Long-term changes in the benthic communities of the Pomeranian Bay (Southern Baltic Sea)

Long-term changes in the macrofauna of the Pomeranian Bay were studied by comparing survey data from the 1950s, 1980s, and 1990s. The study area has undergone significant eutrophication during the period of investigation. Biomass of filter-feeding bivalves increased significantly. Spatial distribution patterns of several species have changed. Strong decreases in species richness were caused by oxygen depletion at stations deeper than 15 m.Saduria entomon, Monoporeia affinis, andPontoporeia femorata vanished entirely between 1981 and 1993. Although a causal relationship between simultaneous increases of nutrient levels and macrobenthic biomass cannot be verified, eutrophication is proposed to be the major process affecing changes in macrofauna assemblages. In addition, changes in hydrography and climate increased frequency and severity of oxygen depletion events in the Pomeranian Bay since the mid 1980s.     

Long-term changes in macroalgal communities along ferry routes in a northern Baltic archipelago

Species composition, abundance and biomass of littoral macroalgae were studied along a ferry route in the and archipelago, northern Baltic Sea. Two areas, originally studied in the 1970s, were revisited in 1999 and 2000. In one area the traffic has strongly decreased since the 1970s, in the other the frequency of the traffic has remained the same, but the size of the ferries has increased. During the revisit the highest number of species was found close to the ferry route, in contrast to the results of the original study. In the area with decreased traffic only minor shifts in species composition were observed. In the heavily trafficked area, red algae in particular, had increased close to the route. New species recorded were Polysiphonia fibrillosa, P.fucoides and Aglaothamnion roseum. On sheltered sites in this area, red and brown algae had decreased as a result of increased sedimentation and occurrence of drift algae, and were replaced by rooted macrophytes (e.g. Zannichellia sp, Ranunculus peltatus ssp. baudotii, Myriophyllum spicatum). In the 1970s a Fucus vesiculosus-belt was present at all the 14 studied sites. During the revisit F.vesiculosus was belt-forming at only 5 sites, mainly close to the ferry route in the heavily trafficked area. The biomass of Cladophora glomerata had increased and the occurrence of F.vesiculosus had decreased since the 1970s. The main reason to the documented changes is the ongoing eutrophication of the Baltic Sea. Close to the ferry route regular strong water movements seems to have a positive local effect on mainly perennial macroalgae by keeping the bottoms free from sediments and drift algae.     

The interaction between nutrient availability and disturbance frequency on the diversity of benthic marine communities on the north-east coast of England

1. Several theoretical models predict under what conditions maximum species diversity can be maintained, and they are often used to develop effective ecosystem management plans. 2. Two models that are currently used to predict patterns of species diversity were empirically tested in marine subtidal benthic communities of different successional stages. 3. The two models were: the interactive effects of nutrient availability and disturbance frequency proposed by Kondoh (2001; Proceedings of the Royal Society London B, 268, 269-271), and the intermediate disturbance hypothesis (IDH) proposed by Connell (1978; Science, 199, 1302-1310). 4. Interactive effects were found to be transient and only occurred in the older communities, while the unimodal pattern suggested by the IDH was not supported in either successional stage. 5. It is concluded that these models are very general and thus lack sufficient explanatory power. Both models require a number of specific prerequisites for maximum diversity to be found, and though applicable in many different ecosystems they need to be refined as tools in order that they can be effectively used in habitat management plans.     

The dynamics of the dune vegetation on the Polish Baltic coast

This paper deals with the Baltic coastline in Poland. Features of the climate, geomorphology, substratum, soils and vegetation are outlined. The historical forest succession is based on the results of palynological studies of fossil soils. The present-day dynamics of the plant communities are examined from the viewpoint of primary succession, regression, regeneration and secondary succession. The primary succession on moving dunes is described with particular reference to deflation fields. Attention is drawn to the spatial changes in the communities from the 16th to the 20th century as a result of natural and human factors. This study shows that during the 19th and 20th centuries and especially in the last 25 years, the dynamics of the dunes and their vegetation have been much reduced, owing to the widespread stabilization of the substratum by forests and the ongoing abrasion of the coastal dunes.     

