Eelgrass Populations Research Articles

Seagrass wasting disease along a naturally occurring salinity gradient

In the 1930s, outbreaks of the wasting disease pathogen Labyrinthula zosterae caused a severe reduction of the eelgrass Zostera marina meadows in the Atlantic Ocean. Many surviving populations were found in low-salinity environments, and low-salinity environments have therefore been hypothesized to act as a refuge for eelgrass against L. zosterae infection. Here, we investigated L. zosterae pathogen load and wasting disease symptoms in eelgrass over a similar to 970 km salinity gradient (6-25 PSU) along the Swedish coast. Furthermore, laboratory infection experiments and studies of inhibitory compounds were carried out to investigated whether resistance against the pathogen is correlated to differences in natural pathogen pressure among eelgrass populations. The degree of L. zosterae infection was positively correlated to salinity and the pathogen was absent in several of the eelgrass meadows in lower salinity (7-8 PSU). However, a low L. zosterae pathogen load was also found in some eelgrass populations in the lowest salinity (6 PSU). No correlation between resistance and pathogen pressure in situ was detected, and all eelgrass shoots produced chemical compounds that inhibited L. zosterae growth. These results imply that positive correlations between L. zosterae and salinity are not due to eelgrass resistance, but rather to the poor ability of L. zosterae to cope with low salinity. However, our results also indicate that some strains of L. zosterae may adapt to low salinity, and therefore there may also be a risk of wasting disease outbreaks in low-salinity eelgrass meadows, in contrast to what so far has been the general hypothesis.

Temporal and depth-associated changes in the structure, morphometry and production of near-pristine Zostera marina meadows in western Ireland

The eelgrass Zostera marina is a dominant, subtidal meadow-forming seagrass in temperate regions in the northern hemisphere. Due to the numerous ecological services they provide, seagrass systems rank amongst the most valuable ecosystems worldwide but there is a lack of data regarding the structure and productivity of Irish seagrass populations. To address this gap, this investigation assessed temporal changes and depth acclimations of vegetative parameters, such as, shoot length and weight, shoot density, seagrass cover and below- and above-ground biomass, in three near-pristine subtidal Z. marina meadows in western Ireland. Most parameters revealed a marked temporal pattern, displaying clear unimodal responses, with peaks attained in July, intermediate values in April and November, and lowest values observed in January. Moreover, eelgrass cover and density decreased from 76.1 ± 6.5% in shallow meadows to 34 ± 4.5% at greater depths; inversely, other parameters such as shoot biomass or shoot length increased 2–3-fold with depth. Furthermore, annual leaf formation rates and above-ground biomass were estimated and compared to those of eelgrass populations from different latitudes (28°–66°) reported in the literature. Results suggest that the vegetative development of Irish populations corresponds to global data reported at different local and global scales of Z. marina populations inhabiting stable environments; our data serve as a first baseline for the assessment of potential future environmental impacts, including climate change and eutrophication.

A Novel Phagomyxid Parasite Produces Sporangia in Root Hair Galls of Eelgrass (Zostera marina)

The objective of this study was to identify the parasite causing the formation of root hair galls on eelgrass (Zostera marina) in Puget Sound, WA. Microscopic and molecular analyses revealed that a novel protist formed plasmodia that developed into sporangia in root hair tip galls and released biflagellate swimming zoospores. Root hair galls were also observed in the basal section of root hairs, and contained plasmodia or formed thick-walled structures filled with cells (resting spores). Phylogenetic analyses of 18S rDNA sequence data obtained from cells in sporangia indicated that the closest relative of the parasite with a known taxonomic identification was Plasmodiophora diplantherae (86.9% sequence similarity), a phagomyxid parasite that infects the seagrass Halodule spp. To determine the local geographic distribution of the parasite, root and soil samples were taken from four eelgrass populations in Puget Sound and analyzed for root hair galls and parasite DNA using a newly designed qPCR protocol. The percent of root hairs with galls and amount of parasite DNA in roots and sediment varied among the four eelgrass populations. Future studies are needed to establish the taxonomy of the parasite, its effects on Z. marina, and the factors that determine its distribution and abundance.

