Sea slugs (Mollusca, Gastropoda, Heterobranchia): the other inhabitants of the city of Barcelona (Spain)

Sea slugs in the broad sense (until recently called «opisthobranchs» and now within the Heterobranchia subclass of the Gastropoda),
have aroused the interest of naturalists since they began to be studied by the end of the XVIII century. Their colorful and varied shapes
make them very attractive to be studied and photographed. Numerous are the published works written to spread the knowledge of the
biodiversity of these molluscs in all marine regions, however very few studies have been carried out to know these species that inhabit
highly anthropized areas, such as the interior of commercial ports, marinas, artificial substrates or the coastal areas of large cities. Here
are the results of a biodiversity study of marine heterobranchs conducted along the coast of the city of Barcelona (Spain). Numerous
specimens of 73 species of sea slugs have been found, belonging to 5 orders: 4 Aplysiida, 5 Cephalaspidea, 3 Runcinida, 47 Nudibranchia
and 4 Pleurobranchida, and 1 superorder: 10 Sacoglossa, including two alien species, Polycerella emertoni and Bursatella leachii, of wide
circumtropical distribution. Our work proves that new habitats, created with the construction of marinas, breakwaters or submerged rock
bars, are being colonized by seaweeds and marine invertebrates that set onto these artificial structures. Surprisingly our study found a high
biodiversity of marine heterobranchs, even in waters with abundant organic matter and subjected to high anthropic pressure.