Spreading and autoecology of the invasive species Gracilaria vermiculophylla (Gracilariales, Rhodophyta) in the lagoons of the north-western Adriatic Sea (Mediterranean Sea, Italy)
Highlights
► Species distribution in the transitional systems of the North Adriatic Sea. ► Annual biomass change in Venice Lagoon. ► Relationship with environmental parameters. ► Additional morphological information.
Introduction
The Venice lagoon is one of the Mediterranean transitional environments considered to be a prime area for the introduction of alien species, especially macrophytes (Verlaque, 1994; Boudouresque and Verlaque, 2002; Occhipinti-Ambrogi, 2002; Sfriso and Curiel, 2007). A revision of the allochthonous species, updated December 2010 (Zenetos et al., 2010), shows that there are 33 non-indigenous species (NIS) of macroalgae recorded in the Venice lagoon, ca. 80% of the number (49 taxa) recorded in the Adriatic Sea and 39% of those (125 taxa) found in the whole Mediterranean Sea. Among them some are considered invasive or potentially invasive: i.e. Codium fragile subsp. fragile (Suringar) Hariot (Sfriso, 1987), Sargassum muticum (Yendo) Fensholt (Gargiulo et al., 1992), Grateloupia turuturu Yamada (Tolomio, 1993, as Grateloupia doryphora (Montagne) M.A. Howe), Undaria pinnatifida (Harvey) Suringar (Rismondo et al., 1993), Heterosiphonia japonica Yendo (Sfriso et al., 2002) and Gracilaria vermiculophylla (Ohmi) Papenfuss (Sfriso et al., 2010a) due to their worldwide spread, but some of them have spread largely only in the lagoons of the North Adriatic and particularly in the Venice lagoon: i.e. Sargassum muticum, U. pinnatifida and G. vermiculophylla. Other NIS, such as Agardhiella subulata (C. Agardh) Kraft & M.J. Wynne and Solieria filiformis (Kützing) P.W. Gabrielson are highly invasive, but only in our lagoons.
Gracilaria vermiculophylla, a species native from Japan and Korea, is the most recent introduced species (Sfriso et al., 2010a). It was firstly recorded in the northern coasts of the Atlantic Sea in 2002 (Rueness, 2005; Thomsen et al., 2007) and has rapidly colonized many European coasts and the transitional systems of the Adriatic Sea. The first record in the Venice lagoon was in March 2009, but in the following months many populations were recorded both in the central and southern basins (Sfriso et al., 2011). In May 2009, high biomasses (5–15 kg fwt m−2) of this species were also found at Pialassa della Baiona (Ravenna), where G. vermiculophylla covered a large part of the southern basin.
This paper maps the presence of this species (Venice lagoon, transitional systems of the Po Delta and Pialassa della Baiona) and analyses the different morphology of non-reproductive and reproductive thalli and their correlation with some physico-chemical parameters and nutrient concentrations in water column, pore-water, surface sediments and particulate matter collected by traps.
Section snippets
Sampling areas
Samples were collected during national and regional programmes carried out in order to monitor the ecological status of the Italian transitional environments according to the requirements of the European Water Framework Directive (2000/60/EC) for the “Macrophytes” biological element (macroalgae and aquatic angiosperms). The Po Delta lagoons were monitored in 2008, 2009, 2010 in late spring and autumn of each year (Sfriso, 2010, Sfriso, 2011; Sfriso et al., 2011 and references therein). Pialassa
Morphology
Thalli of Gracilaria vermiculophylla are blackish to dark-red and for this reason they could be easily recognized. In Venice this species is called the “black Gracilaria” (Fig. 2A, B). Axes, arising from a small basal disk, are cylindrical to slightly compressed, irregularly and densely branched (Fig. 2C), wrinkled and very long: <0.5–1.0 (2.0) m high, especially female gametophytes. Usually axes are larger in the central region where they can reach 1.5–3 mm in diameter and show long
Discussion and conclusions
Gracilaria vermiculophylla is one of the most recently introduced allochthonous species in the lagoons of the Northern Adriatic Sea after its recording on the coast of North Europe in the 2002 (Rueness, 2005; Thomsen et al., 2007). The species has rapidly colonized these transitional systems, except the Marano–Grado lagoon, and it is one of the most abundant invasive species of the confined areas. Usually it is associated with Ulvaceae, such as Ulva rigida C. Agardh, other Gracilariaceae,
Acknowledgements
We thanks the anonimous referees for the suggestions and the English revision and ARPA Veneto and ARPA Emilia-Romagna for logistical support during the sampling.
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