Dwarf Eelgrass Research Articles

Effects of Restoration Through Nature-Based Solution on Benthic Biodiversity: A Case Study in a Northern Adriatic Lagoon

In the Caleri lagoon, a coastal lagoon in the Po River Delta, Northern Adriatic, the transplant of the dwarf eelgrass Zostera noltei was used as a nature-based solution to attempt the ecological restoration of a previously depleted lagoon area. A total of 135 15-cm-diameter sods were transplanted, with the donor site at the Venice lagoon. Using unmanned aerial vehicles (UAVs), eelgrass transplants were mapped and monitored with great precision. After two years, the area covered by eelgrass increased from the initial 2.5 m2 to 60 m2. Changes in the community structure and on the frequency of biological traits of macrobenthos occurred at the transplant site, with a higher frequency of epifaunal predators and herbivores, and of organisms with longer life spans and larger body sizes. Sensitive and indifferent taxa were always higher in the transplant site than in the bare bottom control site, where opportunistic taxa continued to dominate. Ecological quality status measured through M-AMBI and HBFI indices showed a clear improvement in the transplant site. The rapid changes in benthos demonstrate that even relatively small-scale transplantation of dwarf eelgrass can restore faunal communities very rapidly.

Habitat suitability modelling for restoration of intertidal seagrass, Zostera noltei: A case study from the Greater Thames Estuary, UK

Habitat suitability modelling for restoration of intertidal seagrass, Zostera noltei: A case study from the Greater Thames Estuary, UK

Exploring the newly emerging effects of native seagrasses on survival and growth of non-native juvenile clams

The Manila clam (Ruditapes philippinarum) has been introduced into the Atlantic European coast for commercial exploitation. In this region, the population dynamics of this clam species may be determined by the interaction with the native dwarf eelgrass (Zostera noltei). We performed an experiment in the tidal flats of an estuary located in northern Spain to analyse the interaction between Z. noltei and juvenile Manila clams. Based on existing knowledge, it was hypothesised that seagrasses act as a nursery protecting juveniles from predation, which is an important cause of natural mortality, and that seagrass density influences the survival, growth and condition of clams. The results indicate that the effects of seagrasses on juvenile clams depends on shoot density, which mainly determine the relative prevalence of positive versus negative interactions. Dense seagrass meadows protect juvenile clams from predation, likely decreasing their visibility and reducing the efficiency of predators. However, in these dense meadows, a decline in the condition of clams was also observed, although not in shell growth. This decline can be due to the fact that food supply in dense meadows is slow and does not fulfil the replenishment rates required by filter-feeding organisms or because competition for space with the seagrass causes stress. Clams are larger in populations where predator access is prevented, possibly indicating selective predation on larger organisms when this interaction is allowed. The knowledge gained from this experiment is of great interest for analysing possible future trends in clam populations and the derived social implications given its high economic value.

Monitoring the Spatial and Interannual Dynamic of Zostera noltei.

Seagrass is a vital structural and functional element of the marine environment worldwide and is highly valued for its ecological benefits. Monitoring the evolution of the seagrass habitat is essential to understand how this coastal ecosystem changes, and to develop good environmental management practices. For the present study, two remote sensing methods were used to map and monitor Zostera noltei Hornemann, 1832 (Z. noltei), in the Merja Zerga lagoon from 2010 to 2020. These methods which are the random forest algorithm and the object-oriented classification, were convenient to provide significant results. The first approach employed Sentinel-2 images from 2018 to 2020, which were used to extract information on changes in Z. noltei (commonly called dwarf eelgrass) distribution and aboveground biomass estimation. The second involved three orthophotography (orthophoto) mosaics from the years 2010, 2016, and 2018, which were analyzed to map the distribution of the species. It was revealed that Z. noltei coverage has increased by 212ha since 2010, with most of the growth occurring in the center and upstream part of the lagoon. The mean aboveground biomass of dwarf eelgrass in the lagoon was 78.5 DW/m² in 2018, 92.6 DW/m² in 2019, and 115.2g DW/m² in 2020. The approach used in this study has provided important insights into the dynamic and mean biomass of Z. noltei in the Merja Zerga lagoon. It is therefore a valuable, non-destructive method that uses freely-available Sentinel-2 satellite data.

