**4. Case study: continental shelf of the Campos Basin (SE, Brazil)**

The continental shelf of Campos Basin is located on the southeast coast of Brazil between latitude 21° and 23°S, the southwest margin of the Atlantic Ocean, which comprises part of the area occupied by the Marine Sedimentary Campos Basin between the 25 and 150 m isobaths (**Figure 3**). The sedimentary contribution to this region is restricted to the rivers Itapemirim, Paraíba do Sul, Macaé, and São João, and most of the material derived from rivers and coastal erosion seems to be retained in coastal waters; what exceeds in this region is readily carried by oceanic currents. Detrital materials derived from the river discharge of the Paraíba do Sul River are distributed throughout the inner shelf by developing small muddy zones and large mud accumulations in an area adjacent to Búzios and Cabo Frio, where the currents have energy close to zero, 150 km south to the mouth of the river [64].

The South Atlantic Central Waters (SACW), a colder, nutrient-rich water mass, enters the continental shelf increasing local primary production and associated secondary productivity. Many studies have been carried out to investigate aspects related to the coastal upwelling of Cabo Frio, south of the Campos Basin [65].

#### **4.1 Methods applied in Continental Shelf of the Campos Basin**

Sampling methods, preparation of samples, control of quality, and methods of data analysis are described in detail in [66]. Living benthic foraminifera of the Campos Basin continental shelf were studied in 239 samples collected in nine transects (A–I) perpendicular to the coast line. The sampling was performed during the dry season of 2008 and the rainy season of 2009. The dry season, in this region, occurs in winter and corresponds to lowest precipitation and less frequent upwelling events. By contrast, the rainy season takes place in summer and corresponds to the period with higher precipitation and with more frequent upwelling events.

At each transect, five isobaths (25, 50, 75, 100, and 150 m) were sampled with a very large and modified (with an upper opening) Van Veen, which functions as a box corer. In each isobath, three independent samples successfully taken with a 10 cm × 10 cm × 2 cm, a "quadrat" yields samples with 200 cm3 . A fixative solution (4% formalin buffered with sodium borate) with Rose Bengal stain was immediately added to fix and evidence the protoplasm of living foraminifera. In the laboratory, 20 cm3 of sediment from each sample was separated for analysis of living foraminifera.

 The foraminiferal samples were washed trough a 63 μm sieve, dried in an oven (<60°C), and then picked under a stereomicroscope. Density values are equivalent to the total number of living individuals in 20 cm3 (volume) or 10 cm2 (area). Although the 63 μm mesh size was used as the size limit in the washing and screening of samples, many individuals smaller than 63 μm were found alive adhered to the grains; they were removed and incorporated into the slides for study. Careful quality control ensured similar patterns of screening and identification of living foraminifera, making the differences between pickers minimized. The species identification was based on [67, 68], and other specific references, as well as by the analysis of museum collections. The biomass was calculated by the volumetric method [33, 69].

*Response of Benthic Foraminifera to Environmental Variability: Importance of Benthic… DOI: http://dx.doi.org/10.5772/intechopen.81658* 

**Figure 3.** 

*Continental shelf of Campos Basin area. The transects A–I and their sampling points 1–5, according to the isobaths (25 m = 1; 50 m = 2; 75 m = 3; 100 m = 4; and 150 m = 5).* 

According to Pianka [70], k-strategist or conservative species have greater body size, longer life cycle, and population size largely constant in time, being close to the capacity of support of the environment; r-strategist species are known for their opportunistic behavior, small size, short life cycle, and very variable population size without adjustment balance in relation to available resources (mainly space and food). R-strategists can proliferate opportunistically and vary considerably its absolute abundance. According to these characteristics, Warwick [71] developed

 a method based on the abundance and biomass curves (ABC) for the detection of perturbation and to analyze the species response to environmental changes. The ABC curves are compared together with the W statistic calculation [71]. According to Magurran [36], in undisturbed environments, one or two species dominate the biomass and this has the effect of raising the biomass curve in relation to the abundance curve. On the contrary, in highly disturbed environments, a few species have very large number of individuals of small size, but since these species have small size, they do not dominate the biomass and so, the abundance curve is above the biomass curve. In intermediate conditions, the biomass and abundance curves cross each other several times. In this work, the ABC curves were generated for each group in both periods with all the species in which it was possible to calculate the biomass.

