It is late winter. In Trondheimsfjorden in Norway, the corals and all of their inhabitants are waiting for the return of light and warmth.The sea, just like on land, has seasons that affect behaviors and growth.
When we dive there, in early March, the water is still cold and the days are short. Boiling water is poured into the diving gloves to keep the fingers warm. At least for a while.
With the arrival of spring, sunlight increases. Many animals begin their mating season and hurry to grow and reproduce.
In many parts of the world, one of nature’s great spectacles is now taking place. Entire colonies of corals release their small eggs and sperm, called gametes, into the sea at the same time. Billions of colorful flakes swirl around in white, yellow, red, and orange.
Because the gametes of most coral species are viable for only a few hours, they need to be released at the same time.
Researchers still know very little about how this synchronized reproduction can occur. But water temperature and the cycle of the moon appear to be significant factors.
The environment in Trondheimsfjorden is unique. Here, there are corals and organisms that are otherwise only found at a depth of one thousand meters. The stone coral Lophelia pertusa was already described in 1768 by a persistent biology-interested priest. Since then, the corals have grown slowly, only 5 mm per year.
A little further out lies the world’s second-largest reef with stone corals – Sularevet. 13 km long, several hundred meters wide, and 30 meters high. The reef is a nursery for many of the species that the fishing industry is so dependent on. Among the coral branches, the eggs of saithe, cod, ling, lobster, and other crustaceans hatch.
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