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Seagrass meadows provide important ecological services to the marine environment but are declining worldwide. Although eelgrass meadows in the north Pacific are thought to be relatively healthy, few studies have assessed the presence of known disease pathogens in these meadows. In a pilot study to test the efficacy of the methods and to provide foundational disease biodiversity data in the north Pacific, we leveraged metabarcoding of environmental DNA extracted from water, sediment, and eelgrass tissue samples collected from five widely distributed eelgrass meadows in Alaska and one in Japan and uncovered wide prevalence of two classes of pathogenic organisms – Labyrinthula zosterae and other associated strains of Labyrinthula, and the Phytophthora/Halophytophthora blight species complex – known to have caused decline in eelgrass (Zostera marina) elsewhere in the species’ global distribution. Although the distribution of these disease organisms is not well understood in the north Pacific, we uncovered the presence of at least one eelgrass pathogen at every locality sampled.

Climate change is affecting the health and physiology of marine organisms and altering species interactions. Ocean acidification (OA) threatens calcifying organisms such as the Pacific oyster, Crassostrea gigas. In contrast, seagrasses, such as the eelgrass Zostera marina, can benefit from the increase in available carbon for photosynthesis found at a lower seawater pH. Seagrasses can remove dissolved inorganic carbon from OA environments, creating local daytime pH refugia. Pacific oysters may improve the health of eelgrass by filtering out pathogens such as Labyrinthula zosterae (LZ), which causes eelgrass wasting disease (EWD). We examined how co-culture of eelgrass ramets and juvenile oysters affected the health and growth of eelgrass and the mass of oysters under different pCO2 exposures. In Phase I, each species was cultured alone or in co-culture at 12°C across ambient, medium, and high pCO2 conditions, (656, 1,158 and 1,606 μatm pCO2 , respectively). Under high pCO2 , eelgrass grew faster and had less severe EWD (contracted in the field prior to the experiment). Co-culture with oysters also reduced the severity of EWD. While the presence of eelgrass decreased daytime pCO2 , this reduction was not substantial enough to ameliorate the negative impact of high pCO2 on oyster mass. In Phase II, eelgrass alone or oysters and eelgrass in co-culture were held at 15°C under ambient and high pCO2 conditions, (488 and 2,013 μatm pCO2 , respectively). Half of the replicates were challenged with cultured LZ. Concentrations of defensive compounds in eelgrass (total phenolics and tannins), were altered by LZ exposure and pCO2 treatments. Greater pathogen loads and increased EWD severity were detected in LZ exposed eelgrass ramets; EWD severity was reduced at high relative to low pCO2 . Oyster presence did not influence pathogen load or EWD severity; high LZ concentrations in experimental treatments may have masked the effect of this treatment. Collectively, these results indicate that, when exposed to natural concentrations of LZ under high pCO2 conditions, eelgrass can benefit from co-culture with oysters. Further experimentation is necessary to quantify how oysters may benefit from co-culture with eelgrass, examine these interactions in the field and quantify context-dependency.

The algicidal and growth-inhibiting bacteria associated with seagrasses and macroalgae were characterized during the summer of 2012 and 2013 throughout Puget Sound, WA, USA. In 2012, Heterosigma akashiwo-killing bacteria were observed in concentrations of 2.8×106CFUg-1 wet in the outer organic layer (biofilm) on the common eelgrass (Zostera marina) in north Padilla Bay. Bacteria that inhibited the growth of Alexandrium tamarense were detected within the biofilm formed on the eelgrass canopy at Dumas Bay and North Bay at densities of ∼108CFUg-1 wet weight. Additionally, up to 4100CFUmL-1 of algicidal and growth-inhibiting bacteria affecting both A. tamarense and H. akashiwo were detected in seawater adjacent to seven different eelgrass beds. In 2013, H. akashiwo-killing bacteria were found on Z. marina and Ulva lactuca with the highest densities of ∼108CFUg-1 wet weight at Shallow Bay, Sucia Island. Bacteria that inhibited the growth of H. akashiwo and A. tamarense were also detected on Z. marina and Z. japonica at central Padilla Bay. Heterosigma akashiwo cysts were detected at a concentration of 3400cystsg-1 wet weight in the sediment from Westcott Bay (northern San Juan Island), a location where eelgrass disappeared in 2002. These findings provide new insights on the ecology of algicidal and growth-inhibiting bacteria, and suggest that seagrass and macroalgae provide an environment that may influence the abundance of harmful algae in this region. This work highlights the importance of protection and restoration of native seagrasses and macroalgae in nearshore environments, in particular those regions where shellfish restoration initiatives are in place to satisfy a growing demand for seafood.

