Multiannual Chattonella subsalsa Biecheler (Raphidophyceae) blooms in a Mediterranean lagoon (Santa Giusta Lagoon, Sardinia Island, Italy)

Recurrent blooms of Chattonella subsalsa (Raphidophyceae) were associated with fish kills in Santa Giusta Lagoon (Mediterranean Sea). This study investigated the population dynamics of C. subsalsa and its relationship with environmental and meteorological conditions, using multiannual ecological data (1990-2016). In addition, for the first time, this study examined the presence of C. subsalsa cysts in lagoon sediments. The species was first detected in Santa Giusta Lagoon in July 1994. Bloom events coinciding with fish kills were recorded in 1994, 1998, 1999, and 2010. The timing and dynamics of C. subsalsa blooms and fish kills varied over the examined period. Presence of C. subsalsa was strongly influenced by temperature, especially in the early years of the series (1990-2002). Temperature control may have been lesser important in the more recent years, when higher temperature may have generated continuative suitable conditions for C. subsalsa affirmation, especially in July. Thus, the variations in the availability of food (via autotrophy and/or mixotrophy) could be one of the control keys on the proliferation of this species in the future in SG. Cysts of C. subsalsa were present in lagoon sediments at abundances ranging 200-2000 cysts g−1 wet sediment. This study is among a few that have examined C. subsalsa population dynamics and bloom events in the field over a long time period. Findings from this study contribute to a better understanding of C. subsalsa bloom development, by identifying environmental and meteorological variables that may promote blooms of this species in the Santa Giusta Lagoon.