Bacterial interactions in the rhizosphere of seagrass communities in shallow coastal lagoons

Rooted phanerogam communities in the shallow intertidal and subtidal coastal zone represent productive and healthy ecosystems. Inorganic nutrients are assimilated into seagrass biomass. Much of the organic matter resulting from moribund seagrass is rapidly mineralized, principally by bacteria. The microbial community of the rhizosphere is also highly active due to the supply of organic matter released during photosynthesis. This active sediment community plays an important role through carbon, nitrogen and phosphorous cycling in maintaining the stability and productivity of seagrass meadows. Over the last two decades, however, seagrass meadows in European coastal areas have declined due to increasing pollution. As eutrophication advances a trasition occurs from rooted phanerogram dominated communities to planktonic algal blooms and/or cyanobacterial blooms. Such changes represent the decline of a stable, high biodiversity habitat to an unstable one dominated by a few species. These changes of community structure can occur rapidly once the internal nutrient and organic matter control cycles are exceeded. A field investigation was undertaken to establish the spatial distribution of bacterial populations of Zostera noltii colonized and uncolonized sediment in the Bassin d'Arcachon, France. Bacteria were enumerated using both plate count and MPN techniques for different functional groups as well as determining the total bacterial populations present. Nitrogen fixation, ammonification, sulphate reduction rates, as well as alkaline phosphatase activity were also determined. Colonization of the Z. noltii roots and rhizomes was studied by light and scanning electron microscopy. Results confirmed that higher bacterial populations were present in the rhizosphere of Z. noltii compared to uncolonized sediments. Furthermore, electron microscopy identified the rhizome as the main site of colonization for a diverse range of morphological groups of bacteria. Sulphate reducing bacteria were identified as the key group of bacteria involved in N-fixation in the rhizosphere of Z. noltii. The data will be discussed in relation to the role played by the rhizosphere microflora in supplying and mobilising nutrients in Z. noltii.     

Helminth communities in eels Anguilla anguilla from Adriatic coastal lagoons in Italy

The composition and diversity of the total and intestinal component and infra-communities were determined in eels Anguilla anguilla from three shallow lagoons on the Adriatic coast of Italy to determine whether the helminth communities would differ in composition and structure from those in eels from lagoons on the Tyrrhenian coast. The lagoons differed in respect of their management regimes and the extent of freshwater influx. Both freshwater and marine species of helminths were found in the eels in all three lagoons, but the freshwater component was richer in Valle Figheri. A suite of three digenean eel specialist species occurred in all three lagoons, of which any two members dominated each community. This conferred a high degree of similarity between the communities of the three lagoons. The same three species also dominated helminth communities in eels in lagoons along the Tyrrhenian coast of Italy, and compositional similarity levels were similar within and between western and eastern groups. Species richness was higher in the component communities of the eels of the Adriatic lagoons when compared to the Tyrrhenian ones, but diversity and dominance indices were of a similar order of magnitude and range. Intestinal helminth communities were richer and more diverse in two of the Adriatic lagoons because the proportion of eels with zero or one helminth species was, unusually, in the minority. It was nevertheless concluded that infracommunity structure was similar in eels from both western and eastern lagoons and that the hypothesis that it would differ in Adriatic lagoons could not be supported. The findings provide further evidence of the similarity in composition and structure of helminth communities in eels from coastal lagoons throughout Europe.     

Spatio-temporal dynamics of the nematode Anguillicola crassus in Northeast Tunisian lagoons

Anguillicola crassus, parasite nematode of the European eel Anguilla anguilla, was recorded for the first time in Tunisia (1999) in the Ichkeul lagoon. Its distribution has since spread toward Bizerte and Ghar El Melh lagoons. The monthly epidemiological survey reveals that A. crassus exists throughout the year in the Ichkeul lagoon. In this lagoon, its prevalence is low in winter (12% in December), with a marked increases in the spring reaching a maximum in March (35%), before it starts to decrease in summer with a minimum in July (4.35%), which in turn is followed by a pronounced new rise in autumn (30% in November). However, mean intensity values do not show such a marked variation. The majority of the values are between 1 and 1.5 parasites per host. In the Bizerte and Ghar El Melh lagoons, the presence of this nematode is limited only to one to three months. Investigations in the Tunis lagoon did not reveal until now the presence of A. crassus. It has been observed that the length of the eel influences the prevalence values: A. crassus becomes less common if the length of the eel increases. Comparatively with the global epidemiological values of A. crassus signalled subsequently (1999) in the Ichkeul lagoon, we note that the present values record a clean increase.     

