Comparison of recent vegetation and diaspore banks along abiotic gradients in brackish coastal lagoons

Submerged vegetation and diaspore banks were investigated in three shallow brackish lagoons along the German southern Baltic Sea coast. The distribution of vegetation and diaspores was analysed at three depths (0.5, 1.0, 1.5 m) on three transects in each lagoon along salinity and nutrient gradients. Thirteen taxa of submerged vegetation were identified in three lagoons: 8 angiosperms and 5 charophytes. The diaspore analysis yielded 11 taxa of submerged diaspore types: 7 angiosperm taxa and 4 charophyte taxa groups.Salinity and nutrient gradients are the key factors governing the distribution of the vegetation and diaspore banks here. Statistical analysis (SIMPER) of vegetation and diaspore bank show differences in dissimilarities, i.e. Bray-Curtis similarities subtracted from 100, between the lagoon parts and between the lagoons. These differences increased with increasing intensity of the salinity and nutrient gradients. We argue that the diaspore bank reflects the former vegetation gradients shaped primarily by salinity gradients, whereas the present vegetation gradients are more affected by eutrophication. Vegetation surveys and diaspore bank analyses therefore supplement each other, and their combined use provides insight into former as well as recent gradients in the vegetation and the factors governing these gradients.     

Regime shifts: catastrophic responses of ecosystems to human impacts

Evidence of abrupt changes in ecosystem states, such as sudden eutrophication in lakes, has been increasingly reported in a variety of aquatic and terrestrial systems. Ecosystems may have more than one state with a self-stabilizing mechanism, so that a shift between states does not occur frequently and is not readily reversible. These big changes are termed regime shifts where often one state is preferred over another. Thus, regime shifts are problematic for ecosystem managers, and the need exists for studies that lead to the identification of thresholds of key variables that trigger regime shifts. Regime shifts are currently difficult to predict and in many cases may be caused by the human pursuit of efficiency in land and water productivity in the last few decades. Here I briefly introduce a theoretical approach to predict the shift between a clear-water state and a turbid state in lakes, the best-studied example of regime shifts. This paper also discusses alternative states in other natural systems besides ecosystems to draw more attention to the research currently being performed on regime shifts. Motomi Genkai-Kato is the recipient of the 10th Denzaburo Miyadi Award.     

Human-induced Trophic Cascades and Ecological Regime Shifts in the Baltic Sea

Abstract The ecosystems of coastal and enclosed seas are under increasing anthropogenic pressure worldwide, with Chesapeake Bay, the Gulf of Mexico and the Black and Baltic Seas as well known examples. We use an ecosystem model (Ecopath with Ecosim, EwE) to show that reduced top-down control (seal predation) and increased bottom-up forcing (eutrophication) can largely explain the historical dynamics of the main fish stocks (cod, herring and sprat) in the Baltic Sea between 1900 and 1980. Based on these results and the historical fish stock development we identify two major ecological transitions. A shift from seal to cod domination was caused by a virtual elimination of marine mammals followed by a shift from an oligotrophic to a eutrophic state. A third shift from cod to clupeid domination in the late 1980s has previously been explained by overfishing of cod and climatic changes. We propose that the shift from an oligotrophic to a eutrophic state represents a true regime shift with a stabilizing mechanism for a hysteresis phenomenon. There are also mechanisms that could stabilize the shift from a cod to clupeid dominated ecosystem, but there are no indications that the ecosystem has been pushed that far yet. We argue that the shifts in the Baltic Sea are a consequence of human impacts, although variations in climate may have influenced their timing, magnitude and persistence. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The fate of organic matter sources in coastal environments: a comparison of three Mediterranean lagoons

