Eelgrass, Zostera marina, growth along depth gradients: upper boundaries of the variation as a powerful predictive tool

1200 measurements of eelgrass ( Zostera marina ) biomass, shoot density and cover along 19 depth gradients in Øresund, located between Denmark and Sweden, were analysed to characterise growth of eelgrass in relation to depth. The large data set allowed analyses of boundaries of distribution as well as of average trends. Natural variability is large in shallow water where populations are disturbed by wave action and other physical parameters. Models based on average values, therefore, did not adequately describe growth regulation by resources, and only explained a minor part (up to 30%) of the overall variation in data. In contrast, boundary functions, which describe the upper bounds of distributions, focus on the variation produced by the ultimately growth-regulating resource, and therefore provide models with high predictive power. An exponential model explained up to 90% of the variation in upper bounds of eelgrass shoot density as a function of depth and indicated that shoot density was ultimately regulated by light availability. The boundary functions demonstrated that eelgrass shoot density, biomass and cover followed markedly different patterns as functions of depth and were affected differently by the factors governing their distribution. In addition, boundary functions revealed informative spatial structures in data and illustrated whether a given general trend was caused by changes in maximum values, minimum values or both. For example, upper and lower boundaries of biomass-shoot density relations changed markedly with depth, demonstrating depth-related changes in intraspecific succession and competition patterns. Boundary functions are therefore suggested as a promising tool for analysing ultimate regulating factors of distribution and growth of organisms when large data sets are available.     

Role of lipids in molecular thermoadaptation mechanisms of seagrass Zostera marina

By using the combined approaches of microcalorimetric analysis and polarizing microscopy, the crystal-liquid crystal-isotropic melt phase transition of major phospholipids (phosphatidylcholine and phosphatidylethanolamine) and glycolipids (monogalactosyldiacylglycerol and digalactosyldiacylglycerol) isolated from marine seagrass Zostera marina were investigated. Here we discuss the results in view of the fatty acid structures of the lipids studied.     

The mercury binding activity of pectin isolated from the seagrass Zostera marina

The kinetics of mercury binding by pectin isolated from the seagrass Zostera marina was described, and its maximum mercury binding activity at pH from 2.0 up to 6.0 was determined. It was shown that mercury binding by pectin in in vitro conditions did not depend on concentration of hydrogen ions in the environment. The maximum mercury binding activity estimated from the Langmuir equation was 2.64 mmol/g of dry mass of the pectin.     

An upgraded method to relocate marked shoots of the seagrass Zostera marina

This paper presents a new method for the recovery of marked seagrass blades. The introduction of a plastic belt surrounding the marked shoot at a sediment level provided a relocation arrangement which was unloosed by drag forces or grazing. The relocation method was tested on Zostera marina L. It proved to have the advantage of increasing dramatically the number of marked shoots recovered up to 100% while reducing the cost of the procedure to a minimum. An allometric model indicated that the introduced relocation method has no impact on the development of the plant.     

North Atlantic phylogeography and large-scale population differentiation of the seagrass Zostera marina L

As the most widespread seagrass in temperate waters of the Northern Hemisphere, Zostera marina provides a unique opportunity to investigate the extent to which the historical legacy of the last glacial maximum (LGM18 000-10 000 years bp) is detectable in modern population genetic structure. We used sequences from the nuclear rDNA-internal transcribed spacer (ITS) and chloroplast matK-intron, and nine microsatellite loci to survey 49 populations (> 2000 individuals) from throughout the species' range. Minimal sequence variation between Pacific and Atlantic populations combined with biogeographical groupings derived from the microsatellite data, suggest that the trans-Arctic connection is currently open. The east Pacific and west Atlantic are more connected than either is to the east Atlantic. Allelic richness was almost two-fold higher in the Pacific. Populations from putative Atlantic refugia now represent the southern edges of the distribution and are not genetically diverse. Unexpectedly, the highest allelic diversity was observed in the North Sea-Wadden Sea-southwest Baltic region. Except for the Mediterranean and Black Seas, significant isolation-by-distance was found from ~150 to 5000 km. A transition from weak to strong isolation-by-distance occurred at ~150 km among northern European populations suggesting this scale as the natural limit for dispersal within the metapopulation. Links between historical and contemporary processes are discussed in terms of the projected effects of climate change on coastal marine plants. The identification of a high genetic diversity hotspot in Northern Europe provides a basis for restoration decisions.     

