Macrobenthic Assemblages Research Articles

Corrigendum to: Partitioning spatial and temporal variability of tropical near-shore macrobenthic assemblages affected by natural and anthropogenic disturbances

Coastal zones throughout the world are subject to natural and anthropogenic disturbances that modify the natural assemblages. The present study determined the response of the assemblage of macrobenthic invertebrates to the presence of a pier and natural climatic variations. Two analytical models were considered; one was an asymmetric model that permitted the comparison of the sector closest to the pier (impact) with the average of the sectors located further away (controls); the other was a three-way model that enabled the three sectors within the area to be analysed. With both models, the differences were compared among the sampling periods and the scale at which the variation in the data was greatest. No differences were detected among individual sectors or between the control and impact sectors. However, significant differences were found among the four periods. The zone closest to the pier presented greater temporal variability. This relationship suggests that the pier affecting the assemblage and the impact may be increased by the climatic conditions prevalent in the zone. It is necessary to establish a broader temporal analysis and a more detailed analysis of the structure and composition of the benthic assemblage to elucidate this temporal and spatial variability.

Effects of reclamation on macrobenthic assemblages in the coastline of the Arabian Gulf: A microcosm experimental approach

Coastal reclamation and modifications are extensively carried out in Bahrain, which may physically smother the coastal and subtidal habitats resulting in changes to abundance and distribution of macrobenthic assemblages. A microcosm laboratory experiment using three common macrobenthic invertebrates from a proposed reclaimed coastal area was preformed to examine their responses to mud burial using marine sediment collected from a designated borrow area. Significant difference in numbers of survived organisms between control and experimental treatments with a survival percentage of 41.8% for all of the selected species was observed. The polychaete Perinereis nuntia showed the highest percentage of survival (57.1%) followed by the bivalve Tellinavaltonis (42.3%) and the gastropod Cerithidea cingulata (24.0%). Quantifying species responses to sediment burial resulted from dredging and reclamation will aid in predicting the expected ecological impacts associated with coastal developments and subsequently minimizing these impacts and maintaining a sustainable use of coastal and marine ecosystems in the Arabian Gulf.

Factors structuring temporal and spatial dynamics of macrobenthic communities in a eutrophic coastal lagoon (Óbidos lagoon, Portugal)

The present work aimed to identify the main environmental drivers shaping temporal and spatial dynamics of macrobenthic communities within a eutrophic coastal lagoon. Sediments in the Óbidos lagoon showed a gradient of increasing metal contamination from the inlet area to inner branches. The mid-lower lagoon area exhibited an intermediate contaminated condition between the inlet and upstream areas, suggesting that the effects of the organic loadings into the lagoon may be reflected until this area. This transitional feature was corroborated by biological data, with macrobenthic assemblages displaying characteristics of down- and upstream areas. Macrobenthic abundance peaked in winter, which was associated with a higher nutrient availability (mainly ammonium) and the proliferation of green macroalgae in mid-lower and inner lagoon areas. However, massive macroalgae growth resulted in a sharp decrease of macrobenthic diversity and abundance in spring, particularly where the higher amounts of decaying algae were detected. Higher dissimilarities between assemblages were detected during winter (and spring, for trophic composition), while in summer, differences were highly attenuated. The least contaminated area (close to the sea inlet) experienced smaller temporal variations for environmental variables, as well as the lowest temporal biological variability. This area was dominated by carnivores, which were related with increased salinity. Deposit-feeders were numerically dominant in the lagoon, being generally spread within organically enriched sandy and muddy areas. The high concentration of chlorophyll a and suspended particulate matter in water was reflected in the abundance of deposit-feeders/suspension-feeders, taking benefit of the high primary productivity. On the other hand, deposit-feeders/herbivores responded to the decay of macroalgae mats in the sediment. Biological associations varied with the biological data used (taxonomic versus trophic group composition; abundance versus biomass), highlighting the relevance of the combination of different data analysis’ approaches. In general, BIOENV analysis indicated total phosphorus, biomass of Ulva, metals and organic carbon and nitrogen as being significantly influencing benthic patterns. On the other hand, discrepancies in ecological behaviours of some taxa were also detected in the present study stressing the need for additional studies on the relationships between macrobenthic communities and environmental variables. Implications of the present results for monitoring studies are discussed.