Trophic processes in coastal lagoons are strongly influenced by freshwater inputs and water exchanges with the sea. In recent years, stable isotope analysis has become a widespread and reliable method for the examination of trophic structure over time and space, also in complex ecosystems such as coastal lagoons. Stable isotopes of carbon and nitrogen were studied in primary producers and consumers to identify organic matter source pools from terrestrial, benthic and pelagic environments and to characterise the trophic structure in three Mediterranean coastal lagoons (Lake Fusaro, the Lake of Sabaudia and Stagnone di Marsala). The results highlighted the negligible importance of terrestrial production to higher trophic levels in all the ecosystems investigated. Consumer dependence on benthic and pelagic organic matter showed high variability: overall macroalgae were at the base of the food web in Lake Fusaro and the Lake of Sabaudia, while mixed sources (seagrass detritus, epiphytes, macroalgae and sedimentary organic matter) appeared to be the major baseline food resource in the Stagnone di Marsala. We have found evidence for significant changes in the trophic structure in these Mediterranean coastal lagoons and such differences may be triggered by differential environmental features (e.g. freshwater inputs and hydrodynamic regime). Guest editors: A. Razinkovas, Z. R. Gasiūnaitė, J. M. Zaldivar & P. Viaroli European Lagoons and their Watersheds: Function and Biodiversity     

Germination in Baltic coastal wetland meadows: similarities and differences between vegetation and seed bank

The abundance and variety of seedlings in Baltic coastal grasslands was studied in cattle grazed and ungrazed areas in seashore and delta on the western coast of Finland. The vegetation, seed bank and environmental conditions of the same sites were also studied. Altogether 4609 seedlings were observed in 79 field plots (20 cm× 20 cm) making an average of 1458.54 seedlings/m². The majority of the seedlings were dicots (67.5%) and perennials (96.8%). Altogether 44 species and an average of 4.14 species per plot were identified as seedlings. The most abundant taxon, Carex formed 23.2% of all the seedlings observed in the field. In the delta the seedling density was two times that found at the seashore. Also, the numbers of species of seedlings per plot were significantly higher in the delta than in the seashore, but in total, more species germinated from the seashore than from the delta even though the number of plots was higher in the delta (n = 51) than in the seashore (n = 28). The numbers of species and seedlings per plot were smaller in grazed sites than in ungrazed ones similar to the pattern earlier reported concerning the mature vegetation and seed bank. The mean numbers of seedlings were the highest at lower geolittoral plots (about 20 cm elevation), where the seed bank was also densest. About 60.0% of the mature species in the plots were also detected as seedlings and 91.4% of the seedling species were found in the mature vegetation of the plots. The number of seedlings was positively correlated with the cover of mature vegetation giving support to the nurse effect theory. Seedling numbers were negatively correlated with the abundance of litter indicating that litter restricts germination because it is a mechanical barrier but also decreases the amount of light. The number of seedlings and species, both in total and per unit area, were greater in the seed bank than in the field seedling population. The seedling population was more similar to the mature vegetation than to the seed bank. This revised version was published online in August 2006 with corrections to the Cover Date.     

Local completion of the pelagic larval stage of coastal fishes in coral-reef lagoons of the Society and Tuamotu Islands

