Juvenile biology and captive rearing of the freshwater pearl mussel Margaritifera margaritifera

Captive breeding of the freshwater pearl mussel (Margaritifera margaritifera) is an important short-term strategy to conserve this critically endangered species. The aim of this thesis was to improve current knowledge of the factors affecting juvenile M. margaritifera in a captive setting, and to develop understanding of juvenile anatomy, ontogeny and the ecological requirements of juveniles in captivity. The substrate requirements of newly-excysted juveniles were investigated in an experimental flow-through system (Chapter 3) by analysing differences in survival and growth in two different substrate size clasts (0.25 - 1 mm or 1 - 2 mm), and cleaning regimes (weekly or monthly). Factors potentially affecting juvenile survival and growth were further investigated in Chapter 4. Results indicate that dissolved oxygen and flow were crucial for juveniles in this system. Investigations of juvenile anatomy and ontogeny (Chapter 5) using scanning electron microscopy have greatly improved our knowledge of the timing of key developmental stages, such as the onset of gill reflection. Analyses of gill ciliation suggest the species is capable of retaining very small particles (<2 μm diameter), offering a potential reason for why M. margaritifera is so sensitive to turbid and enriched conditions. Improving the efficiency and effectiveness of monitoring juveniles in captivity should be an objective for all rearing programmes. Batch marking of juveniles through immersion in calcein (Chapter 6) was shown to offer a quick and reliable method and has the potential to save rearing programmes time and money whilst improving juvenile monitoring. The findings of these investigations should inform other captive rearing programmes in order to improve juvenile survival. Rearing efforts should focus initially on ensuring sufficient flow and dissolved oxygen for post-excystment juveniles, before tailoring systems to ensure low-stress conditions for transforming juveniles

Étude descriptive des retombées de l’intervention d’une artiste à l’école sur les apprentissages en art dramatique au primaire

Par le biais de ce projet de recherche, nous voulons décrire les résultats d’une intervention pédagogique axée sur la « lecture animée » (forme de communication qui s’apparente au doublage et dont les origines sont décrites par Jean, 1999) réalisée auprès des élèves du primaire par une artiste de théâtre. Cette intention de recherche s’explique, premièrement, par le nombre limité de propositions de techniques théâtrales inscrites au Programme de formation de l’école québécoise (2001) ; deuxièmement, par la place restreinte qui est accordée à l’enseignement de l’art dramatique dans les établissements scolaires, entre autres, ceux de l’Abitibi-Témiscamingue ; troisièmement, par l’absence d’étude réalisée spécifiquement sur ce sujet dans cette région du Québec. Nous cherchons à découvrir plus précisément les retombées de l’intervention pédagogique d’une artiste sur l’autodétermination des élèves (théorie définie par Deci et Ryan, 2000) et leurs attitudes (concept de Rosenberg et Hovland, 1960) dans le contexte de la progression des apprentissages liés à la compétence 2 interpréter des séquences dramatiques du PFÉQ en art dramatique. Notre recherche de terrain échelonnée sur une période de quatre semaines a été effectuée auprès de dix-sept élèves d’une classe en deuxième année du second cycle du primaire. Divers outils de collecte de données nous ont servi pour cette étude descriptive qualitative réalisée dans une école de Rouyn-Noranda (entrevues semi-dirigées, journal de bord, observation participante, questionnaire) ; ils nous ont permis d’apporter des éléments de réponse à nos questions de recherche ainsi qu’à tracer des perspectives de l’applicabilité de la lecture animée comme technique théâtrale dans le développement des compétences disciplinaires des élèves du primaire

Ontogeny of juvenile freshwater pearl mussels, Margaritifera margaritifera (Bivalvia: Margaritiferidae).

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.N/

Captive breeding of European freshwater mussels as aconservation tool: A review

1. Freshwater mussels are declining throughout their range. Their importantecological functions along with insufficient levels of natural recruitment haveprompted captive breeding for population augmentation and questions about the usefulness and applicability of such measures. 2. This article reviews the current state of captive breeding and rearing programmes for freshwater mussels in Europe. It considers the various species, strategies, andtechniques of propagation, as well as the different levels of effort requiredaccording to rearing method, highlighting the key factors of success. 3. Within the last 30 years, 46 breeding activities in 16 European countries have been reported, mainly of Margaritifera margaritifera and Unio crassus. Some facilities propagate species that are in a very critical situation, such as Pseudunio auricularius, Unio mancus, and Unio ravoisieri, or multiple species concurrently. Insome streams, the number of released captive-bred mussels already exceeds the size of the remaining natural population. 4. Rearing efforts range from highly intensive laboratory incubation to lowerintensity methods using in-river mussel cages or silos. Most breeding efforts are funded by national and EU LIFE(+) grants, are well documented, and consider the genetic integrity of the propagated mussels. Limited long-term funding perspectives, the availability of experienced staff, water quality, and feeding/survival during early life stages are seen as the most important challenges. 5. Successful captive breeding programmes need to be combined with restoration ofthe habitats into which the mussels are released. This work will benefit from anevidence-based approach, knowledge exchange among facilities, and an overall breeding strategy comprising multiple countries and conservation units. aquaculture, captive breeding, conservation translocation, freshwater mussel culturing, Margaritifera margaritifera, propagation, reintroduction, Unio crassusCaptive breeding of European freshwater mussels as aconservation tool: A reviewpublishedVersio