Biodiversity of an unknown New Zealand habitat: bathyal invertebrate assemblages in the benthic boundary layer

For the first time in New Zealand waters, marine invertebrate assemblages from the benthic boundary layer were sampled as part of a broad scale national biodiversity programme, Ocean Survey 2020. Macrobenthic assemblages were collected from ∼1 m above the seafloor at 16 sites on the Chatham Rise and five sites on the Challenger Plateau to the east and west of New Zealand. Depths ranged from 218 to 1,239 m. Nearly 80 000 individual organisms were caught and identified to 33 higher taxonomic groups. Taxa of the supra- and epibenthos as well as taxa with suprabenthic affinities were encountered. Relative abundance and taxonomic richness of the invertebrates between the Chatham Rise and the Challenger Plateau were compared. The crustacean superorder Peracarida proved to be a good group to be representative for abundance patterns of the benthic boundary layer. The peracarid order Tanaidacea was identified to species level, showing high species richness, with 77% of the species being new to science. The observed high levels of biodiversity and high abundances, particularly of copepods and peracarid crustaceans, suggest that this component of the marine fauna, in the benthic boundary layer plays a significant role in ecosystem functioning of New Zealand waters.

CARACTERIZAÇÃO AMBIENTAL DA PORÇÃO SUBAÉREA DE PRAIAS ARENOSAS EXPOSTAS COM DIFERENTES CARACTERÍSTICAS MORFODINÂMICAS NO LITORAL CENTRO-NORTE DE SANTA CATARINA, BRASIL

The characterization and temporal monitoring of environmental variables significant to the structure of beach macrobenthic assemblages were carried out in the subaereal sector of three microtidal and exposed sandy beaches varying from dissipative to reflective conditions in the Center-Northern littoral of Santa Catarina. Monthly samples conducted between March 2000 and March 2001 showed that the environmental characteristics which are important to the development of the beach macrofauna were very distinct among the beaches and were related to their respective modal stages. Few morphological and sedimentary changes occurred along the year in Navegantes beach (dissipative), which was characterized by having wide surf and swash zones. Showing a gentle slope, Navegantes beach profile had homogeneous sediments composed by fine and moderately sorted sands with high moisture contents associated to its superficial water table. On the other hand, Taquaras beach (reflective) showed no surf zone and was dominated by surging/collapsing breakers whose energy dissipated directly on the beach face. Compared to the other beaches, Taquaras revealed the highest spatial and temporal changes in its sedimentary and morphological features and was characterized by a steep slope, narrow swash zone and deep water table. Its sediments were composed by moderately well sorted to well sorted coarse sands with reduced moisture contents. Brava beach (intermediate) was composed by moderately well sorted to well sorted medium sands and showed an intermediate pattern in terms of surf and swash zone extension, water table depth, sediment moisture and intensity of sedimentary and morphological changes. In general, the temporal behavior of the environmental variables was not seasonal along the study period and was specific for each beach, as a consequence of distinct hydrodynamic, sedimentary and morphological features associated to each morphodynamic stage.

Integrated assessment of mangrove sediments in the Camamu Bay (Bahia, Brazil)

Camamu Bay, an Environmentally Protected Area, may be affected by the pressures of tourism and oil exploration in the adjacent continental platform. The current quality of the mangrove sediments was evaluated by porewater bioassays using embryos of Crassostrea rhizophorae and by an analysis of benthic macrofauna and its relationships with organic compounds, trace metals and bioavailability. Porewater toxicity varied from low to moderate in the majority of the samples, and polychaetes dominated the benthos. The Grande Island sampling station (Station 1) presented more sandy sediments, differentiated macrobenthic assemblages and the highest metal concentrations in relation to other stations and guideline values, and it was the only station that indicated a possible bioavailability of metals. The origin of the metals (mainly barium) is most likely associated with the barite ore deposits located in the Grande and Pequena islands. These results may be useful for future assessment of the impact of oil exploration in the coastal region.

