Macrozoobenthic Assemblages Research Articles

Do mucous aggregates affect macro-zoobenthic community and mussel culture? A study in a coastal area of the Northwestern Adriatic Sea

In June 2000 and July 2002, two mucous aggregation events of large proportion occurred in the Adriatic Sea. In order to assess the possible effects that the events had on the macrofauna, we studied macro-zoobenthic assemblages and mussel culture ( Mytilus galloprovincialis). Structural parameters of macro-zoobenthos and growth parameters of mussels were recorded. The study area was a mussel farm located 5 nautical miles off Porto Caleri (Rovigo, Italy) in the Northern Adriatic Sea. Between May 2000 and August 2002, two sites were sampled in this area and univariate and multivariate techniques were used to describe the macrobenthic community. Two-way ANOVA showed that mean values of species number, density (individuals m − 2 ) and Shannon–Wiener's diversity were significantly influenced ( p < 0.01) by site and period of sampling and by the interactions of these factors. The Pielou's J averages were significantly influenced only by period ( p < 0.01). Application of Tuckey's HSD test ( p < 0.05) to factors detected to be significant by ANOVA did not show significant differences between samples collected after the mucous aggregation events and the other periods. Cluster analysis and MDS ordination did not allow a clear distinction between the samples. Concerning mussels, one-way ANOVA showed that mean values of the shell length and the condition index (dry weight/shell weight) were significantly influenced ( p < 0.001) by the months. The mean values both for shell length and condition index were higher in 2001. The shell length trend revealed a slowing down of growth in June–July 2000 and July–August 2002, and the condition index trend showed a significant fall in samples of June 2000 and July 2002. The growth of M. galloprovincialis might be influenced negatively by mucous aggregates, whereas the soft-bottom macro-zoobenthos seems not to be directly affected by the event.

Heterogeneity of macrozoobenthic assemblages within a Zostera noltii seagrass bed: diversity, abundance, biomass and structuring factors

The macrobenthic fauna community of a 70-km 2 Zostera noltii seagrass bed (Arcachon bay, France) was studied by sampling 49 stations systematically. A total of 126 taxa were identified. Cluster Analysis based on χ 2 distance showed that in this apparently homogeneous habitat, four distinct macrobenthic communities could be identified. Multiple Discriminant Analysis highlighted the major contribution of the overlying water mass as a forcing variable, and, to a lesser extent, of tidal level and Z. noltii's below-ground parts. Seven stations did not constitute any conspicuous group, and were characterized by a low biomass of leaf (<28 g DW m −2), considered as the lowest value to constitute a Z. noltii community. Less than 24% of the seagrass bed was situated in more oceanic waters and at a quite low tidal level. In this relatively stable environment, the macrofauna community was characterized by a high species richness (mean = 39) and a moderate density and high biomass (12 638 individuals m −2 and 25 g AFDW m −2, respectively). Annelids dominated, particularly the oligochaetes. When physical constraints increased (emersion or brackish water conditions), diversity decreased, abundance and biomass increased. The seagrass bed (55%) was flooded with highly fluctuating waters in term of temperature and salinity, here species richness was low (mean = 27) but abundance and biomass were high (24 384 individuals m −2 and 28 g AFDW m −2, respectively), with a dominance of molluscs. The meadow (7%) was in external waters but at a higher tidal level (2.4 m vs 1.8 m above medium low tide level). This community was characterized by the particularly high density (41 826 individuals m −2) and dominance of oligochaetes (79% of total abundance). Species richness was high (mean = 37) here. A fourth community, extending over 12% of the meadow was dominated by the gastropod Hydrobia ulvae but could not be linked to a specific forcing variable. This study confirmed the almost complete replacement of the native clam Ruditapes decussatus by the Manila clam Ruditapes philippinarum since its introduction in the 1980s.

