Distribution and ecology of green alga Zygnema aplanosporum (Zygnematophyceae) in Californian streams

Background/Question/Methods

The Zygnematophyceae are important components of many freshwater ecosystems worldwide, but their biodiversity and ecological tolerances remain poorly studied due to the taxonomic importance of rarely observed reproductive structures. This study concentrated on benthic algal communities collected from over 1,300 stream locations in California from 2007 to 2011 including preserved quantitative and fresh qualitative samples. A new member of filamentous genus Zygnema was described, and named after its predominant asexual reproduction by aplanospores – Z. aplanosporum. The genetic identity of Z. aplanosporum populations across California was confirmed by rbcL and cox3 analyses. This species was virtually unknown until now because the algal communities in these habitats are poorly examined. The aim of this work is to present the distribution and ecological preferences of Z. aplanosporum in the light of its potentially endemic distribution.

 Results/Conclusions

Z. aplanosporum was recorded in 37 streams across the California from Siskiyou County to the north to San Diego County to the south at elevations 36-2109 m a. s. l. All streams were located in protected forest areas (National Forest or State Parks), except for a few locations in Mendocino and Sonoma County. The habitats of Z. aplanosporum were characterized by minimum human disturbance, high canopy cover (median: 58%, range: 6-91%), dominance of boulders, cobble, gravel (median: 57%, range: 3-58%), and near absence of fine substratum. The water quality parameters were as follow: median pH 7.8 (range 7.1-8.6), median alkalinity 72 mg/L (range 10-155), median specific conductivity 152 µS/cm (range 7.7-402), median TN 0.089 mg/L (range: <0.020-0.302 when detectable), median TP 0.022 mg/L (range: 0.001-0.062). Z. aplanosporum was associated with other algae regarded as indicative of good water quality, such as the red algae Paralemanea catenata, and Batrachospermum boryanum, and several nitrogen-fixing cyanobacteria. We have concluded from these observations that newly described green alga Z. aplanosporum is indicator of good water quality with restricted distribution in protected areas in California.