Tuesday, September 22, 2009

A Seaweed Microcosm....

If you want to explore exotic marine life in shallow seas you could jet off to a warm climate and scuba dive over a coral reef.......or you could just nip along to your nearest stretch of coastline (in our case Whitburn, near the mouth of the River Wear at Sunderland), collect a few small pieces of red seaweed and some seawater, take it home and examine it under the microscope.

This (below) is the piece of seaweed in question, floating in a rockpool.......

....and these (below) are just a few of the animals that I found living in it...

..First to break cover were these little crustaceans called isopods (which literally means 'equal legs' - all their legs are the same length - woodlice are terrestrial isopods). These are highly active little detritus feeders, breathing through gills at their tail end, and belong to a genus called Idotea..

..and they were swiftly followed by this little amphipod (meaning legs of two distinct lengths, long ones at the front, shorter at the back) which emerged from the waving weed fronds. Note the exquisite eyes of these little shrimp-like animals, known as gammarids...(more of those eyes in a future blog).....Whereas isopods tend to be flattened dorsiventrally (i.e. top-to-bottom), amphipods tend to be flatted laterally (side-to-side).

It soon became apparent that the thicker parts of the seaweed were covered with colonies of another phylum of animals called bryozoans (literally 'moss-animals'). These live colonially, interconnected, in little calcareous compartments. In the case of this species, each individual's shell was performated with holes, like an exquisite microscopic ceramic vase. The magnification used here is roughly x50Bryozoans (I haven't identified this species for certain yet, but I think it's Electra pilosa) feed by waving a tentacled arm called a lophophore, that looks a little like an old-fashioned wire egg whisk.

You can see extended lophophores (rather indistinctly, I'm afraid) in the following couple of photos.......

 ....The third phylum of animal to put in an appearance under the microscope (so far we've had crustaceans and bryozoans) was this exquite little sea slug, known as a nudibranch, which belongs to a genus called Eubranchus. Fully extended, this was about 3mm. long - a juvenile, that will probably grow to five or six times this size. Nudibranches are carnivores and it may well have been feeding on the lophophores of some of those bryozoans, although they typically feed on hydroid colonies (more about them in a future post). The back of this nudibranch is covered with strange, skittle shaped objects that wobble from side-to-side as it glides through the water. They're called cerata and are for gas exchange (nudibranch means 'naked gills' and that, in effect, is what these are). Remarkably, some species of nudibranch that feed on hydroids that are armed with stinging nematocysts (for more on nematocysts, see http://cabinetofcuriosities-greenfingers.blogspot.com/2009/09/flower-animal.html) can incorporate the nematocysts of their prey into the body wall of their own cerata, to protect themselves. Nudibranches detect their prey using incredibly sensitive organs called rhinophores, which are the top pair of tentacles at the head end. The pictures below are all of the same animal, but the lighting varies.

So there you have it.........a whole community of weird and wonderful microscopic animals living in a single frond of red seaweed in a rockpool. I spent a couple of very enjoyable hours photographing these but I've not doubt that I could have spent another day, extracting more microscopic marine life, before I exhausted the possibilities of this microcosm. There's a short video of the nudibranch on a separate post, above this one.You can find out more about all of these animals at http://www.marlin.ac.uk/species.php


  1. Amazing beautiful. How do you photograph in micro like that? Great info to with such detailed images. X

  2. Hi Sophie, they were taken by holding a pocket camera (Pentax W20) over the eyepiece of a low power binocular dissecting microscope. This wouldn't work with all digital pocket cameras - the W20 is a waterproof camera with internal focussing, which makes it easy - but you can do the same with some mobile phone cameras. Binocular dissecting microscopes cost about the same as a mid-price digital SLR camera and open up a whole new world to explore. Best wishes, Phil Gates


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