The effect of drought on benthic invertebrate communities in a lowland river

Benthic macroinvertebrates were sampled at regular intervals from rural and urban sections of the River Roding, Essex, England, in 1975 and 1976. During the latter year a severe drought led to a marked decline in flows and to desiccation of parts of the river bed. In general, drought conditions resulted in an increase in invertebrate populations and possible reasons for this are presented. A considerable number of individuals of certain groups such as cased caddisfly larvae and prosobranch molluscs were, however, eliminated from the river at this time, mainly as a result of stranding and chemical changes in the environment. The effect of reduced flows on river faunas is briefly discussed.     

Peculiarities of the copper toxic effect on the phytoplankton communities of the Baltic Sea

The ecotoxicological investigations on the resistance of various phytoplankton communities were performed in the Southern Baltic Sea during summer and winter periods. The primary production rate was studied for different Cu concentrations. The enhancement of the toxic effect as well as total biomass and productivity increase were observed for phytocenosis. Total algae biomass on most of the stations increased accordingly to the dinoflagellate growth. Both dinoflagellate impact and relative copper toxic effect declined in the Gdansk Bay opposite to the high total algae biomass observed. We assume the dinoflagellate abundance is linked with the sensitivity of the phytoplankton cells to copper.     

The effect of salinity on the dominance-diversity relations of experimental coastal macrophyte communities

Salinity and water regime have previously been recognised as the main environmental factors controlling the abundance of coastal submerged macrophytes in temporarily-flooded marshes in the Camargue. The effects of these environmental variables, which are considered interrelated, are tested experimentally by subjecting experimental macrophyte communities from six temporarily flooded marshes to different levels of salinity (from 0 to 6 g/1 Cl^?). Communities subjected to high salinity levels (4 and 6 g/1 Cl~) showed a decrease in species richness and in biomass of all species involved. The species that most frequently dominate these communities, Chara áspera and Zannichellia pedunculata, are tolerant of salt and dominate over the entire salinity range. Three species groups can be distinguished based on the distribution of their biomass and centre of gravity of distribution over the salinity range: (1) non-salt-tolerant species, ‘glyco-phytes’, (2) moderately salt-tolerant species and (3) very tolerant species (‘halophytes’). A species ordination based on the experiments appeared to give results close to those previously obtained from field data.     

Spatio-temporal dynamics of chlorophyll in the open Baltic Sea

Five charts of the chlorophyll and hydrographic fields by verticalprofiles of in situ fluorescence and CTD were made on a stationarygrid of 20 ? 25 nautical miles with a 5-mile spacing in theopen Baltic Sea. Both chlorophyll levels and variability weremaximal close to the spring bloom. High chlorophyll levels insummer are sustained by recurrent nutrient injections from thedeep saline layer. Two of the surveys showed close couplingbetween the coarse-scale (10 km) chlorophyll distribution andthe hydrographic structure determining the intensity of nutrienttransfer. Vigorous advection, stirring and current shear, associatedwith a strong mesoscale eddy, probably dominated the chlorophyllpattern on three surveys. The upward velocities in the cycloniceddy resulted in accumulation of phytoplankton in the aphoticzone. Intensive heat input from the surface caused a suddensinking of the phytoplankton and the formation of a pronouncedsub-surface chlorophyll maximum.     

