Effect of Ecological Recovery on Macrophyte Dominance and Production in the Venice Lagoon

Abstract

In the last decade, the Venice Lagoon showed a significant environmental recovery that changed the assemblages of macroalgal and aquatic angiosperm dominant species and significantly increased the primary production. The decreasing of anthropogenic impacts, such as eutrophication and clam harvesting, favored a strong reduction of Ulvaceae, replaced by species with higher ecological value, and the recolonization of aquatic angiosperms. Consequently, hypo-anoxic conditions, once frequently occurring in the lagoon, have been considerably reduced and aquatic angiosperms have recolonized the area, covering 94.8 km2 in comparison to the 55.9 km2 recorded in 2003 (+70%). Cymodocea nodosa, Zostera marina, and Zostera noltei expanded by 37.5%, 44.6%, and 191%, respectively, with a significant increase in biomass and primary production. In late spring 2018, angiosperms showed a standing crop of approximately 372 ktonnes (+77%) and a net primary production of approximately 1189 ktonnes FW (+67%). In the meantime, Ruppia cirrhosa, which since the 1980s had disappeared from the lagoon areas subjected to tidal expansion, but was still present in some fishing valleys, recolonized the bottoms of the northern lagoon with meadows of over 6 km2; this accounted for a standing crop and net primary production of 8.9 and 18.0 ktonnes, respectively. Based on surveys carried out in 2021, ecological conditions are still improving, and this is increasing both the biodiversity and the production of macroalgae and aquatic angiosperms.

Alien Macroalgal Rearrangement in the Soft Substrata of the Venice Lagoon (Italy): Impacts, Threats, Time and Future Trends

“…The only potentially dangerous species for the environment is Ulva australis, which is strongly invasive in the TWS of the northern Adriatic Sea and is replacing Ulva rigida in areas with relatively low trophic levels. However, U. australis has a biomass significantly lower compared to that recorded for U. rigida in the past [70] and cases of hypo-anoxic conditions, due to its decomposition, are becoming more and more rare.…”

“…Luckily, the macroalgal NIS recorded in the Venice Lagoon have not had significant negative impacts on the other species, and, in general, they have increased the macrophyte biodiversity. Indeed, despite the increasing NIS introduction, in 2018 the number of macroalgae in the lagoon reached up to 323 taxa [30] and aquatic angiosperms almost doubled their cover and production in comparison to 2003 [70].…”

Where, when, how and what seagrass to transplant for long lasting results in transitional water systems: the cases of Cymodocea nodosa, Zostera marina, Zostera noltei and Ruppia cirrhosa

“…In the past, many of these species disappeared due to excessive nutrients, clam fishing, and a bloom of picocyanobacteria (Sorokin et al, 2004). However, efforts have been made to reintroduce aquatic angiosperms into the affected areas, resulting in a significant recolonization and recovery (Sfriso et al, 2022).…”