Pier Francesco Ghetti

Benthic macrofauna changes in areas of Venice lagoon populated by seagrasses or seaweeds

Two areas of the Venice lagoon populated by seagrasses (three stations covered by Cymodocea nodosa (Ucria) Asherson, Zostera marina Linnaeus, Zostera noltii Hornemann) or seaweeds (two stations: one covered by Ulva rigida C. Agardh and another at present without seaweed biomass) were monitored by means of six surveys over a year in order to study macrofaunal composition and seasonal changes. The seagrass stations showed a mean species richness (28-30 S m(-2)), individual abundance (1854-4018 N m(-2)) and biomass (22.3-37.7 g m(-2) ash-free-dry-weight, AFDW) ca. 3-8 times higher than those populated by seaweeds (10-15 S m(-2), 494-1395 N m(-2) and 5.6-13.7 g m(-2) AFDW). Differences among seagrass or seaweed stations were much lower. The Ulva-dominated station showed a macrofauna completely different both from the other stations and the communities recorded ca. 30 years ago, before the prolific growth of Ulva. In this station, frequent biomass decompositions and anoxic crises created critical conditions for life favouring organisms with reduced life cycles, younger individuals and the epifaunal species instead of the infaunal ones. In particular, Ulva grazers and scrapers such as Gammarus aequicauda Stock and Gibbula adriatica Philippi were found to be by far the most abundant species, whereas the taxa characteristic of the associations found in the past, in the presence of seagrasses or seaweeds and typical of low eutrophicated environments, appear strongly reduced. Marked differences in the macrophyte dominance and in the bio-physico-chemical variables which characterise the main environmental conditions of the Venice lagoon support the different distribution and composition of macrofaunal communities. Seaweed stations appear mainly governed by the seasonal cycles of these un-rooted macrophytes which, by alternating periods of production and decomposition, are responsible for the drastic reduction of macrofauna biodiversity and biomass. Conversely, seagrass stations exhibit a better oxidisation of the environment and show conditions more favourable for macrofauna colonisation, especially in the presence of macrophytes which are characterised by very well developed below-ground systems such as Cymodocea nodosa.

Temporal and spatial changes of macroalgae and phytoplankton in a Mediterranean coastal area: the Venice lagoon as a case study.

Since the late 1980s the lagoon of Venice, a shallow Mediterranean coastal area, has experienced strong environmental changes. Macroalgae, which were the predominant primary producers of the lagoon, reduced markedly, but neither phytoplankton nor seagrasses replaced them. Temporal and spatial changes in macroalgal standing crop (SC) and phytoplankton concentration were investigated between 1987 and 1998. Maps of macroalgal SC show a marked declining trend. Biomass in fresh weight decreased from: 558 ktonnes in 1987, to 85 ktonnes in 1993 and to 8.7 ktonnes in 1998. As a whole, the biomass in 1998 was only 1.6% of the biomass recorded in 1987. Similarly the macroalgal net (NPP) and gross (GPP) primary production decreased from ca. 1502 and 9721 ktonnes year(-1) to ca. 44 and 229 ktonnes year(-1), respectively. In the early 1990s the clam Tapes philippinarum Adams & Reeve and seagrasses, especially Zostera marina Linnaeus, colonised the bottoms free of macroalgae, but the development of intense clam-fishing activities prevented both phytoplankton blooms and seagrass spreading. Maps of chlorophyll a drawn according to data collected in parallel to macroalgal standing crop show unchanged concentrations. Macroalgae changes are enhanced by comparing annual trends in four areas of the central lagoon during 1989-1992 and 1998-1999. In those areas phytoplankton also decreased significantly. Marked changes of some environmental variables strongly associated with the primary production were recorded both during the lagoon mapping and in the areas studied on a yearly basis.

