{"id":199,"date":"2009-04-22T22:29:00","date_gmt":"2009-04-22T19:29:00","guid":{"rendered":"http:\/\/klqewmpxo.cyon.link\/?page_id=199"},"modified":"2026-01-10T22:16:33","modified_gmt":"2026-01-10T20:16:33","slug":"infralitoral","status":"publish","type":"post","link":"https:\/\/azalas.de\/en\/infralittoral\/","title":{"rendered":"The Infralittoral"},"content":{"rendered":"

T<\/big>he infralittoral zone begins at the lower waterline, which means that it encompasses the permanently submerged area of the coastal benthal. It extends down to the depth at which light-loving species such as seagrass and many types of algae can no longer thrive. Due to its large extent and the fact that its organisms are not exposed to drying out, the infralittoral is much richer in species than the zones above it. In terms of environmental conditions, the infralittoral offers much more uniform and stable habitats than the supralittoral and eulittoral, especially for swimming organisms. On the sea floor, the living conditions on the sea floor and thus the fauna and flora differ greatly according to the substrate.<\/p>\n

\"Infralittoral\"
\nThe infralittoral is the area from the lower waterline (i.e. the part that never falls dry) to the depth where there is still sufficient light for most plants.<\/small><\/p>\n

\"rocks
\nThe coastal rocks in the infralittoral are usually densely covered with algae and sessile animals.<\/small><\/p>\n

\"Infralittoral\"
\nNumerous free-swimming animals live in the infralittoral, especially many fish.<\/small><\/p>\n

T<\/big>he algae and seagrass populations on the sea floor, as well as the planktonic algae in the water, are of crucial importance not only for the marine ecosystem, but for the entire planet: for example, they produce half of the oxygen in the atmosphere and their productivity rivals that of the rainforests. The algae communities of the Mediterranean are much poorer and less productive than the huge algae and kelp forests of the colder, nutrient-rich oceans closer to the poles. Nevertheless, they also play an important role in the ecosystem and provide numerous animal organisms with shelter, food and habitat. The diversity of the animals living in algae stands and seagrass meadows can only be appreciated when you fish for them with a small hand net, as many species are so well camouflaged that they are almost impossible to spot.<\/p>\n

1. Rocky substrate<\/h3>\n

T<\/big>he rocks in the infralittoral are often densely covered with countless organisms, at least in areas close to the coast. In greater depths that are not affected by the waves, algae and sessile animals, with the exception of a few species, can only grow on more or less sloping or vertical (or overhanging) rock faces, as the horizontal surfaces are continually being covered by sediments sinking to the bottom, making it difficult for sessile organisms to survive there permanently.<\/p>\n

\"Infralittoral,
\nspecies-rich algae populations on well-lit rocks near the water surface<\/small><\/p>\n

\"overhanging,
\nEven in areas that offer less light, dense populations of algae and sessile animals can often thrive on vertical and overhanging rocks.<\/small><\/p>\n

\"Sedimentation
\nFurther down the algae and animal populations on the rocks are usually decrease significantly, mainly due to the reduced movement of the water.<\/small><\/p>\n

\"Worm
\nHorizontal rock surfaces are constantly being covered by sediments, which only a few algae such as large species of Cystoseira<\/em> and Dasycladus vermicularis<\/em> can cope with.<\/small><\/p>\n

1.1. On slate<\/h6>\n

O<\/big>n slate brown algae<\/a> such as Cystoseira spec., Padina pavonina<\/em> and Dictyota dichotoma<\/em> are especially abundant, but also some red algae such as Jania rubens<\/em>. Here, the algae populations often appear somewhat monotonous due to smaller species numbers.<\/p>\n

\"Infralittoral\"
\nAlgae populations in the infralittoral: On slate Cystoseira<\/em> and Padina pavonina<\/em> are especially abundant.<\/small><\/p>\n

\"Cystoseira\"
\nThe larger individuals of Cystoseira<\/em> are often covered with numerous smaller epiphytic algae and provide a habitat for countless small animals.<\/small><\/p>\n

1.2. On marble<\/h6>\n

O<\/big>n marble grow algae communities that are particularly rich in species, especially near the coast. Here non-calcareous red algae<\/a> and calcareous red algae<\/a> are particularly common. Depending on environmental factors such as the exposure to waves and the availability of light, different species predominate. Many of the species also occur in the lower areas of the eulittoral zone<\/a>. (Unfortunately, I cannot present the species restricted to the deeper regions, as I usually take pictures only from land.)<\/p>\n

