Zostera Marina Populations Research Articles

Seasonal Variability in Non-Structural Carbohydrate Content of Warm-Adapted Zostera noltei and Zostera marina Populations

Non-structural carbohydrates (NSCs) are energetic compounds that can be accumulated in tissues and mobilized during periods of unfavorable conditions to maintain the biological functions of plants. The balance of these biochemical compounds is controlled by environmental factors such as temperature and irradiance. Zostera noltei and Zostera marina find one of their southern distribution limits in southern Spain, where relatively high seawater temperatures are reached during summer (23–24 °C). To better understand the effects of elevated temperatures on the concentration of NSCs, we conducted a seasonal study at Cadiz Bay, representing warm-adapted populations of these species. Our results showed a bimodal pattern in both species, with the highest NSC content observed in December and June, followed by a depletion in March and August. In addition, the NSC content observed in the leaves of Z. noltei (71.26 ± 30.77 mg g−1 dry weight) was higher than in the rhizomes and roots (52.14 ± 38.86 mg g−1 DW). The observed patterns suggest that these species accumulated NSCs to cope with periods of unfavorable environmental conditions. We also suggest that the limited concentration of NSCs in Z. noltei rhizomes and roots indicates that this population may be suffering physiological stress.

Heteroplasmy Is Rare in Plant Mitochondria Compared with Plastids despite Similar Mutation Rates.

Plant cells harbor two membrane-bound organelles containing their own genetic material-plastids and mitochondria. Although the two organelles coexist and coevolve within the same plant cells, they differ in genome copy number, intracellular organization, and mode of segregation. How these attributes affect the time to fixation or, conversely, loss of neutral alleles is currently unresolved. Here, we show that mitochondria and plastids share the same mutation rate, yet plastid alleles remain in a heteroplasmic state significantly longer compared with mitochondrial alleles. By analyzing genetic variants across populations of the marine flowering plant Zostera marina and simulating organelle allele dynamics, we examine the determinants of allele segregation and allele fixation. Our results suggest that the bottlenecks on the cell population, e.g. during branching or seeding, and stratification of the meristematic tissue are important determinants of mitochondrial allele dynamics. Furthermore, we suggest that the prolonged plastid allele dynamics are due to a yet unknown active plastid partition mechanism. The dissimilarity between plastid and mitochondrial novel allele fixation at different levels of organization may manifest in differences in adaptation processes. Our study uncovers fundamental principles of organelle population genetics that are essential for further investigations of long-term evolution and molecular dating of divergence events.

Phenolic chemistry of the seagrass Zostera marina Linnaeus: First assessment of geographic variability among populations on a broad spatial scale

The variability of the phenolic content of thirteen populations of Zostera marina L. (six narrow-leaved and seven wide-leaved ecotypes) from different geographical zones, i.e., Baltic Sea, Mediterranean, East and West Atlantic, and East Pacific coasts was evaluated. Depending on the location, three to five phenolic acids and nine to fourteen flavonoids were identified of which an undescribed flavonoid sulfate. The phenolic concentrations of the thirteen populations differ among countries and among sites within countries. However, the same individuals were found almost everywhere. Substantial phenolic concentrations were found at all study sites with the exception of Puck Bay (Baltic Sea). Some geographical differences in the flavonoid content were observed. The highest phenolic diversity was found with specimens from the French Atlantic coast and the lowest with the Northeastern American sample (Cape Cod, MA). Regardless of their leaf width, the content of phenolic compounds was found to be similar and mainly characterized by rosmarinic acid and luteolin 7,3′-disulfate. The results demonstrate that geographic origin influences the phenolic composition of Z. marina primarily in terms of concentration, but not in terms of individual compound identity, despite the large geographic scale and the contrasting climatic and environmental conditions associated with it. This work is the first study to consider the spatial variability of phenolic compounds for a seagrass species on a spatial scale covering four bioregions. This is also the first to compare the phenolic chemistry of the two ecotypes of Z. marina.