In four lagoons at two atolls and one high island in the Tuamotu and Society Islands, French Polynesia, plankton samples were taken weekly during 4 weeks in January/February 1989. A third atoll lagoon was sampled once. The lagoons varied in size and physical openness. We also sampled in the ocean near two atolls and the high island. All locations were sampled during the day, and three lagoons (two atolls and one high island) were also sampled at night. Pelagic fish eggs were more abundant in the ocean than in the lagoons at the atolls, but not at the high island. Larvae of coastal fishes were abundant in all lagoons. In the atoll lagoons, larvae of oceanic fishes were very rare to absent, but in the high-island lagoons and in the ocean, they were commonly encountered. In the ocean, larvae of many typical reef-fish taxa were abundant (58 taxa were represented by at least 10 individuals), but in the lagoons, most of these were rare or absent, and we conclude that these rare and absent taxa normally do not complete their larval phase in lagoons.Taxa were considered to be able to complete their pelagic phase in a lagoon (i.e., were 'completers') if they were present in the lagoon plankton samples from across a full larval size range. In the high-island barrier-reef lagoon, young, preflexion larvae were abundant, but only two taxa (of 56 captured) were present over a wide size range and were considered completers in this lagoon. In the high-island lagoonal bay, 11 taxa (of 67 captured) were considered completers. The numbers of taxa captured in the three atoll lagoons ranged from 39–44, and the number of taxa considered to be completers increased with increasing lagoon size and physical openness. The 17 completer taxa in the smallest, most enclosed atoll lagoon were, with one exception, a subset of those (18) in the second lagoon which, in turn, with one exception, were a subset of those in the largest, most open lagoon (26). Completer taxa were of the families Apogonidae, Blenniidae, Bothidae, Callionymidae, Carangidae, Gobiidae, Microdesmidae, Mullidae, Pomacentridae, Schindleriidae, and Tetraodontidae. The species that can complete their pelagic periods in coral-reef lagoons are a highly predictable group, and not simply a random selection of the potential species pool. Most of these species hatch from non-pelagic eggs. Water renewal times in the atoll lagoons, unlike the high-island barrier-reef lagoon, were much longer than expected pelagic larval durations of completer taxa. Demographically, lagoon populations of completer taxa apparently self-recruit and are probably near the closed end of the open/closed population continuum. The lagoonal bay on the high island differs from the other lagoons in containing larvae of species not found elsewhere, including some completers, and lacking some species that are abundant completers in other lagoons. In French Polynesia, lagoon size is a strong predictor of the number of lagoon completer taxa. The number of completer taxa apparently peaks at intermediate lagoon water-exchange times.     

Phenology of woody species in tropical coastal vegetation, northeastern Brazil

The study was carried out in the Private Nature Reservation Nossa Senhora do Outeiro de Maracaípe, located along the southern coast of Pernambuco state, in the Nossa Senhora do Ó District (08°31′48″S and 35°01′05″W), Ipojuca municipality, northeastern Brazil. The reserve has 76.20 ha of tropical coastal vegetation (Restinga forest). The aims were to determine the existence of seasonal phenological pattern of woody species as a function of rainfall. During the study period, the rainfall was 26.8 mm in the driest month (November 2003) and 538.9 in the wettest (June 2004). Observations on flowering, fruiting, leaf fall, and leaf flushing were recorded monthly, during 16 months (April 2003 to July 2004). All species with a ground level perimeter >10 cm and represented by at least three individuals, were selected and tagged. A total of 51 species represented by 156 individuals were recorded. Leaf flushing and leaf fall did not have seasonal variation and the species continued to gain and loose leaves during the dry (August to February) and rainy (March to July) seasons. Flowering, when evaluated by the Fournier's percentage, varied between 1.9% and 20.2%, with maximum intensity in December 2003 (16.4%) and January 2004 (20.2%). Likewise, fruiting varied between 3.8% and 21.4% with the highest percentages in February (17.2%) and March (21.4%) 2004. The analysis comparing reproductive phenological patterns with monthly rainfall did not show a significant correlation, which may suggest investigations concerning other factors, including biotic ones, as pollination and/or dispersal modes, which can be influencing reproductive events of plants in the studied Restinga forest.     

Assessing maximum depth distribution,vegetated area,and production of submerged macrophytes in shallow,turbid coastal lagoons of the southern Baltic Sea

Submerged macrophytes improve water quality in shallow coastal lagoons but eutrophication often resulted in a degradation of macrophytes. Management measures that protect and restore macrophyte stands require knowledge on what limits macrophyte distribution. Information on macrophyte production and distribution in the Darss-Zingst Bodden Chain (southern Baltic Sea) is lacking since an almost complete loss of submerged vegetation in the 1980s. Nutrient input was reduced in the 1990s and macrophytes seem to recover, although turbidity is high and light conditions are still poor. However, this recovery raised hope that returning macrophytes could stabilize sediments and improve water clarity. In this study, seasonal changes in photosynthesis–irradiance curves of selected macrophyte species were used to calculate potential primary production in different depths and turbidity situations. Bathymetry of the area is then used to assess depth distribution and vegetated area. Since the so-calculated depth limits correspond well with the actual depth distribution in the field, macrophyte depth distribution is concluded to be mostly determined by light conditions. Most macrophytes grow in very shallow areas up to 50 cm depth where also 70% of potential primary production takes place. Present light conditions do not support a further expansion of macrophyte distribution in the DZBC.     

