AME 43:153-163 (2006)  -  doi:10.3354/ame043153

ABSTRACT: Solar salterns in temperate climates commercially produce salt in the summer. To determine whether prokaryotic growth-related variables vary seasonally along the salinity gradient, ectoenzyme activities, prokaryotic abundance (PA), prokaryotic heterotrophic production (PHP) and environmental variables were measured in a solar saltern in 1999 and 2001. In low-salinity (i.e. <120‰) ponds, where marine bacteria are known to dominate the prokaryotic community, positive relationships of ectoenzyme activities with PA (aminopeptidase: r² = 0.51, p < 0.01, n = 16; β-glucosidase: r² = 0.57, p < 0.01, n = 17), temperature (β-glucosidase: r² = 0.56, p < 0.01, n = 17) and PHP (aminopeptidase: r² = 0.25, p < 0.05, n = 16) were observed, as also reported for ordinary marine environments. However, in high-salinity (i.e. ≥120‰) ponds, the relationships became insignificant or weak, and a strongly negative relationship between aminopeptidase activity and salinity (r² = 0.71, p < 0.01, n = 19) was found. Thus, the high salinity seems to significantly reduce ectoenzyme activities. In high-salinity ponds (120 to 390‰) per-cell ectoenzyme activities decreased by as much as 2 to 3 orders of magnitude. Furthermore, substrate-addition and temperature-treatment experiments indicated that limiting factors for PHP vary seasonally in the saltern. PHP was limited by organic compounds (i.e. glucose and an amino acid mixture) in the spring at a salinity of 120‰ and by osmoregulatory substances (i.e. betaine) in the summer at salinities of 260 to 390‰, and temperature in the autumn at 29 to 213‰. Despite the dominant influence of high salinity on prokaryotic activities, relationships between prokaryotic parameters varied seasonally both in low-salinity and in high-salinity ponds. Thus, it seems that prokaryotic variables along the salinity gradient in the saltern are controlled by different factors over seasonal cycles.

KEY WORDS: Ectoenzyme activity · Mono- and polysaccharides · Prokaryotes · Abundance · Production · Solar saltern · Seasonal variation