TUNISIA

Marine Biology in Tunisia

Release Date:  01 June 2021

 

  

TECHNICAL SPECIFICATIONS

Issue Date: 01 June 2021
Designer: Photo by Slim Medimegh
Sheet Composition: 16 stamps
Stamp Size: 40 x 40 mm
Printing Method: Offset lithography
Perforation: 
Printer: 
Quantity: 200,000 stamps

Design #1: 0,25د Serranus scriba

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Design #2: 0,75د Octopus vulgaris

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Design #3: 0,90د Cratena peregrina

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Design #4: د3,0 Loligo vulgaris

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sheet of 16 Stamps

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Miniature Sheet of 4 Stamps

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

First Day Cover

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Marine biology is the scientific study of the biology of marine life, organisms in the sea. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies species based on the environment rather than on taxonomy.

A large proportion of all life on Earth lives in the ocean. The exact size of this large proportion is unknown, since many ocean species are still to be discovered. The ocean is a complex three-dimensional world covering approximately 71% of the Earth’s surface. The habitats studied in marine biology include everything from the tiny layers of surface water in which organisms and abiotic items may be trapped in surface tension between the ocean and atmosphere, to the depths of the oceanic trenches, sometimes 10,000 meters or more beneath the surface of the ocean. Specific habitats include estuaries, coral reefs, kelp forests, seagrass meadows, the surrounds of seamounts and thermal vents, tidepools, muddy, sandy and rocky bottoms, and the open ocean (pelagic) zone, where solid objects are rare and the surface of the water is the only visible boundary. The organisms studied range from microscopic phytoplankton and zooplankton to huge cetaceans (whales) 25–32 meters (82–105 feet) in length. Marine ecology is the study of how marine organisms interact with each other and the environment.

Marine life is a vast resource, providing food, medicine, and raw materials, in addition to helping to support recreation and tourism all over the world. At a fundamental level, marine life helps determine the very nature of our planet. Marine organisms contribute significantly to the oxygen cycle, and are involved in the regulation of the Earth’s climate. Shorelines are in part shaped and protected by marine life, and some marine organisms even help create new land.

Many species are economically important to humans, including both finfish and shellfish. It is also becoming understood that the well-being of marine organisms and other organisms are linked in fundamental ways. The human body of knowledge regarding the relationship between life in the sea and important cycles is rapidly growing, with new discoveries being made nearly every day. These cycles include those of matter (such as the carbon cycle) and of air (such as Earth’s respiration, and movement of energy through ecosystems including the ocean). Large areas beneath the ocean surface still remain effectively unexplored.

The study of marine biology dates back to Aristotle (384–322 BC), who made many observations of life in the sea around Lesbos, laying the foundation for many future discoveries. In 1768, Samuel Gottlieb Gmelin (1744–1774) published the Historia Fucorum, the first work dedicated to marine algae and the first book on marine biology to use the new binomial nomenclature of Linnaeus. It included elaborate illustrations of seaweed and marine algae on folded leaves. The British naturalist Edward Forbes (1815–1854) is generally regarded as the founder of the science of marine biology. The pace of oceanographic and marine biology studies quickly accelerated during the course of the 19th century.

The observations made in the first studies of marine biology fueled the age of discovery and exploration that followed. During this time, a vast amount of knowledge was gained about the life that exists in the oceans of the world. Many voyages contributed significantly to this pool of knowledge. Among the most significant were the voyages of HMS Beagle where Charles Darwin came up with his theories of evolution and on the formation of coral reefs. Another important expedition was undertaken by HMS Challenger, where findings were made of unexpectedly high species diversity among fauna stimulating much theorizing by population ecologists on how such varieties of life could be maintained in what was thought to be such a hostile environment. This era was important for the history of marine biology but naturalists were still limited in their studies because they lacked technology that would allow them to adequately examine species that lived in deep parts of the oceans.

The creation of marine laboratories was important because it allowed marine biologists to conduct research and process their specimens from expeditions. The oldest marine laboratory in the world, Station biologique de Roscoff, was established in France in 1872. In the United States, the Scripps Institution of Oceanography dates back to 1903, while the prominent Woods Hole Oceanographic Institute was founded in 1930. The development of technology such as sound navigation ranging, scuba diving gear, submersibles and remotely operated vehicles allowed marine biologists to discover and explore life in deep oceans that was once thought to not exist.

Tunisia has a 1,000 km-long coastline and holds a central position in the Mediterranean Sea. The country is unusual in that it has access to both the eastern and western Mediterranean.

