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Verrucaria maura

Verrucaria maura (pictured above) is also known as black tar lichen. Most people are amazed to find out that it's actually a living thing because it does look like a black stain on the rocks. It forms a thin crust on the upper shore and just into the splash zone and is responsible for the very distinctive horizontal black band that can be seen on many shores. It is grazed by rough winkles (three in the picture) and can tolerate this because it grows faster than most lichens. Limpets may well have a quick scrape at it too. You could confuse it with another Verrucaria species, Verrucaria maura (the green tar lichen). This lives lower down the shore (middle shore) and sometimes looks quite green. Sadly it quite often doesn't. The way to tell them apart is by location and by scraping a little bit up with your thumb nail. V.mucosa always looks green on your nail. Wetting it helps and also it tends to be a thicker, shinier crust. There may well be competition between the two Verrucarias where they meet. Is it that V.maura is more successful in the (presumably) more favourable terrestrial end of the habitat? Or is it that V. mucosa is better able to tolerate immersion and doesn't compete at all? Or is it a combination of these things and maybe others? How can it be so difficult to answer simple questions about a couple of crusts? Herein lies the fascination of ecology.

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