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

Abstract

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 km 2 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.

Macrophyte Abundance in Waquoit Bay: Effects of Land-Derived Nitrogen Loads on Seasonal and Multi-Year Biomass Patterns

“…Estuaries dominated by Ulva, Enteromorpha, and Chaetomorpha spp. may attain much larger biomasses of 2400-3600 g d.w. m -2 (Sfriso et al 1989;Sfriso and Facca 2007; wet weight converted by 12% dry:wet weight in Morand and Briand 1996). This analysis of macroalgal biomass and canopy height in the three Waquoit Bay estuaries, as well as data presented in Peckol and Rivers (1996), suggest that peak macroalgal accumulation may be spurred by increased nitrogen supply, but ultimately the canopy is limited by light availability.…”

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

“…6). Considering that a high primary production, at first, depletes the dissolved CO 2 in the water column and then the bicarbonates raise the pH value [28], it is not surprising that pH has lowered after the macrophyte reduction in the whole lagoon [12,25]. In 5 years the mean pH in the central basin lowered of 0.4 units (Fig.…”

“…The sampling methods and the results are widely discuss elsewhere [25,26]; here, such data were retrieved for the statistical analyses, described below, in order to complete the trophic profile of the lagoon.…”

An inverse model for the analysis of the Venice lagoon food web

“…References for the sources of data used for constructing the food web model are summarized in Appendix A, Table A1 (Brey, 2001;Buia et al, 2000;Cavraro, 2007;Celussi et al, 2009;Coll et al, 2007;Consorzio Venezia Nuova, 2003, 2005aDanovaro and Fabiano, 1997;Facca and Sfriso, 2007;Facca et al, 2009;Franco et al, 2006a;Froese and Pauly, 2002;Jørgensen et al, 1991;Sfriso and Facca, 2007;Sfriso and Ghetti, 1998;Sorokin and Giovanardi, 1995). The dataset covers areas of the lagoon characterized by different residence times and productivities.…”