Seagrass meadows form ecologically and economically valuable coastal habitat on every continental margin except the Antarctic, but their areal extent is declining by approximately 2–5 % per year. Seagrass wasting disease is a contributing factor in these declines, with the protist Labyrinthula identified as the etiologic agent. To help elucidate the role of Labyrinthula spp. in global seagrass declines, we surveyed roughly one fourth of all seagrass species to identify Labyrinthula diversity at the strain and/or species level, combining results from culturing methods and two common nuclear DNA markers: the ITS and 18S regions of the ribosomal RNA gene complex. After assaying a subset of the resulting isolates (of which 170 were newly sequenced), we produced a cladogenic context for putative seagrass-pathogenic versus non-pathogenic Labyrinthula while also defining host and geographic ranges. Assays also suggest that pathogenicity is consistently high (when present; and, even when comparing susceptibility of US East- versus West Coast Zostera marina hosts) while virulence is variable, that some isolate-host combinations have the potential for host cross-infection, and that several modes of transmission can be effective. Taken together, these data provide additional means for delimiting putative species of Labyrinthula, suggesting at least five seagrass-pathogenic and perhaps ten or more non-pathogenic marine “species”, yielding a working definition for ecologists and epidemiologists attempting to reconcile the sundry data related to seagrass wasting disease.

Seagrasses are ecosystem engineers of essential marine habitat. Their populations are rapidly declining worldwide. One potential cause of seagrass population declines is wasting disease, which is caused by opportunistic pathogens in the genus Labyrinthula. While infection with these pathogens is common in seagrasses, theory suggests that disease only occurs when environmental stressors cause immunosuppression of the host. Recent evidence suggests that host factors may also contribute to disease caused by opportunistic pathogens. In order to quantify patterns of disease, identify risk factors, and investigate responses to infection, we surveyed shoot density, shoot length, epiphyte load, production of plant defenses (phenols), and wasting disease prevalence in eelgrass Zostera marina across 11 sites in the central Salish Sea (Washington state, USA), a region where both wasting disease and eelgrass declines have been documented. Wasting disease was diagnosed by the presence of necrotic lesions, and Labyrinthula cells were identified with histology. Disease prevalence among sites varied from 6 to 79%. The probability of a shoot being diseased was higher in longer shoots, in patches of higher shoot density, and in shoots with higher levels of biofouling from epiphytes. Phenolic concentration was higher in diseased leaves. We hypothesize that this results from the induction of phenols during infection. Additional research is needed to evaluate whether phenols are an adaptive defense against Labyrinthula infection. The high site-level variation in disease prevalence emphasizes the potential for wasting disease to be causing some of the observed decline in eelgrass beds.

Phyllospadix scouleri is a common seagrass along the rocky intertidal coast of the Pacific Northwest. Previously we established a correlation between increased sulfide and hydrogen sulfide (H2S) and Zostera marina seedling senescence. While Z. marina grows in soft sediment environments, here we evaluate the possibility that P. scouleri may experience similar decreases in health when exposed to increasing H2S loading. To do this, seedlings were immersed in various concentrations of H2S, in axenic media, and photosynthetic and respiratory output was measured. We found that at high doses (mM) of H2S Photosystem II was inhibited whereas Photosystem I remained active. At lower levels, total photosynthetic output decreased with increasing H2S concentrations. Using these data we produced an LD50 of 430 μM at 48 h and 86 μM at 7 days. Our study confirms that Phyllospadix seedlings are also vulnerable to increasing sulfide loads.

Climate change is affecting the health and physiology of marine organisms and altering species interactions. Ocean acidification (OA) threatens calcifying organisms such as the Pacific oyster, Crassostrea gigas. In contrast, seagrasses, such as the eelgrass Zostera marina, can benefit from the increase in available carbon for photosynthesis found at a lower seawater pH. Seagrasses can remove dissolved inorganic carbon from OA environments, creating local daytime pH refugia. Pacific oysters may improve the health of eelgrass by filtering out pathogens such as Labyrinthula zosterae (LZ), which causes eelgrass wasting disease (EWD). We examined how co-culture of eelgrass ramets and juvenile oysters affected the health and growth of eelgrass and the mass of oysters under different pCO

It is widely accepted that Zostera japonica, a seagrass species native to estuarine and coastal habitats of the Western Pacific Ocean, invaded these same habitats in the Eastern Pacific early in the Twentieth Century. Based on the supposition that this species causes harm to native species living in the estuarine and coastal regions of Washington State, in 2012 they started legally allowing local enforcement to remove Z. japonica. We executed a literature search to determine if reviewed studies support the contention that Z. japonica harms native species and habitats in Washington State and other locations in the Pacific Northwest region of the eastern Pacific Ocean. We found that studies designed to quantitatively assess Z. japonica's impact are limited but provide a summary that suggests Z. japonica increases overall diversity of infaunal invertebrates, while decreasing large infaunal species, such as Manilla clam and ghost shrimp, and the native seagrass, Zostera marina. Our finding is restricted by a lack of repeated or long-term sampling effort and inadequate treatment of important higher order trophic levels and commercially harvested species in study designs. In this analysis we demonstrate that rigorous scientific investigation is needed before generalized policies, potentially influencing ecosystem productivity, are adopted.