Proposals for macrophyte restoration in eutrophic coastal lagoons

Based on the comparison of environmental requirements forRuppia cirrhosa andPotamogeton pectinatus growth, macrophyteversus phytoplankton biomass and production features, and differences in hydrological and nutrient balances between Tancada lagoon (where macrophytes form dense beds) and Enca?izada lagoon (with no macrophytes at all), several proposals for macrophyte restoration are presented. The highest photosynthetic efficiency ofR. cirrhosa takes place at high irradiance and it grows over a wide range of salinity.P. pectinatus is better adapted to lower light intensity and salinity thanRuppia. R. cirrhosa transplanted from Tancada to Enca?izada was successful in enclosures, where light availability increased (μ=0.013 cm⁻¹), but not in open waters where light extinction coefficient was 0.032 cm⁻¹. Phytoplankton biomass (0.11–2.15 g C m⁻²) is much lower than macrophyte biomass (16–200 g C m⁻²) in Tancada lagoon. However, phytoplankton production (165 g C m⁻² yr⁻¹ in Tancada, 480 g C m⁻² yr⁻¹ in Enca?izada) is the same order of magnitude as macrophyte production (244–467 g C m⁻² yr⁻¹). Turnover rates are 0.3–0.9 day⁻¹ for phytoplankton and 1.2–2.5 yr⁻¹ for macrophytes. Phytoplankton and inorganic particles are responsible for high turbidity of the water in Enca?izada lagoon. Phytoplankton blooms in Enca?izada lagoon are supported by high freshwater inflows from rice field drains from May to November. The Q_s (seawater discharge)/Q_F (Freshwater discharge) ratios are, respectively, 0.24 and 0.48, which denotes a higher seawater influence in Tancada than in Enca?izada lagoon. Decreasing freshwater inputs to Enca?izada lagoon both in May and November thus allowing greater inputs of sea water, is proposed as the most effective way to restore this eutrophic coastal lagoon. The objective being to reduce nutrient loadings to the lagoon and phytoplankton in order to favour macrophyte re-colonization.     

Regional trends in coastal wintering waders in Britain

Regional trends in the populations of waders wintering largely on estuaries were analysed using data collected by the Wetland Bird Survey between the winters of 1969/70 and 1995/96 to assess whether trends seen at the national level were repeated across regions of Britain. Not all were. Over this period, the numbers of seven of the 12 species studied increased in south and southeast England, but remained static or declined in southwest England and south Wales. Possible explanations for this are proposed. Increases in the number of Curlews Numenius arquata in the north and northeast of Scotland occurred after 1981/82, when the species stopped being a legal quarry species. A rapid decline in Oystercatcher Haematopus ostralegus and Knot Calidris canutus numbers in east England after 1988/89 may be linked to a change in the Wash shell-fisheries. Warmer winters may be making it less essential for birds to winter in the milder west of Britain. In two pairs of regions, northeast and southeast Scotland, and in northwest England/north Wales and northeast England, waders showed similar long-term population changes. The long-term population trends of Oystercatchers in the different regions correlate to those of Ringed Plovers Charadrius hiaticula and Knot, while those of Ringed Plovers are very similar to those of Bar-tailed Godwits Limosa lapponica. In some regions of Britain, the population trends of some species varied a lot between sites, a factor that is an important consideration when determining the size and geographical position of regions for future regional indexing. The present separation of regions based on water catchments and geography has given a useful insight into population changes at a finer spatial scale but it could be improved further with added biological input.     

