**2. Materials and variables of database**

As a result of three oceanographic campaigns MARZEE-I (summer, 2010), MARZEE-II (winter, 2011), and MARZEE-III (winter, 2012), aboard the R/V "Justo Sierra," a total of 93 oceanographic stations were sampled (35, 25, and 33, respectively) (**Figure 1**). At each station, water samples were collected at preselected depths (5, 10, 20, 30, 50, 75, 100, 150, and 200 m) in sites where high fluorescence (chlorophyll-*a*) was detected. A rosette device equipped with a conductivity, temperature, and depth sensors (CTD), 10 L Niskin bottles were deployed at each site. Zooplankton was sampled with a double bongo net, and benthos and sediments were obtained with either a Smith McIntyre grab or a Reineck box corer at depths ≤200 and >200, at the points of intersection of the isobaths of 50, 100, 200, 500, and 1500 (>2000 m only for MARZEE-III).

#### **Figure 1.**

*Sampling sites location corresponding to the three oceanographic campaigns: MARZEE-I (M-I), MARZEE-II (M-II), and MARZEE-III (M-III).* 

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

We analyzed a total of 35 variables, distributed in the following manner:


#### **2.1 Data processing**

To test whether there were significant interannual differences among the three sampling periods, and spatial differences in the study area, the environmental and biotic parameters were assessed using an analysis of variance based on permutations PERMANOVA. No transformation was required on environmental data, while biotic data were log transformed. A principal component analysis (PCA) was performed on environmental data. A nonmetric multidimensional scaling (nMDS) was conducted to analyze biotic data. A nonparametric BIO-ENV analysis [13] was also conducted to determine the relationship among environmental variables and biotic components. All these analyses were performed using PRIMER v6 & PERMANOVA *add on* statistical package [14, 15].

#### **3. Study area**

The GoM is one of the most diverse and productive world marine ecosystems. In this semi-closed basin, one can distinguish temperate, subtropical, and tropical habitats [16]. Its surface area is of approximately 1,768,000 km with a maximum depth of 4000 m in the central region [17, 18]. Mexico's EEZ in the Gulf has an extension of nearly 900,000 km2 , which represents 55% of its total surface area [19]. The area of study considered for this project is situated within Mexico's EEZ, on the northwestern corner of GoM. It spans from the northern end of the State of Tamaulipas, near the mouth of the Rio Bravo (approximately 26°N latitude), to the north of the State of Veracruz (22°N latitude) (**Figure 2**).

The study area has a surface area of 10,000 km2 , and its hydrographic conditions are highly influenced by the input of epicontinental, tropical, and subtropical marine waters [20]. The coastal zone of this part of the Gulf receives the runoff of several rivers (Bravo, Tuxpan, Pánuco, Indios Morales, Soto La Marina, and San Fernando or Carbonera). There are also two coastal lagoons systems: (a) the Laguna Madre, bounded on the north by the Rio Bravo's delta and on the south by the mouth of the Rio Soto la Marina and (b) the Laguna de Tamiahua, bounded on the north by the Pánuco River and on the south by the River Tuxpan [21, 22].

Its continental shelf lacks topographic irregularities. Its contour displays a gradual depth gradient ranging from 36 to 360 m. However, the floor of the

#### **Figure 2.**

*Study area (dotted square). Exclusive economic zone (EEZ) (continuous line).* 

continental slope is rather abrupt, reaching depths between 540 and 1260 m. The continental shelf has a variable length—off the Rio Bravo reaches about 72–80 km, but toward the 23°N is close to 33–37 km—and further south just off Los Tuxtlas, Veracruz becomes narrower (between 6 and 16 km) [23].

The sea floor in the area of study is covered by muddy terrigenous sediments [24, 25] whose primary source is the sediment load discharged by the rivers mentioned above. The river runoff contributes to the formation of a strip of silty-sandy sediments running along the inner shelf. In the Tamaulipas coastal zone, sandy sediments prevail, while silts and clays are common far from the coast [17].
