Effects of hydraulic dredging on the physiological responses of the target species <i>Chamelea gallina</i> (Mollusca: Bivalvia): laboratory experiments and field surveys

Abstract

The effects of mechanical stress in the Venus clam Chamelea gallina during hydraulic dredging were assessed in both laboratory and field studies in order to measure physiological biomarkers at organism level (clearance rate, respiration rate, scope for growth, and survival in air test). In the laboratory, mechanical stress was simulated by shaking clams in a vortex mixer. In the field, clams were collected seasonally at two sites along the northern Adriatic coast (Lido and Jesolo) and four levels of stress were applied: the highest was that used in commercial fishing (i.e. high water pressure and mechanised sorting) and the lowest manual sampling by SCUBA divers. Survival in air was the most sensitive biomarker in evaluating mechanical stress in the laboratory. Clearance rate also decreased significantly when shaking was applied. Field results indicated that high water pressure and mechanised sorting affected clearance, scope for growth and survival in air, all showing decreasing trends as mechanical stress increased at both sampling sites. The detrimental effects of mechanical disturbance may be emphasised depending on season, when exogenous and endogenous stress increases. A potential risk is highlighted mostly for undersized clams that are fished and then discarded.