Chiara Facca

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.

Distribution and production of macrophytes and phytoplankton in the lagoon of Venice: comparison of actual and past situation

This paper aims at comparing inedited maps of macrophytes and phytoplankton distribution in the lagoon of Venice in 1980 and 2003. The macrophyte distribution is displayed with reference to different biomass intervals which allow the calculation of the occupied surface, standing crop (SC), net (NPP) and gross (GPP) production. In 1980 the total macroalgal SC was ca. 841 ktonnes whereas the annual NPP and GPP were estimated to be ca. 2912 and 18498 ktonnes, respectively. In 2003 macroalgae displayed a marked regression and the SC, NPP and GPP decreased to ca. 89, 471 and 2336 ktonnes. Maps of the seagrass distribution date back to 1990 but their biomass and production have been quantified only in 2003. On the whole, in 2003, on a surface of ca. 56 km2 the three species living in the lagoon accounted for a SC and a NPP of ca. 209 and 821 ktonnes, whereas the GPP estimated according to literature was about twice as high as the NPP. Cymodocea nodosa was the most abundant phanerogam in the lagoon. Its SC was higher than the total of the macroalgae, although the latter were more productive. Zostera marina covered the highest surface in the lagoon but its biomass and production were a little lower than that of C. nodosa. Nanozostera noltii, which was common and widespread in the past, displayed an evident regression trend which was mainly due to the increase of the water turbidity and the disruptions of its habitat. Similarly, phytoplankton, underwent a descending trend, although data quoted in the present paper display its distribution only in the summer period.

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.

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.

Temporal and Spatial Distribution of Diatoms in the Surface Sediments of the Venice Lagoon

Abstract The aim of this paper was to improve the knowledge of the primary producers living in the Venice Lagoon by studying the composition and the distribution of the benthic diatom communities populating subtidal surface sediments. The upper 5mm of sediment from four areas distributed between the Malamocco inlet and the mainland north of Venice were collected and analysed. Sampling was carried out monthly for one year (1998–99). Species composition, cell abundance and carbon content were determined by light microscopy after separation of cells from the sediment particles using hydrogen peroxide. A total of 147 taxa were identified, mostly pennate diatoms (Bacillariales) belonging to the genera Amphora, Cocconeis, Navicula, Nitzschia and Pleurosigma. Cell abundance ranged from 0.7 x 106 cells cm−3, near the Malamocco inlet (Station A), to 10.46 106 cells cm−3 near the mainland (Station C). Diatom carbon content was between 28 and 380 μg cm−3. Seasonal trends were slight, except at Stations D and C where the lowest abundance was found in October–November and the highest one in summer. Significant relationships between benthic diatoms and macrophyte biomass, sediment grain size, underwater light transmission, sediment fluxes and the salinity gradient were found.

Trophic Conditions in the Waters of the Venice Lagoon (Northern Adriatic Sea, Italy)

Data on nutrient concentrations and environmental parameters, recorded in the waters of the entire Venice lagoon (165 sites) in July 2003 and in two stations monthly sampled for two years (from April 1994 to March 1995 and from January to December 2005), are reported in order to compare the trophic conditions with the past situation. In summer 2003 the dissolved inorganic nitrogen varied between 0.66 and 41.2 µM, whereas the reactive phosphorus fluctuated between 0.01 and 1.75 µM. Values above the imperative values (nitrogen >25 µM, phosphorus >0.81 µM) established by the Italian law were not rare and they were found close to the mainland and the main river outflows. The comparison with previous data to update the knowledge on the trophic conditions of the lagoon showed that the overall trophic load is reducing. Only nitrate concentrations did not change. The seasonal samples allowed to confirm the above observations highlighting the behaviour of nutrients in relation to the weather conditions and to the primary producer fluctuations.

