Anthesis and seed production in Zostera marina L. (eelgrass) from the chesepeak by

Anthesis and seed production in Zostera marina L. were studied in three areas of the Chesapeake Bay from January to June 1980. Inflorescence primordia with distinguishable anthers and pistils were first observed in February when water temperature was 3°C. Development of the reproductive shoots in the field continued after February as water temperature rose, with the first evidence of pollen release in mid-April (water temperature 14.3°C). Stigmata loss was first observed in samples taken in late April at all locations by as water temperatures averaged above 16°C. Pollination was complete at all locations by 19 May and anthers were no longer present. Few reproduction shoots were found on 3–5 June and seed release was assumed to be complete by this time (water temperature 25°C). The density of flowering shoots ranged from 11 to 19% of the total number of shoots, producing an estimated 8127 seeds m^?2.Comparison of flowering events with other areas along a latitudinal gradient from North Carolina to Canada indicated that reproductive events occurred earlier in the most southern locations and at successively later dates with increasing latitude.     

Evidence of Eelgrass (Zostera marina) Seed Dispersal by Northern Diamondback Terrapin (Malaclemys terrapin terrapin) in Lower Chesapeake Bay

The initial discovery in May 2009 of eelgrass (Zostera marina) seeds in fecal samples of wild-caught northern diamondback terrapins (Malaclemys terrapin terrapin) was the first field evidence of eelgrass seed ingestion in this species. This finding suggested the potential of terrapins as seed dispersers in eelgrass beds, which we sampled for two additional years (2010 and 2011). Seeds were only found in feces of terrapins captured prior to June 8 in all three years, coinciding with eelgrass seed maturation and release. Numbers of seeds in terrapin feces varied annually and decreased greatly in 2011 after an eelgrass die off in late 2010. The condition of seeds in terrapin feces was viable-mature, germinated, damaged, or immature. Of terrapins captured during time of seed release, 97% were males and juvenile females, both of which had head widths <30 mm. The fraction of individuals with ingested seeds was 33% for males, 35% for small females, and only 6% for large (mature) females. Probability of seed ingestion decreased exponentially with increasing terrapin head width; only males and small females (head width <30 mm) were likely to be vectors of seed dispersal. The characteristic that diamondback terrapins have well-defined home ranges allowed us to estimate the number of terrapins potentially dispersing eelgrass seeds annually. In seagrass beds of the Goodwin Islands region (lower York River, Virginia), there were 559 to 799 terrapins, which could disperse between 1,341 and 1,677 eelgrass seeds annually. These would represent a small proportion of total seed production within a single seagrass bed. However, based on probable home range distances, terrapins can easily traverse eelgrass meadow boundaries, thereby dispersing seeds beyond the bed of origin. Given the relatively short dispersion distance of eelgrass seeds, the diamondback terrapin may be a major source of inter-bed seed dispersal and genetic diversity.     

Seed germination and seedling growth of Zostera marina L. (eelgrass) in the chesapeake bay

Seed germination and seedling growth of Zostera marina L. were monitored in the Chesapeake Bay in 1979 and 1980. Harvested seeds were placed in small acrylic tubes at several sites representing the salinity range of Z. marina distribution. Seed germination was observed first in late September and continued through May, with peaks in the fall and spring. The majority of seeds that germinated (66%) did so between December and March when water temperatures ranged from 0–10°C. There was no correlation between sites (different salinity regimes) and frequency of germination rates, indicating that salinity was not a major factor in the germination process in this study. Additional information on seed germination was available for seeds collected in 1977 and 1980 and subsequently monitored for germination at only one site. These data were similar to germination frequency recorded in 1979–1980.Seedling growth was measured from individuals collected from an existing Zostera marina bed. Seedlings were collected from November through May, at which time we could no longer distinguish seedlings from existing vegetative stock. Growth was characterized by the increased length of the primary shoot, number of leaves per shoot and numbers of shoots per plant. Seedling growth was slow during the winter months (water temperature ? 10°C) but rapidly increased in the spring (temperatures > 10°C). The size range of the harvested seedlings indicated that seed germination in the field probably occurred from October through April, corroborating evidence from the seed germination experiments.     

