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2384) Seahorse

Gist

The seahorse is a marine fish of the genus Hippocampus and family Syngnathidae, named for its horse-like head and upright posture, resembling a miniature horse in the sea. These bony fish have distinctive features such as a prehensile tail, independently moving eyes, and segmented bony armour, and they are found in shallow coastal waters worldwide. 

Summary

A seahorse, (genus Hippocampus), any of about 50 species of marine fishes allied to pipefishes in the family Syngnathidae (order Gasterosteiformes). Seahorses are found in shallow coastal waters in latitudes from about 52° N to 45° S. Their habitats include coral reefs, mangroves, sea grass beds, and estuaries. They are unique in appearance, with their horselike head, prehensile tail, independently moving eyes, and brood pouch. They have long, tubular snouts and small, toothless mouths. Their bodies are covered with consecutive rings of bony plates. The name of the genus that contains seahorses is taken from the Greek words hippos (meaning “horse”) and kampos (meaning “sea monster”).

Seahorses vary in size, ranging in length from about 2 to 35 cm (about 0.8 to 14 inches). Adults of some of the smallest species—such as Denise’s pygmy seahorse (Hippocampus denise), found in the tropical western Pacific from Indonesia to Vanuatu, and Satomi’s pygmy seahorse (H. satomiae), found in the tropical Indian and Pacific Oceans from the Bay of Bengal to the Coral Sea—are less than 2 cm long. The largest species, the big-bellied seahorse (H. abdominalis), which inhabits the waters off South Australia and New Zealand, can grow up to 35 cm (13.8 inches) in length.

Seahorses are rather immobile, swimming more slowly than other fishes. When swimming they maintain a vertical position and propel themselves forward using a soft-rayed dorsal fin. They use pectoral fins located on the side of the head to maneuver. Some scientists contend that this upright swimming posture evolved shortly after the expansion of sea grasses in the western Pacific roughly 25 million years ago. These plants provided seahorses with useful hiding places to avoid enemies and to capture unsuspecting prey, and ancestors of the seahorse evolved to maximize the opportunities offered by this new habitat.

Seahorses are usually found clinging to plants or corals with their tails. Their sedentary habits coupled with excellent camouflage abilities render them successful ambush predators. When small organisms swim nearby, a seahorse may capture them by rapidly sucking them into the mouth. Seahorses also rely upon camouflage to avoid predators such as crabs and other fishes.

The reproductive behaviour of seahorses is notable in that the male carries the fertilized eggs. After an elaborate courtship, the female uses an ovipositor (egg duct) to place her eggs into a brood pouch located at the base of the male’s tail where the eggs are later fertilized. Depending on the species, the eggs remain in the pouch between 10 days and six weeks. During this time the male nurtures the developing young by regulating the chemistry of the fluid inside the pouch, slowly transforming it from that of his internal body fluids to that of salt water as pregnancy progresses. To nourish the growing young, the male also produces inorganic compounds and releases the hormone prolactin, which helps break down the proteins contributed by the female. Once the eggs hatch, the male convulses his body and expels the young through a single opening in the pouch. The young are miniature versions of their parents that receive no further care. The male can receive another brood of eggs almost immediately after giving birth. In some species a male and female will maintain a monogamous pair bond throughout the breeding season and produce many broods.

Commercially, seahorses are traded live as aquarium animals and dead for use in traditional medicines and as curios. Threatened by direct overfishing, accidental capture (bycatch) in other fisheries, and the destruction of their coastal habitats, some species—such as the Pacific seahorse (H. ingens)—face extinction.

Details:

Scientific classification

Kingdom:  Animalia
Phylum:  Chordata
Class:  Actinopterygii
Order:  Syngnathiformes
Family:  Syngnathidae
Subfamily:  Hippocampinae
Genus:  Hippocampus

A seahorse (also written sea-horse and sea horse) is any of 46 species of small marine bony fish in the genus Hippocampus. The genus name comes from the Ancient Greek hippókampos (ἱππόκαμπος), itself from híppos (ἵππος) meaning "horse" and kámpos meaning "sea monster" or "sea animal". Having a head and neck suggestive of a horse, seahorses also feature segmented bony armour, an upright posture and a curled prehensile tail. Along with the pipefishes and seadragons (Phycodurus and Phyllopteryx) they form the family Syngnathidae.

Evolution and fossil record

Anatomical evidence, supported by molecular, physical, and genetic evidence, demonstrates that seahorses are highly modified pipefish. The fossil record of seahorses, however, is very sparse. The best known and best studied fossils are specimens of Hippocampus guttulatus (though literature more commonly refers to them under the synonym of H. ramulosus), from the Marecchia River formation of Rimini Province, Italy, dating back to the Lower Pliocene, about 3 million years ago. The earliest known seahorse fossils are of two pipefish-like species, H. sarmaticus and H. slovenicus, from the coprolitic horizon of Tunjice Hills, a middle Miocene lagerstätte in Slovenia dating back about 13 million years.