Sediment toxicity measured using Vibrio Fischeri as related to the concentrations of organic (PCBs, PAHs) and Inorganic (metals, sulphur) pollutants

Sediments of the inner canals of the city of Venice (Italy) contain heavy metals and organic contaminants. In order to assess the toxicity of these compounds the Microtox® test was applied to the whole sediment (solid-phase test) and to organic extracts containing separated classes of compounds (i. e. PCBs and PAHs). This study showed that results of solid-phase tests may be correctly interpreted only if supported by results obtained with tests on extracts, An efficient of sulfur and Fe was measured with solid-phase tests of sediments, while an EC50 value for PAHs was detected in tests with organic extracts. The sediment concentrations of heavy metals and PCBs resulted lower than the sensitivity limits of Microtox® test for these compounds.

Validation of the Macrophyte Quality Index (MaQI) set up to assess the ecological status of Italian marine transitional environments.

The paper couples the results obtained by applying the expert and the rapid Macrophyte Quality Indices set up to assess the ecological status of the Italian transitional environments according to the requirements by the Water Framework Directive (2000/60/CE). The indices were validated by comparing the composition of the macrophyte assemblages and the values of some bio-physico-chemical parameters of the water column of 20 stations of the Venice lagoon sampled monthly for one year between 2003 and 2005. In 5 stations out of the 20, the ones which fall within the 5 classes of ecological status suggested by the Water Framework Directive, sedimentation rates, sediment grain-size, and nutrient and pollutant (metals, Polychloro-Dibenzo-Dioxins/Furans, Polycyclic Aromatic Hydrocarbons, Pesticides and Polychlorinated Biphenils) concentrations in surface sediments were also determined. Results showed strong relationships between the trends of these environmental parameters and the composition and structure of macrophyte associations, as well as with the Macrophyte Quality Index assessment. Chlorophyceae showed a trend opposite to Rhodophyceae whose presence was concentrated in oxygenated and transparent environments. Chlorophyceae and the species characterised by low scores prevailed in turbid areas where nutrient and pollutant concentrations were high. Results allowed the identification of the conditions of the “reference sites” (confinement areas and sites with high water renewal) and the integration of the dichotomic key used for the application of the R-MaQI.

An integrated approach to sediment quality assessment: The Venetian lagoon as a case study

Abstract Recent research trends in sediment quality assessment have demonstrated the need for an integrated approach which combines chemical characterisation with biological effects evaluation, both in the laboratory (toxicity bioassays) and in situ (macrobenthic community structure investigations). The Sediment Quality Triad organises these three aspects of sediment quality assessment in a single approach, where each component is complementary to the others. Considering the lack of previous studies, this preliminary work aimed to verify the potential of an integrated approach in a complex ecosystem, the Venetian lagoon. Five sampling stations along a presumed quality gradient were chosen. The chemical analyses of heavy metals and organic pollutants have been compared with the results of the toxicity bioassays (Microtox ® solid phase, saline extracts and pore water, and sea urchin Paracentrotus lividus sperm cell bioassay performed with saline extracts) and with the characterisation of the infaunal community structure. The results of this first application pointed out the complementarity of the three approaches and the ability of the integrated approach in discriminating different levels of environmental stress. Nevertheless, deeper investigations both on the response of the macrobenthic community to natural variability and on the environmental toxicity of several sulphur compounds (i.e. elemental sulphur) will be necessary.

Rapid Quality Index (R-MaQI), based mainly on macrophyte associations, to assess the ecological status of Mediterranean transitional environments

A rapid index for the quality status assessment of Mediterranean transitional environments is proposed. It is based on the study of macrophyte associations (macroalgae and seagrasses) and the gross determination of some environmental parameters. The index was set up in 19 sampling sites of the Venice lagoon monitored during one year on a monthly basis taking into account the flora, the main contaminants and some other variables indicating the presence of gradients of stress conditions. Results were compared and intercalibrated with measurements carried out in Sacca di Goro, placed in Po delta, and in Lesina and Orbetello lagoons.