Environmental heterogeneity can promote coexistence, and is therefore predicted to increase invasibility of communities, but decrease invasion impacts. We examined the role of local-scale environmental heterogeneity in promoting the coexistence of the invasive seagrass, Zostera japonica, and its native congener Zostera marina in a patch mosaic. In its introduced range, Z. japonica often co-occurs with the native Z. marina in a patch mosaic associated with intertidal microtopography (centimeter to decimeter relief over meter to decameter distances). Here, Z. marina inhabits depressions that retain water during low tides, and Z. japonica inhabits well-drained mounds. Transplant experiments revealed that Z. marina suppressed Z. japonica shoot densities, more so in pools than on mounds. Z. marina suppressed Z. japonica above-ground and below-ground biomass by 47 and 19 % respectively, on mounds, and by over 60 % in pools. Z. marina shoot densities and biomass were 40 and 95 % lower, respectively, on mounds, regardless of Z. japonica presence. Topographic context remained the most influential predictor of Z. marina responses, even when we transplanted Z. marina into higher densities of Z. japonica. These results indicate that the native Z. marina is physiologically restricted from mounds and competitively excludes the introduced Z. japonica from pools. We provide empirical evidence of local-scale heterogeneity promoting coexistence of an invasive and a native macrophyte, supporting the hypothesis that environmental heterogeneity increases invasibility and decreases invasion impacts. Furthermore, active control of the invader in mixed beds is unlikely to benefit the native.

Successful establishment of seedlings in populations of Zostera marina (eelgrass), especially for restoration efforts using stored seeds, depends in part on viability and germination of seeds. Seeds of Z. marina were collected from plants and stored in seawater at 5 ◦C for up to several years. Seed viability, assessed with the viability stain, tetrazolium chloride, decreased steadily over a four-year period. There was a strong correlation between age and viability; viability of fresh seeds was approximately 77% whereas for four-year old seeds was 32%. However, only 51 of 975 of fresh seeds that germinated (∼5%) developed leaves. The physical structure of the seed was evaluated to understand the effects of aging. It was determined that as seeds age there is an increase in the number of fractures on the seed coat. These data combined with the recent awareness that global seagrass populations are declining present valuable information to help maintain viable seed repositories which may contribute to the conservation and restoration of these wild plants. © 2013 Elsevier B.V. All rights reserved.

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

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.

The influence of eelgrass (Zostera marina) on near-bed currents, turbulence, and drag was investigated at three sites in two eelgrass canopies of differing density and at one unvegetated site in the San Juan archipelago of Puget Sound, Washington, USA. Eelgrass blade length exceeded 1 m. Velocity profiles up to 1.5 m above the sea floor were collected over a spring-neap tidal cycle with a downward-looking pulse-coherent acoustic Doppler profiler above the canopies and two acoustic Doppler velocimeters within the canopies. The eelgrass attenuated currents by a minimum of 40%, and by more than 70% at the most densely vegetated site. Attenuation decreased with increasing current speed. The data were compared to the shear-layer model of vegetated flows and the displaced logarithmic model. Velocity profiles outside the meadows were logarithmic. Within the canopies, most profiles were consistent with the shear-layer model, with a logarithmic layer above the canopy. However, at the less-dense sites, when currents were strong, shear at the sea floor and above the canopy was significant relative to shear at the top of the canopy, and the velocity profiles more closely resembled those in a rough-wall boundary layer. Turbulence was strong at the canopy top and decreased with height. Friction velocity at the canopy top was 1.5–2 times greater than at the unvegetated, sandy site. The coefficient of drag CD on the overlying flow derived from the logarithmic velocity profile above the canopy, was 3–8 times greater than at the unvegetated site (0.01–0.023 vs. 2.9 × 10− 3).

In the Northeast Pacific the nonnative seagrass Zostera japonica frequently exists at the same sites as the native seagrass Zostera marina. Although at some sites their vertical distributions overlap, at most sites in the Pacific Northwest there is a distinctive unvegetated zone between them. The objective of this study was to better understand why a gap between the lower limit of Z. japonica and the upper limit of Z. marina exists. To address this issue we carried out transplant experiments, conducted in situ monitoring of existing Z. japonica patches, and collected sediment samples at South Beach on Shaw Island, Washington, during the spring and summer of 2006. Transplant and in situ monitoring data indicate that survival and performance of Z. japonica are reduced lower in the intertidal zone. In addition, Z. japonica patches tended to be smaller and more spaced out at lower tidal heights. Although we found no Z. japonica seeds within or outside extant Z. japonica patches, high transplant mortality indicates that Z. japonica dispersal limitation is an unlikely cause of the unvegetated gap zone. Our field observations further suggest that herbivory, bioturbation, and epiphytes are unlikely causes of the gap pattern at our study site. Instead, we hypothesize that light limitation prevents Z. japonica from occurring lower in the intertidal. A review of published vertical distribution data for both Zostera species indicates that the lower limit of Z. japonica is relatively invariant among sites. In contrast, the upper limit of Z. marina is highly variable, ranging by more than 4 m within some subregions in Washington State. Consequently we hypothesize that intersite variability in the vertical distribution of Z. marina is the primary driver of spatial variability in the presence of the unvegetated gap.

