Rehabilitation of Mytilus edulis larvae abnormalities induced by K₂Cr₂O₇ in short-term experiments

Mytilus edulis embryo-larval development is often used as a bioassay to evaluate the negative impact of contaminants and environmental conditions. The toxicity criteria used in most protocols is the proportions of normal and abnormal larvae. The variety of abnormalities were described and classified, but further development of abnormal larvae remains obscure. This study aimed to reveal the possibility of correction of the morphological abnormalities after short-term exposure (48 h) in a variety of K₂Cr₂O₇ concentrations. For this purpose, abnormal larvae, which developed under the negative influence of the series of K₂Cr₂O₇ concentrations were transferred into clean seawater and studied after further 24 and 48 h. The obtained data, concerning changes in larval morphology, growth and survival rates during washing show that the abnormal larvae have enough capability to recover the normal D-shell structure. Moreover, restoration of the D-shell is possible even after exposure with concentration of the toxicant higher than the average effective one. The present research also pointed out that the development of larval shell (even abnormal one) is positively correlated with ability of the larvae to reconstruct D-shell and their survival rate. High mortality during washing occurs only at toxicant concentrations when no shell was formed within 48 h. Thus, the existence of the shell after 48 h exposure in the toxicant could indicate reversibility of the negative impact and help to distinguish the delay in development from its arrest.