Efecto de la profundidad sobre el crecimiento de los mejillones Perna perna y Perna viridis (Bivalvia: Mytilidae) en cultivo suspendidoen el Golfo de Cariaco, Venezuela

The effect of depth (4, 8, and 16 m) on the growth of the mussels Perna perna and Perna viridis was evaluated under culture conditions in the Gulf of Cariaco, Venezuela, during a period of six months. Bimonthly, it was determined the dimension and dry mass of the shell, tissues (somatic and reproductive), and the "fouling" on the shell to both species. At each depth, biweekly registrations of temperature, salinity, dissolved oxygen, and food availability (total, organic seston, and fitoplanktonic biomass) were obtained. At 8 m depth, the highest increments were reached in size, dry mass of the shell, and somatic and reproductive tissues, obtaining P. perna the highest values. The higher growth at this depth was associated with the values of organic seston (>20 mg/L). In both species the mass of the repeat tended to decrease with the increment of the depth, as well as the biomass of the fouling. The lower growth of P. viridis, jointly with the low survival (<30%) in all the experimental depths, suggests little plasticity of this species to adjust to the environmental conditions of the Gulf of Cariaco. However, the continuous growth of P. perna and the high survival (>70%) during the experimental period demonstrates that it was not affected by the environmental changes that took place in the water column. Among the environmental factors, food availability was the most determining on the difference of growth between the species in the experimental depths.