广西阳朔岩溶植被演替过程种群变化及物种多样性

采用时空替代法研究广西阳朔岩溶植被在演替过程中的种群变化和物种多样性。研究表明,随着演替的进展,耐荫种群增加,乔木种群增加,优势种的更替呈现出一定的连续性,后一演替阶段的优势种往往已经隐含在前一演替阶段中;物种丰富度随演替进展表现出草丛<落叶阔叶林<灌丛<常绿落叶阔叶混交林的趋势;灌木层的物种丰富度在各演替阶段中均是最高的;在各演替阶段中,落叶阔叶林阶段的群落均匀度均表现为最大。     

Topographic effects of coastal seas on the composition of the culturable bacterial communities in marine sediments

Five published indirect methods to estimate benthic secondary production of intertidal mudflats and a new proposed formulation based on quarter-power allometric scaling and the “Universal Temperature Dependence” of biological processes (UTD) were compared. For this purpose, a dataset consisting of an annual series of samples, taken from the Lagoon of Venice from March 1996 to March 1997, at sites characterised by different seagrass coverage was used. All methods resulted in that biomass and secondary production decreased progressively when moving from the seagrass meadow toward areas of unvegetated substrate, suggesting an influence of the available marine phanerogams on the neighbouring sites. The equation proposed in this paper gives results comparable with those obtained using empirical regression models from literature. The main conclusion from this study is that general equations proposed by the “metabolic theory of ecology” can be applied for indirect estimations of secondary production of benthic communities.     

On the use of grammars in vegetation analysis

Grammars provide a means of generating large amounts of variability from relatively small resources, and seem especially relevant when the variation to be modelled is discontinuous since they describe the organisation symbols from some alphabet. In order to use grammars, it is desirable that they be inferred from observational data, and we present three examples of such inference. Two involve temporal successions, while the third is based on spatial transects of aquatic vegetation in wetlands in Victoria, Australia. The temporal successions were adequately represented by simpler regular grammars, suggesting that the processes involved may be modelled in a relatively simple manner. The spatial data requires a context-free grammar, reflecting the greater complexity of the spatial series, the uniqueness of each site, and the difficulties of modelling parallel systems with serial models. Examining the grammars further leads to some suggestions concerning the features of them which are important for ecological interpretation. It further leads to a novel view of the nature of groups in classification.     

A causal analysis of diet composition in free ranging cattle in reed-dominated vegetation

Summary Theoretical and observed diets of free-ranging yearling cattle in an area of reed-dominated vegetation were related to constraints inherent to ruminants (rumination time as reflected in the zone of acceptable crude fibre content of the ration; rumen fill) and in more general terms, to requirements for minerals (Na, Ca, Mg, P), for protein and for metabolisable energy in order to balance the growth rate achieved by experimental animals. Theoretical diets in spring were mainly limited by feeding time; theoretical diets in summer and autumn were mainly limited by rumen capacity. The high proteinto-energy ratio in the forage species caused protein intake to exceed the animals' demands. Mineral intake was in excess of requirements except for sodium. Yearling cattle in our study area maximized their energy intake, with feeding time, rumen capacity and crude fibre content of the forage as important constraints.     