Eelgrass (Zostera spp.) associated phytomyxids are host-specific congeneric parasites and predominant eukaryotes in the eelgrass rhizosphere on a global scale.

Together with increasing environmental and anthropogenic pressures, pathogenic diseases are one of the important factors contributing to the ongoing decline of seagrass meadows worldwide; yet the diversity and ecology of the microorganisms acknowledged as seagrass parasites remain critically understudied. Here, we investigate phytomyxid parasites (Rhizaria: Endomyxa: Phytomyxea) of three different eelgrass (Zostera spp.) species found in the Northern hemisphere. We present molecular evidence that Plasmodiophora bicaudata, a long-recognized parasite of dwarf eelgrass taxa, is closely related to the novel phytomyxid recently discovered in root hairs of Zostera marina, and together they form a distinct clade within the order Phagomyxida, proposed here as Feldmanniella gen. nov. A full life cycle is systematically described in a phagomyxid representative for the first time, proving its conformity with the generalized phytomyxid life history, despite previous uncertainties. The presence of primary infection stages in nearly all collected eelgrass specimens, and subsequent analysis of amplicon sequences from a global Z. marina dataset, reveal phytomyxids to be ubiquitous and one of the predominant microeukaryotes associated with eelgrass roots on a global scale. Our discoveries challenge the current view of Phytomyxea as rare entities in seagrass meadows and suggest their generally low pathogenicity in natural ecosystems.

Experimental effects of warming and epiphyte grazing on the ecophysiology of two seagrass morphotypes

Seagrasses form important ecosystems providing essential provisioning and regulating services. They exhibit acclimative properties to contend with environmental change while intrinsic responses allow seagrasses to persist in sub- and supra-optimal temperatures, and are critical to understanding their ability to cope with a changing climate. An indoor mesocosm approach was used to investigate the effects of warming, i.e. mean summer (24 °C) and extreme (30 °C) temperatures, and epiphyte grazing on large-leaved and small-leaved morphotypes of a dwarf eelgrass ( Zostera capensis ) from a temperate lagoon habitat. Both morphotypes displayed similar responses under extreme temperatures with greater losses observed in shoot densities and total biomass compared to summer mean temperatures. However, higher photosynthetic rates and accumulations of carbon, nitrogen and phenolics were observed in small- compared to large-leaved plants. This suggests that small-leaved populations possess a larger propensity to store resources - a potential for resilience. Large-leaved populations appeared to have channelled resources towards growth suggesting a greater susceptibility to stress from e.g. fouling. Epiphyte biomass increased under extreme temperatures and, even though grazing had a positive effect on seagrass biomass under summer mean conditions, grazers did not regulate algal growth under extreme temperatures which may have been too rapid for grazer control. These findings indicate that seagrasses will be negatively affected by extreme warming with ensuing reductions in biomass, increasing their susceptibility to stressors. However, acclimation strategies including carbon and nitrogen stores provide high resilience potential and attest to a system's ability to cope with stress. • Seagrasses exhibit acclimative strategies that allow their persistence and ability to cope with environmental stress. • Sensitivity to extreme warming was greater in low- as opposed to high-shore seagrass plants. • Large-leaved morphotypes appeared to channel carbon and nitrogen towards maintaining growth. • Small-leaved morphotypes had greater reserves in the form of secondary metabolites compared to large-leaved counterparts. • Acclimative strategies including C and N stores allude to resilience potential and a system’s ability to cope with stress.

