23 Jan

Multi – Bristled Worm This species, which belongs to the Serpulidae family, is one of the most beautiful and colorful reef inhabitants. The world’s coral reefs are characterized by the many Christmas-tree worm colors, blue, yellow, orange, purple, brown, red, among others. They are very different to the other bushy and especially lumpy coral species […]

Spanish Dancer – Hexabranchus sanguineus

Very few divers have seen a Spanish dancer dancing; those who have had this opportunity immediately understand the origin of its popular name. The source of its scientific name is Hexabranchus sanguineus from the Latin, Hexabranchus = six gills, and sanguineus = blood colored. This marine dance is reminiscent of the famous flamenco dance, including the body twists, exactly like the gypsies who started dancing in this folkloric style hundreds of years ago.
The Spanish dancer belongs to a group called “sea slugs” (basically snails without shells). The dancer spends most of its time crawling on the sand at the foot of the reef in its search for its favorite food – sponges: these are primitive creatures, living in a fixed place, nourished by filtering small food particles in the water – the filtering is performed by using both an entry, and an exit filter. The dancer can be found in depths of up to 50 or more meters, a depth that most divers do not reach.
The dancing slug can be found anywhere from the tropics to the Indo-Pacific. The Spanish dancer was first identified in the Gulf of Eilat in 1828 by Ruppel and Leuckart. It is one of the largest in its group, and it reaches a length of 40 cm; a few even reach a length of half a meter, or more. This naked snail has six external gill clusters in the rear section of its body. It retracts, and extends its gills from a type of centipede formation that protects the gills. Here too, one notices the fascinating similarity between dancers above, and below water: the gills extend in the same manner as “La Gitana” (the flamenco dancer) waves her fan marking the start of the dance. The dancer has hornlike formations on the front of its body that act as feelers which the Spanish Dancer uses to “smell” the water, and find its favorite food. The Dancer’s eyes, which are more than likely used to find a mate, are situated at the base of these horns.
It feeds mainly on poisonous sponges which it eats while it crawls slowly along the sea floor, leaving a trail of gnawed crumbs.
The Spanish Dancer can be identified by the color of its bright red cloak, and its edges, which are white in some species. In most cases, it is difficult to identify the dancer when its cloak is closed. In certain areas of the world, especially Hawaii and Tanzania, they can also be found in shades of yellow.
The sophisticated dance performance can only be seen when it is escaping from predators. When this slug feels threatened, it swims with a twisting body motion that helps it to maneuver towards a safe haven in the water. The Spanish Dancer received its name because of its fascinating swimming movements. Very little is known about the reasons for its bright colors, most researchers agree that the colors are a warning sign to other fish that they are toxic. In this case the warning is applicable, since while eating the sponges it produces venom made from the different toxins in the sponges with which it protects itself, and its offspring. The Dancer’s eggs are protected from predators by the self-defensive venom inside the egg.
The slug’s similarity to dancers does not end here: the eggs it lays resemble the orange / red lace that gypsy dancers used to add to the hems of their dresses.
In every batch, there are thousands of eggs from which the young slugs hatch. In the initial stage they swim until they change their shape, after which they settle on the seabed, and become young slugs. In principle, all slugs are all hermaphrodites, meaning, each individual has both female and male organs. Despite their ability to self fertilize, in most cases, they prefer donating, and receiving sperm to maximize the diversification of their genes. Sometimes, by looking closely, one can see small crustaceans that live on their bodies, feeding on the food particles that stick to the mucus covering its body. These crustaceans have a red color that makes it difficult to identify them on the slug’s body, and this also serves to protect the crustaceans from predators for most of their lives.

Author: Aviv Levy – Scientific Manager, Underwater Observatory Marine Park

23 Jan

These are fish with a clumsy bodies that live on the sea bed; they are rarely detected because they are beautifully camouflaged in a tangle of seaweed and sea grass, or amongst the rocks where they normally live. Some species are as long as 45 cm. They have two characteristic distinguishing marks; there is a […]

23 Jan

The essential value of marine plant life is in its ability to create photosynthesis (a chemical reaction that takes place in plants, the principle of which is turning inorganic mineral matter and water into organic/carbohydrate matter, under the influence of light and by means of the chlorophyll pigment); this is the same wonderful chemical process […]

The starfish is characterized by a five-sided circular symmetry, which means that each one of the five arms is identical to the others and they all encircle the area of the central ring. The water legs are located inside canals that pass through the bottom part of the starfish’s arms. There are suckers on the base of the feet which enable the starfish to attach itself to a surface. The arms are flexible and are capable of bending and folding and this flexibility allows them to move over the surface. The stomach is composed of two pockets: the upper and the lower stomach. A digestive gland, through which food is absorbed, is connected to the upper stomach.

