 2016–2018. Under heat stress, antioxidant enzyme activity was initially increased, but then decreased under more stressful heat conditions; and the HSP70 protein and its molecular chaperone protein were highly expressed under heat stress. These results demonstrated that suitable eelgrass habitat was now located further north along the eastern coast of China.

Do adult eelgrass shoots rule seedling fate in a large seagrass meadow in a eutrophic bay in northern China?

We conducted field sampling over 19 months to investigate eelgrass population reproduction status and ecological interactions in a large seagrass meadow in a eutrophic bay in northern China. The results showed asexual growth played an important role in the maintenance of existing meadows, and sexual reproduction played a critical role in the colonization of new areas. We conclude that adult eelgrass shoots do rule the fate of seedlings in the large seagrass meadow. Additionally, nutrient resources (N and P) at this location were found to meet eelgrass growth demand. The N/P ratios of seawater and seagrass indicated N limitation relative to P in the eutrophic bay based on the seagrass Redfield ratio (25–30). Nutrient uptake by seagrass might be an important factor in reducing the probability of a red tide in the study area. The results of this study provide fundamental information for eelgrass restoration and conservation.

Sand-capping stabilizes muddy sediment and improves benthic light conditions in eutrophic estuaries: Laboratory verification and the potential for recovery of eelgrass (Zostera marina)

Decades of eutrophication have increased water turbidity in Danish estuaries and led to light limitation of eelgrass (Zostera marina) growth. Former eelgrass areas are now denuded and consist of organic-rich muddy sediment with frequent resuspension events that maintain a high turbidity state. In addition, low anchoring capacity of eelgrass in the soft organic-rich sediments has contributed to eelgrass loss. When navigation channels in Danish estuaries are dredged, large amounts (~100.000 m3) of sandy sediment are shipped to remote dumping sites. Instead, we suggest that the dredged sand is used to consolidate adjacent muddy areas. We demonstrate in the present laboratory study that capping of fluid muddy sediment with 10 cm of sand is feasible without any vertical mixing and that this marine restoration approach potentially can lower the magnitude and frequency of resuspension events. Erosion of suspended solids change from 5 g m−2 min−1 above muddy sediment as to about 0.2 g m−2 min−1 after sand-capping, implying that the application of sand can improve light conditions. Moreover, since erosion thresholds increase from about 10–12 cm s−1 for mud to 40 cm s−1 for sand-capped mud the anchoring capacity of rooted vegetation is increased. However, the full potential of sand-capping to facilitate restoration of otherwise lost eelgrass habitats requires verification by large-scale field experiments.

Increased salinity stress changes plant productivity and biomass by altering the top‐down controls in eelgrass beds

AbstractUnderstanding biological community responses to disturbances such as extreme rainfalls under climate change is crucial when predicting ecosystem changes and functions. However, it is still unclear how species interaction changes with increasing disturbances and how disturbance susceptibility varies among organisms from habitats with different stress levels along stress gradients such as salinity gradients. We examined whether (1) higher frequency (i.e., pulse disturbance) and longer duration (i.e., press disturbance) of salinity change affected the primary producers, animals, and their interactions, and whether (2) organisms from naturally stressful habitats with unstable salinity were more tolerant to salinity changes. We used eelgrass Zostera marina, epiphytic microalgae, and grazer gastropod Lacuna decorata from two sites in each of the two lagoons; Akkeshi with a strong salinity gradient, and Notoro with a weak gradient to do indoor mesocosm experiments for testing the effects of salinity change and grazer presence on eelgrass growth and biomass of epiphytic microalgae, as well as grazer survival, growth, and consumption rates. We established treatments with low, intermediate, and high levels of salinity stress to test the effects of press and pulse disturbances in terms of salinity changes. The findings suggest the presence of a top‐down control of epiphytic microalgae by grazers. Eelgrass growth rate was higher with the presence of grazers but declined with higher salinity stress. The biomass of epiphytic microalgae was higher with the absence of grazers and with higher salinity stress across all sites. Grazer survival varied among individuals raised in habitats with naturally stable or unstable salinity regime and decreased with more frequent and longer salinity changes. Grazer growth rates and grazing rates also decreased with higher salinity stress, but grazing on epiphytic microalgae was highest at the intermediate stress levels across all sites. This study demonstrates that salinity regime shifts that are expected to occur with extreme rainfalls due to ongoing climate change could affect coastal ecosystems such as eelgrass beds, and we call for further investigations on the different stress responses of organisms raised in habitats with stable and unstable salinity to understand the potential effects of the disturbances on ecosystem function.