Soil seed bank in a patchy vegetation of coastal sandy plains in southeastern Brazil

Large seed banks have been found in tropical dry forests and also in habitats with high seasonality in rainfall. However, patchily structured vegetation could induce great spatial variation in the seed bank. We characterized the seed bank in a patchy vegetation of restinga, a common type of coastal vegetation found in the Atlantic forest biome. We also evaluated whether there is any spatial variation between the litter and soil layer, bare sand, and the edge and center of vegetation patches with distinct species dominance. We found 104 seeds/m² in the seed bank using a 5‐cm‐depth sampling. Seven out of 16 species found in the restinga seed bank germinated; two of these were found in the early stages of vegetation patches. We found a higher number of seeds at the edge than in the center of vegetation patches. However, there were no significant differences in the number of seeds in the seed bank between the litter and soil layer, and between vegetation patches with distinct species dominance. Bare sandy soils had lower seed bank densities than vegetation patches. A small seed bank size might be explained by the low proportion of seeds from herbaceous and woody species, which are pioneers in the Atlantic forest. However, seed bank might play an important role in the early stages of the successional process, due to the occurrence of the few species that are able to colonize new young vegetation patches.     

Changes in soil and vegetation following stabilisation of dunes in the southeastern fringe of the Tengger Desert, China

Properties of the soil and sand-binding vegetation were measured at five sites plus a control on dunes of the Tengger Desert stabilized for periods of up to 50 years. In the topsoil, fine particles, total N, P, K and organic matter increased significantly with increasing site age. However, there were no significant changes in deeper soil profiles (>0.4 m depth). Soil pH, calcium carbonate content, and total salt content tended to increase with age. Soil water in the topsoil changed little with increasing age, but was closely related to rainfall during the 50-year period. For deeper soil layers (0.4–3.0 m) soil water decreased significantly with age. After revegetation, the number of herbaceous species increased up to 30 years and then levelled off to 12–14 species, whereas the number of shrub species decreased from the 10 initial sand-binding species to only 3 species. Shrub cover decreased from a highest average of about 33% to the current 9%, whereas cover and biomass of herbaceous species increased throughout succession from 1956 to 2006. The development of soil and cryptogamic crusts on the surface of stabilized dunes enhanced the colonization and establishment of herbaceous plants due to increasing water availability, clay and silt content and soil nutrients. We propose that changes in properties of the surface soil led to increased interception of water, favoring shallow rooted grasses and forbs over perennial shrubs.     

Environmental influences on the qualitative and quantitative composition of phytoplankton and zooplankton in North African coastal lagoons

Within the framework of the international research project MELMARINA, seasonal dynamics of plankton communities in three North African coastal lagoons (Merja Zerga, Ghar El Melh, and Lake Manzala) were investigated. The sampling period extended from July 2003 to September 2004 with the aim of evaluating hydrological and other influences on the structure, composition and space-time development of these communities in each lagoon. Phytoplankton in Merja Zerga showed a quasi-permanent predominance of marine diatoms in the open sea station and in the marine inlet channel. Dinoflagellates were abundant in summer and early autumn in the marine inlet and extended into the central lagoon station. In Ghar El Melh, marine species (especially diatoms and dinoflagellates) dominated despite occasional winter inflows of freshwater. In Lake Manzala, freshwater species generally predominated and the planktonic communities were comparatively very diverse. Chlorophyceae contributed 39% of the total species recorded and diatoms and cyanophyceans were also common; the Dinophyceae, Euglenophyceae, Chrysophyceae and Cryptophyceae less so. Zooplankton communities in both Ghar El Melh and Merja Zerga were dominated by marine copepods. Rotifera, Copepoda, Ostracoda, and Cladocera were recorded in both lagoons as were meroplanktonic larvae of Polychaeta, Cirripedia, Mysidacea and Gastropoda and free living nematodes. Ghar El Melh was the more productive of these two lagoons with spring and early summer being the productive seasons. Zooplankton communities in Lake Manzala were generally dominated by rotifers and highest zooplankton abundances occurred in April (2003). Sampling stations near the marine inlets showed the highest diversity and the zooplankton communities showed considerable spatial variation within this large lagoon. The three lagoons represent very different water bodies contrasted strongly in terms of tidal effects and freshwater availability. Yet, there are some similarities in ecosystem structure. Space-time development of the plankton communities was similar especially in Merja Zerga and Ghar El Melh. Species abundances and specific diversities indicated that seasonal changes in salinity and nutrient concentrations were the main influential factors. Lake Manzala was the most productive lagoon and all the three sites supported toxic algal species. Relatively low plankton biomass in Merja Zerga and Ghar El Melh probably resulted from a combination of factors including highly episodic nutrient inputs, light suppression (by turbidity) and nutrient competition with benthic algae. Water quality variables were largely driven by the hydrological regime specific to each lagoon. Nutrient enrichment and, particularly for Lake Manzala, sea level rise threaten the sustainability of the planktonic ecosystems in all three lagoons. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: J. R. Thompson & R. J. Flower Hydro-ecological Monitoring and Modelling of North African Coastal Lagoons     