Effects of extreme climate events on the macrobenthic communities’ structure and functioning of a temperate estuary

The Mondego estuary (Portugal) experienced profound structural and functional modifications due to eutrophication, which was exacerbated by consecutive weather extremes that compromised a previous restoration project. This work explores multiple climate impacts on macrobenthic communities’ structure and functioning and its implications on ecosystem’s recovery. Floods and heat waves had a stronger negative effect on macrobenthic assemblages than the droughts, imposing a total abundance decline. Contrarily, biomass was not so affected by climate events, being stable and even increased in a mudflat area, where seagrass is re-colonizing. Bivalves and oligochaetes decreased with the flooding episodes, likewise subsurface-deposit feeders and suspension feeders, while crustaceans were particularly sensitive to heat waves. Species richness declined with the floods and heat waves, whilst evenness increased in sandflat area, constituting a positive sign towards recovery. Succession of different climate extremes affected ecosystem structure and functioning, delaying its recovery with possible consequent effects at higher trophic levels.

Macrobenthos–sediment relationships in a sandy bottom community off Mar del Plata, Argentina

The aim of this study is to characterize the different macrozoobenthos communities in Mar del Plata waters (south-western Atlantic) on the basis of their abundance and habitat, and to determine how sediment characteristics, like the grain-size composition, affect macrobenthic community structure. Multivariate techniques indicated that benthic communities and sediments in the surveyed area were included into the following five well-defined groups: (1) a medium sand assemblage dominated by the bivalve Crassinella marplatensis and Diplodonta patagonica, the echinoderm Encope emarginata, the tanaidacean Bacescapseudes sp. and the polychaete Armandia loboi; (2) a medium to very fine sand assemblage dominated by ostracods, the tanaidacean Bacescapseudes sp., amphipods and polychaetes of the family Nephtyidae; (3) a fine to very fine sand assemblage dominated by the tanaidacean Bacescapseudes sp.; (4) a silt and fine sand assemblage dominated by polychaetes particularly Scolelepis sp. and individuals of the family Nephtyidae; and (5) a fine sand assemblage dominated by amphipods and the tanaidacean Bacescapseudes sp. These results revealed the patchy distribution of macrobenthic assemblages as a result of sediment characteristics and serve as baseline information for this area strongly subjected to trawling perturbations.

Anthropogenic disturbance and spatial heterogeneity of macrobenthic invertebrate assemblages in coastal lagoons: the study case of Pialassa Baiona (northern Adriatic Sea)

The distribution patterns of macrobenthic invertebrate assemblages at different spatial scales and in relation to natural and anthropogenic disturbance gradients were investigated in the Pialassa Baiona, a eutrophic and polluted brackish coastal lagoon located along the Italian coast of the northern Adriatic Sea. This coastal lagoon shows a complex physiography with several shallow water ponds and channels separated by discontinuous artificial embankments. Environmental variables and macrobenthic invertebrate assemblages showed higher heterogeneity at small spatial scale (i.e. within channels and ponds). Distinction between channels and ponds is only weakly supported by the distribution patterns of macrobenthic assemblages. Depth was the major factor in structuring benthic communities within ponds, while species distributions along the channels were strongly correlated with the anthropogenic disturbance gradient. Anthropogenic disturbance mainly affected species richness, which was inversely correlated with the organic carbon contents in the sediments and the water surface temperature, which is affected by the input of cooling water from two thermal power plants. Some opportunistic species, like the polychaetes Streblospio shrubsolii and Capitella capitata, were more abundant in the southern polluted areas. In particular, the abundance of S. shrubsolii significantly increased with organic carbon contents in the sediments and water surface temperature, while C. capitata was more abundant in the warmed sites and close to sewages. Conversely, the abundance of the amphipod Corophium insidiosum was inversely related to organic carbon contents.