Effects of Seagrass Wasting Disease on Eelgrass Growth and Belowground Sugar in Natural Meadows

Seagrass meadows provide valuable ecosystem benefits but are at risk from disease. Eelgrass (Zostera marina) is a temperate species threatened by seagrass wasting disease (SWD), caused by the protist Labyrinthula zosterae. The pathogen is sensitive to warming ocean temperatures, prompting a need for greater understanding of the impacts on host health under climate change. Previous work demonstrates pathogen cultures grow faster under warmer laboratory conditions and documents positive correlations between warmer ocean temperatures and disease levels in nature. However, the consequences of disease outbreaks on eelgrass growth remain poorly understood. Here, we examined the effect of disease on eelgrass productivity in the field. We coupled in situ shoot marking with high-resolution imagery of eelgrass blades and used an artificial intelligence application to determine disease prevalence and severity from digital images. Comparisons of eelgrass growth and disease metrics showed that SWD impaired eelgrass growth and accumulation of non-structural carbon in the field. Blades with more severe disease had reduced growth rates, indicating that disease severity can limit plant growth. Disease severity and rhizome sugar content were also inversely related, suggesting that disease reduced belowground carbon accumulation. Finally, repeated measurements of diseased blades indicated that lesions can grow faster than healthy tissue in situ. This is the first study to demonstrate the negative impact of wasting disease on eelgrass health in a natural meadow. These results emphasize the importance of considering disease alongside other stressors to better predict the health and functioning of seagrass meadows in the Anthropocene.

Growth and flowering responses of eelgrass to simulated grazing and fecal addition by Brant Geese

AbstractSeagrasses provide a wide range of ecosystem services and are prioritized in conservation planning. Management of this dynamic community requires describing seagrass responses to repeated grazing by dependent herbivores. Using two experimental randomized block designs in Humboldt Bay, California, we tested responses of eelgrass (Zostera marina) to separate and combined effects of simulated Brant Goose (Branta bernicla) grazing (clipping to a uniform height) and fecal pellet addition, and then to medium (MED) and severe (SEV) intensities of simulated Brant flock visitation. In Experiment 1, clipping with fecal addition (FC) stimulated more clonal addition of shoots than controls or clipping and fecal addition alone (standardized β = 0.26 relative to control). The FC treatment also had the largest positive, delayed effect (β = 0.135) on density of flowering shoots. In Experiment 2, the MED intensity treatment had positive effects on shoot density (β = 0.149), rates of leaf extension (β = 0.16), and leaf productivity (β = 0.20). These MED treatment responses resulted in the highest measures of above‐ground (β = 0.099) and below‐ground (β = 0.32) biomass. Whole shoot (βMED = 0.33, βSEV = −0.36) and landscape (βMED = 0.34, βSEV = −0.23) levels of productivity for the MED treatment reflected the parabolic shape predicted by the compensatory regrowth hypothesis, likely because light and nutrient resources were available to the eelgrass and meristems that were not damaged. Meristem injury in the SEV treatment likely explained why productivity was low, but the high SEV resource levels allowed these plants to recover to control levels in approximately eight to 10 weeks after the last treatment applications. The MED level of shoot and landscape productivity would optimize low intertidal accessibility for Brant to the most nutritiously valuable leaves. Brant grazing and detrital pathways of carbon flow are likely linked with Brant‐induced productivity contributing to the detrital pathway when Brant are present and after the birds leave the estuary. The effect of Brant grazing on eelgrass sexual reproduction may increase long‐term resilience of estuarine ecosystems.

