ABSTRACT1. Transitional waters, described as critical transition zones because of their position at terrestrial, freshwater and marine interfaces, provide essential goods and services to the biosphere including human populations. These ecotones face increasing human influence mainly due to population density increase in coastal areas.2. Transitional water bodies have, to date, received little attention in the development of ecological status indicators; this is a critical deficiency when trying to meet the Water Framework Directive objective of all significant water bodies achieving good ecological status by the year 2015.3. In order to assess changes in transitional water communities many taxonomic-based indicators have already been proposed but there are a number of concerns for their use such as taxonomic classification difficulties, their unsuitability for multi-site comparisons and their inconsistent relationships with disturbance or stress.4. Alternative methods based on body size, abundance distribution among functional groups, functional diversity and productivity descriptors are proposed. These methods offer the opportunity to compare sites with different taxonomic compositions and allow derivation of indicators related to ecological status of communities under scrutiny.5. Finally, the suitability of these taxonomic-free descriptors to provide relevant information for each of the four main biotic compartments in coastal lagoons is discussed. The use of biomass distribution among functional groups for fish, benthos and macrophyte and to use body-size distribution for benthos and plankton is proposed.

ABSTRACT1. Transitional waters are ecotones between terrestrial, freshwater and marine ecosystems, being characterized by high spatial heterogeneity and temporal variability.2. The EU Water Framework Directive (WFD) posed to the scientific community the challenge to classify these ecosystems into a small number of types, while retaining a functional classification of ecosystem types.3. A niche theory approach is proposed to identify the limiting forcing factors organizing biological quality elements, i.e. the limiting niche dimensions.4. The analysis of a macro-invertebrate dataset from published papers on 36 Italian lagoons suggested a two-level typological classification of Mediterranean lagoons.5. Basic ecological theories, such as niche and island biogeography theories, have fundamental implications for the process of developing a typological classification for all aquatic ecosystems, as required by the WFD.

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2. The aim was to differentiate metric variation caused by human or natural processes and thereby to (1) select reliable metrics and (2) develop user-friendly protocols for cost-effective monitoring programmes for coastal lagoon water quality.3. Eight different sites dominated by macrophyte communities characterized by two angiosperms (Ruppia cirrhosa and R. maritima), two opportunistic macroalgae (Ulva sp. and Chaetomorpha linum), and Cyanobacteria colonies were quantitatively and destructively sampled twice.4. Structural metrics showed highest heterogeneity at a local site-specific scale, while functional metrics showed highest heterogeneity at the scale of habitat. As a result the structural metrics appeared inappropriate as indicators of lagoon water quality changes. By contrast shifts of habitat dominated by angiosperms to opportunistic macroalgae owing to nutrient excess, especially nitrogen, can be identified by functional metrics, especially with EEI.

ABSTRACT1. Leaf litter decomposition rates in aquatic ecosystems are known to be related to many abiotic and biotic factors.2. Field experiments were carried out during spring 2005 in 16 ecosystems, each with four sampling sites, using the litter bag technique to investigate the influence of abiotic factors on patterns of reed litter breakdown in different physiographic, hydrological and physico-chemical gradients occurring in transitional water ecosystems in the Eastern Mediterranean and Black Sea.3. Significant differences in leaf litter decomposition were observed among the studied ecosystems along univariate gradients of tidal range, water temperature, salinity and sinuosity index.4. Overall, 71% of variance in the litter breakdown rate was explained by the hydrological, physico-chemical and physiographic components. Specifically, tidal range, salinity and sinuosity index are among the key factors in the most commonly used typological schemes for classifying transitional water ecosystems (i.e. Confinement Concept and Venice System), due to their influence on abundance and distribution of benthic macroinvertebrates and other guilds.5. The patterns observed at the regional scale of the study suggest that certain key abiotic factors are likely to play a major role as drivers of plant detritus decomposition processes, through their influence on the overall metabolism of microorganisms and benthic macroinvertebrates.

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The selection of adequate descriptors of the ecological status in aquatic ecosystem is a major requirement for the implementation of monitoring tools. It requires an analysis of the stress-independent sources of variation of potential descriptors, which need to be taken into account in the definition of ecosystem Typology and Classification. Here, we investigate at what extent the surface area of lagoons accounted for species richness of communities and body size abundance components. To this aim, the speciesarea and body size-area patterns of benthic macroinvertebrates were investigated in Italian lagoons. The analysis was based on a literature survey carried out considering a 30-year period from 1975 to 2004. Overall, 168 papers were selected, reporting taxonomic lists of benthic macro-invertebrates for 26 Italian lagoons, whose surface area ranged from few hectares to some hundreds of square kilometres. The analysis of published taxonomic lists recorded 1,055 taxa, belonging to 13 phyla, 106 orders and 351 families. Measures of standard body size for each of the 1,055 taxa were also obtained from published data as standard individual body length. Significant species-area relationships were observed at each level of taxonomic resolution considered, within dominant phyla (i.e. Arthropoda and Mollusca). Slopes of the power regressions were in the range of 0.11-0.24, increasing consistently with taxonomic resolution. Significant relationships were also observed by comparing the upper limit of the body size spectra to the surface area of the considered lagoons. Maximum body size-area relationships were described by power regressions with slopes in the range of 0.10-0.28. The observed species-area relationships underline the importance of physiographic characteristics of transitional water ecosystems in the identification of transitional water types, as required by the WFD. Moreover, the scaling of average taxonomic richness with lagoon surface, could also represent a standardisation tool for classifying the ecological status of transitional ecosystems. Finally, the patterns of body size area relationships would also have an important application to the field of monitoring transitional ecosystem health.

1. The extent to which conservation of biodiversity enforces the protection of ecosystem functioning, goods and services is a key issue in conservation ecology.2. In order to address this conservation issue, this work focused on community organization, linking community structure, as described both in taxonomic and functional terms, to community functioning and ecosystem processes.3. Body size is an individual functional trait that is deterministically related to components of ecosystem functioning such as population dynamics and energy flow, and which determines components of community structure. Since body size is an individual trait that reflects numerous factors, it is also exposed to trait selection and the niche filtering underlying the community.4. An analysis of the relevance of body size to community organization in transitional water ecosystems in the eastern Mediterranean and Black Sea regions is presented, based on field research conducted on a sample of 15 transitional water ecosystems.5. 250 taxa were identified, clumped in five orders of magnitude of body size. All body size patterns showed triangular distributions with an optimal size range of 0.13 mg to 1.0 mg individual body mass.6. Deterministic components of size structure were emphasized and a hierarchical organization with dominance of large sizes was demonstrated by the slopes of the body size-abundance distributions, consistently larger than the EER threshold (b=À0.75), and by the direct relationship of energy use to body size for most of the body size range.7. Consistent variations of body size-related descriptors were observed on three main gradients of environmental stress: eutrophication, confinement and metal pollution. 8. The results support the relevance of constraints imposed by individual body size on community organization in transitional water ecosystems and the adequacy of size patterns as an indicator for ecological conservation of these fragile ecosystems.