Using data from eight autosomal microsatellite loci, we investigated levels of within- and between-site variation in the seagrass Zostera marina L. (eelgrass) from eight locations in the San Juan Archipelago, located in the northwest corner of Washington, USA. Only 117 of the 365 samples collected were unique individuals, and there were large differences in the estimates of clonality among sites. Site-specific genotypic richness ranged from 0.082 to 0.688, and the distribution of ramets and genets varied widely within sites. No multilocus genotypes were shared between sites. We found significant differences in distribution of alleles and variance in allele frequencies among sites, suggesting substantial genetic population substructuring. We detected low levels of genetic diversity in two sites known to have undergone recent declines and a genetic signature of population expansion in a site known to be increasing. Thus, like elsewhere, we find that genetic studies add an important component to monitoring programs in this region.

Mangrove stands and seagrass beds grow along the coasts of the United Arab Emirates (UAE). These marine plant species are concentrated in specific tidal zones along sheltered intertidal coastlines in association with estuaries and lagoons; mangroves fringe the coastline encroaching into the lower intertidal region, whereas seagrasses populate the adjacent deeper water. In most cases, the distribution of mangroves and seagrasses does not overlap. It is important to monitor the geographic extent and health of mangrove forests and seagrass beds, which serve as an important habitat for juvenile marine species. Remote-sensing data for the Khor Al Bazam area in the vicinity of Abu Dhabi, UAE, covering the years of 1994, 2000, and 2003, were used to determine the change in mangrove and seagrass cover. Since 1994, there has been an increase in mangrove cover, likely because of plantation activity, the closure of nearby shipyards, and an increase in public awareness regarding mangrove preservation. Althou...

The current distribution of the introduced seagrass Zostera japonica is restricted to the mid- to upper intertidal zone in the coastal Pacific Northwest region of North America. The climate in this region is cool and wet, becoming hotter and dryer with increasing distance southward. Since temperature is likely to be an important factor affecting distribution of this species, growth of two populations located near the northern and southern limits of its established range along the Pacific Coast of North America were measured in an experimental setting across a range of temperatures typical of those in the field during the growing season (10, 20, and 30 °C). The effects of temperature and population were both significant. Leaf elongation, growth, and areal productivity rates of the northern population were consistently lower than those of the southern population. Across the range of temperatures, mean leaf elongation rates ranged from 0.47 to 1.40 cm 2 shoot −1 d −1 ; mean growth rates ranged from 0.19 to 0.52 mg dry wt shoot −1 d −1 . Mean areal productivity ranged from 0.54 to 1.92 g dry wt m −2 d −1 . Maximum rates of leaf elongation, growth, and areal productivity for both populations were observed at 20 °C. However, leaf elongation, growth, and areal productivity of the northern population declined markedly at 30 °C, whereas no comparable declines were observed for the southern population. This suggests that Z. japonica populations near the southern limits of its established range may be better adapted to warmer temperatures than populations near the northern range limits and further range extensions southward along the California coast may be likely. These differences could be important in predicting the outcome of competitive interactions between native and introduced seagrass species, and in determining future patterns of distribution and zonation of Pacific Coast seagrasses.

International audience; Infectious marine diseases can decimate populations and are increasing among some taxa due to global change and our increasing reliance on marine environments. Marine diseases become emergencies when significant ecological, economic or social impacts occur. We can prepare for and manage these emergencies through improved surveillance, and the development and iterative refinement of approaches to mitigate disease and its impacts. Improving surveillance requires fast, accurate diagnoses, forecasting disease risk and real-time monitoring of disease-promoting environmental conditions. Diversifying impact mitigation involves increasing host resilience to disease, reducing pathogen abundance and managing environmental factors that facilitate disease. Disease surveillance and mitigation can be adaptive if informed by research advances and catalysed by communication among observers, researchers and decision-makers using information-sharing platforms. Recent increases in the awareness of the threats posed by marine diseases may lead to policy frameworks that facilitate the responses and management that marine disease emergencies require.

Photosynthetic processes in Zostera japonica, an upper intertidal species, were found to be more severely affected by desiccation than Z. marina, a lower intertidal and subtidal species, at comparable levels of tissue water content. The data indicate that photosynthetic responses to desiccation at the level of the individual leaf are insufficient to explain observed patterns of intertidal seagrass zonation. Desiccation tolerance in seagrasses is more likely to involve a complex interaction of morphological traits and growth strategies at the level of the whole plant, such as downsizing (e.g. smaller, narrower leaves), reduced structural rigidity and increased rates of leaf abscission and leaf turnover.