Starfish feed on corpses, organic material, or they prey on invertebrates such as sponges, coral, etc. They swallow their prey whole, and some starfish can extract their stomach from within their body and eat their prey outside of their body. Starfish, which feed on oysters, can insert their stomach into the space between the two shells of the oyster. They swallow their prey – snails and oysters – with their innards and their legs. After digesting the organic tissue, they release the shells through their mouth into the surrounding water. (Most of them do not have an anus).
The body is covered in small thorns and pincers which they use to clean the body from sediment and foreign particles that settle on it.

The starfish has excellent recuperative (regeneration) qualities. An arm that breaks can be regenerated and fully replaced.

Sexual reproduction is carried out by the starfish by dividing its body (the main disk) into two parts, with each part then becoming a whole Star. During sexual reproduction it releases sex cells into the water, and plankton larvae develops from the fertilized egg.

It is easy to identify the members of a school of true jellyfish (scyphozoa). They are typically thatch or flattened bell shape, covered with upside down short antennae. The mouth of the jellyfish is protruding and hangs like a clapper on its underside. The mouth is split into four lobes, which are equipped with many stinging cells. These cells are designed to paralyze the prey – plankton and fish.

Most jellyfish float in the water like plankton. One of the most common species in the Gulf of Eilat is the Golden Moon jellyfish – Aurelia – which, during the spring season, arrive in Eilat in gigantic swarms, evoking considerable anxiety amongst people bathing in the sea, but this is not justified. The degree of burn from a jellyfish sting is minimal, and it poses no threat to human beings.

The Aurelia reaches up to 40 cm in width, and the tentacles can reach up to the width of the jellyfish in length. Jellyfish have a translucent purple hue. They feed on plankton which is trapped by the saliva excreted from their body. They are gender-assigned organisms (male or female) and their fertilization is internal, with the sperm cells entering through the mouth of the female. The eggs become planula-larvae and these are exited from the body of the female through the mouth. It is possible to see the planula below the body of the transparent bell-shaped jellyfish.
The lifespan of a jellyfish is no more than a year, and a large proportion of them live only a few months.
There is another type of jellyfish which lives here and that is the Cassiopea – ‘Upside Down’ jellyfish, which can reach 12 cm in size. The tentacles are located on the top and it lives inversely from the Aurelia. The Cassiopea lives in shallow water of up to 10 meters, primarily near marine foliage. When it swims, the bell is turned inside out. It does not have a mouth in the center, as does the Aurelia, but has several mouths located on its eight tentacles.
The fertilization season for jellyfish is from April until August. This is the period when their sting is stronger. They are more poisonous than the Aurelia jellyfish and their color derives from the symbiotic algae that are to be found inside the tissue.

The genus comprises about 12 genera of 40 species. In Eilat we have five species: Picasso Trigger Fish, Blue Trigger Fish, Orange Striped Trigger Fish, and Blue Throat Trigger Fish.

Trigger fish have flat and tall bodies and are diamond shaped. Their eyes are in the upper part of the head which prevents them being hurt when they devour sea porcupines. Their skin is tough and is covered in large bony scales. Their mouth is relatively small and the lips are thick, both are tough. They are 30 to 75 centimeters in size.

The trigger fish are characterized by the two fins on its back. On the forward fin there are three spikes and the first of them is very developed. This spike can be locked in place when erect by the second spike that faces forward and acts as a lock to keep it erect. With this spike the trigger fish holds onto cracks between corals when hiding.

They feed on mollusks, shrimp, coral, various sea porcupines that they dismember using their strong teeth, and algae that it scrapes off the coral. It finds its prey by blowing streams of water at the target area.

The way it eats the sea porcupine which has long black spikes is very interesting. The fish blows a strong jet of water that overturns the porcupine and so exposes its underside, which has short spikes.

In the breeding phase, the male digs a hole in which the female lays her eggs. These are guarded by the male for a day or more until they hatch and the fry move into the open sea. During this period the male can be aggressive towards anything that approaches the eggs. The meat of many of these species is poisonous and not suitable for consumption.

