Optimisation and use of bivalve mollusk shells as monitors and indicators for chemical and biotic stress detection

Abstract

Bivalve mollusk shells are used traditionally as monitors for chemical stress detection via elemental analysis of a whole multilayered shell or its single layers. The central shell part, as suggested by some authors, has a perspective to be used as a bioarchive of environmental records. Shells as indicators of water pollution with xenobiotics and animals’ infestation with pathogens/parasites are cursorily studied. The aim of this dissertation was to increase our knowledge of bivalve shells, as environmental indicators and monitors, based on their preservation and micromorphology data. Studied chemical stressors include silver and copper in dissolved and nanoparticulate form, and actinides ( 232Th, 241Am) in dissolved form. Studied biotic stressors include pathogenic photosynthetic microalgae Coccomyxa sp. and unknown shell borers. Shells obtained from control and contaminated/infested freshwater and marine bivalves, and shells obtained after laboratory and field-based experiments, were examined by optical, digital and electron microscopy, mass spectrometry, X-ray powder diffraction, γ-spectrometry and α-tracks autoradiography. Where applicable, bivalves’ soft tissues and biological liquids were examined. The most important findings are: 1, the amount of pollutants on the external shell surface depends on its preservation and micromorphology; 2, doughnut shape structures (DSS) were found on the surface of aragonite tablets (nacre) if mussels were exposed to low concentrations of silver (in the form of ions and nanoparticles); 3, infestation of M. edulis with pathogenic photosynthetic microalga Coccomyxa sp. promotes the formation of L-shaped shell deformity (LSSD); 4, infestation with Coccomyxa was experimentally confirmed for mussels pre-exposed to copper; 5, the old (previously secreted) layers of nacre can be transformed to aragonitic lenses of prisms (ALPs) due to early unknown physicochemical mechanism in response to shell attacks with boring organisms. In order to improve environmental monitoring protocols which use bivalves it was recommended: (a) to collect marine blue mussels (Mytilidae) with eroded external shell surface, whereas shells of freshwater unionid and dreissenid bivalves must have intact fleecy periostracum; and (b) to use the presence of DSS, LSSD and ALP as indicators of water pollution with metals, metals/pathogenic alga, and shell-borers, respectively.