Linking food web functioning and habitat diversity for an ecosystem based management : a Mediterranean lagoon case-study

We propose a modelling approach relating the functioning of a transitional ecosystem with the spatial extension of its habitats. A test case is presented for the lagoon of Venice, discussing the results in the context of the application of current EU directives. The effects on food web functioning due to changes related to manageable and unmanageable drivers were investigated. The modelling procedure involved the use of steady-state food web models and network analysis, respectively applied to estimate the fluxes of energy associated with trophic interactions, and to compute indices of food web functioning. On the long term (hundred years) temporal scale, the model indicated that the expected loss of salt marshes will produce further changes at the system level, with a lagoon showing a decrease in the energy processing efficiency. On the short term scale, simulation results indicated that fishery management accompanied by seagrass restoration measures would produce a slight transition towards a more healthy system, with higher energy cycling, and maintaining a good balance between processing efficiency and resilience. Scenarios presented suggest that the effectiveness of short term management strategies can be better evaluated when contextualized in the long term trends of evolution of a system. We also remark the need for further studying the relationship between habitat diversity and indicators of food web functioning.

Interannual heavy element and nutrient concentration trends in the top sediments of Venice Lagoon (Italy)

The elemental composition of surficial sediments of Venice Lagoon (Italy) in 1987, 1993, 1998 and 2003 were investigated. Zn and Cr concentrations resulted in higher than background levels, but only Cd and Hg were higher than legal quality standards (Italian Decree 2010/260 and Water Framework Directive 2000/60/EC). Contaminants with similar spatial distribution are sorted into three groups by means of correlation analysis: (i) As, Co, Cd, Cu, Fe, Pb, Zn; (ii) Ni, Cr; (iii) Hg. Interannual concentrations are compared by applying a factor analysis to the matrix of differences between subsequent samplings. A general decrease of heavy metal levels is observed from 1987 to 1993, whereas particularly high concentrations of Ni and Cr are recorded in 1998 as a consequence of intense clam fishing, subsequently mitigated by better prevention of illegal harvesting. Due to the major role played by anthropogenic sediment resuspension, bathymetric variations are also considered.

Natural recovery and planned intervention in coastal wetlands: Venice Lagoon (northern Adriatic Sea, Italy) as a case study.

The goals of conservation and sustainable use of environmental ecosystems have increased the need for detailed knowledge of ecological evolution and responses to both anthropogenic pressures and recovery measures. The present study shows the effects of natural processes and planned intervention in terms of reducing nutrient inputs in a highly exploited coastal lagoon, describing its evolution over a 16-year period from the late 1980s (when eutrophication was at its peak) until 2003. Changes in nutrient and carbon concentrations in the top layer of sediments were investigated in parallel with macroalgal and seagrass biomass in the most anthropized basin of Venice Lagoon in four surveys conducted in accordance with the same protocols in 1987, 1993, 1998, and 2003. A pronounced reduction in trophic state (mainly total nitrogen, organic phosphorus, and organic carbon concentrations) and macroalgal biomass was recorded, together with the progressive expansion of seagrass meadows. General considerations are also made on the effects of Manila clam farming and the shift from illegal to managed clam farming.

Diatom quantification and their distribution with salinity brines in coastal sediments of Terra Nova Bay (Antarctica).

Benthic diatoms represent an important element of global nutritional productivity; to raise attention on their role, which is often neglected due to analytical difficulties, surface (1 cm top layer) coastal sediments from Gerlache inlet to Penguin Bay at Terra Nova Bay were collected and stored at -20 °C. DNA amplification by real-time PCR, based on diatom-specific oligonucleotide primers designed on small-subunit rRNA (SSU rRNA), was performed in addition to diatom conventional cell counting and spectrophotometric determination of photo-pigments. Moreover, cations and anions were determined in sediments with the aim to identify factors involved in the control of diatom abundance. Diatom distribution was found quite heterogeneous displaying significant differences from site to site. The salinity in sediments ranged from 45.1 at Gerlache inlet to 76.2 at Penguin Bay and it was correlated with cell abundance, biodiversity, amount of pigments and amplified DNA. The dominant species, Fragilariopsis curta, was associated to sediment salinity brines.