Sea Urchin Toxicity Bioassays for Sediment Quality Assessment in the Lagoon of Venice (Italy)

This paper focuses on the evaluation of two sea urchin bioassays (spenn cell and embryo toxicity) using the Paracentrotus lividus, as possible methods for quality assessment and monitoring of estuarine and lagoonal environments. Some queries allow us to describe the reasons which led us to carry out this research. A step-wise method adopted to own reliable and robust techniques based on a QA/QC (Quality Assurance/Quality Control) procedure is briefly illustrated. The suitability of bioassays to assess lagoonal sediments quality was then tested by their application at sites in the Lagoon of Venice characterized by differing kinds and levels of pollution. Elutriates were chosen to assess the potential effects of pollutants which are made available in the water column as a consequence of sediment resuspension (dredging, fishing gear, etc). Both tests were effective in discriminating several different pollution/bioavailability situations, although their combined use showed higher efficacy in discriminating among stations and periods. Embryotoxicity was higher than spenniotoxicity in almost all stations, as expected. Toxicological responses generally fitted contamination levels to a satisfactory extent.

Sulfide as a confounding factor in toxicity tests with the sea urchin Paracentrotus lividus: Comparisons with chemical analysis data

Sperm cell and embryo toxicity tests with the sea urchin Paracentrotus lividus were performed to assess the toxicity of sulfide, which is considered a confounding factor in toxicity tests. For improved information on the sensitivity of these methods to sulfide, experiments were performed in the same aerobic conditions used for testing environmental samples, with sulfide concentrations being monitored at the same time by cathodic stripping voltammetry. New toxicity data for sulfide expressed as median effective concentration (EC50) and no-observed-effect concentration (NOEC) are reported. The EC50 value for the embryo toxicity test (total sulfide at 0.43 mg/L) was three times lower than for the sperm cell test (total sulfide at 1.20 mg/L), and the NOEC values were similar (on the order of total sulfide at 10(-1) mg/L) for both tests. The decrease in sulfide concentration during the bioassay as a consequence of possible oxidation of sulfide by dissolved oxygen was determined by voltammetric analysis, indicating a half-life of about 50 min in the presence of gametes. To check the influence of sulfide concentrations on toxicity effects in real samples, toxicity (with the sperm cell toxicity test) and chemical analyses also were performed in pore-water samples collected with an in situ sampler in sediments of the Lagoon of Venice (Italy). A highly positive correlation between increased acute toxicity and increased sulfide concentration was found. Examination of data revealed that sulfide is a real confounding factor in toxicity testing in anoxic environmental samples containing concentrations above the sensitivity limit of the method.

Separation and quantification of organic micropollutants (PAH, PCB) in sediments. Toxicity of extracts towards vibrio fisheri

Vibrio fisheri test has been used to evaluate the toxicity of contaminated sediment of the Venice lagoon. The following classes of organic microcontaminants were considered in this study: aliphatic hydrocarbons (AHs), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs) and chlorinated pesticides. Contaminants were extracted from samples with n‐hexane/dichloromethane in a sonication bath. Extracts were then purified and fractionated with column chromatography. A solvent exchange into ethanol was made before testing, to reduce toxicity. Preliminary tests were performed to set up the procedure to apply Vibrio fisheri to organic extracts. The application of the test with organic extracts was made at different steps of clean‐up and fractionation into classes of compounds. The purpose of the study was to set up a procedure to comparatively assess sediment contamination with chemical analyses and toxicity bioassays.

H. diversicolor, N. succinea and P. cultrifera (Polychaeta: Nereididae) as bioaccumulators of cadmium and zinc from sediments: Preliminary results in the Venetian lagoon (Italy)

A field investigation was performed to evaluate the suitability of three nereid polychaetes species as biomonitors for sediment contamination by Cd and Zn in the Venetian lagoon (Italy). With regard to the treatment and subsequent chemical analysis of the animals, a specific methodology was set up. Metal concentrations in sediments and tissues were compared for 20 stations. Cd bioaccumulation was detected in all species, although bioaccumulation factors and the concentration trends were different. This finding could be explained by a difference in the metal bioavailability or in the accumulation strategy of species. Zn results have confirmed the presence of a regulation strategy in the nereid polychaetes, as previously reported.