Eelgrass Beds Research Articles

Seasonal and habitat structures of crustacean decapod assemblages associated withZostera marinabeds in northern Jinhae Bay, Korea

Crustacean decapod assemblages were surveyed inZostera marinabeds adjacent to tidal flats (ET) and rocky shore (ER), and in unvegetated habitats (UV). Decapod samples were collected monthly throughout 2002 using a small beam trawl from northern Jinhae Bay, Korea. Water temperature, salinity, eelgrass biomass, sediment composition and organic matter were also monitored to assess any correlation between environmental variables and decapod fauna. A total of 31 decapod species belonging to five taxa (three prawns, 13 caridean shrimps, one hermit crab, one mud shrimp and 13 crabs) were collected at three different habitats. To assess variations in decapod assemblages in relation to habitat type and season, various multivariate analyses were used. The dominant caridean shrimps werePalaemon macrodactylus, Alpheus digitalisandCrangon uritai,and the dominant crabs wereCharybdis japonica, Hemigrapsus penicillatusandCharybdis bimaculata. The number, abundance and diversity of decapod species varied greatly with habitat type and season, peaking in eelgrass beds and during spring, and showing the lowest catch rate in unvegetated habitat and during winter months. The nMDS ordination and multivariate analyses revealed that habitat type and season were determinant factors affecting the structure of decapod assemblages. Seasonal shifts in the abundance of decapods corresponded with changes in eelgrass biomass and loss on ignition (LOI), but not with water temperature or salinity.

Agent Based Modelling (ABM) of eelgrass (Zostera marina) seedbank dynamics in a shallow Danish estuary

Odense Fjord (Denmark) has suffered from a drastic decline in eelgrass (Zostera marina) coverage during the last decades. In 1983 eelgrass still covered about 25% of the estuary, which in 2005 was reduced to less than 2%. The alarming decline in the past decades initiated preliminary restoration activities, where it was questioned whether the present low eelgrass biomass is able to produce a sustainable seed bank to support natural recovery. Field studies verified that the seed bank was hampered. Laboratory experiments were conducted to determine 1) seed dispersion along the sediment surface and in the water column; 2) settling rates of seeds and flowering shoots; 3) critical current speed for seed movement; 4) floating dynamic of flowering shoots and 5) seed dropping dynamics during transport of rafting shoots.These parameters supported the development of an agent based model (ABM) predicting seed movements in estuaries. The model handled two ways of seed dispersal: 1) seeds dropped in eelgrass beds and transport by hydrodynamic forces along the seabed 2) seeds released by rafting shoots. This setup allowed assessment of both eelgrass seed loss and potential connectivity between beds. Seed losses were divided into direct losses, such as seeds lost on land due to desiccation or external boundary, and indirect losses affecting seedling establishment.The model estimates that app. 92% of the seeds would be retained in the Odense fjord, while only 5.0% of the seeds ended up in areas supporting seedling establishment. Eelgrass seeds were also found in areas with insufficient light, high hydrodynamic pressure, excessive sediment reworking by lugworms or poor anchoring capacity. In addition, the model showed potential bed connectivity via rafting shoots, but also with individual seed movement along the bottom, when beds were not separated by deep areas, such as boating channels.

Latitude, temperature, and habitat complexity predict predation pressure in eelgrass beds across the Northern Hemisphere

Latitude, temperature, and habitat complexity predict predation pressure in eelgrass beds across the Northern Hemisphere

Latitude, temperature, and habitat complexity predict predation pressure in eelgrass beds across the Northern Hemisphere.

