Marine Caves of the Mediterranean Sea: A Sponge Biodiversity Reservoir within a Biodiversity Hotspot

Abstract

Marine caves are widely acknowledged for their unique biodiversity and constitute a typical feature of the Mediterranean coastline. Herein an attempt was made to evaluate the ecological significance of this particular ecosystem in the Mediterranean Sea, which is considered a biodiversity hotspot. This was accomplished by using Porifera, which dominate the rocky sublittoral substrata, as a reference group in a meta-analytical approach, combining primary research data from the Aegean Sea (eastern Mediterranean) with data derived from the literature. In total 311 species from all poriferan classes were recorded, representing 45.7% of the Mediterranean Porifera. Demospongiae and Homoscleromorpha are highly represented in marine caves at the family (88%), generic (70%), and species level (47.5%), the latter being the most favored group along with Dictyoceratida and Lithistida. Several rare and cave-exclusive species were reported from only one or few caves, indicating the fragmentation and peculiarity of this unique ecosystem. Species richness and phylogenetic diversity varied among Mediterranean areas; the former was positively correlated with research effort, being higher in the northern Mediterranean, while the latter was generally higher in caves than in the overall sponge assemblages of each area. Resemblance analysis among areas revealed that cavernicolous sponge assemblages followed a pattern quite similar to that of the overall Mediterranean assemblages. The same pattern was exhibited by the zoogeographic affinities of cave sponges: species with Atlanto-Mediterranean distribution and Mediterranean endemics prevailed (more than 40% each), 70% of them having warm-water affinities, since most caves were studied in shallow waters. According to our findings, Mediterranean marine caves appear to be important sponge biodiversity reservoirs of high representativeness and great scientific interest, deserving further detailed study and protection.

Assembling Ecological Pieces to Reconstruct the Conservation Puzzle of the Aegean Sea

“…Most of the information comes from scientific literature, as well as from new records of field surveys and interviews conducted during the present study. Scientific literature includes research that specifically focuses on sponges (e.g., Voultsiadou, 1986;Kefalas and CastritsiCatharios, 2007;Voultsiadou et al, 2008Voultsiadou et al, , 2010Gerovasileiou and Voultsiadou, 2012), as well as studies with a broader ecological scope (e.g., Pérès and Picard, 1958;Antoniadou et al, 2006;Salomidi et al, 2016). Scattered records found in the technical reports of past projects and online databases were also considered, but account only for a small fraction of the dataset.…”

Amphipods from marine cave sediments of the southern Iberian Peninsula: diversity and ecological distribution

“…Anyway, none of the species found in the present study are cave-exclusive, having all been previously cited in open habitats (Ruffo 1982(Ruffo -1998. This is a common feature in marine cave fauna, since most of the species only use the caverns for shelter and can also be found outside the caves in similar habitats (Scipione et al 1981, Gerovasileiou andVoultsiadou 2012). The genus Harpinia, for example, was found predominantly inside marine caves, but was also present at some external stations, thus facilitating intercommunication among cave assemblages.…”

World Register of marine Cave Species (WoRCS): a new Thematic Species Database for marine and anchialine cave biodiversity

“…Marine and anchialine caves are widely acknowledged as biodiversity reservoirs (Gerovasileiou and Voultsiadou 2012), harboring unique faunal elements including, among crustaceans for example, all members of the class Remipedia (Yager 1981), order Mictacea (Bowman et al 1985), and families Macromaxillocarididae (Álvarez et al 2006l) and Speleoithonidae (da Rocha and Iliffe 1991), representing relict lineages that will facilitate our understanding of the evolutionary history of encompassing taxa. Remipedes have recently been shown to be a sister group to hexapods, while the evolutionary relationships of many other anchialine taxa are still under study (von Reumont et al 2011, Fanenbruck et al 2004).…”

“…All taxa in this database were cross-checked and taxonomically updated using WoRMS. The database has been already used as a source of information for studies on diversity of Porifera (Gerovasileiou and Voultsiadou 2012), marine cave biota of the eastern Mediterranean (i.e., Aegean and Levantine ecoregions) (Gerovasileiou et al 2015), and non-indigenous species in Mediterranean caves (Gerovasileiou et al 2016a ).…”