**Abstract**

Foraminifera are eukaryotic unicellular microorganisms inhabiting all marine environments. The study of these protists has huge potential implications and benefits. They are good indicators of global change and are also promising indicators of the environmental health of marine ecosystems. Nevertheless, much remains to be learned about foraminiferal ecology. The goals of this chapter are (1) to provide a few examples from foraminifera studies, presenting possible use of foraminifera as bioindicators for the monitoring of transitional and marine ecosystems and (2) to highlight the importance of applying these organisms in environmental monitoring studies. A semienclosed coastal lagoon (Aveiro Lagoon; Portugal), an estuarine system (São Sebastião Channel; SE Brazil), a continental shelf sector (Campos Basin; SE Brazil), and a segment of continental slope (Campos Basin; SE Brazil) are used as examples.

**Keywords:** foraminifera, marine pollution, marine ecosystems, environmental stress, bioindicators
