The Importance of Thermally Abnormal Waters for Bioinvasions—A Case Study of Pistia stratiotes

Abstract

Thermally abnormal waters represent safe sites for alien invasive plants requiring warmer conditions than provided by the ambient temperatures in the temperate zone. Therefore, such safe sites are frequently inhabited by tropical and sub-tropical plants. By performing a literature review we assessed that at least 55 alien aquatic plant taxa from 21 families were found in thermally abnormal waters in Europe. The majority of these taxa are submerged or rooted macrophytes. Six taxa are listed as quarantine pests according to EPPO. Among these, Pistia stratiotes is present in seven European countries, most of the records of this presence being recent. We studied P. stratiotes in a thermally abnormal stream where a persistent population was able to survive harsh winters. Models showed that the optimum temperature for P. stratiotes biomass was 28.8 ± 3.5 °C. Here, we show that air temperatures had a higher influence on the photosynthetic efficiency of P. stratiotes, estimated by chlorophyll fluorescence measurements, than did water temperatures. Generally, growth, and consequently surface cover for free-floating plants, cannot be explained solely by thermally abnormal water temperatures. We conclude that even though the majority of thermophile alien plant occurrences resulted from deliberate introductions, thermally abnormal waters pose an invasion risk for further deliberate, accidental, or spontaneous spread, which might be more likely for free-floating macrophytes.

Multi-Interacting Natural and Anthropogenic Stressors on Freshwater Ecosystems: Their Current Status and Future Prospects for 21st Century

“…However, the study provides an example of the positive effects of non-native Eurasian Watermilfoil, Myriophyllum spicatum [299]. Kourantidou et al [300] also stated in their recent review that IAS has potentially beneficial roles. It was also reported that IAS's competitive success depends on environmental conditions [302].…”

“…Climate change and global warming can accelerate such local populations of invasive species as stepping stones for further dispersal [299]. Šajna et al [300] recently stated that thermally abnormal waters pose an invasion risk for further deliberation.…”

“…General and specific freshwater ecosystems' complex point and non-point pollution phenomena that impact the fish, too [300], which became stressors for the environment and human health, can be managed in an integrated way only at the watershed level [328][329][330][331].…”

Diversity of Inland Wetlands: Important Roles in Mitigation of Human Impacts

“…The mentioned sites are often colonized by tropical and subtropical plants. Šajna et al [14] studied a case of Pistia stratiotes, which occurs in southeastern Slovenia. Based on a literature review, they found that at least 55 alien aquatic plant taxa from 21 families have been found in thermally abnormal waters in Europe.…”