Beyond the Mediterranean to global observations of coastal lagoons

The United Nations has begun addressing the detection and prediction of global and large-scale change through the development of observing systems. The three observing systems are the Global Climate Observing System (GCOS); the Global Ocean Observing System (GOOS); and the Global Terrestrial Observing System (GTOS). Each of these is designed to be a ‘8user-driven, end-to-end’ system, providing measurements of selected variables and indicators, management and communication of these, and their analysis and synthesis into products for users. The interface between the land and ocean provides complexities that affect the capabilities of the three global observing systems. Understanding the complex interactions between natural and human systems at various scales is central to successful management of the coast in the face of change. Both GOOS and GTOS have organized initiatives for the coast with the GOOS initiative (CGOOS) being more developed. CGOOS is built upon a global network, which focuses on a limited number of phenomena and their associated variables, and regional programs that contribute to the global network and focus on other phenomena. CGTOS (coastal GTOS) has identified a few key phenomena for the development of the future mature system. These phenomena are linked to a framework that incorporates socio-economic variables into the program. To establish proof of concept and early success by CGTOS, four priority products have been identified that address (1) transport of materials, (2) functional typology, (3) integrated assessments of cultural and conservation sites, and (4) assessment of human populations and land use and land cover. The coastal observing systems are in the stages of developing implementation plans and should be operable in coming years.     

Regime shifts in vegetation composition of Baltic Sea coastal lagoons

Vegetation communities, morphometric and water quality variables were sampled in 62 undisturbed coastal lagoons along a natural land-uplift gradient in the northern Baltic Sea. The lagoons had a morphological inlet threshold reflecting habitat isolation (i.e. the diminished connectedness of the lagoon to the sea) and located in different parts of the archipelago (corresponding to altering wave exposure). We used indirect multivariate methods to find changes in vegetation composition, and axes derived from the analyses were used in correlation and stepwise multiple regression analyses together with environmental variables. Habitat isolation proved to be the strongest predictor for vegetation composition. To identify significant change-points we used a method, which detects regime shifts by accounting for differences in chronological series and gives a regime shift index. Significant shifts in habitat isolation, average depth and total nitrogen were followed by shifts in species variables (i.e. dominant species, cover and species richness) and salinity, total phosphorus and turbidity. Of the species, especially Chara tomentosa showed a shift of high magnitude. Also a shift in wave exposure mirroring position of lagoons in the archipelago structured the species, but this division was seen only for less isolated lagoons. Our results suggest that lagoons are primarily structured by habitat isolation forming two structurally different regimes: one of less isolated lagoons dominated by a diverse array of vascular plants and marine algae of both outer and inner archipelago characters, and one with isolated lagoons dominated by high vegetation cover and dominance of Chara. In addition, vegetation seemed to stabilize water quality in the isolated regime by reducing turbidity and phosphorus, indicating a potential feed-back mechanism and a shift in structuring disturbances from abiotic to biotic factors with habitat isolation.     

Prokaryotic diversity in one of the largest hypersaline coastal lagoons in the world

Araruama Lagoon is an environment characterized by high salt concentrations. The low raining and high evaporation rates in this region favored the development of many salty ponds around the lagoon. In order to reveal the microbial composition of this system, we performed a 16S rRNA gene survey. Among archaea, most clones were related to uncultured environmental Euryarchaeota. In lagoon water, we found some clones related to Methanomicrobia and Methanothermococcus groups, while in the saline pond water members related to the genus Haloarcula were detected. Bacterial community was dominated by clones related to Gamma-proteobacteria, Actinobacteria, and Synechococcus in lagoon water, while Salinibacter ruber relatives dominated in saline pond. We also detected the presence of Alpha-proteobacteria, Pseudomonas-like bacteria and Verrucomicrobia. Only representatives of the genus Ralstonia were cosmopolitan, being observed in both systems. The detection of a substantial number of clones related to uncultured archaea and bacteria suggest that the hypersaline waters of Araruama harbor a pool of novel prokaryotic phylotypes, distinct from those observed in other similar systems. We also observed clones related to halophilic genera of cyanobacteria that are specific for each habitat studied. Additionally, two bacterioplankton molecular markers with ecological relevance were analyzed, one is linked to nitrogen fixation (nifH) and the other is linked to carbon fixation by bacterial photosynthesis, the protochlorophyllide genes, revealing a specific genetic distribution in this ecosystem. This is the first study of the biogeography and community structure of microbial assemblages in Brazilian tropical hypersaline environments. This work is directed towards a better understanding of the free-living prokaryotic diversity adapted to life in hypersaline waters.     