Latitudinal gradients in species interactions are widely cited as potential causes or consequences of global patterns of biodiversity. However, mechanistic studies documenting changes in interactions across broad geographic ranges are limited. We surveyed predation intensity on common prey (live amphipods and gastropods) in communities of eelgrass (Zostera marina) at 48 sites across its Northern Hemisphere range, encompassing over 37° of latitude and four continental coastlines. Predation on amphipods declined with latitude on all coasts but declined more strongly along western ocean margins where temperature gradients are steeper. Whereas insitu water temperature at the time of the experiments was uncorrelated with predation, mean annual temperature strongly positively predicted predation, suggesting a more complex mechanism than simply increased metabolic activity at the time of predation. This large-scale biogeographic pattern was modified by local habitat characteristics; predation declined with higher shoot density both among and within sites. Predation rates on gastropods, by contrast, were uniformly low and varied little among sites. The high replication and geographic extent of our study not only provides additional evidence to support biogeographic variation in predation intensity, but also insight into the mechanisms that relate temperature and biogeographic gradients in species interactions.

The Dynamics of the Coastal Land Scapes Over the Last Decades: Wind Drivers for Change Along the North Western Mauritanian Coast

The alterations of the coastline are a major concern for maritime countries. Mauritania is no exception. As one of the countries with the highest marine productivity in the world, it stimulates growth in infrastructure development and jobs with its marine resources exploitation. But, the marine erosion and submersion have never been more critical to the entire coast. Coastal developments are planned, despite these risks both in the north and in the south. What about the coastline dynamic over the last decades and are they the same all along the Mauritanian coastline? What are the consequences on the coastal landscapes? The chronology of the paleo shoreline has been extensively studied near the Arguin Gulf for a better understanding of the infill of this large sedimentary basin and the last marine invasion started during the Nouakchottian period. The current retrospective study gives details on recent dynamics over the last seven decades. It is based on remote sensing images coupled with statistical analyses of climate data. A focus has been chosen on the Arguin Bank Park, which has been protected since 1976, because such wild areas represent a preferred window to evaluate natural responses. It is also home to coastal ecosystems of primary interest such as eelgrass beds. Five patterns differ in the dynamics of coastal segments that are a continuing accretion, a stability or an erosion. In addition, the time scales of these analyses allow for the identification of the impulse response of the environment, in phase or lagged time. Two new lagoons are developing and one of which shows a colonization by an eelgrass meadow system. The flooding of several insular wetland has become increasingly frequent and raises various questions about the mangroves and changes in the attractiveness of birdlife, the park's main richness. The various coastal dynamics may be the consequence of the sedimentary balance driven by northeasterly winds and the coastal drift currents. While the future projection of this coastal area remains complex, a better understanding of the dynamics should help feed the Strategy for managing the Mauritania’s coastline as well as the management of the Park. The ecological approach of the climate impacts opens up new perspective based on equivalent ecological concept.

Volcanic ash deposition, eelgrass beds, and inshore habitat loss from the 1920s to the 1990s at Chignik, Alaska

We quantified the shallowing of the seafloor in five of six bays examined in the Chignik region of the Alaska Peninsula, confirming National Ocean Service observations that 1990s hydrographic surveys were shallower than previous surveys from the 1920s. Castle Bay, Chignik Lagoon, Hook Bay, Kujulik Bay and Mud Bay lost volume as calculated from Mean Lower Low Water (Chart Datum) to the deepest depths and four of these sites lost volume from Mean High Water to the deepest depths. Calculations relative to each datum were made because tidal datum records exhibited an increase in tidal range in this region from the 1920s to the 1990s. Our analysis showed that Mud Bay is quickly disappearing while Chignik Lagoon is being reduced to narrow channels. Anchorage Bay was the only site that increased in depth over time, perhaps due to erosion. Volcanoes dominate the landscape of the Chignik area. They have blanketed the region in deep ash deposits before the time frame of this study, and some have had smaller ash-producing eruptions during the time frame of this study. Remobilization of land-deposited ash and redeposition in marine areas - in some locations facilitated by extensive eelgrass (Zostera marina) beds (covering 54% of Chignik Lagoon and 68% of Mud Bay in 2010) - is the most likely cause of shallowing in the marine environment. Loss of shallow water marine habitat may alter future abundance and distribution of several fish, invertebrate and avian species.

Microbiome succession during ammonification in eelgrass bed sediments.