Dynamic impacts of feral mink predation on vole metapopulations in the outer archipelago of the Baltic Sea

Predation impacts by introduced predators are predicted to be most intense in island ecosystems, and also variable depending on environmental conditions, but large-scale experimental field testing is rare. In this study we examine the factors that determine the distribution and abundance of vole metapopulations preyed upon by feral American mink Mustela vison in the outer Finnish archipelago of the Baltic Sea. Specifically, we follow the dynamics of field voles Microtus agrestis and bank voles Clethrionomys glareolus on 40 small islands under variable rainfall as part of a large-scale mink removal experiment. For both vole species occupancy rates were negatively influenced by island isolation, as were extinction events for field voles. High summer rainfall in 1998 corresponded to large vole populations where mink were absent, populations that then crashed in 1999 and 2000 when below average rains fell during the summer breeding season. Where mink were present however, vole abundance remained more constant between years with no boom-bust apparent. We conclude that weather and predation may drive vole abundance whereas habitat patchiness and metapopulation processes more strongly drive vole distributions. There may also be potential for interaction between these factors: because feral mink prevent rapid vole population growth after good summer rains, and vole dispersal is influenced by population size, feral mink may be changing vole dispersal patterns to disrupt the natural metapopulation dynamic. Hence this indirect impact of mink could lead to gradual erosion of vole populations in the outer archipelago by reducing recolonisation processes.     

Long-term dynamics of zooplankton in the southeastern Baltic Sea

Long-term research in the Baltic Sea revealed the basic trends of zooplankton community variations depending on oceanographic processes. Alternation of the periods of increase and decrease in salinity of the Baltic Sea against the background of climate changes (temperature increase) and eutrophication affect the state of the entire Baltic ecosystem, including zooplankton. For these periods, the dynamics of zooplankton in the Baltic Sea were analyzed based on literature data and results of regular research in the southeastern Baltic Sea during 1998–2007. The changes in the hydrological situation were accompanied by significant changes in the zooplankton community. In the 1990s–2000s, the abundance and biomass of brackish-water and thermophilous species primarily of Cladocera and Copepoda increased markedly. The role of the previously dominant marine copepod Pseudocalanus elongatus decreased due to salinity reduction in the deep-water part of the Baltic Sea. Maximum development of zooplankton occurred in years of the greatest warming-up of the water (2001, 2005–2007) against the background of a general positive trend of zooplankton abundance in the last decade.     

Macrobenthos communities on reefs of the An Thoi archipelago of the South China Sea

Macrobenthos communities were studied on fringing reefs of the An Thoi Islands using scuba-diving techniques. The islands are located in the turbid and highly eutrophic waters of the eastern Gulf of Siam. We studied species composition and population densities and biomasses in common species of algae, coelenterates, mollusks, and echinoderms and also the degree of substrate coverage by macrophytes and corals. A pronounced vertical zonation is revealed in the spatial succession of different macrobenthos communities. The domination of massive porites in almost all reefs of the Gulf of Siam is due to their capability to survive under conditions that are stressful for many corals. They predominate over other scleractinians in terms of the productivity of organic matter, degree of substrate coverage, and species diversity. They also constitute the reef skeleton and play a significant role in the expansion of the reef area in the muddy bottoms of the Gulf of Siam.     

Assessment of quality of three marine benthic habitat types in northern Baltic Sea

The European Union Habitats Directive (HD) obliges member states to assess the conservation status of marine habitat types but no explicit methodologies for assessing the quality of habitats have been stated in the directive or accompanying documents. In this study, a system was developed to assess the structure and functioning of three important marine habitat types in the Estonian sea area: sandbanks (HD code 1110), mudflats (1140), and reefs (1170). The assessment system includes a list of ecological criteria and favourable reference values together with procedural rules and field sampling locations. The habitat types listed in the HD are broadly defined and may encompass different communities depending upon distinct environmental gradients. By considering these environmental gradients the habitat types reefs and sandbanks were zoned and the assessment criteria and corresponding favourable reference values were defined separately for each zone. A set of several metrics like benthos indices, community variables, presence of sensitive or typical species, proportions of functional or taxonomic groups were tested as potential criteria for determining habitat quality. The most appropriate criteria were selected for incorporation into the assessment system based on ecological eligibility, suitability to local conditions, occurrence rates of benthic species, responses to disturbances, statistical properties of distribution of measured values, and practical considerations. Extensive benthos database (records from the whole Estonian sea area, 1995–2014) was used to calculate values of criteria to support the selection of criteria and to derive reference values. In order to fully take into account their crucial role in maintaining the structure and functioning of habitats, the criteria on habitat-forming species were assigned higher hierarchical order in the assessment scheme compared to other criteria. Special field works were carried out to assess the status of the three habitat types in 2015. The quality of all three monitored habitats was assessed to be in a favourable status. Additionally, the distributions of the three habitat types were mapped. To date, this is the first study in the Baltic Sea region that formulates HD compliant explicit criteria, reference values, and assessment procedures for several marine habitat types. The main challenges of the study were to derive assessment criteria and favourable reference values that are ecologically relevant and practically feasible.     

