The area among Budelli, Razzoli e Santa Maria islands (NE Sardinia) re-presents a good field for an interdisciplinary research (geomorphology, sedimentology and actuopaleontology) in order to define the ecological conditions of the seafloor. In particular, this study plans to highlight the value of some proxies to indentify bad-to-good conditions for the benthic life. This research focuses on the ostracods, which are small crustaceans considered by a wide literature as good environmental markers. The material studied derives from some oceanographic cruises (PALEOCLIGE 2000-2002). It consists of 14 grab-samples and 4 other ones collected by scuba divers. The samples were traited with formalin 2% and Rose Bengal to preserve and evidence the living specimens. They are washed through a 63 µm mesh. Once dried, the were analysed from the palaeontological point of view, both to highlight the grain components of the bottom deposits and to identify the ostracod species. The use of Side Scan Sonar Edgetech DF-1000, together with a geomorphological survey realised by scuba divers, performed a high resolution map of the sea floors. From the geomorphological point of view, the seafloors can be subdivided into the following units: granite, fine sandy substrate, Posidonia oceanica meadow with intramatte channels. This palaeontological and sedimentological study refined the data obtained by the acoustic and geomorphological surveys. It concerned the samples collected in selected seafloors of the investigated area. This study highlighted the following major bottom-facies, included into the previously mentioned geomorphological units: -Facies 1 - Fine sandy substrate (samples 200, 214, 215). It is characterised by sand mostly constituted by quartz grains (71%-26%- 49% respectively), by skeletal grains of bryozores (19% - 41% - 35%), calcareous forminifers (3% - 15%, 3%). -Facies 2 - Posidonia oceanica meadow (samples 224, 225). It is constituted by quartz grains (7.7% - 44 %), by skeletal grains of bryozores (45 % - 20%), calcareous forminifers (2%- 8%). Facies 3 - Intramatte channel (samples 216, 767). It is represented by quartz grains (43%-40%), by skeletal grains of bryozores (28%- 16%), calcareous forminifers (16% - 23%). The analysis of the ostracods evidenced their links with the above mentioned facies. These links have been performed by means the autochthonous forms, only. In general, the ostracod fauna consists of 85 species. Forty-nine species of them are considered "autochthonous" in at least in one sampling station. Some species are exclusive of only one bottom-facies: Facies 1: "Bythocythere" minima, Heterocythereis voraginosa, Aurila arborescens, Bairdia corpulenta, Bythocythere turgida, Callistocythere adriatica, Cistacythereis aff. C. rubra, Echinocythere laticarina, Neocytherideis fasciata, Paracytheridea gr. depressa, Pseudocytherura calcarata, Semicytherura cribriformis, Triebelina raripila and Xestoleberis plana, Microcytherura nigrescens. Facies 2: Polycope sp. 1, Sclerochilus levis; Facies 3: Bairdia serrata, Bythoceratina reticolata, Callistocythere sp. 1, He-micytherura defiorei, Loxoconcha ovulata, Loxoconcha rhomboidea, Microxestoleberis nana, Phlyctocythere pellucida, Phlyctocythere pellucida, Pseudopsammocythere reniformis, Semicytherura alifera; Other species occur in a higher number of facies. These species should be able to tolerate a wider range of ecological conditions than those exclusive of only one bottom facies. Thus, it is possible to recognize a hierarchy of species which are more or less tolerant to ecological conditions. This hierarchy may be refined through the application of the Shannon-Weaver (SW) index. In this study, this index records the ostracod specific richness, the equitability/dominance for each sample. It is assumed that low and ligh values of SW index should correspond to bad and good environmental conditions respectively. In this area, SW values vary from 0 to 2.70 Thus it is possible to propose 3 categories: 1) 0 = S.W. < 1 2) 1 = S.W. < 2 3) S.W =2 Through the SW index, it is possible to evidence the sampling stations each one characterised by bad (category 1), good (category 3) and intermediate (category 2) conditions for the benthic life. Excepted for the intramatte channel of sampling station 216, which denotes bad conditions, the best conditions occur in the area among the three islands. Actually, this sector shows sampling stations characterised by good (215, 1, 2) and intermediate (214, 767, 768, 3) conditions. Analysing these data, it appears evident that: 1) the submerged beach of S. Maria Isl. (sampling station 215) records better conditions than that of Budelli Isl. (sampling station 214); 2) the intramatte channels near Chiecca del Morto (sampling station 216) shows worse conditions than that of sampling station 767,maybe in relation a stronger human presence (anchorages evidenced by the acoustic survey). It is evident that: - some ostracod species are present in all the categories; - other species are exclusive of only one category; the remaining species occur in two categories. These species are listed below: Species of all categories: Loxoconcha affinis e Tenedocythere prava; Species exclusive of category 1: Microxestoleberis nana; Species exclusive of category 2 : Polycope sp. 1, Microcytherura nigrescens, Sclerochilus levis Species exclusive of category 3: Aurila arborescens, Bairdia corpulenta, Bairdia