2008 Elsevier B.V. All rights reserved. Elements are basic building blocks combining with one another in specific proportions to form molecules via constrained chemical and physical processes. Trace elements perform essential roles in assimilation, biological energy capture, information transfer and control, development and reproduction. Many of them are biologically essential but have the potential to be toxic to biota above a threshold concentration. Ratios of elements in everything from the smallest bacterium to the largest blue whale are regulated by their physiochemical properties and by feedback regulation, to the environment. Aquatic organisms accumulate elements from water, food, sediments, and/or discharge of wastewater. Inputs of many trace elements to the environment have increased as a result of industrialization and urbanization. Concerns regarding the possible adverse effects of metals on aquatic life, particularly on long-lived species, arise because of their potential to bioaccumulate. One of the biggest ecological challenges is linking molecular biomarkers of metal pollution with ecologically relevant life-history characteristics including growth, survival, reproduction, and recruitment. This article focuses on the interactions between trace elements, aquatic organisms, and their environment. The cellular functions of the physiologically important trace elements are described. Ecological stoichiometry is used to provide a conceptual framework to examine how trace elements are bioaccumulated, biomagnified, and/or biodiluted through trophic levels.