Contrasting oxygen dynamics in the freshwater isoetid Lobelia dortmanna and the marine seagrass Zostera marina

BACKGROUND: and Aims Submerged plants possess well-developed aerenchyma facilitating intra-plant gas-phase diffusion of O2 to below-ground tissues, which are usually buried in anoxic sediments. However, aquatic habitats differ in terms of O2 fluctuations in the water column and in O2 consumption of the sediment, and aquatic plants differ in aerenchymal volume and resistance to O2 diffusion through the plant and across leaf and root surfaces. The hypothesis that the freshwater isoetid Lobelia dortmanna and the marine seagrass Zostera marina should display pronounced contrasts in intra-plant O2 dynamics because of differences in morphology/anatomy, physiology and growth habitat was tested. METHODS: In order to determine the O2 dynamics and relate this to the anatomy and morphology of the two species, O2 microelectrodes were inserted in the aerenchyma of leaves and roots, the sediment pore-water, and the water column in the field. Manipulation of water column O2 in the laboratory was also carried out. KEY RESULTS: It was found that intra-plant transport of O2 between leaf and root tips takes place more readily in L. dortmanna than in Z. marina due to shorter distances and greater cross-sections of the aerenchyma. The major exchange of O2 across roots of L. dortmanna can be accounted for by small intra-plant resistances to diffusion, larger root than leaf surfaces, and greater radial diffusive resistance of leaves than roots. In contrast, the major O2 exchange across leaves than roots of Z. marina can be accounted for by the opposite anatomical-morphological features. The larger aerenchymal volume and the smaller metabolic rates of L. dortmanna compared to Z. marina imply that turnover of O2 is slower in the aerenchyma of L. dortmanna and O2 fluctuations are more dampened following changes in irradiance. Also, O2 accumulated in the aerenchyma can theoretically support dark respiration for a few hours in L. dortmanna but for only a few minutes in Z. marina. CONCLUSIONS: The build-up of O2 in the pore-water of L. dortmanna sediments during the day as a result of high release of photosynthetic O2 from roots and low O2 consumption of sediments means that sediment, aerenchyma and water are important O2 sources for respiration during the following night, while Z. marina relies on the water column as the sole source of O2 because its sediments are anoxic. These differences between L. dortmanna and Z. marina appear to represent a general difference between the isoetid species mainly inhabiting sediments of low reducing capacity of oligotrophic lakes and the elodeid freshwater species and marine seagrasses mainly inhabiting sediments of higher reducing capacity in more nutrient-rich habitats.     

Small-scale removal of seagrass (Zostera marina L.): effects on the infaunal community

Eelgrass meadows are a common feature in shallow waters along the Norwegian coast, where they provide a habitat for a diverse infaunal community. Recreational boat anchoring and moorings physically scour seagrass and may affect the ecosystem functioning and resilience of the system to natural and anthropogenic disturbances. A small-scale eelgrass (Zostera marina) removal experiment was conducted to study the effects on macro- and meiofauna. Entire plants, including the rhizomes, were removed from 4?m² patches in three eelgrass meadows in the inner Oslofjord in October 2010. Core samples were taken after a recovery period of 10 months, from the removed patches as well as from the surrounding meadow. Macrofauna (>500?μm) and meiofauna (63–500?μm) in the sediment were investigated for possible effects of the eelgrass removal. Macrofauna and meiofauna composition were site specific and therefore location was identified as the main determinant for the infaunal community. The eelgrass did not regrow within the recovery period and bare sediment patches with only single eelgrass shoots were present during the sampling. Our analyses support an influence of the removal on individual species, but not the complete community. In particular one species, the gastropod Peringia ulvae, was encountered in higher numbers in samples from the removed patches than in control samples. From a management perspective, such minor removal of eelgrass, on the scale of square metres, appears to have no long-lasting detrimental effect to the infaunal community in sheltered meadows with muddy sediments.     

Length‐weight relationships of 4 fish species from a seagrass Zostera marina bed in Koje Bay,Korea

Length‐weight relationships of 4 fish species collected from a seagrass Zostera marina bed in Koje Bay on the southern coast of Korea were analyzed. The fish samples were captured using a seine net (mesh size 6 mm) at water depth of approximately 1.5 meters during low tide. Fishes were collected 8 times from summer 2016 to spring 2017. The regression parameter b varied between 2.47 for Favonigobius gymnauchen and 3.03 for Ditrema temminckii temminckii.     

