Fungal Diversity Freshwater and marine lichen-forming fungi

Lichen-forming fungi can occur on river and lake margins subjected to varying water levels, and on tidal coastal rocks where they can constitute major components of the biota. There are approximately 700 species known from coastal rocks and 200 from freshwater river and lake margins. Most cannot survive constant immersion although there are exceptions. Some species are only exposed at the lowest tides or when there are exceptional droughts. Vertical zonations of lichens are characteristic of freshwater and marine habitats. The heights of zones vary according to the degree of exposure and periods of inundation. Measurements of these zones can be of value in assessments of risks due to storms and of river channel capacity. Attention is also drawn to mycophycobioses in freshwater as well as maritime situations. Most work on coastal and freshwater lichens has been in temperate regions. In the tropics lichens are less well developed on coastal rocks, but tropical stream margins are yielding species new to science. The ecophysiology and biology of these fungi is scarcely explored, but some key features are highlighted. Many fundamental aspects of these fascinating fungi remain uncertain, for example where different species of the same genus occur in both habitats. The systematics, ecology and physiology ofthl~se fascinating fungi merit increased attention by mycologists.