The sharks, above all after the diffusion of films that have given a distorted image of their behaviors, have been considered as murderous raiders, in the continuous search of food, activity that would bring them to feed of anything they see behind, without distinction..
Reality is very different; these elegant cartilagineous fishes are only great raiders, inserted to the vertexes of the food chain of the environment in which they live and as such they have some notable offensive potentialities. Every kind of shark uses to feed itsels of determine preys, which are outcast with techniques that nothing leave to the case or to the fatality and the search of food, as in every living organism, spends important times within the life of these animals. It is not plundered everything the shark see, but in the 99% of the known kinds there is a real discrimination, based on instincts and preferences.
The man in fact, not doing part of aquatic fauna and probably because of the little adipose fabric present in his bodily structure, doesn't reenter in the preys of any shark! Only some kinds that reach great dimensions can represent a danger for the man, as all the great raiders that live on the earth. (The 50% of the sharks doesn't overcome the meter of length, the 82% doesn't overcome the 2 meters, and only 4% reach superior dimensions to the 4 meters, such to represent a serious danger).
Every year, in all the seas of the globe, there are about 60 attacks, about 0-6 deadly. In almost all these cases the death is caused by the gravity of the first and only bite that the shark uses, together with the other senses, to become account of that that is found in front, because it really uses to select its preys and to discriminate what doesn't reenter in its diet. The shark in fact usually doesn't continue the attack and it doesn't swallow the prey but it gets further..
There are very dangerous situations that can attract the sharks and to increase the risk of an attack, as during a food frenzy, in presence of issue of sounds to low frequency or with blood and other bodily liquids in water.
Also the outline of a surfer that swims with the hands toward the outside above its table can be exchanged for that a sea mammal, prey aspired by the great sharks..
Some attacks are known to underwater fishermen that swam in waters where great quantity of blood had been poured because of their fishing and where the dying preys were fixed dangerously to the belt..
All these considerations, united to the datum of fact what the man capture and kill every year around 100 million sharks, to feed the food and commercial market, can let us think that currently the shark is transformed by great raider to.. great prey.
Many aspects of the sharks biology and ethology are not very well known, above all because of the difficulty to study these fishes in their natural environment and for their bashful and solitary behavior Here you can read many informations about their evolution, biology and morphology.
There are about 450 kinds of
Sharks, an about fifty of which present in the Mediterranean, with
dimensions that go from the only 24 cm of the Pygmy Shark from the
ribbon tail (Eridacnis radcliffei) to the 18 meters of the Whale
Shark (Rhincodon typus), that represents with these measures also
the greatest fish actually known. (sharks
possess the same senses of the man, more other two to us strangers, that
are the ability to perceive the electric fields and the waves of
pressure spreaded in water.
is covered with placoid scales, also called like small teeth. They have
the same structure of those of greater dimensions, that are found in the
In the sharks jaws the teeth are prepared in more file, six and the last toward the inside of the mouth are generally tilted, covered by a fold of fabric and not yet completely developed. During the growth the tooth is subject to a move in ahead for the continuous formation of the gengival fabric to which is connected. In their advancement they progressively straighten, because of the simple mechanical tension, until they don't become entirely functional. After a few times the teeth of the anterior lines are destined to fall, following traumatic breakups or spontaneously and the biologist think they are singly replaced every 8-15 days, more frequently in the youngest samples. The biologist think that some kinds of sharks renew a whole line of teeth to the time.
The day December 23 year 2004, in the north of the
Macquarie Islands (near Australia) it happen one of the strongest
earthquakes that can be remembered in the history of that angle of the
planet. The magnitudo is 8,5 of the Richter scale, a very high value and
in the following hours there are many arrangement shakes.
On December 26 in fact it happen an earthquake with
epicentre in northwestern of the island of Sumatra, in the backdrops of
the Indian ocean, it frees an energy equal to that that would be had
with the explosion of 20000 atomic bombs..
The tsunami, from the Japanese “wave of the port”,
can be caused, as in this situation, from a strong submarine earthquake
that upsets and it moves upward very violently the column of impending
water from the lower part.
The areas struck by the tsunami of December 26 have been Thailand,
India, the Sri Lanka, Indonesia, the Malesia, the Maldives and the waves
have also arrived in Africa, on the coasts of Somalia, Kenya and
(Zones struck by the
tsunami. The red zone points out the
All the coral formations of these zones, the richest of the globe as biodiversity (with around 1700 different kinds of fishes and 400 of madrepore) have harshly been stricken from the destroying strength of the waves and on them there are poured great quantities of mud, sand and refusals.
The waves of return that have invaded the dry land have in fact dragged in water deposits, refusals, poisons and hydrocarbons torn from the industries and from the man residences. They are still few, to two months from the event, the underwater surveys effected to know the state of the flora and fauna, but they immediately result evident the great quantities of sand that have covered the coral reefs..
This coverage can put to risk the survival of the same coral, in fact it
doesn't allow the algas zooxantelle that live inside of it to receive
the light of the sun and to effect the chlorophyllose photosynthesis.
