Invasion of alien macroalgae in the Venice Lagoon, a pest or a resource?
Alien macroalgae, mostly invasive species, are a constant concern for coastal areas, especially in the northern Adriatic Sea where several taxa have colonized the main transitional environments. A revision of the alien macroalgae in the Venice Lagoon shows that, currently, the number of valid non-indigenous species (NIS) is 29, and this number is growing steadily. On the basis of numerous surveys carried out in the last decade the total alien standing crop (SC) was estimated to be ca. 146,534 tonnes fresh weight (fw), i.e. 32% of the total species SC (ca. 456,000 tonnes fw) measured in May-June 2014 in the whole lagoon. The most abundant species were the invasive Agarophyton vermiculophyllum (approx. 66,383 tonnes fw), Agardhiella subulata and Hypnea cervicornis (approx. 36,714 and 28,305 tonnes fw, respectively). These species grow mainly free-floating and usually colonize the soft substrata of the lagoon. Two other invasive species, Sargassum muticum and Undaria pinnatifida, grow mainly on the docks of Venice historical centre, therefore their distribution is significantly more limited. Recent studies have shown that A. vermiculophyllum in protected, eutrophic areas produced a biomass of approx. 24 kg fw m-2 y-1. This species can replace Ulvaceae with positive effects on the environment and the presence of macrofaunal taxa. Indeed, historical data analysis shows that, despite the high presence of NIS, biodiversity is increasing. In addition, A. vermiculophyllum, S. muticum, U. pinnatifida, A. subulata and Solieria filiformis may be promising species for phycocolloid and antioxidant or cosmetic productions.