When will the zebra mussel reach Florence? A model for the spread of Dreissena polymorpha in the Arno water system (Italy)

Abstract

The zebra mussel (Dreissena polymorpha) is a freshwater bivalve that has caused dramatic ecological and economic impacts worldwide in past decades. Its success as ecosystem invader is mainly due to the species ability of spreading along rivers, together with the extremely high population densities that can be reached by local populations. Here we propose a spatially explicit model aimed at describing the population dynamics of mussel colonies in rivers represented as oriented graphs. We specifically apply the model to the Bilancino-Sieve-Arno water system (Tuscany, Italy), where D. polymorpha has been recently sighted. The model accounts for local-scale demographic processes and along-stream transport mechanisms. Because of the different temporal scales involved, we couple continuous-and discrete-time dynamics. Our model produces spatiotemporal scenarios of invasion that present several distinctive features of the zebra mussel invasion patterns observed in nature, including the spatial patchiness and the temporal irregularity of local populations, and the so-called domino effect. The application of our model to the Arno case study shows that D. polymorpha could severely threaten the city of Florence within a few years. Control measures aimed at limiting the impact of the species can significantly alter the ecological and environmental parameters. We find that such variations may profoundly impact spatiotemporal invasion patterns, possibly with counter-intuitive effects. For instance, reduced larval input from Lake Bilancino can in some cases produce higher mussel densities in downstream colonies. Therefore, the control of D. polymorpha must be planned with care in order to prevent unwelcome outcomes.

Biological control of the chestnut gall wasp with T. sinensis: A mathematical model

“…There are essentially two main causes for LDD events: transport due to antropic activities, and transport with the wind of individuals that ventured above the forest canopy (particularly on occasion of storms). Transport processes can easily produce patchiness (see, for example, the case of zebra mussels carried downstream a river: Mari et al, 2009). In addition, in our case, they are also completely random and unpredictable: while the outcome of each LDD event could be forecast by a model, after its occurrence, and provided the availability of sufficient observational data, the occurrence of the event itself can not be forecast.…”

Metapopulation persistence and species spread in river networks

“…See Appendix S6 for details on the parameterisation of the model. We have parameterised model (1) to describe zebra mussel invasion dynamics (Casagrandi et al 2007;Mari et al 2009Mari et al , 2011, namely by considering sessile adults and a juvenile stage during which veligers can undergo dispersal through hydrological transport and port-to-port relocation (described by a port-to-port connectivity matrix G with characteristic dispersal distance D; see Appendix S8). The resulting value of E 0 ≫ 1 implies that the zebra mussel can persist and spread in the MMRS (as indeed observed; note that a high value of E 0 corresponds to a great risk of invasion).…”

Recreational angling as a vector of freshwater invasions in Central Italy: perceptions and prevalence of illegal fish restocking

“…For example, in winter, rainfalls range from over 2000 mm on the mountains in the North-Western portion of the basin, to 700 mm in the lowlands at its Easternmost border, and in the central portion of the Arno river, flows range from 3-4 m 3 /s in summer to 2000 m 3 /s in late autumn. Biological invasions strongly affected freshwater ecosystems in the basin, as about 70% of total aquatic animal species are invasive and some major ecosystem engineers are present (Gualtieri and Mecatti, 2005;Mari et al, 2009;Nocita, 2017). A complete list of native and invasive fish species for the Arno river is available in Nocita (2007), with the exclusion of the Albanian roach (Pachychilon pictum), which was recorded for the first time after 2007.…”