Molecular dating implies that pipefish and seahorses diverged during the Late Oligocene. This has led to speculation that seahorses evolved in response to large areas of shallow water, newly created as the result of tectonic events. The shallow water would have allowed the expansion of seagrass habitats that served as camouflage for the seahorses' upright posture. These tectonic changes occurred in the western Pacific Ocean, pointing to an origin there, with molecular data suggesting two later, separate invasions of the Atlantic Ocean. In 2016, a study published in Nature found the seahorse genome to be the most rapidly evolving fish genome studied so far.

The evolution of seahorses from pipefish may have been an adaptation related to the biomechanics of prey capture. The unique posture of the seahorse allows them to capture small shrimps at larger distances than the pipefish is capable of.

Description

Seahorses range in size from 1.5 to 35 cm (0.6 to 13.8 in). They are named for their equine appearance, with bent necks and long snouted heads and a distinctive trunk and tail. Although they are bony fish, they do not have scales, but rather thin skin stretched over a series of bony plates, which are arranged in rings throughout their bodies. Each species has a distinct number of rings. The armor of bony plates also protects them against predators, and because of this outer skeleton, they no longer have ribs. Seahorses swim upright, propelling themselves using the dorsal fin, another characteristic not shared by their close pipefish relatives, which swim horizontally. Razorfish are the only other fish that swim vertically. The pectoral fins, located on either side of the head behind their eyes, are used for steering. They lack the caudal fin typical of fishes. Their prehensile tail is composed of square-like rings. They are adept at camouflage, and can grow and reabsorb spiny appendages depending on their habitat.

Unusual among fish, a seahorse has a flexible, well-defined neck. It also sports a crown-like spine or horn on its head, termed a "coronet", which is distinct for each species.

Seahorses swim extremely poorly, rapidly fluttering a dorsal fin and using pectoral fins to steer. The slowest-moving fish in the world is H. zosterae (the dwarf seahorse), with a top speed of about 1.5 m (5 ft) per hour. Since they are poor swimmers, they are most likely to be found resting with their prehensile tail wound around a stationary object. They have long snouts, which they use to drag up food, and their eyes can move independently of each other like those of a chameleon.

Habitat

Seahorses are mainly found in shallow tropical and temperate salt water throughout the world, from about 45°S to 45°N. They live in sheltered areas such as seagrass beds, estuaries, coral reefs, and mangroves. Four species are found in Pacific waters from North America to South America. In the Atlantic, Hippocampus erectus ranges from Nova Scotia to Uruguay. H. zosterae, known as the dwarf seahorse, is found in the Bahamas.

Colonies have been found in European waters such as the Thames Estuary.

Two species live in the Mediterranean Sea: H. guttulatus (the long-snouted seahorse), and H. hippocampus (the short-snouted seahorse). These species form territories; males stay within 1 sq m (10 sq ft) of habitat, while females range over about one hundred times that.

Feeding habits

Seahorses rely on stealth to ambush small prey such as copepods. They use pivot feeding to catch the copepod, which involves rotating their snout at high speed and then sucking in the copepod.
Seahorses use their long snouts to eat their food with ease. However, they are slow to consume their food and have extremely simple digestive systems that lack a stomach, so they must eat constantly to stay alive.[28] Seahorses are not very good swimmers, and for this reason they need to anchor themselves to seaweed, coral or anything else that will keep the seahorse in place. They do this by using their prehensile tails to grasp their object of choice. Seahorses feed on small crustaceans floating in the water or crawling on the bottom. With excellent camouflage, seahorses ambush prey that floats within striking range, sitting and waiting until an optimal moment. Mysid shrimp and other small crustaceans are favorites, but some seahorses have been observed eating other kinds of invertebrates and even larval fish. In a study of seahorses, the distinctive head morphology was found to give them a hydrodynamic advantage that creates minimal interference while approaching an evasive prey. Thus the seahorse can get very close to the copepods on which it preys. After successfully closing in on the prey without alerting it, the seahorse gives an upward thrust and rapidly rotates the head aided by large tendons that store and release elastic energy, to bring its long snout close to the prey. This step is crucial for prey capture, as oral suction only works at a close range. This two-phase prey capture mechanism is termed pivot-feeding. Seahorses have three distinctive feeding phases: preparatory, expansive, and recovery. During the preparatory phase, the seahorse slowly approaches the prey while in an upright position, after which it slowly flexes its head ventrally. In the expansive phase, the seahorse captures its prey by simultaneously elevating its head, expanding the buccal cavity, and sucking in the prey item. During the recovery phase, the jaws, head, and hyoid apparatus of the seahorse return to their original positions.