Dwarf eelgrass (Zostera noltii) fatty acid remodelling induced by climate change

Dwarf eelgrass Zostera noltii meadows are found in estuarine coastal areas across the north-eastern Atlantic, where they provide key ecosystem services, including nursery grounds, sediment stabilization, nutrient cycling and carbon sequestration. These blue carbon ecosystems are being subjected to several anthropogenic pressures, including climate change-related effects. In the present study, we investigated the biochemical changes (fatty acid profiling) under different climate change scenarios (present-day conditions, ocean acidification, ocean warming and combined warming and acidification), following IPCC RCP scenario 8.5. Significant modifications in the percentage of saturated (SFA) and polyunsaturated fatty acids (PUFAs) in response to warming and low pH levels were detected. The changes suggest a rearrangement of membrane composition to maintain membrane fluidity, especially under warming conditions. Individuals under warming treatment showed higher plastidial pathway activity, while acidification induced a shift in the fatty acid synthesis pathway towards the extra-plastidial pathway, indicating a need to readjust the chloroplastidial monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) lipids under thermal stress to counteract excessive membrane fluidity. Regarding PUFA fatty acids, α-linolenic acid (ALA, C18:3, n-3) showed a pronounced decrease under the combined treatment, a tendency that can be connected to reactive oxygen species (ROS) quenching and membrane remodelling. Thus, and observing the changes in the fatty acid profile, these essential molecules appear as good candidate biomarkers to detect changes in seagrass ecophysiology under acute climate change-related events. Our findings suggest that future global warming will pose a serious threat to these already endangered blue ecosystems. • Seagrasses are marine founding species threatened by climate change. • These plants are sources of essential fatty acids (FAs) for the marine heterotrophic life. • Leaf saturated and polyunsaturated FAs in response to warming and acidification. • Linolenic acid decrease appears to be connected to reactive oxygen species quenching. • Seagrass FAs profile appear as good candidate biomarkers for climate change related stress.

Mapping and Quantification of the Dwarf Eelgrass Zostera noltei Using a Random Forest Algorithm on a SPOT 7 Satellite Image

The dwarf eelgrass Zostera noltei Hornemann (Z. noltei) is the most dominant seagrass in semi-enclosed coastal systems of the Atlantic coast of Morocco. The species is experiencing a worldwide decline and monitoring the extent of its meadows would be a useful approach to estimate the impacts of natural and anthropogenic stressors. Here, we aimed to map the Z. noltei meadows in the Merja Zerga coastal lagoon (Atlantic coast of Morocco) using remote sensing. We used a random forest algorithm combined with field data to classify a SPOT 7 satellite image. Despite the difficulties related to the non-synchronization of the satellite images with the high tide coefficient, our results revealed, with an accuracy of 95%, that dwarf eelgrass beds can be discriminated successfully from other habitats in the lagoon. The estimated area was 160.76 ha when considering mixed beds (Z. noltei-associated macroalgae). The use of SPOT 7 satellite images seems to be satisfactory for long-term monitoring of Z. noltei meadows in the Merja Zerga lagoon and for biomass estimation using an NDVI–biomass quantitative relationship. Nevertheless, using this method of biomass estimation for dwarf eelgrass meadows could be unsuccessful when it comes to areas where the NDVI is saturated due to the stacking of many layers.

Dwarf eelgrass (Zostera noltii) leaf fatty acid profile during a natural restoration process: Physiological and ecological implications

Abstract Seagrass beds are among the most relevant ecosystem engineers, providing essential ecosystem services for the surrounding coastal communities. Alongside, these ecosystems are among the most threaten in the world, and thus several restoration projects have been developed in the past years. Seagrasses are important sources of essential fatty acids (FA) for animals, which are unable to synthetize them. During the seagrass growth and photochemical maturation, there is a membrane remodelling, where some fatty acids are synthetized. When analysing the FA changes at different development stages, one of the first noticeable changes is the increase in C16:1t (trans-hexadecenoic acid), associated to an increase in the chloroplast membrane fluidity, essential for the efficient energy transduction processes to occur in the thylakoids. Also, interesting to observe are the high levels of omega-3 and -6 (30–43% and 18–31% of total fatty acid content, respectively) present in this seagrass, reinforcing the nutritional value of this species as source of essential fatty acids for the primary consumers. Additionally, it is possible to observe that in the more mature plants there is a high leaf concentration of C18:3. Recent reports suggest that C18:3 can act as a direct scavenger of reactive oxygen species (ROS), indicating a lower stress level, as suggested by the higher photochemical efficiency previously observed. Moreover, it is also interesting to observe that total long-chain polyunsaturated fatty acids (LC-PUFAs) content show a significant increase with the biomass development. These LC-PUFAs are not produced by higher plants and their production in animals occurs at low rates, suggesting they may have as origin the microalgae in the grass surface, adding another important ecosystem service to these prairies, as support for microalgae development and carriers of LC-PUFAs into the food web. This membrane remodelling appears to be on the basis of the photochemical maturation of these seagrasses observed in previous studies and can be used as potential and efficient tool to monitor the development stage of the prairies and its physiological status in future restoration processes. Moreover, it becomes evident that highly developed seagrass beds are crucial food source providers in terms of essential fatty acids to the estuarine heterotrophic life.