longevaginata, Bairdia serrata, Bythocythere minima, Bythocythere turgida, Bythoceratina reticolata, Caudites calceolatus, Callistocythere adriatica, Callistocythere sp. 1, Cistacythereis aff. C. rubra, Cytheretta adriatica, Echinocythereis laticarina, Hemicytherura defiorei, Loxoconcha ovulata, Microcythere inflexa, Neocytherideis fasciata, Paracytheridea gr. depressa, Phlyctocythere pellucida, Propontocypris pirifera, Pseudocytherura calcarata, Triebelina raripila, Urocythereis margaritifera, Urocythereis cf. favosa, Semicytherura alifera, Semicytherura cribriformis e Xestoleberis plana Intermediate-bad species: Cytherelloidea sordida Intermediate-good species: Cytheretta subradiosa, Hemicytherura videns, Heterocythereis voraginosa, Loxocauda decipiens, Loxoconcha rhomboidea, Loxoconcha stellifera, Aurila convexa, Aurila fallax, Aurila prasina, Pontocythere turbida, Pseudopsammocythere reniformis, Semicytherura dispar, Xestoleberis communis, Xestoleberis dispar e Xestoleberis pellucida The species occurring in all the categories are able to live a wide range of ecological conditions and, thus, to tolerate environmental changes. The species exclusive of only one category denote a precise ecological meaning: those occurring in low, high or intermediate SW index values indicate bad, good or intermediate conditions, respectively. The species present in two categories indicate intermediate conditions: intermediate-bad (categories 1-2) and intermediate-good (categories 2-3). Moreover, in general, the species occurring in all the categories correspond to those present in all the bottom-facies. Several exclusive species of categories 2 and 3 correspond to those which are exclusive of well defined bottom-facies. Summarising, these data evidence some ostracod species as environmental markers. In particular, bad environmental conditions are usually indicated by species occurring in SW category 1 (Microxestoleberis nana) and/or by assemblages of very tolerant species (Loxoconcha affinis, Tenedocythere prava and, subordinately, Cytherelloidea sordida). Viceversa, good environmental conditions are indicated by species and assemblages of species which are generally exclusive of a well defined categories 2 and/or 3. This research concerns geomorfological, oceanographical studies and sampling operation for sedimentological and paleontological analysis. Moreover, this research included within projects: INTERREG II "Protezione, valorizzazione e gestione dell'ambiente Sardo-Corso", Tema 2B 3°; INTERREG III "Ambiente fisico, valorizzazione della fascia costiera Sardo-Corsa e gestione delle risorse".
ENVIROMENTAL MARKERS OF THE SEA FLOORS AMONG BUDELLI, RAZZOLI AND SANTA MARIA ISLANDS (NE SARDINIA-ITALY)
DEMURO, SANDRO;
2003-01-01
Abstract
The area among Budelli, Razzoli e Santa Maria islands (NE Sardinia) re-presents a good field for an interdisciplinary research (geomorphology, sedimentology and actuopaleontology) in order to define the ecological conditions of the seafloor. In particular, this study plans to highlight the value of some proxies to indentify bad-to-good conditions for the benthic life. This research focuses on the ostracods, which are small crustaceans considered by a wide literature as good environmental markers. The material studied derives from some oceanographic cruises (PALEOCLIGE 2000-2002). It consists of 14 grab-samples and 4 other ones collected by scuba divers. The samples were traited with formalin 2% and Rose Bengal to preserve and evidence the living specimens. They are washed through a 63 µm mesh. Once dried, the were analysed from the palaeontological point of view, both to highlight the grain components of the bottom deposits and to identify the ostracod species. The use of Side Scan Sonar Edgetech DF-1000, together with a geomorphological survey realised by scuba divers, performed a high resolution map of the sea floors. From the geomorphological point of view, the seafloors can be subdivided into the following units: granite, fine sandy substrate, Posidonia oceanica meadow with intramatte channels. This palaeontological and sedimentological study refined the data obtained by the acoustic and geomorphological surveys. It concerned the samples collected in selected seafloors of the investigated area. This study highlighted the following major bottom-facies, included into the previously mentioned geomorphological units: -Facies 1 - Fine sandy substrate (samples 200, 214, 215). It is characterised by sand mostly constituted by quartz grains (71%-26%- 49% respectively), by skeletal grains of bryozores (19% - 41% - 35%), calcareous forminifers (3% - 15%, 3%). -Facies 2 - Posidonia oceanica meadow (samples 224, 225). It is constituted by quartz grains (7.7% - 44 %), by skeletal grains of bryozores (45 % - 20%), calcareous forminifers (2%- 8%). Facies 3 - Intramatte channel (samples 216, 767). It is represented by quartz grains (43%-40%), by skeletal grains of bryozores (28%- 16%), calcareous forminifers (16% - 23%). The analysis of the ostracods evidenced their links with the above mentioned facies. These links have been performed by means the autochthonous forms, only. In general, the ostracod fauna consists of 85 species. Forty-nine species of them are considered "autochthonous" in at least in one sampling station. Some species are exclusive of only one bottom-facies: Facies 1: "Bythocythere" minima, Heterocythereis voraginosa, Aurila