The amount of available cover influences the seahorse's feeding behaviour. For example, in wild areas with small amounts of vegetation, seahorses will sit and wait, but an environment with extensive vegetation will prompt the seahorse to inspect its environment, feeding while swimming rather than sitting and waiting. Conversely, in an aquarium setting with little vegetation, the seahorse will fully inspect its environment and makes no attempt to sit and wait.

Additional Information

Seahorses are members of the pipefish family. In addition to their iconic appearance, seahorses possess many interesting attributes. Among them are specialized structures in their skin cells, called chromatophores, which allow the mostly sessile seahorses to change color to mimic their surroundings. Well camouflaged as they cling to stalks of seagrass in their shallow habitats, seahorses can be hard to see.

Their truly remarkable biological claim to fame, however, is that male seahorses and sea dragons get pregnant and bear young—a unique adaptation in the animal kingdom.

After completing an elaborate courtship dance that may go on for hours or days, the female seahorse transfers her mature eggs into the male’s brood pouch, where they are fertilized. At the end of a gestation period usually lasting from two to four weeks, the pregnant male’s abdominal area begins to undulate rhythmically, and strong muscular contractions eject from a few dozen to as many as 1,000 fully formed baby seahorses into the surrounding water. After that, the offspring must fend for themselves. Large litters are necessary because only about 0.5 percent will survive to adulthood.

Many, if not all, of the 47 known seahorse species—14 of which were identified only in the 21st century—are in decline worldwide.

Because seahorses generally live in shallow, near-coastal waters, human activities including development, pollution, fisheries, and traditional medicine have reduced their numbers. At the same time, their universal appeal has worked against them; until recently, wild seahorses were often captured for the aquarium trade. The delicate creatures tend to fare poorly in aquaria, however. In recent years, captive-bred seahorses have shown promise as hardier tank-dwellers than their wild relatives.

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2382) Congo River

Gist

The deepest river in the world is the Congo River in Africa, with recorded depths reaching at least 220 meters (720 feet). Recognized by Guinness World Records, its maximum depth surpasses that of any other river and was confirmed by scientists in 2008.

Summary

The basin of the deepest river in the world provides food, water, medicines and transportation to about 75 million people, according to Yale University’s Global Forest Atlas.

1 . Where does the Congo river flow through?
The Congo is the deepest river in the world. Its headwaters are in the north-east of Zambia, between Lake Tanganyika and Lake Nyasa (Malawi), 1760 metres above sea level; it flows into the Atlantic Ocean.

The Congo river flows through the Republic of the Congo, the Democratic Republic of the Congo, the Central African Republic, western Zambia, northern Angola, Cameroon and Tanzania. The lower course of the Congo river has large gorges and falls, which makes it one of the most dangerous rivers.

2 . How deep and how long is the Congo river?
The Congo river, formerly known as the Zaire, is the deepest river in the world: at some points the water can be up to 220 metres deep; the basin has a surface area of 3,457,000 square kilometres.

The Congo river is 4,700 kilometres long, which makes it the second longest river in Africa, the tenth longest river in the world and the second largest river by discharge volume in the world, only after the Amazon.

3 . What are the environmental threats in the Congo river basin?
One of the main threats in the Congo river basin is deforestation to accommodate modern agricultural practices; moreover, industrial logging accelerates the rate of deforestation.

The other major threat is food demand due to rapid population growth in the region, which leads to excessive hunting of wild animals such as bats, monkeys, rats and snakes.

Summary

he Congo River, formerly also known as the Zaire River, is the second-longest river in Africa, shorter only than the Nile, as well as the third-largest river in the world by discharge volume, following the Amazon and Ganges–Brahmaputra rivers. It is the world's deepest recorded river, with measured depths of around 220 m (720 ft). The Congo–Lualaba–Luvua–Luapula–Chambeshi River system has an overall length of 4,700 km (2,900 mi), which makes it the world's ninth-longest river. The Chambeshi is a tributary of the Lualaba River, and Lualaba is the name of the Congo River upstream of Boyoma Falls, extending for 1,800 km (1,100 mi).

Measured along with the Lualaba, the main tributary, the Congo River has a total length of 4,370 km (2,720 mi). It is the only major river to cross the equator twice. The Congo Basin has a total area of about 4,000,000 sq km (1,500,000 sq mi), or 13% of the entire African landmass.

Name

The name Congo/Kongo originates from the Kingdom of Kongo once located on the southern bank of the river. The kingdom in turn was named after the indigenous Bantu Kongo people, known in the 17th century as "Esikongo". South of the Kingdom of Kongo proper lay the similarly named Kakongo kingdom, mentioned in 1535. Abraham Ortelius labelled "Manicongo" as the city at the mouth of the river in his world map of 1564. The tribal names in Kongo possibly derive from a word for a public gathering or tribal assembly. The modern name of the Kongo people or Bakongo was introduced in the early 20th century.

