Invasion of Nostocales (cyanobacteria) to Subtropical and Temperate Freshwater Lakes - Physiological, Regional, and Global Driving Forces

Abstract

Similar to the increased number of studies on invasive plants and animals in terrestrial and aquatic ecosystems, many reports were recently published on the invasion of Nostocales (cyanobacteria) to freshwater environments worldwide. Invasion and proliferation of Nostocales in new habitats have the potential to significantly alter the structure of the native community and to modify ecosystem functioning. But most importantly, they influence the water quality due to a variety of toxic compounds that some species produce. Therefore a special attention was given to the invasion and persistence of toxic cyanobacteria in many aquatic ecosystems. Here we summarize the currently published records on the invasion of two Nostocales genera, Cylindrospermopsis and Aphanizomenon, to lakes and water reservoirs in subtropical and temperate zones. These invading species possess traits thought to be common to many invasive organisms: high growth rate, high resource utilization efficiency and overall superior competitive abilities over native species when local conditions vary. Assuming that dispersion routes of cyanobacteria have not been changed much in recent decades, their recent establishment and proliferation in new habitats indicate changes in the environment under which they can exploit their physiological advantage over the native phytoplankton population. In many cases, global warming was identified as the major driving force for the invasion of Nostocales. Due to this uncontrollable trend, invasive Nostocales species are expected to maintain their presence in new habitats and further expand to new environments. In other cases, regional changes in nutrient loads and in biotic conditions were attributed to the invasion events.

Keywords: Aphanizomenon; Cylindrospermopsis; Nostocales; climate change; cyanobacteria; eutrophication; invasive species.

Figure 1

The expansion of the Nostocales Cylindrospermopsis raciborskii (triangles) and Aphanizomenon ovalisporum (squares) to temperate and subtropical regions shown in a world climate zones map. (Map source: http://sedac.ciesin.columbia.edu/place/mapCollection/Climate_Zone).

Figure 2

Traits and process that support the invasiveness of cyanobacteria according to its three major components: dispersion, establishment, and ecological impact. References (1) Neilan et al., ; (2) Kaplan-Levy et al., ; (3) Wiedner et al., ; (4) Suikkanen et al., ; (5) Rücker et al., ;(6) Padisák, ; (7) Isvánovics et al., ; (8) Posselt et al., ; (9) Hadas et al., submitted; (10) Bar-Yosef et al., ; (11) Briand et al., .

Figure 3

Schematic presentation illustrating the proliferation and bloom potential of invasive Nostocales in eutrophic and oligotrophic lakes. Higher water temperatures open new habitats in which many Nostocales species can proliferate, taking advantage of their efficient physiological process. In eutrophic waters, a massive bloom and scum production is expected (depicted by a dense green patch) due to high external nutrient load and intense internal nutrient recycling (wide arrows). In oligotrophic waters a moderate bloom is likely to occur based on heterocysts formation and N₂ fixation and is controlled by restricted external and internal P load (narrow arrows). Dormant cells, akinetes, are formed in both cases (more akinetes are expected in eutrophic systems due to high biomass content) and provide the basis for perennial blooms. Note that nutrient recycling from bottom sediments occur in both systems but is more essential source for N and P in oligotrophic system. Nitrogen fixation is also evident in eutrophic systems only when the ample inorganic N provided by external and internal sources is exhausted.