The forgotten world of subaerial desmids (Zygnematophyceae) in the Atlantic Forest, southeast Brazil

Abstract

Although desmids (Zygnematophyceae) are widely distributed, their diversity in subaerial environments remains little known and explored. Subaerial algae live above the soil in a thin water film, directly exposed to the air. Desmids possess specific strategies to face environmental stress, such as mucilaginous sheaths that enable them to adhere to the substrate and protect the cells against desiccation. Also, zygospore production may be a strategy to survive. We conducted a taxonomic survey of the subaerial desmids in the Atlantic Forest biome (Rio de Janeiro city and other municipalities in the state of Rio de Janeiro). Briefly, we analyzed their strategies to resist sudden environmental changes, especially desiccation, a common condition in this environment. From 2006 through 2008, 100 samples were taken from natural and artificial vertical wet surfaces and tree bark. The material collected was identified based on morphological and metric characteristics of the vegetative and reproductive phases of the life cycle. We identified 57 species, varieties, and taxonomic formae, distributed in 12 genera, 2 orders, and 4 families. The study revealed that most subaerial algae were previously reported for Europe and North and South America. From the total taxa, 12% are reported for the first time for Brazil and 14% for South America. Even though subaerial environments are subject to stressful conditions, only three of the 57  taxa showed adaptive structures such as thick mucilage envelopes, spores, or zygospores.