Mussel of the Month

We will get to Beringiana beringiana at the end of this post, but to start, we need to take a step back to look at the whole world.

With the latest influx of new freshwater mussel species in our tally (Lopes-Lima et al. 2020, Bolotov et al. 2020), the balance of species richness has shifted. For a long time, it has been taken for granted that North America is the freshwater mussel diversity hotspot of the world. Our checklist (Graf & Cummings, 2007 and this web site) provided a reference to go with that view. Before that time, we Americans could boast various tallies of our own species (Burch, 1975; Turgeon et al., 1988., 1998; Williams et al., 1993), but to get numbers for the rest of the world, few people had a access to Haas (1969), and Simpson (1914) was grossly outdated. In 2007, we calculated that the 302 North American species represented 36% of the global fauna of 840 spp. — more than any other region.

Nowadays, we still count 302 species in North America*, but East Asia has ticked up to 320 — an increase of 78 species in 13 years! Much of this has to do with the rapid rate of discovery and revision of species in that region over the last few years (a topic we have frequently noted — as recently as last month). Since 2007, East Asia has netted 32 species just through revision (55 elevated from synonymy, 23 sent back down to invalid roster) and 46 species described as new to science. That is 75% of all new species described during that time period!

Another important factor in this shift in regional freshwater mussel species diversity is our revision of biogeographical boundaries. For our previous tallies, we used the traditional physiographic divisions for Eurasia, dividing the continent(s) into Palearctic and Indotropical regions. To better reflect actual areas of freshwater mussel generic endemism, our current tallies divide that part of the Old World into North Eurasia and East Asia. East Asia accounts for the old Indotropics plus the most species-rich parts of the former eastern Palearctic like the Amur Basin and Japan. If we only consider the species flux in the old Indotropics (from the Yangtze through Indochina to India, including the Sunda and Philippine Islands), the new regional total would be 281 species. That represents a gain of 62 species since 2007. So, if we used the old biogeographic regions — that don’t reflect freshwater mussel biogeography as well — the Nearctic region (i.e., North America) would still have the most species.

For those Americans that feel as though we have lost some bragging rights about our freshwater mussel diversity, please consider the following. First, that’s a weird thing to brag about. Second, you might ponder that our regional divisions are person-made imaginary boundaries** and the traditional regions are “better.” But, America can rest easy that, in terms of areas of endemism and species richness, the North American Mississippi-Great Lakes and Gulf-Florida subregions each harbor more total and endemic species than any of the Yangtze-Huang, Indochina (including the Mekong), or India-Myanmar subregions that are the richest in East Asia. During this messed up June of 2020, America can at least cling to that.

We would rather look to freshwater mussels as beacons of unity rather than division, and in that light, we have selected Beringiana beringiana as the Mussel of the Month. Only a handful of mussel species have native ranges that extend across regional boundaries, and B. beringiana is one of them, occurring in both East Asia and North America — it gets counted in both tallies!

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* However, it isn’t the same 302 now as then. Since 2007, we have gain 39 species that were either new to science or resurrected from synonymy that have been exactly matched by 39 formerly valid species that are no longer considered so.
** Although the new regional boundaries sure look like they provide more explanatory and predictive power with regard to freshwater mussel systematics and biogeography.
*** These numbers change quickly nowadays. Check our Biogeography Summary Page for the latest tallies.