The objectives of this study were to determine the distribution and abundance of Zostera marina (eelgrass) in relation to the distribution of the mat forming bacteria Beggiatoa spp., and the levels of sulfide and organic material (wood waste) in the sediment. Underwater videography and intertidal surveys were used to map the distribution and abundance of Z. marina beds and Beggiatoa in the nearshore area of Commencement Bay, WA (USA), a location that has a long history of sawmill activity. Zostera marina occurred from the intertidal to −6 m mean lower low water (MLLW) on sandy substrates in areas with low levels of sulfide ( 200 μm) occurred where there were significant amounts of organic material in the sediments, which was found to be wood waste that had been discarded from sawmills. Zostera marina was absent from the intertidal and occurred at lower densities in areas with high sulfide levels. In contrast, mats of Beggiatoa were only found in areas where the sulfide levels were >1000 μm and there were significant deposits of wood. Thus, the negative correlation between the distribution and abundance of Z. marina and Beggiatoa suggests that the presence of Beggiatoa mats could be used as a biological indicator of inhibiting levels of hydrogen sulfide in the marine environment.

This study evaluated whether light-permeable deck grating could mitigate impacts of residential mooring floats constructed over eelgrass ( Zostera marina L.) in Puget Sound, Washington. Eelgrass shoot densities in undisturbed control areas and underneath and adjacent to 11 residential floats (16–50% of each float was grated) were monitored prior to float installation and annually for 3 years following installation. Using linear regression analysis, a decline in eelgrass shoot densities relative to controls was detected underneath three floats (eelgrass was eliminated under only one float) and adjacent to two floats. When control data were used to represent 100% grated, there was a weak relationship between eelgrass bed quality and percent of the deck grated ( r = 0.46, p = 0.032), but no relationship when the range of grating was 16–50% ( p = 0.90). The percent of a float deck grated did not contribute significantly to a multiple regression model examining change in eelgrass density that included five other dependent variables associated with the design of the floats. We conclude that either there was no effect of grating up to 50% of a float deck or we could not detect an effect. We hypothesize that the large number of site and landscape scale variables associated with a float influenced the effect (and our ability to detect it) of any one variable (such as grating). Consequently, we recommend that managers manipulate as many attributes of a float as possible (including grating) in order to reduce risks to eelgrass.

We gathered sequence information from the nuclear 5.8S rDNA gene and associated internal transcribed spacers, ITS-1 and ITS-2 (5.8S rDNA/ITS), and the chloroplast maturase K ( matK ) gene, from Zostera samples collected from subtidal habitats in Monterey and Santa Barbara (Isla Vista) bays, California, to test the hypothesis that these plants are conspecific with Z. asiatica Miki of Asia. Sequences from approximately 520 base pairs of the nuclear 5.8S rDNA/ITS obtained from the subtidal Monterey and Isla Vista Zostera samples were identical to homologous sequences obtained from Z. marina collected from intertidal habitats in Japan, Alaska, Oregon and California. Similarly, sequences from the matK gene from the subtidal Zostera samples were identical to matK sequences obtained from Z. marina collected from intertidal habitats in Japan, Alaska, Oregon and California, but differed from Z. asiatica sequences accessioned into GenBank. This suggests the subtidal plants are conspecific with Z. marina , not Z. asiatica . However, we found that herbarium samples accessioned into the Kyoto University Herbarium, determined to be Z. asiatica , yielded 5.8S rDNA/ITS sequences consistent with either Z. japonica , in two cases, or Z. marina , in one case. Similar results were observed for the chloroplast matK gene; we found haplotypes that were inconsistent with published matK sequences from Z. asiatica collected from Japan. These results underscore the need for closer examination of the relationship between Z. marina along the Pacific Coast of North America, and Z. asiatica of Asia, for the retention and verification of specimens examined in scientific studies, and for assessment of the usefulness of morphological characters in the determination of taxonomic relationships within Zosteraceae.

Recent studies found seed size variation within the seagrass Zostera marina, one of nine species in the genus Zostera. The objectives of this study were to determine if variation also exists in the seeds of two other species Zostera japonica and Zostera asiatica within this genus. Results indicate that: (1) length and weight varied between two populations (one indigenous population from Akkeshi-Ko, Japan, and one exotic population from Willapa Bay, Washington, USA) of the small-bodied intertidal seagrass species Z. japonica, and (2) seed-size classes were discernable. Preliminary investigations were also initiated with a Japanese population of Z. asiatica, a large-bodied subtidal seagrass species. Z. japonica seeds from the exotic population were significantly (P < 0.001) longer and heavier when compared to those from the indigenous population, a finding which may help explain both the process of the earlier introduction and the recent expansion of this exotic in the northeastern Pacific. Also, preliminary results indicate that Z. asiatica seeds are heavier than both those of Z. marina and Z. japonica, which suggests that larger seeds may be associated with large-bodied plants in this genus, an observation that should direct future seed ecology studies within the genus. These findings demonstrate that, similar to the study of terrestrial angiosperms, investigations designed to describe the comparative ecology of marine seed-bearing plants should include an evaluation of seed size.

