A discreet treasure lies in the depths: maerl. Free-living calcareous algae accumulate grain by grain in pink and purple carpets, weaving living beds over centuries that support unsuspected biodiversity. Nearby, sand may seem no more than a shifting, featureless marine desert. Yet beneath its unstable surface, worms, shellfish and fish find refuge, burrowing and disappearing like shadows. Two discreet worlds, mineral and plant, united by their silence but essential to the balance of the sea.

Beneath the apparent simplicity of sand and maerl lies a world teeming with life. These environments, often seen as inert, play a crucial role in maintaining marine ecological balance. Maerl, made up of free-living calcareous algae, forms a complex habitat offering shelter and breeding grounds for many marine species. Sandy sediments shelter burrowing and microscopic organisms that contribute to seabed fertility and nutrient recycling. The slow growth of maerl and the fragility of these habitats make their preservation essential to the biodiversity and health of Mediterranean ecosystems.

Beyond shifting sand and maerl beds are other worlds easily missed by a hurried glance. Microalgae, sponges, bryozoans and foraminifera* live in the gaps, weaving the web of marine life on a tiny scale. These often overlooked microscopic or colonial organisms contribute to sediment fertility and the formation of structures, and provide nursery areas** and food for many species. Sand, maerl and the almost invisible world around them all share their space with countless tiny, indispensable living things.

*Foraminifera are very small, single-celled marine organisms, often with a calcareous shell pierced by tiny holes. Through these holes, they extend fine arm-like structures called pseudopodia, which allow them to move and capture food.

**A nursery is an area where young fish or other organisms find abundant shelter and food, allowing them to grow before moving into adult habitats.