**1. Introduction**

The anthropic activity has been causing more and more negative effects on nature, among which includes the discharge of several types of pollutants from either domestic or industrial sources. The final destination for a majority of the pollutants are frequently the coastal areas where the pollutants may cause deleterious effects as harm to living resources and marine life, hazards to human health, hindrance to marine activities, including fishing and other legitimate uses of the sea [1]. Persistent pollutants like polycyclic aromatic hydrocarbons (PAHs),

 polychlorinated biphenyls (PCBs), pesticides (dichloro diphenyl trichloroethane), toxic metals (Cd, Hg, Ag, Co, Cr, Ni, Pb, Zn, and Cu), and others may cause deleterious effect in marine life. The pollutants can enter the food chain and may even reach the highest trophic levels [2]. As microorganisms are among the lowest levels of the food chains, they are the first to denounce the negative effects of pollution. Among the vast variety of microorganisms, foraminifera have shown potential for effective pollution biomonitoring, apart from many other applications [1].

 These unicellular microorganisms are effective environmental indicators as they respond quickly to small environmental changes. Foraminifera are abundant and preserve the changes in their tests, making possible to study even the past environmental standing. Foraminifera are widely distributed in marine environments. In fact, they have been successful inhabitants from deep oceans to brackish water lagoons, estuaries, and even rarely in freshwater streams, lakes, and so on [3].

 Foraminifera are excellent bioindicators of environmental changes resulting from both natural processes and by human interference. Most of the recent studies carried out with foraminifera are focused on the application of these organisms as environmental bioindicators. Most baseline studies arrived from natural distribution patterns like those reported in the classical literature by [4–6]. After this first step, the detection of patterns associated with natural disturbances or pollution related to human activities can be carried on [7–10]. The environmental studies using foraminifera were started by the end of the 1950s. In a study performed in Santa Monica Bay, California, Zalesny [11] stated that environmental factors such as currents activity, nutrients, salinity, characteristics of bottom sediments, and especially temperature should control the distribution patterns of the living benthic species in that bay. Since then, the number of works aiming to study the response of benthic foraminifera to environmental changing, namely to pollution, increased significantly [12].

Foraminifera have been applied to study areas with different kind of pollutants and in different kind of environments including heavily polluted harbors, such as French coast, Rio de Janeiro, Montevideo, and Eastern Sicily. Armynot du Châtelet et al. [10], Debenay et al. [13], Vilela et al. [14], and Burone et al. [15] observed that foraminifera distribution in the harbor of Port Joinville, at the Atlantic French coast, was influenced by the significant increase of pollution by metals such as Cu, Pb, and Zn and sediment texture. In the most polluted areas, they observed the increasing abundance of pollution-tolerant species. Armynot du Châtelet et al. [10] observed that foraminifera density and diversity were negatively correlated with heavy metal and PAHs in four moderately polluted harbors of the French coast.

Romano et al. [16] studying the effect of heavy pollution mainly due to Hg, PAHs, and PCBs on the foraminiferal assemblages from the Augusta harbor (Eastern Sicily, Italy) observed that the clearest response of foraminifera to environmental degradation was the increased percentages of abnormal specimens exceeding the background, the increase of pollution-tolerant species, and the reduced size of the specimens.

 Furthermore, they have been used as suitable bioindicators owing to their immediate response to the environmental changes such as hydrodynamic [17, 18], salinity [19, 20], pH [21], Eh [22], heavy metals [13, 15, 18, 22, 23], hydrocarbon pollution [10, 23], and organic matter [8, 24].

The main goal of this chapter is to provide information about environmental factors that may influence the patterns of distribution of living benthic foraminifera in transitional and marine ecosystems. 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. Each area has different particularities that condition the type of living foraminifera associations that occur *Response of Benthic Foraminifera to Environmental Variability: Importance of Benthic… DOI: http://dx.doi.org/10.5772/intechopen.81658* 

in them, being the first two areas highly anthropized. This work also emphasizes the importance of these organisms as environmental bioindicators and their application in biomonitoring studies.
