**5. Challenges and gaps in** *Planktothrix* **spp. risk assessment and management**

Usually, *Microcystis* is the genus that occurs more frequently and is usually considered the main responsible for the production of microcystins. However, there is another emergent genus that has also the ability to produce microcystins, which is *Planktothrix*.

The cyanobacteria of the genus *Planktothrix* have a planktonic life style, occur in solitary filaments and lack sheaths, heterocysts and akinetes. Formerly classified into to the genus *Oscillatoria*, *Planktothrix* now represents a well-defined independent genus based in phylogenetic and morphologic characteristics and comprises 13 species (Komárek & Komárkova 2004). Similar to other cyanobacteria, *Planktothrix* can achieve high cellular densities in water forming blooms that unbalance the ecosystem and it can also produce several types of cyanotoxins, namely microcystins, homoanatoxin-a, anatoxin-a, aplysiatoxins, saxitoxins, anabaenopeptins, (Luukkainen et al., 1993; Erhard et al., 1999; Kouzminov, 2001; Viaggiu et al., 2004; Wood, 2005; Kosol et al., 2009), thus threatening humans and animals.

From the 13 species described, *Planktothrix rubescens* and *Planktothrix agardhii* are the most studied and common species reported to cause water related problems. A summary of *Planktothrix* occurrence in European lakes where they form recurrent blooms and the associated toxicity found is presented in Table 4.

Unlike other cyanobacteria, *P. agardhii* and *P. rubescens* are well adapted to very low light intensities and this characteristic provides to them several advantages. For *P. agardhii* it allows them to grow in waters with high turbidity, in which it can be homogeneously dispersed throughout the epilimnion in eutrophic waters having a competitive advantage upon other phytoplankton species. For *P. rubescens* the low light intensity requirements together with the high content of the red pigment phycoerythrin enables it to growth in the metalimnetic layer in thermally stratified waters away from the phototic surface zone (Mur et al., 1999; Bright & Walsby, 2000). Furthermore, these two species have different irradiance tolerances; *P. agardhii* is more tolerant to high irradiance than *P. rubescens*, what is related with their occurrence in different ecological niches in the water column and inhabit in different types of water systems (Oberhaus et al., 2007). Therefore *P. agardhii* grows well in the upper part of the water column of shallow eutrophic lakes, however it can also grow at several depths along the water column (Halstvedt et al., 2007). On the other hand, *P. rubescens* is well adapted in forming metalimnic populations of deep stratified lakes in spring and summer and when the lake loses its thermal stratification in the winter, it can be dispersed through the entire water column (Bright & Walsby, 2000; Briand et al., 2005). *Planktothrix* also has different water temperature tolerances when compared to other cyanobateria, making them organisms that can be easily found in subalpine lakes or in temperate regions during winter, so *Planktothrix* blooms may persist all year around and not only during summer or spring where temperatures and light irradiance are higher. *P. agardhii* has been found viable under ice covers (Sivonen & Jones 1999; Oberhaus et al., 2007). Since both species occupies different water niches they can coexist in the same water body forming surface and deep layer blooms, althougth this coexistence is rare it has been reported (Davis & Walsby, 2002; Halstvedt et al., 2007).

Regarding the risk management measures that are usually followed to overcome the presence of cyanobacteria and cyanotoxins in the freshwater, *Planktothrix* has some particularities that need to be taken into account. One of them is *Planktothrix*´s ability to


Usually, *Microcystis* is the genus that occurs more frequently and is usually considered the main responsible for the production of microcystins. However, there is another emergent

The cyanobacteria of the genus *Planktothrix* have a planktonic life style, occur in solitary filaments and lack sheaths, heterocysts and akinetes. Formerly classified into to the genus *Oscillatoria*, *Planktothrix* now represents a well-defined independent genus based in phylogenetic and morphologic characteristics and comprises 13 species (Komárek & Komárkova 2004). Similar to other cyanobacteria, *Planktothrix* can achieve high cellular densities in water forming blooms that unbalance the ecosystem and it can also produce several types of cyanotoxins, namely microcystins, homoanatoxin-a, anatoxin-a, aplysiatoxins, saxitoxins, anabaenopeptins, (Luukkainen et al., 1993; Erhard et al., 1999; Kouzminov, 2001; Viaggiu et al., 2004; Wood, 2005; Kosol et al., 2009), thus threatening humans and animals.