High temperatures cause reduced growth, plant death and metabolic changes in eelgrass Zostera marina

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 604:121-132 (2018) - DOI: https://doi.org/10.3354/meps12740 High temperatures cause reduced growth, plant death and metabolic changes in eelgrass Zostera marina Kathrine Jul Hammer1, Jens Borum1,*, Harald Hasler-Sheetal2,3, Erin C. Shields4, Kaj Sand-Jensen1, Kenneth A. Moore4 1Freshwater Biological Laboratory, Biological Institute, University of Copenhagen, 2100 Copenhagen, Denmark 2Nordcee, Department of Biology, University of Southern Denmark, 5230 Odense M, Denmark 3Villum Center for Bioanalytical Sciences, University of Southern Denmark, 5230 Odense M, Denmark 4Virginia Institute of Marine Science, School of Marine Science, College of William and Mary, Gloucester Point, VA 23062, USA *Corresponding author: jborum@bio.ku.dk ABSTRACT: We investigated temperature effects on eelgrass Zostera marina L. growing close to its southern distribution limit along the eastern coast of North America in Virginia, USA. We combined growth and survival experiments with microelectrode measurements of internal meristematic oxygen and analyses of metabolic compounds. Eelgrass shoots were grown at 3 different temperatures (22, 26 and 30°C) and field equivalent light levels (23% of sea surface insolation) for 28 d while water column oxygen concentration was kept at air saturation. Meristematic oxygen concentrations did not vary significantly with temperature, and meristems maintained a relatively high oxygen concentration (average: 38% air saturation) during dark hours. Despite high meristematic oxygen concentrations, shoots growing at 30°C exhibited increased mortality, reduced growth and reduced leaf production compared to shoots growing at 22 and 26°C. The leaf metabolome was significantly altered at 30°C, indicating an increase of reactive oxygen species. In addition, total nitrogen and metabolites related to the nitrogen cycle (amino acids, urea and γ-aminobutyric acid [GABA]) were low in the heat-stressed shoots, whereas soluble sugars increased. In conclusion, high temperature (30°C) has strong negative effects on eelgrass in the lower Chesapeake Bay, affecting growth, tissue integrity, nitrogen metabolism and protein/enzyme synthesis. Future global warming may likely deteriorate populations of eelgrass at its present southern distribution limit. KEY WORDS: Zostera marina · Temperature stress · Growth · Metabolomics · Climate change Full text in pdf format Supplementary material PreviousNextCite this article as: Hammer KJ, Borum J, Hasler-Sheetal H, Shields EC, Sand-Jensen K, Moore KA (2018) High temperatures cause reduced growth, plant death and metabolic changes in eelgrass Zostera marina. Mar Ecol Prog Ser 604:121-132. https://doi.org/10.3354/meps12740 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 604. Online publication date: October 04, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Understanding Aquaporin Transport System in Eelgrass (Zostera marina L.), an Aquatic Plant Species.

Aquaporins (AQPs) are a class of integral membrane proteins involved in the transport of water and many other small solutes. The AQPs have been extensively studied in many land species obtaining water and nutrients from the soil, but their distribution and evolution have never been investigated in aquatic plant species, where solute assimilation is mostly through the leaves. In this regard, identification of AQPs in the genome of Zostera marina L. (eelgrass), an aquatic ecological model species could reveal important differences underlying solute uptake between land and aquatic species. In the present study, genome-wide analysis led to the identification of 25 AQPs belonging to four subfamilies, plasma membrane intrinsic proteins (PIPs), tonoplast intrinsic proteins (TIPs), nodulin 26-like intrinsic proteins (NIPs), small basic intrinsic proteins (SIPs) in eelgrass. As in other monocots, the XIP subfamily was found to be absent from the eelgrass genome. Further classification of subfamilies revealed a unique distribution pattern, namely the loss of the NIP2 (NIP-III) subgroup, which is known for silicon (Si) transport activity and ubiquitously present in monocot species. This finding has great importance, since the eelgrass population stability in natural niche is reported to be associated with Si concentrations in water. In addition, analysis of available RNA-seq data showed evidence of expression in 24 out of the 25 AQPs across four different tissues such as root, vegetative tissue, male flower and female flower. In contrast to land plants, higher expression of PIPs was observed in shoot compared to root tissues. This is likely explained by the unique plant architecture of eelgrass where most of the nutrients and water are absorbed by shoot rather than root tissues. Similarly, higher expression of the TIP1 and TIP5 families was observed specifically in male flowers suggesting a role in pollen maturation. This genome-wide analysis of AQP distribution, evolution and expression dynamics can find relevance in understanding the adaptation of aquatic and land species to their respective environments.

