Pearl mussels (Margaritifera marocana) in Morocco: Conservation status of the rarest bivalve in African fresh waters

The fingernail clams (Bivalvia: Veneroida: Sphaeriidae) of Morocco: Diversity, distribution and conservation status

Background

In Morocco, many uncertainties surround the current diversity and distribution of the bivalve family Sphaeriidae. Such information, including taxonomy and conservation status, are vital for further studies to improve the knowledge of this family in Morocco and represents the first step towards the development of a national conservation plan for all freshwater bivalves.Between 2016 and 2019, several investigations were carried out to assess the diversity and distribution of Sphaeriidae in the different basins of Morocco, covering different types of habitat (lakes, springs, rivers and small ponds). The identification of specimens and their morpho-ecological features was based on morphological and morphometric analyses. The data on the general distribution of the collected species allowed the evaluation of their conservation status as well.The shell morphology and morphometric analyses revealed the existence of five species belonging to the genus Pisidium [P.casertanum (Poli, 1791), P. (cf.) personatum Malm, 1855, P.subtruncatum Malm, 1855, P.amnicum (O. F. Müller, 1774) and Pisidium sp.] and one species to the genus of Musculium [M.lacustre (O. F. Müller, 1774)]. Sphaeriidae were found in all Moroccan basins, except Bouregreg and Sakia El Hamra-Oued Eddahab Basins. The results showed that Sebou Basin was the species richest with the occurrence of the five species, while Loukkos and Sous-Massa Basins had the lowest-species richness with one species only. The conservation status of sphaeriids in Morocco was evaluated for the first time and resulted in P. (cf.) personatum and P.subtruncatum being proposed as Least Concern and Vulnerable, respectively, while the status of Regionally Extinct is suggested for both species P.amnicum and M.lacustre.

New information

First evaluation of the diversity and species richness of the family Sphaeriidae in Morocco with an assignment of an updated conservation status of the recorded species.

Alarming decline of freshwater trigger species in western Mediterranean key biodiversity areas

Theidentification of key biodiversity areas (KBA) was initiated by the International Union for Conservation of Nature in 2004 to overcome taxonomic biases in the selection of important areas for conservation, including freshwater ecosystems. Since then, several KBAs have been identified mainly based on the presence of trigger species (i.e., species that trigger either the vulnerability and or the irreplaceability criterion and thus identify a site as a KBA). However, to our knowledge, many of these KBAs have not been validated. Therefore, classical surveys of the taxa used to identify freshwater KBAs (fishes, molluscs, odonates, and aquatic plants) were conducted in Douro (Iberian Peninsula) and Sebou (Morocco) River basins in the Mediterranean Biodiversity Hotspot. Environmental DNA analyses were undertaken in the Moroccan KBAs. There was a mismatch between the supposed and actual presence of trigger species. None of the trigger species were found in 43% and 50% of all KBAs surveyed in the Douro and Sebou basins, respectively. Shortcomings of freshwater KBA identification relate to flawed or lack of distribution data for trigger species. This situation results from a misleading initial identification of KBAs based on poor (or even inaccurate) ecological information or due to increased human disturbance between initial KBA identification and the present. To improve identification of future freshwater KBAs, we suggest selecting trigger species with a more conservative approach; use of local expert knowledge and digital data (to assess habitat quality, species distribution, and potential threats); consideration of the subcatchment when delineating KBAs boundaries; thoughtful consideration of terrestrial special areas for conservation limits; and periodic field validation.

The role of anthropogenic habitats in freshwater mussel conservation

Anthropogenic freshwater habitats may provide undervalued prospects for long-term conservation as part of species conservation planning. This fundamental, but overlooked, issue requires attention considering the pace that humans have been altering natural freshwater ecosystems and the accelerated levels of biodiversity decline in recent decades. We compiled 709 records of freshwater mussels (Bivalvia, Unionida) inhabiting a broad variety of anthropogenic habitat types (from small ponds to large reservoirs and canals) and reviewed their importance as refuges for this faunal group. Most records came from Europe and North America, with a clear dominance of canals and reservoirs. The dataset covered 228 species, including 34 threatened species on the IUCN Red List. We discuss the conservation importance and provide guidance on how these anthropogenic habitats could be managed to provide optimal conservation value to freshwater mussels. This review also shows that some of these habitats may function as ecological traps owing to conflicting management practices or because they act as a sink for some populations. Therefore, anthropogenic habitats should not be seen as a panacea to resolve conservation problems. More information is necessary to better understand the trade-offs between human use and the conservation of freshwater mussels (and other biota) within anthropogenic habitats, given the low number of quantitative studies and the strong biogeographic knowledge bias that persists.

Fish hosts, glochidia features and life cycle of the endemic freshwater pearl mussel Margaritifera dahurica from the Amur Basin

Margaritiferidae is a small freshwater bivalve family with 16 species. In spite of a small number of taxa and long-term history of research, several gaps in our knowledge on the freshwater pearl mussels still exist. Here we present the discovery of host fishes for Margaritifera dahurica, i.e. Lower Amur grayling, sharp-snouted lenok, and blunt-snouted lenok. The host fishes were studied in rivers of the Ussuri Basin. The identification of glochidia and fish hosts was confirmed by DNA analysis. The life cycle of M. dahurica and its glochidia are described for the first time. The SEM study of glochidia revealed that the rounded, unhooked Margaritifera dahurica larvae are similar to those of the other Margaritiferidae. Margaritifera dahurica is a tachytictic breeder, the larvae of which attach to fish gills during the Late August – September and finish the metamorphosis in June. Ancestral host reconstruction and a review of the salmonid - pearl mussel coevolution suggest that the ancestral host of the Margaritiferidae was a non-salmonid fish, while that of the genus Margaritifera most likely was an early salmonid species or their stem lineage. The overfishing of lenoks and graylings appears to be the most significant threat for this rare mussel species.

Phylogeny, phylogeography, and evolution in the Mediterranean region: News from a freshwater mussel (Potomida, Unionida)

The Potomida genus (Bivalvia, Unionida) has a Circum-Mediterranean distribution and like other freshwater mussel species, its populations have suffered dramatic declines. Although this genus is currently considered as monotypic, it has a long history of taxonomic revisions and presently many aspects of its systematics and evolutionary history are unclear. We sampled a total of 323 individuals from 39 different sites across the Potomida genus distribution, and sequenced two mitochondrial (16S rDNA and Cytochrome c Oxidase Subunit I) and one nuclear (28S rDNA) genes to clarify its phylogeny and phylogeographic history. Our results show that the genus includes two well-supported clades, one comprising solely the western Mediterranean species Potomida littoralis, and the other including two eastern Mediterranean species, the Greek endemic P. acarnanica and the Anatolian and Middle Eastern P. semirugata. We suggest that Potomida started radiating during the upper Miocene, and that both vicariance and dispersal events shaped the diversification and distribution of the genus along the Mediterranean region. P. littoralis is further divided in two mitochondrial lineages, one restricted to Europe and the other occurring mostly in North Africa. Moreover, some European basins present both lineages in sympatry. The conservation status of the three recognized species should be reevaluated, particularly P. acarnanica, since it is restricted to two Greek river basins presenting a high risk of extinction. Overall, our results clarify some important gaps in knowledge concerning the phylogeny, phylogeography and evolution of the Potomida genus in the Mediterranean region with important taxonomical, ecological and conservational implications.