In the present study, we investigated the applicability of the Pearson-Rosenberg (P-R) conceptual model describing a generalized pattern of response of benthic communities in relation to organic 25 enrichment to a specific typology of marine systems, i.e. coastal lagoons. The study was performed with independent matching data on the structure of macrobenthic communities and total organic carbon (TOC) content of sediments obtained from 349 stations representing three of the most ecologically and economically relevant coastal lagoons in the Mediterranean Sea, i.e. the lagoons of Cabras, Orbetello, and Venice (Italy). Consistent with P-R model predictions, we 30 found two different peaks in benthic diversity and abundance at low (> 2.5-5 mg g -1 ) and high (> 25-30 mg g -1 ) TOC ranges, respectively. We identified TOC thresholds indicating that risks of reduced benthic diversity from organic loading and other associated stressors in sediments should be relatively low at TOC values < about 10 mg g -1 , high at TOC values > about 28 mg g -1 , andintermediate at values in-between. Predictive ability within these ranges was high based on 35 results of re-sampling simulation. Our results validate and support a prior independent study that identified similar TOC thresholds for assessing risks of benthic impacts in samples from seven coastal regions of the world. While not a measure of causality, it is anticipated that these TOC thresholds should serve as a general screening-level indicator for evaluating the likelihood of reduced sediment quality and associated bioeffects in such eutrophic systems of the 40 Mediterranean Sea, which also are exposed to a variety of stressors from multiple human uses.

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Toxic hazard in sites with varying types and levels of contamination in the Lagoon of Venice was estimated by means of toxicity bioassays based on the early life-stages of the autochthonous sea urchin Paracentrotus lividus. Elutriate was chosen as the test matrix, due to its ability to highlight potential toxic effects towards sensitive biological components of the water column caused by sediment resuspension phenomena affecting the Lagoon. Surficial sediments (core-top 5 cm deep), directly influenced by resuspension/redeposition processes, and core sediments (core 20 cm deep), recording time-mediated contamination, were sampled in some sites located in the lagoonal area most greatly influenced by anthropogenic activities. Particle size, organic matter and water content were also analysed. In two sites, the results of physical parameters showed that the core-top sediments were coarser than the 20-cm core sediments. Sperm cell toxicity test results showed the negligible acute toxicity of elutriates from all investigated sites. The embryo toxicity test demonstrated a short-term chronic toxicity gradient for elutriates from the 20-cm core sediments, in general agreement both with the expected contamination gradient and with results of the MicrotoxR solid-phase test. Elutriates of the core-top 5-cm sediments revealed a totally inverted gradient, in comparison with that for the 20-cm core sediments, and the presence of a ''hot spot'' of contamination in the site chosen as a possible reference. Investigations on ammonia and sulphides as possible confounding factors excluded their contribution to this ''hot spot''. Integrated physico-chemical and toxicity results on sediments at various depths demonstrated the presence of disturbed sediments in the central basin of the Lagoon of Venice.

Five published indirect methods to estimate benthic secondary production of intertidal mudflats and a new proposed formulation based on quarter-power allometric scaling and the ''Universal Temperature Dependence'' of biological processes (UTD) were compared. For this purpose, a dataset consisting of an annual series of samples, taken from the Lagoon of Venice from March 1996 to March 1997, at sites characterised by different seagrass coverage was used. All methods resulted in that biomass and secondary production decreased progressively when moving from the seagrass meadow toward areas of unvegetated substrate, suggesting an influence of the available marine phanerogams on the neighbouring sites. The equation proposed in this paper gives results comparable with those obtained using empirical regression models from literature. The main conclusion from this study is that general equations proposed by the ''metabolic theory of ecology'' can be applied for indirect estimations of secondary production of benthic communities.

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