Mar 24, 2025
Blooming and fruit production of Posidonia oceanica
Spring in the sea: even aquatic plants bloom and bear fruit
Do marine plants bloom? Yes, just like land plants! Posidonia oceanica, an aquatic plant endemic to the Mediterranean Sea, also produces flowers and seeds, a rare and fascinating event that provides valuable opportunities for study for biologists and researchers around the world.
The blooming and subsequent seed dispersal are crucial events for reproduction and the colonization of new areas. Now let’s dive deeper and give a detailed overview.
Unlike terrestrial plants that bloom every year, Posidonia oceanica blooms rarely and irregularly. The most common blooming period is autumn, between September and November, but under particular conditions, it can occur at other times of the year. This phenomenon happens mostly in shallow waters, up to 10-15 meters deep, where sunlight stimulates the production of flowers.
The flowers of Posidonia are small and inconspicuous, greenish with reddish hues. They grow on a spike-like structure called a spadix and are hermaphroditic, containing both male and female organs. Pollination happens entirely underwater: the filamentous pollen is carried by marine currents without the need for pollinating insects, as is the case for land plants.
After pollination, the flowers transform into fruits known as "sea olives" due to their shape and color. These fruits mature in spring, between March and May, and contain seeds that, thanks to their ability to float, are dispersed by marine currents over long distances. When the fruit decomposes or breaks, the seeds sink and settle on the seabed.
The seeds of Posidonia oceanica are small (about 5-10 mm) but have good germination capacity. However, the growth of new plants depends on several factors:
· Seabed stability: Seeds are better established on sandy or muddy substrates.
· Light: Essential for photosynthesis and the development of young shoots.
· Temperatureand water quality: Optimal conditionsfavor growth.
After germination, the young plant begins to develop roots and leaves. The initial growth is slow, but once established, Posidonia expands through rhizome growth, forming dense, long-lived meadows.
At the One Ocean Foundation, together with the marine biologists we collaborate with, we study the blooming of Posidonia to better understand its role in the marine ecosystem and to find effective strategies for its protection. The initiatives of our Blue Forest project in Puglia (Torre Guaceto) and Sardinia (Cala di Volpe) aim to preserve these valuable underwater meadows, true "blue lungs" of the Mediterranean.
Next time you look at the sea, remember that even underwater, spring brings an extraordinary explosion of life!