Recovery of the Macrozoobenthic Community after Severe Dystrophic Crises in a Mediterranean Coastal Lagoon (Orbetello, Italy)

The Orbetello lagoon, one of the largest Western Mediterranean lagoons, was affected by high algal blooms and severe anoxic crises in 1992 and 1993, with fish mortality throughout most of the lagoon and a drastic reduction of benthic species. Many measures were undertaken between 1994 and 1996 to remove the severe eutrophication of this lagoon. Such measures included harvesting of the floating seaweed biomass, removal of all wastewater and sea channel enlargement by dredging activity. The aim of the present research was to study the macrozoobenthic assemblage in 1999 and to compare it with previous research in order to assess the recovery of the lagoon. A total of 106 taxa and 45 175 individuals were collected in three areas (sea inlets, western and eastern lagoon) having different organic matter loading during winter and summer. The results of multivariate and correlation analyses indicated that trophic status and its seasonal dynamics were crucial in determining species distribution among the different areas. Moreover, comparison of the macrozoobenthic structure between winter 1995 and 1999 showed differences in species composition and structural parameters in the western and eastern lagoon, where a clear recovery of benthic assemblages was observed in 1999. However, the dominance of opportunistic species in most of the lagoon and the decrease in some structural parameters during summer suggested that this basin still presented signs of disturbance in 1999, six years after the last extended anoxic crises and even after completion of the restoration measures carried out in the environment. It was hypothesized that a secondary disturbance, sustained by a high seasonal release of nutrients from the sediments, could create considerable deviations from the expected improvement in benthic conditions.

Loss of Heterotrophic Biomass Structure in an Extreme Estuarine Environment

Macrozoobenthic assemblages inhabiting estuarine mudflats in areas located at high intertidal levels or close to the mouth had: (1) higher values of abundance, biomass and production; (2) larger mean body sizes; and (3) lower turnover rates than at the remaining stations located elsewhere in the organically enriched, severely polluted Bilbao Estuary. All these community descriptors were similar to those from the nearby and relatively unpolluted Plentzia Estuary, considered here as a reference location.Biomass was irregularly distributed among logarithmic classes of individual body dry weight (DWi). However, a tendency to increase biomass with mean DWiwas found at the reference estuary and at the seaward end of the polluted estuary. This indicated the prevalence of more stable and regular environmental conditions which favoured larger-bodied,K-selected species. In fact, a biomass ‘sink’ was identified in the adult individuals of the bivalveScrobicularia plana(Da Costa), which were only found at the reference estuary (DWi=256 to 512mg) and close to the mouth of the polluted estuary (DWi=128 to 256mg). However, biomass was strongly centred around the smallest size classes (DWi<0·250mg) in the middle and upper reaches of the polluted estuary. Onlyr-selected species of Oligochaeta and Nematoda were favoured under the influence of catastrophic events, indicating the existence of heavily disturbed habitats.Oxygen depletion in the water column was causing a clear segregation of two ecological strategies along the longitudinal axis of the polluted estuary. On the one hand, large sized ‘persisters’ were successful close to the mouth of the polluted estuary. On the other hand, small sized ‘invaders’ (or even the absence of macrofauna) characterized the other extreme of the gradient. Spectral methods revealed a reliable tool for quantifying faunal responses in relation to the stress induced by adverse environmental conditions.

Analysis of macrozoobenthic community structure after severe dystrophic crises in a Mediterranean coastal lagoon

The macrozoobenthic assemblages of the Orbetello lagoon was studied in 1994. This basin, one of the widest western Mediterranean lagoons, showed, at the end of 1970s, very rich and highly structured communities, mainly due to the heterogeneity of its habitats and also presented large prairies of marine phanerogams. An increase in organic pollution over recent years has progressively brought about change in the environment, eventually leading in 1992 and 1993 to extended spring macrophyte blooms followed by severe dystrophic crises with high fish mortality in most of the lagoon. The aim of this study was to describe the zoobenthic community structure after these crises in order to assess the ecological conditions of the lagoon. A total of 70 species and 15332 individuals were collected at the 9 stations sampled quarterly (March, June, September, December). The results of ordination and correlation analysis indicated that the oxygen level and organic matter percentage in the sediment mainly influenced horizontal species distribution in the different sites at each sampling date. Furthermore, a clear impoverishment of the communities in comparison to previous researches was also observed. Species reduction affected not only marine taxa but also the so-called opportunistic species (primarily annelids) which were confined near sea inlets. Such patterns, which were quite unusual and differed from those described in other brackish environments with high organic pollution, gave evidence of a reduced resilience of the community despite a moderate recovery in December. The Orbetello lagoon in 1994 was therefore to be considered as under severe environmental stress and it was difficult to assess when or whether these drastic changes will be reversible.

