Dominance of Cylindrospermopsis raciborskii (Nostocales, Cyanoprokaryota) in Queensland tropical and subtropical reservoirs: Implications for monitoring and management

Abstract

Since October 1997, 47 reservoirs and weir pools across tropical and subtropical Queensland have been regularly monitored for the occurrence of planktic cyanoprokaryotes. Cylindrospermopsis raciborskii (Woloszynska) Seenaya & Subba Raju (Nostocales, Cyanoprokaryota) was found in 70% of the storages, with one storage displaying year‐round dominance, 50% of the reservoirs seasonally dominated and a seasonal presence in 46% of the weir pools. Maxima for the majority of storages occurred from late summer through to early autumn. The precise timing of onset of seasonal maxima varied considerably between storages and regions. Temperature and stratification patterns influenced seasonal recruitment with C. raciborskii reaching seasonal maxima in southern storages generally later than the northern storages. Overall peak seasonal abundance occurred in deep strongly stratified storages. The majority of storages experiencing concentrations > 15 000 cells mL–1 tested positive to the presence of the alkaloid cytotoxin, cylindrospermopsin. Median cylindrospermopsin concentration across the 14 reservoirs in which toxin was recorded was 3.4 μg L–1. The highest toxin concentrations were generally associated with storages in which C. raciborskii had been established for a considerable period of time, or occurred after the peak summer population maxima. Toxin concentrations of 1 μg L–1 were generally associated with cell concentrations of approximately 20 000 cells mL–1, hence this cell concentration threshold was adopted as a health trigger level at which to begin monitoring for toxicity. The morphology of this species was highly variable and included straight, coiled and sigmoid‐shaped trichomes. Populations were routinely recorded as mixtures of all three morphotypes or proceeded as transitions from one morphotype to another throughout the year. The dominance of C. raciborskii appears to be favoured by a set of environmental and hydrological factors that include long water residence time, high pH, high temperature, high incident irradiation and a thermally stratified water column. The lack of visual monitoring cues, such as scum formation, variation in colour of the water body, rapid germination of large numbers of cells, highly variable morphology, relative toxicity and persistence of this species year round in many areas, continues to make this species a primary focus of water managers.

Recent occurrence ofCylindrospermopsis raciborskiiin Waikato lakes of New Zealand

“…The first confirmed identification of this species in New Zealand was by Wood & Stirling (2003) in Lake Waahi in March 2003. There is considerable morphological variation in C. raciborskii (McGregor & Fabbro 2000) and this is one of the reasons for its recent appearance in water bodies where it has been previously unrecorded. A morphologically similar species, Cylindrospermum minutissimum Collins, has previously been described in lakes in close proximity to our study lakes (Etheredge & Pridmore 1987).…”

“…The identification was based upon earlier keys, and the emphasis on the position of the heterocyst being adjacent to the akinete led to material being identified as C. minutissimum, while the absence of heterocysts and tapering of trichomes led to identifications of the material as Raphidiopsis; both of these forms are described in the New Zealand literature. Correct identification of Cylindrospermopsis raciborskii is very difficult, due in part to the large range of morphological variants which have been documented in recent taxonomic investigations (McGregor & Fabbro 2000) and using genetic studies Wilson et al 2000).…”

Molecular separation of two long taxonomically debated cyanobacterial genera Cylindrospermopsis and Raphidiopsis (Nostocales) based on the ITS-L phylogeny

“…However, distinction between these two genera is difficult when heterocytes are not shown in Cylindrospermopsis strains (Li et al, 2001;Moustaka-Gouni et al, 2009;Alster et al, 2010). The coexistance of Cylindrospermopsis and Raphidiopsis in the same waters has been widely reported (McGregor and Fabbro, 2000;Moustaka-Gouni et al, 2009;Wu et al, 2011). Raphidiopsis-like trichomes are regarded as only environmental types of Cylindrospermopsis (McGregor and Fabbro, 2000).…”

“…They share similar ecological niches, in which Raphidiopsis species have been found to co-occur with Cylindrospermopsis raciborskii (Woloszyń ska) Seenayya et Subba Raju in a range of waters (Moustaka-Gouni et al, 2009;Wu et al, 2011;Hill, 1970). McGregor and Fabbro (2000) proposed that Raphidiopsis-like trichomes are only environmental morphotypes and the heterocyst-omission phase of C. raciborskii. Moustaka-Gouni et al (2009) suggested that Raphidiopsis mediterranea Skuja represents nonheterocytous life-cycle stages of C. raciborskii in Lake Kastoria (its type locality), Greece, as evidenced by morphological and 16S rRNA phylogenetic analyses.…”

Initial growth phases of two bloom-forming cyanobacteria (Cylindrospermopsis raciborskiiandPlanktothrix agardhii) in monocultures and mixed cultures depending on light and nutrient conditions

“…However, blooms are complex events, involving multiple environmental factors simultaneously (Heisler et al, 2008), which have led to some inconsistencies in the literature, related to the environmental parameters tested (Posselt et al, 2009). The main shortcoming is that many studies have provided specific information about the environmental requirements of the two species occurring separately (McGregor and Fabbro, 2000), while very few of them have recently reported the co-occurrence of C. raciborskii and P. agardhii in lakes and reservoirs (Stefaniak and Kokocinski, 2005;Kokocinski et al, 2009). For example, in the Tunisian Bir M'Cherga reservoir, from which the strains used in this study were obtained, P. agardhii occurs as a perennial biomass and dominates the phytoplankton community, whereas C. raciborskii is favored by higher temperatures and light intensities that only occur for a short period each year (Jenhani et al, 2012).…”