The name Zaire is from a Portuguese adaptation of a Kikongo word, nzere ("river"), a truncation of nzadi o nzere ("river swallowing rivers"). The river was known as Zaire during the 16th and 17th centuries; Congo seems to have replaced Zaire gradually in English usage during the 18th century, and Congo is the preferred English name in 19th-century literature, although references to Zahir or Zaire as the name used by the inhabitants remained common. The Democratic Republic of the Congo and the Republic of the Congo are named after it, as was the previous Republic of the Congo which had gained independence in 1960 from the Belgian Congo. The Republic of Zaire during 1971–1997 was also named after the river's name in French and Portuguese.

Details

Congo River, river in west-central Africa. With a length of 2,900 miles (4,700 km), it is the continent’s second longest river, after the Nile. It rises in the highlands of northeastern Zambia between Lakes Tanganyika and Nyasa (Malawi) as the Chambeshi River at an elevation of 5,760 feet (1,760 metres) above sea level and at a distance of about 430 miles (700 km) from the Indian Ocean. Its course then takes the form of a giant counterclockwise arc, flowing to the northwest, west, and southwest before draining into the Atlantic Ocean at Banana (Banane) in the Democratic Republic of the Congo. Its drainage basin, covering an area of 1,335,000 square miles (3,457,000 square km), takes in almost the entire territory of that country, as well as most of the Republic of the Congo, the Central African Republic, eastern Zambia, and northern Angola and parts of Cameroon and Tanzania.

With its many tributaries, the Congo forms the continent’s largest network of navigable waterways. Navigability, however, is limited by an insurmountable obstacle: a series of 32 cataracts over the river’s lower course, including the famous Inga Falls. These cataracts render the Congo unnavigable between the seaport of Matadi, at the head of the Congo estuary, and Malebo Pool, a lakelike expansion of the river. It was on opposite banks of Malebo Pool—which represents the point of departure of inland navigation—that the capitals of the former states of the French Congo and the Belgian Congo were founded: on the left bank Kinshasa (formerly Léopoldville), now the capital of the Democratic Republic of the Congo, and on the right bank Brazzaville, now the capital of the Republic of the Congo.

The Amazon and the Congo are the two great rivers of the world that flow out of equatorial zones where heavy rainfall occurs throughout all or almost all of the year. Upstream from Malebo Pool, the Congo basin receives an average of about 60 inches (1,500 mm) of rain a year, of which more than one-fourth is discharged into the Atlantic. The drainage basin of the Congo is, however, only about half the size of that of the Amazon, and the Congo’s rate of flow—1,450,000 cubic feet (41,000 cubic metres) per second at its mouth—is considerably less than the Amazon’s flow of more than 6,180,000 cubic feet (175,000 cubic metres) per second.

While the Chambeshi River, as the remotest source, may form the Congo’s original main stream in terms of the river’s length, it is another tributary—the Lualaba, which rises near Musofi in southeastern Democratic Republic of the Congo—that carries the greatest quantity of water and thus may be considered as forming the Congo’s original main stream in terms of water volume.

When the river first became known to Europeans at the end of the 15th century, they called it the Zaire, a corruption of a word that is variously given as nzari, nzali, njali, nzaddi, and niadi and that simply means “river” in local African languages. It was only in the early years of the 18th century that the river was first called the “Rio Congo,” a name taken from the kingdom of Kongo that had been situated along the lower course of the river. During the period (1971–97) when the Democratic Republic of the Congo was called Zaire, the government also renamed the river the Zaire. Even during that time, however, the river continued to be known throughout the world as the Congo. To the literary-minded the river is evocative of the famous 1902 short story “Heart of Darkness” by Joseph Conrad. His book conjured up an atmosphere of foreboding, treachery, greed, and exploitation. Today, however, the Congo appears as the key to the economic development of the central African interior.

Physical features:

Physiography

The expression “Congo basin,” strictly speaking, refers to the hydrographic basin. This is not only vast but is also covered with a dense and ramified network of tributaries, subtributaries, and small rivers—with the exception of the sandy plateaus in the southwest.

The Congo basin is the most clearly distinguished of the various geographic depressions situated between the Sahara to the north, the Atlantic Ocean to the south and west, and the region of the East African lakes to the east. In this basin, a fan-shaped web of tributaries flows downward along concentric slopes that range from 900 to 1,500 feet (275 to 460 metres) in elevation and that enclose a central depression. The basin itself stretches for more than 1,200 miles (1,900 km) from north to south (from the Congo–Lake Chad watershed to the interior plateaus of Angola) and also measures about 1,200 miles from the Atlantic in the west to the Nile-Congo watershed in the east.

