Cenotes – Lakes of the Yucatan Peninsula (Mexico)

Cenote lakes are natural sinkholes or depressions resulting from the collapse of limestone bedrock exposing the groundwater underneath. Thousands of such lakes are particularly encountered on the Yucatan Peninsula (Mexico). These lakes were of great significance for the Maya culture as important religious places and primary source of drink­ing water. They permitted the survival of Mayan communities through dry periods known as “Maya drought”. Most of the cenote lakes are large open water pools measuring tens of meters in diameter. The majority of cenotes are smaller sheliered sites. Their waiers are usually very clear and oligotrophic, originating from rain waier filtering slowly through the ground. The auihors visited and coliected zooplankion samples from eight cenotes in November 2013, namely: Ik-Kil, Samula, Zaci, X-Kekn, Actum Ha, Cristal, Sian Ka’an, and Chan Chemuxil (transect Merida-Tulum- Cancun). The analysed lakes differ considerably in morphological terms, varying from very deep to shallow. Some of them are under human impact (tourists). The water samples were anaiysed for zooplankton content, but the phyto­plankton frequently occurring was also taken into account. The obtained results are largely varied, indicated big eco­logical verity among cenotes which depended on lake age, localization and morphometry. As showed our study Cladocera zooplankion was very rare and only present at several sites. Beiween the fauna community Copepoda and Ostracoda species were the most abundant. Phytoplankton were present in all studied lakes and it sees that played the central role in those ecosystems.

THE WING LENGTH OF LENTIC CAPNIIDAE (PLECOPTERA) AND ITS RELATIONSHIP TO ELEVATION AND WISCONSIN GLACIATION

Along the Continental Divide in Alberta, British Columbia, and Montana three species of Capniidae were common at some lakes (Capnia confusa Claassen, Isocapnia integra Hanson, and Utacapnia trava (Nebeker and Gaufin)). Females of all three species had substantial reduction in wing length at least at one lake, while most lentic populations had slightly shorter wings than a macropterous river population of the same species. For females of all three species there was a weak positive relationship between functional wing length and lake elevation. Furthermore, there was also a significant negative relationship between functional wing length and the approximate year of Wisconsin deglaciation for C. confusa and U. trava. Suitable data were not available to test the significance of this relationship for I. integra. However, the relationships between wing length and elevation, and between wing length and Wisconsin deglaciation, suggest that wing length of these three capniid species is related to lake age. Present day wing length might be explained by selection for brachypterism over recent millennia.