Introduction
If one views the Earth from space or glances at a geographical map, one can notice the predominance of blue and light-blue colors. These are the seas and oceans; they occupy a considerable part of the Earth’s surface. The oceans are where life originated many millions of years ago. During that time, primitive forms evolved into a variety of modern organisms that inhabited the aquatic environment and transitioned to life on land. The abundance of marine life forms substantially exceeds the number of life forms on land (Woodhead et al., 2019). Thus, it is essential to characterize a coral reef and describe flora and fauna living in coral ecosystems.
The Coral Reefs
A coral reef is special, spectacular, and full of a mysterious world. It is inhabited by reef-building organisms and various creatures that have settled on them. Coral reefs are formed only in the tropical zone of the ocean; the temperature limits their life – are from +18 to +29oS, and at the slightest deviation from the boundaries of the coral die. Lighting must be the highest, unstained water, transparent, depth of – 10-20 m and salinity of – 33-35% (Eddy et al., 2021, p. 1279). That is, desalination or pollution of water corals cannot sustain. When corals die, their skeletons become solid foundations to which new colonies expand. In this way, the natural process of coral reef growth is permanent.
Coral reefs are wall or rampart-like formations in the coastal zone of tropical seas, either just below the water’s surface or deep into the sea. These reefs are studded with many living creatures, mainly calcareous, soft, and horny corals, sponges, and many other animals, together with small and large algae (Eddy et al., 2021). Thus, each coral reef represents some biological and ecological unit found only in tropical seas, built by lime-releasing living creatures. At present, coral reefs are mostly confined to the warm zones of the Atlantic, Indian, and Pacific Oceans and do not extend beyond 22° south or north latitude (Servis et al., 2020, p. 178). The composition and appearance of corals and other reef inhabitants can reconstruct the composition and location of an ancient reef and the characteristics of water currents that once dominated.
It is important to note that among modern coral reefs, there are three types. The first one, the fringing, or shore reefs, stretches along the shore and is separated by an intermediate zone with a sandy bottom, usually referred to as a lagoon. This area of the sandy bottom can reach a width of several hundred meters; its depth rarely exceeds 30 m (Bellwood et al., 2019, p. 949). The reef itself is mostly no more than 50 m wide. Fringing reefs are located along the coast of East Africa and the islands of the Indo-Australian archipelago (Bellwood et al., 2019). The second type is barrier reefs formed from fringing reefs.
They are several kilometers away from the shore; the channel between the coast and the reef is much deeper, and the reef itself is more powerful than the shore reef. It can reach several kilometers in width and stretch for hundreds of miles. For instance, the Great Barrier Reef on the northern coast of Australia is 1200 kilometers long and 30-150 kilometers wide Bellwood et al., 2019, p. 949). The third kind is ring-shaped reefs, or atolls, which are more or less circular and rise from the ocean depths to the surface. Atolls are predominantly found in the central Indian Ocean and the central and west Pacific (Bellwood et al., 2019, p. 951). Thus, coral reefs are highly diverse and have a unique nature.
Plants in the Coral Ecosystems
In this system, one can find different kinds of marine plants, but the primary role is played by algae that live in symbiosis with polyps. In coral gardens, the lack of plants is immediately noticeable on land and in many other areas of the ocean. However, plants on a reef are quite inconspicuous does not mean that they are almost non-existent (Lesser, Slattery and Mobley, 2018). They are present in the reef biocoenosis and have just as prominent a role in it as in other ecosystems. The fact is that most of the available plant mass is not directly visible because it is actually inside the tissues of the most numerous subgroups of reef animals, madrepores corals, alcyonarians, and their relatives (Lesser, Slattery and Mobley, 2018). The other portion of it appears quite unusual, which baffled biologists for a long time until they resorted to the help of a microscope.
The smooth blocks of pink rock, which together can sometimes form massive rocky ramparts, appeared to be calcareous red algae. They, like madrepore corals, have a carbonate skeleton, which is then incorporated into the reef limestone and settled where the strongest surf occurs (Lesser, Slattery and Mobley, 2018). The bottom line is that reef plants fulfill an essential function in two ways. First, they serve as a source of energy, converting solar power into chemical energy, which is the basis of life on Earth. Second, since this is a coral reef built from limestone, plants are a significant contributor to the deposition of calcium carbonate.
Fauna in the Coral Ecosystems
It is essential to mention that the primary inhabitants of coral reefs are coral polyps. Coral polyps are a class of marine invertebrates of arrow-type, colonial, and solitary benthic organisms. Numerous coral polyp types have calcareous bones and are implicated in the development of reefs. This group contains many species whose entire structure is composed of protein and without a solid body structure. (McClanahan, 2019, p. 77). There are about 6 thousand species, along with aquarium fish and plants, and coral polyps are contained in aquariums (McClanahan, 2019, p. 77). At the same time, the skeletons of some species are used in jewelry.