\"Infralittoral\"
\nrich algae populations on marble rocks in the uppermost regions of the infralittoral<\/small><\/p>\n

Animals on rocky substrate<\/h3>\n

I<\/big>t is particularly wonderful to discover the countless marine animals<\/a> that live in the infralittoral zone. Interesting species can be found especially in areas that are less densely covered with algae. Particularly striking and characteristic are the sponges<\/a>, the sea urchins<\/a> and starfish<\/a> as well as numerous fish species<\/a> such as various species of bream, combers, the damselfish, mullets, various wrasses as the colourful Mediterranean rainbow wrasse and the ornate wrasse, and various goby and blenny species<\/a>.<\/p>\n

\"Black
\nBlack sea urchins in shallow water<\/small><\/p>\n

\"Bream\"
\nVarious species of bream search for food in a mixed shoal.<\/small><\/p>\n

\"Sponge\"
\nLarge sponges often grow on the rocky seabed.<\/small><\/p>\n

L<\/big>ess conspicuous, but equally characteristic, are species such as the Glass anemone<\/a> (Aiptasia mutabilis)<\/em>, the Pig-tooth coral<\/a> Balanophyllia europaea<\/em>, hydrozoans<\/a> such as those of the genus Aglaophenia<\/em>, worms<\/a> such as the calcareous tube worms Protula tubularia<\/em> and Bispira volutacornis<\/em> and the Bearded fireworm Hermodice carunculata<\/em>, various snails<\/a> and bivalvia<\/a>, various crabs and shrimps<\/a> such as the rock shrimp (Palaemon<\/em> spec.) and the rarer sea squirts<\/a>.<\/p>\n

\"Glass
\nThe Glass anemone grows on rocks near the coast.<\/small><\/p>\n

\"Rock
\nRock shrimp can be found in small crevices.<\/small><\/p>\n

\"Aplysia
\nThe small Dwarf sea hare (Aplysia parvula)<\/em> is less common.<\/small><\/p>\n

\"Tarantinaea
\nTarantinaea lignaria<\/em> is an effective predator.<\/small><\/p>\n

\"Calcareous
\nCalcareous tube worms are rather rare in our region.<\/small><\/p>\n

\"Bearded
\nIt is best not to touch the Bearded fireworm!<\/small><\/p>\n

\"Ophioderma
\nIf you’re lucky, you might find a brittle star, here a specimen of Ophioderma longicaudum<\/em>.<\/small><\/p>\n

N<\/big>ot to be forgotten are the many organisms living in the stone<\/a>, such as boring sponges (e.g. Cliona celata<\/em>), which are mostly invisible except for the tiny outlets that protrude from small holes in the rock. Only with great luck can one discover a date mussel as it also lives in holes it bores into the rock. Traces of the existence of rock boring animals can be found in the pebbles on the beach, many of which display holes in their surface.<\/p>\n

\"boring
\nThe boring sponges are really not boring at all, but quite amazing animals!<\/small><\/p>\n

M<\/big>any of the sessile species of the marine fauna are inedible or display effective defensive mechanisms, so that they have little to fear from predators. As a result, they often show striking colours, like many sea anemones and sponges. Many of the mobile sea organisms that are armoured or poisonous are also brightly coloured, such as some starfish and nudibranchs. Other species are so well camouflaged that they are almost impossible to spot, such as many species of snail, scorpion fish, many blennies and gobies, and shrimp. Some crab species live hidden in dense algae beds and even camouflage themselves with algae that they plant on their backs.<\/p>\n

\"Felimare
\nThe poisonous Felimare tricolor<\/em> is one of many colourful species of nudibranch snails.<\/small><\/p>\n

\"European
\nThe European spider crab covers itself densely with algae so that it is almost impossible to spot unless it moves.<\/small><\/p>\n

