Mara Marzocchi

Distribution of introduced Japanese macroalgae Undaria pinnatifida, Sargassum muticum (Phaeophyta) and Antithamnion Pectinatum (Rhodophyta) in the Lagoon of Venice

The present distribution of invasive seaweeds Undaria pinnatifida (Phaeophyta, Laminariales) and Sargassum muticum (Phaeophyta, Fucales) in the Lagoon of Venice is updated in this work. The distribution of Antithamnion pectinatum (Rhodophyta, Ceramiales) is presented for the first time. All these species have quickly colonized the hard substrata competing with indigenous species. Competition acts differently in the two species, U. pinnatifida competing for the substratum and S. muticum for light. On tidal flats composed of silt and sand, the growth of two brown seaweeds is restricted owing to the lack of a solid substrata. While Undaria pinnatifida and Sargassum muticum have colonized only some areas of the lagoon in a short vertical range (from 0 to -3 m), Antithamnion pectinatum is present on the three portmouths, along the inner shores of the city of Venice, and in the lagoon islands with extensive vertical distribution (from +0.2 to -8 m).

The introduced alga Undaria pinnatifida (Laminariales, Alariaceae) in the lagoon of Venice

Since its appearance in 1992 in the lagoon of Venice, the brown algae Undaria pinnatifida (kelp) has gradually expanded along the banks of canals both at Chioggia and Venice, becoming the dominant species in the local algal community chiefly from February to July. In Chioggia Island, where another brown seaweed (Sargassum muticum) is present since 1992, the spreading of Undaria reaches a plateau. In Venice Island, instead, the colonisation process is still in progress. During 1999, the kelp has colonised the main canals (e.g. The Grand Canal) and, subsequently, the small inner ones. In order to evaluate the dynamics of substrate re-colonisation by Undaria, two mechanical eradications were carried out during (March) and after the fertile period (July) of the algae. Such experimental manipulations provided evidence of the fast re-colonisation potential of the algae mainly attributable to its efficient reproductive system. Eradication made during the fertile period, in fact, permitted the kelp development during the following year, while re-colonisation has started 2 years later where eradication was performed after the reproductive period. A significant decrease in the surface covered by other species has been observed both in shallow (Ulva rigida, Enteromorpha spp., Antithamnion pectinatum, Chondracanthus acicularis) and deeper areas (Rhodymenia ardissonei) during the period of maximum development of U. pinnatifida. On the basis of the results of this study, the following conclusions can be drawn: (1) the alga U. pinnatifida is continuously expanding in lagoon environments of Venice; (2) in order to limit its spreading, mechanical eradications would be done on a large spatial scale and before the zoospores release; (3) there is suggestive evidence of competition between Undaria and the remaining indigenous algae.

Seasonal pattern of Cymodocea nodosa biomass and production in the lagoon of Venice

Abstract Primary production and the biomass cycle of a shallow Cymodocea nodosa (Ucria) Ascherson meadow in the lagoon of Venice (Italy-Northern Adriatic) were measured from February 1993 to February 1994. Leaf growth was estimated by the Zieman method; rhizome production was estimated by marking rhizome terminals. All data showed a clear seasonality. In general, maximum growth was reached in July. Leaf production (a maximum of 12.3 g dry weight m−2 day−1 in July) and leaf biomass (a maximum of 810 g dry weight m−2) were much higher than in other Mediterranean localities. Cymodocea nodosa contributes significantly in stabilizing lagoon bottom sediments. The percentage of the belowground fraction of total biomass varied from 85% in winter to 58% in summer, and maximum shoot density was 2302 shoots m−2.

Sexual reproduction of Zostera noltii Hornemann in the lagoon of Venice (Italy, north Adriatic)

Abstract Flowering of Zostera noltii Hornemann in Venice lagoon (Italy, north Adriatic) has been observed in 1993 and 1994, from May to October. Measurements at three stations at different depth included vegetative and generative shoot density, number of spathes per generative shoot, length of spathes, numbers of male and female flowers and seed size.

Dinamica dei sistemi a Cymodocea nodosa, Zostera marina e Zostera noltii nel Mediterraneo

Abstract Data on geographical and depth distribution, sediment granulometry, salinity, biomass variability, below/aboveground biomass ratio, and reproductive strategies of seagrass communities in the Mediterranean Sea were analysed to describe their dynamics patterns. Notwithstanding their different latitudinal distribution, they have a similar seasonal biomass variability, deriving both from extrinsic forcing (e.g. light and temperature) and intrinsic species-specific components (e.g. reproduction pattern), these latter being responsible for their different structure and seasonal dynamics.

Metals in Undaria pinnatifida (Harvey) Suringar and Sargassum muticum (Yendo) Fensholt edible seaweeds growing around Venice (Italy)

Undaria pinnatifida and Sargassum muticum are the most abundant invasive edible algae species that have colonized the hard substrate around Venice. The contents of Ca, Mg, Fe, Zn, Cu, Mn, Sr, Pb, Cr, Al, Co, Cd, Ni, As, Hg and Ba, were investigated by ICP-MS in seaweed samples collected (Spring 2013) in six different sites of Venice. A correlation analysis of the results was performed. Sargassum muticum exhibited overall higher contents than U. pinnatifida for many of the considered elements. The elemental contents in both species were in ranges comparable to those reported for seaweeds subjected to anthropogenic impact. Considering the French legislation as a working reference for Pb, Cd and inorganic As limits for seaweed for human consumption, the present results pointed out that in both species Pb content was on average higher than the French limits, whereas the Cd and Hg contents were much lower than the same legislation limits.

Plankton dynamics across the freshwater, transitional and marine research sites of the LTER-Italy Network: patterns, fluctuations, drivers

A first synoptic and trans-domain overview of plankton dynamics was conducted across the aquatic sites belonging to the Italian Long-Term Ecological Research Network (LTER-Italy). Based on published studies, checked and complemented with unpublished information, we investigated phytoplankton and zooplankton annual dynamics and long-term changes across domains: from the large subalpine lakes to mountain lakes and artificial lakes, from lagoons to marine coastal ecosystems. This study permitted identifying common and unique environmental drivers and ecological functional processes controlling seasonal and long-term temporal course. The most relevant patterns of plankton seasonal succession were revealed, showing that the driving factors were nutrient availability, stratification regime, and freshwater inflow. Phytoplankton and mesozooplankton displayed a wide interannual variability at most sites. Unidirectional or linear long-term trends were rarely detected but all sites were impacted across the years by at least one, but in many case several major stressor(s): nutrient inputs, meteo-climatic variability at the local and regional scale, and direct human activities at specific sites. Different climatic and anthropic forcings frequently co-occurred, whereby the responses of plankton communities were the result of this environmental complexity. Overall, the LTER investigations are providing an unparalleled framework of knowledge to evaluate changes in the aquatic pelagic systems and management options.