Spengler’s freshwater mussel faces many threats, most of which are the result of human activities (1).
Historically, overexploitation by pearl and nacre collectors was the major cause for the decline of the highly valued Spengler’s freshwater mussel (5) (6) (7) (8). However, more recently pollution has become a key threat (1) (2) (6) (8), as bivalves are sensitive to both pollutants dissolved in the water and those that accumulate in sediment in the river bed (5). Pesticides leaching into the water from the large irrigated fields along the banks of the River Ebro pose a major threat (1) (2).
Badly planned water use is frequently named as the reason behind all of the problems faced by Spengler’s freshwater mussel (1) (2), and the habitat of this species is altered in many ways through human activities such as water extraction and engineering works (2) (6).
Spengler’s freshwater mussel is extremely dependent upon its fish hosts (4), and therefore any activities which impact upon the fish and their habitat will also negatively affect this Critically Endangered mussel (1) (2) (5). For example, the European sturgeon, the main host fish for Spengler’s freshwater mussel, is thought to be extinct in the River Ebro, and is suffering severe declines in most other western European rivers (1). A lack of host fish due to dams, which block migration routes, and dredging, which may prevent the fish from breeding (1) (2) (7), could be a major cause for the decline in Spengler’s freshwater mussel (2) (3) (8).
Plans to modernise the Canal Imperial in Spain by laying down concrete slabs are expected to potentially kill the entire population of Spengler’s freshwater mussel in the area (2) (7). Very little or no reproduction is occurring in the various subpopulations of this species, and in 2010 it was estimated that nearly all of these smaller, isolated populations will disappear in the next 20 to 50 years (1).
A further potential threat to Spengler’s freshwater mussel is poaching, once the risk to the species becomes well known and its value increases (2).