BackgroundEelgrass (Zostera marina) is a marine angiosperm and foundation species that plays an important ecological role in primary production, food web support, and elemental cycling in coastal ecosystems. As with other plants, the microbial communities living in, on, and near eelgrass are thought to be intimately connected to the ecology and biology of eelgrass. Here we characterized the microbial communities in eelgrass sediments throughout an experiment to quantify the rate of ammonification, the first step in early remineralization of organic matter, also known as diagenesis, from plots at a field site in Bodega Bay, CA.MethodsSediment was collected from 72 plots from a 15 month long field experiment in which eelgrass genotypic richness and relatedness were manipulated. In the laboratory, we placed sediment samples (n = 4 per plot) under a N2 atmosphere, incubated them at in situ temperatures (15 °C) and sampled them initially and after 4, 7, 13, and 19 days to determine the ammonification rate. Comparative microbiome analysis using high throughput sequencing of 16S rRNA genes was performed on sediment samples taken initially and at seven, 13 and 19 days to characterize changes in the relative abundances of microbial taxa throughout ammonification.ResultsWithin-sample diversity of the sediment microbial communities across all plots decreased after the initial timepoint using both richness based (observed number of OTUs, Chao1) and richness and evenness based diversity metrics (Shannon, Inverse Simpson). Additionally, microbial community composition changed across the different timepoints. Many of the observed changes in relative abundance of taxonomic groups between timepoints appeared driven by sulfur cycling with observed decreases in predicted sulfur reducers (Desulfobacterales) and corresponding increases in predicted sulfide oxidizers (Thiotrichales). None of these changes in composition or richness were associated with variation in ammonification rates.DiscussionOur results showed that the microbiome of sediment from different plots followed similar successional patterns, which we infer to be due to changes related to sulfur metabolism. These large changes likely overwhelmed any potential changes in sediment microbiome related to ammonification rate. We found no relationship between eelgrass presence or genetic composition and the microbiome. This was likely due to our sampling of bulk sediments to measure ammonification rates rather than sampling microbes in sediment directly in contact with the plants and suggests that eelgrass influence on the sediment microbiome may be limited in spatial extent. More in-depth functional studies associated with eelgrass microbiome will be required in order to fully understand the implications of these microbial communities in broader host-plant and ecosystem functions (e.g., elemental cycling and eelgrass-microbe interactions).

Distribution of juvenile Pacific herring relative to environmental and geospatial factors in Prince William Sound, Alaska

Documenting distribution patterns of juvenile Pacific herring (Clupea pallasii) can clarify habitat preferences and provide insight into ecological factors influencing early life survival. However, few analyses relating juvenile Pacific herring density to habitat characteristics have been conducted. We sampled age-0 Pacific herring in nine bays and fjords distributed throughout Alaska's Prince William Sound during November over a 3-year period (2013–2015) and investigated associations between catch rate and habitat covariates using generalized linear mixed models. Our results indicated that the night-time distribution of age-0 Pacific herring in the pelagic environment was influenced by proximity to eelgrass (Zostera marina) beds, salinity, and water depth. Age-0 Pacific herring catch rate was negatively associated with tow depth, with herring favoring shallower water across the range of depths sampled (7.2–35.4m). In addition, Pacific herring distribution was positively associated with fresher water within the sampled salinity gradient (24.1–32.3 psu) and proximity to eelgrass beds. Seasonal changes in juvenile Pacific herring distribution were investigated by sampling one bay over a seven month period (October-April). Age-0 Pacific herring tended to remain in the inner bay region throughout the seven months, while age-1 Pacific herring had shifted from the inner to the outer bay by spring (March-April). Additionally, catch rate of age-0 Pacific herring in areas where ice breakup had just occurred was higher than in open water, suggesting that age-0 herring preferentially select ice-covered habitats when available. Based on our results we recommend that habitat preferences of age-0 Pacific herring should be considered in the development of Pacific herring year-class strength indices from catch data.