Impacts of Spartina alterniflora invasion on the benthic communities of salt marshes in the Yangtze Estuary, China

As a species for ecological engineering, Spartina alterniflora was introduced to Chongming Dongtan in 1995, and over the last 10 years, this species has rapidly invaded large areas of the Chongming Dongtan nature reserve. In this study, use of a normalized biomass size-spectra (NBSS) approach was explored to evaluate the possible impacts of S. alterniflora invasion on the benthic communities along gradients of intertidal zones and the invasion history of S. alterniflora within the nature reserve. The results showed that the characteristics of macrobenthic communities and the variation in macrobenthic communities described by the first two CCA axes revealed clearly the gradients of elevation and invasion history of S. alterniflora. The differences in the macrobenthic assemblages between the Spartina alterniflara marshes and the native Phragmites australis marshes decreased with increasing of invasion history of S. alterniflara. The macrobenthic biomass showed a decreasing trend, while the meiobenthic biomass showed a reverse trend along the elevation gradient. The macrobenthic biomass of S. alterniflora marshes with longer invasion history was higher than that at recently invaded S. alterniflora marshes, while the meiobenthic biomass was lower. The slopes of NBSS for the sampling sites showed a trend of steeper slopes with decreasing of elevation and at the recently invaded S. alterniflora marshes than that at marshes with longer invasion history, while the differences between the native P. australis marshes and the S. alterniflora marshes with long invasion history tended to be diminished. The NBSS approach could thus be used more widely to detect possible impacts of S. alterniflara invasion on benthic assemblages. This study also indicated the potential for this approach to provide valuable insights into the ecosystem ecology of invasive species, which could be very important for wetland biodiversity conservation and resource management in the Yangtze River Estuary and other such impacted areas.

Influence of Monsoon on Macrobenthic Assemblage in Outer Channel Area of Chilika Lagoon, East Coast of India

Abundance of macrobenthos in the outer channel area of Chilika lagoon in the east coast of India was studied during Monsoon season of 2007 & 2008. In total 27 species of macrobenthic organisms were collected during the study period season. Crustacea was emerged as the most dominate group representing 9 species followed by polychaetes with 8 species while 5 species belonged to bivalvia and 3 species to gastropoda. The others group in the study area included nematodes and echiurids. The mean density of macrobenthos was 378 organism m-2 and 392 organism m-2 in 2007 & 2008.The biomass was measured as and biomass 0.525 g m-2 and 0.575 g m-2 during 2008 &2007. Mean values of diversity indices like Margalef's richness index was 2.7 in 2007 and 3.0 in 2008. While Shannon's H' was 1.7 of 2008 and 1.8 in 2007. The Evenness J was calculated as 0.76 in 2008 and 0.94 in 2007. The result of the study shows that hydrographical parameters like Temperature (°C), pH and Salinity (psu) parameters had modest relationship with population density and biomass. The preference of macrobenthic organism to any specific parameter couldn't be established clearly and this would be due to the presence of more opportunistic filters feeders than the deposit feeders. The opening of a new outlet connecting with the sea had good influence on species richness and population density. Key words: Chilika lagoon; Macrobenthos; Population density; biomass; diversity indices DOI: 10.3126/jowe.v3i0.2223 Journal of Wetlands Ecology, (2009) Vol. 3, pp 56-67

