Stability of the sponge assemblage of the Mediterranean coralligenous along a millennial span of time (original) (raw)
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Marine Ecology, 2014
The Mediterranean coralligenous substratum is a hard bottom of biogenic origin, mainly composed of calcareous algae, growing in dim light conditions. Sponges are among of the most representative taxa of the coralligenous assemblages, with more than 300 recorded species of different habits: massive, erect, boring and insinuating. When sponges die, their siliceous spicules remain trapped in the biogenic concretion, offering the opportunity to describe the coralligenous spongofauna over a very long span of time, virtually dating back to a large part of the Holocene period. The data reported here were obtained from core samples collected from four coralligenous concretions. Each block was collected in a different locality of the Ligurian Sea: Santo Stefano Shoals, Bogliasco, Punta del Faro (Portofino Promontory) and Punta Manara. Radiocarbon age determinations indicate for these conglomerates a maximal age between 1600 and 3100 years. The spicules trapped in the cores show deep dissolution marks in the form of circular holes on their surface or present an enlargement of the axial canal. However, their original shape, generally intact, suggests the absence of mechanical injuries and allows a tentative identification at the species level. The analysis of these old spicules reveals an ancient sponge assemblage composed of 30 recognisable species. This indicates that almost one half of the sponge community today settled on coralligenous substrata has been present in the conglomerates for their entire existence.
Facies, 2019
The demosponge siliceous spicules, entrapped in the Mediterranean coralligenous bioherms, are a good tool for reconstructing the sponge ancient communities across time, also allowing a comparison with the current biodiversity. The aim of this paper has been the description of the ancient sponge assemblages of the coralligenous bioherms grown up in the Tavolara-Capo Coda Cavallo Marine Protected Area (northeastern Sardinia, Tyrrhenian Sea) between 5800 and 3700 YBP and its comparison with the living sponge community. On the base of radiocarbon age determinations, it was possible to estimate that these bioherms cover a span of time ranging from the Holocene Climatic Optimum until the Bronze Age Crisis. Their growth rates, 0.21-0.24 mm year −1 , were of the same order of estimations conducted around the Mediterranean. The Tavolara ancient sponge diversity was compared with those found in ancient accretions from Ligurian Sea and Ionian Sea. Our results supported the already-described general trend, supporting the hypothesis that the genus richness in the coralligenous bioherms was driven by climatic vicissitudes. Nevertheless, our data strongly indicated that the sponge diversity is also related to the conditions of the coralligenous structures: in the accretions characterized by an active growth of coralline algae the number of sponge genera is similar to those recorded in the ancient assemblages while in coralligenous where the accretion is stopped the number of sponge genera strongly decreases probably due to the competition with frondose macroalgae.
PloS one, 2017
This paper concerns the changes occurred over both decennial and millennial spans of time in a sponge assemblage present in coralligenous biogenic build-ups growing at 15 m depth in the Ligurian Sea (Western Mediterranean). The comparison of the sponge diversity after a time interval of about 40 years (1973-2014) showed a significant reduction in species richness (about 45%). This decrease affected mainly the massive/erect sponges, and in particular the subclass Keratosa, with a species loss of 67%, while the encrusting and cavity dwelling sponges lost the 36% and 50%, respectively. The boring sponges lost only one species (25%). This changing pattern suggested that the inner habitat of the bioconstructions was less affected by the variations of the environmental conditions or by the human pressures which, on the contrary, strongly affected the species living on the surface of the biogenic build-ups. Five cores extracted from the bioherms, dating back to 3500 YBP, allowed to analyse...
Facies
The Messinian Salinity Crisis (MSC) created a substantial negative impact on the Mediterranean marine fauna and flora because hypersaline conditions were established in many marginal basins. At the northern margin of the Tertiary Piedmont Basin, Northern Italy, the Messinian successions exposed at Banengo and Moncalvo recorded the transition into and through the MSC with well-preserved nanno-, micro-and macrofossils. Siliceous sponge spicules present in these pre-MSC sediments reflect the sponge population in this area with twenty different morphological types of spicule identified, twelve of them attributable to sponge genera of the modern Mediterranean sponge fauna. The most common genera were Stelletta, Geodia and Dercitus, with fewer records of Tethya, Chondrilla, Alectona and Samus. Only two types of spicule belong to species not currently present in the Mediterranean sponge fauna and are putatively attributed to the tropical species Stelletta purpurea and Diplastrella megastellata. The sponge assemblage thriving before the onset of the MSC provided new information on the sponge diversity and palaeoenvironment of this northern sector of the palaeo-Mediterranean basin over this crucial period. These data, integrated with information derived from the associated fossils (nannofossils, benthic and planktic foraminifers, and bryozoans), indicate that the considered sites were coastal localities, with sediments rich in an organic matter likely derived from phytoplankton blooms. At both sites, the presence of patchy rocky substrates on the seafloor is testified by a diversified group of sponges typical of hard substrata. These rocks were, very likely, carbonate as suggested by the presence of spicules of typical boring sponges. In the studied sites, common epiphytic foraminifers and bryozoan segments indicate the presence of Posidonia seagrass or algal meadows.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2017
Changes occurring over a pluri-millennial span of time (6207-1767 yr B.P.) within the sponge assemblages present in two coralligenous pillars, about 60 cm high, collected at 20 m depth, inside the Marine Protected Area of Porto Cesareo (Ionian Sea, Mediterranean Sea) have been studied. The sponge diversity has been analyzed at generic level, using as a proxy the siliceous spicules trapped into the sediment present into the crevices of these bioherms. In total, 41 genera of ancient demosponges were identified. The modern sponge fauna of these coralligenous pillars totals 31 genera, 15 of them shared with the ancient assemblages. The sponge biodiversity during the considered span of time showed critical changes, with remarkably similar trends in both the considered pillars. Tentatively, these changes were attributed to different climatic events that affected the Mediterranean area during the studied time span. The number of genera, 6000 yr B.P., was low and increased between 5500 and 4000 yr B.P. During the Late Bronze Age (4000-3000 yr B.P.), a new decrease was recorded, followed by a further increase around 2000 yr B.P. Afterwards, the bioherms stopped growing and no more siliceous spicules were trapped. From a biogeographic point of view, the wide presence of spiny microrhabdose microscleres belonging to the genus Alveospongia (Heteroxyidae), recently described from the tropical Atlantic and still unknown in the Mediterranean Sea, has to be underlined. In addition the trends recorded over time in the Ionian Sea match with those already observed in the Ligurian Sea. The comparison between the past periods and the modern one shows evident changes in biodiversity in both areas. The sharp variations of the seawater temperature-occurred in both the Mediterranean regions-could have driven the changes in genus richness. Using sponges to interpret the effects of climate changes can be a profitable strategy to unravel long term changes in biodiversity, supporting future predictions.