The central part of the Congo basin—often called the cuvette (literally “saucer” or “shallow bowl”)—is an immense depression containing Quaternary alluvial deposits that rest on thick sediments of continental origin, consisting principally of sands and sandstones. These underlying sediments form outcrops in valley floors at the eastern edge of the cuvette. The filling of the cuvette, however, began much earlier. Boreholes have revealed that since late Precambrian times (i.e., since at least 570 million years ago) considerable sediment has accumulated, derived from the erosion of formations situated around the periphery of the cuvette. The arrangement of surface relief, thick depositional strata, and substratum in amphitheatre-like fashion around the main Congo channel, which has been uniform across time, is evidence of a persistent tendency to subsidence in this part of the continent. This subsidence is accompanied by uplifting on the edges of the cuvette, principally on its eastern side—which has also been influenced by the formation of the Western Rift Valley.

From its sources to its mouth, the Congo River system has three contrasting sections—the upper Congo, middle Congo, and lower Congo. The upper reaches are characterized by three features—confluences, lakes, and waterfalls or rapids. To begin with, several streams of approximately equal size unite to form the river. In a little more than 60 miles (100 km), the upper Lualaba joins the Luvua and then the Lukuga. Each stream for part of its course undergoes at least a lacustrine type of expansion, even when it does not form a lake. Thus, Lake Upemba occurs on the upper Lualaba; Lakes Bangweulu and Mweru occur on the Chambeshi–Luapula–Luvua system; and Lake Tanganyika, which is fed by the Ruzizi (flowing from Lake Kivu) and by the Malagarasi, itself flows into the Lukuga. Rapids occur not only along the headstreams but also in several places along the course of the main stream. Navigation thus is possible only along sections of the upper Congo by vessels of low tonnage. Even so, these stretches are in danger of being overgrown by aquatic vegetation, particularly water hyacinths.

Kisangani (formerly Stanleyville)—located just downstream of the Boyoma Falls, a series of seven cataracts—marks the real beginning, upriver, of the navigable Congo. This central part of the river flows steadily for more than 1,000 miles (1,600 km) to within 22 miles (35 km) of Kinshasa. Its course at first is narrow but soon grows wider, after which many islands occur in midstream. This change in the character of the river corresponds to its entry into its alluvial plain. From that point onward, with the exception of a few rare narrow sections, the Congo divides into several arms, separated by strings of islands. It increases from a width of more than 3.5 miles (5.5 km) downstream from Isangi (where the Lomami enters the Congo) to a width of 5 to 7 miles (8 to 11 km) and on occasion—for example, at the mouth of the Mongala—to 8 miles (13 km). Beyond the natural levees (formed by silt deposits) occurring on either bank, some areas are subjected to extensive flooding that increases the river’s bounds still further. It is not always easy to distinguish such areas from the “rain swamps” in regions lying between rivers. The middle course of the Congo ends in a narrow section called the Chenal (“Channel”), or Couloir (“Corridor”). Between banks no more than half a mile to a mile wide, the riverbed deepens and the current becomes rapid, flowing through a valley that cuts down several hundreds of yards deep into the soft sandstone bedrock of the Batéké Plateau. Along this central reach the Congo receives its principal tributaries, primarily the Ubangi and the Sangha on the right bank and the Kwa on the left bank. An enormous increase in the average rate of flow results, rising from less than 250,000 cubic feet (7,000 cubic metres) a second at Kisangani to nearly its maximum flow at Kinshasa.

Upon leaving the Chenal, the Congo divides into two branches, forming Malebo Pool, a vast lacustrine area about 15 by 17 miles (24 by 27 km), which marks the end of the middle Congo. Immediately downstream occur the first waterfalls of the final section of the river’s course. Cataracts and rapids are grouped into two series, separated by a fairly calm central reach, in which the elevation drops from a little less than 900 feet (275 metres) to a few yards above sea level. The Congo’s estuary begins at Matadi, downstream from the rapids that close off the interior Congo; 83 miles (134 km) in length, it forms the border between Angola and the Democratic Republic of the Congo. At first the estuary is narrow—less than half a mile to about a mile and a half in width—with a central channel 65 to 80 feet (20 to 24 metres) deep, but it widens downstream of Boma. There the river, obstructed by islands, divides into several arms, and in some places the depth does not exceed 20 to 25 feet (6 to 7.5 metres), which makes dredging necessary to allow oceangoing vessels to reach Matadi. Beyond the estuary’s mouth, the course of the Congo continues offshore as a deep underwater canyon that extends for a distance of about 125 miles (200 km).

Hydrology of the Congo River

The Congo has a regular flow, which is fed by rains throughout the year. At Kinshasa the flow has for many years remained between the high level of 2,310,000 cubic feet (65,000 cubic metres) per second, recorded during the flood of 1908, and the low level of 756,000 cubic feet (21,000 cubic metres) per second, recorded in 1905. During the unusual flood of 1962, however, by far the highest for a century, the flow probably exceeded 2,600,000 cubic feet (73,000 cubic metres) per second.