Potential biological indicators of heavy metal stress in mangrove ecosystems

The effects of heavy metals Cu, Pb, and Zn on a number of biological structural components of Avicennia dominated mangrove ecosystems is reviews and their potential as biological indicators of metal stress discussed. Three main taxa groups were chosen for examination, representing key structural components of Avicennia systems at different trophic levels. As the primary producer, Avicennia marina (Forsk.) Vierh, the grey mangrove, was studied most intensely. Heloecious cordiformis (Milne Edwards, 1852), the semaphore crab, was chosen as a higher level consumer. A suite of benthic organisms were also studied, representing a range of trophic associations at the community level. Potential biological indicators of metal stress were investigated in each group, at various organisational levels. A combination of laboratory and field based experiments have shown that most biological indicators investigated have merit in terms of reflecting exposure and effect of heavy metal stress in Avicennia systems. Avciennia marina was found to be highly tolerant to Cu, Pb and Zn. Both field and laboratory studies revealed the three metals were accumulated in root tissue in proportion to sediment metal loadings, and Cu and Zn showed some limited mobility to leaf tissue. Zn was the only metal in leaf tissue. Zn was the correlated with sediment loadings. All metals in root tissue and Zn in leaves were appropriate for accumulative indication. In both field and laboratory studies, increases in peroxidase activity and decreases in photopigments (most notably the chlorophyll a/b ratio) were found with increasing Cu and Zn. Significant relationships with peroxide ase activity only, were found for Pb. Both peroxidise activity and photopigment may be employed as sensitive early warning biomarkers of metal stress in A. Marina. For H. Cordiformis, Cu and Zn were regulated in the hepatopancreas. Lead was accumulated in the hepatopancreas in proportion to sediment Pb levels, and Pb was the main metal loadings tended to support lower numbers of crabs, greater proportions of females with purple chelae (rather than orange) and less females in the population, and thus may be employed as population level indicators of metal stress. Monitoring of macrobenthic community assemblage diversity and abundance along with natural variables and low-level anthropogenic contaminnts including Cu, Pb, Zn, revealed no significant pollutant related patterns. Natural physiochemical sediment differences were found to be the main determinants in species assemblage patterns among sites. An integrated approach of both field and laboratory based testing, with a range of species measured at various organisational hierarchies, is most instructive in the assessment of metal impacts on mangrove ecosystems.

Influence of the choice of physical and chemistry variables on interpreting patterns of sediment contaminants and their relationships with estuarine macrobenthic communities

A primary objective of contaminated sediment risk assessments is to identify if contaminant enrichment is eliciting an ecological response. Using complementary environmental and biotic datasets, we examined five scenarios with respect to: dataset complexity; metal extraction; normalisation of organics; the inclusion/exclusion of acid-volatile sulfide data, and iron and manganese concentrations. Spatial distributions of abiotic variables were examined by principal components analysis, with canonical correspondence analysis used to examine the total and partitioning of biological variation. Metals were the dominant contaminant and explained the largest proportion of variation in the macrobenthic data. Extraction procedure and carbon normalisation of organics had little influence on the overall analysis. Porewater metal data was essential for interpretation, with excess of acid-volatile sulfide over simultaneously extractable metals being a poor surrogate. In the canonical correspondence analyses, the inclusion of Fe/Mn accentuated the covariation between the ecological and contaminant variables. Multimodel comparisons aided interpretation by emphasising specific relationships among environmental variables and their interactions with the biotic data. Furthermore, for future examinations of the described system, the findings can be used to reduce the collection of redundant environmental variables or variables that are poorly correlated with changes in macrobenthic assemblages.

한려해상국립공원 관음포 갯벌의 대형저서동물 군집 구조

This study was performed to investigate the community structure of the macrobenthic invertebrates on the Gwaneumpo tidal flat, Hallyeohaesang National Park, Korea. Benthic invertebrates were collected between April and September 2006 at each five station. A total of 67 macrobenthic species were collected. The overall average macrobenthos density and biomass were 1,429 individuals/m² and 154.40 gWWt/m², respectively. Based on the abundance and biomass data, there were 10 dominant species accounting for approximately 86.4% of total individuals. The highest densities were found in the polychaetes Heteromastus filiformis, Ceratonereis erythraeensis, the brachyura Ilyoplax pusilla and the amphipoda Corophidae unid. On the contrary, the top ten species made up 94.2% of the total biomass while the three most abundant, the bivalve Cyclina sinensis, the brachyura Macrophthalmus japonicus and the anomura Upogebia major. The conventional multi-variate statistics(cluster analysis and non-metric multi-dimensional scaling) applied to assess spatial variation in macrobenthic assemblages. Cluster analysis and nMDS ordination analysis based on the Bray-Curtis similarity identified 2 station groups. The group 1 was associated with upper tidal flat station(station 1) and was characterized by high abundance of the polychaetes C. erythraeensis, Cirriformia tentaculata, the brachyura I. pusilla, the amphipoda Corophidae unid. and the isopoda Paranthura japonica. However, group 2 was consisted with middle and lower tidal flat station(Station 2～5) and was numerically dominated by the polychaetes Capitella capitata, Glycera chirori, the brachyura M. japonicus, the amphipoda Pleustes sp. and the anomura U. major.

