Effect of grazing and mowing on the clonal structure of Elytrigia atherica: a long-term study of abandoned and managed sites

Physical disturbance by large herbivores can affect species diversity at the community level and concurrently genetic diversity at the species level. As seedling establishment is rarely observed in clonal plants, short-term experiments and demographic studies are unlikely to reveal the response of clonal plants to disturbances. A long-term (30-year) field experiment and the availability of molecularmarkers allowed us to investigate the clonal structure of populations of Elytrigia atherica subjected to different management regimes. The long-term field study provided us with five replicated blocks that had been subjected to three different management regimes, grazing by cattle, mowing and abandonment. In this study we examined the effects of herbivore grazing andmowing on clonal richness and genetic diversity of populations in salt marshes using multilocus microsatellite genotypes. In addition, phenotypic traits and spatial positions of E. atherica ramets were determined for 20 samples in a 5 × 10m plot in each of the blocks. Abundance and phenotypic traits were affected by the management regimes, resulting in a higher abundance in abandoned fields and plants having shorter and narrower leaves in managed fields. Biomass removal did affect the clonal structure of populations and increased the genetic diversity compared to that in abandoned fields. However, no distinct difference was found between the two management regimes, mowing and grazing. Although seedling recruitment has rarely been observed, the present study shows that such rare events have occurred within the populations studied. Thus, molecular tools can greatly increase our understanding of vegetation dynamics and processes within populations growing under different conditions

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

Modulation of the Eelgrass – Labyrinthula zosterae Interaction Under Predicted Ocean Warming, Salinity Change and Light Limitation

Marine infectious diseases can have large-scale impacts when they affect foundation species such as seagrasses and corals. Interactions between host and disease, in turn, may be modulated by multiple perturbations associated with global change. A case in point is the infection of the foundation species Zostera marina (eelgrass) with endophytic net slime molds (Labyrinthula zosterae), the putative agent of eelgrass wasting disease that caused one of the most severe marine pandemics across the North-Atlantic in the 1930s. The contemporary presence of L. zosterae in many eelgrass meadows throughout Europe raises the question whether such a pandemic may re-appear if coastal waters become more eutrophic, warmer and less saline. Accordingly, we exposed uninfected Baltic Sea Z. marina plants raised from seeds to full factorial combinations of controlled L. zosterae inoculation, heat stress, light limitation (mimicking one consequence of eutrophication) and two salinity levels. We followed eelgrass wasting disease dynamics, along with several eelgrass responses such as leaf growth, mortality and carbohydrate storage, as well as the ability of plants to chemically inhibit L. zosterae growth. Contrary to our expectation, inoculation with L. zosterae reduced leaf growth and survival only under the most adverse condition to eelgrass (reduced light and warm temperatures). We detected a strong interaction between salinity and temperature on L. zosterae abundance and pathogenicity. The protist was unable to infect eelgrass under high temperature (27°C) in combination with low salinity (12 psu). With the exception of a small positive effect of temperature alone, no further effects of any of the treatment combinations on the defense capacity of eelgrass against L. zosterae were detectable. This work supports the idea that contemporary L. zosterae isolates neither represent an immediate risk for eelgrass beds in the Baltic Sea, nor a future one under the predicted salinity decrease and warming of the Baltic Sea

Distribution, structure and function of Nordic eelgrass (Zostera marina) ecosystems: implications for coastal management and conservation

This paper focuses on the marine foundation eelgrass species, Zostera marina, along a gradient from the northern Baltic Sea to the north-east Atlantic. This vast region supports a minimum of 1480 km2 eelgrass (maximum >2100 km2), which corresponds to more than four times the previously quantified area of eelgrass in Western Europe. Eelgrass meadows in the low salinity Baltic Sea support the highest diversity (4–6 spp.) of angiosperms overall, but eelgrass productivity is low (<2 g dw m-2 d-1) and meadows are isolated and genetically impoverished. Higher salinity areas support monospecific meadows, with higher productivity (3–10 g dw m-2 d-1) and greater genetic connectivity. The salinity gradient further imposes functional differences in biodiversity and food webs, in particular a decline in number, but increase in biomass of mesograzers in the Baltic. Significant declines in eelgrass depth limits and areal cover are documented, particularly in regions experiencing high human pressure. The failure of eelgrass to re-establish itself in affected areas, despite nutrient reductions and improved water quality, signals complex recovery trajectories and calls for much greater conservation effort to protect existing meadows. The knowledge base for Nordic eelgrass meadows is broad and sufficient to establish monitoring objectives across nine national borders. Nevertheless, ensuring awareness of their vulnerability remains challenging. Given the areal extent of Nordic eelgrass systems and the ecosystem services they provide, it is crucial to further develop incentives for protecting them

Current European Labyrinthula zosterae Are Not Virulent and Modulate Seagrass (Zostera marina) Defense Gene Expression