The chemical character and burial of phosphorus in shallow coastal sediments in the northeastern Baltic Sea

The chemical composition and vertical distribution of sediment phosphorus (P) in shallow coastal sediments of the northeastern Baltic Sea (BS) were characterized by sequential extraction. Different P forms were related to chemical and physical properties of the sediments and the chemistry of pore water and near-bottom water. Sediment P composition varied among the sampling sites located in the Archipelago Sea (AS) and along the northern coast of the Gulf of Finland (GoF): the organic rich sites were high in organic P (OP), while apatite-P dominated in the area affected by sediment transportation. Although the near-bottom water was oxic, the sediments released P. Release of P was most pronounced at the site with high sediment OP and reduced conditions in the sediment-water interface, indicating that P had its origins in organic sources as well as in reducible iron (Fe) oxyhydroxides. The results suggest that even though these coastal areas are shallow enough to lack salinity stratification typical for the brackish BS, they are vulnerable to seasonal oxygen (O₂) depletion and P release because of their patchy bottom topography, which restricts mixing of water. Furthermore, coastal basins accumulate organic matter (OM) and OP, degradation of which further diminishes O₂ and creates the potential for P release from the sediment. In these conditions, an abundance of labile OP may cause marked efflux of P from sediment reserves in the long-term.     

The role of alien plants in the natural coastal vegetation in central-northern Spain

Alien plants in coastal habitats and their influence on natural vegetation are studied. After 5 years working on this subject in the Basque Country and surrounding areas, a number of results from the coastal ecosystems are presented. These ecosystems are one of the most threatened and affected by the invasion of alien plants, especially shore dunes, saltmarshes and cliffs. These kinds of habitats, especially the dunes, experience significant pressure from human activities which favours the expansion of some of these species: Arctotheca calendula, Sporobolus indicus and Oenothera spp. The presence and abundance of these invasive plants and others such as Baccharis halimifolia, Cortaderia selloana, Spartina patens and Carpobrotus edulis in the plant communities in an area between the French border and the western part of the region of Cantabria have been studied. The degree of invasion of each plant in each syntaxonomic unit has been analysed.     

Organochlorine,Organophosphoric and Organotin Contaminants,Aromatic and Aliphatic Hydrocarbons and Heavy Metals in Sediments of the Ports from the Polish Part of the Vistula Lagoon (Baltic Sea)

The concentrations of polycyclic aromatic and petroleum hydrocarbons, polychlorinated biphenyls, dioxins, organochlorine and organophosphoric pesticides, tributyltin and metals were determined in sediments of the approach fairways to the main ports in the Polish part of the Vistula Lagoon and of the Elbl?g River. Analyzed sediments contained low concentrations of all contaminants, except petroleum hydrocarbons. The average petroleum hydrocarbons’ (PHCs) concentration was 630 mg kg^?1, indicating significant pollution with petroleum hydrocarbons. The highest concentrations of analyzed contaminants were identified in the vicinity of Elbl?g, part of the Vistula Lagoon under the most anthropogenic pressure.