Sulfur accumulation in eelgrass (Zostera marina) and effect of sulfur on eelgrass growth

Eelgrass (Zostera marina) was grown under exposure to high levels of sediment sulfides to examine their ability to reoxidize sulfides intruding into the plants. The plants were kept under full light (control and high sulfide level) and at 10% of light saturation (high sulfide level) for 3 weeks and growth and accumulation of elemental sulfur (S⁰) in the plants were examined. The growth rate was reduced with ∼75% in the low light treatment, whereas there was no significant difference between the rates at full light saturation. S⁰ was accumulating in the below-ground structures of the plants exposed to high sulfide concentrations with highest concentration in the youngest roots and oldest internodes. There was no accumulation of S⁰ in the leaves, suggesting that the intruding sulfides were reoxidized in the below-ground structures before reaching the leaves. The accumulation of S⁰ was higher in the roots of the low light treatment (up to two times) suggesting a larger intrusion of sulfides. These plants also appeared highly affected by the treatment with rotting meristems and increased mortality after the 3-week growth period. These results are the first to show an accumulation of sulfur compounds internally in seagrasses as a result of reoxidation of sulfides. The reoxidation is facilitated by the internal transport of oxygen and is an example of the advantage of the internal lacunae system in seagrasses.     

Characterization of single nucleotide polymorphism markers for eelgrass (Zostera marina)

We characterized 37 single nucleotide polymorphism (SNP) makers for eelgrass Zostera marina. SNP markers were developed using existing EST (expressed sequence tag)-libraries to locate polymorphic loci and develop primers from the functional expressed genes that are deposited in The ZOSTERA database (V1.2.1). SNP loci were genotyped using a single-base-extension approach which facilitated high-throughput genotyping with minimal optimization time. These markers show a wide range of variability among 25 eelgrass populations and will be useful for population genetic studies including evaluation of population structure, historical demography, and phylogeography. Potential applications include haplotype inference of physically linked SNPs and identification of genes under selection for temperature and desiccation stress.     

Population structure and genetic diversity among eelgrass (Zostera marina) beds and depths in San Francisco Bay

The seagrass Zostera marina is widely distributed in coastal regions throughout much of the northern hemisphere, forms the foundation of an important ecological habitat, and is suffering population declines. Studies in the Atlantic and Pacific oceans indicate that the degree of population genetic differentiation is location dependent. San Francisco Bay, California, USA, is a high-current, high-wind environment where rafting of seed-bearing shoots has the potential to enhance genetic connectivity among Z. marina populations. We tested Z. marina from six locations, including one annual population, within the bay to assess population differentiation and to compare levels of within-population genetic diversity. Using 7 microsatellite loci, we found significant differentiation among all populations. The annual population had significantly higher clonal diversity than the others but showed no detectible differences in heterozygosity or allelic richness. There appears to be sufficient input of genetic variation through sexual reproduction or immigration into the perennial populations to prevent significant declines in the number and frequency of alleles. In additional depth comparisons, we found differentiation among deep and shallow portions in 1 of 3 beds evaluated. Genetic drift, sweepstakes recruitment, dispersal limitation, and possibly natural selection may have combined to produce genetic differentiation over a spatial scale of 3-30 km in Z. marina. This implies that the scale of genetic differentiation may be smaller than expected for seagrasses in other locations too. We suggest that populations in close proximity may not be interchangeable for use as restoration material.     