From the 13 species described, *Planktothrix rubescens* and *Planktothrix agardhii* are the most studied and common species reported to cause water related problems. A summary of *Planktothrix* occurrence in European lakes where they form recurrent blooms and the

Unlike other cyanobacteria, *P. agardhii* and *P. rubescens* are well adapted to very low light intensities and this characteristic provides to them several advantages. For *P. agardhii* it allows them to grow in waters with high turbidity, in which it can be homogeneously dispersed throughout the epilimnion in eutrophic waters having a competitive advantage upon other phytoplankton species. For *P. rubescens* the low light intensity requirements together with the high content of the red pigment phycoerythrin enables it to growth in the metalimnetic layer in thermally stratified waters away from the phototic surface zone (Mur et al., 1999; Bright & Walsby, 2000). Furthermore, these two species have different irradiance tolerances; *P. agardhii* is more tolerant to high irradiance than *P. rubescens*, what is related with their occurrence in different ecological niches in the water column and inhabit in different types of water systems (Oberhaus et al., 2007). Therefore *P. agardhii* grows well in the upper part of the water column of shallow eutrophic lakes, however it can also grow at several depths along the water column (Halstvedt et al., 2007). On the other hand, *P. rubescens* is well adapted in forming metalimnic populations of deep stratified lakes in spring and summer and when the lake loses its thermal stratification in the winter, it can be dispersed through the entire water column (Bright & Walsby, 2000; Briand et al., 2005). *Planktothrix* also has different water temperature tolerances when compared to other cyanobateria, making them organisms that can be easily found in subalpine lakes or in temperate regions during winter, so *Planktothrix* blooms may persist all year around and not only during summer or spring where temperatures and light irradiance are higher. *P. agardhii* has been found viable under ice covers (Sivonen & Jones 1999; Oberhaus et al., 2007). Since both species occupies different water niches they can coexist in the same water body forming surface and deep layer blooms, althougth this coexistence is rare it has

Regarding the risk management measures that are usually followed to overcome the presence of cyanobacteria and cyanotoxins in the freshwater, *Planktothrix* has some particularities that need to be taken into account. One of them is *Planktothrix*´s ability to

**5. Challenges and gaps in** *Planktothrix* **spp. risk assessment and** 

genus that has also the ability to produce microcystins, which is *Planktothrix*.

associated toxicity found is presented in Table 4.

been reported (Davis & Walsby, 2002; Halstvedt et al., 2007).

**management** 


Table 4. Lakes were *Planktothrix* spp. has been reported to form recurrent blooms. **(a)** Bloom Sample/Environmental sample, **(b)** Filaments isolated from bloom samples,

**(c)** anti-Adda ELISA Kit, **(d)** HPLC, **(e)** protein phosphatase 2A inhibition assay (PP2A),

**(f)** Mean depth., (---) Information not available.

#### 74 Novel Approaches and Their Applications in Risk Assessment

Risk Assessment of Cyanobacteria and Cyanotoxins,

2008; Ernst et al., 2009).

since 2006 (Fig. 5).

samples (WHO, 1999).

**6.** *Planktothrix* **spp. occurrence in Portugal** 

the Particularities and Challenges of *Planktothrix* spp. Monitoring 75

establish populations at several depts. in the water column that allows them to access nutrients located near the bottom and still have enough light for photosynthesis, making them able to form blooms away from the surface. This unique characteristic of *Planktothrix* may possess a problem for the water monitoring authorities, since their bloom may be overlook by surface monitoring inspection (Sivonen & Jones 1999). Furthermore, *Planktothrix* blooms may co-occur with other cyanobacterial surface blooms what can also be misleading in water monitoring. Generally cyanobacteria blooms are expected to occur in highly nutrient rich waters during summer or spring months (Chorus et al., 2000). The responsible agencies for the reservoirs monitoring often restricts or increases to normal level the water inspection and water sampling frequency. *Plantothrix* species such as *P. rubescens* occurs in low nutrient oligotrophic waters forming perennially blooms that can prevail for many years. Furthermore since nutrients are not a limiting factor for *P. rubescens* it has been reported the lodging and development of population of this species after restoration lake activities and decrease in nutrient input since it improves trophic level and increases water transparency (Jacquet et al., 2005; Legnani et al., 2005; Ernst et al., 2009). So, in lakes were *Planktothrix* species occur the surveillance must be during all year (Utkilen et al., 1999; Naselli-Flores et al., 2007). Other important feature is that *Planktothrix* may contain higher microcystins content per cell, when compared with other microcystins producers; and that the proportion of toxic strains is higher in *Planktothrix* blooms than for example *Microcystis* blooms, this may result in the occurrence of high toxin concentrations in water without scum formation (Falconer et al., 1999; Briand et al.,

