2.1.2 Chinchorro Bank

Their geographical location is 18°47<sup>0</sup> –18°23<sup>0</sup> N, 87°14<sup>0</sup> –87°27<sup>0</sup> W, and 24 km off coast of southeastern Quintana Roo, México, between Xcalak and the Ubero and about 100 km north from Turneffe Island in Belize. This reef is part of the Great Atlantic Reef Belt (second world barrier). Chinchorro has an area of 53.379 ha. It is a kidney-shaped prominence and is separated from the mainland by a 1000-m-deep channel [14]. The current is very strong (often over two knots). There are four cays: Cayo Norte (two mangrove-covered islands with an area of 2645.2 ha, destined for the protection of the reef); Cayo Centro, the largest, is a mangrove island with few little inner lagoons with an area of 1263.76 ha, comprises the entire cay and adjacent waters; and Cayo Sur (or Lobos), the smallest (300 m long), is a sandy bank, the only close to the windward margin of the atoll, with 678.53 ha, destined mainly to the protection of the elkhorn corals; all the cays represent 5.82% of the total area of the reserve [15]. The reef has an area of 1443.6 km<sup>2</sup> ; lagoon reef maximum depth is 21 m in the south, 3–4 m near Cayo Centro, and 2 m in the north. A Thalassia testudinum seagrass bed and garden eels, sometimes at high densities, are found in the reef lagoon. The reef lagoon extends for several tens of kilometers west of the bank and is extremely productive [13]. Under its waters the first thing we identify are sponges, fans and sea whips, and isolated colonies of stony corals and a huge diversity of multicolored reef fishes or small fish that are by hundreds hidden under the rocky cavities of where they come out and create a lively silver spot. However, the diversity and abundance of someone groups (e.g., the management program [14] reports 95 species of Cnidaria, 35 sponges, 96 birds, 11 reptilian, 135 algae, and 104 species of mollusk), the main fauna inhabiting this tropical ecosystem is practically unknown (cichlid, crocodiles, etc.). Some of this species have never been described; maybe others are relict species, and others are a complex of subspecies interacting biologically and ecologically between them. Aggregation of the queen conch (Strombus gigas) and spiny lobsters (Panulirus argus) and abundance of large fish are frequent; turtles probably occur too. Cayo Centro is an important breeding site for frigate birds (Fregata magnificens) and olivaceous cormorant (Phalacrocorax olivaceous). The area is fished for queen conch (Strombus gigas) and lobster (Panulirus argus) by fishermen from Xcalac and Chetumal; there are three fishery cooperatives with 60–70 elements each one; the current disturbance for fishing is probably small, because of a forbidden period for the Fishery Secretary decree [14]. There are two lighthouses and many wrecks. The reef is gradually becoming popular with scuba divers who make 4- to 5-day trips from Cancún, Cozumel, and Quintana Roo coasts. The area has frequent climatological disturbance (winds of the north and south and hurricanes) (Figure 1).

2.2 Methods

2.2.1 Sampling

1904 cm2

2.2.2 Data analysis

whose expression is

tor value i in the entity j:

213

The sampling was developed in two periods with a 2-year interval (2015–2017), for each reef. Each reef complex was divided into three main areas: north, central, and south. We established 35 sites for Alacranes reef and 36 stations for Chinchorro Bank, positioned with GPS (Garmín inReach Explorer+). The stations were distributed in the following ways: 16 sites in the southern zone of both reefs; 10 and 17 for

Alacranes and Chinchorro, respectively, in the central zone and 9 and 3 for

Lagoons Reefs of Alacranes Reef and Chinchorro Bank: Ocean Reef of Mexican Atlantic

consisted of 20 photographs that covered each one an area of (56 � 34 cm)

and the total number of photographs analyzed was 2802 (533.5 m<sup>2</sup>

risks of navigating the low sand and shallow depths.

DOI: http://dx.doi.org/10.5772/intechopen.88662

the importance value [24]; its formula is as follows:

where A—relative abundance, F—relative frequency

Alacranes and Chinchorro, respectively, in the north zone. The differences between the south and central areas with the northern area were mainly the difficulty and

Two 20-m-long randomized photographic transects [16] for each site, transect

were disposed by out of focus. To obtain the coverage of the species, each photograph was superimposed on a grid with 10 cm2 divisions for the coverage calculation. In parallel with the photographic transects, a selective collection of species was carried out for their precise identification in the laboratory and to serve as a basis for photointerpretations. The bibliography used depended on the phylum [18–23].

The coralline coverage data matrix for each reef was used in different numerical analyses. A single matrix was formed by reef, where the most common community parameters were determined in the sites, with the purpose of obtaining a robust quantitative descriptive synthesis: the dominance was determined by the index of

and biological diversity was quantified with the Shannon-Wiener index [25]

i¼1

The sites were classified with the Bray-Curtis similarity index, using the flexible

<sup>i</sup>¼<sup>1</sup> Xi,j � Xi,k �

<sup>i</sup>¼<sup>1</sup> Xi,j � Xi,k

where j, k—objects j and k that are evaluated, i—i-ésimo descriptor, Z—number of descriptors, dj,k—affinity value determined as geometric distance, Xi, J—descrip-

A main coordinate analysis was used for spatial distribution of the species [27].

� �

�

<sup>H</sup><sup>0</sup> ¼ �<sup>X</sup> S

union criterion with a β = 0.25 [26]; the coefficient has the following equation:

P<sup>Z</sup>

P<sup>Z</sup>

where pi is the proportion of the abundance of the species i.

di,k ¼

IVI ¼ A% þ F% (1)

pi log pi (2)

� � (3)

, were used [17]. The photographs were taken with a Nikonos V camera,

); 38 photographs

Figure 1. Sampling sites in both oceanic reefs.

Lagoons Reefs of Alacranes Reef and Chinchorro Bank: Ocean Reef of Mexican Atlantic DOI: http://dx.doi.org/10.5772/intechopen.88662