Population genetic structure of eelgrass (Zostera marina) on the Korean coast: Current status and conservation implications for future management.

Seagrasses provide numerous ecosystem services for coastal and estuarine environments, such as nursery functions, erosion protection, pollution filtration, and carbon sequestration. Zostera marina (common name “eelgrass”) is one of the seagrass bed-forming species distributed widely in the northern hemisphere, including the Korean Peninsula. Recently, however, there has been a drastic decline in the population size of Z. marina worldwide, including Korea. We examined the current population genetic status of this species on the southern coast of Korea by estimating the levels of genetic diversity and genetic structure of 10 geographic populations using eight nuclear microsatellite markers. The level of genetic diversity was found to be significantly lower for populations on Jeju Island [mean allelic richness (AR) = 1.92, clonal diversity (R) = 0.51], which is located approximately 155 km off the southernmost region of the Korean Peninsula, than for those in the South Sea (mean AR = 2.69, R = 0.82), which is on the southern coast of the mainland. South Korean eelgrass populations were substantially genetically divergent from one another (FST = 0.061–0.573), suggesting that limited contemporary gene flow has been taking place among populations. We also found weak but detectable temporal variation in genetic structure within a site over 10 years. In additional depth comparisons, statistically significant genetic differentiation was observed between shallow (or middle) and deep zones in two of three sites tested. Depleted genetic diversity, small effective population sizes (Ne) and limited connectivity for populations on Jeju Island indicate that these populations may be vulnerable to local extinction under changing environmental conditions, especially given that Jeju Island is one of the fastest warming regions around the world. Overall, our work will inform conservation and restoration efforts, including transplantation for eelgrass populations at the southern tip of the Korean Peninsula, for this ecologically important species.

Long-term Patterns of Eelgrass (Zostera marina) Occurrence and Associated Herbivorous Waterbirds in a Danish Coastal Inlet

Seagrasses in coastal areas have substantial importance for the marine environment and also serve as food for herbivorous waterbirds. We investigated potential relationships between the autumn population of herbivorous waterbirds and eelgrass (Zostera marina) abundance in the EU protected area, Nibe-Gjol Bredning, a broad of the Limfjorden estuarine complex in Denmark.This is an important site for migratory herbivorous waterbirds such as mute swan (Cygnus olor), coot (Fulica atra), brent goose (Branta bernicla), and wigeon (Anas penelope). We explored long-term (27 yr) changes in eelgrass and bird-populations and relationships between eelgrass- and bird abundance. We applied trend- and correlative analyses of yearly monitoring data on eelgrass and waterbirds between 1989 and 2015 coupled with estimates of the potential grazing pressure exerted by the birds. Around 1990 eelgrass was abundant in this area covering more than 40 km2, but eelgrass coverage and biomass declined drastically around 1995 and remained low until 2011 when natural recolonization accelerated and by 2015 had restored the lost meadows. The number of herbivorous waterbirds also fluctuated substantially during the monitoring period with large abundance until the mid-end 1990s followed by reduced abundance in the 2000s and recovery after 2010. The number of bird-days showed a positive relationship with the same year’s eelgrass abundance in the 1-2 m depth stratum. For the 0-1 m depth stratum, where the eelgrass meadows are most exposed to bird grazing but also to physical control from e.g. wind and ice, only a particularly detailed eelgrass data set available for a subset of the study period, showed a significant relationship with bird grazing. The potential waterbird consumption of eelgrass, estimated by multiplying average intake rate and number of bird-days for each species, ranged from less than 16 % of the eelgrass biomass in most years to more than 40 % of the eelgrass biomass in years with extremely sparse eelgrass populations. Hence, the study suggests that dense eelgrass populations stimulate herbivorous waterbirds whereas top-down control is only likely when abundant bird populations graze on sparse eelgrass populations.

