Water colours at Juva & a new optical phenomenon

Jari Piikki have also found some ponds with algal films that show optical phenomena. The ponds were sampled and the alga allowed to breed for some weeks. Extracts were photographed through a microscope. In one pond, Botryococcus alga was abundant nine years ago but then disappeared. Now it is back and quite large Quetelet rings and a corona were visible. Another pond on one island possibly contained Chromulina rosanoffi and microscope images showed it floating on the water surface.

Jari Piikki also found a new optical phenomenon. He took (like Marko) some samples from ponds and cultivated them. In one of them Chromulina disappeared and some other alga appeared. There could be seen a very colourful ring with two zones of spectral colours around the reflection from the surface of the Sun or an artificial light. The ring was oval and became smaller, when the light was brought closer to the water surface. Its diameter in sunlight was about 30 degrees and the inside was dark, so it was not an aureole. also visible when the light shone through the alga from below. Many photographs of the surface were taken with a microscope to show its structure. You can see it in some photos. The alga constantly changes constantly and now shows small colourful blotches.

[Text: Jari Piikki]

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