Population Reinforcement of the Endangered Freshwater Pearl Mussel (<i>Margaritifera margaritifera</i>): Lessons Learned

Freshwater mussel populations are in sharp decline and are considered to be one of the most imperilled groups globally. Consequently, the number of captive breeding programmes has increased rapidly in recent years, coupled with subsequent reintroductions/population reinforcements to reverse these declines. The outcomes of mussel conservation translocations are seldom reported in the primary literature, hindering opportunities for learning and for population recovery at pace. Here, we describe the methods employed to carry out a successful conservation translocation of the freshwater pearl mussel (Margaritifera margaritifera) in a declining population in northwest England. Following a small-scale pilot release in 2017, four release sites were identified for a population reinforcement of over 1300 tagged mussels in 2021. Monitoring during 2022 showed high levels of retention of juveniles at three out of the four release sites, despite the occurrence of a significant flood event during October 2021. Subsequent releases of 1100 juveniles were carried out across the three successful sites in 2023. Ongoing and regular monitoring is essential in order to provide data on the longer-term fate of propagated juveniles in the wild. This will allow for adaptive management of release activities in this river. These data will be useful to design conservation translocation strategies for other imperilled pearl mussel populations in the UK and throughout Europe

Substrate parameters affecting propagation of juvenile freshwater pearl mussels margaritifera margaritifera (bivalvia: margaritiferidae)

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.N/

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

This study tested a culture system for rearing Margaritifera margaritifera at the Freshwater Pearl Mussel Ark in Windermere and investigated the effects of substrate size (0.25-1 mm and 1-2 mm) and cleaning regime (weekly and monthly) on survival and growth. At 362 days (12 months) and 758 days (25 months), a total of 1207 and 518 juveniles were reared successfully in the system described here. 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). Survival rates in this investigation were comparable to, if not better than, other published studies culturing M. margaritifera of this age. Juveniles from most treatments did not display size-dependent over-winter survival, but a significant correlation was found between shell length and survival in the 0.25-1 mm weekly treatment which was the least suitable treatment. Additionally we examined the effects of flow rate, dissolved oxygen concentration, ammonia concentration and biofilm as factors which may affect growth and survival of juveniles between July - September 2015. These results provide an insight into findings from the initial work and discussion is offered on the challenges for practically applying this method to captive rearing at the Ark in future

Main anatomical features of juvenile mussels.

<p>a) Foot (FO), unreflected filaments (FI), gill axis (GA), left and right labial palps (LP). b) Distal tips of filaments are joined to each other by thin tissue connections (arrow heads); c) Gill reflection of the inner demibranch. Thin tissue connections join filaments at the ventral bend (VB) and the thicker fused dorsal bend (FDB) joins the terminal ends of the ascending arms. All three cilia types are present on the ascending limbs (AL); lateral cilia (LC), laterofrontal cirri (LFC) and frontal cilia (FC). The ascending limb is longer on medial filaments compared to those at either anterior or posterior ends (to the left and right of frame). Other features of note are the filament abfrontal surface (AS), descending limb (DL) and mantle (MA); d) Oral groove on inner demibranch (left) and absence of groove on outer demibranch (right); e) Ciliary junctions between approximately filaments 11–14 (*), after which tissue junctions were present (†); f) Right ID, OD and labial palps (LP). Inset: Labial palps are highly ciliated on the inner surface but devoid of cilia externally.</p

Diagram of gill position and cross-section through a lamella showing ascending and descending limbs of a filament.

<p>A: Gill position within a valve showing positioning of the anterior adductor (aa) and posterior adductor muscles (pa), budding zone (bz) and filaments (fi). B: A dorso-ventral section though a eulamellibranch showing the foot (ft), gill base (gb), inner demibranch (id), interlamellar junction (ilj), interlamellar space (ils), mantle (m) and outer demibranch (od). Used with permission from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193637#pone.0193637.ref038" target="_blank">38</a>].</p

Interfilamentary space vs length (mm) and age (months).

<p>There was no significant trend of interfilamentary space with length nor age.</p