Can pesticides, copper and seasonal water temperature explain the seagrass Zostera noltei decline in the Arcachon bay?

Dwarf eelgrasses (Zostera noltei) populations have decreased since 2005 in Arcachon Bay (southwest France). Various stressors have been pointed out, however the role of xenobiotics like pesticides or copper (Cu) and of parameters like water temperature warming have not yet been explored. To determine their impact, Z. noltei individuals were collected in a pollution-free site and transferred to the laboratory in seawater microcosms. This dwarf eelgrass was exposed to a pesticide cocktail and copper, alone or simultaneously, at temperatures (10°C, 20°C, 28°C) representative of different seasons. After a two-week contamination, leaf growth, leaf bioaccumulation of Cu, and differential expression of target genes were studied. Eelgrasses bioaccumulated Cu regardless of the temperature, with reduced efficiency in the presence of the Cu and pesticide cocktail at the two higher temperatures. High temperature also exacerbated the effect of contaminants, leading to growth inhibition and differential gene expression. Mitochondrial activity was strongly impacted and higher mortality rates occurred. Experimental results have been confirmed during field survey. This is the first report on the impacts on Z. noltei of pesticides and Cu associate to temperature.

A Preliminary Study on the Heavy Metal Levels of Dwarf Eelgrass Zostera Noltii Homermann in the Black Sea

In the present study, the concentrations of aluminium, arsenic, copper, zinc, mercury, iron, cadmium and lead have been measured in sediment and in dwarf eelgrass Zostera noltii, collected from Sinop coast of the Black Sea, Turkey in 2013. Concentrations of Al, As, Cu, Zn, Pb and Fe were generally higher in sediment than those in dwarf eelgrass. Cd concentrations, however, were higher in the dwarf eelgrass samples. Hg was below the limit of detection (<0.05 mg/kg dry wt) in dwarf eelgrass, and it was detected mean 0.02 mg/kg dry wt. in sediment. Cd had the highest CF mean and As showed the lowest CF value. It may be concluded that dwarf eelgrass is able to accumulate the heavy metals from the marine environment and is suitable as bio-indicator to assess the fluctuations in metal pollution in the Black Sea.

Ecological periodic tables for benthic macrofaunal usage of estuarine habitats: Insights from a case study in Tillamook Bay, Oregon, USA

This study validates the ecological relevance of estuarine habitat types to the benthic macrofaunal community and, together with previous similar studies, suggests they can serve as elements in ecological periodic tables of benthic macrofaunal usage in the bioregion. We compared benthic macrofaunal Bray–Curtis similarity and the means of eight benthic macrofaunal community measures across seven habitat types in Tillamook Bay, Oregon, USA: intertidal eelgrass ( Zostera marina ), dwarf eelgrass ( Zostera japonica ), oyster ( Crassostrea gigas ) ground culture, burrowing mud shrimp ( Upogebia pugettensis ), burrowing ghost shrimp ( Neotrypaea californiensis ), sand and subtidal. Benthic macrofaunal Bray–Curtis similarity differed among all the habitats except ghost shrimp and sand. The habitat rank order on mean benthic macrofaunal species richness, abundance and biomass was dwarf eelgrass ≈ oyster ≥ mud shrimp ≈ eelgrass > sand ≈ ghost shrimp ≈ subtidal. The benthic macrofaunal habitat usage pattern in Tillamook Bay was, with a few exceptions, similar to that in two other US Pacific Northwest estuaries. The exceptions indicate variants of eelgrass and ghost shrimp habitat that differ in benthic macrofaunal usage perhaps due to differences in the coarseness of the sand fraction of the sediments in which they live. The similarities indicate periodic benthic macrofaunal usage patterns across the other habitat types extend over a wider geographic scale and range of environmental conditions than previously known. ► There are benthic macrofaunal community across-habitat patterns in Tillamook Bay, OR. ► Most of the patterns are similar to those in Willapa Bay and Grays Harbor, WA. ► Most habitats can serve as elements in benthic macrofaunal ecological periodic tables. ► Operational definitions of eelgrass and burrowing ghost shrimp habitat are incomplete.