Structure and bioassessment of benthic communities of a lagoonal ecosystem of the Atlantic Moroccan coast

The Merja Zerga lagoon is a semi-enclosed marine ecosystem in which various types of human activities have been developed. This paper characterizes the biosedimentary units of the lagoon and defines a reference status of the quality and health of the macrozoobenthic communities that can be used as bioindicators of the quality of the global marine environment. Specific and functional diversity were high: 147 taxa were identified; they were distributed within seven main trophic groups. Trophic structure is dominated by the suspension-feeding bivalve Cerastoderma edule and the deposit-feeding bivalve Scrobicularia plana, while micrograzers and macroherbivores remain low. Biotic index values indicated that the site is moderately perturbed and that the benthic communities are unbalanced. Nevertheless, the communities showed a seasonal stability of abundances and a high specific richness all through the year.     

Succession of sea-ice bacterial communities in the Baltic Sea fast ice

Coastal fast ice and underlying water of the northern Baltic Sea were sampled throughout the entire ice winter from January to late March in 2002 to study the succession of bacterial biomass, secondary production and community structure. Temperature gradient gel electrophoresis (TGGE) and sequencing of TGGE fragments were applied in the community structure analysis. Chlorophyll-a and composition of autotrophic and heterotrophic assemblages were also examined. Overall succession of ice organism assemblages consisted of a low-productive stage, the main algal bloom, and a heterotrophic post-bloom situation, as typical for the study area. The most important groups of organisms in ice in terms of biomass were dinoflagellates, plasticidic flagellates, rotifers and ciliates. Ice bacteria showed a specific succession not directly dependent on the overall succession events of ice organisms. Sequenced 16S rDNA fragments were mainly affiliated to α-, β-, and γ-proteobacterial phyla and Cytophaga–Flavobacterium–Bacteroides-group, and related to sequences from cold environments, also from the Baltic Sea. Temporal clustering of the TGGE fingerprints was stronger than spatial, although lower ice and underlying water communities always clustered together, pointing to the importance of ice maturity and ice–water interactions in shaping the bacterial communities.     

Habitat-mediated impact of alien mink predation on common frog densities in the outer archipelago of the Baltic Sea

Alien predators have been recognised as one possible cause for amphibian declines around the world, but little is known of habitat-mediated predation impacts especially on adult amphibians. We studied common frog Rana temporaria under American mink Mustela vison predation in the outer archipelago of the Baltic Sea, south-western Finland. Using egg batches as an index of breeding frog female numbers we compared frog numbers and densities between a large, long-term mink-removal area and a comparable control area. Frog numbers in the removal area were at least 2.7-fold higher than those in the control area. In the presence of mink, frog densities increased with the amount of vegetation cover on the islands, indicating that mink predation affected frog densities especially on less-vegetated islands. An opposite trend appeared to be true for frogs in the mink-removal area, where other predators like snakes could induce a decline of frog densities on more vegetated islands. Shrub or grass vegetation seems to provide frogs shelter against alien mink predation. Our result highlights the importance of landscape-level habitat management as a conservation tool for amphibian populations.     

