DOES ALLELOPATHY CONTRIBUTE TO CYLINDROSPERMOPSIS RACIBORSKII (CYANOBACTERIA) BLOOM OCCURRENCE AND GEOGRAPHIC EXPANSION?¹

Abstract

Cylindrospermopsis raciborskii (Wołosz.) Seenayya et Subba Raju is a planktonic filamentous cyanobacterium whose sudden worldwide proliferation and ability to produce toxins are a reason for concern. In this paper, we suggest that its ecological dominance might be explained by antagonistic interaction with other phytoplankton species due to production of allelopathic metabolites. To test this hypothesis, experiments were run with exudates of natural phytoplankton and C. raciborskii strains isolated from Lagoa Santa, a small natural lake in southeastern Brazil, where this species has become dominant in recent years. The exudates were added to different algal species obtained from the same environment and maintained in culture. After 24 h incubation, PAM fluorometry was used to compare control and treatment photosynthetic responses (relative electron transport rate) to the dissolved extracellular products. Results indicate that most of the target species were sensitive to C. raciborskii exudates, which showed strong inhibitory effects on their photosynthetic activities. These results provide evidence that allelopathy may offer a competitive benefit to C. raciborskii and contribute to its stable dominance in Lagoa Santa. A potential allelopathic advantage could also help to explain the geographic expansion of this species at midlatitudes.

Synergistic allelochemicals from a freshwater cyanobacterium

“…The ubiquity of all of these various strains of cyanobacteria and microalgae as well as that of the Oscillatoria genus makes it likely that they encounter one another in natural water systems, and this is especially true given the recent geographical expansion of C. raciborskii (28). The lower susceptibility of A. falcatus to the portoamides as compared to C. vulgaris may explain why inhibition of the former was not observed when exposed to OSC exudates (36).…”

“…that inhibit cyanobacteria and microalgae (25,26). Different ecological roles have been attributed to the production of allelochemicals by cyanobacteria, including phytoplankton succession, bloom formation, resource and interference competition (27), and invasive fitness (28). In order to understand the ecological significance of allelopathy in cyanobacteria, several studies have characterized environmental factors that may modulate allelopathic events.…”

Extracellular polysaccharide-protein complexes of a harmful alga mediate the allelopathic control it exerts within the phytoplankton community

“…Although there have been various biological and non-biological studies of the distribution and growth of flagellate populations (Erga and Heimdal, 1984;Karentz and Smayda, 1984;Haigh et al, 1992;Smayda, 1997;Miralto et al, 1999;Diehl et al, 2002;Ianora et al, 2004;Bruggeman and Kooijman, 2007), it is not always clear how certain phytoplankton species can come to dominate a community. Empirical approaches to studying the allelopathic effects and inter-specific interactions among phytoplankton have developed relatively slowly (Figueredo et al, 2007;Gentien et al, 2007;Strom, 2008).…”

Inhibition effect of green alga on cyanobacteria by the interspecies interactions

“…Different ecological roles have been attributed to the production of the allelochemicals by cyanobacteria, including phytoplankton succession, bloom formation, resource and interference competition and invasive fitness (Figueredo et al 2007). However, the influence of the allelochemicals by other species on cyanobacteria has been overlooked in the past study.…”