Population dynamics of a fragmented subtidal Zostera marina population affected by shell fishing

This investigation illustrates the spatial and temporal dynamics of a Zostera marina seagrass meadow affected by clam harvesting. Photointerpretation of satellite imagery corresponding to years 2007, 2013, 2017 and 2018, combined with field monitoring in 2019 allowed assessing the spatial coverage, population dynamics and genetic characterization of the Z. marina population in areas impacted and non-impacted by the shellfishing activity. The impacted meadow displayed a highly fragmented and discontinuous seagrass matrix anthropogenically induced by the periodical disturbance associated with bottom raking. A continuous colonization process characterized the seagrass landscape, where the area occupied by the meadow varied by a two-fold factor, with changes even exceeding 86% in some years. Only 740 m2 (ca. 15%) of the seagrass matrix remained vegetated in the four years monitored in this investigation. The number of patches showed a large interannual variability, exceeding 100% in the four years studied, ranging from 58 to 199, while the border effect perimeter/area indicator showed a two-fold variation ranging between 1 and 2. Clearly differentiated patterns were observed in shoot density, biomass, and flowering density between shellfishing-induced patches of different sizes and the long-term non-impacted areas. A significant pattern of genetic differentiation among impacted and control populations were also found. Our results showed that population dynamics varied as a function of Z. marina patch-sizes, thus reinforcing the need for a combined approach involving seascape structure and patch dynamics with population dynamics and genetic structure to assess the impact of disturbances on seagrass ecosystems.

Influence of environmental disturbances and reproductive strategy on genetic diversity and differentiation of Zostera marina populations on the southern coast of Korea

AbstractThe genetic diversity and differentiation of four Zostera marina populations along the southern coast of Korea were estimated using random amplified polymorphic DNA (RAPD) markers to determine the effects of natural and anthropogenic stresses and reproductive strategy on within‐population genetic diversity. The mean number of alleles and gene diversities, indicating population genetic diversity, was highest in the Z. marina population that was exposed to repeated environmental disturbances, and lowest in the most undisturbed population. The higher genetic diversity in the disturbed population was associated with a higher contribution of sexual reproduction to population persistence. This suggests that both the level of disturbances and the reproductive strategy for population persistence contributed significantly to population genetic diversity at the study sites. According to the analysis of molecular variance (AMOVA), 76% genetic variation was attributable to differences among individuals within populations. The observed genetic differentiation (FST = 0.241) among Z. marina populations at the study sites appeared to result from reduced meadow size, increased genetic drift, and a high incidence of asexual reproduction. Increased population genetic diversity can enhance resistance and resilience to environmental disturbances; thus, this investigation of seagrass population genetics provides valuable new insights for the conservation, management, and restoration of seagrass habitats.

Growth characteristics of a restored Zostera marina population in the Shandong Peninsula, China: A case study

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.

Seagrass wasting disease: Nitrate enrichment and exposure to a herbicide (Diuron) increases susceptibility of Zostera marina to infection

Seagrass meadows suffered large-scale declines in the past century. The ‘wasting disease’, pathognomonically associated with Labyrinthula zosterae, reduced populations of Zostera marina on both sides of the North Atlantic in, and since, the 1930s, coinciding with intensive agricultural use of artificial fertilizers and herbicides. This study tests the long-standing hypothesis that nutrient enrichment and a herbicide increases vulnerability to pathogens.Z. marina shoots from the Thames Estuary grown in elevated nitrate concentrations had significantly higher rates of infection by L. zosterae than controls, but not by Aplanochytrium sp., another slime-mould like protist. Z. marina shoots grown in 2μg·l−1 Diuron solutions and infected separately by L. zosterae and Aplanochytrium sp. had significantly higher wasting indices than controls. The results identified Aplanochytrium sp. as another opportunistic pathogen causing a seagrass wasting-type disease and support the hypothesis that pollution by herbicides and nitrate increases the susceptibility of Z. marina to infections.

Seagrass wasting disease varies with salinity and depth in natural Zostera marina populations

In the 1930s the wasting disease pathogen Labyrinthula zosterae is believed to have killed 90% of the temperate seagrass Zostera marina in the Atlantic Ocean. Despite the devastating impact of this disease the host–pathogen interaction is still poorly understood, and few field studies have investigated factors correlating with the prevalence and abundance of L. zosterae. This study measures wasting disease in natural populations of Z. marina, showing a strong correlation between the disease and both salinity and water depth. No infection was detected in Z. marina shoots from low salinity (13–25 PSU) meadows, whereas most shoots carried the disease in high salinity (25–29 PSU). Shallow (1 m) living Z. marina shoots were also more infected compared to shoots in deeper (5 m) meadows. In addition, infection and transplantation experiments showed that Z. marina shoots from low salinity meadows with low pathogen pressure were more susceptible to L. zosterae infection. The higher susceptibility could not be explained by lower content of inhibitory defense compounds in the shoots. Instead, extracts from all Z. marina shoots significantly reduced pathogen growth, suggesting that Z. marina contains inhibitory compounds that function as a constitutive defense. Overall, the results show that seagrass wasting disease is common in natural Z. marina populations in the study area and that it increases with salinity and decreases with depth. Our findings also suggest that low salinity areas can act as a refuge against seagrass wasting disease.