#### **4.2 Discussion of results of continental shelf of the Campos Basin**

The composition of the foraminifera assemblages allowed to detect areas under upwelling influence on the continental shelf. *Epistominella exigua*, *Adercotryma glomeratum*, *Bulimina marginata*, *Pappina compressa*, *Angulogerina angulosa* s.l., *Nonionella stella*, *Nonionella opima*, *Hopkinsina pacifica, Bolivina fragilis, Bolivinellina translucens, Fursenkoina pontoni*, and *Stainforthia complanata* can be considered as indicators of seasonality-enriched areas with phytodetrital material signaling the upwelling events in the study region of Campos Basin. The continental shelf presents many encrusting foraminifera, both large and small adults, as well as juveniles of larger species that are adhered to the sediment grains, indicating that it is a region with a predominance of high hydrodynamic energy near the bottom. Small individuals play an important role in the ecological characterization of oligotrophic areas where organic carbon is scarce and rapidly consumed, transported, or oxidized.

The increase of the continental discharge during rainy season brings more inorganic and organic nutrients to the coastal system, increasing the primary production. The high supply of continental nutrients in addition to the nutrients of the coastal upwelling of Cabo Frio and adjacent areas disturbs the natural equilibrium of the biological communities of this area.

 The results of the ABC curves by isobaths evidence that in the 25 m isobath of the dry season of 2008, there was some disturbance (W = 0.0332), but in the rainy season of 2009, the disturbance was much high (W = − 0.0071), so that the abundance curve overlaps with that of biomass (**Figure 4**). The ABC curves indicate the 25 m isobath as the most disturbed one within the continental shelf and the upwelling/organic enriched group as an area of moderated disturbance. During the rainy season, the 25 m isobath is disturbed by natural eutrophication phenomena and it may be significantly amplified by anthropogenic activities in the catchment area of Paraiba do Sul river and other anthropogenic disturbances, once this segment of the Brazilian coast is strongly influenced by agricultural, industrial, and urban activities as well as by fishery and many other coastal activities. In the southern region, the disturbed patterns seem to be strongly related to natural phenomena due to the presence of many species who indicate upwelling events, which are well known near the Cabo Frio area.

In his final remarks, Warwick [71] does not believe that this method can be applied to meiobenthic species, because according to him, there are no obvious size differences between k species and meiobenthic r-strategists. He mentioned Oncholaimidae nematodes and Tisbidae copepods as dominant species in polluted environments and reminds that they are often larger. However, among the foraminifers, there are species known as k-strategists that correspond to the characteristics mentioned by Pianka [70], and therefore, the application of the ABC curves to assess environmental disturbance could be successful. Although the foraminifera belong to both micro- and meiofauna, the results obtained with the ABC curves in

*Response of Benthic Foraminifera to Environmental Variability: Importance of Benthic… DOI: http://dx.doi.org/10.5772/intechopen.81658* 

**Figure 4.** 

*ABC curves of the continental shelf assemblages of foraminifers. Groups 1–4 of the cluster analysis from rainy period (2009).* 

this work evidence they can be used to trace environmental disturbance. In fact, it is expected that the ABC curves can be used to identify both natural and anthropogenic stressors. However, without complementary studies that allow to qualify and quantify the disturbance origin by applying the ABC curves, we will have only the sign of the environmental disorder. On the other hand, we still have little information on the response of some species to natural and anthropogenic stressors, but this integrated study will allow the construction of a more effective monitoring plan, which can provide subsidies for preserving the integrity of the environment.
