Response of bivalve populations to drying disturbance and life history traits of twoPisidiumspecies (Bivalvia: Sphaeriidae) in a reservoir of the French Upper Rhone river

Abstract

-The dam reservoirs of the Upper Rhone were drained every three years until 2003, and the water level of the Villebois reservoir was lowered by 1.5 m. This resulted in considerable drying of its littoral habitats and the disappearance of the abundant macro-invertebrates that live in them. This study investigates the response to this drying disturbance of bivalve populations and especially of the life history traits of the two potamic species, Pisidium moitessierianum and Pisidium supinum. The low density of these bivalves observed during the months following the drying of May 2003May until spring 2004 shows that the contribution of drift in population recovery was very limited during this period. Due to the faster turnover of its cohorts and a higher increase in litter size in 2004, P. moitessierianum once again dominated bivalve communities from 2005 onwards. In the Villebois reservoir recovery of bivalve communities in terms of structure and density was total three years after the drying of 2003. Observations suggest an increase in litter size and continuous recruitment: the reproductive strategy adopted by these bivalves represent response to the fall in numbers on the one hand, and to considerable magnitudes of temperature and flow rates on the other hand, enabling the rapid adjustment of populations to drying disturbance and variations in environmental conditions. Taking into account the response of bivalve populations to this event, its effects are comparable to those of a supra-seasonal drought (Lake, 2003, Freshw. Biol., 48, 1161-1172.

On the reproduction of Pisidium C. Pfeiffer, 1821 (Bivalvia: Sphaeriidae) from Sąpolno (NW. Poland)

“…In the culture the smallest offspring-releasing (3 young) individual had shell 2.51 mm long. The maximum number of offspring in one reproductive period was 46 (Table 1) and was close to that reported by Mouthon (2011). That author observed offspring release in France in two periods: May-June and August, and the smallest adults with shelled embryos had shells 1.68 mm long.…”

“…The offspring reached on average 33.9% of the parent's shell length (SD=3.7, n=550, range 26.1-45.9%). The juvenile measurements reported in the literature were within the above variation range (holopainen 1979, holopainen & hanSki 1986, Mouthon 2011.…”

“…In Finland the species had one reproductive period in a year and released offspring in July (holopainen 1979). In France offspring was released in two periods: May-June and August-September (Mouthon 2011). In France the maximum number of offspring in one reproductive period was 17 (Mouthon 2011), according to other authors it was much smaller (holopainen 1979(holopainen , GriGoroVich et al 2000.…”

Reproduction of Pisidium casertanum (Poli, 1791) in Arctic lake

“…Greater mortality of larvae occurred during early, rather than later, stages of larval development [ 19 ]. Some authors consider the intramarsupial suppression to be a powerful strategy which is used by the parent to control the number of progeny [ 11 , 20 ].…”

“…The species of the bivalve genus Pisidium are frequently dominant in lakes within the Arctic region (Y. V. Bespalaya 2014, unpublished data), they are important ecosystem components and often constitute a large portion of the benthic communities [9]. Pisidium species are simultaneous hermaphrodites, synchronously incubating their progeny in brood sacs inside the inner gills and extramarsupially on later stages [9][10][11]. Some authors presume that evolution of brooding explains the success of sphaeriids in colonizing extreme freshwater habitats [12,13].…”