At Brazzaville and Kinshasa, the river’s regime is characterized by a main maximum at the end of the year and a secondary maximum in May, as well as by a major low level during July and a secondary low level during March and April. In reality, the downstream regime of the Congo represents climatic influence extending over 20° of latitude on both sides of the Equator a distance of some 1,400 miles (2,250 km). Each tributary in its course modifies the level of the main stream. Thus, for example, the low level in July at Malebo Pool results from two factors: a drought that occurs for several months in the southern part of the basin at that time, as well as a delay before the floods of the Ubangi tributary flowing down from the north arrive, which does not happen before August. The Congo basin is so vast that no single meteorologic circumstance is capable of disturbing the slow movement of the waters’ rise and fall. The annual fluctuations may alter drastically, however, when floodwaters from different tributaries that normally coincide with each other arrive at different times.

Lake Tanganyika, apart from brief seiches caused by wind drift and sudden changes in atmospheric pressure, may experience considerable variations in its water level from year to year. In 1960, for example, its waters flooded parts of Kalemi, Democratic Republic of the Congo, and Bujumbura, Burundi. A series of particularly rainy years followed by a blocking of the outlet by floating vegetation may explain this phenomenon.

Climate

Typical climate in regions through which the Congo flows is that of Yangambi, a town situated on the river’s right bank slightly north of the Equator and a little downstream of Kisangani. Humidity is high throughout the year, and annual rainfall amounts to 67 inches (1,700 mm) and occurs fairly regularly; even in the driest month the rainfall totals more than 3 inches (76 mm). Temperatures are also uniformly high throughout the year, and there is little diurnal variability. The average temperature at Yangambi is in the mid-70s F (mid-20s C).

From the pluviometric equator (an imaginary east-west line indicating the region of heaviest rainfall), which is situated slightly to the north of the geographic equator, the amount of rainfall decreases regularly in proportion to latitude. The northernmost points of the basin, situated in the Central African Republic, receive only from 8 to 16 inches (200 to 400 mm) less during the course of a year than points near the Equator. The dry season, however, lasts for four or five months, and there is only one annual rainfall maximum, which occurs in summer. In the far southern part of the basin, at a latitude of 12° S, the climate becomes definitely Sudanic in character, with marked dry and wet seasons of approximately equal length and with rainfall of about 49 inches (1,250 mm) a year.

Plant life

The Congo basin is home to the second largest rainforest in the world. The equatorial climate that prevails over a significant part of the Congo basin is coextensive with a dense evergreen forest. The Congolese forest spreads out over the central depression, extending continuously from about 4° N to about 5° S; it is interrupted only by clearings, many of which have a natural origin. The forest region is bordered on either side by belts of savanna (grassy parkland). The forest and savanna often meet imperceptibly, blending together in a mosaic pattern; more rarely, strips of forest invade the grassland. Farther away from the Equator, and to the extent that the Sudanic features of the climate become evident, the wooded savanna region, with its thin deciduous forest, is progressively reached.

As it courses through the solid mass of the Congolese forest, the Congo and its tributaries are bordered by discontinuous grassy strips. Meadows of Echinochloa (a type of grass), papyrus, and Cyperaceae (sedge) occupy abandoned river channels, fringe the banks, or, behind a curtain of forest, blanket the depressions in the centre of the islands, They also spring up on sandbanks, as well as on the downstream ends of islands that are fertilized by the floods. A shrub, Alchornea, frequently marks the transition to the high forest that grows on the levees behind the banks.

Animal life

The animal life of the Congo basin is identified to a certain extent with that of the equatorial forest, which is sharply distinct from the wildlife of the savannas. Within this equatorial domain, the Congo and its principal tributaries form a separate ecological milieu. The animal population of the great waterways often has fewer affinities with the neighbouring marshes or the forests on dry land than it has with other river systems, whether of the coastal region or the savannas.

Numerous species of fish live in the waters of the Congo; more than 230 have been identified in Malebo Pool and the waters that flow into it alone. The riverine swamps, which often dry up at low water, are inhabited by lungfish, which survive the dry periods buried and encysted in cocoons of mucus. In the wooded marshlands, where the water is the colour of black tea, the black catfish there assume the colour of their environment. The wildlife of the marshes and that of the little parallel streams do not mix with the wildlife of the river itself.

The waters of the Congo contain various kinds of reptiles, of which crocodiles are the most striking species. Semiaquatic tortoises are also found, as are several species of water snakes.

