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STRUCTURal vaRIaBIlITy of ThE EpIphyTIC CoMMUnITy In a Posidonia oceanica MEaDow
| Content Provider | Semantic Scholar |
|---|---|
| Author | Ea, L. I. G. U. R. Ian S. Ean, Nw M. E. D. I. T. E. R. Ran |
| Copyright Year | 2007 |
| Abstract | several factors influence the epiphytic assemblage of posidonia oceanica (L.) delile (Monocotyledones, Posidoniaceae) leaves. The aim of this study was to investigate the epiphytic community structure in the p. oceanica meadow of Prelo cove (Ligurian sea, nW Mediterranean) along a yearly cycle and a depth gradient. sampling was carried out monthly from september 2003 to august 2004 at three different depths: 4, 9 and 14 m. each month, 10 randomly selected p. oceanica shoots were collected by scUBa diving in each station. Percentage cover of the most representative taxa was estimated and subjected to multivariate analysis in order to detect seasonal changes in the epiphytic assemblage along the bathymetric gradient. in all stations, the epiphytic assemblage exhibited cyclic variability, and two major phases were distinguished: an autumnal one dominated by hydrolithon-pneophyllum spp, and a spring-early summer one in which the algae were flanked by Electra posidoniae. a poorer but more various assemblage, with the appearance of the erect hydrozoans and bryozoans, was found in the deep station. Key-words: posidonia oceanica, epiphytic assemblage, depth gradient, seasonal cycle, Mediterranean sea. Introduction The most important seagrass in the Mediterranean Sea is Posidonia oceanica (l.) Delile, an endemic species that forms wide meadows. This plant hosts on its leaves and rizhomes a characteristic epiphytic community. Several factors influence the epiphytic assemblage, such as the cyclic phenology of the host plant, hydrodynamic forces, light intensity and anthropogenic disturbances (Mazzella et al., 1989; Dalla via et al., 1998; piazzi et al., 2004; Montefalcone et al., 2006). In this work the epiphytic community structure of P. oceanica leaves was investigated in a yearly cycle and along a depth gradient in order to describe its spatial and temporal variation. Materials and methods The study was carried out in the Posidonia oceanica meadow of prelo cove (ligurian Sea, nw Mediterranean). along a depth transect (directed perpendicularly to the shoreline, 270°n), three stations were identified: 4 m (44°20’12” n, 009°13’33” E), 9 m (44°20’11” n, 009°13’36” E) and 14 m (44°20’11” n, 009°13’39” E), where 10 randomly selected P. oceanica shoots were collected by SCUBa diving monthly, from September 2003 to august 2004 (December data are missing). In the laboratory both sides of each P. oceanica leaf blade were analysed using a binocular stereomicroscope to estimate the percentage cover of the following taxa: Hydrolithon-Pneophyllum spp., Myrionema orbiculare, Giraudia sphacelarioides, electra posidoniae, aetea truncata, Fenestrulina johannae, Plumularia obliqua, sertularia perpusilla. all the other organisms were grouped in: other E. GiovannEtti, M. MontEfalconE, c.n. Bianchi, c. Morri, G. alBErtElli 146 Bryozoans, Serpulids, other animals and other algae. The cover data per shoot were analysed with multivariate techniques (anoSIM, MDS, SIMpER) in order to detect spatial and temporal variability of the epiphytic community structure. Results Two-way crossed analysis anoSIM test revealed clear differences in the epiphytic community structure among depths (R = 0.456; p = 0.1 %) and months (R = 0.692; p = 0.1 %); the month factor determined the major dissimilarity. The MDS ordination showed, at three depths, a cyclic seasonal variability of the epiphytic community structure (fig. 1). The vicinity of the ending point (8= august 2004) to the starting point (9= September 2003) was greater at 14 m than at the shallow and the intermediate stations. Moreover the MDS ordination showed, at all stations, differences in dispersion (variability) of the epiphytic assemblage in each month, with the greatest dispersion observed in the autumn-winter months. fig. 1 MDS ordination comparing the epiphytic community structure at the three stations (4 m, 9 m, 14 m) along a yearly cycle. The three depths have been plotted separately (Stress = 0.14). The numbers indicate the months: from September 2003 (9) to august 2004 (8). December data are missing (dashed lines). The centre of the ellipses corresponds to monthly means, ellipses depict 95 % confidence intervals. arrows indicate the tendency to close the cycle. The cross indicates the centre of the axes. Results Two-way crossed analysis ANOSIM test revealed clear differences in the epiphytic community structure among depths (R = 0.456; P = 0.1 %) and months (R = 0.692; P = 0.1 %); the month factor determined the major dissimilarity. The MDS ordination showed, t three depths, a cyclic seasonal variability of the epiphytic community structure (Fig. 1). The vicinity of the ending point (8=August 2004) to the starting point (9=September 2003) was greater at 14 m than at the shallow and the intermediate stations. Moreover the MDS ordination showed, at all stations, differences in dispersion (variability) of the epiphytic assemblage in each month, with the greatest dispersion observed in the autumn-winter months. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.portofinoamp.it/articoli/Giovannettietal.2006.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