(Images drawn from the
Italian giornal “Il corriere della sera”: the anomalous wave reaches the
If this situation persisted different months the algas they would risk to die, putting also in serious difficulty the coral that he/she lives in symbiosis with them, receiving important organic substances for the development and for the construction of the barrier.
A solution could be that to organize a plan of “cleaning” of the corals that involves numerous and willing scuba divers making to literally return to the light these wonder of the nature. We hope that the strong tides that are present in a lot of of these zones can naturally polish up the barrier and to contribute to the return of a situation of normalcy.
The strength of the waves has caused besides the
breakup of many branched corals, landslides of portions of reef (even
stop of 1-2 ms cubes eradicated by the walls) with the accumulation of
them on the backdrops, inclusive those of the passes, that have
decreased their depth of 2-3 meters in some zones!
(Images of the coral
barrier struck by the tsunami, with fans and corals branched broken)
The numerous destroyed areas could have left besides the abundant tropical fauna of which this area is rich without shelter, as for example the parrot fish that is usual to use the hollow among the corals as mend for the night. This fish nourishes him of algas that it tears from the barrier with its horny beak and the zones where usual feed could have been destroyed.
The lobster as other kinds of shellfishes and tropical molluscs that hide him in the ravines of the madrepores, could be found again without habitat and forced to adapt again and to colonize other zones. The "barracuda", great raider that can reach 2 meters length that it stirs at night in flock during the day and hunting, needs to live in clear waters and the movements caused by the tsunami could now create difficulty.
Which zones has been mostly struck by the violence of the tsunami ?
The Asian area and particularly the coral barriers of the islands Andamene and Nicobare have mostly been reached by the violence of the anomalous waves. Here numerous bushes of corals have been observed branched broken, heaps of fragments, deposits in the backdrops and portions of collapsed reef and partially covered of sand..
In the most distant areas, reached by a smaller violence of the waters, the coral barriers seem to have brought damages of smaller entity.
To the Maldives for instance, in base to the preliminary study effected by the Marine Science Group of the university in Bologna, the damages would be more contained and they would represent only the 6% of the whole coral system, recoverable in brief times.
In this case a function of protection of the island of Sri Lanka is hypothesized. The island would have braked the run of the anomalous waves and also the particular conformation of the depths backdrops of the Maldive.
These are the effects that the impact of the anomalous waves has directly produced and indirectly on the natural environment of the coral barrier of the Asian area. Which have been the direct effects of the arrival of the tsunami on the sea fauna and earthling instead?
The results of the first searches seem amazing. All the animals that had the possibility to get further in hurry would have done it just before the arrival of the anomalous waves reducing their losses to very low levels. As it surely regards the sea fauna some fishes, molluscs and shellfishes of small dimensions will have surely been beaten with deadly result on the barrier but the majority of them will have perceived with good advance the arrival of the masses of water. This thanks to their acute senses, above all the ability to gain tall or low frequencies that would have alerted them with good advance giving them the permission to shelter in sure depht waters.
(Obviously the underwater surveys have noticed that in some zones there is no more abundance of fishes but this situation it is probably connected to the alteration of the habitat, with the destruction of shelters and dens in the barriers, referable situation to normalcy in brief times).
These “information” about the arrival of so that anomalous situation have also been perceived by the terrestrial animals, making them get further in territories distant from the coasts and to greater heights on the level of the sea.
In the Yala National Park of the Sri Lanka in fact, house of hundreds of buffalos, elephants, crocodiles, leopards, monkeys and other numerous mammals there has not been found anybody trace of carcasses even if the tsunami in that territories of the park has arrived with great violence flooding it almost entirely!
- “Tsunami Survey Expedition, Maldivian Coral Reefs, 2 weekses after” Marina Science Group.
- “The risk tsunami” of L. Bignami.
- Articles: “Tsunami, thing has favorite the Maldives” and “You truth on the Maldives.”
- Article: “The sixth sense has saved all the animals.”
The alarm launched the last 26 December 2004, after the strong tsunami caused by a submarine earthquake of magnitudo 8,5 of Richter staircase in the area of the Asian Southeast, is judged excessive today.
The coral reef in fact, present on the planet from more than two million years, seems to have overcome this catastrophic natural event.
Particularly two studies realized in Thailand confirm that few more than the 10% of the stricken zones (on 174 examined sites) have brought remarkable damages (stricken above all the Phi Phi and Surin islands)
However also in these sites the coral reef and its inhabitants are "reacting" and in relatively brief times this environment should return to the ancient shines.
The strong tides, present in many sites influenced by
the waves of return of the tsunami, are getting further the refusals,
the polluting agents and the sands that has been deposited above the
corals, allowing the asimbiotic algas and therefore to the same barrier
to survive. Also the tropical fauna would be again populating the reef,
doing so to return intact that unbelievable biodiversity of which this
environment has always been characterized.
