04/08/2026

The grooved carpet-shell clam (Ruditapes decussatus) is a native clam species that inhabits estuaries, lagoons, and coastal flats along the Mediterranean Sea and the northeast Atlantic. This highly prized bivalve is an ecosystem engineer that provides major ecological functions, including water filtration and sediment bioturbation. A decline in production has recently been observed in several areas of southwestern European and the Mediterranean region; however, data documenting this phenomenon remain scarce and are largely unpublished. To address this knowledge gap, we conducted a study based on official statistics, the expertise of 24 marine ecosystem experts from eight countries covering 17 coastal sites, and a preliminary literature map. This approach enabled the development of an expert-informed regional perspective on the reported declines of R. decussatus, as well as a synthesis of the regulatory measures and restoration actions implemented across the study area. The findings indicate a sharp decline in both production (-32 to -100%) and stocks (˜ -80%) over the past two decades. The onset of the decline varied among sites, occurring between 2003 and 2024. According to the participating experts, the main suspected drivers of the decline were disease, overfishing, competition with alien species, and climate change. The most common regulatory measures were minimum conservation reference sizes, closed fishing seasons, and licenses. Only a few restoration projects were identified, focusing on restocking through seeding, the collection of natural broodstock, harvesting natural spat or substrate modification. This study provides a preliminary overview of the seemingly widespread decline of R. decussatus across the southwestern European and Mediterranean region and highlights the need for coordinated research to elucidate the causes of this reported decline, as well as for restoration actions to support the recovery of this native species.

Reported declines of the grooved carpet-shell clam (Ruditapes decussatus) across southwestern Europe and the Mediterranean: insights from expert knowledge