Range-edge genetic diversity: locally poor extant southern patches maintain a regionally diverse hotspot in the seagrass Zostera marina

Refugial populations at the rear edge are predicted to contain higher genetic diversity than those resulting from expansion, such as in post-glacial recolonizations. However, peripheral populations are also predicted to have decreased diversity compared to the centre of a species' distribution. We aim to test these predictions by comparing genetic diversity in populations at the limits of distribution of the seagrass Zostera marina, with populations in the species' previously described central diversity 'hotspot'. Zostera marina populations show decreased allelic richness, heterozygosity and genotypic richness in both the 'rear' edge and the 'leading' edge compared to the diversity 'hotspot' in the North Sea/Baltic region. However, when populations are pooled, genetic diversity at the southern range is as high as in the North Sea/Baltic region while the 'leading edge' remains low in genetic diversity. The decreased genetic diversity in these southern Iberian populations compared to more central populations is possibly the effect of drift because of small effective population size, as a result of reduced habitat, low sexual reproduction and low gene flow. However, when considering the whole southern edge of distribution rather than per population, diversity is as high as in the central 'hotspot' in the North Sea/Baltic region. We conclude that diversity patterns assessed per population can mask the real regional richness that is typical of rear edge populations, which have played a key role in the species biogeographical history and as marginal diversity hotspots have very high conservation value.     

Characteristics of adhesion of epiphytic bacteria on leaves of the seagrass Zostera marina and on abiotic surfaces

A comparative study of the adhesion of epiphytic bacteria and marine free-living, saprophytic, and pathogenic bacteria on seagrass leaves and abiotic surfaces was performed to prove the occurrence of true epiphytes of Zostera marina and to elucidate the bacterium-plant symbiotrophic relationships. It was shown that in the course of adhesion to the seagrass leaves of two taxonomically different bacteria, Cytophaga sp. KMM 3552 and Pseudoalteromonas citrea KMM 461, isolated from the seagrass surface, the number of viable cells increased 3-7-fold after 60 h of incubation, reaching 1.0-2.0 x 10(5) cells/cm2; however, in the case of adhesion of these bacteria to abiotic surfaces, such as glass or metal, virtually no viable cells were observed after 60 h of incubation. Such selectivity of cell adhesion was not observed in the case of three other bacterial species studied, viz., Vibrio alginolyticus KMM 3551, Bacillus subtilis KMM 430, and Pseudomonas aeruginosa KMM 433. The amount of viable cells of V. alginolyticus KMM 3551 adsorbed on glass and metal surfaces increased twofold after 40 h of incubation. The cells of saprophytic B. subtilis KMM 430 and pathogenic P. aeruginosa KMM 433 adsorbed on three studied substrata remained viable for 36 h and died by the 60th hour of incubation.     

Effect of patch size and in-patch location on the infaunal macroinvertebrate assemblages of Zostera marina seagrass beds

Much recent work on patch-occupancy dynamics has been concentrated in terrestrial ecosystems, with few examples evident from soft-sediment marine habitats. Seagrass landscapes have recently been recognised to be potentially ideal marine models for the study of such ecological concepts. Infaunal macroinvertebrate assemblages of two patch sizes of the seagrass Zostera marina were compared: small (<15 m diameter) and large (>30 m diameter), using an unreplicated random block design. Further comparison was made between infaunal assemblage composition at the edge and centre of each patch. Univariate statistical analysis of data indicated significantly greater total numbers of taxa in samples from large patches than in small. Multivariate analyses indicated significant differences in assemblage composition due to both patch size and in-patch location, and revealed that differences were due to small changes in the relative abundances of many taxa. Possible mechanisms underlying the observed variations of assemblage composition with patch size and in-patch location are discussed. Although the present results support some of the theories relating to the control of infaunal assemblage composition, explanations are not applicable across all taxonomic groups. At the scale of the present study, seagrass patch size and edge-effects appear to be less significant than 'regional' factors, which relate to relatively small variation in environmental parameters, for the structuring of infaunal macroinvertebrate assemblages.     

