Effect of Bacillus thuringiensis on physiological rates of Mediterranean marine intertidal Mytilaster minimus (Mollusca, Bivalvia)

Abstract

The aim of the present research is to evaluate the impact of agricultural products in the marine environments. Indeed in a country such as Italy and in particularly Sicily where agricultural areas nearshore marine waters, predicting where, when and with what magnitude the impact of xenobiotics derived from agriculture is imperative. In this contest we use as model a biological product (Bacillus thuringiensis) in understanding its potential effects on non target species and on marine biodiversity. Bivalves are important elements of marine biodiversity and very often they play a role of ecosystem engineers in that many other species structurally depend on their presence. Moreover as they consume bacteria, to investigate the effect of the enthomopathogenic bacteria B. thuringiensis on this non target organisms could be useful to implement environmental risk assessment and data on food biosafety. Oxygen consumption through respiration in these organisms varies with natural physical and chemical factors like temperature and food availability. However, it has been demonstrated that also several contaminants may affect respiration rates in intertidal bivalves like the small Mediterranean Mytilid, Mytilaster minimus. Since the respiration is an important component of energy budget, deviation of its magnitude from common natural patterns may alter the amount of energy available for growth and reproduction. Such a fact, by cascade, may induce alteration of biodiversity. Here we focus on effects of two different concentrations of commercial products containing B. thuringiensis (50 and 100 J.II r1) compared with non treated control (i.e., noBt; CTRL) on energy budget of M. minimus. Experiments have been carried out with adult mussels of about 1.4 ± 0.3 cm collected in March 2010 from the coasts around Palermo (Northern Sicily). We measured standardised respiration rates (J.Imoli h-1 g-1) at ambient temperature (20.0 ± 1.00 C) in mesocosmal tanks both in presence of Bt and without. No difference was detected in size of experimental animals. Ingestion rates were significant different among three treatments; respired energy; peaked significantly at 100 J.II r1, and CTRL was different respect to both treatments while assimilated energy was higher in CTRL (87%) than 50 J.II r1 (57%) and 100 J.II r1 (70%). The total amount energy actually absorbed was maximum in CTRL and significantly decreased at 100 and 50 J.II r1. These novel risk assessment strategies may help to more comprehensively