*Planktothrix* species can be commonly found in Portuguese freshwater reservoirs. Some of the species reported are *P. mougeotii/P. isothrix* from a wastewater treatment plant in the north of Portugal (Vasconcelos & Pereira 2001, Martins et al. 2010), *P. rubescens* from Beliche reservoir in the South of Portugal (Paulino et al. 2009a) and *P. agardhii* and *P. pseudoagardhii* isolated from several reservoirs in the center and south of Portugal that are maintained in laboratory cultures (Paulino et al. 2009b). However, their occurrence is more pronounced in the center and south of Portugal where it has been increasing and causing problems in some water reservoirs over the last years, such as the deep layer *P. rubescens* bloom with associated microcystin production reported by Paulino et al. 2009. Another example is the particular case of a drinking water reservoir located in the center of Portugal that has been monitored over the last eight years and where a continuous *Planktothrix* spp. bloom persists

As it can be depicted from Fig. 5 high *Planktothrix* cell concentrations started to appear in the reservoir in 2006 and microcystin concentration increased significantly since 2007. Furthermore, the microcystin concentrations in raw water does not correlate will *Planktothrix* cell numbers, since a high cell concentration does not indicate the presence of high microcystin concentrations and high concentrations of microcystins are not directly associated with high cell densities. This is probably because distinct strains/species of this genus with distinct ability to produce microcystins may occur together. In fact, a natural cyanobacterial population is usually a consortium of toxic and nontoxic strains, and this is believed to be the reason why the population toxicity can vary over time and between

Table 4. Lakes were *Planktothrix* spp. has been reported to form recurrent blooms. **(a)** Bloom Sample/Environmental sample, **(b)** Filaments isolated from bloom samples, **(c)** anti-Adda ELISA Kit, **(d)** HPLC, **(e)** protein phosphatase 2A inhibition assay (PP2A),

**(f)** Mean depth., (---) Information not available.

establish populations at several depts. in the water column that allows them to access nutrients located near the bottom and still have enough light for photosynthesis, making them able to form blooms away from the surface. This unique characteristic of *Planktothrix* may possess a problem for the water monitoring authorities, since their bloom may be overlook by surface monitoring inspection (Sivonen & Jones 1999). Furthermore, *Planktothrix* blooms may co-occur with other cyanobacterial surface blooms what can also be misleading in water monitoring. Generally cyanobacteria blooms are expected to occur in highly nutrient rich waters during summer or spring months (Chorus et al., 2000). The responsible agencies for the reservoirs monitoring often restricts or increases to normal level the water inspection and water sampling frequency. *Plantothrix* species such as *P. rubescens* occurs in low nutrient oligotrophic waters forming perennially blooms that can prevail for many years. Furthermore since nutrients are not a limiting factor for *P. rubescens* it has been reported the lodging and development of population of this species after restoration lake activities and decrease in nutrient input since it improves trophic level and increases water transparency (Jacquet et al., 2005; Legnani et al., 2005; Ernst et al., 2009). So, in lakes were *Planktothrix* species occur the surveillance must be during all year (Utkilen et al., 1999; Naselli-Flores et al., 2007). Other important feature is that *Planktothrix* may contain higher microcystins content per cell, when compared with other microcystins producers; and that the proportion of toxic strains is higher in *Planktothrix* blooms than for example *Microcystis* blooms, this may result in the occurrence of high toxin concentrations in water without scum formation (Falconer et al., 1999; Briand et al., 2008; Ernst et al., 2009).
