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

(the second form of environmental change). In turn, environmental variability has been conceptually used to frame all possible values that may exhibit the physical and chemical characteristics of a benthic habitat [37, 38].

Alacranes reef can be considered as the most studied coral complex of the Mexican seas due to its extraordinary characteristics, which place it within the most extensive and important coralline masses of the country [39]. The reef was described for more than a century [40] but, until the late 1950s, began to be studied more or less constantly, mainly by foreigners [41]. Alacranes has a vast history of shipwrecks and has been a point of attraction of visitors since colonial times [42].

The Yucatan Peninsula is a platform of sedimentary origin, constituted by a karstic Quaternary complex. It is the most recent emersion area in the country, and its growth is associated with sediment coastal transport processes and marine transgression and regression cycles. Therefore, Alacranes is of recent formation, originated by the biological action of the corals with the gradual deposit of calcareous material during the Pleistocene and Cretaceous, favored by the slow immersion of the Yucatan Peninsula [43]. Alacranes sits on a terrace of 51–64 m that is supposed to be carved during the descent eustatic sea level at the end of Wisconsin or at the beginning of the transgression Holocene (11,000 years ago), hence began the modern reef growth, arriving some 5000 years, both the reef and the sea level, to its current values [44]. The area is a platform reef of approximately 300 km<sup>2</sup> , which rises 50 m from the seabed. According to several investigations [45], it is known that the pattern of currents and the contribution of nutrients for the Alacranes reef come from the upwelling process that originates in the eastern end of the Yucatecan platform. The current of the Caribbean, as it passes through the Yucatán Strait and ascends on the platform, contributes high values of nutrients and therefore a high productivity [46]. Thanks to this contribution, there are commercial fisheries of lobster (Panulirus argus) and the groupers (Epinephelus sp.) [47]. The general state of conservation of the reef can be considered good [48].

Alacranes is a resting area for migratory birds that cross the Gulf of Mexico; particularly one of the islands of the Alacranes reef is considered one of the most important breeding areas in the world for the bird Sula dactylatra. Thus, it is considered an important area for the conservation of birds of the country [49], especially with a record of 110 species between accidental and permanent residents in the reef. In the reef environment, the management program has registered 34 species of corals, some of which are considered species under special protection [50] —in this assessment we report 28. According to the Alacranes bathymetric characterization, the slope of windward descends to an average of 55 m of depth; in the north part there is a marked inflection of the profile in comparison of the areas center and south, where the slope descends gently. The windward slope is the only site on the Alacranes reef where the stony corals of the genus Orbicella/Montastraea are not dominant. The dominance corresponds to Siderastrea radians. One of the characteristics of this area is the high density of soft corals or octocorals; the dominant genus is Pseudopterogorgia, although Gorgonia flabellum is also frequent and reaches large size. In addition to these, the genera Eunicia, Plexaura, and Plexaurella are represented in this part, like the one reported by other studies [42, 51]. The barrier reef is physiographically one of the most conspicuous elements of the system, and like any barrier reef, in turn is divided into outer barrier, west in the case of Alacranes, reef crest, and inner barrier [52]. The outside is the one that is exposed to the prevailing winds and the persistent swell train. Along the barrier at different points, it reaches the surface. The notorious dominance of the Palythoa caribbeaerum colonial anemone extends to the areas of the crest and the inner barrier. In the shallow part, between three and four meters of depth, the Hydrozoa Millepora alcicornis is frequent, like Gorgonia flabellum. In this area, the hard corals

4. Discussion

Figure 6.

