Underwater Fluorescence

It has been three months since the last blog post so high time for an update. I have not been out much as the weather has been grim. In fact, the photos in this post are one year old! I bought a blue LED light for fluorescence photography which has been gaining popularity in recent years. Many organisms and fluoresce (i.e. absorb light and emit it at a longer wavelength), although the function of this is generally not well-understood (perhaps in some cases it might not even have a function and just be a byproduct). Coral reefs can especially be spectacularly fluorescent but the cold waters of the UK harbour a variety of fluorescent organisms too, most notably anemones and corals, see here for great marine fluorescence photos from Scotland by James Lynott. Anyway, I bought my light and a yellow barrier filter (which serves to let the emitted fluorescent light through but not the blue light) to be held in front of the camera housing, as well as a headset barrier filter from a very knowledgable German chap here; his site contains a lot useful information for those interested in the background and applications of this type of photography (see also here, here and here). The photography is very tricky: the ISO needs to be bumped up in the dark which results in a lot of noise. The dark also requires long shutterspeeds which results in shaky images. A large aperture for more light is best, but since the subjects are usually small this results in suboptimal depth of field.  I have only been out twice last January, and only whilst rockpooling (I have not done a single nightdive or nightsnorkel in Cornwall and I am not overly tempted to do so!). The very shallow rockpools high up at Castle Beach in Falmouth reveal some fluorescent animals, including hermit crabs but I focused on anemones. Snakelocks are big and very fluorescent (the green ones, the grey variety is not, although it does emit red light via its symbionts) but not common high up the shore. Hardly visible normally due to their small size and inconspicous colours, red-speckled anemones, daisy anemones and gem anemones become apparent using a blue light (in fact, this method is use to study tiny coral recruits in the tropics). The top photo shows two green gem anemones Aulactinia verrucosa (with red and purple coralline algae in the background). The anemones are very small (2 cm max) and I used my CMC-1 wetlens on my Canon G16. The other two photos show Daisy anemones Cereus pedunculatus. I only later noticed the tiny anemone babies (this is a livebearing species). I hope when the rain and wind disappear and the evenings still start early to go out again and post some more photos. Also, I have bought both a new camera and a new aquarium so I have plenty more to post about!

Snakelocks Anemones Anemonia viridis

I have been snorkelling a few times in recent days and it has been generally fantastic. The pools are probably at their peak now when it comes to seaweeds, I hope it lasts a little while longer (in June it will most definitely be over, see this old post, actually, they are in decline in May already). It is the plan to get in the water again this week to take some more seaweed photos, but in the meantime some photos on one of the more common anemone species: the Snakelocks anemone Anemonia viridis. There are two colour morphs: the greys and the purple-tipped greens. In Falmouth, they seem equally common, no matter if it is high on the shore or subtidally. I recently learned that in Scotland there are almost only greys, perhaps in the Med there are mainly the other type and it has something to do with temperature tolerance, if you know please let me know in the comments! I really like thuis species, in fact, the very first blog post back in 2013 consisted of a photo of these anemones in my aquarium. I have two of these in my aquarium at the moment, they are very easy to keep. This might be because in addition to being voracious predators, they are also capable of living on sunlight, as they harbour photosynthesizing algae. In any case they grow rapidly (and very occasionally split into two).I took these photos in very shallow water. When scuba diving you can commonly observe the commensal Leach’s spider crab Inachus phalangum sitting under the anemones (see here in the aquarium and here in the wild). (In Dorset there is a beautiful little prawn that lives as a commensal, and in the Mediterranean there is a goby that is associated with this species.) Only very occasionally do Snakelocks attempt to retract their tentacles (see here); tentacles can be quite long and slender or more stout (see here), probably a response to the strength of the currents. I have tweaked some of the photos a tiny bit (but not the nicest one on top for instance). Below two photos taken on different days of the same three anemones with different light conditions and different camera settings (most importantly probably the white balance, which I use to tone down the reds caused by the seaweeds).