Response to experimental warming in northern eelgrass populations: comparison across a range of temperature adaptations

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 589:59-72 (2018) - DOI: https://doi.org/10.3354/meps12439 Response to experimental warming in northern eelgrass populations: comparison across a range of temperature adaptations P. Beca-Carretero1,2,*, B. Olesen3, N. Marbà1, D. Krause-Jensen4,5 1Department of Global Change Research, IMEDEA (CSIC-UIB), Institut Mediterrani d’Estudis Avancats, Miquel Marques 21, 07190 Esporles (Illes Balears), Spain 2Botany and Plant Science, School of Natural Sciences, and Ryan Institute, National University of Ireland Galway, University Road, Galway H91 TK33, Ireland 3Department of Bioscience, Aarhus University, Ole Worms Allé 1, Building 1135, 8000 Aarhus C, Denmark 4Department of Bioscience, Aarhus University, Vejlsøvej 25, 8600 Silkeborg, Denmark 5Arctic Research Centre, Aarhus University, Ny Munkegade 114, Building 1540, 8000 Aarhus C, Denmark *Corresponding author: pedropersiobk@hotmail.es ABSTRACT: Global warming may exert diverging effects on eelgrass (Zostera marina L.) populations originating from the northern versus the central part of the distribution range and on populations growing at saturating versus limiting light. We experimentally examined growth and physiological temperature responses of 3 eelgrass populations adapted to different temperature regimes in subarctic Greenland (2 populations) and in Denmark (1 population). Shoots were incubated at 5 different temperatures (10, 15, 20, 25 and 28°C) for 15 to 16 d at a saturating irradiance (200 µmol m-2 s-1) and one of the populations was also incubated at a limited irradiance of 50 µmol m-2 s-1. All populations exhibited optimum temperatures of 20 to 25°C for photosynthesis and growth under saturating light, while light limitation reduced the optimum by 5 to 10°C. When compared at their respective in situ summer temperature (i.e. 10, 15 and 20°C), all populations exhibited similar relative growth rates, indicating a capacity for local adaptation. The 2 subarctic populations exhibited higher activation energy for growth and, hence, greater responsiveness to warming than the centrally located population. However, subarctic populations were also more sensitive to extreme high temperatures, showing faster increases in respiration rates and declines in photosynthesis. Sensitivity to warming varied across light conditions with light-limited plants being most vulnerable to extreme temperatures, causing a negative carbon budget. In conclusion, projected warming would stimulate the performance of subarctic eelgrass populations but could eventually compromise populations in the center of the distribution range, which currently grow close to their temperature optimum. KEY WORDS: Experimental warming · Latitude comparison · Production · Energy activation · Photosynthetic response · Greenland · Denmark · Seagrass · Zostera marina Full text in pdf format Supplementary material PreviousNextCite this article as: Beca-Carretero P, Olesen B, Marbà N, Krause-Jensen D (2018) Response to experimental warming in northern eelgrass populations: comparison across a range of temperature adaptations. Mar Ecol Prog Ser 589:59-72. https://doi.org/10.3354/meps12439 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 589. Online publication date: February 23, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Forty years of seagrass population stability and resilience in an urbanizing estuary

Summary Coasts and estuaries contain among the most productive and ecologically important habitats in the world and face intense pressure from current and projected human activities, including coastal development. Seagrasses are a key habitat feature in many estuaries perceived to be in widespread decline owing to human actions. We use spatio‐temporal models and a 41‐year time series from 100s of km of shoreline which includes over 160 000 observations from Puget Sound, Washington, USA, to examine multiscale trends and drivers of eelgrass (Zostera spp.) change in an urbanizing estuary. At whole estuary scale (100s of km), we find a stable and resilient eelgrass population despite a more than doubling of human population density and multiple major climactic stressors (e.g. ENSO events) over the period. However, the aggregate trend is not reflected at the site scale (10s of km), where some sites persistently increase while others decline. Site trends were spatially asynchronous; adjacent sites sometimes exhibited opposite trends over the same period. Substantial change in eelgrass occurred at the subsite (0·1 km) scale, including both complete local loss and dramatic increase of eelgrass. Metrics of local human development including shoreline armouring, upland development (imperviousness) and human density provide no explanatory power for eelgrass population change at any spatial scale. Our results suggest that the appropriate scale for understanding eelgrass change is smaller than typically assumed (approximately 1‐ to 3‐km scale) and contrasts strongly with previous work. Synthesis. Despite ongoing conservation concern over seagrasses world‐wide, eelgrass in Puget Sound has been highly resilient to both anthropogenic and environmental change over four decades. Our work provides general methods that can be applied to understand spatial and temporal scales of change and can be used to assess hypothesized drivers of change.

