Seasonal variations in population dynamics and biomass of two Unio pictorum mancus (Mollusca, Unionidae) populations from two lakes of different trophic state

Abstract

Samples of Unio pictorum mancus collected monthly from spring 2003 to summer 2004 in the meso-oligotrophic Lake Maggiore and the eutrophic Lake Candia were compared to evaluate the influence of lake trophic conditions on mussel populations. Shell form, maximum age (8 years) and percentage of organic matter in the shell and soft tissues were similar in both lakes. However, comparisons between same size classes revealed that mussels from Lake Maggiore were generally older, their shells heavier and their soft tissues lighter than those from Lake Candia. Recruitment occurred in both populations in June-July. The frequency distributions of adult mussels (>30 mm) and their soft tissues and shell biomasses in all size classes (range = 2 mm) were normal, but the curves of the mussels from Lake Candia were flat in comparison to those of mussels from Lake Maggiore. The median body size of Lake Maggiore mussels was 58 mm, while that of the Lake Candia population was 72 mm. During the study period the population density of each lake was fairly constant, whereas the population structure, and consequently the biomass, showed seasonal variations.

When and how? Freshwater mussel recolonization in Lake Orta

“…The annual phosphorus load from the tributaries decreased from 6-10 t P yr -1 before 2004 to values close or below 2 t P yr -1 in very recent years (Rogora et al, 2016). Though admittedly speculative for the small number of individuals we sacrificed, this hypothesis is matched by the evidence that Unio elongatulus has higher growth rates and larger size in eutrophic than in oligotrophic water bodies (Ravera et al, 2003(Ravera et al, , 2007. Lake Orta can be classified as oligotrophic or ultra-oligotrophic, with very low total phosphorus concentrations (Rogora et al, 2016).…”

Bad taxonomy can kill : molecular reevaluation ofUnio mancusLamarck, 1819 (Bivalvia : Unionidae) and its accepted subspecies

“…U. mancus has not been found in the Meuse River. Specimens from Lake Maggiore in Italy have been referred to "U. pictorum mancus" by Ravera et al (2007), while Gavetti et al (2008) identify them as U. mancus. The specimens from Lake Maggiore form a distinct lineage from U. mancus (Figure 2, clade 2), which is identifiable as Unio elongatulus, after Bodon et al (1995) and the Italian fauna Checklist (www.faunaitalia.it).…”

Limnological research in the deep southern subalpine lakes: synthesis, directions and perspectives

“…All the Italian samples joined with both German and mid-European samples, suggesting a mixed origin of the Italian Dreissena. Further studies concerned other larger molluscs, such as the populations of Unio pictorum mancus and Viviparus ater in Lake Maggiore [151,152].…”