The Quantitative Distribution of Subtidal Macrozoobenthic Assemblages in Arcachon Bay in Relation to Environmental Factors: a Multivariate Analysis

The species composition and spatial distribution of macrozoobenthic assemblages in the subtidal, unvegetated areas of Arcachon Bay (a mesotidal coastal lagoon on the SW coast of France) were investigated through a quantitative survey of 18 stations, sampled during a winter period. Factorial correspondence analysis (FCA) of the distribution of main species among stations and automatic hierarchical classification identified seven species groups and five station groups or faunal assemblages, the latter being also characterized in terms of species constancy and fidelity. These assemblages were: (1) a Gastrosaccus spinifer –Nephtys cirrosacommunity on clean, medium sands in the deep entrance channel; (2) a fine –medium sand assemblage characterized by the amphipods Bathyporeia sarsiand Melita palmatain the two main tidal channels, which penetrates deeply in the bay along the hydrological axes of the system; (3) a very localized assemblage of epi- and infauna on a heterogeneous substratum; (4) a modified Abra albacommunity in the muddy, transverse channels; and (5) a facies of the latter dominated by the oligochaete Tubificoides benedeni.Multiple discriminant analysis including seven environmental variables revealed that the most important factors in the ordination of stations were the sediment parameters, especially organic matter and Zosteradebris, followed by the salinity range and water depth. The spatial organization of subtidal infauna in Arcachon Bay appears to be characteristic of a mesotidal coastal lagoon with important water exchanges with the ocean. Average abundance and biomass of macrofauna amounted to 1719 individuals m −2and 6 ·10 gm −2DW, respectively. Density, biomass and species richness were, on average, higher in muddy sands than in clean, sandy bottoms. Comparison of available quantitative data for Arcachon Bay shows that abundance and biomass of macrozoobenthos are lower in subtidal areas than in intertidal habitats.

Sublittoral macrozoobenthic assemblages in the enclosed sediment-polluted Rhine-Meuse Delta; their relationship to environmental conditions

Composition, densities and biomass of sublittoral macrozoobenthos were investigated at 14 sites in the enclosed Rhine-Meuse Delta. The aim was to identify the main macrozoobenthic assemblages and to establish their relationship with environmental conditions, including sediment pollution. Most sites were dominated by the tubificidsLimnodrilus hoffmeisteri andL. claparedeanus. Four zoobenthic assemblages could be identified. They are related to different geomorphological phases of a basin filling up with fluvial sediment causing a longitudinal sediment gradient. The ’Rhine river’ assemblage was found in the Nieuwe Merwede, filled up in the 1970's, the ’soft mud’ assemblage in the Hollands Diep at sites with high sedimentation rates; the ’basin silt’ assemblage in the Amer, Hollands Diep and Haringvliet, at sites with lower sedimentation rates, and the ’basin shoal’ assemblage at former flats with low sedimentation rates. CANOCO was used to relate the TWINSPAN indicator species to a selection of environmental parameters. Sediment pH, water content, sand fraction, total polycyclic aromatic hydrocarbons (PAH) and current velocity explained 44% of the variance of the average abundance of the indicator taxa per site. Sediment firmness, indicated by sediment water content, and high ammonium concentrations probably were together responsible for the very low densities in the ’soft mud’ assemblage. Densities and biomasses in the other assemblages were low as well, except for theDreissena polymorpha habitat, where very high total zoobenthic biomass values (max. 55.8 g m−2) were observed. It is argued that sediment contamination has a considerable impact on macrozoobenthic densities and species composition in all assemblages, the ’basin shoal’ assemblage excepted.

Macrozoobenthic Assemblages of the Evros Delta (North Aegean Sea)

AbstractThe composition of the macrozoobenthic assemblages of the Evros Delta (North Aegean Sea) has been investigated by means of 4 replicate quantitative samples, collected at 35 sites. The information obtained from the numerical analysis of the faunal samples and the analysis of other data (values of the main physico‐chemical parameters) revealed the presence of a single community. The faunal composition of this community varies locally according mainly to the salinity and secondly to the particle size of the substrate. The community is described on the basis of its biological parameters and compared with corresponding assemblages from other areas.

Large-scale patterns of dynamics in subtidal macrozoobenthic assemblages in the Skagerrak: effects of a production-related factor?

Large-scale patterns of dynamics in subtidal macrozoobenthic assemblages in the Skagerrak: effects of a production-related factor?