Testing taxonomic resolution levels for detecting environmental impacts using macrobenthic assemblages in tropical waters

Macrobenthic assemblages are widely used as a tool for ecological assessment studies and monitoring programs. However, studies of macrobenthic assemblages have been limited in tropical coastal and marine environments in comparison with those in temperate zones. This study characterized at different resolution of taxonomic levels the responses of macrobenthic assemblages inhabiting subtidal areas in Bahrain to sewage effluents and heavy metal contamination. Macrobenthic assemblages impacted by nutrient enrichment showed lower levels of biodiversity, richness and evenness, and higher degree of disturbance. Multivariate statistical analyses revealed that faunal patterns of species were sufficiently comparable to those of genus and family taxonomic levels and showed 98% and 95% similarity, respectively. Ammonia, phosphate, and depth were the main environmental parameters responsible for explaining 41% of the community patterns in the study areas.

Spatial variability of benthic macrofauna in the Ria of Vigo (NW Spain): Effect of sediment type and food availability

The rias are incised and/or drowned river valleys with a high biological productivity dominated by estuarine circulation. This ecosystem provides diverse habitats due to spatial heterogeneity in physical and chemical conditions. The main objective of this study is to determine the structure and spatial distribution, both vertical and horizontal, of subtidal macrobenthic assemblages in relation to sediment type and food availability. A total of 12 sites belonging to 4 different soft-sediment localities in the Ria of Vigo (Spain) were sampled in order to reveal the relative importance of the environmental factors in controlling benthic fauna. The distribution of macrofauna communities was related to the type of sediment, which is linked to a wider set of environmental conditions, such as food availability and hydrodynamics. Multivariate analysis used to relate biochemical characteristics of the sediment and faunal parameters suggests that biopolymeric carbon fraction (BPC) and lipids are the best descriptors of sediment nutritional value, indicating the importance of food quality as a structuring factor in macrobenthic communities. This result suggests that the use of BPC and lipids as a proxy for benthic macrofauna quantitative changes and dynamics may be an effective tool in the study of soft-bottom benthic ecosystems.

Benthic assemblage composition on subtidal reefs along a latitudinal gradient in Western Australia

At regional scales, the distribution of species and the structure of assemblages vary with latitude within many marine and terrestrial systems. The oligotrophic coastal waters of Western Australia (WA) support highly speciose and endemic assemblages, yet spatial patterns in benthic structure are currently poorly known. We examined benthic assemblage composition along a latitudinal gradient of 28.5–33.5°S and a depth gradient of 14–62 m, on subtidal reefs in warm-temperate WA. We surveyed benthos using a remotely triggered digital stills camera. In total, we sampled macroalgae and sessile invertebrates at 201 sites spread across four locations. Percent cover of coarse taxonomic groups and dominant species was estimated from over 2000 photoquadrat samples. We recorded significant differences in benthic assemblage composition between locations, and along depth gradients within each location. However, the magnitude of change with depth was not consistent between locations, and shifts in assemblage composition along the depth gradients were not as pronounced as expected. The percent cover of all dominant benthic groupings differed between locations, and several key taxa, such as the kelp Scytothalia dorycarpa, brown foliose macroalgae, hard corals and sponges, changed predictably along the latitudinal gradient. Our study adopted a coarse taxonomic, but assemblage-wide, approach to describing macrobenthic assemblages, and clear differences between locations and depths were detected. The surveys have provided baseline data on broad scale ecosystem structure against which to detect future ecological change.

Historical macrobenthic community assemblages in the Avilés Canyon, N Iberian Shelf: Baseline biodiversity information for a marine protected area

Deep-sea ecosystems are highly diverse, and European countries seek to protect these environments by identifying conservation targets. One of these is the Avilés Canyon, southern Bay of Biscay, NE Atlantic, Spain. We present the first analysis of historical benthic communities (1987–1988) of this canyon ecosystem, which is a valuable source of biodiversity baseline information. We found 810 taxa divided in five main macrobenthic assemblages, showing a highly diverse benthic community. Bathymetry was the major structuring agent of benthic community, separating shallow (assemblages I and II, 31 to 307 m depth) from deep stations (assemblages III, IV and V, 198 to 1400 m depth). Especially diverse was assemblage IV, located at the easternmost part of the continental slope (378–1100 m depth) where we found reef-forming corals Lophelia pertusa and Madrepora oculata. These and other communities (sea-pens [Order Pennatulacea, Phylum Cnidaria] and burrowing macrofauna) represent key habitats in NE Atlantic continental slopes, which are currently threatened. The present dataset has produced the most comprehensive assessment of diversity in this area to date, focusing on the taxonomic groups which may best reflect the health of the marine ecosystem and supporting previous studies which indicate that the continental slope of the southern Bay of Biscay hosts key benthic habitats.