We describe an innovative method of dispersing Zostera marinaL. (eelgrass) seed that has the potential to facilitate large-scale, citizen-based restoration programs. Mature reproductive shoots of eelgrass were collected during the second week of seed release and stocked into mesh pearl nets suspended from buoys set in 0.04 ha plots. As the seeds ripened, they were naturally released from the nets, fell to the bottom and germinated to form a distinct arc-shaped meadow under each buoy. A survey of seedling survival indicated that recruitment was at least 6.9% based on estimated seed abundance within each net. The advantages of this method are that (1) harvest and deployment of reproductive shoots takes place on the same day, eliminating the need to store reproductive shoots in an on-shore storage facility, to obtain a sufficient number of seeds for large-scale restoration programs and (2) once trained, citizens can participate in both the collection and seeding phases, thereby, increasing awareness and value of Z. marina restoration programs. The technique presented allows for a low-cost, efficient, and simple method for successfully dispersing seed, which consequently has a significant impact on establishment of plants from seed. These attributes can also influence restoration programs for other species of aquatic plants for which the seeding of sites, historically degraded but now habitable, is possible. © 2005 Published by Elsevier B.V.

Endophytes are bacterial or fungal organisms inhabiting plants and algae. This study addressed the research questions of whether fungal and/or bacterial endophytes inhabit the rhizomes of Zostera marina , Zostera japonica and Phyllospadix scouleri and whether the number of endophyte taxa differs between seagrass species in the San Juan Archipelago of Washington State, USA. A total of 42 endophyte taxa were isolated with 37 taxa inhabiting Z. marina , 31 inhabiting Z. japonica and 27 inhabiting P. scouleri

This study experimentally assessed the impact of gastropod grazing on epiphyton biomass and taxonomic composition on leaves of the seagrass Zostera marina L. along the coasts of Brittany, France. Image analysis was used to measure the same section of a leaf before and after grazing and assess grazing pressure. It was found that: (1) both grazers, Gibbula umbilicalis and Jujubinus striatus, were highly efficient in reducing epiphytic cover; (2) J. striatus showed a higher specific grazing rate than G. umbilicalis at an equivalent animal biomass; (3) J. striatus increased its activity when epiphytic biomass increased. Analysis of the variability of epiphytic cover along the leaves showed considerable heterogeneity from the basal part of the external leaves of a shoot to the apex. The development of long filamentous algae (mainly ectocarpales) in spring and summer and their concentration at the apex intensified shading impact on the seagrass bed. The grazing of both gastropod species was also concentrated at the apex, thereby enhancing their role in moderating the shading effect.

Two species of seagrasses frequently co-occur with extensive thalassinid shrimp populations and aquaculture operations in the intertidal zone of estuaries along the west coast of North America. Although thalassinid shrimp are known to be strong bioturbators and affect both aquaculture operations and benthic intertidal community structure, few studies have investigated shrimp–seagrass interactions. Application of the pesticide carbaryl to control shrimp populations for oyster aquaculture in Willapa Bay, Washington provided us with an experimental tool to investigate one such interaction. We found that the seagrass Zostera japonica colonized areas where ghost shrimp ( Neotrypaea californiensis ) had been removed via carbaryl application. We applied carbaryl to small (900 m 2 ) experimental plots and compared seagrass colonization on these to that on control plots where shrimp remained abundant (100 m −2 ). The cumulative proportion of Z. japonica seeds and sprouts was slightly higher in the surface layer of treated plots (presumably due to the lack of shrimp bioturbation distributing them to depth), but seedling abundance was not significantly different between treated (no shrimp) and untreated control plots when they first emerged in early spring. As the season progressed however, and shrimp became more active, fewer seedlings survived in the untreated areas, and those that did survive grew much more slowly than those in the treated plots. We suspect that this was due to the effects of shrimp bioturbation and either light limitation (shoots that survived were much smaller) or direct burial and loss. Although it is an introduced plant, the natural distribution of Z. japonica is high in the intertidal zone and it is often separated from its congener Zostera marina by an expansive sandflat that is dominated by the ghost shrimp N. californiensis in west coast estuaries. The treatment of intertidal oysterbeds with carbaryl clearly reduces abundance of shrimp in this zone and we documented the same pattern of seagrass colonization on a commercial oyster bed and lack of seagrass in an adjacent unsprayed area. Density of native seagrass Z. marina shoots was also enhanced in plots treated with carbaryl, but only at lower tidal elevations or in intertidal pools where it could survive. We believe the removal of shrimp will continue to broaden the distribution of Z. japonica in Washington coastal estuaries where carbaryl use is permitted and add an interesting perspective to this controversial management issue.