The forest birdlife constitutes, together with the birdlife of the East African mountains, the most specifically indigenous birdlife found on the African continent. In the Congo region more than 265 species typical of the equatorial forest have been recorded. Occasionally or seasonally, however, nontypical birds may be observed. Seabirds, such as the sea swallow, fly upstream from the ocean. Migratory birds from Europe, including the blongios heron and the Ixobrychus minutus (little bittern), pass through the region. Species with a wide distribution within Africa, such as the Egyptian duck, also have been sighted. Ducks, herons, storks, and pelicans are abundantly represented.

Aquatic mammals are rare, consisting of the hippopotamus, two species of otters, and the manatee. The manatee (sea cow), which lives entirely in the water, has been officially identified only on the Sangha tributary but appears to have given rise to some curious legends on the lower Congo, including its association with a creature called Mami Wata (a kind of siren), stories of which were carried by African slaves to the Americas.

The people and the economy:

Life of the river peoples

Three types of environments are found, either juxtaposed or in succession, along the river and its tributaries: the narrower sections, bordered by firm ground; the wider stretches, dotted with islands and accompanied by backwaters; and the zones where flooding occurs or where there are extensive marshes.

Almost all the river peoples engage in fishing. Along the narrow sections, where rapids often occur, fishing is only of interest to a small number of villages. The Enya (Wagenia) of Boyoma Falls and the Manyanga living downstream from Malebo Pool attach fish traps to stakes or to dams built in the rapids themselves. Fishing of a very different nature, notably by poison, is conducted in the marshy areas, where the population is more extensive than might be imagined. Among these peoples are the Ngombe—“water people”—who inhabit the Itimbiri-Ngiri and the triangle formed by the Congo and the Ubangi. Other fisherfolk of the marshes dwell in the lagoons and the flooded forests of the region where the confluence of the Congo and the Alima, Likouala, and Sangha occurs.

Despite unfavourable conditions, all these peoples are also cultivators. They raise dikes, often of monumental size, to plant cassava (manioc) on the land thus sheltered from flooding. Other minor crops, such as sweet potatoes, bananas, and yams, are also found. The Congo basin has the continent’s most important timber resources, but the timber industry is developing slowly, mainly because the interior is so inaccessible and because the cost of transporting timber to the coast is so high.

Few modes of existence have undergone such profound changes as a result of contact with the modern world as has that of the river’s fisherfolk. The growth of the towns on the banks of Malebo Pool as well as the taste of urban dwellers for river fish have served to stimulate fishing by tying it to a cash economy. It is not just a question of villagers smoking fish that they sell to passing traders. Increasingly numerous fishing crews sail up the Congo, the Ubangi, and the Kasai, well above their confluences, to fish in the shallows.

Transportation

The Congo is an important navigational system in Africa. Within the territorial limits of the Democratic Republic of the Congo alone, there are some 8,700 miles (14,000 km) of navigable waterway. Of this total, 650 miles (1,050 km) are accessible at all seasons to barges with capacities between 800 and 1,100 tons, depending upon the height of the water. The amount of goods transported by water—consisting mainly of agricultural produce, wood, minerals, and fuel—is very modest in comparison with the traffic on European rivers (for example, the commercial traffic from the port of Kinshasa does not reach a million tons), but river transport remains essential for communications with regions that are inaccessible by road, especially in the cuvette. The three principal routes, all of which converge on the downstream terminus at Kinshasa on the Malebo Pool, run from Kisangani, from Ilebo (formerly Port-Francqui) on the Kasai, and from Bangui on the Ubangi. River transport, however, falls short of the role it could play in development. It has actually declined since the states of the Congo basin became independent in 1960, because of serious problems with aging equipment, a lack of maintenance of the infrastructure, and the poor functioning of the public waterway agencies. In the Democratic Republic of the Congo only the section from Ilebo to Kinshasa is still important, because it constitutes the river link (the other link being a railway between Kinshasa and Matadi) used to transport the copper production of Katanga to the coast.

This network has fostered economic development in inland areas, far from the coast. Varied activities include the production of palm oil on the banks of the Kwilu, centred on the port of Kikwit, and the establishment of plantations of robusta coffee in the Kisangani area.

Before such developments could be undertaken, however, it was necessary to overcome the barrier to the sea formed by the Congo’s lower course. That feat was accomplished in 1898 with the opening of the railway between Matadi and Léopoldville (now Kinshasa) and in 1934 by the completion of the Congo-Ocean rail line on the right bank between Brazzaville and Pointe-Noire.

While the river system facilitates navigation, it also hinders land transportation. Only a small number of bridges cross the Congo and its tributaries. The Kongolo rail-and-road bridge over the Lualaba was reconstructed in 1968, and a bridge over the Congo at Matadi was opened in 1983. Numerous projects to improve the situation nevertheless exist, notably a link between Kinshasa and Brazzaville. This project has long been under discussion, although to financial obstacles are added difficulties caused by political dissension. Several times since the two countries gained independence in 1960, dissension has interrupted the ferry traffic between the two capitals.

