On the current status of Spongia officinalis (the sponge by definition), and implications for conservation. A review

Spongia officinalis is, and will remain, the oldest nominal species of the phylum Porifera, and its name is the only one still valid among those originally described by Linnaeus. As for the biogeographic pattern, records of S. officinalis are known at the global scale, but its geographic range is probably restricted to the Mediterranean Sea. Over 500 taxa have been described under the genus Spongia, but only 41 species are verifiably valid. S. officinalis is notably plastic. Due to re-modelling of morphotraits, it is difficult to describe it in a precise and accurate way and to distinguish and identify it among the many other Mediterranean and extraMediterranean bath sponge species. An irreversible depletion of the bath sponge banks of the Mediterranean Sea, due to the combined effects of over-fishing and disease, has brought several populations to the brink of extinction since the mid-1980s. The recovery of affected populations has been long and difficult, despite the sponge’s extraordinary regenerative capability due to the perennial morphogenesis of the sponge body. S. officinalis has undergone a major population decline. Since 1999 the situation has evolved dramatically for S. officinalis, and some of the few populations for which ascertained historical data are available are definitely extinct in the Mediterranean. This could be considered the beginning of a final catastrophe. On the other side of the Atlantic Ocean, due to similar feral events, the species Hippospongia gossypina has also become locally extinct from the Florida coasts, and other commercial sponge species are disappearing from the waters around Cuba. In principle, mariculture techniques are available which make it possible to perform in situ culture of sponges, as a way of dealing with this population depletion. For Spongia officinalis, it is possible that the wild populations will die out and only the “domestic” variety will survive, and that by means of farming. Historical notes (the beginning) Spongia is the pre-Linnaean term (meaning sponge in the Latin language) used in the very early days of natural history to indicate any species of sponges. This name entered into scientific usage in the Middle Ages among surgeons such as Nicholas of Salerno (late XIIth century), Theodoric of Lucca (1205-1298), Al Koff (1232-1286) and Arnold of Villanova (Arnaldus Villanovanus) (1238-1310 ca.) (Keil, 1989; Al-Bakri et al., 1999; Pronzato et al., 2012). Spongia somnifera was a medieval milestone in the history of general anaesthesia. The “soporific sponge” was applied to the nostrils of the patient after boiling the sponge in a mixture of opium and hemlock, together with juice of mandragora, ivy and unripe mulberry. The anaesthetic effect of this cocktail was usually interrupted by applying a sponge soaked in vinegar to wake the patient after surgery. On the other hand, numerous references to the treatment of goitre are found in Chinese medical writings. According to Bircher (1922) the ashes of sea sponges (Spongia usta) in vine or as powder and pill form were used by the Chinese in the treatment of goitre as far back as 1500 BC. The book Pen T'Sao Kang-Mu, on Chinese medicinal plants (1578 final edition), recommends medicinal algae, including sponges, for the treatment of goitre (see T.A.H, 1936; Hume, 1948). The Greeks have had the same experience, as indeed have probably all the other ancient peoples living on the shores of the Mediterranean Sea. In the twelfth century, Ruggiero Frugardi (Roger of Salerno) recommended an Electruarium containing the ashes of sea sponges for the treatment of Roberto Pronzato and Renata Manconi 4 goitre, and this remedy has been used for centuries (Matovinović & Ramalingaswami, 1958). The Bibliography of Sponges from 1551 to 1913 by Vosmaer (1928) reports ca. 80 titles of pre-Linnaean books and papers discussing sponges, prior to the first edition of Systema Naturae (1735). Linnaeus listed 11 sponge species in the second volume of the Xth edition (1759), including two freshwater species, all ascribed to the genus Spongia (Fig. 1 A, B). The XIIth edition (1767) reports 16 species, and supplies synonyms and geographic distribution. As for S. officinalis, the junior synonyms were S. globosa and S. schiaccatae from the Mediterranean Sea (Fig. 1 C, D). In the XIIIth edition (1789), the geographic range of S. officinalis is extended to “Mari Mediterraneo, Rubro, Indico? , Americano? , Norvegico? ” (Fig. 1 E, F), marking the beginning of a persistent biogeographical confusion that continues to the present day. Thereafter, up to date, new records determined the enlargement of the geographic range up to the global level with the consequent status of S. officinalis as a “false” cosmopolitan species. Only an integrative revision of diagnostic morphotraits vs. molecular traits at the population level for the entire geographic range of S. officinalis could address the existence of species complexes. At the local scale (Mediterranean Sea), on the basis of a significant amount of variation detected by molecular analyses between the Aegean Sea vs. Gulf of Lions populations, Dailianis et al. (2011) propose that S. officinalis can be viewed as a single, morphologically variable species. The same authors suggest also the existence of a cryptic species from the Gibraltar area (Dailianis et al., 2011). Although its biogeographic pattern – extended up to the Macaronesian subregion (East Atlantic) – needs to be tested, at present we consider S. officinalis a Mediterranean endemic excluding the Black Sea. __________________________ Figure 1 [below]: In the Xth edition of Systema Naturae, Linnaeus (1759) lists 11 sponge species ascribed to the genus Spongia (A, B). Synonyms and geographic distribution were supplied in the 1767 XIIth edition, reporting 16 species; as for S. officinalis, the junior synonyms are S. globosa and S. schiaccatae; the habitat is the Mediterranean Sea (C, D). In the 1789 XIIIth edition, the geographic range is extended to “Mari Mediterraneo, Rubro, Indico? , Americano? , Norvegico? ” (E, F). Source: Different editions of Systema Naturae. On the current status of Spongia officinalis