Seagrass and Oyster Reef Restoration in Living Shorelines: Effects of Habitat Configuration on Invertebrate Community Assembly

Restoration projects provide a valuable opportunity to experimentally establish foundational habitats in different combinations to test relative effects on community assembly. We evaluated the development of macroinvertebrate communities in response to planting of eelgrass (Zostera marina) and construction of reefs intended to support the Olympia oyster (Ostrea lurida) in the San Francisco Estuary. Plots of each type, alone or interspersed, were established in 2012 in a pilot living shorelines project, and quarterly invertebrate monitoring was conducted for one year prior to restoration, and three years post-restoration using suction sampling and eelgrass shoot collection. Suction sampling revealed that within one year, oyster reefs supported unique invertebrate assemblages as compared to pre-restoration conditions and controls (unmanipulated mudflat). The eelgrass invertebrate assemblage also shifted, becoming intermediate between reefs and controls. Interspersing both types of habitat structure led eelgrass invertebrate communities to more closely resemble those of oyster reefs alone, though the eelgrass assemblage maintained some distinction (primarily by supporting gammarid and caprellid amphipods). Eelgrass shoot collection documented some additional taxa known to benefit eelgrass growth through consumption of epiphytic algae; however, even after three years, restored eelgrass did not establish an assemblage equivalent to natural beds, as the eelgrass sea hare (Phyllaplysia taylori) and eelgrass isopod (Pentidotea resecata) remained absent or very rare. We conclude that the restoration of two structurally complex habitat types within tens of meters maximized the variety of invertebrate assemblages supported, but that close interspersion dampened the separately contributed distinctiveness. In addition, management intervention may be needed to overcome the recruitment limitation of species with important roles in maintaining eelgrass habitat.

Incorporating facilitative interactions into small‐scale eelgrass restoration—challenges and opportunities

Marine ecosystem engineers such as seagrasses and bivalves create important coastal habitats sustaining high biodiversity and ecosystem services. Restoring these habitats is difficult due to the importance of feedback mechanisms that can require large‐scale efforts to ensure success. Incorporating facilitative interactions could increase the feasibility and success of small‐scale restoration efforts, which would limit pressure on donor sites and reduce costs and time associated with restoration. Here, we tested two methods for providing facilitation in small‐scale eelgrass (Zostera marina) restoration plots across northern Europe: (1) co‐restoration with blue mussels (Mytilus edulis, M. trossulus); and (2) the use of biodegradable establishment structures (BESEs). Eelgrass‐mussel co‐restoration showed promise in aquaria, where eelgrass growth was nearly twice as high in treatments with medium and high mussel densities than in treatments without mussels. However, this did not translate to higher shoot length or shoot densities in subsequent field experiments. Rather, hydrodynamic exposure limited both eelgrass and mussel survival, especially in the most exposed sites. The use of BESEs showed more potential in enabling small‐scale restoration success: they effectively enhanced eelgrass survival and reduced mussel loss, and showed potential for enabling mussel recruitment in one site. However, eelgrass planted in BESE plots along with mussels had a lower survival rate than eelgrass planted in BESE plots without mussels. Overall, we show that though co‐restoration did not work at small scales, facilitation by using artificial structures (BESEs) can increase early eelgrass survival and success of small‐scale eelgrass and bivalve restoration.

Sediment Transport Model Quantifies Plume Length and Light Conditions From Mussel Dredging