Effects of edge/interior and patch structure on reproduction in Zostera marina L. in Chesapeake Bay,USA

We examined the effects of location (patch edge vs. interior) and shoot density (individual, patchy, continuous) on reproduction in three natural and two transplanted Chesapeake Bay (USA) stands of the submerged marine angiosperm Zostera marina L. (eelgrass; Zosteraceae). There were no edge effects on demographic-based reproductive effort or reproductive output (propagule production), and patch structure (individual, patchy, continuous) alone never accounted for the majority of variability in any metric. Transplant site was the most important predictor of eelgrass reproduction response, and relationships among metrics were predictable within sites. Our results suggest that, in Chesapeake Bay eelgrass, environmental factors acting at a regional scale (km) have a stronger impact on reproductive investment than those at a patch scale (1–10 m). Since tradeoffs between clonal and sexual production are mediated primarily by exogenous environmental factors, site selection may be more critical than transplant configuration for producing self sustaining stands, and achieving long-term restoration success.     

In situ phytoremediation of PAH- and PCB-contaminated marine sediments with eelgrass (Zostera marina)

In view of the fact that there are presently no cost-effective in situ treatment technologies for contaminated sediments, a 60-week-long phytoremediation feasibility study was conducted in seawater-supplied outdoor ponds to determine whether eelgrass (Zostera marina) is capable of removing polynuclear aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) from submerged marine sediments. It was determined that all PAHs and PCBs, independent of the number of aromatic rings and degree of chlorination, respectively, were removed to a much larger extent in planted sediments compared to unplanted controls. After 60 weeks of treatment, the concentration of total PAHs decreased by 73% in planted sediments but only 25% in unplanted controls. Similarly, total PCBs declined by 60% in the presence of plants while none were removed in the unplanted sediment. Overall, the apparent PAH and PCB biodegradation was greatest in the sediment layer that contained most of the eelgrass roots. Abiotic desorption tests conducted at week 32 confirmed that the phytoremediation process was not controlled by mass-transfer or bioavailability limitations since all PAHs and PCBs desorbed rapidly and to a large extent from the sediment. PAHs were detected in both roots and shoots, with root and shoot bioaccumulation factors for total PAHs amounting to approximately 3 and 1, respectively, after 60 weeks of phytoremediation treatment. Similarly, the root bioaccumulation factor for total PCBs was around 4, while no PCBs were detected in the eelgrass leaves at the end of the experiment. The total mass fraction of PAHs and PCBs absorbed and translocated by plant biomass during the 60-week period was insignificant, amounting to less than 0.5% of the total mass of PAHs and PCBs which was initially present in the sediment. Finally, the number of total heterotrophic bacteria and hydrocarbon degraders was slightly but not statistically significantly greater in planted sediments than in unplanted controls. After ruling out contaminant loss to the water column or absorption and transformation within plant cells, it is most likely that the presence of eelgrass stimulated the microbial biodegradation of PAHs and PCBs in the rhizosphere by releasing root exudates, plant enzymes, or even oxygen. Additional research is needed to further elucidate these potential phytoremediation mechanisms.     

Effectiveness of pectin extracted from the eelgrass Zostera marina for alleviating lead-induced liver injury

The effects of pectin from the eelgrass Zostera marina on toxic liver injury induced by enteral administration of lead acetate are examined in experiments on rats. The results show that pectin helps to rapidly reduce lead concentration in liver, to decrease lipid peroxidation, and to normalize the levels of total cholesterol and triglycerides in blood serum and liver.     

Effects of the herbicide atrazine on adenine nucleotide levels in Zostera marina L. (eelgrass)

Response of adenine nucleotides (ATP, ADP, AMP) and adenylate energy charge (EC) to atrazine, a triazine herbicide, was evaluated as an indicator of metabolic state in Zostera marina L. (eelgrass), a submerged marine angiosperm. Short-term (6 h) atrazine stress reduced ATP and total adenylates (AT) at both 10 and 100 ppb, but EC remained constant. Net productivity decreased at 100, but not at 10 ppb atrazine over 6 h. Long-term (21 day) atrazine stress was evidenced by growth inhibition and 50% mortality near 100 ppb. EC was reduced at 0.1, 1.0 and 10 ppb atrazine, but ATP and EC increased with physiological response to severe stress (100 ppb) after 21 days. Apparently, ATP and AT decrease over the short-term but rebound over the long-term with severe atrazine stress, increasing beyond control levels before plant death results. Supplementing adenine nucleotide and EC results with more conventional quantitative analyses should afford greater knowledge of physiological response to environmental variation.     