Depth-Related Changes in Reproductive Strategy of a Cold-Temperate Zostera marina Meadow

Biomass allocation and demographic characteristics of a Danish Zostera marina population were determined along a depth gradient of light and exposure to evaluate the reproductive strategy for meadow maintenance and recovery. From May to September, biomass, shoot growth and reproductive allocation were measured monthly at three depths (1.8, 4 and 6 m). Also, seedling survival along the deep edge (6.2 m) of the studied meadow was followed over a 12-month period. Shoot density and biomass showed pronounced differences among depths with up to 12-fold lower shoot density and 6-fold lower biomass at deep compared to shallow sites. Comparatively, little variation was found in leaf formation rates and rhizome elongation rates among depths. However, new shoots formed through vegetative reproduction and surviving until September constituted a significantly higher fraction of total shoot density in shallow water (45.7 %) than in deep water (17.3–21.1 %). Conversely, allocation to sexual reproduction was highest at intermediate and high water depths where the proportion of reproductive shoots to total shoot density at time of maximum density was 21.1 and 10.6 %, respectively, and only 3.9 % at the shallow depth. Seed production was also higher at intermediate depth (1970 seeds m−2) than at the upper (1230 seeds m−2) and lower (760 seeds m−2) distribution limit. Seedling recruitment within the meadow took place at all sampling depths but no seedlings persisted throughout the summer period, whereas 8 % of the seedlings established in bare areas along the deep meadow edge (0.43 seedlings m−2) survived their first year. Overall, the results suggest that the shallow edge of the meadow is primarily maintained by vegetative recruitment whereas the deep edge to larger extent relies on sexual recruitment. The intermediate depth zone may act as a buffer zone supporting the maintenance of shallower and deeper eelgrass through seed supply and vegetative expansion, thereby stabilizing the meadow by increasing its resilience towards disturbances and its recovery potential upon disturbances.

Assessing establishment success and suitability analysis of Zostera marina transplants using staple method in northern lagoons

Aims Zostera marina populations in northern China are rapidly declining due to both natural and anthropogenic disturbances. Efforts to prevent further losses and restore disturbed Z. marina habitats through transplanting are desirable. In this study, a transplanting experiment was conducted using the staple method in Swan Lake, which is a typical lagoon in the Rongcheng region of Shandong Peninsula, China. The objectives of this research are to: 1) investigate the plant response in terms of survivorship, morphology, and growth; 2) assess the establishment suc- cess of transplants; and 3) analyze the suitability of applying staple method in northern China. Methods Ninety planting units (PUs, 3 shoots/PU) with 4-6 leaves and about 10 cm rhizome on each shoot were monthly transplanted using the staple method in the subtidal zone of Swan Lake (water depth 0.5 m) from April to September 2009. Ten replicated plots of 50 cm × 50 cm were set up and nine PUs were randomly planted in each plot. Survival rate was calculated as the percentage of PUs that survived. Shoot morphology and individual shoot biomass of transplants and reference plants in the donor bed were monthly monitored from May to December 2009. Important findings Survival rate of transplants planted during spring (April, May, and June) ranged from 76.5% to 90.4% with the minimum value in April; whereas the survival rate of transplants planted during summer (July, August, and September) was 100%. The time required for the establishment of transplants was on average 1.0 month when planted from June to September, 2.0 months when planted in May, and 4.0 months when planted in April. With exception of some monitoring months, the leaf length and sheath length of transplants were signifi- cantly lower than those of reference plants; whereas no significant differences were found in rhizome diameter and root length between transplants and reference plants. Habitat suitability analysis showed that transplanting site should be chosen in shallow subtidal zone (water depth <1 m) with high transparency and high-silted sandy mud

Annual and perennial life history strategies of Zostera marina populations under different light regimes

The seagrass Zostera marina is geneti- cally considered to be perennial, but annual popula- tions of this species exist as well and are under severe environmental stress in many geographical locations. We investigated why Z. marina in Jindong Bay (Korea) exhibited a typical perennial life history at a shallow site but an annual life history at a deep site. We hy- pothesized that Z. marina shoots in the deep popula- tion die off after fall due to severe light reductions, and that the re-establishment of this population is completely dependent on sexual reproduction. Life histories of these populations were examined by con- structing life tables using monthly measurements of shoot recruitment and mortality. In the deep popu - lation, new shoot recruitment was only achieved by seedlings, and approximately 95% of the surviving seedlings flowered. No shoots overwintered in the deep population. In contrast, shoot recruitment in the shallow population was primarily achieved by asexual reproduction. High summer water temperatures and subsequent severe underwater light reduction during summer and fall probably led to the high mortality in Z. marina shoots in the deep population, resulting in no shoot survival after fall. The deep population likely exhibits an annual life history strategy to achieve pop- ulation persistence under repetitive and acute unfa- vorable environmental conditions. From an evolution- ary perspective, the life history traits of Z. marina would define this species as an intermediate between annual and perennial.

