Coral reefs, the spectacular marine ecosystems near the coasts in warm tropical seas where they soak up sunlight for their growth

Famous for their beauty among natural treasure hunters, coral reefs are also the most complex and diverse ecosystems in the underwater world. They provide humans with valuable resources, but with the intensification of fishing and tourist exploitation, overharvesting, and local or planetary environmental changes, reef harmony is being disturbed.

Undoubtedly the largest reef system in the world is the famous Australian Great Barrier Reef. In Mexico there are also large reef formations, the largest extends in the Caribbean from the northern end of the Yucatan Peninsula to Belize; others of more importance are found in the Gulf of Mexico off Veracruz and in the continental shelf of Campeche. Some authors also mention Cape Pulmo, between La Paz and Cabo San Lucas in the south of the Baja California peninsula.

According to researchers Horta-Puga and Carricart Ganivet, the diversity of reef-forming corals in Mexico's seas amount to 63 species, of which 46 live in the Atlantic and 17 in the Pacific. However, corals are not the only richness of these ecosystems; the associated flora and fauna are catalogued in thousands of different organisms, including isopods, amphipods, annelids, polychaetes, anemones, sponges, mollusks, crustaceans, and fish; and a great diversity of algae that participate in the primary production of the ecosystem, or directly in the reef construction if they are calcareous species, which provide calcium carbonate.

It is known that reef flora and fauna can be suppliers of useful substances in pharmacology. It has been verified that some species of marine algae have antibiotic, anticoagulant, and antiagglutinant properties. The applied phycology group of the Department of Hydrobiology of the UAM-Iztapalapa carries out interesting research in this sense and has proven the antibiotic action of some species of algae on Escherichia coli and Micrococcus lisodeikticus bacteria. Mexican algae are still in the research process, and it seems that they are not yet used in the medical industry.

In the reef fauna, we also find species with pharmacological properties. Years ago it was discovered that the soft coral, Plexaura homomala, has a high content of prostaglandins, substances with effects on the smooth-fiber muscles of humans that can be used, for example, to facilitate labor. These corals are a natural source of prostaglandins, and therefore a very important economic resource given how expensive the synthesis of the compound still is.

In Mexico, the feasibility of using this resource has been evaluated, and the technology has also been developed to make large-scale semi-cultures of this species, but these projects have not yet been put into practice. And marine sponges, used since ancient times for different purposes, are also valued today for their pharmacological potential, and research on them continues. The pharmacological values of Mexico's reef flora and fauna are still a universe to be explored.

Until the middle of the last century, the reefs were mainly used for subsistence fishing by the inhabitants of nearby coasts, but in recent years this fishing has become more intensive and for commercial purposes, aided in many cases by the advances in marine technology of the last few decades.

Formed by corals, algae, sponges and many other organisms, reefs rise above the seafloor thanks to the calcareous structure of reef-building corals, called hermatypes. Corals are colonial organisms, and their polyps, of various sizes, live side by side in close communication with each other, which allows them to have a common skeleton and to adopt shapes adapted to the conditions of waves, sea currents, light, etc. This colonial organization also gives them the advantage of being able to regenerate their damaged tissues with relative ease or to react as a single organism to food and other substances.

They live in warm waters and can grow and form reefs where the concentration of nutrients is low, and also where there is good lighting, so they are found mainly up to 30 or 40 meters. Not all corals form reefs, some grow more slowly on shallow rocky bottoms, but without covering continuous and extensive areas. Instead, reef-building corals are associated with symbiotic microalgae, commonly known as zooxanthellae, which live within their tissues. Because of the exchange of nutrients between the zooxanthellae and the animal, and the catalytic action of the zooxanthellae in the process of precipitation of calcium carbonate in the coral skeleton, hermatypic corals grow relatively faster than non-symbiotic corals, about 1 cm per year. The structures they form resist waves and can extend for kilometers along the coast, sometimes forming islands.

There are four types of coral reefs in the world: coastal, barrier, platform, and atoll. All of them are found in Mexico.

In Veracruz, the Veracruz Reef System is divided into two areas by the mouth of the Jamapa River: one in front of the port of Veracruz, and the other in front of the town of Antón Lizardo. Three rivers discharge their waters in the region, and each one of them carries a large number of suspended solids to the sea during the rainy season. Throughout the year, the reefs are also at risk from other waste dumped into the sea and carried by ocean currents, such as waste from hotels and the port, from different industries, sugar mills, oil production, as well as sewage from the city.

In Veracruz, it has been said that corals are not affected by the pollution because their growth continues to be normal. However, studies have shown other results. It is true that they grow the same, but their skeleton does not have the same density, which shows that there are problems in the deposition of calcium carbonate. This situation makes them more fragile. It is known that heavy metals carried by polluted waters or dumped directly into the sea can accumulate in the tissue and skeleton of corals and cause alterations.

The Veracruz Reef System was declared a Natural Protected Area in 1992, which despite the efforts that have been made, has not yet been accompanied by an adequate management and control plan for the area. Not all Mexican reef formations are subject to the same pressures, and therefore are not in the same degree of conservation or danger. The Caribbean reefs, for example, have been subject to limited exploitation, and although in recent decades fishing for certain species has been intense, it is considered that they still maintain their values in good condition.

As in Veracruz, multiple investigations have also been carried out in the Caribbean region. The two main resources being exploited in the reefs of southern Quintana Roo are lobster and pink snail, followed by bony (scale) fish, black coral, and others. Among the mollusks of the Mexican Caribbean reefs are several species currently used by man, such as the sacabocado, white snail, pink snail, black snail, which are of food and ornamental interest, and others that are only of ornamental interest such as the trompillo, chivita, chacpel, triton, etc.

In the reefs of Banco Chinchorro, the pink snail has been exploited mainly, in addition to the spiny lobster, as well as snappers, barracudas, jacks, and groupers. It is feared that here, too, intense fishing exploitation is beginning to threaten species of economic interest. Also in the Caribbean, in the reefs of Sian Ka'an, marine biodiversity has been reported that includes more than 20 species of sponges, more than 80 species of corals, and almost 200 species of fish, while the main fishery in the region is lobster, in many cases juveniles caught by the method of "casitas" (small houses) placed on the bottom. Sian Ka'an was declared a World Heritage Site in 1987.

As can be seen, the resources of reefs are multiple, but there are also many impacts and threats to which they are subjected. The great majority of reef structures in Mexico are in good condition. There are, however, specific cases of destruction in places where works such as canals, docks, breakwaters, etc. have been or are being carried out. The degree of impact that reefs have suffered and are suffering from human activities or natural catastrophes depends on their intensity and frequency. Practically all national reefs, like those of the rest of the world, have a continuous but variable impact from fishing activities, which in some cases is severe.

The indirect impacts of industrial, urban, agricultural, and forestry activities are also highly variable. They are presumed to be of great importance, but unfortunately, they are very complex to assess, because reefs tend to develop in highly dynamic waters. Some of the most relevant factors that influence indirect impacts are proximity to the coast, fluvial and pluvial inputs, and coastal and oceanic marine current systems, depending on the nature, intensity, and frequency of such impacts. Other impacts are recreational, developmental, and transformational activities related to the tourism industry.

Coral reefs, like tropical rainforests, are among the most productive ecosystems on the planet.

By Emma Romeu, Source: CONABIO, Biodiversitas (3)