Temperature-dependent physiological responses of the dogwhelk Nucella lapillus to cadmium exposure

Abstract

The combined effects of cadmium (Cd) and temperature on the physiology (oxygen consumption rate (MO2)) and biochemistry (glycogen, metallothionein (MT) and Cd concentrations) of fasted dogwhelks Nucella lapillus were investigated using two Cd concentrations (<0.01 or 500 μg l-1) and two water temperatures (5 or 10°C). After 20 days of exposure, the MO2 of dogwhelks of various sizes (12-32 mm in shell length) were measured individually. Dogwhelks exposed to Cd exhibited significantly lower MO2 at 10°C but not at 5°C when compared with controls at the same temperature. Inhibition of MO2 by Cd increased with increasing water temperature and decreasing animal size. Cadmium exposure caused significant reductions in glycogen concentrations in foot muscle and digestive gland at both temperatures. Cadmium-exposed dogwhelks showed significantly higher MT concentrations in the Leiblein gland at 10°C but not at 5°C, indicating that MT synthesis is temperature dependent and temperature is an important factor affecting toxicity of Cd in N. lapillus. Activity of dogwhelks and oxygen carrying capacity of the haemolymph, were significantly reduced as a result of Cd-exposure at 10°C. In addition, mucus secretion and necrotic cells were observed on the gill surface of Cd-exposed individuals. Therefore, reduction in MO2 may be directly linked to Cd-induced mucus production, structural damage to gills and reduction in oxygen carrying capacity of haemocyanin. However, metabolic depression, including low MO2 and activity, in Cd-exposed N. lapillus may be a strategy to: (i) minimize the uptake and toxicity of Cd; and (ii) minimize energy expenditure to spare energy reserves for detoxification (e.g. MT synthesis) and maintenance (e.g. repair of cellular damage). The results are discussed with reference to the use of MT and glycogen as biomarkers for metal exposure and toxicity in marine molluscs.