Nature Diary

Life in the Mar Menor – Part 1 : Sealife

During the past couple of years Mollymawk has been based in the Mar Menor. It’s not the most attractive or exciting place in the world, but the Ship’s Naturalist has found plenty here to interest her. In this three part series she begins by telling us about the life which lurks in the water.

Hello Everyone!

Well, here I am, paper and pencil in hand, ready to tell you all about life in the Mar Menor.

The Mar Menor is an inland sea, near Cartagena, in Southern Spain. It is surrounded by beaches and tower blocks, and divided from the Mediterranean by a thin, sandy strip called La Manga. There is only one way where boats can get from the Mediterranean into the Mar Menor, and we are living in it. There is not much wildlife in the Mar Menor. There are no mammals here, except people and their dogs. So instead we will poke our heads in the water. But there doesn’t appear to be much there. The biggest reason is there isn’t – in the marina. But even in the oily mucky water in the corner of the marina I was surprised to find there were still some animals.

The first animal I saw was, of course, the fish. Shoals of fish, usually mullet, spend their time weaving in and out between the motor boats in numbers of about two to ten. I used to think the tiny bright blue fish were a different species, but it’s clear they’re the bigger one’s young. Very early in the year I see shoals of two to ten tiny, bright blue specks. They gradually, in a week or so, get big enough to be recognised as tiny fish. Then I started seeing little miniature fish, looking just like their parents, but only about 4 cm long. After that I suddenly started seeing young adults, and then the adults themselves, (about 20 cm long). The mullet suck the weed on our boat but they don’t do a very good job of cleaning it!

Two-banded sea breamI also noticed, close to the quay, there lurked a little flattish fish, with a black spot on their tails. I looked them up and found oblandas, or saddled bream in English. There are also fish with two black spots called mojarra or two-banded sea bream, and fish with thin yellow stripes called salpa in Spanish or salema in English. I once caught a cuttlefish in my net, and I very rarely catch a thing that Mummy calls a pipefish, but it’s actually a garfish (aguja). It’s long and thin and it stays near the surface, but it swims very fast.

The crab who lives in our cockpit drainThe next animals I saw were the crabs. Mottled black and green, they crouch in the cracks in the jetty, grabbing at anything – a string, some bread, but never, to my annoyance, catching or eating anything in my presence. Recently I found a spider crab.

Last summer there were lots of jellyfish in the Mar Menor. We found four types – purple, brown, white, and brown. The purple and brown came first in the year, bringing with them a mild sting which often itched me as I caught them to draw and look at. They were both the same shape as each other, long tentacles, and a star shape in its bell. Some people say the males are purple and the females brown. Humph. I don’t know if the jellies are male and female, or hermaphrodite. This lot of jellies didn’t come this year, so we’ll skip straight to Rhizostoma pulmo, known here as aguamala, or bad water. I call this the rice pudding. It’s a white pudding bowl with a frilled edge which is a deep, dark, purple. The rest of this stingy cnidarian is white, with a tint of blue. The English name is supposed to be “Shiffarms jelly fish”. Pelagia noctiluca is a stingerLastly, and latest in the year, comes the cow pat. This is what I named it. The other names it collected during the summer were cauliflower and custard pudding The Spanish call it huevos fritos, which means fried egg. It is actually called Cotylhoriza tuberculata, or Aguacaujada (Curd water). This jelly doesn’t sting at all, unlike Aguamala. Often, last year, when I was swimming last or when Caesar was windsurfing, we found ourselves in huge groups of them. Terrifying as they appear, they are quite harmless, and in fact, good enough to play to under water foot ball with, and for Xoë to use as an underwater punch bag, while I dived down and attempted to restrain her. (And failed.) This year there have not been many jellyfish.

Once when I was trying to catch a fish – a darting risky little animal – I shoved the net under a boat. The fish flicked away at the last moment, and I pulled up the net and saw that it was full of shrimps! Obviously, the shrimps had been hiding in the weed. I spent the morning studying them. Some had eggs. After catching the shrimps while chasing fish in the morning, that afternoon I caught the little fish while chasing the shrimps!

Friendly cow-pat jellyfishesI also found there was plenty of life on the crowded sun parched beach nearby. If you swim along with your head under the water you can see the sea cucumbers (Holothuria sp.) dully rolling about on the bottom. The first time I found a pepino de Mar was when I found one stranded on a beach. I soon saw them on the bottom when we were out at anchor, and dived down to look at them. The nearest thing they resemble is a turd, and for this reason the rest of the family don’t touch them, because they look ‘’ squidgy and turdish”.

There are also fish at the beach. The little silver bream and some that live on the bottom and are camouflaged. They’re gobies, I think, but Mummy’s scared that they might be stonefish or weevers.

If you further go in ( but still in my depth) you find the hermit crabs (Dardanus arrosor) and the whelks., the hermit crabs living in empty whelks shells. They run around on the bottom and you can see their trails, but the whelks leave trails too so you can’t tell which ones have crabs living in them.