Persistence of Zostera marina L. (eelgrass) seeds in the sediment seed bank

Two separate field experiments in the Newport River/Back Sound, North Carolina (NC) and the lower Chesapeake Bay (CB), Virginia were conducted in 2007 and 2008 to quantify the effects of time (6, 12, 15months), seed source (mixed-annual, perennial NC; perennial CB), site (local environmental factors), and sediment type (fine, coarse) on the persistence of Zostera marina seeds in the sediment seed bank. It is here, at the southern limit of the species distribution along the western Atlantic, that the probability of population loss may be high and the importance of a seed bank in the resilience and recovery of these populations great. Experimental results indicate that viability of both NC and CB seeds decreased significantly after just 6months in the sediment following the seasonal period of maximum germination and continued to decline over time with no seeds viable remaining in CB cores and <5% of seeds remaining viable after 15months in NC treatments. In these experiments time was the overriding factor affecting the persistence Z. marina seed banks for all treatments in both NC and CB and viability was not significantly affected by seed source, site, or sediment type. Based on the results of the in situ experiments, mixed-annual and perennial Zostera marina populations in North Carolina and perennial populations in Virginia produce transient seed banks (seeds viable <12months). The lack of a persistent seed bank may reduce the resilience of Z. marina at the limits of the species distribution to repeated stress events. As a result these populations may be particularly susceptible to disturbance with only a limited capacity for recovery if sexual reproduction is impaired.

Genetic characteristics of three Baltic Zostera marina populations

We performed genetic analyses of three Baltic eelgrass (Zostera marina) populations in Puck Bay (PB), Cudema Bay (CB) and Greifswalder Bodden (GB). The aim of this study was to identify the eelgrass population genetically closest to that from the PB, which could potentially serve as a reservoir for the restoration of the underwater meadows in this bay, seriously degraded in the past. We applied a 12-microsatellite assay to test the genetic distance between the target eelgrass populations. We found that the allelic richness values of the GB, PB and CB populations were 2.25, 3.77 and 3.50 respectively. The genetic diversity found in GB was low and could be explained by the population’s history, whereas the diversity of CB was higher than expected in a population located at the edge of the species’ range. Analyses of genetic differentiation and structure showed that of the three populations studied, PB and CB were closer to each other than to the GB population. The reasons for this differentiation in eelgrass populations and the implications of the results of their genetic analysis on the planned restoration of the PB populations are discussed.

Genetic characteristics of three Baltic Zostera marina populations

Abstract We performed genetic analyses of three Baltic eelgrass (Zostera marina) populations in Puck Bay (PB), Cudema Bay (CB) and Greifswalder Bodden (GB). The aim of this study was to identify the eelgrass population genetically closest to that from the PB, which could potentially serve as a reservoir for the restoration of the underwater meadows in this bay, seriously degraded in the past. We applied a 12-microsatellite assay to test the genetic distance between the target eelgrass populations. We found that the allelic richness values of the GB, PB and CB populations were 2.25, 3.77 and 3.50 respectively. The genetic diversity found in GB was low and could be explained by the population’s history, whereas the diversity of CB was higher than expected in a population located at the edge of the species’ range. Analyses of genetic differentiation and structure showed that of the three populations studied, PB and CB were closer to each other than to the GB population. The reasons for this differentiation in eelgrass populations and the implications of the results of their genetic analysis on the planned restoration of the PB populations are discussed.

窪地の埋め戻し場所に出現したアマモの遺伝的多様性と種子供給源

窪地の埋め戻し場所に出現したアマモの遺伝的多様性と種子供給源

Eelgrass Zostera marina populations in northern Norwegian fjords are genetically isolated and diverse