Mussel dredging causes resuspension of sediment particles that reduce water clarity and potentially leads to reduced eelgrass growth. In order to study the impact of resuspension from mussel dredging on light conditions in the water column, field experiments were conducted at two sites in the Limfjorden. Light loggers were placed in two circular arrays around the dredge area. Vertical profiles of current velocity were measured by an ADCP and the sediment particle size composition was obtained from sediment core samples. The field data was used to force, calibrate and validate a sediment transport model developed in the FlexSem model system. Changes in sediment concentrations during and after mussel dredging were modelled for the two sites and for seven scenarios. We found that the distance and direction of the plume in the model was in good agreement with light logger data. The plume duration was less than 1 hour, and the impact range was between 260-540 m. The scenarios showed that fishing intensity and current speeds were most important for shaping the sediment plumes. Changes in suspended sediment concentrations were 0.62 to 1.79 mg/l on median average and 1.22 to 11.61 mg/l for the upper quantile of the plume, which were on the same order of magnitude as background values in the Limfjorden. The amount of fishing days during the eelgrass growth season was 6-8% in Lovns Bredning and 16-35% in Logstor Bredning and less than 1-2% of the total area was dredged per season. Even though there are substantial changes in the light conditions from the sediment plumes, the overall spatio-temporal impact in the study area is considered low. We recommend that management plans in other areas could sustain a shellfish fishery by limiting fishing intensity and frequency near eelgrass beds. The presented approach combines observational data, sediment transport modelling and reported fishing activity. It is a step forward within sediment transport modelling and could be incorporated into environmental impact assessments. The results have recently been used as scientific background for recommendations to improve the management plans according to the Danish Mussel Policy and relevant EU Directives.

Research on innovative marine environmental conservation with no environmental impact using marine bio-cement

According to a growing body of research from scientists all over the world, the Earth is heading towards a global catastrophe. Polar ice caps are melting due to rising global temperatures and there have been many consequences for our oceans. The impact of human activity on the oceans has led to growing acidity of the water, as well as rising sea levels. Pollution and physical damage from human activities such as dredging and shipping have hit marine life hard, reducing animal and plant populations and decreasing species diversity. This reduction in key marine components such as the seaweed beds has a massive impact on other species, causing ripple effects that can be felt by humans. Providing food, shelter and breeding grounds for fish, squid, crustaceans and many other organisms, a decrease in the seaweed forests directly correlates to a reduction in sea life in the area, which affects the marine environment as a whole as well threatening the local fishing industry. Scientists have been trying to tackle this damage to the seaweed beds by developing ways in which to re-seed areas of the seabed. A variety of approaches have been taken to growing new seaweed to restore these habitats, but many of these methods are expensive and labour intensive. Associate Professor Masataka Kusube, from the Department of Applied Chemistry and Biochemistry, National Institute Technology at Wakayama College in Japan, is working with a number of industrial partners, including Mitsui Chemicals Inc. to produce large scale marine microbe cultures by pilot test facility and KYC Machine Industry Co., Ltd. to generate large scale marine bio-cement production, Kusube and his team have developed an innovative material dubbed 'marine bio-cement' to support the growth of eelgrass in the waters surrounding Japan.

Acute and prolonged effects of variable salinity on growth, gas exchange and photobiology of eelgrass (Zostera marina L.)

Sea level rise and more frequent storm and precipitation events associated with climate change are predicted to increase salinity fluctuations in estuarine and inshore areas, where foundation species such as eelgrass (Zostera marina L.) will be exposed to more frequent salinity changes. Effects of acute hyposalinity exposure on seagrasses remain poorly understood compared to the effects of more prolonged, constant salinity. Here, we examined growth and photo-physiological responses of Z. marina to 5 levels of stable salinity (5, 12 19, 25, 33) and compared effects of prolonged (16 days) versus acute (24 and 48 hours) exposure to hyposalinity (salinity 5 and 12) using fluorescence imaging. We also examined if fluorescence kinetics were affected by age differences across leaves. Growth reached an optimum at salinity 19 and was more affected by hyposalinity than hypersalinity. Rapid reduction from salinity 25 to 5 decreased the maximum quantum yield (Fv/Fm) after just 48 h. In contrast with prolonged exposure, non-photochemical quenching processes were not increased at salinity 5 after 48 h. Young leaves were more susceptible to extreme hyposalinity than older leaves (e.g., lower photosynthetic quantum yield), which emphasizes the importance of considering shoot-scale and within-shoot variations in studies of stress response patterns. Differences between hyposalinity and hypersalinity responses were generally replicated in the literature, but we were not able to detect any differences across studies. Overall, these results suggest that eelgrass is tolerant to large fluctuations in salinity, but sudden extreme reductions may act as a severe co-stressor, and contribute to accumulated stress-exposure effects (chronic or lasting effects).