Power

It has been estimated that the hydroelectric potential of the Congo basin amounts to about one-sixth of the known world resources, but only a fraction of this potential has been harnessed. The single site of Inga, just upriver from Matadi, has a power potential estimated at more than 30,000 megawatts. Two hydroelectric projects, called Inga I and Inga II, have been completed there since the independence of the Democratic Republic of the Congo. Further development of the region’s hydropower potential, as outlined in the ambitious “Grand Inga” scheme, would create one of the world’s largest hydroelectric power systems.

Study and exploration

The question of the source of the Congo confronted European explorers from the time that the Portuguese navigator Diogo Cão encountered the river’s mouth in 1482, which he believed to be a strait providing access to the realm of the mythical Prester John, a Christian priest-king. It is virtually certain that, well before the Welsh explorer Henry Morton Stanley arrived in 1877, some 17th-century Capuchin missionaries reached the shores of Malebo Pool. This exploit, however, was not followed up, even by the amply supplied expedition led by James Kingston Tuckey, which was sent out by the British Admiralty in 1816 but was decimated and had to retrace its footsteps even before it had surmounted the cataracts. Preposterous hypotheses about the river continued to be entertained, connecting, for example, the upper Niger to the Congo or maintaining that the Congo and the Nile both flowed from a single great lake in the heart of Africa.

Even after the European discovery of Lake Tanganyika by the British explorers Richard Burton and John Speke (1858), then of the Lualaba (1867) and of Lake Bangweulu (1868) by the Scottish explorer David Livingstone, uncertainty remained—uncertainty that Stanley was to dissipate in the course of his famous expedition in 1876 and 1877 that took him by water from the Lualaba to the Congo’s mouth over a period of nine months. In the interior of the Congo basin and above all on the right bank, the final blank spaces on the map could not be filled in until about 1890, when the exploration of the upper course of the Ubangi was completed.

Additional Information

The Congo River (also known as Zaire River) is the largest river in Africa. Its overall length of 4,700 km (2,922 miles) makes it the second longest in Africa (after the Nile). The river and its tributaries flow through the second largest rain forest area in the world, second only to the Amazon Rainforest in South America.

The river also has the second-largest flow in the world, behind the Amazon, and the second-largest watershed of any river, again trailing the Amazon. Its watershed is a little larger than that of the Mississippi River. Because large parts of the river basin sit north and south of the equator, its flow is steady, as there is always at least one river having a rainy season. The Congo gets its name from the old Kingdom of Kongo which was at the mouth of the river. The Democratic Republic of the Congo and the Republic of the Congo, both countries sitting along the river's banks, are named after it. From 1971 to 1997, the Democratic Republic of the Congo was called Zaire and its government called the river the Zaire River.

The sources of the Congo are in the Highlands and mountains of the East African Rift, as well as Lake Tanganyika and Lake Mweru, which feed the Lualaba River. This then becomes the Congo below Boyoma Falls. The Chambeshi River in Zambia is usually taken as the source of the Congo because of the accepted practice worldwide of using the longest tributary, as with the Nile River.

The Congo flows mostly west from Kisangani just below the falls, then slowly bends southwest, passing by Mbandaka, joining with the Ubangi River, and running into the Pool Malebo (Stanley Pool). Kinshasa (formerly Léopoldville) and Brazzaville are on opposite sides of the river at the Pool, where the river narrows and falls through a few cataracts in deep canyons (collectively known as the Livingstone Falls), running by Matadi and Boma, and into the sea at the small town of Muanda.

History of exploration

The mouth of the Congo was visited by Europeans in 1482, by the Portuguese Diogo Cão, and in 1817, by a British exploration under James Kingston Tuckey that went up the river as far as Isangila. Henry Morton Stanley was the first European to travel along the whole river.

Economic importance

Although the Livingstone Falls stop ships coming in from the sea, almost all of the Congo is navigable in parts, especially between Kinshasa and Kisangani. Railways cross the three major falls that interrupt navigation, and much of the trade of central Africa passes along the river. Goods include copper, palm oil, sugar, coffee, and cotton. The river can also be valuable for hydroelectric power, and Inga Dams below Pool Malebo have been built.

In February of 2005, South Africa's state owned power company, Eskom, said that they had a proposal to increase the amount of electric power that the Inga can make through improvements and the building of a new hydroelectric dam. The project would bring the highest output of the dam to 40 GW, twice that of China's Three Gorges Dam.

Geological history

In the Mesozoic period before the continental drift opened the South Atlantic Ocean, the Congo was the upper part of a river about 12,000 km (7,500 miles) long that flowed west across the parts of Gondwanaland, now called Africa and South America.