Relict sand dredging for beach nourishment in the central Tyrrhenian Sea (Italy): effects on benthic assemblages

AbstractThe aim of this study is to analyse the effects in space and time of relict sand‐dredging activities on macrobenthic assemblages, in an area situated offshore Montalto di Castro (central Tyrrhenian Sea, Italy), and to analyse the recolonisation processes of macrobenthos in the dredged areas. The area in question is characterised by relict sand deposits (Holocenic paleo‐beaches), used for beach nourishment along the Latium coast. The effects of sand extraction on benthic assemblages were investigated before, during and after three dredging operations. The sites analysed are located within the dredged areas (inside stations) and in neighbouring, not dredged, areas (outside stations). The results showed that the impact of sand extraction was confined to the dredged stations and to the areas in proximity to the dredged areas. During dredging activities, the structure of benthic assemblages within the impacted stations was characterised by low species richness and diversity. Both the direct removal of sediment and the re‐suspension and consequent deposition of fine sediment affected benthic assemblages of the impacted stations. A few months after the dredgings, a recolonisation process was still observed at all the impacted stations. A gradual recolonisation process was observed at those stations affected by only one dredging, whereas a different recolonisation was observed at those stations affected by two dredgings over time. This study suggests that differences of re‐colonisation processes of benthic assemblages are related to the intensity of dredging operations in terms of dredging frequency.

The zebra mussel (Dreissena polymorpha) and the benthic community in a coastal Baltic lagoon: another example of enhancement?

AbstractThe zebra mussel (Dreissena polymorpha), a sessile suspension feeder, has been known to enhance the benthos in the sediment around mussel beds and druses. The enhancement is mainly due to biodepositing activity of the mussel and the resultant organic enrichment of the sediment. In addition, mussel beds increase habitat complexity. In June 2007, we studied the distribution of D. polymorpha beds and their effects on the benthos in Kleines Haff, the western part of the Szczecin Lagoon, a Southern Baltic coastal water body. We expected that: (i) the sediment near a Dreissena bed will support meio‐ and macrobenthic assemblages more abundant than those living away from the bed, and (ii) the meio‐ and macrobenthic assemblages close to the Dreissena bed will show a stronger dominance of the taxa relying on the organic enrichment (nematodes among the meiofauna; oligochaetes and chironomids among the macrobenthos). Meiobenthos was sampled at two localities, one (MB4) featuring D. polymorpha druses and the other (MB5) supporting a distinct zebra mussel bed. The two localities differed in their meiobenthic communities: whereas no difference in abundance and composition was observed between the sets of samples collected at MB4, MB5 showed a distinctly more abundant meiobenthos in the uppermost sediment layer near the zebra mussel bed, but the overall abundance was lower than that away from the bed. We conclude that the meiobenthic response to the presence of D. polymorpha was, at least in part, mediated by site‐specificity of sediment characteristics. Macrozoobenthos was sampled at four stations in the vicinity of MB5 and around another Dreissena locality (MB10), and was also identified in the sediment samples collected for the meiobenthos. The macrobenthic abundance was higher by a factor of 2.4 (sandy sediment) to 4.9 (silty bottom) near the Dreissena beds than away from them. Irrespective of their situation relative to Dreissena aggregations, both meio‐ and macrobenthos were dominated by the taxa associated with organic enrichment. The macrobenthos associated with Dreissena beds included Gammarus tigrinus, a non‐indigenous amphipod, whereas another non‐native species, the polychaete Marenzelleria neglecta, was present in the macrobenthos of sandy sediments of the area.