Development of an epiphyte indicator of nutrient enrichment: Threshold values for seagrass epiphyte load

Metrics of epiphyte load on macrophytes were evaluated for use as quantitative biological indicators for nutrient impacts in estuarine waters, based on review and analysis of the literature on epiphytes and macrophytes, primarily seagrasses, but including some brackish and freshwater rooted macrophyte species. An approach is presented that empirically derives threshold epiphyte loads which are likely to cause specified levels of decrease in macrophyte response metrics such as biomass, shoot density, percent cover, production and growth. Data from 36 studies of 10 macrophyte species were pooled to derive relationships between epiphyte load and −25 and −50% seagrass response levels, which are proposed as the primary basis for establishment of critical threshold values. Given multiple sources of variability in the response data, threshold ranges based on the range of values falling between the median and the 75th quantiles of observations at a given seagrass response level are proposed rather than single, critical point values. Four epiphyte load threshold categories − low, moderate, high, very high, are proposed. Comparison of values of epiphyte loads associated with 25 and 50% reductions in light to macrophytes suggest that the threshold ranges are realistic both in terms of the principle mechanism of impact to macrophytes and in terms of the magnitude of resultant impacts expressed by the macrophytes. Some variability in response levels was observed among climate regions, and additional data collected with a standardized approach could help in the development of regionalized threshold ranges for the epiphyte load indicator.     

Seasonal shifts in seagrass bed primary producers in a cold-temperate estuary: Dynamics of eelgrass Zostera marina and associated epiphytic algae

The seasonal dynamics of seagrass and epiphytic algal primary production were measured in an eelgrass (Zostera marina) bed in the Akkeshi-ko estuary, Hokkaido, Japan (43°02′N, 144°52′E). During spring and early summer, eelgrass biomass increased, with a high production (maximum: 2.89 g C m⁻² day⁻¹), but the production and biomass of epiphytic algae remained low. In contrast, epiphytic algae bloomed in August, with a high production (5.21 g C m⁻² day⁻¹), but eelgrass production ceased and its biomass subsequently decreased. Therefore, the major primary producers in this eelgrass bed switched seasonally from eelgrass in spring and early summer to epiphytic algae in late summer and autumn. Epiphytic algae maintained similar productivity because of the change of photosynthetic kinetics and the dominant epiphytic diatom changed from highly adhesive species to less adhesive or filamentous small species during the bloom. This suggests that the change of epiphyte density and biomass was due to change of its loss rate, possibly due to herbivorous grazing rate. Moreover, competition between epiphytic algae and eelgrass for nutrients and light may also affect the dramatic seasonal changes in the major primary producers.     

大叶藻(Zostera marina)海草床沉积物细菌和古菌丰度及组成的垂直剖面特征

【背景】海草床是重要的"蓝碳"生态系统,对全球碳汇有重要贡献。海草床沉积物剖面的垂直梯度特征显著,表层呈现氧化态,富含活性有机质,而深层呈还原态,以惰性有机质为主。【目的】探究这种垂直特征如何影响微生物的丰度和群落分布。【方法】利用荧光定量PCR和16SrRNA基因高通量测序等手段,测定了山东荣成天鹅湖大叶藻海草床不同深度(5、10、15、20、25和30 cm)沉积物中细菌和古菌丰度、多样性和群落结构的变化。【结果】细菌和古菌16S rRNA基因拷贝数随深度的增加而降低,在沉积物5cm深处,细菌的16SrRNA基因拷贝数显著高于20cm和30cm层(ANOVA,P<0.05)。深度对细菌和古菌α多样性指数没有显著影响(P>0.05)。细菌中相对丰度最高的是变形菌门,其次是绿弯菌门,拟杆菌门,浮霉菌门等,其中δ-变形菌和浮霉菌的相对丰度随深度显著增加(P<0.05)。古菌群落中深古菌门比例最高,在25cm深处达到70%以上;其次是乌斯菌门、洛基古菌门、广古菌门和奇古菌门等。奇古菌门比例随深度增加而显著降低(P<0.05),其他古菌类群在不同深度间差异不显著(P&...     

Effects of changes in seagrass shoot density and leaf height on the abundance of juveniles of Acentrogobius pflaumii in a Zostera marina bed

The effects of changes in the structural complexity of a seagrass (Zostera marina) habitat on the density of juveniles of the streaked goby, Acentrogobius pflaumii, were investigated by field experimentation at Moroiso Bay, Miura Peninsula, Japan. The experimental design, which included seven treatments plus a control, included reduction of seagrass shoot densities and leaf heights as well as complete removal of seagrass. Throughout the study period, juvenile densities remained similar among the experimental quadrats, including the completely cleared quadrat. On the other hand, juveniles did not appear over the bare sandy substratum surrounding the experimental seagrass bed. Within the bed, prey densities were high, being similar among the experimental quadrats, whereas prey were relatively scarce over the surrounding bare substratum. This result suggested that streaked goby juveniles were not attracted to the structure of the Zostera bed per se and that their distribution patterns may be determined by other factors, such as prey availability. Received: September 25, 2000 / Revised: November 22, 2000 / Accepted: January 16, 2001     

