The Conero and the seasons of nudibranchs

Questo articolo è disponibile anche in: Italiano (Italian)

Perhaps not many people know that the part of Adriatic Sea in front of Monte Conero (familiarly called the “Conero Sea” by locals) is extremely rich in nudibranchs, both in terms of quality (about 50 species surveyed) and quantity (in the right season for the same species you can have an incredible concentration in a small patch of wall).

Cratena laying eggs over the hydrozoan covered of sediments– Cratena peregrina

The nudibranchs are mollusks belonging to the class of Gastropoda, infraclass Opisthobranchia, namely sea snails with gills in the back of the body; another feature common to most of the sea slugs is the absence of the shell, lost during the process of evolution. Because of similar appearance (soft body, crawling movement and lack of shell), the sea slugs are often mistaken for nudibranchs, but actually among the various orders of this infraclass (Anaspidea, Cephalaspidea, Pleurobranchomorpha, Sacoglossa, Nudibranchia etc.) there are quite significant differences. Sometimes even the flatworms are mistaken for nudibranchs, although they are not mollusks but Platyhelminthes. The nudibranchs are slow, but they have not many predators, as they are often indigestible because of their diet. Their garish colours are a sort of warning for the “forgetful” predators. To understand better and take a deeper look into the ecological, behavioral and morphological aspects, I highly recommend the nice guide on Opistobranches of the Conero Sea, “Il Regno dei Nudibranchi”, written with great passion and skills by my friend Federico Betti, where he highlights the differences among the main subgroups of nudibranchs. In the recent years, these organisms have become source of great interest for many divers all over the world. Probably because there are many different species, most of them very colourful and with original shapes, but also for their proverbial slowness, that make them excellent subjects for photo and careful observation. But please do not forget that they are very fragile and therefore “do not handle”…… not even with care!

The different species of nudibranchs alternate on the reefs of the Conero Sea all year round. The strong temperature excursion of the sea between summer and winter (about twenty degrees along the coast) produces different environmental conditions, providing food for species used to live in cold water and for those used to live in warm water. It is easy to meet our “little friends” in all the most famous dive spots of the Conero Sea. Of course, you have to keep in mind the seasonality of the different species. For choosing the right dive spot, pay attention to the concentration of the favourite food of the species you are looking for. The diet changes from species to species, ranging from sponges to bryozoans, from hydroids to sea squirts. As mentioned above, a good way to find nudibranchs is to search for their favorite food, but it is not enough. You have also to be patient and pay a great attention: often they are colourful, but at the same time very small. So, let’s go dive very concentrated! Do not get distracted by other fish around!

Since it is possible to find different species of nudibranchs all year round, let’s start from January. In the dive spot called “Trave”, between Sabellaria alveolata (honeycomb worm) and the tiny mussels, the first nudibranchs, so young to remember when they were larvae and small enough to fit on a fingernail, begin to appear. During this time and until the water warms up a bit, you can see Flabellina pedata, Flabellina lineata and paying particular attention, Doto coronata. From March the Bugula, the Bryozoan that the Janulus cristatus eats, begins to cover the rocks in many areas of Conero reefs. This is the right moment to look for this small chubby yellow friend. The Janulus cristatus is usually very common at “Trave”. Its body is covered with semi-transparent balloons, its color ranges from light yellow to ocher and it’s bigger than the three nudibranchs mentioned above. Thanks to this shape, Janulus crisatus is an interesting photographic subject, assuming that you are able to find his head!

Speaking of head, where is the head of the nudibranchs? It is the part where are the rhynophores, namely the antennas on top of which is the nose, in other words their greater sensory organ. Under the rhinophores there is the mouth, from where our tiny slugs pull out the radula, a kind of strong serrated tongue, with which rasp off food bringing it into the mouth. Around the mouth a couple of oral tentacles are sometimes visible (in some cases they are very similar to rhinophores). By the way, do not look for the eyes, it could be a fruitless exercise as they are small and well hidden beneath the epithelium.

In April and in May it is not difficult to see Felimare villafranca, small size but with unmistakable blue livery. To be honest, it is not so simple to determinate without any doubt every encounter as F. villafranca. The small details to distinguish the different species of this genus are often not so easy to recognize (F. gasconi, F.tricolor, F. bilineata)

During the same period at “Trave” it is also easy to sight Polycera qualineata, white translucent body with bright yellow stripes and growths. It lays egg masses in a spiral ribbon shape that makes you wonder how they can be contained in its tiny body. At least until someone explain you that the mucus, that contains the individual eggs, as soon as it is exposed to water tends to absorb it and swell.

In June at “Sassi Neri” dive spot, if you are lucky, it is possible to encounter Rostanga rubra, one of the rarest nudibranch in our area. A nice orange plush toy. In the same period at many dive spots, especially at “Trave”, it is possible to sight another orange nudibranch, Discodoris rosi.

In summer the sediment tends to cover everything giving a mud-colored uniform upholstery; no exception even for the hydrozoans, whose fragile branches are bent and suffering under the weight of this impalpable sediment. In this gray scenery, stand out “clusters” of Cratena peregrina with their garish red and blue cerata.

The cerata are gills (and not just it to tell the truth, but let’s not make it too complicated!). In specific groups of nudibranchs the “naked gills” seem to be a kind of hair (typically in Aeolidina and in some Arminina), while in other cases the gills consist of typical rear tuft, which can also be retractable. Cratena peregrina usually loves warm water and it is probably the most common nudibranch in the Conero Sea. It may happens to find several dozen in a square mater at “Trave”. They eat hydrozoan, mate and lay eggs side by side with Flabellina affinis, that is also very famous in our area.

If from June to October Cratena peregrina and Flabellina affinis crowd the area north of Portonovo bay (but it is possible to spot some of them in the south area as well), Felimida luteorosea is the permanent presence in the area south of the bay. It is a freak of nature with its yellow paint on a purple background. It has the stereotypical shape of nudibranchs, dorso-ventrally flattened body, gills and visible rhinophores. Actually, its shape is not typical of nudibranchs, but of a particular group of nudibranchs called Doridina.

Always at “Trave”, from late summer to early October, you can find Calmella cavolini (one of the smallest sea slugs at the Conero Sea). A thin white body, few millimeters long, with huge (if compared to the body) and swollen red or orange cerata.

It is time to end this overview through the seasonality of nudibranchs at Conero. Please be aware that it is a brief and not exhaustive vista, considering the dozen and dozen species you can encounter diving here. Strength and courage! Regulator in mouth and down, they are there waiting for us. They are just one of the many hidden wonders that you can meet at the Conero Sea.

Questo articolo è disponibile anche in: Italiano (Italian)