Characterization of three novel species of Labyrinthulomycota isolated from ochre sea stars (Pisaster ochraceus)

The Labyrinthulomycota (Stramenopiles) is an enigmatic group of saprobic protists that play an important role as marine decomposers, yet whose phylogenetic relationships and ecological roles remain to be clearly understood. We investigated whether members of this group were present on ochre sea stars (Pisaster ochraceus) showing symptoms of sea star wasting disease. Although largely decomposers, some members of the Labyrinthulomycota are also known to be opportunistic pathogens of animals such as abalone, clams and flatworms and cause severe wasting diseases in eelgrass populations worldwide. Three new isolates of Labyrinthulomycota were discovered from the tissues of P. ochraceus collected at Bamfield Marine Research Centre (48°83.6′N, 125°13.6′W) and Reed Point Marina (49°29.1′N, 122°88.3′W) in British Columbia. The new isolates were kept in culture for several months and characterized at the morphological level and with 18S rDNA sequences. Molecular phylogenetic analyses demonstrated that each of the three new isolates clustered within a different subclade of the Labyrinthulomycota: (1) Oblongichytrium, (2) Aplanochytrium and (3) an early diverging clade of environmental DNA sequences. These data enabled us to establish one new genus and three new species of Labyrinthulomycota: Stellarchytrium dubum gen. et sp. nov., Oblongichytrium porteri sp. nov. and Aplanochytrium blankum sp. nov. This is the first account of the Labyrinthulomycota isolated from the tissues of sea stars with a potential link to sea star wasting disease reported for P. Ochraceus.

The Structure of Genetic Diversity in Eelgrass (Zostera marina L.) along the North Pacific and Bering Sea Coasts of Alaska.

Eelgrass (Zostera marina) populations occupying coastal waters of Alaska are separated by a peninsula and island archipelago into two Large Marine Ecosystems (LMEs). From populations in both LMEs, we characterize genetic diversity, population structure, and polarity in gene flow using nuclear microsatellite fragment and chloroplast and nuclear sequence data. An inverse relationship between genetic diversity and latitude was observed (heterozygosity: R2 = 0.738, P < 0.001; allelic richness: R2 = 0.327, P = 0.047), as was significant genetic partitioning across most sampling sites (θ = 0.302, P < 0.0001). Variance in allele frequency was significantly partitioned by region only in cases when a population geographically in the Gulf of Alaska LME (Kinzarof Lagoon) was instead included with populations in the Eastern Bering Sea LME (θp = 0.128–0.172; P < 0.003), suggesting gene flow between the two LMEs in this region. Gene flow among locales was rarely symmetrical, with notable exceptions generally following net coastal ocean current direction. Genetic data failed to support recent proposals that multiple Zostera species (i.e. Z. japonica and Z. angustifolia) are codistributed with Z. marina in Alaska. Comparative analyses also failed to support the hypothesis that eelgrass populations in the North Atlantic derived from eelgrass retained in northeastern Pacific Last Glacial Maximum refugia. These data suggest northeastern Pacific populations are derived from populations expanding northward from temperate populations following climate amelioration at the terminus of the last Pleistocene glaciation.