Hydrographic,geomorphologic and fish assemblage relationships in coastal lagoons

In this study, 40 Atlanto-Mediterranean coastal lagoons were analyzed in order to evaluate the extent to which their ecological characteristics depend on hydrographic, trophic or geomorphologic features. Fish species richness increases with lagoon volume and the openness parameter, which characterizes the potential influence of the sea on general lagoon hydrology and is related to the total transversal area of the inlets, which connect the lagoon to the sea. On the other hand, the number of species decreases exponentially with the phosphate concentration in water. The fishing yield increases with the chlorophyll a concentration in the water column and exponentially with shoreline development. With respect to the fish assemblage composition, geomorphologic features alone explain 22% of the variance in the canonical analyses and an additional 75% when including the hydrographic and trophic characteristics of the lagoon, the latter on its own explaining only 3% of the observed differences.     

Integrated modelling in coastal lagoons: Sacca di Goro case study

A coupled 3D hydrodynamic-biogeochemical model was developed and implemented for the Sacca di Goro coastal lagoon. The model considers nutrient and oxygen dynamics in water column and sediments. Among the biological elements, phytoplankton, zooplankton, bacteria, Ulva sp. and commercial shellfish (Tapes philippinarum) were taken into consideration. Nutrients fluxes from the watershed and open sea, as well as atmospheric inputs, heat flux, light intensity and wind shear stress at the water surface constituted the model forcing functions. The comparison of numerical results with available measurement data indicated that the model was able to capture the essential dynamics of the lagoon. This model has also been used to estimate clam productivity and its impacts on water quality and lagoon properties. Guest editors: A. Razinkovas, Z. R. Gasiūnaitė, J. M. Zaldívar & P. Viaroli European Lagoons and their Watersheds: Function and Biodiversity     

Heterotrophic microbial activity and organic matter degradation in coastal lagoons of Colombia

In this study we measured the community respiration and the bacterial respiration as part of the overall degradation process of organic material. Additionally, the turnover rates of the pools of dissolved free glucose and acetate as representatives of the fraction of easily degradable low molecular organic solutes were determined. The study was performed in several coastal lagoons of the "Outer Delta of the Río Magdalena" in northern Colombia. The lagoons can be separated into two groups: The first group contains highly productive brackish lagoons with chl a concentrations ranging from 62-130 micrograms/l. The second group consists of less productive freshwater lagoons with chl a between 5.5-19 micrograms/l. Turnover rates of glucose and acetate were very fast in the highly productive lagoons resulting in turnover times of less than 20 min for both compounds. In the less productive systems the cycling of glucose and acetate was much slower. Here the mean values of the turnover times were 2 hr for glucose and 1.5 hr for acetate. The rates of bacterial DNA-formation measured as thymidine incorporation differed significantly between both groups of lagoons, being very high (1.86-2.76 nmol/l/hr) in the highly productive and relatively low (0.073-0.55 nmol/l/hr) in the less productive group. Water column community respiration ranged between 122 and 16 micrograms C/l/hr with means of 88 micrograms C/l/hr in the highly and 19 micrograms C/l/hr in the less productive group. In the first group the mean values of the bacterial contribution to community respiration amounted to 37% and in the second group to 18%. The bacterial respiration was determined in an indirect way via bacterial biomass production and assuming a growth efficiency of 50%. It is discussed whether this relatively high growth efficiency allows reasonable results in both groups of lagoons.     

