Already decades ago, allelopathic effects of cyanobacteria have been suggested as
a major controlling factor for successions of phytoplankton communities [2, 3].
Cyanobacteria, prokaryotic bacteria with photosynthetic ability, and important autotrophic producers are reported in each continent except Antarctica [10]. Anthropogenic eutrophication has resulted in the occurrence of harmful cyanobacterial
blooms in many marine and freshwater ecosystems that can cause severe problems
[11, 12]. Certain cyanobacterial species outcompete other members of the phytoplankton communities and form thick mats in the upper layer of water bodies that
can cause decline and deaths of other members of the aquatic community [11]. The
reasons accounting for this phenomenon have not been fully understood [13].
Buoyancy regulation, the higher optimal temperature, and efficient nutrient uptake
systems have been suggested to be involved [10, 14, 15]. Keating (1977, 1978)
presented the first evidence for cyanobacterial allelopathy as a major controlling
factor in bloom sequence determination [2, 3]. The huge variety of secondary
metabolites produced by cyanobacteria has stimulated their isolation and characterization for potential commercial use, e.g., in pharmacy [16–19]. These studies have
also advanced research on allelopathic interactions among phytoplankton.
In this chapter, we summarize the known effects of cyanobacterial allelochemicals
on different aquatic organism groups, their specific mechanisms, regulatory factors,
and ecological consequences of cyanobacterial allelopathic effects in aquatic ecosystems to evaluate the state of the art and detect major knowledge gaps.
2
Effects of Cyanobacterial Allelochemicals
Allelopathic activity includes both inhibitory and stimulatory effects of the donor on
the acceptor [2, 20, 21]. The majority of studies published about the allelopathic
effects of cyanobacteria in aquatic systems have been focused on negative impacts.
Allelopathy of cyanobacterial species is considered as one of the reasons for their
bloom formation in the early stages by outcompeting other autotrophs. On the other
hand, allelochemicals mediating these effects are also toxic to organisms of other
trophic levels.
2.1
Effects on Planktonic Phototrophs
All phytoplankton species compete with cyanobacteria for light and nutrients;
among them green algae are often concerned by researchers as a target of allelopathic
inhibitory effects by cyanobacteria. Allelopathic effects of cyanobacteria on
Chlorophyta are species-specific. Figueredo et al. [22] found allelopathic effects of
Cylindrospermopsis raciborskii cells on two species of Chlorophyta, Coelastrum
sphaericum and Monoraphidium contortum. Even at low cell density, some
cyanobacteria (e.g., species in genera Oscillatoria and Cylindrospermopsis) were
shown to strongly suppress the growth of Chlorophyta, Ankistrodesmus falcatus and
Chlorella vulgaris [23]. Bittencourt-Oliveira et al. [24] investigated the effects of
14 Effects of Cyanobacterial Secondary Metabolites on Phytoplankton Community. . . 325
a major controlling factor for successions of phytoplankton communities [2, 3].
Cyanobacteria, prokaryotic bacteria with photosynthetic ability, and important autotrophic producers are reported in each continent except Antarctica [10]. Anthropogenic eutrophication has resulted in the occurrence of harmful cyanobacterial
blooms in many marine and freshwater ecosystems that can cause severe problems
[11, 12]. Certain cyanobacterial species outcompete other members of the phytoplankton communities and form thick mats in the upper layer of water bodies that
can cause decline and deaths of other members of the aquatic community [11]. The
reasons accounting for this phenomenon have not been fully understood [13].
Buoyancy regulation, the higher optimal temperature, and efficient nutrient uptake
systems have been suggested to be involved [10, 14, 15]. Keating (1977, 1978)
presented the first evidence for cyanobacterial allelopathy as a major controlling
factor in bloom sequence determination [2, 3]. The huge variety of secondary
metabolites produced by cyanobacteria has stimulated their isolation and characterization for potential commercial use, e.g., in pharmacy [16–19]. These studies have
also advanced research on allelopathic interactions among phytoplankton.
In this chapter, we summarize the known effects of cyanobacterial allelochemicals
on different aquatic organism groups, their specific mechanisms, regulatory factors,
and ecological consequences of cyanobacterial allelopathic effects in aquatic ecosystems to evaluate the state of the art and detect major knowledge gaps.
2
Effects of Cyanobacterial Allelochemicals
Allelopathic activity includes both inhibitory and stimulatory effects of the donor on
the acceptor [2, 20, 21]. The majority of studies published about the allelopathic
effects of cyanobacteria in aquatic systems have been focused on negative impacts.
Allelopathy of cyanobacterial species is considered as one of the reasons for their
bloom formation in the early stages by outcompeting other autotrophs. On the other
hand, allelochemicals mediating these effects are also toxic to organisms of other
trophic levels.
2.1
Effects on Planktonic Phototrophs
All phytoplankton species compete with cyanobacteria for light and nutrients;
among them green algae are often concerned by researchers as a target of allelopathic
inhibitory effects by cyanobacteria. Allelopathic effects of cyanobacteria on
Chlorophyta are species-specific. Figueredo et al. [22] found allelopathic effects of
Cylindrospermopsis raciborskii cells on two species of Chlorophyta, Coelastrum
sphaericum and Monoraphidium contortum. Even at low cell density, some
cyanobacteria (e.g., species in genera Oscillatoria and Cylindrospermopsis) were
shown to strongly suppress the growth of Chlorophyta, Ankistrodesmus falcatus and
Chlorella vulgaris [23]. Bittencourt-Oliveira et al. [24] investigated the effects of
14 Effects of Cyanobacterial Secondary Metabolites on Phytoplankton Community. . . 325