Sponges Bristle worms

Cnidarians

Moss animals

Cephalopods

Sea squirts

Fish

Spoon worms

Echinoderms

Gastropods

Chitons

Bivalves

Crustaceans

National park MljetLife in the lakes

The lakes of the island of Mljet are not trully lakes, but an unusual bay which originated from flooding of three karst depressions due to the sea level rising after the last glacial period.The Soline Channel (Solinski kanal) connects the Lakes with the open sea and allows entering and withdrawal of water during high and low tides. Tidal currents are par-ticularly strong and can be seen at the entrance to Great Lake (Veliko jezero) in the area of the Great Bridge (Veliki most).Great Lake covers the area of 1.45 square kilometers and reaches the depth of 46 meters, while Small Lake (Malo je-zero) is 29 meters deep. It is considered that the Lakes are home for some specific organisms that survived from the tropical Tethys sea that covered this area 40 million years ago, like moon jellyfish Aurelia.The Lakes’ coastline is well-indented, dense with forest, especially Alpine pines. “Trees descend from the tops to the surface of the sea, overshading coast; sailing in a boat, you re-ally drift through the forest.”, impression of Ignjat Đorđić, the poet that lived in Dubrovnik at the beginning of the 18th century.

Supralittoral – Supralittoral zone is placed between the highest point of high tide and the highest point of wave spraying. It is constantly above the surface of the sea and thus exposed to the frequent temperature, moisture and salinity changes. In the Lakes, this zone is mostly up to 0.5 meters high due to the weak influence of wind and narrow range of wave splashing. A small number of organisms are adapted to the extreme conditions, like halophilic plants sea lavender, rock samphire and golden samphire and specific animals like small periwinkle, sea roach and poli’s stellate barnacle.

Midlittoral – Midlittoral zone covers the area of tidal ran-ge and its height in the Lakes is up to 0.3 meters. Orga-nisms are adapted to the great oscillations of moisture, temperature, salinity and wave splashing. The solid mid-littoral sea bottom is covered with growth of bluegreen algae which colour the zone in brownish–green and make the bottom slimy and slippery. Characteristic organisms for this area are barnacles, limpets, turbinate monodont, beadlet anemone, marbled rock crab and mussels.

Infralittoral – Infralittoral zone spreads between low tide and the deepest points of the Lakes (46 in the Great and 29 in the Small). The richest area with life forms is the upper part of infralittoral to 5 meters under the surface. Li-ght conditions are favorable to dense population of algae and sea grasses. Numerous species live among them, like bivalves, gastropods, sponges and fish. Deeper than 20 meters there are no more algae and the muddy sea bottom is inhabited only by animal species.

Aplysina aerophoba / yellow sponge

Ircinia sp./ ball sponge

Protula sp./ tube worm

Sabella spallanzani/ tube worm

Actinia equina/ beadlet anemone

Anemonia viridis/ snakelocks anemone

Cladocora caespitosa/ coral cladocora

Aurelia sp./ moonjellyfish

Schizobrachiella sanguinea/ red sea mat

Sphaerechinus granularis/ purple-spined sea urchin

Paracentrotus lividus/ urple sea urchin

Arbacia lixula/ black sea urchin

Holothuria tubulosa/ sea cucumber

Ophioderma longicaudum/ brown brittle star

Marthasterias glacialis/ spiny starfish

Echinaster sepositus/ red starfish

Coscinasterias tenuispina/ blue starfish

Chiton sp./ chiton

Arca noae/ noah’s arc

Lithophaga lithophaga/ date mussel

Ostrea edulis/ native oyster

Pinna nobilis/ pen shell

Pecten jacobaeus/ st. james’s scallop

Venus verrucosa/ warty venus

Cratena peregrina/ hervia

Littorina neritoides/ small periwinkle

Hexaplex trunculus/ purple murex

Bolinus brandaris/ spinous murex

Gourmya vulgata/ common cerith

Monodonta turbinata/ turbinate monodont

Patella sp./ limpet

Palaemon elegans/ prawn

Acetabularia acetabulum/ mermaid’s wineglass

Haliotis lamellosa/ ormer

Octopus vulgaris/ octopus

Bonellia viridis/ green spoon worm

Chthamalus stellatus/ poli’s stellate barnacle

Balanus perforatus/ acorn barnacle

Pachygrapsus marmoratus/ marbled rock crab

Ligia italica/ sea roach

Eriphia verrucosa/ warty crab

Pagurus sp./ hermit crab

Halocynthia papillosa/ red sea squirt

Blennius sp./ blenny

Gobius sp./ goby

Coris julis/ rainbow wrasse

Serranus scriba/ painted comber

Chromis chromis/ damselfish

Diplodus vulgaris/ annular seabream

Symphodus ocelatus/ wrasse

Sarpa salpa/ salema

Epinephelus marginatus/ dusky grouper

Codium bursa/ sea ball

Dictyota dichotoma/ alga dictyota

Halimeda tuna/ alga halimeda

Padina pavonica/ peacocks tail

Valonia utricularis/ alga valonia

Cystoseira adriatica/ alga cystoseira

Crithmum maritimum/ rock samphire

Inula crithmoides/ golden samphire

Limonium cancellata/ sea lavender

Cymodocea nodosa/ lesser neptune grass

Animals

Algae

Plants

WANTED!