(Images from the coral reef)
whale shark (Rhincodon typus) is currently the greatest known
Despite the dimensions, the whale shark is harmless, he is a fish that
feeds him of plankton and small fishes that the shark captures swimming
with the open mouth and making the water pass through the filtrator
apparatus connected to the gills.
An Australian search has made to emerge an alarming situation towards
the whale shark. The Australian Institute of Marine Sciences, analyzing
the relative statistic data to every animal sighted in the sea reserve
of Ningaloo (northwest of Australia), has officially communicated that
the middle ransom of the whale shark is reduced by seven to five meters.
The solution, as for other kinds of animals submitted to indiscriminate
hunting, could be to turn fishing activity into tourist observation,
transporting tourists in a "shark watching" that could save the life to
these proud and mysterious inhabitants of the sea and also bring new and
meaningful economic resources. In the alone reserve of Ningaloo the
"shark watching" would be able in fact to produce a flow of around 60
million of Euro for year!
medie: 7-12 m.
Into the sea there are some microscopic organisms,
"relatives" to the soft natural sponges (Spongia officinalis) with which
our grandparent usually washed, that however have lot of differences..
The excavating sponges are organisms, belonging to the phylum of the Porifera, that have the ability to puncture the carbonatic substrata, mineral and biogenic, present into the sea. The substratum can be constituted, over that from rocky backdrops, also from shells of Molluscs, algas corallinacea and calcareous skeletons of madrepore and corals.
The perforation happens through sour secretions that
allow the sponge to create a complex net of rooms and galleries inside
which the development happens.
The body of the sponge is sustained by a whole fibers of "collagene",
the "SPONGINA" and from inorganic elements, the "SPICOLES". The
calcareous spicoles are the most primitive, while those made of silisium
are the most frequent and both the types, with dimensions and
characteristic forms for every kind, are fundamental elements for the
systematic recognition of the sponges.
Excavating sponges: Cliona orientalis, galleries into a madrepora,
staircase 4 mm.
The excavating sponges of some kinds, under favorable
conditions, not finding the space anymore to dig new galleries, continue
their development to the outside assuming the typical encrusting form.
In the coral barriers the growth of the madrepores is hindered, producing a weakening of the colonies and an acceleration of the demolitive action of the waves. The shells of the Molluscs result particularly fragile, weaken and they have the tendency to break themselves with serious economic results in the areas where the breeding is practised.
To have information about the spicoles, the fabric of
the sponge is dissolved in hot nitric acid and what remains is seen
through an electronic microscope.
Very beautiful forms, elegant, eccentric, a fabulous micro-architecture
that remembers that some crystals of snow for shine and unbelievable
sense of brittleness. (even if in reality they are not fragile,
considering that they result uninjured from the action of the nitric
There are a lot the names that have been given to the
spicoles of various form and dimensions (the dimensions of the spicoles
in image have gone since 5 to the 50 millesimis of mm!). In order of the
greatness we can distinguish them in "megasclere" and "microsclere" and
here following are described some types.
The microscleres can have starry form "pluriraggiata" (aster); the rays
are born from a more narrow central part (euaster, sferaster) or from an
axle more or less folded up (metaster, spiraster), etc..
microrabdi tilostilo, anfiaster,
The Spongia officinalis the "natural sponge" used
especially in past in our bathrooms, has an elastic and soft
consistence, without spicoles, alone "spongina" and it is for this
motive that the contact with the skin doesn't create abrasions or
Effect of the action of the excavating sponges:
The excavation of the carbonate from the boring sponges is an important biological trial in the ecology of the sea. In the tropical and subtropical waters the numerous kinds of excavating sponges are among the principal agents (together with bacterias, algas, molluscs, echinoderma, fishes, etc.) in the processes of erosion of calcareous substrata; particularly in the coral barriers the sponges, balancing or at times overcoming the rates of calcification of the corals, develop a key function in the evolutionary processes.
The active erosion determines the production of great quantities of end calcareous sediment that will go to constitute the coral carbonatic beaches.
The action of weakening of the coral structures, caused by the rooms and by the galleries of perforation, reflects him in the ecological relationships among the corals of the barriers, modifying them: the most fragile colonies (because of attach) can easily be broken and detached by the atmospheric agents and perhaps replaced by other kinds of coral; the corroded superficial parts can be colonized by numerous organisms.
Also in the moderate seas as the Mediterranean the bioerosio of the excavating sponges is important in the rehash and in the evolution of the coast, and it produces meaningful quantity of sediment in the form of fragments to elegant nuisance. The activity of perforation of these kinds can have almost catastrophic effects with remarkable economic lapels in those areas where the breeding is practised (of bivalve, oysters particularly) and the fishing to the red coral. The attached oysters result particularly fragile and they have the tendency to break themselves when they are handled, both during the consumption, and during the phases of the seeding in the breedings of manufacturing oysters of pearls.
Shell (Trochus niloticus) attached by excavating sponges
Articles written by Marco Angelozzi - www.prionace.it
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