A simulation model of production,seasonal changes in biomass and distribution of eelgrass (Zostera marina) in Lake Grevelingen

Summary A simulation model has been described, based on data from Lake Grevelingen, The Netherlands, as a predictive tool for lake management. The model has been developed as part of a large-scale aquatic modelling effort in Lake Grevelingen, carried out in close cooperation with the Delft Hydraulics Laboratory and the Delta Department, Environmental Research Division of the Ministry of Transport and Public Works. Available data on growth rates per unit eelgrass biomass, obtained with the leaf-marking technique, and on above- en below ground biomass and shoot density changes per unit area have been used. A space limitation depending on density of the above ground biomass and a growth limitation due to shortage in below ground biomass have been introduced. The seasonal changes in eelgrass production, both above and below ground, have been simulated as functions of the external forcing variables light, water temperature, wind generated water movements and of the internal control variables due to aging of the plant material. The vertical distribution of eelgrass can be partly explained from the modelling results on space, light and below ground biomass limitations. From the shore down to about 1 m waterdepth the above ground eelgrass biomass suffers from space limitation. Between 1 and 2 m production and biomass reach maximum values. Between 2 and 3 m waterdepth the above ground eelgrass growth is limited by the availability of below ground biomass. Between 3 and 5 m waterdepth both below ground biomass and light are the growth-limiting factors. Below 5 m waterdepth light is not sufficient to sustain net growth of eelgrass from rhizomes. Together with additional data — not used in the model — on seed production and growth of eelgrass shoots from seeds the vertical and horizontal distribution of the dominant macrophyte in the lake can be explained.     

Relationships between bed age,bed size,and genetic structure in Chesapeake Bay (Virginia,USA) eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis> L.)

Genetic structure and diversity can reveal the demographic and selective forces to which populations have been exposed, elucidate genetic connections among populations, and inform conservation strategies. Beds of the clonal marine angiosperm Zostera marinaL. (eelgrass) in Chesapeake Bay (Virginia, USA) display significant morphological and genetic variation; abundance has fluctuated widely in recent decades, and eelgrass conservation is a major concern, raising questions about how genetic diversity is distributed and structured within this metapopulation. This study examined the influence of bed age (<65years versus<6years) and size (>100ha versus<10ha) on morphological and genetic (allozyme) structure and diversity within Chesapeake Bay eelgrass beds. Although both morphology and genetic diversity varied significantly among individual beds (F _ST=0.198), neither varied consistently with bed age or size. The Chesapeake eelgrass beds studied were significantly inbred (mean F _IS=0.680 over all beds), with inbreeding in old, small beds significantly lower than in other bed types. Genetic and geographic distances within and among beds were uncorrelated, providing no clear evidence of isolation by distance at the scale of 10's of km. These results suggest that local environmental conditions have a greater influence on plant morphology than do bed age or size. They support the hypotheses that eelgrass beds are established by multiple founder genotypes but experience little gene flow thereafter, and that beds are maintained with little loss of genetic diversity for up to 65 years. Since phenotypic and genotypic variation is partitioned among beds of multiple ages and sizes, eelgrass conservation efforts should maximize preservation of diversity by minimizing losses of all beds.     