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4.1 Biodiversity

The marine benthic communities have been evaluated from different points of view, which respond to their distribution, interests, or incidental events. The most common assessments are those focused on establishing the community structure and distribution patterns of temperate and boreal zones [28, 29], while in the tropical coastal zone are the evaluations focused on determining the response of these communities to changes caused by seasonal fluctuations and/or physicochemical or structural modifications of the environment, by natural or anthropogenic sources [30–32]. Precisely, an indicator related to environmental services is biodiversity. It is essential to know the ecological characteristics of reefs and coralline communities, because it allows to identify the stability of these ecosystems as well as the manifestations that these present in the face of natural and anthropogenic disturbances. The most obvious indication of the effect of natural and anthropogenic disturbances on coral systems is the death of corals. However, if the damage is not massive, sometimes there is a change of species, in which other types of coral species or various organisms in the bottom, such as carbonated or fleshy algae, arrive and occupy the position of the species that originally resided in the site, causing the so-called phase change [33, 34]. Consequently, the functions of the system are affected, since the corals that arrive are not always so efficient to produce carbonate, to generate sediments or sands, and above all, to give food or refuge to other species, so even if there is live coral, the environmental service is not the same. Meanwhile, environmental variability is one of the two forms of environmental change, with alterations in the intensity or frequency of stochastic events [35, 36].

Spatial ordination of the species found in the reef lagoons. (A) Alacranes reef, (B) Chinchorro Bank.

Lagoon Environments Around the World - A Scientific Perspective

Its raise is associated with the increment in disturbances and variability of

resources, imposing challenges that have a greater influence on biological communities, than those generated by changes in the average environmental condition

are represented by Porites asteroids, Pseudodiploria strigosa, Acropora palmata, and A. cervicornis, mainly. In the southern part of the barrier, Acropora prolifera, a rare species in the Caribbean reefs, is located. The reef crest reaches up to 400 m wide and marks the maximum growth of the reef and is only interrupted by two channels of flow and reflux tidal in the area known as the flooded. The boundary between the crest and the inner barrier is not clearly defined, but it can be said that it starts in the area where the swell train begins to disappear. In the inner barrier, in the closest part to the crest, Acropora palmata, A. cervicornis, Porites porites, P. astreoides, and Millepora alcicornis are the corals competing with Palythoa. To the west the inner barrier comprises the meadows of seagrass and the canals near the barrier. Of these components, the seagrass meadows play an important role in the system [53]. They are presented in shallows of sandy bottoms covered by meadows of Thalassia testudinum, Cymodocea manatorum, and Diplanthera wrightii whose roots and rhizomes form a dense plot that functions as a sediment trap and stabilizes the substrate. Associated with the meadows are presented corals Manicina areolata, Oculina diffusa, and Porites porites. The reef plateau is the most complex area of reef lagoon and includes shallow seagrass meadows, pinnacular reefs, and microatolls, as well as an intricate network of canals, the result of these morphological structures that rise abruptly from 12 to 15 m deep, until almost reaching the surface. Orbicella annularis is dominant and accompanies M. cavernosa, Pseudodiploria strigosa, Colpophylia natans, Porites porites, P. astreoides, and Stephanocoenia intersepta.

species of birds are registered. Several of them registered in NOM-059-ECOL-1994 as subject to special protection, for example, the blue-winged teal (Anas discors) and the roadside hawk (Buteo magnirostris). The brown heron (Ardea herodias) is considered rare. For example, the blue-winged teal (Anas discors) and the road hawk (Buteo magnirostris), the brown heron (Ardea herodias) is considered rare, the stork (Mycteria americana) and the rabies or rabihorcado (Fregata magnificens) as it is known in the locality where, according to fishermen's reports, this bird reached great abundance they have the category of threatened. Within the reptiles, the American crocodile (Crocodylus acutus) is listed as endangered, although apparently

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

The known composition of the coral taxa is represented by hexacorals, octocorals, and hidrozoarios with 95 species reported [14]; in this assessment we report 31. Among the Scleractinian Orbicella annularis, M. cavernosa, Porites astreoides, Agaricia tenuifolia, A. agaricites, Acropora palmata, and A. cervicornis dominate, while of the gorgonian the dominant ones correspond to Eunicea mammosa, Gorgonia flabellum, P. americana, Briareum asbestinum, and Plexaura

flexuosa. The hidrozoarios are represented by Millepora complanata and

M. alcicornis like the report by other investigation [57]. The macroinvertebrates are conspicuous elements of the coral reef; they are even organisms of great scientific, tourist, and commercial interest, but little is known of those that are presented in the reserve. The available records, which are not exhaustive, correspond to 35 species of sponges, 78 gastropods, 26 bivalves, and 6 crustaceans [14]. For Chinchorro Bank, faunal and floristic inventories with which it is counted in the reserve are partial. It is not known the composition of zooplankton, phytoplankton, microzoobenthos, and microphytobenthos, among others, as well as taxonomic groups of which there are no records such as the case of echinoderms, jellyfish, anemones, crustacean by marine fauna, and arachnids, insects, and mammals for

