The invasive alien mytilid species, Brachidontes pharaonis, forms a biogenic habitat in the mediolittoral and upper-infralittoral zones of the Levantine Sea, hosting a number of alien and native species. Examinations of samples taken from dense, continuous mussel beds at seven stations along the coast of northern Levantine Sea yielded 187 macro-benthic invertebrate species belonging to 11 taxonomic groups. Polychaeta accounted for 46% and 37% of the total number of species and individuals, respectively. The top three dominant species in the mussel beds were Stenothoe gallensis, Spirobranchus kraussi and Mytilaster minimus. The species with the highest frequency values on the mussel beds were Pseudonereis anomala, Phascolosoma stephensoni and Elasmopus pocillimanus. The highest density and biomass of the associated fauna were estimated as 42,550 ind m−2 and 1503 wwt g m−2, respectively. The species number in samples varied between 14 and 47 species. The environmental variables best explaining variations in zoobenthic community structures were salinity, dissolved oxygen and total inorganic nitrogen in the water column. The biotic indices, TUBI and ALEX, classified the ecological status of one or two stations as moderate or poor, based on the relative abundances of ecological and zoogeographic groups, respectively. A total of 21 alien species were found to be associated with the mussel bed, of which Syllis ergeni is being newly considered as a new established alien species for the Mediterranean Sea. The maximum density of associated alien species was calculated as 30,300 ind m−2. The alien species assemblages were greatly affected by salinity and total inorganic nitrogen.

The lagoon of El Bibane (Tunisia) is a Mediterranean coastal area that is affected by an increasing human impact. Thus, an estimation of its biodiversity and an ecological quality assessment are very urgent. This study investigates the meiofaunal and nematode communities of the El Bibane lagoon both from a taxonomic and a functional point of view. Nematodes were the dominant group as is common in brackish water systems. The nematode community was made up of 62 genera in 22 families. Xyalidae, Chromadoridae and Cyatholaimidae were the richest and most abundant families. The taxonomic composition and biodiversity of nematodes were comparable to those found in other European and Mediterranean transitional areas. Both meiofauna and nematodes showed a clear subdivision between marginal and central areas. The central stations, represented by fine sediments and higher amounts of organic carbon, seemed to be characterized by low meiofaunal densities, nematode diversity and a strong dominance of 1B and 2B trophic guilds. These trends could be related not only to the grain size and organic load, but also to a possible influence of tidal currents that can transport pollutants in the central area of the lagoon coming from the adjacent coastal areas. Shannon diversity and life strategies are not always in agreement in defining the ecological quality, but an overall worse ecological quality was detected especially at S6. The results of this study are an important starting point for the future monitoring of the potential and actual human impact on the El Bibane area over time.

Spatial variation in the structure of macrobenthic assemblages on intertidal flats is known to be related to different environmental variables. Most of the studies have observed that along the estuarine gradient, salinity is the most important variable driving the patterns of the macrobenthic assemblages. However, the great majority of studies have been done on single estuarine systems in temperate regions. We investigated the relationship between the macrobenthic assemblages in intertidal habitats and the environmental variables along three tropical estuaries. From lower to upper estuarine regions we sampled benthic macrofauna, salinity and sediments. The structure of the benthic assemblages was primarily related to salinity. There was a decrease in the number of taxa from the upper to the lower estuarine regions, indicating important deviation from Remane's model of estuarine diversity. There were important similarities of taxa abundance along different estuarine salinity gradients which can be properly tested in other tropical and temperate regions. We advocate that in order to adopt general and robust management practices it is essential to identify broad patterns and general rules governing estuarine systems.

The hypothesis tested in this study is that changes in benthic ecosystem components interrelationships may mirror the degree of environmental stress in the Mediterranean coastal lagoons. Multivariate matrices deriving from four benthic components (macrophytes, zoobenthos, epibenthic decapods and demersal fish) from four lagoonal stations along a well-defined disturbance gradient were compared by means of second-stage non-metric multidimensional scaling (MDS). The resulting inter-matrix distances were used as a proxy for the identification of the degree of disturbance. The approach followed is novel in that it uses information from higher levels of the biological organization by taking into account more than a single benthic component, thus representing broad categories of functional groups. The second-stage MDS plots depict differences between inter-component distances in the sampling stations according to the degree of disturbance they experience and the BIOENV analysis demonstrates that certain components are correlated with the environmental variables at a higher degree in the most disturbed stations.

A checklist of 53 soft-bottom species of polychaetes from the coastal lagoon Estero de Urías is presented here. Depth, sediment temperature, salinity, grain size, organic matter content, and dissolved oxygen ranges where polychaete species were found are provided. Twenty-six species are reported for the first time for the Estero de Urías coastal lagoon. This is the first report of the sabellid Amphicorina gracilis, the spionid Marenzelleria viridis, and the syllid Exogone (Parexogone) molesta for the Pacific coast of Mexico.

Une campagne de prélèvements réalisée en 1999, de façon comparable à celle effectuée en 1994, montre que la compositiondes communautés d'oligochètes et de Chironomidés a changé dans cet intervalle de temps en réponse à la baisse des concentrationsen phosphore dans l'eau du Petit Lac, le bassin ouest du Léman (Suisse et France). Les larves de Chironomidés étaient présentesdans 66 % des 159 sites visités en 1999 contre 40 % en 1994 tandis que l'abondance des oligochètes a diminué. De plus,l'abondance relative des taxons indicateurs de conditions oligotrophes (Micropsectra et Spirosperma velutinus) a augmenté en1999. Ces changements indiquent qu'en 1999 la restauration biologique des sédiments profonds se trouve à mi-chemin entrel'état méso-eutrophe des environs de 1980 et l'état oligotrophe d'avant 1950. Cependant, l'ampleur de la restauration n'est pas lamême dans les trois bassins du Petit Lac: elle varie en fonction de l'intensité de la sédimentation organique.

A new corer is described which may be used in sediments of shallow standing waters, such as in rice fields, and which facilitatesthe study of the vertical distribution of the invertebrate fauna at 2 cm depth intervals. Its small surface area permits quantitativesampling of the sediment-dwelling fauna, particularly the chironomid larvae, around the roots of rice-plants. Results arepresented and the efficiency of the sampling method is discussed.