CHLfuzzy: a spreadsheet tool for the fuzzy modeling of chlorophyll concentrations in coastal lagoons

Our purpose was to explore relationships of freshwater planktonic and benthic community species richness with water chemistry parameters using a dataset of biological, chemical, and physical data from 550 lakes. This was done using multivariate (ordination), graphical, and correlation analyses. Although the lakes are rather similar in location (Belarus) and in being mostly eutrophic, they do show variations in water chemistry. We ordinated lakes by water chemistry variables, and then looked for correlations between the ordination axes and species richness in 10 taxonomic groups: Cyanobacteria, Chlorophyta, Bacillariophyta, Cladocera, Copepoda, Rotatoria, Mollusca, Trichoptera, Chironomidae, and aquatic macrophytes. The first four Principal Components Analysis (PCA) axes explained about 67% of the total variability in water chemistry. The axes represent water hardness (DIC, dissolved inorganic carbon), organic content (DOC, dissolved organic carbon), nutrients, and chlorides and sulfates. The PCA ordination revealed environmental gradients, but not the distinctive clusters of lakes. Species richness was most strongly correlated with the first PCA axis (DIC), which accounted for 29% of the total variation in water chemistry. Species richness was positively correlated with DIC for eight of 10 taxonomic categories. The second PCA axis (DOC), which accounted for 20% of total variation in water chemistry, was correlated with species richness in the three phytoplankton groups, and with chironomid species richness. The third PCA axis (nutrients, especially nitrogen, 11%) was correlated with species richness of copepoda, chironomids, and macrophytes. The fourth PCA axis (chloride and sulfate) accounted for only 7% of the total variance in water chemistry, and was significantly negatively correlated with species richness of rotifers, molluscs, and chironomids. In addition to these linear correlations, there were several significant non-linear relationships. DIC variables showed curvilinear (hump-shaped) relationship with benthos (all groups combined) and especially with molluscs, and DOC variables—with phytoplankton and benthos. Each community, and often separate taxonomic groups within community have their own optimal ranges of chemical concentrations, and various water chemistry variables showed significant curvilinear relationships with biodiversity, suggesting that the diversity of different major aquatic groups may be influenced by different chemicals. Handling editor: S. Declerck     

Trophic state and water turn-over time in six choked coastal lagoons in Brazil

Comparison of total phosphorus and chlorophyll-a concentration, nutrient loading, and water turn-over time in six shallow choked lagoons along the coast of the state of Rio de Janeiro, Brazil, established that water turn-over time is related to the trophic state of the lagoons with additional anthropogenic nutrient loading affecting this relationship. Turnover time was calculated as a flushing half-life from rainfall, evaporation, runoff, and tidal exchange data, and trophic state was calculated from the quantity and quality of dissolved inorganic nutrients, total phosphorus, and chlorophyll-a standing stock. Flushing half-life of the lagoons ranged between 1 and 27 days, annual phosphorus areal loading from 3 to 18 mg m^–2d^–1, and chlorophyll-a standing stock from 6 to 160 mg M^–2     

Characterization of arbuscular mycorrhizal fungal communities with respect to zonal vegetation in a coastal dune ecosystem

Coastal dune vegetation distributes zonally along the environmental gradients of, e.g., soil disturbance. In the preset study, arbuscular mycorrhizal fungal communities in a coastal dune ecosystem were characterized with respect to tolerance to soil disturbance. Two grass species, Elymus mollis and Miscanthus sinensis, are distributed zonally in the seaward and landward slopes, respectively, in the primary dunes in Ishikari, Japan. The seaward slope is severely disturbed by wind, while the landward slope is stabilized by the thick root system of M. sinensis. The roots and rhizosphere soils of the two grasses were collected from the slopes. The soils were sieved to destruct the fungal hyphal networks, and soil trap culture was conducted to assess tolerance of the communities to disturbance, with parallel analysis of the field communities using a molecular ecological tool. In the landward communities, large shifts in the composition and increases in diversity were observed in the trap culture compared with the field, but in the seaward communities, the impact of trap culture was minimal. The landward field community was significantly nested within the landward trap culture community, implying that most members in the field community did not disappear in the trap culture. No nestedness was observed in the seaward communities. These observations suggest that disturbance-tolerant fungi have been preferentially selected in the seaward slope due to severe disturbance in the habitat. Whereas a limited number of fungi, which are not necessarily disturbance-sensitive, dominate in the stable landward slope, but high-potential diversity has been maintained in the habitat.     