arborescens, Bairdia corpulenta, Bythocythere turgida, Callistocythere adriatica, Cistacythereis aff. C. rubra, Echinocythere laticarina, Neocytherideis fasciata, Paracytheridea gr. depressa, Pseudocytherura calcarata, Semicytherura cribriformis, Triebelina raripila and Xestoleberis plana, Microcytherura nigrescens. Facies 2: Polycope sp. 1, Sclerochilus levis; Facies 3: Bairdia serrata, Bythoceratina reticolata, Callistocythere sp. 1, He-micytherura defiorei, Loxoconcha ovulata, Loxoconcha rhomboidea, Microxestoleberis nana, Phlyctocythere pellucida, Phlyctocythere pellucida, Pseudopsammocythere reniformis, Semicytherura alifera; Other species occur in a higher number of facies. These species should be able to tolerate a wider range of ecological conditions than those exclusive of only one bottom facies. Thus, it is possible to recognize a hierarchy of species which are more or less tolerant to ecological conditions. This hierarchy may be refined through the application of the Shannon-Weaver (SW) index. In this study, this index records the ostracod specific richness, the equitability/dominance for each sample. It is assumed that low and ligh values of SW index should correspond to bad and good environmental conditions respectively. In this area, SW values vary from 0 to 2.70 Thus it is possible to propose 3 categories: 1) 0 = S.W. < 1 2) 1 = S.W. < 2 3) S.W =2 Through the SW index, it is possible to evidence the sampling stations each one characterised by bad (category 1), good (category 3) and intermediate (category 2) conditions for the benthic life. Excepted for the intramatte channel of sampling station 216, which denotes bad conditions, the best conditions occur in the area among the three islands. Actually, this sector shows sampling stations characterised by good (215, 1, 2) and intermediate (214, 767, 768, 3) conditions. Analysing these data, it appears evident that: 1) the submerged beach of S. Maria Isl. (sampling station 215) records better conditions than that of Budelli Isl. (sampling station 214); 2) the intramatte channels near Chiecca del Morto (sampling station 216) shows worse conditions than that of sampling station 767,maybe in relation a stronger human presence (anchorages evidenced by the acoustic survey). It is evident that: - some ostracod species are present in all the categories; - other species are exclusive of only one category; the remaining species occur in two categories. These species are listed below: Species of all categories: Loxoconcha affinis e Tenedocythere prava; Species exclusive of category 1: Microxestoleberis nana; Species exclusive of category 2 : Polycope sp. 1, Microcytherura nigrescens, Sclerochilus levis Species exclusive of category 3: Aurila arborescens, Bairdia corpulenta, Bairdia longevaginata, Bairdia serrata, Bythocythere minima, Bythocythere turgida, Bythoceratina reticolata, Caudites calceolatus, Callistocythere adriatica, Callistocythere sp. 1, Cistacythereis aff. C. rubra, Cytheretta adriatica, Echinocythereis laticarina, Hemicytherura defiorei, Loxoconcha ovulata, Microcythere inflexa, Neocytherideis fasciata, Paracytheridea gr. depressa, Phlyctocythere pellucida, Propontocypris pirifera, Pseudocytherura calcarata, Triebelina raripila, Urocythereis margaritifera, Urocythereis cf. favosa, Semicytherura alifera, Semicytherura cribriformis e Xestoleberis plana Intermediate-bad species: Cytherelloidea sordida Intermediate-good species: Cytheretta subradiosa, Hemicytherura videns, Heterocythereis voraginosa, Loxocauda decipiens, Loxoconcha rhomboidea, Loxoconcha stellifera, Aurila convexa, Aurila fallax, Aurila prasina, Pontocythere turbida, Pseudopsammocythere reniformis, Semicytherura dispar, Xestoleberis communis, Xestoleberis dispar e Xestoleberis pellucida The species occurring in all the categories are able to live a wide range of ecological conditions and, thus, to tolerate environmental changes. The species exclusive of only one category denote a precise ecological meaning: those occurring in low, high or intermediate SW index values indicate bad, good or intermediate conditions, respectively. The species present in two categories indicate intermediate conditions: intermediate-bad (categories 1-2) and intermediate-good (categories 2-3). Moreover, in general, the species occurring in all the categories correspond to those present in all the bottom-facies. Several exclusive species of categories 2 and 3 correspond to those which are exclusive of well defined bottom-facies. Summarising, these data evidence some ostracod species as environmental markers. In particular, bad environmental conditions are usually indicated by species occurring in SW category 1 (Microxestoleberis nana) and/or by assemblages of very tolerant species (Loxoconcha affinis, Tenedocythere prava and, subordinately, Cytherelloidea sordida). Viceversa, good environmental conditions are indicated by species and assemblages of species which are generally exclusive of a well defined categories 2 and/or 3. This research concerns geomorfological, oceanographical studies and sampling operation for sedimentological and paleontological analysis. Moreover, this research included within projects: INTERREG II "Protezione, valorizzazione e gestione dell'ambiente Sardo-Corso", Tema 2B 3°; INTERREG III "Ambiente fisico, valorizzazione della fascia costiera Sardo-Corsa e gestione delle risorse".
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