Algae optics in Wisconsin

While on my 4-wheeler riding around in the wood in Lakewood Wisconsin I came upon a puddle with a green film in it in the middle of a dirt road and I drove up to check it out and I am glad I did! As I was dismounting from my 4-wheeler colors on the puddle caught my attention and I found the same thing Marko Riikonen found algal optics. Over the period of 10 minutes or more I observed corona similar to pollen corona around sun’s reflection and Quetelet rings which I have always wanted to see. I also saw glory with the similar brightening’s like pollen corona and a white fogbow like glow around the glory. More pictures here.

Author: Michael Ellestad, Wisconsin, USA

Algae corona

This photograph was taken by Hans-Jürgen Heyen from Meerbusch. “I discovered the glory effect in August 2012 at the pond of Hugenpoet Castle in Essen-Kettwig. It made me take a closer look at the water because one tends to think that there are mineral oil products on the surface. But there were gigantic carps in the pond and also some big golden fish which looked like koi-carps. And also a beautiful demoiselle flew over the water. And especially this species of dragonflies is very sensitive against environmental pollution. However, what really was there in the water were algae which caused a significant clouding of the water, and this obviously was the reason for the formation of the algae glory.”

These coronae are caused by light diffraction on very small particles. In most cases, they are caused by algae, but there were also such coloured rings observed around pollen which had landed on the water surface. The coronae are caused when a ray of light is split up into partial beams by such a small particle. These partial beams go on into different directions and interfere in the observer´s eye.

Just like pollen coronae, also algae coronae are not always round. When there are unusually shaped algae are involved, also their ring systems on the water surface can be ovally shaped or have bright spots.

Algal optics

The season for algal optics has started, the first display was seen here in Finland already in the beginning of April.

The algal films that display optical phenomena are clearly not as rare as have been thought. In the Baltic sea rocky islands about every 10th freshwater pool came with algal optics last summer. In Bulgaria, the species Chromophyton rosanoffii, which is responsible for the phenomena in the photo, has been described as common.

When it has not been raining for some days, go look for any freshwater ponds, puddles and pools. If the water surface is covered by a thin film, chances are that some sort of optical phenomena is visible in the sun light.

Author: Marko Riikonen

Small coronas from bacterial film on water surface

Most of the cultivation pools in my room are now showing much smaller coronas than earlier. In each pool the corona is of constant size over the whole bacterial film surface, but from pool to pool their size vary.

Even though these coronas are smaller than before, they still are large as compared to pollen coronas. Unfortunately I have no photos for comparison.

In the composite image are two coronas photographed with same lens (not to scale with upper single image, which has been taken with zoom lens). The microphotograph of the bacterial film is from the smaller corona on the left.

The light source was a 50 W halogen spotlight that I made even more concentrated by placing the lamp in a cardboard box, into which a small hole was made for light to come through. When taking photos, the room was otherwise darkened.

[Posted by Marko Riikonen]

Chromulina rosanoffii as a cause of optical phenomena on water surface

Excavating the literature finally gave confirmation that it is the alga Chromulina rosanoffii that causes Quetelet rings and glory on water surface. This unique sort of alga separates itself from the water surface by forming a stalk on top of which it rests. This is seen in the right hand microphoto which is taken parallel to the water surface. Light blue is air and black is water. On the left is a photo taken at right angle to the water surface, thus giving a look at the C. rosanoffii forest from above (transmitted light). If the alga is for some reason submerged in the water, it sheds its stalk and starts immediately swimming. The b&w photos here show C. rosanoffii submerged in water.

Also two photos of the optical phenomena caused by this alga are displayed in the composite. On the left is a fisheye view with Quetelet rings. The glow around the camera shadow is fogbow. Notice the brightening towards nadir in fogbow, indicating possibly non-spherical particles. The photo on right is taken further away from the cultivation tub, showing spectral colored glory rings. Attached to the outmost glory ring is faint, white fogbow.

All said here about the biology of C. rosanoffii was known long time ago. The alga was described in 1880 by Russian botanist Woronin, who encountered it while visiting Finland. One aspect of the studies carried since has been the golden glow that well developed C. rosanoffii surface film displays, as shown beside and here. But I have not yet met in the literature any mention of the spectral colors, which strikes me as a small wonder. However, there is still plenty of reading to be done, so something may come up.

[Posted by Marko Riikonen]

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]

Optical phenomena from algal film on water surface

Here are some results from the work I have done this summer on the phenomena caused by algal film on water surface.

The upper pair of photographs shows elliptical corona and the alga that caused it. Pine pollen gives the scale. This corona-type display has no other phenomena.

The lower photo shows another type of display, which exhibits Quetelet rings, brightenings around sun””s reflection image, glory and fogbow. In this case there is also unidentified diffuse feature marked with arrows. In addition, fogbow and glory have spot-like brightening towards nadir. Two B&W photos of the algae causing this type of display are shown. In the lower photo the algae are possibly turned 90° in comparison to upper, showing elliptical shape. This species might be Chromulina rosanoffii. It””s about 5-10 µm in size (not to scale with upper color photo) and well transparent to make glory.

These phenomena turned out to be common, at least this summer. They were most abundant on rocky Finnish archipelago islands, which harbour endless number of small rock pools.

[Posted by Marko Riikonen]