**9.1 Genotoxicity and bioassays**

 The short-term bioassays conducted to assess the toxicity of surface sediments, employing biomarkers, *Tetraselmis suecica* (microalgae), *Artemia franciscana* (crustacean), and *Brachionus plicatilis* (rotifers), revealed different responses (**Table 1**). The evaluation of toxicity using as indicator *T. suecica* showed a significant relationship with the presence of PAH, AH, and Fe. In contrast, *A. franciscana* showed distinct mortality pattern when exposed experimentally to the sediments from certain sites of the study area. For instance, significant toxicity was well-defined at sites on the continental shelf and slope just off the Rio Bravo, Soto La Marina, and Carrizales Rivers. The geochemical variables with the highest correlation with mortality of this species were the Zr and Rb during M-I, Ni in M-II, and PAH in M-III. The rotifer *B. plicatilis* served for the identification of areas of low and high toxicity through time. Not a defined pattern for both conditions was recognized, but there was clearly an increase in the temporary toxicity; during M-I, the high toxicity was reduced to two sites: one in front of Laguna Madre and another next to the Soto La Marina River. In the subsequent winter periods (2011–2012), the high toxicity initially corresponded to sites located between 500 and 1500 m of depth and then expanded onto the continental shelf. The mortality of this rotifer showed a significant correlation with the presence of Zr, Nb, Rb and SiO2 in M-I, and PAH in both winter seasons.

 Regarding the genotoxic effects of sediments analyzed, we were able to establish a significant correlation in the 3-year monitoring study, between the damage in the DNA structure and the concentration of PAH. Most of the stations with the highest levels of genotoxicity also presented the highest PAH concentrations. Statistically, we demonstrated an interannual decline of genotoxicity values. However, the percentage of sites containing sediments with substances fostering genotoxicity increased in M-III. The toxicity and genotoxicity are strongly linked to factors such as wastewater and industrial discharge and agrochemicals inputs in the coastal zone. However, in


#### **Table 1.**

*Stations percentage by level of toxicity for each species, in the three MARZEE campaigns.* 


**Table 2.**  *Average concentrations (μg/g) and standard deviation of the metals detected in muscle and liver tissues of fish in the three MARZEE campaigns.* 

#### *Monitoring of Marine Pollution*

*The Hazards of Monitoring Ecosystem Ocean Health in the Gulf of Mexico: A Mexican Perspective DOI: http://dx.doi.org/10.5772/intechopen.81685* 

deep zones (>500 m), the levels herein detected in both variables reflect the influence of different sources other than the regionals. Both the toxicity and genotoxicity of sediment can be attributed to the synergy between the PAH and other contaminants detected in sediments, including trace metals such as V, Ni, Cr, Co, Fe, and Al.

#### **9.2 Trace metals in demersal fauna**

 The toxicity analysis of trace metals (vanadium, nickel, cadmium, and lead) in 250 tissues samples of demersal fauna (fish, crustaceans, and mollusks) showed that the vanadium was the metal less concentrated in the muscle tissue of fish. Concentrations of this metal showed variability over time, decreasing sequentially toward the M-III in muscle, and increasing in liver tissue, reflecting a null or low recent exposure to this metal. In contrasts, the nickel presented the highest concentration average values in liver tissue, in comparison with the muscle, throughout the three oceanographic campaigns. The high concentrations of Ni in some demersal fish may reflect its incorporation by benthic pray or sediment ingestion. The cadmium reached significant concentrations in the liver tissue of demersal fishes but lower concentrations in the muscle. Hence, according to the standard guidelines for human health, such concentrations did not pose any risk for direct consumption. The concentrations of lead recorded in muscle and liver tissues of fish did not exceed critical values of intake and therefore did not represent a risk for its consumption either (**Table 2**).

The vanadium appeared with a higher concentration in the muscle of macroinvertebrates (mollusks and crustaceans) (**Tables 3** and **4**). Nickel was also a persistent metal in macroinvertebrates, with highest concentrations at the end of the study (M-III). This metal showed different concentrations between crustaceans and mollusks, presumably due to their different capacities for bioaccumulation


#### **Table 3.**

*Average concentrations (μg/g) and standard deviation of the trace metals detected in crustaceans during the three MARZEE campaigns.* 


#### **Table 4.**

*Average concentrations (μg/g) and standard deviation of the trace metals detected in mollusks during the three MARZEE campaigns.* 

and regulatory mechanisms of excretion. The cadmium represented the metal with lower concentrations in the tissue of macroinvertebrates. The recorded values of Cd did not exceed those established by the safety guidelines for human health. Only in the case of a crustacean predator (*Squilla* sp.), an average concentration of 0.592 ± 0.394 μg g<sup>−</sup>1 was registered during M-I, which exceeded the safety limits. In the case of lead, its concentration in the muscle of crustaceans and mollusks fit for human consumption remained below 1 μg/g, except for three species of crustaceans recorded in M-III. This value is considered as critical threshold for human health. In summary, the analysis conducted of metals in tissues of demersal fish, crustaceans, and mollusks did not indicate life-threatening concentrations for the individuals nor to the human health in most of the cases. However, one cannot overrule the possible existence of bioaccumulation and biomagnification phenomena that eventually might affect the demersal trophic web.

#### **10. Plankton**

#### **10.1 Phytoplankton**

According to the taxonomic composition and abundance of phytoplankton algae, it was found that the values obtained coincided with those previously reported for this region (**Table 5**) [46]. These results suggest oligotrophic conditions, as confirmed by the low nutrients (nitrates, 29.3–37.9 μM; silicate, 3.5–8.2 μM; phosphates, 1.9–3.4 μM) and chlorophyll-*a* concentrations (>0.25 ± 0.14 μg/L). The abundance of dinoflagellates and phytoflagellates, and the low diatom abundance in most of the analyzed samples, adds support to the oligotrophic condition of this region in the summer and winter seasons. The Chlorophyceae algae were responsible for the blooms recorded in coastal waters (652, 179 cells/L). No significant differences were found in abundance among the three campaigns.