The Mediterranean, which supports several industries such as fishing, tourism and maritime transport, is threatened by intensive, seasonal fishing as well as urban, industrial and tourist development. This has resulted in stagnation of fish production around the 110-tonne mark with over-fishing of bottom-dwelling species, pollution and erosion of certain coasts as well as problems of conflict over the use of the coast.

These issues leave Tunisia faced with the challenge of finding a balance between social and economic development and the preservation of the marine environment. Tunisia has made several provisions and undertaken scientific research with the aim of understanding the potential and problems of the marine environment and of trying to find suitable solutions for the problems posed.

Painted comber

The painted comber (Serranus scriba) is a species of marine ray-finned fish, a sea bass from the subfamily Serraninae, classified as part of the family Serranidae which includes the groupers and anthias. It is found in the eastern Atlantic Ocean, the Mediterranean Sea, and the Black Sea. Confusingly, a synonym of this species is Perca marina, but that name (as Sebastes marinus) has incorrectly been used for a separate species, the rose fish.

The painted comber has a laterally compressed, elongate body with a pointed snout. The dorsal fin has 10 spines and 4-16 soft rays and the anal fin has 3 spines and 7-8 soft rays. The caudal fin is truncate. It has a very large mouth for its size, which has many sharp teeth, and is protractile. The overall color may be grey, purplish or reddish with 5-7 dark brown bars on the flanks. The head is marked with many narrow, wavy blue lines and red blotches. The dorsal, anal and caudal fins are marked with red dots. There is a diffuse, purplish-blue blotch in the middle of the body. The pelvic and pectoral fins are normally uniform pale yellow. The maximum recorded fish measurement is 36 centimeters (14 inches), although 25 centimeters (9.8 in) is more typical.

The painted comber is found in the eastern Atlantic Ocean where its core range extends from the Straits of Gibraltar to Senegal, including the Canary Islands but it occurs as far north as the Bay of Biscay. Its range extends into the Mediterranean and Black Seas.

The painted comber occurs over rocky bottom and among beds of Posidonia at depths of 5 to 150 metres (16 to 492 feet). It normally spends the day sheltering in rocky caves and is normally either solitary or found in small groups. It emerges at dusk to hunt. It is a carnivorous species which is a territorial ambush hunter and has a diet made up of cephalopods, bivalves, crustaceans, fishes, and worms. It is often used to indicate sites occupied by octopuses as it waits at the entrance scavenging the octopus’s discarded parts of shellfish. The spawning season runs from late spring to early summer with the eggs being laid under stones near the shore. It is a synchronous hermaphrodite, i.e. each individual has both male and female gonads and may be capable of self-fertilization. They have a maximum life expectancy of 16 years.

Common octopus

Te common octopus (Octopus vulgaris) is a mollusk belonging to the class Cephalopoda. Octopus vulgaris is the most studied of all octopus species. It is cosmopolitan, that is, a global species, which ranges from the eastern Atlantic, extends from the Mediterranean Sea and the southern coast of England, to the southern coast of South Africa. It also occurs off the Azores, Canary Islands, and Cape Verde Islands. The species is also common in the Western Atlantic. The common octopus hunts at dusk. Crabs, crayfish, and bivalve mollusks (two-shelled, such as cockles) are preferred, although the octopus eats almost anything it can catch. It is able to change colour to blend in with its surroundings, and is able to jump upon any unwary prey that strays across its path. Using its beak, it is able to break into the shells of shelled mollusks. Training experiments have shown the common octopus can distinguish the brightness, size, shape, and horizontal or vertical orientation of objects.

Octopus vulgaris grows to 25 cm (10 inches) in mantle length with arms up to 1 m (3.3 feet) long. It lives for a couple of years and may weigh up to 9 kg (20 pounds). Mating may become cannibalistic. O. vulgaris is caught by bottom trawls on a huge scale off the northwestern coast of Africa. More than 20,000 tonnes (22,000 short tons) are harvested annually.

The common octopus hunts at dusk. Crabs, crayfish, and bivalve mollusks (such as cockles) are preferred, although the octopus eats almost anything it can catch. It is able to change colour to blend in with its surroundings, and is able to jump upon any unwary prey that strays across its path. Using its beak, it is able to break into the shells of shelled mollusks. It also possesses venom to subdue its prey.

They have evolved to have large nervous systems and brains. An individual has about 500 million neurons in its body, almost comparable to dogs. They are intelligent enough to distinguish brightness, navigate mazes, recognize individual people, learn how to unscrew a jar or raid lobster traps. O. vulgaris was the first invertebrate animal protected by the Animals (Scientific Procedures) Act 1986 in the UK.

