Riparian detritus vs. stream detritus: food quality determines fitness of juveniles of the highly endangered freshwater pearl mussels (Margaritifera margaritifera)

Abstract

Detritus is an important energy source of stream food webs. Being a mix of allochthonous and autochthonous sources, it is often unknown, which components contribute to the growth of stream organisms. This study focussed on the comparison of two different detritus types (riparian detritus and stream detritus) with respect to food quality and effects on growth as a fitness parameter of juvenile freshwater pearl mussels (FPM). We performed feeding experiments with juvenile FPM under laboratory conditions using the two detritus types from four different natural sources each. Food quality was determined by analysing the fatty acid composition. Stream detritus (conditioned to stream environment including autochthonous microbes) resulted in significantly higher growth rates of juvenile FPM than predominately terrestrial-based riparian detritus indicating higher food quality. Significantly positive correlations were found between mussel growth and different groups of polyunsaturated fatty acids (PUFA). This suggests that especially trace substances such as long-chained n-3 PUFAs and a high ratio of n-3 to n-6 PUFAs enhance the food quality of stream detritus for juvenile FPM. These results highlight the importance of instream conditioning of detritus for the food mix in headwater streams and the importance of PUFAs for the development of juvenile FPM.

Captive breeding of European freshwater mussels as a conservation tool: A review

“…Where specialist facilities are available and there are staff to monitor broodstock, fish, and juveniles, high and medium intensity methods, as described in Figure 1, can be used. Pulsed flow‐through systems (Patterson et al, 2018; Hyvärinen et al, 2021), incubator/detritus boxes (Eybe et al, 2013; Scheder et al, 2014; Nakamura et al, 2018; Grunicke et al, 2023), flumes, aquaria systems (Lavictoire et al, 2016; Lavictoire et al, 2020), and the Floating Upweller System (FLUPSYS) (Patterson et al, 2018) all require medium to high levels of attention. The most resource‐intensive systems per juvenile reared are the incubator/box and the pulsed flow‐through systems (Kunz et al, 2020; Hyvärinen et al, 2021).…”

“…;Scheder et al, 2014;Nakamura et al, 2018;Grunicke et al, 2023), flumes, aquaria systems(Lavictoire et al, 2016;Lavictoire et al, 2020), and the Floating Upweller System (FLUPSYS)(Patterson et al, 2018) all require medium to high levels of attention. The most resource-intensive systems per juvenile reared are the incubator/box and the pulsed flow-through systems(Kunz et al, 2020;Hyvärinen et al, 2021).…”

Thermal Tolerance and Vulnerability to Climate Change of a Threatened Freshwater Mussel

“…As FPMs are protected under national legislation and within the European Union (IUCN, 2022), our experimental studies were performed with FPMs from a captive-breeding program in Saxony [49], applying standard propagation and culture methods following Hruška [50], modified after [45,47]. Host fish (Salmo trutta) from a local hatchery were infested with glochidia that were collected yearly in July or August from gravid females of a regional free-living, natural FPM population and were kept for 8-months at the fish farming station (Rösch, Bärnau, Germany).…”

“…After glochidia grow and metamorphose on the gills into a tiny mussel, the fish were transferred to the mussel rearing station (Raun, Saxony, Germany) and excystment occurred when mussels reached a length of ~350 µm usually form April to May. The post-parasitic mussels were kept for the first 1-2 months in small plastic boxes (500 mL) at water temperatures between 15-16 • C. They were fed with a detritus-algae suspension [45]. The food mixture was refilled twice a week and dead mussels were removed.…”

“…Buddensiek [39] stated that temperature effects are difficult to determine in field studies because the accelerated growth might be caused by temperature effects on metabolism or changes in food quality or uptake as observed later by Brauns et al [44] or Grunicke et al [45]. Therefore, our study combines field mesocosm studies in five streams and across four years with laboratory experiments at summer and winter conditions in semi-natural but controlled and replicated conditions.…”