Coregonus spp

Alexander, Timothy & Seehausen, Ole, 2021, Diversity, distribution and community composition of fish in perialpine lakes – “ Projet Lac ” synthesis report, Eawag: Swiss Federal Institute of Aquatic Science and Technology : 133

Coregonus spp (whitefish)

Since recolonization of the lakes after the retreat of the ice-sheets across Europe around 15,000 years ago, whitefish ( Coregonus ) have diversified into different ecological niches within each larger lake or set of connected lakes [155]. This has resulted in up to six ecologically differentiated species within a lake. At least 25 perialpine lakes were known to support native Coregonus species , the majority of which were endemic. The ecosystem changes resulting from eutrophication in the second half of the 19 th century led to extinction and speciation reversal of Coregonus species in many lakes. Almost 40% of Coregonus species went extinct across the region. Detailed information on the diversity of perialpine Coregonus species and the effects of human activities is available in Vonlanthen et al [42], with two key figures provided in Figure 24 .

[24, 48]

[42]

[42]

Coregonus spp can occupy many different spatial habitats, from the shallow benthic to open pelagic and the profundal zone down to 300 m of depth. No other group of fish occupies such a wide range of habitats in these lakes. Known ecologically relevant differences among Coregonus species include body size and growth rate, number, length and shape of gill rakers, eye size and visual pigments, diet and spawning habitat. The most distinct ecological types are the following:

1. large, fast growing, sparsely gill rakered, benthivorous species, which spawn in shallow water, referred to as “Balchen”- type whitefish (e.g. Coregonus duplex in Zurich/Walen, C. alpinus in Thun/Brienz, Coregonus litora - lis in Lucerne, C. arenicolus in Constance, C. suidteri in midland lakes and C. palaea in Neuchatel).

2. small sized, slow growing, densely rakered, zooplanktivorous species that live in the pelagic zone and spawn in deeper water, referred to as “Albeli”- type whitefish (e.g. Coregonus heglingus in Zurich/Walen, C. albellus in Thun/Brienz,C. muelleri in Lucerne).

3. small or medium sized, slow growing, sparsely rakered, benthivorous species that live and spawn in the deep profundal zone of lakes (e.g. Coregonus gutturosus in Constance, C. profundus in Thun).

Species with other combinations of these or other characteristics occur in lakes with more than three Coregonus species. For instance a type that is in many regards intermediate between the “Balchen”- type and “Albeli”- type whitefish, referred to as “Felchen”- type (e.g. Coregonus fatio in Thun, C. zuerichensis in Zürich, Walen, C. macrophthalmus in Constance), or large-bodied, fast growing, densely rakered pelagic zooplanktivores such as the Blaufelchen, C. wartmanni of Lake Constance. Reproductive isolation among members of lake radiations is maintained by differences in spawning depth, spawning season, possibly mate choice [39, 156] and possibly natural selection against intermediate phenotypes resulting from hybridisation.

[157, 158]

Coregonus spp were recorded in Projet Lac in all northern perialpine lakes, except Bret.The highest number of Coregonus species recorded in the same lake was in LakeThun, where all six species known to occur in the lake were recovered. All four species known from Lake Brienz were also recorded in Projet Lac [24, 160]. Three Coregonus species were recorded in Upper Constance, Upper Zurich, Lucerne and Biel. Coregonus spp were most commonly caught between 10 and 40 meters and dominated the biomass in the open water of many lakes. One species of Coregonus presumed to be extirpated in one lake was re-discovered in that lake in Projet Lac. In upper Lake Zurich, genetic analyses of samples collected in Projet Lac revealed the presence of three species, C. duplex , C. zuerichensis and C. heglingus [161], whereas C. heglingus was previously thought believed to have been extirpated in Lake Zurich. In Lake Lucerne, one individual resembling the deep-water adapted Coregonus nobilis (Edelfisch) was also recovered in Projet Lac. This species had also almost gone extinct (and was at some point believed to be extinct) during eutrophication, but was rediscovered in 2004 [162]. None of the other believed extinct Coregonus species , such as the profundal C. gutturosus in Lake Constance, C. fera and C. hiemalis in Lake Geneva, or C. restrictus in Lake Morat were recorded by Projet Lac.

Figures

Figure 24: Relationship of the maximum total phosphorus concentration experienced by each lake versus the proportion of Coregonus species lost in each lake (left) and the genetic differentiation (global Fst) among the post-eutrophication Coregonus species within those lakes that retain native Coregonus species (right). Modified from [42].