• Effects of substrate size and cleaning regime on growth and survival of captive-bred juvenile freshwater pearl mussels, Margaritifera margaritifera (Linnaeus, 1758)

      Lavictoire, Louise; Sinclair, William; Sweeting, Roger A.; Moorkens, Evelyn; Ramsey, Andrew; University of Derby (Springer, 2015-09-04)
      The freshwater pearl mussel is critically endangered and most English populations are at risk of extinction unless conservation measures are implemented immediately. The study objectives were to test a culture system for rearing Margaritifera margaritifera in captivity, and to investigate the effects of substrate size (0.25–1 and 1–2 mm) and cleaning regime (weekly and monthly) on survival and growth. In total, 1207 and 518 juveniles were reared to 362 (12 months) and 758 days (25 months), respectively. After 362 days, survival was significantly higher in 1–2 mm substrate treatments cleaned monthly (55 ± 6 %) and lowest in 0.25–1 mm substrate cleaned weekly (14 ± 3 %). Growth was significantly higher in 1–2 mm substrates cleaned weekly (length = 1.15 ± 0.21 mm) and lowest in 0.25–1 mm substrates cleaned monthly (length = 0.83 ± 0.23 mm). Juveniles from most treatments did not display sizedependent over-winter survival, but a significant correlation was found between shell length and survival in the 0.25–1 mm weekly treatment. This low-maintenance system utilised features of previously described systems and growth and survival rates were comparable to, if not better than, other studies culturing M. margaritifera. The system could be scaled up to rear significant numbers of juveniles in captivity.
    • Ontogeny of juvenile freshwater pearl mussels, Margaritifera margaritifera (Bivalvia: Margaritiferidae).

      Lavictoire, Louise; Ramsey, Andrew; Moorkens, Evelyn; Souch, Graham; Barnhart, M. Christopher; University of Cumbria; University of Derby; Trinity College Dublin; Missouri State University (Public Library of Science (PLOS), 2018-03-28)
      The gills of juvenile freshwater bivalves undergo a complex morphogenesis that may correlate with changes in feeding ecology, but ontogenic studies on juvenile mussels are rare. Scanning electron microscopy was used to examine the ultrastructure and ontogeny of 117 juvenile freshwater pearl mussels (Margaritifera margaritifera) ranging in age from 1–44 months and length from 0.49–8.90 mm. Three stages of gill development are described. In Stage 1 (5–9 inner demibranch filaments), only unreflected inner demibranch filaments were present. In Stage 2 (9–17 inner demibranch filaments), inner demibranch filaments began to reflect when shell length exceeded 1.13 mm, at 13–16 months old. Reflection began in medial filaments and then proceeded anterior and posterior. In Stage 3 (28–94 inner demibranch filaments), outer demibranch filaments began developing at shell length > 3.1 mm and about 34 months of age. The oral groove on the inner demibranch was first observed in 34 month old specimens > 2.66 mm but was never observed on the outer demibranch. Shell length (R2 = 0.99) was a better predictor of developmental stage compared to age (R2 = 0.84). The full suite of gill ciliation was present on filaments in all stages. Interfilamentary distance averaged 31.3 μm and did not change with age (4–44 months) or with size (0.75–8.9 mm). Distance between laterofrontal cirri couplets averaged 1.54 μm and did not change significantly with size or age. Labial palp primordia were present in even the youngest individuals but ciliature became more diverse in more developed individuals. Information presented here is valuable to captive rearing programmes as it provides insight in to when juveniles may be particularly vulnerable to stressors due to specific ontogenic changes. The data are compared with two other recent studies of Margaritifera development.
    • Substrate parameters affecting propagation of juvenile freshwater pearl mussels margaritifera margaritifera (bivalvia: margaritiferidae)

      Lavictoire, Louise; Notman, Gill; Pentecost, Allan; Moorkens, Evelyn; Ramsey, Andrew; Sweeting, Roger A.; University of Derby (Conchological Society, 2020)
      Interstitial habitat conditions are of critical importance to species inhabiting the hyporheic zone, particularly for moderately immobile species incapable of escaping poor habitat conditions. The critically endangered freshwater pearl mussel (Margaritifera margaritifera Linnaeus, 1758) has seen increasing propagation effort over the last three decades, often with mixed success. This study aimed to investigate parameters with the potential to affect juvenile survival in captivity by considering a range of habitat conditions within the substrate of a previously described propagation system using different substrate size classes (0.25–1 and 1–2mm) and cleaning regimes (weekly and monthly). Juvenile survival was highest in larger substrates, likely because of higher flow through larger pore spaces. This provided higher dissolved oxygen delivery in 1–2mm substrates cleaned weekly (8.26 ± 0.19 mg/L) and monthly (8.24 ± 0.44 mg/L), compared with 0.25–1mm substrates cleaned weekly (7.98 ± 0.44 mg/L) and monthly (6.78 ± 1.27 mg/L). The amount of organic material trapped in the substrate did not differ between treatments but the high concentrations of inorganic phosphorus liberated from ashed organic matter indicated phosphorus storage in phytoplankton. High dissolved oxygen concentrations and good water replacement between the water column and the substrate are crucial for survival in captive freshwater pearl mussels.