2. Sea beds of loose stones<\/h3>\n

A<\/big> distinct category of sea bed substrate consist of loose stones that are not fixed in place but can be rolled around by the waves in shallow sea areas. At greater depths, the stones are moved only by heavy storms in winter. Accordingly, during the summer months they are overgrown with fast-growing algae. Though this algae covering does not look very attractive, it is quite natural, and it is worn off again during the winter storms. The fauna of these stony areas is similar to that of rocky bottoms in terms of mobile species such as fish, snails, sea urchins and starfish; however, sessile species are largely absent. Typical animals that live on the stony sea beds are the sea cucumbers<\/a>.<\/p>\n

G<\/big>ravel sea beds form a transition to sandy sea beds and thus an intermediate state in terms of fauna and flora.<\/p>\n

\"Algae
\nSea beds with loose stones often only support unattractive growths of small, fast-growing green algae.<\/small><\/p>\n

\"Mullet\"
\nA shoal of young mullet grazes on the algae covering the stones.<\/small><\/p>\n

\"Holothuria
\nSea cucumbers live on the sea floor, especially on rocky and stony bottoms.<\/small><\/p>\n

\"Octopus
\nHere, an octopus has hidden itself between the stones.<\/small><\/p>\n

3.: Sandy sea beds<\/h3>\n

S<\/big>andy sea beds in shallow areas where the sand is moved by the waves lack any plants. However, at a depth of a few meters, species of seagrass<\/a> often appear, forming dense meadows<\/a>.<\/p>\n

\"Infralittoral
\nAt first glance, a sandy sea floor often appears quite lifeless.<\/small><\/p>\n

\"Seagrass,
\nThe seagrass Cymodocea nodosa<\/em> grows in many places in a few meters depth.<\/small><\/p>\n

\"seagrass
\nSeagrass meadows of Neptune grass (Posidonia oceanica)<\/em> occur at somewhat greater depths. They are among the most important habitats in the sea and provide shelter and food for countless animals.<\/small><\/p>\n

Animals on sandy substrate<\/h3>\n

S<\/big>essile animals are naturally absent from sand, as well as from stones and gravel; and even mobile animals can be seen only in small numbers on the sea floor. Various fish species<\/a> such as the broad-eyed flounder, the red mullet, the marbled bream and the weever fish are common close to the beach. With a little luck, in greater depths you may also encounter a ray.<\/p>\n

H<\/big>owever, sandy soils are much richer in organisms than can be seen from above: most animals live buried in the ground, such as many species of crab<\/a>: these can only be discovered by chance when they leave the sand for a short time. Other animals that live in the sandy sea floor and are (almost) never seen alive include bivalvia<\/a>, snails<\/a> and worms<\/a>, heart urchins<\/a> and some starfish species<\/a>. The sand also harbours an interesting microscopic fauna in the so called “sand gap system (mesopsammon)” that can only be studied with special equipment.<\/p>\n

\"Wide-eyed
\nThe well-camouflaged Wide-eyed flounder is perfectly adapted to life on sandy sea floors.<\/small><\/p>\n

\"Red
\nA Red mullet searches for prey in the sand.<\/small><\/p>\n

\"Portumnus
\nThe small crab Portumnus latipes<\/em> is found in shallow sandy areas, but it is rarely seen because it burrows in the sand.<\/small><\/p>\n

\"Gari
\nThe bivalve Gari depressa<\/em> lives buried in the sand.<\/small><\/p>\n

\"heart
\nHeart urchins also live in sandy sea floor, which is why they are almost never seen alive. Here is a small heart urchin.<\/small><\/p>\n

4.: Muddy sea beds<\/h3>\n

A<\/big>reas of the sea floor covered with fine mud are found mainly at the mouths of large rivers and in deeper regions, where they form from the constantly sinking fine sediment. They are less rich in species than sandy soils, as the spaces between the particles are too small for the organisms that inhabit sand gap system. In addition, the fine grain size prevents water circulation in the soil, resulting in a lack of oxygen. Accordingly, muddy soils are mostly inhabited by bacteria, which produce foul-smelling marsh gas when oxygen is lacking, and a few burrowing worms. The muddy sea floors of the open sea are home to various detritus feeders (sea cucumbers, fish species, crabs, etc.) that feed on all kinds of organic debris that sinks to the bottom.<\/p>\n

Here you find more underwater pictures: underwater landscapes<\/a><\/p>\n

continue: The Circalittoral<\/a><\/p>\n

back: The zones of the Mediterranean Sea<\/a><\/p>\n

see also:<\/p>\n