Corals live in the sea; they are motionless and resemble vegetation branches, but they are not plants. Each branch of coral is a collection of small creatures, coral polyps; these groups are named colonies. Once a new polyp is formed, it adheres to the preceding one and begins to create a new coral shell; thus, the coral increases. “Growth” of a coral is about 1 cm per year under favorable conditions; large clusters of corals form coral reefs (Montano, 2020, p. 350). Coral polyps live in warm tropical seas, where water temperatures are at least 20 °C, and at depths of no more than 20 meters, with abundant plankton, which they consume (Montano, 2020, p. 352). Some coral polyp species live in symbiosis with autotrophic protozoa in their mesh globe.
Coral reefs are inhabited by many mollusk species, from chitons to giant bivalves and octopuses, and countless sponges, anemones, worms, crustaceans, and echinoderms. Reefs worldwide are famous for their diversity of fish and are valuable even for some species of whales, which breed only in “near-coral” waters. Six of the world’s seven species of sea turtles live there, and more than 240 species of sea birds nest on the coral islands (Pearman et al., 2018, p.17). They are home to bristle worms, animals with elongated, segmented bodies that have paired bristle tufts on each segment. In some species, these bristles develop into a spiny protective mechanism. Others have powerful jaws with which they can inflict painful bites Pearman et al., 2018). The peristyle tentacles assist the worms in moving around in the water tubular as required. Tubular polychaetes are almost impossible to swim and lead a sessile life.
The fish that inhabit a coral reef are strikingly brightly colored and varied in shape. The coloration makes the fish invisible against the background of the multicolored coral reef, hiding from predators and helping to stealthily approach their prey. It can warn of the fact that its owner has reliable means of protection. Fish, change their coloration, communicate with each other, expressing calm, anger, and fear (Montano, 2020). A gregarious fish coloration helps to quickly build a tight row and coordinated movement without disturbing the order in the right direction. In coral reefs, there are different types of fish, such as spinor ogi are medium-sized fish with body length ranging from 15 to 50 cm, the largest species, can reach 1 m (Montano, 2020, p. 352). At the same time, it narrows to the end. Hence the body spinorogi has a rounded-rhomboidal shape.
The pectoral fins are relatively small, and located high, and the tail fin is often simple rounded shape. These specific structural features make spinorogi easy to recognize among other fish. In all species, there is no spinor hag sex dimorphism, meaning that males and females appear to be the same. For movement, they use the pectoral fins, and use the caudal fin only for sprinting (Montano, 2020). The basis of feeding are corals, sea urchins, crabs, and mollusks. Spinorogi occupies separate areas, but there may be several females in the male’s territory.
The next fish to watch on coral reefs are angelfish. This is a family of tropical marine fish from the order Sharks. Their average size is 20-30 cm, but there are species up to 60 cm in length, and the minor family representatives have a distance of 12-15 cm (Brandl et al., 2019, p. 445). The body of these fish flattened at the sides, a large head and tail shortened, making the body appears rectangular. Angelfish permanently inhabit small coral reefs, the borders of which they defend. These fish have a distinctive diurnal activity; during the day, they search for food, and at night they sleep in sheltered reef splits. In this way, the fish interact with the corals and function.
Besides the previous fish species, other fish live in coral reefs. It is possible to see butterflyfish on coral reefs; they have a length of 15 to 30 cm (Brandl et al, 2019, p. 448). Their body is strongly flattened on the sides and appears tall. The head is relatively large, the mouth is tiny, and the lips can be extended into an elongated tube in some species. This mouth structure enables them to get food from the hard-to-reach slots of the coral reef (Brandl et al, 2019). They eat different small invertebrates, which they catch in different ways. Most species search for small critters among the corals and often steal tidbits from the tentacles of coral polyps.
It is essential to mention the existence of seahorses in coral reefs. The appearance of seahorses is unusual; the body of seahorses is curved, the back bulges out with a hump, the abdomen protrudes forward, and the front of the body is thin and curved. The head is small; its front part is an elongated tube, and the eyes are convex. The coloration of these fish is often monochromatic, but different species are colored differently. Seahorses that live among aquatic plants are often brown, yellowish, or greenish; seahorses that live among corals can be red, bright yellow, or purple (Pearman et al., 2018). Their range envelopes the entire Earth layer; seahorses live in shallow waters among the thickets of seaweed or the corals.
Interestingly, other unusual organisms inhabit a small coral world. One can observe both sea urchin and flute fish, sea eels and zebrafish, poisonous sea snails and rockfish, grouper, parrotfish, reef sharks, and whale sharks. In addition to large organisms, there are bacteria, fungi, and protozoa (Francini-Filho et al., 2018). The coral reef world is fascinating in its colors and intensity of life. Altogether, the diverse species on the reefs represent a quarter of all ocean life.
Conclusion
Hence, coral reefs are among the richest in biodiversity and highest in productivity of ecosystems on the planet. Much of their biodiversity consists of tiny organisms that live deep within the three-dimensional space of reefs. Coral reef biodiversity includes algae that live in symbiosis with polyps, clams, and various fish species. Accordingly, coral reefs aim to protect shorelines from the ravages of waves and tropical storms and offer habitat and shelter for many marine organisms.
Reference List
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