Pro- and eukaryotic microbes associated with multi-cellular organisms are receiving increasing attention as a driving factor in ecosystems. Endophytes in plants can change host performance by altering nutrient uptake, secondary metabolite production or defense mechanisms. Recent studies detected widespread prevalence of Labyrinthula zosterae in European Zostera marina meadows, a protist that allegedly caused a massive amphi-Atlantic seagrass die-off event in the 1930's, while showing only limited virulence today. As a limiting factor for pathogenicity, we investigated genotype×genotype interactions of host and pathogen from different regions (10–100 km-scale) through reciprocal infection. Although the endophyte rapidly infected Z. marina, we found little evidence that Z. marina was negatively impacted by L. zosterae. Instead Z. marina showed enhanced leaf growth and kept endophyte abundance low. Moreover, we found almost no interaction of protist×eelgrass-origin on different parameters of L. zosterae virulence/Z. marina performance, and also no increase in mortality after experimental infection. In a target gene approach, we identified a significant down-regulation in the expression of 6/11 genes from the defense cascade of Z. marina after real-time quantitative PCR, revealing strong immune modulation of the host's defense by a potential parasite for the first time in a marine plant. Nevertheless, one gene involved in phenol synthesis was strongly up-regulated, indicating that Z. marina plants were probably able to control the level of infection. There was no change in expression in a general stress indicator gene (HSP70). Mean L. zosterae abundances decreased below 10% after 16 days of experimental runtime. We conclude that under non-stress conditions L. zosterae infection in the study region is not associated with substantial virulence

Quantitative PCR reveals strong spatial and temporal variation of the wasting disease pathogen, Labyrinthula zosterae in northern European eelgrass (Zostera marina) beds

Seagrass beds are the foundation species of functionally important coastal ecosystems worldwide. The world’s largest losses of the widespread seagrass Zostera marina (eelgrass) have been reported as a consequence of wasting disease, an infection with the endophytic protist Labyrinthula zosterae. During one of the most extended epidemics in the marine realm, ~90% of East and Western Atlantic eelgrass beds died-off between 1932 and 1934. Today, small outbreaks continue to be reported, but the current extent of L. zosterae in European meadows is completely unknown. In this study we quantify the abundance and prevalence of the wasting disease pathogen among 19 Z. marina populations in northern European coastal waters, using quantitative PCR (QPCR) with primers targeting a species specific portion of the internally transcribed spacer (ITS1) of L. zosterae. Spatially, we found marked variation among sites with abundances varying between 0 and 126 cells mg−1 Z. marina dry weight (mean: 5.7 L. zosterae cells mg−1 Z. marina dry weight ±1.9 SE) and prevalences ranged from 0–88.9%. Temporarily, abundances varied between 0 and 271 cells mg−1 Z. marina dry weight (mean: 8.5±2.6 SE), while prevalences ranged from zero in winter and early spring to 96% in summer. Field concentrations accessed via bulk DNA extraction and subsequent QPCR correlated well with prevalence data estimated via isolation and cultivation from live plant tissue. L. zosterae was not only detectable in black lesions, a sign of Labyrinthula-induced necrosis, but also occurred in green, apparently healthy tissue. We conclude that L. zosterae infection is common (84% infected populations) in (northern) European eelgrass populations with highest abundances during the summer months. In the light of global climate change and increasing rate of marine diseases our data provide a baseline for further studies on the causes of pathogenic outbreaks of L. zosterae

Beitrag zur Gesundheit und Parasitenbelastung von Konik Wildpferden in Naturschutzgebieten

Die Geltinger Birk ist eines der größten Naturschutzgebiete Schleswig Holsteins. Sie ist Lebensraum für Vögel, Amphibien und seltene Pflanzen. Über das ganze Jahr ist das Gebiet am Ausgang der Flensburger Förde Ziel für Wanderer, Radfahrer und Naturtouristen. Zuständig für die Pflege des Gebietes ist Diplom Biologe Nils Kobarg. Einfach alles verwildern lassen geht nicht, die Landschaft soll zurückgebaut werden in ihren ursprünglichen Zustand. Ein aufwendiges Projekt, so sollen Teile der Birk wieder unter Wasser gesetzt werden. Die Biologen setzen verschwundene Arten wie die Kreuzkröte wieder aus. Gleich mehrere Wildpferdherden und Hochlandrinder beweiden die Birk als lebendige Landschaftspfleger. Doch Anna Bockelmann kann alles verändern. Sie untersucht die Wildpferde auf Parasiten und andere Erreger. Für die Meeresbiologin leben die Tiere trotz ihrer Freiheit in Gefangenschaft. Vielleicht ist das Gebiet für die Herden zu klein? Die Ergebnisse der Forscherin geben daher nicht nur Aufschluss über die Gesundheit der Tiere, sondern könnten sich auch auf die Zukunft der Wildpferde auf der Birk auswirken. Nicht das einzige Problem mit dem sich Nils Kobarg und sein Team herumschlagen. Wildschweine zieht es immer weiter in den Norden. Im Naturschutzgebiet sind sie willkommen, doch die Bauern aus der Umgebung haben etwas dagegen. Also muss gejagt werden. Alles andere als ein ruhiger Winter auf der Geltinger Bir