Picasso Trigger Fish
A species of the Trigger fish genus that is impressive in color and shape. It is 30 centimeters long, active by day and lives a solitary life in the shallow waters of the coral reefs.
It is characterized by the alternately striped blue and black lines in its eyes. Around the eyes, and the last three protruding rows of scales at the base of the tail, are decorated with a yellow – orange color. It has thick yellow lips.
It feeds on mollusks, shrimp and coral.

Sea horses are fish by every definition. In the gulf of Eilat there are at least 7 species while worldwide there are about 200 species.
The head of the sea-horse resembles that of a horse and that is the origin of its name. Its body is covered partly with spikes and partly with lumps.
Unlike most fish, they have an outer skeleton that is designed to give them protection from predators. It does not have teeth in its mouth and because of the complexity of its body it is a weak swimmer. Fins on its front and back are used to swim in the ocean and the tail is used to grasp with. (It swims upright.)
Sea horses can change their coloring in a very short period of time, from yellow brown to be bright and colorful. The objective of the color change is to match the surrounding colors and help camouflage it from its enemies.
It is mainly found in fields of marine grass where the currents are weak and where their camouflage can be optimized.
They are between a half a centimeter and four centimeters in size.
They feed mainly on tiny shrimp (plankton) and invertebrates that they suck in through their long mouths.
They live for between two to four years.

The Pregnant Male
The abdomen of the male is round and barreled and has a pouch. The abdomen of the female has a laying tube. At the breeding time, the male begins a “courting dance” to indicate to the female that he is ready. They wrap around each other and the female lays her eggs in the male’s pouch, and then the male fertilizes the eggs.
The male incubates the eggs in his pouch and during this period the embryo feed on the nutrients within the egg.
After 10 days to two weeks, depending on the temperature of the water, little fry about 1 cm in size are hatched in the pouch. The seas horse fry leave the pouch and disperse in shallow waters.
Their unique shape is already recognizable at this early age, except for their snout that grows with age.

In the vicinity of the Eilat corals, there are 2 of the 7 species
Porcupine Sea Horse –it is characterized by 4 spikes on the top of its head. Its body and head are covered with many sharp spikes.
Smooth Sea Horse – has one spike on the top of its head and its body has no protruding spikes and is more or less smooth.

Fish from the butterfly family are among the most beautiful and colorful reef fish.
These fish were named after the butterfly because of their multi-colored hues, and their hovering swimming action.
Its body shape is elliptical (its height and length are almost identical), and it has flattened sides which easily allows its to pass through the coral’s cracks and narrow passages.
The front of its head ends in a pointed snout at the tip of which it has a small mouth with many strong teeth, which are suitable for munching algae and small animals on the coral reef.
The butterfly fish have a variety of bright colors, and most of them have a line or an “eye-shadow” which camouflages the pupil and serves as an eye protector.

Its body colors are striking, and are a means of communication with other animals, announcing their presence while they protect their permanent habitat.
The butterfly fish have a diverse social structure, some of them move along the reef alone, some live as couples, and others travel in schools.

The butterfly fish are active during the day, and at night they hide in the reef’s crevices. The different types of food among the many species create an ecological separation which decreases the level of aggression between the species. They feed on coral polyps, zooplankton, algae plankton, and mollusks.
They reproduce by releasing eggs and sperm into a body of water. The eggs are plankton.
In the Gulf of Eilat there are 10 known types of butterfly fish, some of which are: the striped butterfly fish, the crown butterfly fish, the antenna butterfly fish, and the masked butterfly fish.

The Striped Butterfly Fish
This type of butterfly fish is indigenous to the Red Sea, it moves in groups of 2-6 along the reef wall, up to a depth of 20m. Its name is derived from the prominent white stain on its forehead, and the fish reaches an adult length of 22cm.
It has a dark stain on its head which covers its eyes, and dark diagonal stripes divide its yellow body.
During the breeding season they gather in large groups.
They are also active at night, and they feed mainly on coral stone polyps, sea anemones, multi-bristled worms, sponges, and algae.

The Crown Butterfly Fish
This is a small fish, up to 12cm in length. It is active during the day, lives in a permanent spousal relationship, on and in front of the coral reef, up to a depth of 12m.
Its eyes are camouflaged by an eye strip that crosses the pupil, and it has a black stain on its forehead. It gets its name from the large red stain on the rear section of its body. The rest of its body is colored in yellow shades with dashed brown stripes, and it has a yellow tail fin with a red stripe on its edge.
It feeds on crustaceans and coral polyps.