Biol. Mar. Mediterr. (2012), 20 (1): 116-117
G. Atzori, F. Palmas, S. Vittori, S. Cabiddu Department of Life Science and Environment, University of Cagliari, Via T. Fiorelli, 1 - 09126 Cagliari, Italy.
[email protected]
FIRST RECORD AND POPULATION STRUCTURE OF THE INVASIVE SPECIES MUSCULISTA SENHOUSIA (BIVALVIA: MYTILIDAE) IN THE SANTA GILLA LAGOON (SOUTH SARDINIA) SEGNALAZIONE E STRUTTURA DI POPOLAZIONE DELLA SPECIE INVASIVA MUSCULISTA SENHOUSIA (BIVALVIA: MYTILIDAE) NELLA LAGUNA DI SANTA GILLA (SUD SARDEGNA) Abstract - Musculista senhousia (Benton 1842) is a small mytilid mussel, native to the Indopacific Ocean, and by now recorded worldwide. In this paper the presence of this species in the Santa Gilla lagoon (Sardinia, Cagliari) was reported. A total of 1442 specimens, with the greatest number in the station nearest to the freshwater sources, were collected. The abundance of the specimens collected in this lagoon seems to show that the population is already stabilized. Key-words: Musculista senhousia, introduced species, Santa Gilla lagoon, population structure.
Introduction - The green bugmussel, Musculista senhousia (Benton 1842), is a small mytilid, native to the Indopacific Ocean, and by now recorded worldwide. This species is reported in the list of the 100 ‘Worst Invasive’ alien marine species in the Mediterraean (Streftaris and Zenetos, 2006), where it was recorded for the first time in the early 1970s. In the Tyrrhenian area M. senhousia has been recorded firstly in 2004 (Campani et al., 2004) and in Sardinian waters it has been found in the Gulf of Olbia (Munari et al., 2004) and in some Oristano lagoons (unpublished data). This species is a great invader owing to its small dimension, short life, rapid growth rate and high fecundity (Willan, 1987). The aim of this study is to report the presence of M. senhousia in the Santa Gilla lagoon (South Sardinia) and to give some information about its population structure, being population dynamics of non-native species essential to understand the invasive process and impacts on the invaded ecosystems. Materials and methods - The specimens were collected seasonally from summer 2010 to spring 2011, in 3 stations along a salinity gradient. The samples were taken with a Van Veen grab, washed through a 1 mm mesh screen, and immediately fixed in 4% buffered formaldehyde. Each specimen was photographed and the total length was measured using the tpsDig software (version 2.0). The length-frequency distributions were analysed and comparison among distributions for each station and season were performed using the Kolmorov-Smirnov test. Results - A total of 1442 specimens were collected and the greatest number of specimens (1031) was found in the station nearest to the freshwater sources, followed by the intermediate station (376), and the station nearest to the sea (51), where no specimens were found during winter and spring. The greatest number of specimens was collected in autumn (480) and winter (799), while a few number was found in summer (70) and spring (91). This species showed a range in size between 0.1 mm and 20.5 mm (mean±SD=3.3±2.0) (Fig. 1). The largest specimens were collected in the station nearest to the sea (mean±SD=4.2±5.1), followed by the individuals from the station nearest to the freshwater sources (mean±SD=3.8±1.8) and the intermediate
First record and population structure of the invasive species M. senhousia in the Santa Gilla lagoon
117
nearest to the freshwater sources (mean±SD=3.8±1.8) and the intermediate station (mean±SD=1.8±0.6). During the year the total length of specimens showed the highest station (mean±SD=1.8±0.6). During the year the total length of specimens showed values in spring (2.3-13.4 mm mean±SD=7.0±2.4), followed by winter (0.1-13.4 mm the highest values in spring (2.3-13.4 mm mean±SD=7.0±2.4), followed by winter (0.1mean±SD=3.7±1.6), summer (0.7-20.5 mm mean±SD=3.5±4.4) and autumn (0.7-8.6 13.4 mm mean±SD=3.7±1.6), summer (0.7-20.5 mm mean±SD=3.5±4.4) and autumn mm mean±SD=2.0±0.8). Differences between stations and and between seasons were (0.7-8.6 mm mean±SD=2.0±0.8). Differences between stations between seasons were always significant (P