Large-Scale Differences in Community Structure and Ecosystem Services of Eelgrass (Zostera marina) Beds Across Three Regions in Eastern Canada

Eelgrass (Zostera marina) forms extensive beds in temperate coastal and estuarine environments worldwide and provides important ecosystem services, including habitat for a wide range of species as well as nutrient cycling and carbon storage. However, little is known about how eelgrass ecosystem structure and services differ naturally among regions. Using large-scale field surveys, we examined differences in eelgrass bed structure, carbon and nitrogen storage, community composition, and habitat services across three distinct regions in Eastern Canada. We focused on eelgrass beds with low anthropogenic impacts to compare natural differences. In addition, we analyzed the relationships of eelgrass bed structure with environmental conditions, and species composition with bed structure and environmental conditions, to elucidate potential drivers of observed differences. Our results indicate that regional differences in eelgrass bed structure were weakly correlated with water column properties, whereas differences in carbon and nitrogen storage were mainly driven by differences in eelgrass biomass. There were distinct regional differences in species composition and diversity, which were particularly linked to temperature, as well as eelgrass bed structure indicating differences in habitat provision. Our results highlight natural regional differences in ecosystem structure and services which could inform spatial management and conservation strategies for eelgrass beds.

Eelgrass Bed Structure, Leaf Nutrient, and Leaf Isotope Responses to Natural and Anthropogenic Gradients in Estuaries of the Southern Gulf of St. Lawrence, Canada

Seagrasses are declining globally; understanding and monitoring these trends forms an important basis for management practices. This study examined eelgrass (Zostera marina) structural and isotopic indicators as a means of characterizing stress from the impacts of agricultural land use in four estuaries in the Southern Gulf of St. Lawrence, Canada. These estuaries ranged from 5 to 62% agricultural land use in their respective watersheds. Anthropogenic stressors such as increased nutrient loading and decreased light penetration (from sedimentation and phytoplankton) and natural stressors such as low salinity and temperature were measured concurrently with plant structural indicators, e.g., aboveground biomass, belowground biomass, canopy height, and root-to-shoot ratio, across the spatial range of eelgrass presence in each estuary. Plant isotopic indicators included leaf tissue concentrations of C, N, S, and stable isotopes thereof and were measured at each station in eelgrass leaf tissue. Eelgrass plant indicators varied significantly across the gradients within each estuary as well as throughout the growing season, but due to the very high within-estuary variability indicators did not vary significantly between estuaries. Eelgrass leaf nutrients and stable isotopes also varied significantly between stations within estuaries though in this case, among-estuary differences were detected. A distance-based linear model was employed to examine the ability of estuarine characteristics and plant isotopic and elemental variables to predict the plant structural indicators. Results showed that factors related to both salinity and nitrogen loading influenced the biomass and structure of this plant but in different ways. Belowground biomass most correlated to salinity, and aboveground biomass most related to nitrogen loading with a strong relationship with light attenuation. Overall, the high level of within-estuary variability, and the strong influence of salinity, suggests that comparison of plant structural indicators between estuaries may have limited utility as a monitoring tool; eelgrass coverage throughout an estuary may better reflect the influence of land use at a regional scale.

Eelgrass beds and bare substrata – sparid and mugilid composition in contrasting littoral estuarine habitats