Caulerpa taxifolia a fluorescent green alga, has a recognizable stem which spreads horizontally and out of this stem there grow vertical feather-like leaves which are 5 cenimeters to 65 centi-meters long. It outgrows other autochthonous algae, marine plants and sedentary animals what results in the drastical changes of biodi-versity and ecodiversity of the sea bottom. It produces many toxic substances that are pre-venting potential Mediterranean herbivorous from feeding on it which could stop alga’s wi-despreading.

Caulerpa racemosa is a dark green alga with recognizable ramified stem which spreads ho-rizontally and 1 to 20 centimeters long leaves with globular ends. Alga completely outgrows autochthonous algae and sedentary animals what results in the drastical reduction of the sea bottom biodiversity. This invasive species has been found on several places in the Nati-onal Park Mljet. In order to protect the coral reef, the programme of removal of algae in the area of the Soline Channel and entrance to Gre-at Lake.

Caulerpa taxifolia Caulerpa racemosa

Animals and plants that inhabit the coast and the sea from the surface to the depth of several meters are easily visible and reveal astonishing diversity of life, colours and shapes. The coast and the seabed are divided into zones according to their specific ecological conditions.

Cladocora caespitosa is formed of many individual polyps which excrete skeleton composed of calcium carbonate. Altho-ugh this endemic coral is widespread in Mediterranean, the biggest coral reef is in Great Lake near the Great Bridge. It in-habits sandy and muddy sea bottom and

feeds on organic matter while swallowing sediment. The reef is placed between 5 and 15 meters under the surface and covers 650 square meters. Organisms are adapted to the great oscillations of moisture. Diameters of some colo-nies reach more than two meters. Strong currents formed here bring food and oxygen to polyps what contributes to the development of the reef.

Pecten jacobaeus, St. James’s scallop, is a fan-shaped bivalve. As a juvenile it is attached to a substrate, later it is free living lying on the right side of the shell on the sandy and shelly bottom. When an active swimmer, it pushes the water by closing and opening the shell. It swimms

like that while running away from predators, for example sea stars. It is very common in the Lakes.

Paracentrotus lividus, purple sea urchin, always has brownish or purple colour of spines and numerous tube feet which it uses for moving. Its gonades are ta-sty delicacy. It usually covers itself with some objects. It was thought that this characteristic belonged to females, but it

is not true. The reason for doing this is still unknown, one possible explanation is mimicry or UV protection. Arbacia lixula is always pitch black, without tube feet except aro-und oral region. It is not used as food. It feeds on algae and sometimes it can completely browse the whole area. Though it is very common in Adriatic, it is very rare in the Lakes. The reason is still unknown.

Among holothureans, the most common species is sea cucumber, Holothuria tubu-losa. Along the Adratic coast it has many different names, like kacamarin, pistej, kukumar. It inhabits sandy and muddy sea bottom and feeds on organic matter while swallowing sediment. During the

reproduction period it raises one end of its body above the bottom. Males and females simultaneously release their eggs and sperm in the sea.

Epinephelus marginatus, dusky grouper, can be 1.4 meters long and reach the we-ight of 100 kilograms during its 50 years lifetime. All young specimens are females but after 9-12 years they change their sex and become males. It prefers holes and crevices in the rocky sea bottom. During

the summer it moves to shallow water. In the Lakes it can often be seen on the coral reef.

Coris julis, Mediterranean rainbow wra-sse, is the fish with the largest number of Croatian names, more than 130! Ma-lea adults usually reach 25 centimeters and are lively coloured. Females are more frequent, shorter (to 20 centimeters) and brown. They usually come in smaller sc-

hools. They are known for their exceptional curiosity.

Octopus vulgaris, octopus, cephalopod with eight arms, each with two rows of suckers. Octopus is the biggest Croatian cephalopod which can weigh 15 and even 20 kilograms. It likes to hide in holes in front of which it leaves rocks and shells of eaten bivalves and crustaceans. Females

keep their eggs in holes, do not eat during that period whi-ch sometimes results in death. When attacked, it releases ink.

Lithophaga lithophaga, date mussel, an endemic species of Mediterranean whose length reaches 12 centimeters. It lives in rocks where it makes holes by means of its excreted acid. Although this bivalve is very common, it is protected by law. The reason is people’s destruction of the roc-

ky areas it inhabits. Before being protected, it was one of the most valuable delicacies.

Hexaplex trunculus, purple murex, is a common Adriatic marine snail. In ancient times it was especially valuable on sho-reline because its glands were used for getting the special purple dye (crimson). Murex is a vulture which, during the sum-mer, they gather to spawn and lay eggs in

one common sticky pile.

