The Manila clam, Ruditapes philippinarum, introduced in the Venice lagoons in 1983 and rapidly spread to the nearby coastal lagoons represents one of the most important commercially-exploited resources of this area. Abundance, size-class and biomass distribution of the wild population living in the Pialassa Baiona lagoon were assessed and related to the hydrological and sediment characteristics. Despite the lagoon being affected by eutrophication, chemical and thermal pollution, the clams were harvested by about thirty professional fishermen until 2003. The commercially available stock was estimated at 36.8 10 3 kg in July 2002, 29.3 10 3 kg in April 2003, and 10.3 10 3 kg in October 2003. Stock estimations and observed mortality were in good accordance with the fishermen data. The decline of the available stock could be due to both overfishing and the extraordinary summer heat wave occurred in 2003, which may have reduced larval recruitment and increased the mortality. Overall, the juvenile recruitment appeared insufficient to annually restore the natural stock. Although the national and regional high relevance of clams market, local harvesting of wild populations appeared marginal and inadequate to support a remunerative commercial activity, due to the variability and unpredictability of the annual yield and the lack of a sustainable management based on a production chain’s approach.

The Manila clam, Ruditapes philippinarum , introduced in the Venice lagoons in 1983 and rapidly spread to the nearby coastal lagoons represents one of the most important commercially-exploited resources of this area. Abundance, size-class and biomass distribution of the wild population living in the Pialassa Baiona lagoon were assessed and related to the hydrological and sediment characteristics. Despite the lagoon being affected by eutrophication, chemical and thermal pollution, the clams were harvested by about thirty professional fishermen until 2003. The commercially available stock was estimated at 36.8 10 3 kg in July 2002, 29.3 10 3 kg in April 2003, and 10.3 10 3 kg in October 2003. Stock estimations and observed mortality were in good accordance with the fishermen data. The decline of the available stock could be due to both overfishing and the extraordinary summer heat wave occurred in 2003, which may have reduced larval recruitment and increased the mortality. Overall, the juvenile recruitment appeared insufficient to annually restore the natural stock. Although the national and regional high relevance of clams market, local harvesting of wild populations appeared marginal and inadequate to support a remunerative commercial activity, due to the variability and unpredictability of the annual yield and the lack of a sustainable management based on a production chain’s approach. ISSN:

Sandy shores on the West coast of the North Adriatic Sea are extensively protected by different types of defence structures to prevent coastal erosion. Coastal defence schemes modify the hydrodynamic regime, the sediment structure and composition thus affecting the benthic assemblages. This study examines the effectiveness in detecting changes in soft bottom assemblages caused by coastal defence structures by using different levels of taxonomic resolution, polychaetes and/or bivalves as surrogates and different data transformations. A synoptic analyses of three datasets of subtidal benthic macrofauna used in studies aimed at assessing the impact of breakwaters along the North Adriatic coast has been done. Analyses of similarities and correlations between distance matrices were done using matrices with different levels of taxonomic resolution, and with polychaetes or bivalves data alone. Lentidium mediterraneum was the most abundant species in all datasets. Its abundance was not consistently related to the presence of defence structures. Moreover, distribution patterns of L. mediterraneum were masking the structure of the whole macrofaunal assemblages. Removal of L. mediterraneum from the datasets allowed the detection of changes in benthic assemblages due to coastal defences. Analyses on different levels of taxonomic resolution showed that the level of family maintained sufficient information to detect the impacts of coastal defence structures on benthic assemblages. Moreover, the outcomes depended on the transformation used. Patterns of distribution of bivalves, used as surrogates, showed low correlations with the patterns of the total macrofaunal species assemblages. Patterns of polychaetes, if identified to the species or genus level showed higher correlations with the whole dataset. However, the identification of polychaetes to species and genus level is as costly as the identification of all macrobenthic taxa at family level. This study provided additional evidences that taxonomic sufficiency is a useful tool in environmental monitoring, also in investigations on the impacts of coastal defence structures on subtidal macrofauna. The use of coarser taxonomic level, being time-efficient, would allow improving sampling designs of monitoring programs by increasing replication in space and time and by allowing long term monitoring studies.