Zostera marina meadows from the Gulf of California: conservation status

Eelgrass (Zostera marina) population estimates show a decreasing trend worldwide in the second half of the twentieth century. Mexico lacks long-term time series to determine trends for major eelgrass populations and has made no conservation efforts. Therefore, we present the first report on the historic presence of this annual coastal ecosystem in two wetlands of the Gulf of California (GC), the Infiernillo Channel (CIF, largest Z. marina population inside GC) and Concepcion Bay (BCP, the only eelgrass population along GC’s west coast), combining field surveys (1999–2010), aerial photography (2000–2010), satellite imagery (1972–2005), and published reports (1994–2007). Three parameters were used as indicators of conservation status: shoot density, seed banks, and aerial coverage. Average shoot density in the CIF (741 shoots m−2) was 3.8 times higher than in BCP (194 shoots m−2), and average seed bank density was similar in both wetlands (17,442 seeds m−2 vs. 17,000 seeds m−2). Opportunistic seagrass Ruppia maritima was observed in both wetlands, with higher abundance in summer when Z. marina disappears due to high water temperatures. Eelgrass coverage was three orders of magnitude greater in the CIF (9725 ha) than in BCP (3 ha). The striking difference between these wetlands is the lack of environmental protection for BCP and the protection of the CIF by the Seri indigenous community, which increases human pressure in the former, putting it at high risk of disappearing. Conservation of eelgrass meadows is not only necessary to preserve their ecosystem services but to insure the survival of migratory populations (Pacific brant goose, Branta bernicla), endangered species (Black turtle, Chelonia mydas), and fisheries-related species.

High ammonium availability amplifies the adverse effect of low salinity on eelgrass Zostera marina

Climate change intensifies the frequency and intensity of rainfall events, which increases the discharge of freshwater and nutrients to coastal areas. This may lower salinity and increase nutrient availability and, thus, affect estuarine eelgrass populations. We studied the interactive effect of increasing NH4 + levels and low salinity on estuarine eelgrass Zostera marina, grown in microcosm at various combinations of NH4 + enrichment (0, 10 and 25 μM) and salinity (5, 12.5 and 20). Increasing NH4 + had a positive effect on eelgrass performance as long as salinity was kept at ambient level (20). N enrichment was followed by an increase in pigments, photosynthesis and various growth variables and a decrease in stored carbon concentrations (sucrose and starch). Low salinity had an overall negative effect on plant fitness; pigment concentration, photosynthesis and growth were reduced while mortality increased. Exposure to low salinity was also followed by a decrease in sucrose, suggesting that it was used as an osmolyte and/or that photosynthesis could not cover energy requirements needed for osmoregulation or repairing processes. Concomitant exposure to high NH4 + and low salinity turned the positive effect of NH4 + into a strong, negative synergistic effect. Several growth-related variables were affected significantly and mortality increased substantially. We suggest that this simultaneous exposure intensified competition for energy and C skeletons affecting other metabolic processes (e.g. growth, repair processes) negatively. Our results suggest that climate change driven alterations in precipitation and NH4 + loading might seriously impact estuarine eelgrass communities.

Predicting effects of ocean warming, acidification, and water quality onChesapeake region eelgrass

AbstractAlthough environmental requirements of seagrasses have been studied for years, reliable metrics for predicting their response to current or future conditions remain elusive. Eelgrass (Zostera marinaL.) populations of the Chesapeake region lie near the southern limit of their range in the Western North Atlantic, exposing them to increasing thermal stress as the climate warms. However, CO2stimulated photosynthesis may offset some of the negative effects of temperature stress. The combined effects of temperature, CO2, and light availability controlled by water quality and epiphytes were explored usingGrassLight, a bio‐optical model that provided a predictive environment for evaluating the interaction of multiple stressors on eelgrass distribution and density across the submarine landscape. Model predictions were validated against in situ measures of spectral diffuse attenuation, eelgrass density, and distribution. The potential for photosynthesis stimulated by ocean acidification to mitigate the effects of high temperature on eelgrass populations growing near the southern limit of their distribution was explored. The model accurately reproduced the submarine light environment from measured water quality parameters, and predicted their impacts on eelgrass distribution. It also reproduced the negative effects of warm summer temperatures on eelgrass distributions, and demonstrated that CO2increases projected for the next century should stimulate photosynthesis sufficiently to offset the negative effects of thermal stress on eelgrass growing in the Chesapeake region, even in the presence of epiphytes. Thus, improved water quality should facilitate the survival of eelgrass populations in Chesapeake region, even in the face of a warming climate.

