Coinciding with world seagrass day, today at Club Nàutic Estartit we had the honor of hosting a talk organized by Gisfera, the entity responsible for environmental education at the Montgrí, Medes Islands, and Baix Ter Natural Park. The event took place in the classroom of the club’s activity center and featured the presence of biologist and speaker Boris Weitzman, who provided an in-depth discussion on the importance of seagrass meadows for our marine ecosystems.

Ecosystems and wildlife are fundamental elements for the health of our planet. Their preservation ensures ecological balance and the sustainability of natural resources. Aware of this reality, at Club Nàutic Estartit, we are committed to providing space and resources to carry out activities like this, with the goal of spreading knowledge about the natural environment and promoting its protection and conservation.

What are seagrass meadows?

Seagrass meadows are composed of phanerogamous plants that colonize soft seabeds, unlike algae, which grow on rocky substrates. These meadows create diverse habitats that promote biodiversity, acting as natural nurseries for many marine species. Additionally, they help stabilize the seabed and sand, contributing to water clarity and serving as bioindicators, as their presence reflects the good health of nearby marine ecosystems.

Posidonia Oceanica: A jewel of the mediterranean

Posidonia oceanica is one of the most emblematic marine phanerogams in our waters and the most important in the Mediterranean, as it is endemic and forms underwater meadows of great ecological value along our coasts. It is considered an “engineer species” due to its ability to create complex structures that give rise to highly important ecosystems at depths between 0 and 50 meters. In addition to its dense, visible leaf forests, this plant forms reef-like structures of roots, rhizomes, and dead leaves, known as “mattes”, which provide habitat and substrate for numerous species. One of the most symbolic is the noble pen shell (Pinna nobilis), a highly vulnerable bivalve mollusk that is closely linked to Posidonia meadows.

Posidonia oceanica provides multiple ecosystem services: it retains natural and artificial particles, such as microplastics; protects beaches and dunes from erosion; supplies oxygen to the water through photosynthesis, helping to prevent anoxia; and acts as a carbon sink, capturing and storing CO₂, thus contributing to the fight against climate change. Its leaves also host small invertebrates and calcifying algae, which, upon dying, release calcium carbonate structures that contribute sand to the beaches.

Other marine phanerogams

In addition to Posidonia oceanica, there are other, less well-known but equally important marine phanerogams for the marine ecosystem. One example is Cymodocea nodosa, commonly known as gram or gram meadow. It is especially present in the two gulfs of Empordà and within our natural park. This phanerogam is less recognized and often undervalued, but it plays a crucial ecological role. Although it does not form meadows as dense or structures as long-lasting as Posidonia, its rapid growth significantly contributes to the resilience of marine ecosystems, fulfilling similar functions. Recently, the book “Una planta sota el mar” was published, dedicated to the Cymodocea meadows in the Bay of Roses.

Posidonia in our local environment

In the Montgrí, Medes Islands, and Baix Ter Natural Park, Posidonia oceanica has a significant presence. Since the park’s creation, various protection measures have been implemented, such as the installation of mooring buoy fields to prevent direct anchoring on Posidonia meadows. This strategy has yielded positive results, as it helps minimize the impact of recreational nautical activities on these sensitive ecosystems.

Threats and Protection Measures

Despite its protected status, Posidonia meadows and other marine phanerogams face multiple threats, such as rising sea temperatures, coastal urbanization, the arrival of invasive species, pollution, destructive anchoring, and bottom trawling. To mitigate some of these issues, various initiatives have been implemented. One of them is the FanCat application, which allows boaters to identify the presence of Posidonia on the seabed through geolocation, helping to prevent anchoring over these sensitive habitats. Additionally, there is a guide for responsible anchoring along the Montgrí coast and the Medes Islands, providing key recommendations to minimize the impact on these essential ecosystems.