Composición específica de las comunidades zooplanctónicas de 153 lagos de los Pirineos y su interés biogeográfico

Zooplankton samples from 170 lakes of the Spanish Pyrenees were collected with the help of hiking clubs and university students, mainly in a campaign in summer 1976. Data on species composition could be obtained from 153 of those lakes. The lakes are situated between 1650 and 2960 m in elevation and range from 0,5 to 61 Ha in surface and from 1 to 101 m in depth. They represent wide ranges of transparency, temperature, chlorophyll contents, trophic state, but are rather uniform for salinities and alcalinities, wich are very low (alcalinities varíate from 0,01 to 1,2 meq/l). A total number of 48 crustaceans where identified, 17 copepods, 29 cladocerans, 1 amphipod and 1 anostracean. Among them, only 6 copepods and 8 cladocerans can be considered euplanktonic. Main results are a striking uniformity of species composition throughout the whole area and a very reduced number of species per community, a mean of 2-3 crustaceans and 3-4 rotifers in the plankton. The same results are apparent from any study of alpine lakes. Communities were composed by 0, 1 or 2 species of each of the groups of crustaceans: diaptomids, ciclopoids and cladocerans, and 2 to 5 species of rotifers (when sampled with appropiate mesh). The most frequent species are Cyclops abyssorum (Einsle, 1975), and Daphnia longispina, occurring in the 69 % of the lakes studied, which constitute a planktonic community by themselves (46 % of
the lakes studied) or a part of more complex communities with diaptomids. The communities are grouped into five types on the basis of the diaptomid species present. Smaller species, Eudiaptomus vulgaris or Mixodiaptomus laciniatus, are dominant in permanent, not extremely high waters (24 % of the lakes studied) and Diaptomus cyaneus or D. castaneti are characteristic of higher and more oligotrophic lakes or ponds and temporal waters (25 % of the lakes studied). In large and deep lakes a complex community with two diaptomids, Diaptomus cyaneus and one of the smaller forms, can be found (3,3 % of the lakes studied).
Specific composition of the zooplanktonic communities of the Pyrenees is strikingly similar to that of the Alps and also to other high mountain zones if diaptomids are not considered. Diaptomids differenciate the Pyrenean lakes zooplankton from that of other mountain systems of Europe and approximate them to the african Atlas zooplankton. The most common species in the Alps, Arctodiaptomus baccilifer and Acanthodiaptomus denticornis, are not found in the Pyrenees, where, instead, Diaptomus cyaneus of a marked mediterranean character is the most frequent species. The species of the genus Diaptomus found in the Pyrenees, D. cyaneus and also D. castaneti (may be a synonim of D. kenitraensis) have a Western Mediterranean distribution. Their main populations are restricted to the Pyrenees and the Atlas. D. castaneti is also very similar to D. castor, a Northwestern European form. M. laciniatus occurs in the Western half of the Pyrenees and is a boreoalpine species with Atlantic distribution, not frequent in the high mountain lakes of the Alps, and frequent in Northwestern Spain, Scotland and Norway. E. vulgaris occurs in the Eastern part of the Pyrenees and is a middle European species.
The four species of diaptomids found in the Pyrenees belong to very different biogeographic distributions (fig. 3). This accounts for the importance of historical, biotic or competition factors in the community species composition.