Antonio Mazzola

Effects of trophic and environmental conditions on the growth of Crassostrea gigas in culture.

Abstract In order to study the possibility of exploiting protected marine areas, comparative data on the cultivation of the oyster Cassostrea gigas in the South Tyrrenian Sea are reported. The oysters were cultured at −7 and −13 m on long lines linked to artificial reefs. The observations, made during a 12-month period, were of the chemical-physical and trophic properties of the water column and growth rates of the oysters. Temperature ranged between 19.81 ± 4.67 °C at −7 m and 18.03 ± 3.03 °C at −13 m. Salinity showed typical Mediterranean values. The area presented oligotrophic features: the chlorophyll-a (CHLa) concentration ranged between 0.05 ± 0.01 and 0.04 ± 0.02 μg l −1 at −7 and −13 m, respectively. The labile particulate organic matter (LPOM) ranged between 344 ± 201 and 334 ± 228 μg l −1 at −7 and −13 m, respectively, and the CHLa carbon/POM carbon ratio (index of the autotrophic vs heterotrophic conditions) was never above 3%. POM concentration and POM gross energy content showed significant differences ( P

Spatial variability of soft-bottom macrobenthic communities in northern Sicily (Western Mediterranean): Contrasting trawled vs. untrawled areas

This study examines the impact of bottom trawl fishing on the macrobenthic communities inhabiting the coastal terrigenous mud off the northern coast of Sicily (Western Mediterranean). Two intensely trawled gulfs were compared with two gulfs from which trawling has been excluded for 15 years. The results show a significant effect of trawling on the faunal assemblage and when comparing the mean biomass and the whole isotopic composition of the benthic communities. A similar pattern, although not significant, was found for total abundance, biomass, production/biomass ratio and diversity. Higher abundance and lower biomass were found in the untrawled areas, attributable to the presence of more numerous yet smaller individuals, possibly a consequence of more abundant larger predators that are not removed by trawling, and consequent higher predatory pressure on the benthic macrofauna. The SIMPER analysis evidenced a dominance of burrowing deposit feeding worms (Paraonidae and Cossuridae) in trawled areas, as a result of increased mechanical alteration and hence more organic matter available as food. In contrast, the response to trawling as drawn by the use of trophic markers (i.e., stable isotopes) was less clear. While δ15N of benthic taxa did not vary significantly between untrawled and trawled areas, δ13C was higher in trawled areas possibly due to high sediment resuspension and consequent intense microbial activity. Mixing models confirmed higher reliance to a detritus-based food web for benthic organisms in the trawled areas. Standard Ellipse Areas (SEAc) as a measure of community niche width were slightly larger in trawled areas, likely due to higher generalism triggered by alteration/removal of the original benthic community.