Freshwater Pearl Mussel

Extrapolation à partir de l'étude 2026 sur l'ingénierie d'écosystème par la moule perlière (Freshwater Biology), qui compare des tronçons de rivière avec et sans lit de moules selon le débit, pas le même tronçon avant et après la disparition du lit.

The study establishes that the physical presence of a pearl mussel bed changes brown trout behavior depending on flow, suggesting the bed's structure creates shelter or resting zones the trout actively use. Nothing directly measures how long it would take, after a bed's actual disappearance, for that behavior to change — the reasoning assumes the effect fades about as quickly as it appears.

What's missing to confirm it: Monitoring the same river reach before and after a mussel bed's actual disappearance would confirm the real timeline of this behavioral change in trout.

Extrapolation à partir de la capacité de filtration documentée de la moule perlière (The Wildlife Trusts ; U.S. Fish & Wildlife Service) et du constat que cette fonction a déjà largement disparu là où la population a reculé de 90 à 98 %.

An adult pearl mussel filters up to 50 liters of water a day, removing algae, bacteria, and particles, and moving nutrients from the water column down to the streambed — a role documented in freshwater mussels generally and measured in this species. A bed gone for ten years would have stopped that transfer long enough for effects on water quality and the streambed community to show, but no study directly measures that exact timeline.

What's missing to confirm it: A comparison between comparable watersheds with and without the pearl mussel, measuring water quality and downstream benthic community structure, would confirm the real scale of this effect after ten years.

Extrapolation à partir du déclin de 81,5 % sur 90 ans mesuré en Europe (synthèse sur le « vortex d'extinction » de la moule perlière) — un chiffre de population, pas une mesure directe de la fonction filtrante perdue à cette échelle.

The synthesis on the pearl mussel's extinction vortex puts the European decline at 81.5% over the past 90 years, and 61.5% worldwide over the same period. A decline of this scale, sustained for roughly a century, implies the filtration and nutrient-deposit function has vanished from most of the streams that once benefited from it — but no study directly measures the current state of water quality or the streambed community in these rivers.

What's missing to confirm it: A direct measurement of water quality and streambed community in European rivers where the mussel has been gone for roughly a century would confirm the true scale of this lost function.