Wednesday 27 May 2015

Creatures of the Blue Lagoon

Last week we finished our wander along the sands of Ferma Bay at a place where a ring of rocks form a sort of lagoon. This is a perfect swimming hole with the water no more than three to four metres deep and it’s absolutely teeming with marine wildlife. So, cozzies on, snorkels to hand and we’ll go and meet some of our watery cousins.

If we occupy this nice big flat rock here it will be ideal for setting out our samples. No, you can’t take half of it with your towel – there will be plenty of time for sunbathing later on. 

Peacock's Tail, Padina pavonica
Just take a look down among the rocks and you’ll see that we have some delicate funnel shaped growths of a seaweed called Peacock’s Tail. It is somewhat unusual in that instead of being brown, green or red like most seaweeds it’s a lovely pearly white colour. Technically it’s a brown alga but the whiteness is caused by deposits of calcium carbonate (as in chalk). If I tell you that it’s scientific name is Padina pavonica some of you of a certain age may be thinking “I’ve heard of that somewhere.” You probably have - Extract of Padina Pavonica or EPP is sold in beauty shops as anti-wrinkle cream. I see that one of the strands down there is growing a blue-green beard which is a trifle unusual and requires investigation. I think we’ll take that home and pop it under the microscope. I wonder if it could cause a similar side-effect in EPP users? Probably not but it’s an amusing thought.

Isopods caught with a simple net and tray
All you need to have hours of amusement down here is a simple net for catching specimens (a couple of euros from any beach shop) and a container to put them in (this one held last week’s pork joint). A quick tip; the net works better if you flatten it at the top. A quick sweep of the surface and one of the floor and we’ll see who’s about. Quite a variety here, including two of the 250+ species of Isopod to be found in the temperate waters of the Mediterranean and the North Atlantic. Isopods are crustaceans, related to crabs and lobsters but working on the theory that more is better they have seven pairs of legs (all roughly similar hence Iso = same and Pod = foot), two pairs of antennae and two penises. Well, if you’ve got it, flaunt it I say.

Crabs are Decapods (Deca = 10 and Pod = foot)
Talking of crabs I see that you have a little Hermit Crab in the tray there. These are the guys that prefer to rent a shell as they go along rather than going for the self-build option that other crabs adopt. They are soft bodied and their abdomens have evolved with a kink to one side, the better to fit into the spirals of discarded mollusc shells. Whilst you’ve been examining him I’ve found a little red job floating around between the rocks. Quite dead unfortunately but in life I suspect he was one of the Spider Crab family which are quite diverse in their appearance but often have a tendency to be red and spiny. A cautious tickling around my heels tells me that while we’ve been investigating them a little Shore Crab has emerged from a crack in the rocks and started to investigate me. Nice to know that curiosity about other species works both ways.

Banded-dye Murex
What else have you got in the tray – a snail giving birth? Let me see. Now that is curious. The animal in question is, I believe, a Murex. Back in ancient times these were big news in the eastern Mediterranean as a magnificent purple-blue dye could be obtained from them. It took so many snails to make one gram of dye that it was prohibitively expensive for all but the highest aristocracy, hence the name for one of the colours it produced: Royal Blue. As to whether it is giving birth, I rather think not. Although some snails do give birth to live young the Muricidae family, to which this one belongs, deposit capsules of eggs in tide pools and the like. However, they’re a carnivorous species, often boring holes into other molluscs to extract the soft parts, so with a small snail like this one maybe they ingest the whole animal, suck out the juicy bits then spit out the shell like we do with olives and their stones.

Baby Squid
On the other hand, this little string of red tinged translucent jelly, squirming around in the tray like someone trying to snuggle down into a duvet with their hands tied behind their back, most definitely is a baby. It’s a baby squid. Squid are related to the Murex and other snails and slugs but they are part of a specific group of molluscs called cephalopods who have their feet attached to their head (kefalo = head pod = foot).  The feet have evolved into tentacles for catching prey and the group includes squid, cuttlefish and octopuses and also the Nautilus which, unlike the other three, has kept its external shell. Maybe we should keep it and raise it to become a politician? After all the best part of presidential or prime ministerial elections are the gaffes made by prospective candidates and cephalopods are always putting their foot in their mouth.

Until next week – happy hunting and I’ll leave you with a video link to watch all these creatures swimming about in the tray.
See all the pictures including insets in detail on Flickr

Naturalists (the facebook page that accompanies this blog)



  1. Tyrian purple came from Murex? Or was that amethyst?

    1. Yes Simon, Tyrian Purple is also obtained from Murex.

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  3. cephalopods are always putting their foot in their mouth
    That's a good one! :)
    I did a rundown of the different numbers of -pods on my blog, long ago.
    I'm going to update it to add your foot-in-mouth comment. (With a link, of course.)

  4. Thanks Susannah, I'll take a look.

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