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Coral alga with a growth of small calcareous spiral-formed tubes that contain the tubeworm Spirorbis corallinae. In the picture, a ormstjärna is seen.

Sea-mats of the Flustrellidra family can both collect its food from the surrounding water and
from the alga it is atached to. A great many algae emit large quantities of organic compounds into the water, and it is said that Flustrellidra gets about 17% of its energy needs from the toothed wrack upon which it is atached. The toothed wrack is probably not harmed by the Flustrellidra as it only utilizes those organic compounds that are emitted into the water. The biggest damage that Flustrellidra is that it prevents the flow of light to the effected areas and therefore, photosynthesis is not as effective.

Grazers help and upset

Some of the roaming animals that congregate around the algae, also eat them. These grazers do not necessarily cause great damage to the algae, if they only eat those parts that are old and need to be replaced, whereas if they assault those areas that are important for growth and reproduction they can cause serious damage. This is especially true if they are not restrained by some form of regulating factor. For example, in certain areas of the world, sea-urchins and certain shellfish have grazed heavily on the kelp forests so that the kelp population has nearly been eradicated. Great damage can be caused, even if grazing is not too heavy, for example the Laminaria-skålsnäckor can instead of eating the leaf-like parts of the kelp, graze on the more vital parts of the stem or torso. It is enough that they graze just a little bit for the kelp to lose some of its anchor power, and with the with the next storm they are torn lose and washed up onto the beach.
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Cliffs and rocks are fantastic!
Zoning and flecked occurrence
Animals that are attached
Modular construction
Variation and change
Variations in water level
Wave exposure
Both cliffs and rocks
Freshwater and saltwater
Geography, climate and history
Organisms life cycles
Organisms effect on each other
Energy and the flow of material

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Bo Johannesson | Martin Larsvik | Lars-Ove Loo | Helena Samuelsson