In 1997 and 1998 seeds were collected from the seagrass, Zostera marina L. (Zosteraceae) from Long Island, New York, USA (var. typica), Shaw Island, Washington, USA (var. latifolia) and Izembek Lagoon, Alaska, USA (var. izembekensis) to determine if seed size varied between the varieties, if seed size varied within the same variety, and if the relationship between seed length and seed weight was linear. Measurements of seed length revealed statistically significant differences in this metric between varieties associated with smaller intertidal plants (var. typica and var. izembekensis) and larger plants from the subtidal region (var. latifolia). It was also found that seed length varied within the same variety and verified that the cross-sectional shape of these seeds was primarily elliptical. Using seed cross-sectional area and weight from a randomly selected batch of seeds from the three locations sampled in 1998, a linear model was created to determine seed weight and seeds from var. latifolia were found to be heavier than seeds from var. typica. The potential advantage of heavy seeds for subtidal seeds in search of safe sites is discussed, together with the merit of using the model to calculate the weight of other elliptical seeds within the Zosteraceae and other seagrass families. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 142, 281–288.

Wild gathering of the leaves of the submerged marine monocotyledon Zostera marina L. once formed the basis of a vigorous insulation industry in North America. Since European colonization, fishing communities used detached leaves, deposited on the beach by tide and wind, as green manure and domestic insulation, but beginning in the late 1800s, these leaves were utilized in a commercial insulating product. Two companies manufactured seagrass “quilts” that were installed in many buildings of the period including some of the first skyscrapers. We here describe the importance of seagrass gathering for the coastal community of Yarmouth County, Nova Scotia, Canada. Interviews with older residents and analysis of county and company archives facilitate the reconstruction of what was once a seasonally important activity. Our findings have direct application to global seagrass protection initiatives.

Many marine pathogens are opportunists, present in the environment, but causing disease only under certain conditions such as immunosuppression due to environmental stress or host factors such as age. In the temperate eelgrass Zostera marina, the opportunistic labyrinthu- lomycete pathogen Labyrinthula zosterae is present in many populations and occasionally causes severe epidemics of wasting disease; however, risk factors associated with these epidemics are unknown. We conducted both field surveys and experimental manipulations to examine the effect of leaf age (inferred from leaf size) on wasting disease prevalence and severity in Z. marina across sites in the San Juan Archipelago, Washington, USA. We confirmed that lesions observed in the field were caused by active Labyrinthula infections both by identifying the etiologic agent through histology and by performing inoculations with cultures of Labyrinthula spp. isolated from observed lesions. We found that disease prevalence increased at shallower depths and with greater leaf size at all sites, and this effect was more pronounced at declining sites. Experimental inoculations with 2 strains of L. zosterae confirmed an increased susceptibility of older leaves to infection. Overall, this pattern suggests that mature beds and shallow beds of eelgrass may be especially susceptible to outbreaks of wasting disease. The study highlights the importance of considering host and environmental factors when evaluating risk of disease from opportunistic pathogens.

Eelgrass (Zostera marina) forms the foundation of an important shallow coastal community in protected estuaries and bays. Widespread population declines have stimulated restoration efforts, but these have often overlooked the importance of maintaining the evolutionary potential of restored populations by minimizing the reduction in genetic diversity that typically accompanies restoration. In an experiment simulating a small-scale restoration, we tested the effectiveness of a buoy-deployed seeding technique to maintain genetic diversity comparable to the seed source populations. Seeds from three extant source populations in San Francisco Bay were introduced into eighteen flow-through baywater mesocosms. Following seedling establishment, we used seven polymorphic microsatellite loci to compare genetic diversity indices from 128 shoots to those found in the source populations. Importantly, allelic richness and expected heterozygosity were not significantly reduced in the mesocosms, which also preserved the strong population differentiation present among source populations. However, the inbreeding coefficient F IS was elevated in two of the three sets of mesocosms when they were grouped according to their source population. This is probably a Wahlund effect from confining all half-siblings within each spathe to a single mesocosm, elevating F IS when the mesocosms were considered together. The conservation of most alleles and preservation of expected heterozygosity suggests that this seeding technique is an improvement over whole-shoot transplantation in the conservation of genetic diversity in eelgrass restoration efforts.

Although seagrasses have been identified as vital living marine resources, their distribution has not been rigorously quantified at many locations. This fact is often due to the high cost of sampling seagrass habitats, especially those with deep-water plants that cannot be sensed from aerial platforms. We present a cost-effective method of estimating basal area coverage of submersed vegetation that uses differential global positioning system data linked to underwater video images of the bottom. Our sampling design and statistical procedures are identical to estimating proportions using cluster sampling with unequal cluster sizes. This method has several advantages over other techniques: (1) confidence intervals around basal area coverage estimates permit hypothesis testing of changes over time; (2) sampling efficiency is better than simple random sampling with quadrats; (3) deep-water zones out of the range of aerial platforms can be sampled; (4) video images provide positive identification of plants which is not possible with acoustic techniques; and (5) the techniques provide a permanent archive of visual images that can be analyzed for other bottom attributes, such as other vegetation, macro-invertebrates, and gross sediment types. This method has some limitations: (1) it is not possible to sample extremely shallow or turbid waters and under some physical structures; (2) it is impractical to sample very large regions; (3) errors in differential global positioning system data must be accounted for; and (4) seagrass density must be measured subjectively. We illustrate our sampling methods and data analysis with an example from Puget Sound, Washington, USA.