Macrobenthic invertebrate assemblages were investigated monthly, from June 1998 to October 1999, at four sites in Valle Smarlacca pond, a north-western Adriatic coastal lagoon, in order to estimate secondary production exploitable for extensive fish aquaculture and to investigate the factors affecting this production. Benthic assemblages comprised 28 taxa, of which Hydrobia sp., Chironomus salinarius and Abra segmentum were the main contributors to both overall biomass and secondary production. Annual secondary production varied from 102.7gAFDMm−2y−1, in the unvegetated perimeter channel, to 152.6gAFDMm−2y−1 in the shallowest area where a Ruppia cirrhosa meadow was present. Multivariate correlations between environmental variables and the macrobenthic assemblage biomass highlighted the role of the water level, temperature, sediment organic carbon content and dissolved oxygen in the differentiation of the communities in the pond. Composition, biomass and secondary annual production of macrobenthic communities were dramatically affected by summer dystrophic crises. The isolation of this habitat limits the recovery of the invertebrate benthic assemblages. Only populations of two species, Hydrobia sp. and C. salinarius, seemed to be able to recover quickly after the dystrophic crises, which, in turn, could compromise the overall secondary production, with negative effects on the aquaculture activities. Water renewal and nutrient inputs should be regulated in this pond to reduce the risk of zoobenthic mass mortality and to ensure a sustainable extensive aquaculture based on natural primary and secondary production.

This study analysed the benthic compartment at Lido di Dante (Northern Adriatic Sea, Italy) within the frame of an integrated European project (DELOS), which aimed to identify, describe and quantify the effects of the Low Crested Structures (LCS) on the beach environment of many European coastlines. Both macrofaunal benthic communities and sediment characteristics were analysed in a sandy beach protected by a LCS parallel to the shoreline and laterally connected to land by two groynes, which have been responsible for changes of hydrodynamic patterns. A first survey (2001) focused on three exposure levels with respect to wave action. A higher species richness and a different community structure were found in the sheltered site as compared to the exposed and partially exposed sites. In addition, changes in sediment variables were found according to the exposure levels. A second survey (2002) assessed the combined effects of exposure and depth on both benthic communities and sediment variables. Our results suggest that both exposure and depth interact on measured biotic and abiotic variables. Species richness, community structure and size-classes distribution of the macrofauna, as well as the sediment composition, showed the greatest differences among the shallowest exposed zone and the deepest sheltered ones. On the contrary no difference at all occurred between the shallowest sheltered zone and the deepest exposed ones.

The impact of predation by juvenile marbled gobies,Pomatoschistus marmoratus, on the meiobenthic harpacticoid copepodCanuella perplexa was investigated at a subtidal station located in a shallow-water, brackish embayment of the Po River delta, northern Italy, in summer and fall 1978. In august, predation mainly centered on adults, with a very large number of prey for each predator; the energy supplied by the harpacticoid is high enough to sustain, almost entirely, the gobies’ daily energy requirement. The situation is different in September and October, when the adult copepod population declines dramatically and predation is shifted to less energy-providing copepodites and marbled gobies sensibly widen their prey spectrum.C. perplexa showed alterations of biological parameters, such as clutch size and average brood size, to cope with such a heavy predation pressure.

The nutrients released from the sea bottom through resuspension or diffusion may play an important role in determining the trophic state of aquatic environments. As well as quantifying the nutrients, it is important to recognize the factors and mechanisms which mostly subject their release and determine their extent. Direct measurements of NH 3 , PO 4 and SiO 2 fluxes were made by means of benthic chambers in the Sacca di Goro (a lagoon within the Po River Delta), as an obvious consequence of previous investigations into the processes of nutrient regeneration and release form the sea bottom in the coastal areas facing the Po River Delta

Over a period of about 3 years, 120 quantitative zooplankton samples were taken at five stations of the Valli of Comacchio, a wide shallow-water lagoon system of the north Adriatic Italian coast which has seasonally limited manregulated communications with the sea. The high density of the meroplanktonic forms and the prevalence of phytal copepods, mainly harpacticoids, over the typical euplanktonic ones, such as calanoids, are the main characteristics of the zooplankton assemblages of these lagoons. Acartia clausi, the only representative marine calanoid, was a passive immigrant in the valli. The zooplankton structure showed striking analogies with that of similar brackish environments lacking in free water exchanges with sea, e.g. the ‘dead’ Lagoon of Venice. Statistical analyses carried out on density data assessed significant differences between mean station densities of total zooplankton, polychaete trochophores and copepod nauplii. A significant year-station interaction variance for phytal harpacticoids was detected. The main source of variability of the zooplankton was represented by strong seasonal fluctuations of the various systematic groups which resulted in a fairly characteristic and recurrent pattern of their occurrence year by year.