Seagrass beds serve as nursery grounds for many fish species and often play an important role in the juvenile stages of economically and recreationally important fishes. The eelgrass Zostera capensis is the dominant submerged macrophyte in permanently open South African estuaries and occupies large intertidal and subtidal areas within the Knysna system. The primary objective of this study was to compare the occurrence of sparids and mugilids in eelgrass and nearby bare sediment areas using sampling with seine nets. The hypothesis that was tested is that mugilids are dominant in unvegetated areas of the Knysna Estuary littoral whereas sparids predominate within eelgrass beds located in the same zone. The results indicate that the family Mugilidae is better represented at unvegetated sites when compared to members of the family Sparidae, with the exception of Lithognathus lithognathus, but that the dominant three sparids and dominant two mugilids were most abundant in sparse eelgrass beds that included both bare and vegetated areas within this habitat type. The main fish species responsible for the separation of fish assemblages associated with unvegetated sites versus those associated with vegetated areas were Rhabdosargus holubi, Liza dumerili, Liza richardsonii, Lithognathus lithognathus, Sarpa salpa and Diplodus capensis, with R. holubi, S. salpa and D. capensis being mainly attracted to eelgrass habitats and L. dumerili, L. richardsonii and L. lithognathus having a stronger affinity for bare areas. This finding confirms a previous estuarine study in the nearby Swartvlei lake littoral, which found that sparids dominated areas where aquatic macrophytes were extensive and that mugilids became more prevalent at those same sites when the macrophytes underwent complete senescence. The length-frequency distributions of some sparid and mugilid species differed considerably between eelgrass and bare sediment areas, whereas those of other species showed little or no difference between these two habitat types.

Regional-Scale Differences in Eutrophication Effects on Eelgrass-Associated (Zostera marina) Macrofauna

Eutrophication has caused strong shifts from perennial seagrass to opportunistic macroalgae and phytoplankton in many coastal ecosystems worldwide, yet responses of the primary-producer assemblage can vary with regional environmental and nutrient-loading conditions. The wider consequences of this variable primary-producer response on the associated animal community are little known. We used large-scale field surveys across 12 study sites with low or high eutrophication levels in two geographic provinces in Atlantic Canada to examine region-specific responses of macrofauna associated with eelgrass beds. In both regions, abundances of all groups increased with eutrophication, but species richness of mobile fishes and invertebrates decreased. Generally, filter feeders, epibenthic detritivores and some herbivores increased, while more hypoxia sensitive species declined. Small fishes and invertebrate predators increased with eutrophication mirrored by decreases in their prey. Despite similar general trends, our results show distinct shifts in species composition in each geographic region associated with differences in food availability and predation refuge offered by phytoplankton and opportunistic epiphytic or benthic macroalgae as well as tolerance to an increasingly hostile physico-chemical environment. So far, the continued persistence of eelgrass beds at our “highly” eutrophied sites indicates intermediate eutrophication levels with short-term benefits for some species. However, the loss of sensitive species and decrease in species richness highlight that eutrophication has already changed seagrass ecosystems in Atlantic Canada. Our work suggests that mitigating these changes will require regional-scale management.

Influence of different types of sessile epibionts on the community structure of mobile invertebrates in an eelgrass bed.

Eelgrass (Zostera marina) beds are known to have high ecological and economical values within coastal ecosystems of the temperate northern hemisphere although their biodiversity and functions varied greatly from sites to sites. The variation in the biomass, abundance and diversity of mobile invertebrates in eelgrass beds has been examined in relation to various abiotic and biotic factors, such as water temperature, salinity, eelgrass biomass and epiphytic microalgae presence. However, the importance of sessile epibionts, such as macroalgae and calcific spirorbid polychaetes attached to eelgrass blades, has not been the focus of previous studies. In the present study, we examined the effects of three different sessile epibionts, namely, branched red algae, filamentous green algae, and calcific spirorbid polychaetes, on the biomass and diversity of mobile invertebrates in the eelgrass beds of Akkeshi in northeastern Japan. The relationships between seven abiotic and biotic variables including three types of epibionts, and biomass of 11 dominant mobile invertebrate species as well as three community-level variables (the total biomass of mobile invertebrates, species richness and the Shannon-Wiener species diversity index) were analyzed using a linear mixed model. Our results show that branched red algae are correlated with Pontogeneia rostrata, Lacuna spp., Nereis sp., Syllis sp. and the total biomass of mobile invertebrates, filamentous green algae with P. rostrata, Ansola angustata and the species diversity of mobile invertebrates, and spirorbid polychaetes with A. angustata, Lacuna spp., Siphonacmea oblongata, Syllis sp., the species richness and diversity of mobile invertebrates. The effect size of the epibionts was similar or even higher than that of abiotic and eelgrass factors on the total biomass of mobile invertebrates, species richness, species diversity and most of dominant invertebrate populations across the taxonomic groups. Consequently, epibiotic macroalgae and spirorbid polychaetes can be good predictors of the variation in the total biomass, species richness and species diversity of mobile invertebrates and the biomass of major dominant species, especially for species that have a relatively high dependency on eelgrass blades. These results suggest that the different functional groups of sessile epibionts have significant roles in determining the biomass and diversity of mobile invertebrates in eelgrass beds.