Macrobenthic assemblage structure in a cool-temperate intertidal dwarf eelgrass bed in comparison with those from lower latitudes

The evolution and ecology of latitudinal patterns in marine macrofaunal biodiversity and assemblage structure are contentious. With the aim of investigating the occurrence of such patterns in intertidal dwarf eelgrass beds (Nanozosteraspp.), those at cool-temperate Scolt Head Island, UK (latitude 52°N), were examined and compared with equivalent systems in warm-temperate Knysna, South Africa (34°S), and subtropical Moreton Bay, Australia (27°S): systems that had earlier been examined using an identical methodology. The Scolt Head bed supported the highest faunal density (mean 6568 0.1m -2), lowest observed and estimated species richness (32 and 33 spp., respectively), lowest species diversity (Simpson's index of diversity 0.34), highest mean constancy index (23.0), lowest proportion of total numbers contributed by singletons or doubletons (0.06%), largest Berger-Parker dominance index (0.81), and least degree of variability between component samples. The beds at Knysna were intermediate between those at Scolt Head and at Moreton Bay in all those respects, as well as in nature and composition of the fauna. Similar dwarf eelgrass beds at Arcachon, France, likewise appear intermediate between those of Scolt Head and Knysna. Community variance in all three regions was greatest at the smallest spatial scale of ≤1m, at which scale two of the three sites also displayed randomly organized faunal assemblages, although this changed to non-random at larger spatial scales. Assemblages were deterministically structured at all spatial scales at Knysna. A consistent series of changes in structural characteristics of macrofaunal dwarf-eelgrass assemblages therefore occurred along the latitudinal sequence of Scolt Head (53°), Arcachon (45°), Knysna (34°), and Moreton Bay (27°). Community assembly patterns did not change with latitude, however, but did so with spatial scale in two of the three regions. © 2011 The Linnean Society of London.

Ecological periodic tables for benthic macrofaunal usage of estuarine habitats in the US Pacific Northwest

Abstract This study shows that spatially and temporally recurring benthic macrofauna–habitat patterns validate the ecological relevance of habitat types to benthic macrofauna and suggest they can serve as elements in ecological periodic tables of benthic macrofaunal usage. We discovered patterns across nine habitat types (intertidal eelgrass [ Zostera marina ], dwarf eelgrass [ Zostera japonica ], oyster [ Crassostrea gigas ] ground culture, burrowing mud shrimp [ Upogebia pugettensis ], burrowing ghost shrimp [ Neotrypaea californiensis ], shell, sand, mud, and subtidal) on a variety of benthic macrofaunal community state variables in Grays Harbor, Washington, USA and compared them to those in Willapa Bay, Washington, USA. There were nominal differences in benthic macrofaunal Bray–Curtis similarity between all the habitats investigated except eelgrass and oyster in both estuaries. Across-habitat patterns on mean benthic macrofaunal species richness, abundance, biomass, abundance of deposit, suspension and facultative feeders, a dominance and a diversity index for the five habitats common to both studies were the same on a rank measurement scale: eelgrass ≈ oyster > mud shrimp > ghost shrimp ≈ subtidal. The patterns for most of the habitats and benthic macrofaunal measures were the same on a ratio measurement scale.

