. The Canadian field-naturalist. Natural history; Sciences naturelles. 2005 Mann and Nambudiri: Charophytes of Insular Newfoundland II 33 to be capable of adapting to chemically different sati- nities, but also to a wide range of salinities. Winter and Kirst (1991) and Winter et al. (1996) determined that C. canescens has an upper salinity tolerance in the mesohaline range of approximately 20 parts per thou- sand (ppt) and a lower limit of ppt in the low oligo- haline range. It may be assumed that this is equally probable for C evoluta since both are often associates in inland and coastal
. The Canadian field-naturalist. Natural history; Sciences naturelles. 2005 Mann and Nambudiri: Charophytes of Insular Newfoundland II 33 to be capable of adapting to chemically different sati- nities, but also to a wide range of salinities. Winter and Kirst (1991) and Winter et al. (1996) determined that C. canescens has an upper salinity tolerance in the mesohaline range of approximately 20 parts per thou- sand (ppt) and a lower limit of ppt in the low oligo- haline range. It may be assumed that this is equally probable for C evoluta since both are often associates in inland and coastal waters. A few authors report C. evoluta from non-saline freshwater habitats (Allen 1900; Leake 1945). Also V. W. Proctor (personal com- munication) indicates that both species can be success- fully cultured under low salinity conditions to produce viable oospores. Brock (1986), however, suggests that for submerged aquatic plants in saline environments, extremes of tolerance are not the primary factors in determining the flora, but rather evolved life cycle mechanisms which allow survival under widely fluc- tuating conditions. Thus fluctuating salinities and/or ephemeral habitats would foster different floras than permanent water bodies with little salinity fluctuation. Some degree of salinity and/or particular ionic com- position appears to be required by C. evoluta (and C. canescens), but within this broad tolerance range from lower oligohaline (oligosaline) to mesohaline (meso- saline), presence or absence in water bodies may be a function of biotic community structure. This concept suggests that salinity may set the extreme boundaries for such species, but that community structure in- cluding competition, predation, herbivory, allelopathy, and others may determine the colonization ability of any given species. Barnes (1999) states that there is evidence that brackish water communities are not phys- ically structured by salinity, but by biotic processes such as predation and
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