Sarah Shaw’s Marine Species Log – Sponges

Sponges

Great to have you back! Now, following on from my first blog . . . . Aplysina Aerophobas form characteristic bright yellow masses of stubby projections, which when taken out of the water turn dark blue-black. The sponges are compressible and feel rubbery but please don’t try this! It is a Mediterranean species which penetrates into the Atlantic along the coasts of Portugal and NW Spain. What is she talking about I hear you say?

If you have ever followed me on a dive on Divewise’s house reef, you will have found that on our way back to the exit, we take a route over a flat expanse of bare rock at 5mtr depth. Why? That’s because there is one of two communities of Aplysina Aerophoba living there. What’s so special about this sponge? Well, before I divulge that piece of information, let me take the time to describe sponges and this particular species. Sponges. They are found in a very wide range of habitats from tidal zones to almost 9,000 meters depth and from polar regions to the tropics. Most live in quiet, clear waters, because sediment stirred up by waves or currents would block their pores, making it difficult for them to feed and breathe. Most sponges are anchored to hard surfaces like rocks, but some sponges can attach themselves to sediments using a root-like base.

Adult sponges can be asymmetrical or radially symmetrical and come in a variety of sizes, colours and shapes including tree-like, fan-shaped, cup-shaped, tube-shaped, ball-shaped and shapeless. Sponges are from the Phylum Porifera. The members of the phylum Porifera, are multicellular organisms that have bodies full of pores and channels allowing water to circulate through them, consisting of jelly-like gelatinous matrix sandwiched between two thin layers of cells.

You’ve read in the above that Aplysina Aerophoba is a Mediterranean species. Its common name is Golden sponge. These are within the class of Demosponge, often brightly coloured and growing to be the largest of all sponges. They make up more than 90% of all sponge species. Now don’t get this confused with Golden Tube sponge (Aplysina Fistularis). The Golden Tube sponge grows in the Caribbean and as its name suggests, it grows in colonies of tubes.

Picture cigars upright next to each other. The Aplysina Aerophoba have a base from which grow irregular tubular digitations. These digitations are 3-4 cm high, 1-2.5 cm in diameter, and end in a flattened top in the centre of which is an osculum (a mouth like aperture, the opening in a sponge out of which water passes). The surface of the basal mass, as well as the tubes, frequently bare thin long solid Fistules of variable length. These are defined as a canal or a cavity, created by necrotic degradation of the tissue, which may, (but not necessarily has to) communicate directly with the digestive tract via an internal orifice. The surface is slippery to the touch and irregularly covered with small conical elevations. Their ecology is shallow water (0 – 20m) and exposed to sunlight. Its name Aerophoba, is derived from the Greek “afraid of air”, referring to the colour change effected by exposure to the air.

sponges sarah 1

So why is it so significant? Well to me, it is because it can hide an opisthobranch called Yellow Umbrella slug or to give its scientific name, Tylodina Perversa. These lovely guys are quite hard to spot. They are not a true nudibranch, but a cousin in the order of Umbraculida. There are only two Umbraculida within the Mediterranean Sea, The Yellow Slug and the Umbraculum Umbraculum or Warty Umbrella Slug. Both species are round in shape and have, as the name suggests, an appendage on the top shaped like an umbrella. Both eat sponges and the Yellow slug takes on the colour of the sponge it eats, hence why it’s hard to find.

Their habitat on our house reef is only at 5 – 6 meters in depth. This is good for those interested in nudibranchs as we can spend a slightly longer time there hunting them out. You will need this extra time as the Yellow Umbrella slug is very well camouflaged and not sitting on the top waving its flag to attract attention. To make life even more difficult it also burrows into the sponge. They are also only 2 – 3cm in size. You can on the odd occasion find them on various reefs around the islands. These are more than likely foraging for a new colony of Aplysina Aerophoba to eat. The picture to the right is of an Aplysina Aerophoba

If you want to find out more about nudibranchs and their habitats such as Aplysina Aerophoba, then why not indulge yourself in joining me at Divewise on a one day course learning about nudibranchs. I have written my own Distinctive Specialty (Mediterranean Sea Slug) which is a PADI recognised course and includes some theory, knowledge review, and 2 dives solely about finding and identifying types of nudibranchs. If you would like some more information regarding the course please email Viv at Divewise on info@divewise.com.mt.

The first photo in this blog is taken on our house reef and there are two yellow slugs here.

Enjoy and hope to see you soon.


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