Infauna evolution of the invertebrate community after a severe eutrophic crisis in the coastal lagoon of the Mar Menor (W Mediterranean)

The coastal lagoon of the Mar Menor (SE Spain) has undergone a critical transformation in the last decade due to a dramatic eutrophication crisis, primarily as a direct consequence of very-intensive agriculture along the adjacent coast. This has compromised the ecosystem balance, resulting in irreversible impacts such as the proliferation of macro and microalgae, biodiversity loss, and the formation of dead zones. The Mar Menor's resilience has been tested, showing serious environmental degradation evidenced by a significant shift in ecological state around 2016. During a two-year study period (2017–2018), 25 taxa belonging to 5 phyla were identified, with the phylum Annelida (class Polychaeta) being the best represented, followed by the phylum Mollusca. Initially, the benthic fauna was dominated by species tolerant to hypoxia, such as polychaetes. Over time, other species that can withstand slightly less eutrophication have also emerged and integrated with the polychaetes, indicating a complex dynamic in response to environmental changes.