Vegetation zonation in dune slacks on the Leba Bar,Polish Baltic Sea coast

Vegetation zones in dune slacks on the Leba Bar on the Polish Baltic Sea coast are described. Plant colonization starts on moist sand in eastern ends of slacks, in the wake of receding mobile dunes. Communities on deflation ribs, dominated by psammophytic grasses, sedges and lichens, are structurally simple. Communities in troughs, dominated by species of fresh habitats, become structurally more complex in a western direction and they culminate with the Pinus silvestris forest. The main lines of vegetation variation correlate with groundwa-ter depth, micro topography, soil profile build-up and substrate acidification.     

In-situ investigations on the echinodermAsterias rubens as a predator of soft-bottom communities in the western Baltic Sea

In-situ investigations on the life of the common sea star (Asterias rubens L.) were carried out in 1976, employing the Underwater Laboratory Helgoland in Lübeck Bay (Western Baltic Sea). The abundance ofA. rubens amounted to 2–31 m^–2 on sediment (fine sand), and to 324–809 m^–2 on mobile algal carpets drifting over the bottom. Actual population parameters (abundance, size class distribution) are influenced by both substrate quality and drifting. Stomach investigations revealed prey-size selectivity: Small sea stars feed mainly on the snailHydrobia ulvae when living on the sediment, but on mussel brood(Mytilus edulis) in the phytal. The principal food items of larger sea stars are the sand-dwelling clamMacoma baltica and the phytal-living isopodIdotea baltica respectively.A. rubens is very adaptive to the food available; the diversity of its diet corresponds to the species diversity found in its environment. A change of biotope during active or passive migrations causes switching. The sea star is able to catch motile animals and to dig out infaunal clams. It exhibits a diurnal feeding pattern related to light periodicity; the activity decreases at night. The average frequency of feeding is highly dependent on predator body size; it declines with growth. In-situ experiments indicate an exponential relationship between the feeding duration uponM. baltica and the quotient of clam size to logarithm of sea-star size. An approach is made toward a rough estimate of macrofauna consumption byA. rubens on sediment. The sea star seems to be an important predator and thus a competitor of demersal fishes on soft bottoms of the western Baltic Sea.     

The benthic invertebrates of the Salton Sea: distribution and seasonal dynamics

The Salton Sea, California's largest inland water body, is an athalassic saline lake with an invertebrate fauna dominated by marine species. The distribution and seasonal dynamics of the benthic macroinvertebrate populations of the Salton Sea were investigated during 1999 in the first survey of the benthos since 1956. Invertebrates were sampled from sediments at depths of 2–12 m, shallow water rocky substrates, and littoral barnacle shell substrates. The macroinvertebrates of the Salton Sea consist of a few invasive, euryhaline species, several of which thrive on different substrates. The principal infaunal organisms are the polychaetes Neanthes succinea Frey & Leuckart and Streblospio benedicti Webster, and the oligochaetes Thalassodrilides gurwitschi Cook, T. belli Hrabe, and an enchytraeid. All but Neanthes are new records for the Sea. Benthic crustacean species are the amphipods Gammarus mucronatus Say, Corophium louisianum Shoemaker, and the barnacle Balanus amphitrite Darwin. Neanthes succinea is the dominant infaunal species on the Sea bottom at depths of 2–12 m. Area-weighted estimates of N. succinea standing stock in September and November 1999 were two orders of magnitude lower than biomass estimated in the same months in 1956. During 1999, population density varied spatially and temporally. Abundance declined greatly in offshore sediments at depths >2 m during spring and summer due to decreasing oxygen levels at the sediment surface, eventually resulting in the absence of Neanthes from all offshore sites >2 m between July and November. In contrast, on shoreline rocky substrate, Neanthes persisted year round, and biomass density increased nearly one order of magnitude between January and November. The rocky shoreline had the highest numbers of invertebrates per unit area, exceeding those reported by other published sources for Neanthes, Gammarus mucronatus, Corophium louisianum, and Balanus amphitrite in marine coastal habitats. The rocky shoreline habitat is highly productive, and is an important refuge during periods of seasonal anoxia for Neanthes and for the other invertebrates that also serve as prey for fish and birds.