With the high values of diversity in Alacranes reef, one would think that it is the

There are distinct morphological variations between leeward and windward sectors. A shallow and extensive reef flat is a common feature in most of leeward part of these reefs. Coralline algae are quite abundant in these flats, and rubble of coral skeletons in ample dead beds of hard corals is evident. With both data sets, the classification

most diverse and most conserved reef; however, the high coverage values in Chinchorro Bank belie that assumption. It is very important to mention that the coverage composition of benthic organisms is a variable that determines total biodiversity or specific group biodiversity, such as benthic organisms, invertebrates, or reef fish [58]. Both lagoons have hard and soft corals in different proportions, but abundance has a high variation in soft corals. This may be related to the high colonization capacity of soft corals which adhere to different types of substrate. The south part of Chinchorro Bank recorded the highest diversity of benthic groups, but Alacranes reef was in the north. Density and percentage of live coral coverage, particularly reef building corals in these areas, are slightly over the average recorded in coral reefs from the Mesoamerican Reef [59]. It is possible that these corals enhance considerably the growth of new colonies, which will make possible the persistence of reefs and the habitat they provide to other species. In the north of Chinchorro and the south of Alacranes, it is highly probable that sedimentation condition will affect and reduce the live coral coverage, since this condition persists for a period; about 7% of coral coverage in this area could be lost because it is well known that sediments damage coral polyp tissues by abrasion

in the bank, this species is abundant.

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

terrestrial fauna is not known.

and asphyxia.

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4.2 Site affinity

For its biological characteristics, the reserve of Chinchorro Bank is a natural laboratory, practically unaltered, partially known, and even unknown in many of its aspects, to develop innovative scientific research and quality focused both on the execution of floristic and faunal inventories that enrich and update existing ones, as well as to understand in detail the biological and ecological relationships and processes that develop there. Due to Chinchorro Bank's geographical isolation and its position in the hurricanes and tropical storms route, it is important to establish mechanisms to facilitate the knowledge of the prevailing meteorological conditions to increase the safety degree of visitors and fishermen. Unlike other Mexican reefs, Banco Chinchorro does not develop on a continental or insular shelf but on a deep underwater crest (more than 400 m deep about 30 km out coast), which rises like a pinnacle [54, 55]. Little is known of its origin; we have the theory that in the past, the reef complex was formed by separation and derives from a portion of the continental coastal area, possibly in the Cenozoic era in the late Tertiary period or early Quaternary (in the Pliocene-Pleistocene age). The separate fraction of the coastline contained a fringe or marginal reef and coastal lagoons with typical fauna. The detachment of part of the coast was possibly of a single plate, which took with it a large reservoir of ancient water which possessed characteristics of a continental mass of water, which has maintained its characteristics with the contribution of the rains. Due to its geographical position in the Western Caribbean and their influence in the Gulf Stream, it is an intermediate point compared to other reef systems located downstream in the Lesser Antilles, which allows it to receive larvae of these distant places and in turn export larvae of different organisms generated in Chinchorro to systems located upstream, like Cozumel, Alacranes reef, and the keys of Florida, among others [56].

The Chinchorro Bank is of great ecological importance due to the high diversity of organisms that are there. By remaining practically isolated for a long time, some areas are unchanged, allowing for a comparable study with other similar ecosystems. Banco Chinchorro is nominated by UNESCO as a World Heritage Site and as a Ramsar site for the protection of migratory birds and wetlands. It was recently designated as the Man and Biosphere (MAB) site [50]. The fauna inventoried by the management program [14] is dominated by local and migratory birds that use the keys permanently or during the time of migration to rest and feed. Ninety-six
