The ichthyotoxic genus Pseudochattonella (Dictyochophyceae): Distribution, toxicity, enumeration, ecological impact, succession and life history - A review.

The marine genus Pseudochattonella is a recent addition to the list of fish killing microalgae. Currently two species are recognised (viz. P. verruculosa and P. farcimen) which both form recurrent coastal blooms sometimes overlapping in space and time. These events and their ecological and economic consequences have resulted in great interest and concern from marine biologists and the aquaculture industry. Since the first recorded blooms in Japanese (late 1980s), Scandinavian (1993) and Chilean (2004) waters numerous studies have focused on understanding the causative means of the fish killing. Mortality is probably due to Pseudochattonella discharging mucocysts that cause gill irritation and damage to the fish fills. Here, a review is provided of the literature on Pseudochattonella that covers the last ca. 25 years and focus on a number of topics relevant to understanding the general biology of the genus including ways to distinguish the two species. The literature addressing biogeography and known harmful events is evaluated and based on these findings an updated distribution map is proposed. P. farcimen is presently restricted to North European waters. Despite being very difficult to delineate based on morphology alone the two Pseudochattonella species seem to have separate growth optima. In laboratory experiments P. verruculosa consistently has higher temperature growth optima compared to P. farcimen though periods of overlap have been noted in the field. The review ends by proposing five areas with knowledge gaps and each of these could form the basis of future studies.