Pfiesteria shumwayae
Sexual
In sexual reproduction of P. shumwayae, (see diagram below) two gametes fuse (1) to form a planozygote (2). The cell engages in nuclear cyclosis[1] (3) which produces two flagellated offspring (4). Some of the steps in reproduction are unknown because of the difficulty researchers have in documenting information. The vegetative cells and the gametes look very similar, and fusion can easily be confused with division, making it difficult to differentiate between cycle phases. <ref name=Parrow2003> That is why after nuclear cyclosis, it is unknown whether another division takes place before the excystment of offspring (5) and (6). According to Parrow and Burkholder’s research, reproduction in P. shumwayae seems to be unlinked to a survival strategy, and reverts to a sexual cycle because of self- sterility factors that favor outbreeding while taking advantage of food availability and environmental quality.
Ecology
Fish kills in warm coastal estuarine waters are usually attributed to harmful algal blooms of Pfiesteria. It is not typical for these blooms to occur after hurricanes and storms or in “high-wave-action, wind mixed” surface waters because Pfiesteria prefers calm, quiet water conditions, like poorly drained brackish water.[1] It is implicated that the stress of low oxygen and hypoxia in such waters is the primary cause of these manifestations.
Current Research
It has been established that Pfiesteria shumwayae kills fish by feeding on its epidermis. Research by Skelton, Burkholder and Parrow (2008), supports the idea that Pfiesteria is responsible for fish kills and lesions on wild fish due to myzocytosis and not so much exotoxin release. Many fish kills documented in their on- site field research show that non-inducible and temporarily non-toxic strains of Pfiesteria were present during kills and were not actively toxic. But Vogelbein et al. (2002) stated that there is some ambiguity of the role Pfiesteria plays in the mortality of wild fish due to pathogenicity via micro-predation versus exotoxin release. This conclusion is logical because in vitro assays sometimes cannot discriminate fish kills caused by exotoxins of toxic strains or myzocytosis. It can be suggested that more research be done to propose a definite conclusion to this issue. However, retrieving substantial and accurate information on fish kills using traditional research methods is difficult for several reasons: 1). Pfiesteria zoospores change phases or life cycle stages, and may settle out of the water column making it harder to detect and quantify 2). Since these occurrences are in the form of blooms, they tend to be ephemeral and 3). There are Pfiesteria–like species present in the field that are morphologically similar to Pfiesteria, making it difficult for researchers to identify and distinguish one from the other.[1]