Role of deep sponge grounds in the Mediterranean Sea: a case study in southern Italy

Abstract

The Mediterranean spongofauna is relatively well-known for habitats shallower than 100 m, but, differently from oceanic basins, information upon diversity and functional role of sponge grounds inhabiting deep environments is much more fragmentary. Aims of this article are to characterize through ROV image analysis the population structure of the sponge assemblages found in two deep habitats of the Mediterranean Sea and to test their structuring role, mainly focusing on the demosponges Pachastrella monilifera Schmidt, 1868 and Poecillastra compressa (Bowerbank, 1866). In both study sites, the two target sponge species constitute a mixed assemblage. In the Amendolara Bank (Ionian Sea), where P. compressa is the most abundant species, sponges extend on a peculiar tabular bedrock between 120 and 180 m depth with an average total abundance of 7.3 ± 1.1 specimens m -2 (approximately 230 gWW m -2 of biomass). In contrast, the deeper assemblage of Bari Canyon (average total abundance 10.0 ± 0.7 specimens m -2 , approximately 315 gWW m -2 of biomass), located in the southwestern Adriatic Sea between 380 and 500 m depth, is dominated by P. monilifera mixed with living colonies of the scleractinian Madrepora oculata Linnaeus, 1758, the latter showing a total biomass comparable to that of sponges (386 gWW m -2 ). Due to their erect growth habit, these sponges contribute to create complex three-dimensional habitats in otherwise homogenous environments exposed to high sedimentation rates and attract numerous species of mobile invertebrates (mainly echinoderms) and fish. Sponges themselves may represent a secondary substrate for a specialized associated fauna, such zoanthids. As demonstrated in oceanic environments sponge beds support also in the Mediterranean Sea locally rich biodiversity levels. Sponges emerge also as important elements of benthic-pelagic coupling in these deep habitats. In fact, while exploiting the suspended organic matter, about 20% of the Bari sponge assemblage is also severely affected by cidarid sea urchin grazing, responsible to cause visible damages to the sponge tissues (an average of 12.1 ± 1.8 gWW of individual biomass removed by grazing). Hence, in deep-sea ecosystems, not only the coral habitats, but also the grounds of massive sponges Guest editors: M. Maldonado, X. Turon, M. A. Becerro & M. J. Uriz / Ancient animals, new challenges: developments in sponge research

Macro- and megafauna recorded in the submarine Bari Canyon (southern Adriatic, Mediterranean Sea) using different tools

“…1: Uniqueness or rarity; 3: Importance for threatened, endangered or declining species and/or habitats; 5: Biological productivity; 7: Naturalness) as well as the VME (Vulnerable Marine Ecosystem) criteria (1: Uniqueness or rarity; 2: functional significance of the habitat; 3: fragility; 4: life-history traits that make recovery difficult; 5: structural complexity) (FAO, 2009) could also be assigned to the Bari Canyon in planning future marine protected areas and management measures in order to preserve its high biodiversity level in relation to the presence of cold-water coral species. Freiwald et al, 2009;Bo et al, 2012;Sanfilippo et al, 2013;Angeletti et al, 2014;D'Onghia et al, 2014; present paper; B: Tursi et al, 2004;Longo et al, 2005;Schönberg & Beuck, 2007;Carlier et al, 2009;Freiwald et al, 2009;D'Onghia et al, 2010D'Onghia et al, , 2011D'Onghia et al, , 2012Mastrototaro et al, 2010Mastrototaro et al, , 2013Mastrototaro et al, , 2014.…”

“…Solitary corals, sponges, serpulids, boring clams, and colonies of bryozoans were also recorded during these cruises Bo et al, 2012;Sanfilippo et al, 2013). In particular, the sponge Pachastrella monilifera mixed with living colonies of the scleractinian M. oculata dominates the deep assemblage in the Bari Canyon, between 380 and 500 m (Bo et al, 2012). A remarkable abundance of the tubeworm Serpula vermicularis associated with M. oculata build-ups and other stony corals were also observed to increase the biogenic frameworks and habitat complexity .…”

“…In this respect, the Bari Canyon was explored during the HERMES and HERMIONE cruises, using Remotely Operated Vehicles (ROVs) and revealing a CWC community mainly structured by Madrepora oculata and to a lesser extent, by Lophelia pertusa and Dendrophyllia cornigera . Solitary corals, sponges, serpulids, boring clams, and colonies of bryozoans were also recorded during these cruises Bo et al, 2012;Sanfilippo et al, 2013). In particular, the sponge Pachastrella monilifera mixed with living colonies of the scleractinian M. oculata dominates the deep assemblage in the Bari Canyon, between 380 and 500 m (Bo et al, 2012).…”

“…Some studies carried out on the biological community of the Bari Canyon have only recently documented a very abundant sponge fauna referred to five sponge taxa (Rhizaxinella pyrifera, Poecillastra compressa, Pachastrella monilifera, Haliclona sp., Hexadella sp.) (Anonymous, 2009;Freiwald et al, 2009;Bo et al, 2012;Angeletti et al, 2014). The present study, recording 29 sponge taxa, demonstrates that, as already known in Mediterranean and Atlantic CWC communities, poriferans are one of the most common benthic organisms inhabiting these deep biocoenosis, also in terms of species richness (Longo et al, 2005;Soest & Lavaleye, 2005;Soest et al, 2007;Mastrototaro et al, 2010;Calcinai et al, 2013).…”

First report of live deep-water cnidarian assemblages from the Malta Escarpment

“…By and large, the most relevant actors of such aphotic communities are cnidarians and sponges associated with poorly sampled hard bottoms at depths exceeding 200 m. This is primarily the case for the so-called white coral communities documented at bathyal depths in the Strait of Sicily, southern Adriatic, Ionian, Ligurian, Marmara, northwestern Mediterranean and Alboran seas (Tursi et al 2004;Taviani et al 2005aTaviani et al , 2005bTaviani et al , 2011aFreiwald et al 2009;Mastrototaro et al 2010;Vertino et al 2010;Gori et al 2013;Angeletti et al 2014;Fabri et al 2014), the sponge-dominated habitats in the Tyrrhenian, Ionian and Adriatic seas (Bo et al 2012;Calcinai et al 2013), and antipatharian-gorgonacean communities in the Tyrrhenian, Ionian and Adriatic seas and in the Strait of Sicily (Costantini et al 2010;Taviani et al 2010;Bo et al 2011;Angeletti et al 2014;Deidun et al 2014). From this ecological perspective, the Malta Escarpment in the central Mediterranean happens to be one of the least explored in European waters.…”