Survival and reproduction of the aquatic fern Salvinia natans (L.) All. during expansion in the Vistula Delta, south Baltic Sea coast

Abstract

In this study we examined the survival, reproduction, and population size of the aquatic fern Salvinia natans (L.) All. during its expansion in the Vistula Delta (south Baltic Sea coast, northern Poland) with observations every 14 days for five consecutive years at 10 permanent plots in one river. Young sporophytes (genets from gametophytes and ramets resulting from vegetative propagation of sporophytes) appeared in the watercourses of the delta from April to October. The number of genets, which formed mainly in May, was positively correlated with April temperatures (r = 0.93; p = 0.026), and the number of ramets, which were produced in summer, with July temperatures (r = 0.91; p = 0.039). Population abundance in a given year depended mainly on the mortality rate of gametophytes in early spring and the intensity of vegetative reproduction in summer. Two types of vegetative propagation and ramet formation were observed: clone fragmentation and budding along the peripheral parts of the modules forming a clone (4.2 ± 3.7 buds/module). The intensity of each reproduction type was positively correlated with the mean monthly water temperature (r = 0.91 and r = 0.87, respectively).

Keywords:

• macrophyte growth
• vegetative growth
• population dynamics
• mortality rate
• invasive species

Acknowledgements

We thank our colleagues for discussions and valuable comments on the manuscript. Michael Jacobs edited the manuscript for language. The paper is based on results obtained in work under Project N N304 411 638 funded by the Polish Ministry of Science and Higher Education.