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FEATURE Unfortunately, the toxic dinoflagellate Alexandrium ostenfeldii seems able to withstand changes in both temperature and salinity without affecting how its dormant cysts germinate. There is significant genetic variation within this dinoflagellate, and it is well-equipped to meet climate change.
Resting stages in the form of cysts is an effective method for plankton to ensure its survival through periods of poor environmental conditions. The stocks of dormant cysts function as reserves, often with a higher genetic variation than the part of the population that is in the growth phase. As a result, these cysts can be an important factor for survival in a changing environment.
Many phytoplankton species have these resting stages. Cysts can survive in bottom sediment in lakes and seas for years, sometimes even for decades. In dinoflagellates, this type of cyst is common, and effective for survival.
The process of when cysts emerge from the dormant stage to germinate, can be triggered by favorable environmental conditions. This can mean that a large proportion of the cysts germinate in synchronization for a limited period of time. In other cases, germination is spread out over longer periods of time, which indicates that they can withstand a great variation in environmental conditions.
The dinoflagellate Alexandrium ostenfeldii causes toxic algal blooms in the shallow, coastal Baltic Sea waters. Like many other dinoflagellates, it produces resting stages as part of its life cycle. Previous studies have shown that the supply of dormant cysts in coastal sediments reveals a large genetic variation.
The increase in temperature of 3 to 5 degrees that has been forecast for the Baltic Sea is likely to be even greater in the shallow, stratified waters where A. ostenfeldii is most common. Elevated summer temperatures could increase A. ostenfeldii blooms, which could cause problems due to its ability to produce toxins. It is therefore important to have a thorough understanding of the mechanisms behind the growth of the species, in order to predict the species' impact on the sea of the future.
The researchers therefore wanted to investigate whether changes in salinity and temperature affect the extent to which the resting cells awaken and begin to divide. By exposing dormant cells to different salinities and temperatures, the researchers investigated whether special strains of the dinoflagellate are selected by the changed environmental conditions when the resting stages come to life, or if this selection occurs later in the growth phase.
Surprisingly, results showed that the germination rate was largely unaffected by the changes in salinity and temperature. Thus, it does not appear that certain strains of the species are selected at the germination of salinity and temperature changes. It is possible that the rate of germination was slightly affected, but in the end, an equal proportion of the resting cells germinated regardless of whether salinity and temperature had changed. In later growth phases, however, salinity and temperature can have a major impact on this species.
A. ostenfeldii does not appear to have a distinct resting stage during the year. The dormant cells can come to life at any time during the year, even though it mainly occurs during spring and summer. The resting cells appear to have a wide genetic variation, and thus the species is inherently tolerant to varying environmental conditions. Unfortunately, it seems to be well-equipped to cope with changing environmental conditions, due to its high tolerance to different conditions, its adaptability and the standing genetic variation of the population.
The article has earlier been published in the EcoChange annual report 2019. The text is based on:
Jerney, Jacqueline; Suikkanen, Sanna; Lindehoff, Elin; et al. 2019. Future temperature and salinity do not exert selection pressure on cyst germination of a toxic phytoplankton species. Ecology and Evolution, WILEY 2019, Vol. 9, (8) : 4443-4451.