An evaluation of small-scale genetic diversity and the mating system in Zostera noltii on an intertidal sandflat in the Wadden Sea

The dwarf eelgrass, Zostera noltii, is a predominant inhabitant of soft-bottom intertidal regions along the coasts of northern Europe. It is a monoecious, protogynous angiosperm in which the potential for self-fertilization and inbreeding are high, especially if clone sizes exceed pollen dispersal distances. The aim of the present study was to determine the relationship between mating system and clonal structure, examine the relative roles of geitonogamous selfing and biparental inbreeding, measure pollen availability (multiple paternities) and estimate pollen dispersal. A 100-m(2) plot was established in a large, intertidal Z. noltii meadow on the island of Sylt in the German Wadden Sea. A total of 256 adult shoots was sampled: one from the centre of 100 fixed 1-m(2) quadrats (large scale resolution) and an additional 156 from within eight randomly selected 1-m(2) sub-quadrats (small-scale resolution). DNA was extracted from seeds and leaf tissue of all samples and genotyped with nine microsatellite loci. Mating system analysis revealed high multilocus and single locus outcrossing rates. Average pollen dispersal distance was nearly the same as the average genet (clone) size. Multiple paternity was common and 20-30 % of mature seeds originated from matings within the plot. Among inbred seeds, most resulted from geitonogamy rather than biparental inbreeding. Moderate disturbances intrinsic to the intertidal habitat appear to facilitate seed recruitment by gap formation. Pollen dispersal distances are sufficient to maintain outcrossing and high clonal diversity.

섬진강 하구에 자생하는 잘피의 분포 현황 및 생태적 특성

Among common estuarine submerged plants, seagrasses are the most extensively studied due to their ecological importance in estuarine ecosystems. Seagrass meadows are important biological habitats for a wide variety of marine animals and plants. They are a source of organic carbon for commercially important animals. Furthermore, seagrasses act as nutrient filters in estuarine and coastal marine ecosystems. As such, mapping the distribution of seagrass beds is important for management and conservation strategies. In order to survey the seagrass distribution within the Seomjin Estuary, We directly observed seagrass beds in Kwangyang and Hadong using SCUBA. The distribution area, species composition, morphology, density, biomass and productivity of seagrass meadows were examined. Seagrass meadows were distributed in the intertidal and subtidal zones of the Galsa tidal flats, and in the subtidal zone of the neighboring POSCO area. Patches of Zostera japonica was found at patches at the Galsa tidal flats intermediate point. The total estimated seagrass distribution area of the Seomjin Estuary was <TEX>$1.84\;km^2$</TEX>. Of the total, <TEX>$1.83\;km^2$</TEX> was Zostera marina (eelgrass) and <TEX>$0.01\;km^2$</TEX> was Zostera japonica (dwarf eelgrass). Zostera japonica was found in intertidal zones. Zostera marina was found from the intertidal to subtidal zones at a 2 m mean sea level (MSL) depth. The leaf productivity of Zostera marina was <TEX>$4.47g\;DW\;m^{-2}\;day^{-1}$</TEX>. The annual production of eelgrass was <TEX>$1,632\;g\;DW\;m^{-2}\;yr^{-1}$</TEX>, which corresponds to <TEX>$731g\;C\;m^{-2}\;yr^{-1}$</TEX>. The total production of eelgrass was <TEX>$3,002\;tons\;DW\;yr^{-1}$</TEX>, which corresponds to <TEX>$1,343\;tons\;C\;yr^{-1}$</TEX>.

Interactions between two introduced species: Zostera japonica (dwarf eelgrass) facilitates itself and reduces condition of Ruditapes philippinarum (Manila clam) on intertidal flats

Dwarf eelgrass (duckgrass; Zostera japonica) and Manila clams (Ruditapes philippinarum) are two introduced species that co-occur on intertidal flats of the northeast Pacific. Through factorial manipulation of clam (0, 62.5, 125 clams m−2) and eelgrass density (present, removed by hand, harrowed), we examined intra- and interspecific effects on performance, as well as modification of the physical environment. The presence of eelgrass reduced water flow by up to 40% and was also observed to retain water at low tide, which may ameliorate desiccation and explain why eelgrass grew faster in the presence of conspecifics (positive feedback). Although shell growth of small (20–50 mm) clams was not consistently affected by either treatment in this 2-month experiment, clam condition improved when eelgrass was removed. Reciprocally, clams at aquaculture densities had no effect on eelgrass growth, clam growth and condition, or porewater nutrients. Overall, only Z. japonica demonstrated strong population-level interactions. Interspecific results support an emerging paradigm that invasive marine ecosystem engineers often negatively affect infauna. Positive feedbacks for Z. japonica may characterize its intraspecific effects particularly at the stressful intertidal elevation of this study (+1 m above mean lower low water).

