The development of the protistan species-maximum concept for the critical salinity zone

Abstract

Until recently, the general biodiversity concepts have suggested common patterns of species richness dynamics for both small planktonic and large benthic organisms in the gradients of environmental factors, including salinity, which is the major abiotic characteristic that influences the diversity of flora and fauna in coastal marine ecosystems. Recent studies discovered an extremely species-rich aquatic microworld and resulted in proposing new concepts and shifting the paradigms in biodiversity studies, including those on planktonic unicellular eukaryotes such as protists. As a result, Remane’s species-minimum concept has been revisited and the range of its application updated. This paper provides a review of the studies dedicated to establishing, developing, and analyzing the novel protistan species-maximum concept for the critical salinity zone (5–8‰), or the horohalinicum. The obtained new data contribute to the formation of the modern views on aquatic ecosystem dynamics, biodiversity conservation, and effective ecological management aimed at maintaining the environmental balance and the rational use of marine biological resources.