Comparative embryo/larval sensitivity of Australian marine bivalves to ten metals: A disjunct between physiology and phylogeny

Metal contamination within the urbanized coastal zon is one threat linked to a decline in the abundance, distribution and/or species diversity of wild marine bivalve populations. This study determined the 48-h embryo/larval sensitivity (no-effect concentration (NEC) and median-effect concentration (EC50)) of ten marine bivalve species (nine endemic to Australia) to aluminium (Al), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), nickel (Ni) and zinc (Zn), key metal contaminants impacting urbanized coastal zones in south-eastern Australia, in natural seawater (20-22 degrees C, 30 parts per thousand salinity, pH 7.8-7.9, 1.2 mg/L dissolved organic carbon). For all metals, except Fe, the order of sensitivity was oysters >= mussels >= scallops >= cockles >= clams, where the economically-important oysters, Magallana gigas and Saccostrea glomerate, were 2.6 (Al) to 4.2 (Cd) times more sensitive than the least sensitive clam species. For all bivalve species, the order of metal sensitivity was Cu > Pb > Zn = Ni > Co > Cd > Al > Cr(VI) > Mn >= Fe( III), where Cu was eight times more toxic than Zn or Ni, 28 times more toxic than Cd, 220 times more toxic than Cr(VI) and 570 times more toxic than Fe(III). Iron, unlike the other nine soluble metals, occurred as particulate Fe(III) oxyhydroxide, where EC50 values decreased with increasing exposure time as the larval (D-veliger) stage. There was no significant (p > 0.05) effect ofembryo/larval mass, or surface area/volume, on metal sensitivity. Further, there was no significant (p > 0.05) relationship between metal sensitivity and phylogeny (genetic distance). Divalent metal sensitivity was positively related (r(2) = 0.87) to cell surface metal-binding affinity. The current Australian marine water quality guideline for Ni is not protective of the ten bivalve species (NECs were 2-6-fold below the guideline), while the guideline for Zn is not protective of oysters. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

For most bivalve species, copper is the most toxic metal, while aluminum and chromium are relatively less toxic. Iron occurred as Fe(III), with EC50 values decreasing with exposure time as the larval stage developed.