(This post is participating in a Pacific NorthWest scavenger hunt today. Details and links on Patricia Lichen's blog.)
The first time I saw the splotches on my underwater photos, I thought I had dirt on the lens. I wiped it (smearing the oil slick around a bit), took more photos of the same area, and the screen showed me even more spots. Dirt in the water, I figured; caught by the flash.
|Spots, ruining a photo of anemones and mussels on a pipe. (I increased the contrast and de-saturated the colours a bit, to make them easier to see.)|
|But why are all those dirt specks so perfectly round? Click on the photo to get the full impact; they go on and on into the background.|
It wasn't until I was inspecting a photo at home, wondering if it was salvageable, that I saw a pattern in one:
|A cross jellyfish, almost completely transparent. I highlighted it. .|
Looking back at the previous photos, now I recognize the hints of structure in what looked, on site, like clear water. At least some of the photos may have captured jellyfish.
But we had seen none floating near the surface; last year, there were quite a few, close enough to photograph with the above-water cameras. I dug up the old photos and inspected the under-the-dock ones.*
|A large anemone, and some small jellies. One, beside the stalk, looks like a moon jelly. Taken without flash.|
I thought, then, that maybe most of the other circles, the ones without crosses, could also be jellies, like some we photographed last year. They showed a distinct centre circle, then a rayed "doughnut" around them, like the Aequorea species. I wrote the post up this way, then Tim came along to correct me. He said dust caught in the flash made those circular shapes, too.
Yes, but ... on some the rays were too evident to be an illusion. Or were they? I mulled it over, then tried an experiment. I filled a large black bucket with water from the tap. I didn't wash the bucket first, so it was dusty. I added a white kitchen utensil for a focal point, dunked the camera, and took a few photos.
And the "jellies" turned up there, too! So much for that. Some of the circles had the same rayed doughnut shape. None had the cross on the top, so at least those were probably really jellies.
|Sample section from bucket photo.|
These next photos were taken last year, with the dry-land camera. They were swimming just under the surface, in full sunlight. The water was clear, but there was a sprinkling of dust over the surface.
|A doughnut, one of the "water jellies", Aequorea spp. Look closely to see the trailing tentacles at the bottom.|
|Top view of a water jelly. Like the cross jelly, it is bioluminescent, giving out a green light when disturbed.|
These two jellyfish are leptomedusas. ("Lepto-" means "flat"; the bell is wider than it is deep.) They spend part of their life as hydroids, fixed to a solid surface. The jelly, or medusa, is the adult stage. They reproduce by spawning eggs or sperm freely into the water; once the egg is fertilized, it sinks to the bottom and grows a new hydroid. In this stage, it is a colonial animal, where each member has its own function. Some bud; the buds sometimes develop into new medusae. When they are ready, they break off and swim away.
|Anemones, June 2010. Flash used.|
*How to get an underwater shot with a dry-land camera: worm yourself into a position close to the water surface and completely in shadow. Arrange it so that there is more light on your subject than on the water surface. Aim from a low angle to the surface. Don't use the flash. Don't fall in, either.