Main Ecological Features of Benthic Macrofauna in Mediterranean and Atlantic Intertidal Eelgrass Beds: A Comparative Study

Main Ecological Features of Benthic Macrofauna in Mediterranean and Atlantic Intertidal Eelgrass Beds: A Comparative Study The present study compares the intertidal eelgrass macrofauna in two geographically and ecologically disparate localities (central Mediterranean and eastern Atlantic). Both coastal ecosystems are developed on extensive large mudflats with eelgrass beds, hosting a great diversity of water birds and providing important socio-economic assets. These two distinct and distant geographical ecosystems are affected by numerous anthropogenic pressures. By reflecting the response of the structure and functioning of benthic communities to climate change, the two eelgrass ecosystems provide a natural laboratory to investigate global warming. The macrobenthic fauna community of Zostera (Zosterella) noltei eelgrass beds was studied by sampling 34 stations in the Kneiss Islands and 48 stations in Arcachon Bay. A total of 148 species are identified in the Kneiss islands and 117 species in Arcachon Bay, but only 23 species are common to both ecosystems. Diversity, abundance and community structure are significantly different between the two study areas, which could be explained by differences between Mediterranean and Atlantic climatic conditions and by anthropic factors (e.g. fishing pressure, pollution, nutrient inputs) affecting each ecosystem. Multidimensional scaling (n-MDS) analysis identifies two distinct geographical station groups on the basis of species and familylevel abundance. On the contrary, three assemblages are identified on the basis of trophic groups distributed between the separate ecosystems. In terms of ecological quality status, the Kneiss site appears to have a good ecological condition and hosts a variety of sensitive species. On the other hand, biotic indices indicate that the Arcachon site is moderately perturbed and that the benthic communities are unbalanced. It is expected that the present-day functioning of the Kneiss Islands ecosystem will become typical of the situation in Arcachon Bay in several decades time, with the development of warmer and drier conditions.

Effects of submarine topography on the formation of the eelgrass bed

Effects of submarine topography on the formation of the eelgrass bed

Comparing Automated Classification and Digitization Approaches to Detect Change in Eelgrass Bed Extent During Restoration of a Large River Delta

Abstract Native eelgrass (Zostera marina) is an important contributor to ecosystem services that supplies cover for juvenile fish, supports a variety of invertebrate prey resources for fish and waterbirds, provides substrate for herring roe consumed by numerous fish and birds, helps stabilize sediment, and sequesters organic carbon. Seagrasses are in decline globally, and monitoring changes in their growth and extent is increasingly valuable to determine impacts from large-scale estuarine restoration and inform blue carbon mapping initiatives. Thus, we examined the efficacy of two remote sensing mapping methods with high-resolution (0.5 m pixel size) color near infrared imagery with ground validation to assess change following major tidal marsh restoration. Automated classification of false color aerial imagery and digitized polygons documented a slight decline in eelgrass area directly after restoration followed by an increase two years later. Classification of sparse and low to medium density eelgrass w...