Means of rapid eelgrass (Zostera marina L.) recolonisation in former dieback areas

Recolonisation of eelgrass (Zostera marina L.) was studied in a Danish estuary during summer 2001 following an anoxia event the previous summer. Leaf bundles had detached from the rhizomes while healthy-looking roots and rhizomes remained in the sediment. We hypothesise that the stabilising effect of remaining belowground biomass, the presence of rhizomes with buds, the presence of a large seed bank and the potential surviving shoots from the previous population may stimulate and speed up recovery in previously colonised areas compared to bare areas.A large seed bank containing more than 11,000 seeds m⁻² was found in the dieback area. Seeds were found in the upper 14 cm of the sediment but judging from the length of the hypocotyle of the seedlings, only seeds from the upper 5.5 cm of sediment germinated successfully. The upper 5.5 cm represented a seed pool of approximately 1000 seeds m⁻². Germination of these seeds was the primary mode of recolonisation in the estuary, since 96% of the plants in the investigated plot were seedlings. Only 4% of the plants were survivors from the previous year.Although densities of seedlings may exceed densities of surviving shoots, we argue that plants surviving oxygen depletion may still contribute considerably to the recolonisation of a former dieback area as these plants have faster elongation and branching rates and lower mortality rates relative to seedlings.There was no indication of recolonisation from dormant buds on rhizomes. This finding was confirmed in laboratory experiments where buds failed to germinate in the absence of the apical shoot. We examined the structure and ageing of buds and found general withering with age, indicating that buds should germinate shortly after the dieback if at all. Our results, therefore, suggest that rhizome buds are not dormant buds but simply side shoots that have failed to grow.     

Production and decomposition of eelgrass (Zostera marina L.) in saline Lake Grevelingen

Summary During five 28-hours measurements in 1981, the oxygen production and consumption in an eelgrass community in saline Lake Grevelingen were investigated using light plexiglass enclosures. Applying a conversion factor of 0.29 the amount of carbon fixed and the amount of organic carbon mineralized were estimated. Gross and net production were estimated over 24-hours periods.There appeared to be a good correlation between production and insolation on the water surface. For every measurement period the production as a function of light and aboveground eelgrass biomass in the enclosure were calculated. This showed a maximum of 5.10^–6 mg C.J.^–1 g dry weight^–1 in April and minimum of 1.4.10^–6 mg C.J.^–1 g^–1 in August.Using the calculated production coefficients, the insolation and the eelgrass biomass the gross production, net production and consumption during the growing season of 1976 were calculated. Gross production amounted to 340 gC.m^–2, and net production came to 130 g C.m^–2. Approximately 60 gC.m^–2 was respired by the eelgrass plants while the remaining 150 gC.m^–2 was consumed or mineralized by other organisms on the sampling spot. Approximately 120 g C.m^–2.yr^–1 was transported by wind and wave action towards the eastern part of the lake where it became anaerobically degraded. This resulted in the formation of sulfide and methane.Communication no. 236 of the Delta Institute for Hydrobiological Research, Yerseke, The Netherlands.     

A Comparative Test of Mechanized and Manual Transplanting of Eelgrass, Zostera marina, in Chesapeake Bay