Populations along the northern boundary of a marine species' distributional range in the NE Atlantic are expected to harbor lower standing genetic variation as a consequence of post- glacial expansion following the last glacial maximum. Founder events and marginal habitat avail- ability may render the edge populations more vulnerable to anthropogenic stress and less cap - able of rapid adaptation to global climate change, a concern for conservation and management. We analyzed meadow architecture, persistence and connectivity within and among 15 locations (600 samples genotyped with 8 microsatellite loci) in 3 fjords in Troms County, Norway (69° N). Whereas global mean allelic diversity (standardized for sample size) was in accordance with pre- vious studies using the same markers, more extensive sampling revealed a broader range of allelic richness (mean = 2.85; range = 1.84 to 4.21) in the regional pool. Genotypic diversity was typically high, whereas large genets were rare (2 out of 15 locations). Population differentiation (FST) was 2 to 6 times higher between fjords than within fjords. A Bayesian (STRUCTURE) analysis also strongly supported the genetic distinctness of each fjord. Although 9 locations within the 60 km long Bals- fjord were connected by gene flow, demographic connectivity may actually be low, as fixed differ- ences were observed at 6 of the 9 locations, along with significantly positive inbreeding coeffi- cients and strong substructure. Overall, our results suggest that these northern, leading-edge meadows are healthy, but vigilance is required to avoid further losses. Fjord-level management, especially of the larger fjords, will be sufficient to capture the range of variation.

Long-term seed storage and viability of Zostera marina

Successful establishment of seedlings in populations of Zostera marina (eelgrass), especially for restoration efforts using stored seeds, depends in part on viability and germination of seeds. Seeds of Z. marina were collected from plants and stored in seawater at 5°C for up to several years. Seed viability, assessed with the viability stain, tetrazolium chloride, decreased steadily over a four-year period. There was a strong correlation between age and viability; viability of fresh seeds was approximately 77% whereas for four-year old seeds was 32%. However, only 51 of 975 of fresh seeds that germinated (∼5%) developed leaves. The physical structure of the seed was evaluated to understand the effects of aging. It was determined that as seeds age there is an increase in the number of fractures on the seed coat. These data combined with the recent awareness that global seagrass populations are declining present valuable information to help maintain viable seed repositories which may contribute to the conservation and restoration of these wild plants.

Genetic diversity and gene flow in Zostera marina populations surrounding Long Island, New York, USA: No evidence of inbreeding, genetic degradation or population isolation

Since the 1930s, eelgrass around Long Island, New York, USA, has experienced significant ecological and anthropogenic disturbances reducing areal coverage of the species. Patchiness, low density or isolation of these remaining populations increase susceptibility of this aquatic angiosperm to extinction. The loss of genetic diversity and patch connectivity, may contribute to lower fitness of eelgrass thus affecting recovery potential. Previous studies of eelgrass populations around Long Island report genetically isolated populations with low diversity. In contrast, this study found neither the evidence of inbreeding nor indications of genetic degradation for the same populations. Measures of genetic diversity such as average alleles (A=7.59) and fixation index (F=0.02) suggest no significant impediments to genetic connectivity among populations sampled. Gene flow (Nm=4.58) and bottleneck analyses suggest the major disturbances of the past have not strongly affected population structure in the Long Island system. These findings have significant implications for both management and restoration. Locally, eelgrass populations in Long Island waters are unlikely to decline through genetic erosion or inbreeding processes alone. Plants from within these populations possess adequate genetic diversity to undertake restoration activities. On a larger geographic scale, the ability of these plants to maintain such high levels of genetic diversity and connectivity despite the significant areal losses historically provides optimism for the recovery potential of this species despite recent global losses.

Tolerance and response of Zostera marina seedlings to hydrogen sulfide

Populations of Zostera marina L., the common seagrass of Pacific Northwest shallow marine environments, has undergone local extinction in coastal embayment's where it has traditionally existed. Because the habitat created by these plants is important for near-shore productivity and biodiversity, declining populations and local extinctions can have serious ecosystem consequences. One possibility for the failures of population increase and re-colonization of embayment's with complete loss is an increase in sediment H2S. We designed experiments to test the influence of various H2S concentrations on Z. marina seedlings. To do this we immersed seedlings in five different concentrations of H2S (68μM, 204μM, 680μM, 2.04mM and 6.8mM) in 2010, and three additional concentrations (400μM, 500μM and 800μM) in 2011. Treated seedlings were consistently killed above 680μM. In addition, high doses (680μM, 800μM, 2.04mM and 6.8mM) of H2S caused depression of photosynthetic output, as well as causing Photosystem II to become inactive whereas Photosystem I remained active. At low doses of H2S (68μM) it appears that photosynthesis increases. Our observations also suggest that this plant may adapt to lethal H2S concentrations if subjected to multiple, but gradually increasing sub-lethal H2S concentrations. These results suggest that Z. marina seedlings are consistently killed at concentrations of hydrogen sulfide found in localities that have experienced declines and local extinctions, and ultimately can be used to explain the lack of re-colonization in these sites.

Estimation of Production in Zostera marina Population by Biomass Method

Estimation of Production in Zostera marina Population by Biomass Method