Creating Eelgrass Beds Using Granulated Coal Ash

Creating Eelgrass Beds Using Granulated Coal Ash

Experimental test of oyster restoration within eelgrass

Abstract Both seagrasses and oysters are foundation species valued for their wide range of ecosystem services, but their space competition sets a constraint on joint benefits. A reserve for native Olympia oysters (Ostrea lurida) was established in lower Hood Canal (Washington State, USA) more than a century ago but is now devoid of that species and dominated by native eelgrass (Zostera marina). This situation sets up a conservation conflict because management activities for one species are at odds with the protection of another. In experimental enhancement plots, Olympia oysters were outplanted at low density, which successfully maintained eelgrass density and production. One method was used in 2013 (seeded cultch, 8% cover) and two additional methods in 2015 (anchored cultch and single oysters, the latter at 4% cover). For all outplant methods, oysters experienced 99% annual mortality, associated with the attraction of non‐native and native predators. Shell cover remained steady for a year and then declined rapidly, as shell accumulation did not exceed sedimentation rates. Eelgrass per se does not preclude Olympia oysters, given that the two species were observed to co‐occur at a coastal estuarine site (Willapa Bay, Washington). However, even when socio‐political constraints on restoration activities were overcome, ecological constraints remained from predation. Competition between these two protected species was avoided, but it may be the case that top‐down control on oysters was particularly acute owing to low oyster density and/or the environmental conditions of eelgrass beds.

Seed Predation by the Shore Crab Carcinus maenas: A Positive Feedback Preventing Eelgrass Recovery?

There is an increasing interest to restore the ecosystem services that eelgrass provides, after their continuous worldwide decline. Most attempts to restore eelgrass using seeds are challenged by very high seed losses and the reasons for these losses are not all clear. We assess the impact of predation on seed loss and eelgrass establishment, and explore methods to decrease seed loss during restoration in the Swedish northwest coast. In a laboratory study we identified three previously undescribed seed predators, the shore crab Carcinus maenas, the hermit crab Pagurus bernhardus and the sea urchin Strongylocentrotus droebachiensis, of which shore crabs consumed 2–7 times more seeds than the other two species. The importance of shore crabs as seed predators was supported in field cage experiments where one enclosed crab caused 73% loss of seeds over a 1-week period on average (~ 21 seeds per day). Seedling establishment was significantly higher (14%) in cages that excluded predators over an 8-month period than in uncaged plots and cages that allowed predators but prevented seed-transport (0.5%), suggesting that seed predation constitutes a major source of seed loss in the study area. Burying the seeds 2 cm below the sediment surface prevented seed predation in the laboratory and decreased predation in the field, constituting a way to decrease seed loss during restoration. Shore crabs may act as a key feedback mechanism that prevent the return of eelgrass both by direct consumption of eelgrass seeds and as a predator of algal mesograzers, allowing algal mats to overgrow eelgrass beds. This shore crab feedback mechanism could become self-generating by promoting the growth of its own nursery habitat (algal mats) and by decreasing the nursery habitat (seagrass meadow) of its dominant predator (cod). This double feedback-loop is supported by a strong increase of shore crab abundance in the last decades and may partly explain the regime shift in vegetation observed along the Swedish west coast.

Does the eelgrass meadow influence the macrobenthic community structure in Swan Lake, Northern China?

Seagrass beds provide habitat for a wide array of organisms. Among these, macrobenthos constitute a major group in seagrass bed communities. The effects of seagrass meadows on macrobenthic community structure have been studied in many areas, and have revealed contradictory results regarding the meadow’s effects. In this study, sediment environment and macrobenthic community structure and diversity were investigated in an eelgrass bed and an adjacent unvegetated area in Swan Lake, northern China, from November 2011 to October 2012. Sediment grain size and organic matter did not differ significantly between the two areas. Polychaeta were the most abundant taxon, and herbivores, detritivores, and deposit feeders were the main functional feeding groups. Carnivores were slightly more abundant in the eelgrass bed than in the unvegetated area. Permutational multivariate analysis of variance (PERMANOVA) indicated that the macrobenthic assemblage differed between the two habitats, but analysis of similarities (ANOSIM) did not validate this result. Analysis of similarity percentages (SIMPER) demonstrated that Polychaeta was the largest contributor to dissimilarity between the macrobenthic assemblages; however, diversity was similar throughout the year, and theoretical species richness was equivalent (80 species) between the two areas. Thus, the presence of eelgrass did not affect macrobenthic community structure or diversity in the Swan Lake ecosystem.