Chromis chromis, damselfish, comes in schools along the rocky shore and is also common above the meadows of le-sser Neptune grass. Juveniles are purple blue, and, before becoming completely black adults, they have light blue stripes on their heads and backs. On the islands

they are traditionally preserved in salt, like sardines. In old days you could get one litre of olive oil for three kilograms of salted damselfish.

Cymodocea nodosa, lesser Neptune grass, is not an alga but a marine plant which, like all land plants, has a root, le-aves and a flower. On the sandy seabed it forms meadows where pen shell is very common.

Moon jellyfish Aurelia that lives in the Lakes, does not live anywhere else in the world. Even though the Lakes are connec-ted with the sea, it has not been found outside the Lakes. Certain specimens are particularly big with diameter of their be-lls reaching 55 centimeters. Mostly they

dwell in deeper and colder areas of the Lakes, but some-times they come to the surface in thousands. They are not dangerous for swimmers.

Pinna nobilis, pen shell, is the biggest Croatian bivalve which can reach more than a meter and lives more than 20 ye-ars. Prawns or pea crabs often live inside the shell. Pen shell sometimes forms a pearl of irregular shape but it is not va-luable. It is an endemic species of Medi-

terranean and it is protected by law.

Anemonia sulcata, snakelocks anemone, uses its tentacles with stinging cells to paralyze and entangle small crustaceans and fish. Despite of that, small prawns and gobies often hide within its tentac-les. Anemones form an important symbi-osis with certain single-celled algae spe-

cies which reside in their body. Those algae need constant sunlight which is the reason why anemones prefer bright, shallow areas.

supralittoral

midlittoral

infralittoral

Sponges

Bristle worms

Cnidarians

Moss animals

Echinoderms

Chitons

Ircinia sp./ ball sponge

Aplysina aerophoba/ yellow sponge

Sabella spallanzani/ tube worm

Protula sp./ tube worm

Actinia equina/ beadlet anemone

Anemonia viridis/ snakelocks anemone

Aurelia sp./ moon jellyfishCladocora caespitosa/ coral cladocora

Schizobrachiella sanguinea/ red sea mat

Paracentrotus lividus/ purple sea urchin

Sphaerechinus granularis/ purple-spined sea urchin

Holothuria tubulosa/ sea cucumber

Coscinasterias tenuispina/ blue starfish

Echinaster sepositus/ red starfish

Chiton sp./ chiton

Gastropods

Cephalopods

Spoon worms

Crustaceans

Bivalves

Ostrea edulis/ nativ oyster

Arca noae/ noah’s arc

Pecten jacobaeus/ st. james’s scallop

Pinna nobilis/ pen shell

Lithophaga lithophaga/ date mussel

Venus verrucosa/ warty venus

Cratena peregrina/ hervia

Gourmya vulgata/ common cerith

Haliotis lamellosa/ ormer

Littorina neritoides/ small periwinkle

Monodonta turbinata/ turbinate monodont

Patella sp./ limpet

Bolinus brandaris/ spinous murex

Octopus vulgarisoctopus

Bonellia viridis/ green spoon worm

Ligia italica/ sea roach

Sea squirts

Fish Algae

Balanus perforatus/ acorn barnacle

Chthamalus stellatus/ poli’s stellate barnacle

Palaemon elegans/ prawn

Pachygrapsus marmoratus/ rock crab

Eriphia verrucosa/ warty crab

Pagurus sp./ hermit crab

Halocynthia papillosa/ red sea squirt

Blennius sp./ blenny

Gobius sp./ goby

Chromis chromis / damselfish

Coris julis/ rainbow wrasse

Symphodus ocelatus/ wrasse

Sarpa salpa / salema

Diplodus vulgaris/ annular seabream

Serranus scriba/ painted comber

Epinephelus marginatus/ dusky grouper

Codium bursa / sea ball

Cystoseira adriatica/ alga cystoseira

Plants

Halimeda tuna/ alga Halimeda

Acetabularia acetabulum/ mermaid’s wineglass

Limonium cancellata/ sea lavender

Inula crithmoides/ golden samphire

Cymodocea nodosa/ lesser neptune grass

Crithmum maritimum/ rock samphire

Dictyota dichotoma/ alga dictyota

Padina pavonica/ peacocks tail

Valonia utricularis/ alga Valonia

Monodonta turbinata, turbinate mono-dont, has a green shell which is spiraled and pearl-like inside. It inhabits only roc-ky shore in tidal zone. During the night it comes out for feeding on tiny algae.

For last ten years two invasive species of algae have been spreading across the Mediterranean. If you find any of those two algae, please call the headquarters of the National Park or any autho-rised person. WANTED! WANTED! WANTED!

Authors: Ante Žuljević, Vedran Nikolić, Pavica Sršen - Photographs: Vedran Nikolić, Ante Žuljević, Petar Kružić, Ivan Cvitković - Translation: Sandra Weitner - Design and typeset: Columna, Split - Publisher: Public institution “Nacionalni park Mljet”Buying this brochure you support the programme of removal of invasive alga Caulerpa racemosa from the Lakes.