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Autecology of Ctenocladus (Chlorophyceae) in saline environments Blinn, Dean Ward

Abstract

Ctenocladus circinnatus Borzi, a member of the Ulotrichales, has a limited distribution being restricted to saline aquatic environments of specific physico-chemical composition. Most of the collections of this alga have been in North America, with a few scattered collections in Peru, Sicily and Siberia. Confusion in the nomenclature of this taxon has led to the use of two generic names Ctenocladus and Lochmiopsis. Based on field observations, laboratory cultures and herbarium material it appears that Lochmiopsis and Ctenocladus are one with Ctenocladus a monotypic genus. In order to study the ecology of Ctenocladus, seasonal physico-chemical parameters of seven saline habitats were investigated over a two year period in the dry interior zone of British Columbia. Three of the sites contained Ctenocladus while the remaining four habitats were used for comparative purposes. Additional collections of Ctenocladus and water analyses were made from several saline habitats in California and Nevada. In addition, controlled laboratory regulation of environmental parameters (pH, temperature, light, osmotic potential and specific ions) considered to be important in the ecology of Ctenocladus were conducted and correlated with field observations. The cation composition of the waters appears significant in the distribution of Ctenocladus. Waters composed predominately of Na⁺ salts with Na⁺:Mg⁺ ratios greater than 1.5 were required for normal vegetative growth. Cultured material placed in the field in various investigated saline habitats substantiated this as well. Akinete germination could only be induced with Na⁺ salt solutions, while other cations (K⁺, Mg⁺⁺, Ca⁺⁺) were extremely toxic to these cells. Anion constituents do not appear to be significant in the distribution of Ctenocladus as collections were made in all of the major anion solutions in nature (S0₄⁼, CO₃⁼,Cl⁻) and substitution of various anion salts to laboratory cultures showed no significant changes in growth and development. Temperature may also be significant, particularly in shallow open waters of semi-permanent habitats where temperatures rise above 35°C during the summer. Corresponding laboratory experiments indicated that resting akinetes were extremely susceptible to these high temperatures. Light intensity appears to influence the condition of akinetes with levels above 12,000 lux detrimental to viability. Salt encrustment of clones of akinetes and burial beneath the sediment and precipitated salt deposits may play an important role in survival of these resting stages. Waters of saline habitats with Ctenocladus were above pH 9.0 during most of the year while other sites without the alga were generally below this value. Laboratory studies showed pH below 7.5 to be detrimental to akinetes indicating pH to be indirectly significant as it reflects the ionic constituents of the natural solutions. Akinete production appears to have substituted for the resting zygote in maintaining the population in these extreme environments as shown in both field and laboratory experiments. Most cells are converted into akinetes at osmotic levels above 3000 mOsm and remain in this condition for most of the year. Massive akinete germination occurs following spring dilution from runoff and when water temperatures are above 5°C. Zoosporangia production may not occur every year in shallow saline habitats when high salinities are achieved early in the season. Zoosporangia were only induced in laboratory cultures at osmotic potential levels below 1300 mOsm. Field observations substantiated this as well. The total lack of genetic recombination in Ctenocladus populations may have restricted the organism to a very narrow ecological niche as witnessed both in the field and the laboratory.

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