Abstract The laborious process of manual seagrass transplanting has often limited the size of seagrass restoration efforts. This study tested the efficiency of a mechanized planting boat, previously used for transplanting Halodule wrightii, relative to manual transplanting methods for establishing Zostera marina in Chesapeake Bay. Eelgrass planting was conducted at two sites, one each in the Rappahannock and James rivers, in October 2001. The methods were evaluated by three criteria: (1) initial planting success = proportion of attempted planting units (PUs) initially established (number confirmed in sediment by divers/number attempted); (2) survival = proportion of the initially established PUs persisting over 1, 4, and 24 weeks; and (3) efficiency = labor (in person·seconds) invested in each surviving PU. Initial planting success was significantly lower for the planting boat (24 and 56% at the Rappahannock and James sites, respectively) than for manual transplanting (100% at both sites). At the Rappahannock site, survival of initially established PUs declined over time for both methods, but while mean survival was always higher for manually planted rows, differences in survival between methods were not statistically significant. At the James site, survival to 1 and 4 weeks was significantly lower for the machine than for the manual method, but survival to 24 weeks was not significantly different. While the machine was able to attempt PUs faster than the manual method (2.2 s/PU vs. 5.8 s/PU, respectively), this speed was offset by poorer planting success rates, resulting in a much greater total labor investment for each machine‐planted PU that persisted to 24 weeks than for each similarly persisting manually planted PU (40.6 person·seconds/PU and 22.4 person·seconds/PU, respectively, averaged across sites). In summary, those PUs successfully planted by the machine survived similarly to PUs planted by hand, but as a result of poorer initial planting success, the machine required a greater investment of labor and plant donor stock for each PU surviving to 24 weeks. Therefore, in its tested configuration this planting boat is not a significant improvement over the manual method for transplanting eelgrass.     

Control of microbial growth on eelgrass (Zostera marina L.: Spermatophyta) by leaf-derived metabolites

Curie point pyrolysis-mass spectrometry is a powerful method for fast characterization of complex, nonvolatile materials. Fast, reproducible heating of the material results in a characteristic mixture of volatile fragment products, which is analyzed on-line by mass spectrometry. The method can be used for various purposes ranging from classification and identification to quality control and biochemical analysis and has already proven to be a versatile tool in the fields of (micro-) biology, biochemistry, soil science and geochemistry. Our fully automated Py-MS system for batch-wise analysis of series of samples will be presented, together with computer methods for multivariate analysis of the spectral data. Some results obtained within the application-fields mentioned above will also be given.     

Toxicity of reduced nitrogen in eelgrass (Zostera marina) is highly dependent on shoot density and pH

In sheltered, eutrophicated estuaries, reduced nitrogen (NHx), and pH levels in the water layer can be greatly enhanced. In laboratory experiments, we studied the interactive effects of NHx, pH, and shoot density on the physiology and survival of eelgrass (Zostera marina). We tested long-term tolerance to NHx at pH 8 in a 5-week experiment. Short-term tolerance was tested for two shoot densities at both pH 8 and 9 in a 5-day experiment. At pH 8, eelgrass accumulated nitrogen as free amino acids when exposed to high loads of NHx, but showed no signs of necrosis. Low shoot density treatments became necrotic within days when exposed to NHx at pH 9. Increased NH3 intrusion and carbon limitation seemed to be the cause of this, as intracellular NHx could no longer be assimilated. Remarkably, experiments with high shoot densities at pH 9 showed hardly any necrosis, as the plants seemed to be able to alleviate the toxic effects of high NHx loads through joint NHx uptake. Our results suggest that NHx toxicity can be important in worldwide observed seagrass mass mortalities. We argue that the mitigating effect of high seagrass biomass on NHx toxicity is a positive feedback mechanism, potentially leading to alternative stable states in field conditions.     

The response of interstitial ammonium in eelgrass (Zostera marina L.) beds to environmental perturbations

Natural and human-induced perturbations of eelgrass (Zostera marina L.) beds were used to examine the interaction between the sediment interstitial ammonium pool and nitrogen uptake by the plants. Eelgrass colonization of unvegetated areas was accompanied by a substantial decrease in the interstitial ammonium pool over a 4-yr period. The changes in interstitial ammonium and shoot density during colonization support an already determined relationship between shoot density and ammonium pool measurements. In field perturbation experiments, removing eelgrass leaves and sealing the sediment surface altered the flux of ammonium from the interstitial ammonium pool, and resulted in a rapid increase in interstitial ammonium concentrations. Measurements of ammonium accumulation under the various perturbation conditions and a control permitted calculation of the sediment ammonium flux. These estimates include uptake by eelgrass roots, regeneration in the root zone, and diffusion from the sediments. Nitrogen limitation was observed in some eelgrass beds.