Photoadaptation and growth of Zostera marina L. (eelgrass) transplants along a depth gradient

Photosynthetic and growth responses were assessed in Zostera marina L. transplants within and beyond the natural extent of an eelgrass meadow in Great Harbor, Woods Hole, MA. Transplant survival and rapid growth inshore of the shallow edge of the meadow (0.5 and 0.8 m water depth) indicated a periodic disturbance factor maintaining the shallow edge of the meadow. Transplant mortality, reduced growth, and a negative carbon balance of eelgrass transplanted offshore the deep edge of the meadow (7 and 10m) supported the hypothesis of light-limited eelgrass growth in the deep regions of the Great Harbor meadow. Photoadaptive responses occurred along the water depth gradient, and both photosynthesis and growth responses were used to assess the genetic vs. phenotypic components of eelgrass response to the water depth gradient. Reciprocal transplants between shallow (1.3 m) and deep (5.5 m) areas within the eelgrass meadow indicated photosynthetic and growth responses were primarily a result of growth habitat rather than genetic differentiation within the eelgrass meadow.     

An analysis of the population genetics of restored Zostera marina plantings in Barnegat Bay, New Jersey

Within Barnegat Bay, New Jersey, eelgrass (Zostera marina) populations have declined by 62 % over the last 20 years. To better understand the consequences of this devastation, we have previously employed microsatellite DNA polymorphisms to analyze the population structure of Z. marina within Barnegat Bay, as well as along the eastern United States seaboard. We have restored populations of Z. marina in Barnegat Bay over the last 10 years to help assess the best planting conditions and ecotypes that might be used in long-term restoration strategies. In this study, we examined the genetic health of the restored populations compared to that of the donor eelgrass populations within the bay. Using microsatellites, we can identify which parental founding ecotypes survived the restoration process over multiple generations. The frequency of observed heterozygotes, although higher than in the natural populations, still indicates reduced levels of diversity and connectivity. The inbreeding frequency is high in the restored populations, but lower than what is seen in the native populations. All restored populations have effective population values >50, suggesting a high probability of survival in the short term.     

Intrashoot distributions of leaf dwelling harpacticoid copepods on the seagrass Zostera marina L.: implications for sampling design

The distribution of leaf dwelling harpacticoid copepods within seagrass (Zostera marina L.) shoots was investigated on four dates in 1986 and 1987. Copepods were found to be non-uniformly distributed on shoots, with higher abundances observed on older leaves. Patterns of abundance within shoots could not be explained by the surface area of individual leaves except on the sampling date with the highest copepod densities. It is suggested that harpacticoid copepod distributions on seagrass shoots are primarily determined by the pattern of epiphytic biomass. However, at high population densities, habitable surface area may be the limiting factor. Increased habitat complexity at high epiphyte loads does not seem to be the cause of the copepod distributions observed in this study. An accurate method for estimating seagrass copepod abundance per unit sediment area using intrashoot distributions is described and compared to existing methodology.     

Copepods as environmental indicator in lakes: special focus on changes in the proportion of calanoids along nutrient and pH gradients

Copepods are important contributors to the zooplankton community in lakes. Being “sandwiched” between predators and resources, they are sensitive to changes in the environment. It has been proposed that the proportion of calanoids of total copepod abundance or biomass could be a valuable indicator of eutrophication. We investigated relationships between environmental factors and the abundance, biomass and size of calanoid and cyclopoid copepods as well as their proportions in summer in 68 Danish freshwater lakes (587 lake years) with contrasting nutrient levels and pH. When lake pH was?<?6.0, mean lake depth and trophic state were the most important factors and calanoids completely dominated the copepod community. In shallow lakes with a mean depth?<?2.5 m and with pH?>?6.0, the proportion of calanoids in terms of biomass decreased substantially with increasing phosphorus and chlorophyll a concentrations but stayed around 50% at?>?2.5 m depth irrespective of nutrient level. Time series of the lakes, recovering from eutrophication, confirmed this multi-lake pattern although the trajectory varied from lake to lake. We conclude that the proportion of calanoids in terms of biomass might be a valuable indicator of trophic state in shallow but not deep lakes and only when pH?>?6.