Captive breeding of Margaritifera auricularia (Spengler, 1793) and its conservation importance

Abstract

Margaritifera auricularia is one of the most endangered freshwater mussels (Bivalvia, Unionida) in the world. Since 2013, the abundance of this species in the Ebro River basin (Spain) has sharply declined, driving the species to the verge of regional extinction. Therefore, any management measures that might facilitate the recovery of this species would be essential for its conservation. During 2014–2016, captive breeding of M. auricularia allowed the production of >106 juveniles, out of which 95% were released into the natural environment, and 5% were grown in the laboratory under controlled conditions. The aim of this experimental work was to establish the best culture conditions for the survival and growth of M. auricularia juveniles in the laboratory. The experiment was divided into two phases: phase I, in which juveniles recently detached from fish gills were cultured in detritus boxes until they reached a shell length of 1 mm; and phase II, in which these specimens were transferred to larger aquaria to grow up to 3–4 mm. The best experimental conditions for juvenile survival and growth corresponded to treatments in glass containers at a density of 0.2 ind. L−1, using river water, with added substrate and detritus, enriched with phytoplankton, and avoiding extra aeration. The highest survival and growth rates attained, respectively, values of c. 60% at 100 days and 2.56 mm in shell length at 30–32 weeks. This is the first study to report on the long‐term survival and growth of juvenile M. auricularia in the laboratory, providing essential information in order to implement future conservation measures addressed at reinforcing the natural populations of this highly threatened species in European water bodies.

Translocation as an ultimate conservation measure for the long-term survival of a critically endangered freshwater mussel

“…Translocation of P. auricularius was assumed by the Aragón governmental authorities as an emergency task in order to save the last living specimens found in the CIA. This, in addition to captive breeding (Nakamura et al 2019), is probably one of the few remaining options to avoid the extinction of the species in Spain. In the CIA, the protection of P. auricularius and other mussel species is a conservation issue with conflicting interests.…”

“…Localities with previous presence of the species or at least the presence of other living mussel species were especially taken into consideration. The range of values for each variable included in the index was based on available literature about the optimum habitat conditions for the species (Altaba, 1990Araujo & Ramos, 2000;Araujo & Álvarez-Cobelas, 2016;Soler et al, 2018) and on 20 years of experience gathered in several projects aiming at conserving the species, both in the natural environment and in captivity (Wantzen & Araujo, 2018;Nakamura et al 2018bNakamura et al , 2019Nakamura et al , 2021. In each recipient locality, a plot (surface area 8-20 m 2 ) was chosen to assess ten physical and chemical variables, plus four biological and five anthropogenic variables (Table 1).…”

“…Living specimens were left back in the transect, naturally Table 1 Limiting environmental values of P. auricularius used for the selection of recipient localities in the Ebro River. Based on Altaba (1990, Araujo and Ramos (2000), Araujo et al (2001Araujo et al ( , 2003; Araujo & Álvarez-Cobelas (2016), Nakamura et al (2018bNakamura et al ( , 2019, Soler et al (2018) buried in the substrate. In addition, three samples were extracted (initial, middle, and end of the transect; variable length in each plot) using 30 × 30-cm squares to assess the density of C. fluminea.…”

A brief global agenda for advancing the study of molluscs

“…Recent methodological and technological advances are turning possible the production of juveniles ready to colonize new habitats, even in species with very complicated life cycles such as freshwater mussels (order Unionida) that need a suitable fish host to complete the life cycle (e.g. Nakamura et al, 2019). Despite the great advancements, these possible translocation or propagation actions need to be carefully scrutinized because there is always the risk of moving parasites and/ or diseases (Brian et al, 2021).…”

Reproduction of the endangered fan mussel Pinna nobilis under natural and captivity conditions

“…One example is the emblematic Iberian species Lynx pardinus , which was on the brink of extinction with less than 200 individuals in 2002, which now numbers more than 1,000 individuals after 20 years of captive breeding and recovery programmes (Vargas et al, 2008). Critically endangered bivalve species, such as Margaritifera margaritifera and Margaritifera auricularia , have benefited from restoration programmes to improve the population status, and in parallel activities for the recovery/restoration of their natural habitat (Thomas, Taylor & Garcia de Leaniz, 2010; Nakamura et al, 2019). Also, the developments of aquaculture techniques have provided restoration opportunities to several threatened spondylid bivalve species (Lodeiros et al, 2016) and to the flat oyster ( Ostrea edulis ), whose populations have been severely decimated (Pogoda, 2019; zu Ermgassen et al, 2020; Colsoul et al, 2021).…”