#### **10.2 Zooplankton**

The zooplankton biomass values registered in the three oceanographic campaigns fluctuated between 1.20 and 19.38 g/100 m3 . These values were considered impoverished when compared to those registered in the SW Gulf, which exceed 40 and 100 g/100 m3 [47]. In the two winter seasons (2011 and 2012), the


*The Hazards of Monitoring Ecosystem Ocean Health in the Gulf of Mexico: A Mexican Perspective DOI: http://dx.doi.org/10.5772/intechopen.81685* 

#### **Table 5.**

*Phytoplankton abundance by groups (cells/L) recorded in the water samples obtained during the three MARZEE campaigns.* 

**Figure 5.**  *Zooplankton biomass (g/100 m3 ) distribution for the three campaigns M-I, M-II, and M-III.* 

zooplankton revealed a significant decrease in biomass in both neritic and oceanic waters. In 2011 the biomass varied between 2.9 and 19 g/100 m3 , and in 2012 it reached 1.2–15.8 g/100 m3 . The neritic waters showed high variability in biomass (2–7 g/100 m3 ), due to the influence of river discharges and the intrusion of ocean water near the coast. The zooplankton biomass was less than 8 g/100 m3 in M-I and in M-II, while in M-III, it was less than 3 g/100 m3 (**Figure 5**).

### **11. Infaunal benthic community**

The taxonomic composition, density, and biomass of the infaunal benthic biota constituted a valuable analytical asset in the effort of identifying the magnitude of natural changes opposed to those potentially caused by anthropogenic disturbances.

In M-I, an impoverished infaunal benthic community was recorded, with only five taxa recorded and an average density value of 4.64 ± 7.03 individuals/10 cm2 . In M-II, the diversity of taxa continued being poor, recording seven taxa (**Table 6**), but


**Table 6.** 

*Densities per taxon (ind/10 cm<sup>2</sup> ) recorded in the three MARZEE campaigns.* 

 the density values showed a small increase: 7.33 ± 8.48 individuals/10 cm2 . In M-III, the highest diversity and density values were recorded: eight taxa and 13.67 ± 22.71 individuals/10 cm2 , respectively [48]. The pattern of density in both seasons maintained the same negative exponential correlation with respect to the depth. Interestingly, there were significant density values at sites on the shelf rich in organic materials exported from the coastal zone; similar density values were also recorded in deeper sites in which presumably deposition and sediment transport occur. The nonmetric multidimensional scaling (nMDS) analysis applied to the estimated infaunal density in the three campaigns confirmed that M-I was different to the winter of 2011 and 2012; while the latter were similar to each other.

Significant temporal differences among the three campaigns were detected through the PERMANOVA analysis. Pairwise test indicated that such differences were interannual rather than seasonal. Spatially, only significant bathymetrical differences were detected; no latitudinal significant differences were noted. The pairwise test showed differences among the benthic infauna of the inner continental shelf (50 m) and deeper strata [48].

Based on the interpretation of abundance/biomass comparison curves (ABC) of the macroinfaunal community, it was possible to assess its interannual ecological equilibrium expressed as a stress factor. A clear trend of position of the curves since 2010–2012 revealed an interannual intensification of the stress degree. We inferred that the proliferation of nematodes in the latter season is symptomatic of such stress condition (**Figure 6**) [48].

 In M-III, the infaunal community experienced a substantial change in its composition. The nematode worms reached a high dominance (44%). Even though no statistically significant latitudinal or bathymetric patterns of dispersion were distinguished, high density values were concentrated near the 50 m isobaths. The notorious abundance of the genus *Sabateria* in our samples deserves special attention. This genus represents an invaluable biomarker due to its tolerance to high concentrations of organic matter, degraded, heavy metals, and hydrocarbons [49]. *Sabateria* is known as an opportunistic nematode which, together with other infaunal dwellers like *Terschellingia*, *Paracomesoma*, and *Daptonema*, are normally found in highly contaminated sediments by organic matter characterized by a low redox potential [49, 50].

Metazoan organisms that make up the infaunal community are particularly sensitive to alterations in the geochemical properties of the sediments. A multivariate analysis BIO-ENV was performed to relate the set of environmental sedimentary variables to the macrofauna community structure. The correlation values obtained

*The Hazards of Monitoring Ecosystem Ocean Health in the Gulf of Mexico: A Mexican Perspective DOI: http://dx.doi.org/10.5772/intechopen.81685* 

**Figure 6.**  *Abundance/biomass comparison curves (ABC) for the three MARZEE campaigns.* 

**Figure 7.**  *Spatial distribution of macrofauna density values (individuals/10 cm<sup>2</sup> ) in the three MARZEE campaigns.* 

 from the BIO-ENV were rather low in the three campaigns (<0.4). However, it was possible to identify the geochemical variables that seem to govern the macroinfauna distribution in each season. In M-I the variables were percentage of sand, the concentration of Al and V, and the δ 15N values. In M-II, important variables were Al PAH, Ni, and AH. In M-III, the variables were Al, V, and AH. However, the correlation values were not significant. Nonetheless, in the summer season (2010), the influence of natural variables is more obvious than in the following periods (2011 and 2012), in which variables linked to crude oil become more relevant (**Figure 7**).

The changes observed in the community variables such as taxonomic composition and density of the macroinfaunal components were attributed to the gradual increase recorded in the study area of MO, HA, PAH, and metals such as Ni, V, and Co.