The effect of parameter variability in the allometric projection of leaf growth rates for eelgrass (Zostera marina L.)

Restoration of eelgrass Zostera marina meadows from harmful anthropogenic influences has made it essential to evaluate these efforts by using non-destructive assessments. Allometric methods provide a convenient framework for the derivation of reliable indirect assessments of leaf biomass and leaf growth of eelgrass. Invariance of the involved parameters could grant truly nondestructive assessments because previously fitted values could be used to produce consistent estimations. In order to explore this property we analyzed data from two natural eelgrass populations in the East Pacific (Mexico), as well as populations in the West Pacific (two natural in Korea and one mesocosm in Japan). When we compared observed leaf growth rates with those projected allometrically by using parameter values fitted at different sites, we found that only parameter values fitted at sites within the same geographical region can produce consistent results. Therefore if this restriction holds previously fitted parameters can indeed be used to produce reliable non-destructive assessments of eelgrass leaf growth rates.

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.

Restoration recovers population structure and landscape genetic connectivity in a dispersal‐limited ecosystem

SummaryEcological restoration assists the recovery of degraded ecosystems; however, restoration can have deleterious effects such as outbreeding depression when source material is not chosen carefully and has non‐local adaptations.We surveyed 23 eelgrass (Zostera marinaL.) populations along the North American Atlantic coast to evaluate genetic structure and connectivity among restored and naturally recruited populations.While populations along the North America Atlantic coast were genetically distinctive, significant migration was detected among populations. All estimates of connectivity (FST, migration rate base on rare alleles, and Bayesian modelling) showed a general north to south pattern of migration, corresponding to the typical long‐shore currents in this region.Individual naturally recruited meadows in the Virginia coastal bays appear to be the result of dispersal from different meadows north of the region. This supports the hypothesis that recruitment into this region is typically a slow, episodic process rather than a permanent, continuous connection between the populations.While natural recovery of populations that were catastrophically lost in the 1930s has been slow, large‐scale seed‐based restoration has been very successful at quickly restoring landscape‐scale areal coverage (over 1600 ha in just 10 years). Our results show that restoration was also successful at restoring meadows with high genetic diversity. Naturally recruited meadows were less diverse and exhibited signs of genetic drift.Synthesis. Our analyses demonstrate that metapopulation dynamics are important to the natural recovery of seagrass ecosystems that have experienced catastrophic loss over large spatial scales; however, natural recovery processes are slow and inefficient at recovering genetic diversity and population structure when recruitment barriers exist, such as a limited seed source. Seed‐based restoration provides a greater abundance of propagules, rapidly facilitates the recovery of populations with higher genetic diversity, and when seed sources are chosen carefully protects regional genetic structure. First‐order estimates indicated that the genetic diversity achieved by active restoration in 10 years would have otherwise taken between 125 and 185 years to achieve through natural recruitment events.

An allometric method for measuring leaf growth in eelgrass, Zostera marina, using leaf length data

Abstract The rate of production of leaf biomass in eelgrass (Zostera marina L.) is an indicator variable for environmental influences on the growth of this important seagrass species. The efforts to restore eelgrass meadows from the harmful human influences make the use of nondestructive evaluations essential. We present, here, an indirect procedure for the estimation of the growth rates of eelgrass leaves by using easily obtained measurements of leaf length and increases in leaf length, and allometric parameters linked to the scaling of leaf biomass and leaf length. This allometric method includes criteria that allow the estimation of leaf growth rates even when the sizes of some of the leaves cannot be determined because of herbivory or other environmental factors. To validate the proposed method, we performed simulation studies and analyzed data from two natural eelgrass populations in the East Pacific (México). These allometric projections of leaf growth rates displayed a high level of correspondence with observed values. We show that whenever the allometric parameters for the scaling of eelgrass leaf dry weight in terms of leaf length have been previously fitted, the method proposed here can provide an alternative for estimating biomass production that is both accurate and nondestructive and uses easily obtained data on leaf length and increases in leaf length between the sampling periods.

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.