MAERL
These calcareous branches form an uneven carpet on the sediment surface, creating countless small spaces where many organisms can live or shelter. Maerl thus provides a structure and complexity absent from a bare sandy seabed.
Discreet and fragile, this environment shows that an apparently mineral landscape can actually be built by living organisms.
The seabed takes on a pink, reddish, purple or whitish colour. It appears to consist of countless small calcareous fragments.
Yet this is not gravel.
Some of these pieces are calcareous red algae living freely on the seabed.
They are not attached to rock.
As they grow, branch and accumulate, they can form areas called maerl beds.
The algae forming it deposit calcium carbonate in their tissues. They become rigid and take on the appearance of small branches, nodules or concretions.
The nodular forms produced by these algae are generally called rhodoliths.
Their morphology depends in particular on the species present and environmental conditions. Some are highly branched. Others form more compact structures.
In the Mediterranean, these formations can occur on soft seabeds of the continental shelf, often several tens of metres deep.
What might be taken for a field of small pebbles partly consists of living organisms.
AMIGANSEAU CONTENT
The rest of this article is for subscribers
Log in with your AMIGANSEAU licence to continue reading.
All active AMIGANSEAU licences give access to the full article.Explore the same world