Nutrients related to the hydrologic regime in the coastal lagoons of Viladecans (NE Spain)

This study presents the major water characteristics of the Viladecans coastal lagoons in the Llobregat Delta (NE Spain), and the interpretation of their functional relationships with freshwater discharges. Ranges of conductivity show that Murtra, Remolar and Vidala are strongly influenced by freshwater. A second group (Reguerons, Braç Vidala) is characterised by brackish water with intermediate values of conductivity. In contrast, the lower part of the water column of Remolar and Vidala is quite salty water. A permanent pycnocline is established causing meromixis. Finally in Sant Climent a great variation is observed from fresh to seawater. Nutrient inputs are related to freshwater discharges. The range of DIN/SRP ratios observed (0.1–71) shows that a great variety of biogeochemical processes take place in these lagoons. High DIN/SRP ratios occur in water masses receiving high freshwater discharges (Murtra, Remolar and Vidala surface). In contrast, low DIN/SRP ratios correspond to water masses (Reguerons, Braç Vidala, Sant Climent) receiving water discharges from the groundwater and to those in the lower part of the water column of Remolar and Vidala. The SRP and DIN concentrations of the water in Remolar, Vidala and Murtra are very high (higher than any other with similar morphological characteristics in Spain). However, the trophic state of Reguerons, Sant Climent and Braç Vidala is lower. The data presented indicate that the Viladecans coastal lagoons are in a hypereutrophic state, as the result of receiving over a long period of time nutrient discharges associated to man-made freshwater inputs higher than their carrying capacity or capacity to metabolise the nitrogen and phosphorus discharges. Remedial measures should include reducing nutrient discharges into the lagoons and favouring water turnover in the lagoons.     

The role of microphytobenthos on shallow coastal lagoons: a modelling approach

Ria Formosa is a Region of Restricted Exchange given its limited connection to coastal water circulation. Furthermore, it is subject to several anthropogenic activities that can lead to an increase in nutrients and potentially to eutrophication. Previous studies have shown the importance of the benthic compartment, specifically the microphytobenthos (MPB) in this shallow coastal lagoon. The dCSTT–MPB model [new version of the dynamic Comprehensive Studies Task Team (dCSTT) model] here described couples the benthic and pelagic compartments. Due to the shallowness of the system, the benthic microalgae are one of the most important primary producers of the system. Preliminary results of the model show a large biomass of benthic microalgae, which strongly influences the pelagic chlorophyll concentration by resuspension. However, algae concentrations in the water column are relatively small due to the high flushing rate of the lagoon. The MPB community is mainly supported by nutrients in the pore water. A sensitivity analysis (SA) has revealed that the factors associated with the benthic compartment were the most important and sensitive to changes. Porosity, benthic chlorophyll recycling, loss of MPB due to grazing and the yield of microphytobenthic chlorophyll from nitrogen were some of the most sensitive parameters, as well as the ones associated with decay of particulate organic nitrogen. The development of our dCSTT–MPB model has itself provided insights into benthic function.     

Characterization of tropical near-shore fish communities by coastal habitat status on spatially complex island systems

Synopsis We present a protocol for characterizing near-shore fish habitat as well as fish communities for Andros Island, Bahamas, a complex coastal-reef island system. Benthic assessments and beach seine surveys were carried out at sites varying in coastal and benthic characteristics. Temporal variability affected fish community composition, indicating that attempts to characterize a fish community should include sampling evenly across tides, times of day, and seasons. Univariate and multivariate analyses revealed that each site harbored a unique fish community, with the greatest variability within each site attributed to seasonal changes. Measures of diversity (Shannon–Weiner Index and number of species) were markedly different at sites with varying coverage of seagrass and macro-algae and extents of disturbance. Total abundance of fishes was positively related to the percent of bare sand. We suggest that thorough sampling of coastal fish communities can be applied to comparative and long-term studies. This protocol for the characterization of complex island habitats can be applied to ecological studies aimed at understanding the responses of fishes to small-scale changes in coastal areas and habitat structure due to land use and shoreline alterations.