The Role of Sponge Bioerosion in Mediterranean Coralligenous Accretion
2001
Coralligenous biocoenoses developed almost 10,000 years ago in the Mediterranean Sea, form· ing environments characterized by high levels of biodiversity. They are complex biogenic struc· tures growing through the continuous overlapping of organogenic layers, between 20 and 130 m depth. The coralligenous substrate, for the concurrent presence of bio-builders (algae, ser· pulid worms, bryozoans,and scleractinians) and destroying elements (clionid sponges, bivalves) is subject to dynamic evolution. Studies conducted on sections of corall igenous blocks show that algae are the main component responsible for the bui lding of these concretions. Calcareous remains of benthic animals lack in mineral structures and are one of the most impor· tant detritus·forming elements at the bottom of vertical cliffs. This seems to be due to the attack of clionids which selectively bore animal rather than plant carbonates. A study on the population dynamics of some anthozoans with a calcareous skeleton has shown that about 100% of the newly settled specimens are probably removed by cl ion· ids. ln th is way, the substratum is cyclically renewed by the continuous boring action of clionids. It is a sort of intermediate disturbance which controls the evolution and the structure of skio-philous zoocoenosis, through primary space regeneration. A high specific richness, typical of coralligenous biocoenosis, is developed by this action. From a geological point of view, it form s a kind of limestone, characteristic of biogenic constructions and detritic bottoms under the cliff.
Coralligenous habitat results from a multi-stratified accumulation of crustose coralline algae and animal builders in a dynamic equilibrium with disruptive agents. The result is a complex architecture crossed by crevices and holes. Due to this three-dimensional structure, the coralligenous habitat may host a rich and diversified fauna, more abundant than in any other Mediterranean habitat. Unfortunately, very few data are available about the cryptic fauna that lives inside the conglomerate. As already reported for coral reefs, the cryptic fauna plays an important role in the exchange of material and energy between water column and benthic assemblages. In this study, we compare the sponge community present inside and outside the coralligenous framework of the Portofino Promontory (Ligurian Sea) at different depths (15 and 30 meters) not only in terms of taxonomic diversity but, for the first time, also in terms of biomass. Sponges present on the surface of each block were collected, weighed and identified; after the dissolution of blocks in HCl, target cryptic sponges were separated from other organisms, weighed, and identified. We recorded a total of 62 sponge species. The average number of sponge taxa occurring outside the coralligenous accretions is lower than the number of taxa identified inside. This pattern is confirmed also regarding sponge biomass. These results underline that studies focused on coralligenous functioning should take into account the important contribution of cryptic fauna, as recently evidenced also for tropical reef habitats.
Deep-sea Research Part Ii-topical Studies in Oceanography, 2010
Thanatofacies and the skeletonized components of the living facies, from which they originate have been studied from the Santa Maria di Leuca (SML) deep-water coral mound province. Faunal analysis was carried out by means of bottom sampling and underwater video observations, taking into account all benthic taxonomic groups, mostly corals, molluscs, serpulids, bryozoans, ostracods, foraminifers and barnacles, which permitted recognition of six different facies. These thanatofacies are easily distinguishable and appear to be largely corresponding and overlapping with related living facies. Some occur in mound areas, others in the intermound ones. They are as follows: the Frameworkbuilding Coral facies (FC), characterised by colonial corals, mostly Madrepora oculata; the Coral Rubble facies (CR), with proximal and distal aspects, characterised by large-to small-sized and densely to loosely packed coral fragments; the Solitary Coral facies (SC), dominated by different species depending on the availability and dimensions of hard exploitable surfaces; the Gryphus and Isidella facies (GI) in relatively coarse-grained bottoms; the Mollusc Mud facies (MM) and the Foraminifer Mud facies (FM) in comparably homogeneous silty bottoms. Facies distribution and spatial variability are discussed, in relation to hydrology and sea-floor topography. Furthermore, the SML facies are compared with living facies from the present-day Mediterranean and Pleistocene sediments of the same area. Data on bioclastic assemblages can serve for comparison with other recent aphotic, non-tropical carbonates.
ZooKeys, 2013
Temperate reefs, built by multilayers of encrusting algae accumulated during hundreds to thousands of years, represent one of the most important habitats of the Mediterranean Sea. These bioconstructions are known as "coralligenous" and their spatial complexity allows the formation of heterogeneous microhabitats offering opportunities for a large number of small cryptic species hardly ever considered.