The common octopus has world wide distribution in tropical, subtropical and temperate waters throughout the world. They prefer the floor of relatively shallow, rocky, coastal waters, often no deeper than 200 m (660 feet). Although they prefer around 36 grams per liter (0.0013 lb/cu in), salinity throughout their global habitat is found to be between roughly 30 and 45 grams per liter (0.0011 and 0.0016 lb/cu in). They are exposed to a wide variety of temperatures in their environments, but their preferred temperature ranges from about 15 to 16 °C (59 to 61 °F). In especially warm seasons, the octopus can often be found deeper than usual to escape the warmer layers of water. In moving vertically throughout the water, the octopus is subjected to various pressures and temperatures, which affect the concentration of oxygen available in the water. This can be understood through Henry’s law, which states that the concentration of a gas in a substance is proportional to pressure and solubility, which is influenced by temperature. These various discrepancies in oxygen availability introduce a requirement for regulation methods.

Primarily, the octopus situates itself in a shelter where a minimal amount of its body is presented to the external water. When it does move, most of the time it is along the ocean or sea floor, in which case the underside of the octopus is still obscured. This crawling increases metabolic demands greatly, requiring they increase their oxygen intake by roughly 2.4 times the amount required for a resting octopus. This increased demand is met by an increase in the stroke volume of the octopus’ heart.

The octopus does sometimes swim throughout the water, exposing itself completely. In doing so, it uses a jet mechanism that involves creating a much higher pressure in its mantle cavity that allows it to propel itself through the water. As the common octopus’ heart and gills are located within its mantle, this high pressure also constricts and puts constraints on the various vessels that are returning blood to the heart. Ultimately, this creates circulation issues and is not a sustainable form of transportation, as the octopus cannot attain an oxygen intake that can balance the metabolic demands of maximum exertion.

Pilgrim hervia

Cratena peregrina, commonly called the pilgrim hervia, is a species of sea slug, an aeolid nudibranch, a marine gastropod mollusk in the family Facelinidae. Its average size is between 3 and 5 cm. The body is thin and slender, with a long sharply pointed tail. Its body coloration is milky white with 8 to 10 clusters of dorsal cerata which can be bright red, purple, brown or blue, with the tips coloured in luminescent blue. Those cerata act like gills, and each one contains a terminal outgrowth of the digestive gland, a diverticulum.

The head, which is the same colour as the body, has a pair of bright orange rhinophores, and with two whitish long buccal tentacles, which look like horns.

This species occurs in the Mediterranean Sea and in the eastern Atlantic Ocean from the Channel south to Senegal. This sea slug prefers to live on rocky bottoms and slopes in clear and well-oxygenated water, between 5 and 50 m in depth. The pilgrim hervia feeds on hydroids in the genus Eudendrium.

European squid

The European squid or common squid (Loligo vulgaris) is a large squid belonging to the family Loliginidae. It occurs abundantly in coastal waters from the North Sea to at least the west coast of Africa. This species lives from sea level to depths of 500 m (1,600 feet). Its mantle is up to 40 cm (16 inches) long. The species is extensively exploited by commercial fisheries.

Loligo reynaudii, the Cape Hope squid, was previously treated as a subspecies of L. vulgaris.

The European squid has a long, moderately slender and cylindrical body. Rhomboid fins comprise two-thirds of the mantle length, though locomotion is via jet propulsion. The posterior border is slightly concave. The head is relatively small and has large eyes which are covered with a transparent membrane. Like almost all squid, this species has ten limbs surrounding the mouth and beak: eight are relatively short arms, and two, which form the tentacles, are long, as they are used to catch prey. The fourth left arm of males is a hectocotylus. The European squid can grow up to 30–40 cm in the mantle length, but more usually they are 15–25 cm long. The males are generally bigger than the females and exhibit more rapid rates of growth.

The colour of the European squid is greyish-transparent or reddish, depending on the expansion of chromatophores in the dermis. Males have small chromatophores on their mantle.

The European squid is a neritic, semidemersal species, which undertakes distinct horizontal and vertical migrations, depending on the environment. In the Adriatic Sea, European squid can be found above various substrates, from sandy through to the muddy bottoms.

L. vulgaris is found throughout the Mediterranean and in the eastern Atlantic Ocean from the North Sea to the Gulf of Guinea. In British waters, it is mainly found in the Irish Sea, along the south coast of England, and off northern Scotland.

The European squid is a commercially valuable species. It is caught in multispecies trawl fishing throughout the year and, seasonally, in small scale and recreational fishing with a variety of gear.

In the Adriatic Sea, the total annual catch of the species is around 1,000 to 1,500 tonnes. This is very variable and is probably linked to the annual reproduction cycle that is typical for many cephalopods.

 

SOURCES

ADDITIONAL INFO

 

La Poste Tunisienne

Wikipedia (linked above)

 

 

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.