Regional and latitudinal variation in the diversity, dominance and abundance of microphagous microgastropods and other benthos in intertidal beds of dwarf eelgrass, Nanozostera spp.

The smaller macroscopic members of the epifauna and shallowly-burrowing infauna of comparable intertidal beds of dwarf eelgrass and associated areas of non-vegetated sediment were investigated with uniform methodology in the cool-temperate English southern North Sea (Nanozostera noltii), warm-temperate southern coast of the Western Cape, South Africa (N. capensis) and in subtropical southern Queensland, Australia (N. muelleri capricorni), together with equivalent seagrass sites in tropical Sulawesi, Indonesia, and Seychelles, Western Indian Ocean. Epifaunal microphagous microgastropods dominated both the eelgrass and non-vegetated cool- and warm-temperate sites with >80% of macrofaunal individuals, but decreased markedly in density and dominance with decreasing latitude, down to near zero in the tropics; microgastropod species diversity in the Nanozostera increased with decreasing latitude, whilst their species richness per core sample was highest in the warm temperate zone. Other co-existing—largely infaunal—taxa (mainly annelid worms, bivalve molluscs and crabs), however, showed less marked latitudinal variation in density and no relationship of taxon diversity with latitude. With few exceptional cases, microgastropod density, dominance, species richness and diversity were greater in the eelgrass beds than in adjacent non-vegetated sediments, as were the densities and taxon diversities of the associated faunal groups, although within the beds themselves there were no significant correlations between seagrass density and the density or diversity of either the microgastropods or their associated fauna. The extent to which the presence or absence of seagrass influenced the underlying community composition of the benthic fauna varied between localities. These results are consonant with an increasing effect of predation in low latitudes on small epifauna.

Evidence for persistent seed banks in dwarf eelgrass Zostera noltii in the German Wadden Sea

The intertidal dwarf eelgrass Zostera noltii is a dominant species in the Dutch and Ger- man Wadden Sea. Although numerous studies of its reproductive ecology have been conducted, few have examined the importance of seeds and seed banks for meadow maintenance. We investigated the contribution of a seed bank (size, genetic potential and persistence) to annual recruitment of dwarf eelgrass in the German Wadden Sea using temporal sampling of seeds from the sediment and genetic assignment tests of seedlings to populations of adult shoots from previous years. Annual sed- iment seed density (SD) was 487.5 m -2 (269.4) and 367.3 m -2 (95.5) in 2004 and 2005, respectively, and distribution of seeds in the sediment was highly aggregated. The proportion of over-wintering seeds that germinated under laboratory conditions was 16 to 25%, and field-germination revealed a 12% survival to the seedling stage. Nearly 20% of all shoots present in May 2004 were seedlings. Using 9 microsatellite loci, seedlings sampled in 2004, 2005 and 2006 were compared with adults sampled in 2002, 2003 and 2004; results revealed that 7 to 33% of seedlings could be assigned to the local adult population in current or previous years. Although new recruitment plays an important role in the maintenance of these meadows, considerable new recruitment comes from within the meadow itself. Seeds are viable for at least 3 yr, thereby forming a relatively short-term, but persistent, seed bank.

Monitoring the expanding distribution of nonindigenous dwarf eelgrass zostera japonica in a pacific northwest USA estuary using high resolution digital aerial orthophotography

The paper describes a method of mapping the intertidal distribution of the nonindigenous seagrass Zostera japonica in a Pacific Northwest (PNW) USA estuary from color infrared aerial orthophotography using a hybrid digital classification technique. A random ground survey indicated an overall accuracy exceeding 80 percent for this procedure in the lower estuary, where this invasive species may interfere with mudflat foraging of the commercially important Dungeness crab. Knowledge of the areal distribution of Z. japonica from this digital classification will aid in planning studies to evaluate impacts of expansion of the nonindigenous seagrass in PNW estuaries.