SummaryMany natural and human-induced events create disturbances in seagrasses throughout the world, but quantifying losses of habitat is only beginning. Over the last decade, 90000 ha of seagrass loss have been documented although the actual area lost is certainly greater. Seagrasses, an assemblage of marine flowering plant species, are valuable structural and functional components of coastal ecosystems and are currently experiencing worldwide decline. This group of plants is known to support a complex trophic food web and a detritus-based food chain, as well as to provide sediment and nutrient filtration, sediment stabilization, and breeding and nursery areas for finfish and shellfish.We define disturbance, natural or human-induced, as any event that measurably alters resources available to seagrasses so that a plant response is induced that results in degradation or loss. Applying this definition, we find a common thread in many seemingly unrelated seagrass investigations. We review reports of seagrass loss from both published and ‘grey’ literature and evaluate the types of disturbances that have caused seagrass decline and disappearance. Almost certainly more seagrass has been lost globally than has been documented or even observed, but the lack of comprehensive monitoring and seagrass. mapping makes an assessment of true loss of this resource impossible to determine.Natural disturbances that are most commonly responsible for seagrass loss include hurricanes, earthquakes, disease, and grazing by herbivores. Human activities most affecting seagrasses are those which alter water quality or clarity: nutrient and sediment loading from runoff and sewage disposal, dredging and filling, pollution, upland development, and certain fishing practices. Seagrasses depend on an adequate degree of water clarity to sustain productivity in their submerged environment. Although natural events have been responsible for both large-scale and local losses of seagrass habitat, our evaluation suggests that human population expansion is now the most serious cause of seagrass habitat loss, and specifically that increasing anthropogenic inputs to the coastal oceans are primarily responsible for the world-wide decline in seagrasses.

The relationship between turbidity and light availability, and its subsequent effect on the depth distribution of Zostera marina L. (eelgrass) in San Francisco Bay was explored. The average daily period of irradiance-saturated photosynthesis (Hsat) required for the maintenance of whole plant carbon balance and growth, based on measured rates of photosynthesis and respiration as well as data available in the literature, were estimated to be between 3 and 5 h. Estimates of average Hsat availability in the field were determined from laboratory measurements of the phytosynthesis vs. irradiance (P vs. I) response and from field observations of light attenuation measured at five sites in San Francisco Bay. Although plants were found to be low-light adapted with regard to their P vs. I response, they were limited to depths shallower than −2 m mean lower low water (MLLW) at all sites. The −2 m depth limit corresponded fairly well to predicted Hsat requirements at two sites where turbidity was relatively low and constant, but depth limits of eelgrass were less than 1.5 m at three sites subjected to extremely turbid and variable light environments, much shallower than predicted from calculations of mean daily carbon requirements and Hsat availability. Thus, in addition to the mean light environment, periods of extreme light attenuation that last from days to weeks may be important in controlling eelgrass growth and productivity in highly turbid and dynamic estuaries such as San Francisco Bay.

In the past three decades seagrass research has adopted several disciplines and matured into a global science. One of the approaches we can use to focus our science to benefit the management and protection of seagrass is that of Conservation Biology; a proactive field of science bringing together academic, government, and nongovernmental organizations from a wide range of disciplines to understand and conserve biodiversity. This relatively recent field synthesises and directs insights from many disciplines for direct application to the protection and conservation of species, communities, and biomes (Fig. 1). While the primary focus for conservation biology comes from ecology, genetics, landscape ecology, population biology and taxonomy, the discipline also incorporates analytical procedures associated with the social sciences, biogeography, and evolutionary biology (Soule and Wilcox, 1980; Soule, 1985; Meffe and Carroll, 1994; Primack, 2000). Conservation biology recognizes that humans derive both extractive and intrinsic benefit from the natural world and embraces methods and analyses utilized in fisheries science, agriculture, anthropology, economics, law, philosophy, and sociology. Today, unlike traditional approaches that were rooted in the preservation and management of selected species, conservation biologists are advising natural resource managers to focus more on an ecosystem approach that includes entire biomes, and to recognize that public trust demands comprehensive protection of biodiversity as much as sustaining the yield of harvestable organisms. Conservation biology endeavors to maintain and protect biodiversity at all spatial scales, including a variety of little understood and often overlooked life forms. In the broader meaning of biodiversity we are interested in conserving ecological services as much as life forms (sensu Randall, 1986).

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.

Marine diseases can decimate populations and can have substantial ecological, economic, and social impacts. Recent disease outbreaks in marine mammals, shellfish, sponges, seagrasses, crustaceans, corals, and fishes demonstrate the potential for catastrophic effects, including reduced biodiversity