Sea-spider clowning around in a jam jarThere are starfish in the Mediterranean but in the Mar Menor I’ve only seen tiny baby brittle stars. Last summer I found nudibranchs but this year I haven’t found any. My latest discovery is a sea spider. It’s not really a spider but it does have 8 legs. It reminds me of a ballet dancer or a clown dancing. It flops about all the time. Mummy read a book which says that its reproductive organs and its stomach are in its legs!

So now you know just how much life there is. I suppose it’s not much, compared to all the boars and bats, bears and bee-eaters, and grouse and griffon that live in the middle of Spain, in the mountains, but there’s more than one expects at a glance. And I have managed, without thinking, to write six pages. It will shrink depressingly whilst I type it up, but there’s life for you.


By the way, do any of you know why fish swim up and breathe air? Is it because the water’s dirty? Or is it because they’re eating something that I can’t see that’s on the surface?


  1. Can you please tell me the name of the jellyfish shown in the second picture Sandy colour on top, frilly underneath and with mauve traces on the tentacles.
    We have a home by the Mar Menor. I love to watch these attractive creatures and am always upset to see the locals reaction to them, picking them up or catching them in plastic bags and throwing them onto the beach to die in the hot sun. This year they were being thrown about like footballs by people. WHY? They are part of our ecosystem. They were harming no-one and as they were being handled obviously NOT stinging anyone. I watched helplessly on 2 or 3 days as hundreds were destroyed. Apparently the ones caught in the nets end up in a huge decaying pile near the airport.
    I would like to learn more about where they come into the Mar Menor from, or if they are always there. Do they spawn there or proliferate to feed, if so what is the attraction. Are they any threat?

    1. Hullo Chris,

      The cow pat jellfish is more properly known as Cotylhoriza tuberculata. The spanish name is aguacuajada – which I think means curd-water – but the locals in the Mar Menor call them huevos fritos (fried eggs).

      Yes, we too used to get upset when we saw the fishermen rounding them up by the net full and dumping them……. but, to tell the truth, the jellyfish population explosion is not remotely natural. Their abundance in the Med is due to the run off of fertilisers which cause invisibly small phyto-plankton to flourish (or bloom). If I remember correctly, the jellies eat the plankton.
      So, that’s why the Mar Menor is so attractive to them: plenty of run off of fertiliser.

      They are not so abundant in the winter. Maybe they all die off and the new ones haven’t yet matured into a form which we would recognise. Their life cycle is pretty weird. They start out looking like part of a plant, if I recall correctly. (Rox should be writing this reply………..)

      The fishermen are paid, by the local council I believe, to round up the jellies. Of course, the council is not actually trying to correct the imbalance which man has created; they just want to make sure that the tourists keep on coming – and they won’t come if they can’t swim; and they can’t (or won’t) swim if the sea is full of jellies.

      The Mar Menor, as you will no doubt have noticed, is pretty much dead. A friend who used to be a nature warden on Isla Grosa used to say (jokingly) that he thought they should just fill it up with chlorine and advertise it as the world’s biggest swimming pool.

      Do these ones sting, you ask? No; not in my experinece. I’ve picked them up and trodden on them (by mistake, of course) and I’ve even seen a guy wearing one as a hat! But the Spanish tourists (who come from Madrid for the most part) are apt to be a bit hysterical about this kind of thing. And it is true that ALL jellyfish have stinging cells, so I suppose that if someone were sensitive to this particular toxin they might feel a stinging sensation or get a rash. (Rox has arrived and is reading over my shoulder. She says, “Rubbish! That kind of jelly couldn’t hurt anybody!”) The fact that the kids throw them around like balls rather proves the point, as you say.

      The jellies which are the worst stingers are the very small ones (see the third photo, labelled Pelagia noctiluca). When they arrive on the beach or get into the beach nets they break up, and the invisible bits and pieces and nematocysts are still just as potent. So, we reckon that if a tourist gets stung by a nematocyst, she is likely to look round and see the much larger, much more obvious Fried Egg and make that organism the scapegoat.

      As I recall – and I must point out that I’m working from memory and haven’t read anything on this subject for a couple of years – but as I recall it scientists are rather worried about the radical interest in numbers of jellyfish in places like the Med, because this super-abundance shows that the water is being polluted with fertilisers, and because it demonstrates that other animals are now missing from the local environment. Turtles, for example, are pretty keen on jellyfish.

      The good news is that the Spanish naturalists are trying to reintroduce turtles to the area by burying turtles’ eggs on appropriate, un-touristed beaches. (Where the heck are they going to find those in Mediterranean Spain, you ask………… but there are a few.)


  2. the jellyfish are very interesting!
    i went out on my mates cannoe and altogehter we seen 48 jellyfish(yes we counted them).
    one of the times there was a massive group of 5 jellyfish al togehter.
    when u went near them or splashed the water around them they turned upside down, they had blue tentacles on their underside!
    it looks alot like an egg on top of the water !
    hope this helps
    i wouldnt advise swimming deep int the water

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.