The
maar lakes, or
axalpazcos, of the Oriental Basin are home to a closely knit set of endemic species, one at each crater lake. Some of these include the Atherinopsid fishes
Alchichica silverside (Poblana alchichica),
La Preciosa silverside (P. letholepis),
Chignahuapan silverside (P. ferdebueni), and
Quechulac silverside (P. squamata). Three species of
dace (Evarra bustamantei, E. eigenmanni, and
E. tlahuacensis) formerly native to the basin are presumed extinct since about 1970. The
WWF-
Nature Conservancy system of freshwater ecoregions includes the Oriental Basin with the Valley of Mexico, Lerma River, and Lake Chapala in their
Lerma-Chapala freshwater ecoregion, based on faunal similarities, especially among the Atherinopsids.
Lake Alchichica Lake Alchichica () in
Tepeyahualco (municipality),
Puebla, is the largest of the maar lakes of the Oriental Basin, and lies at an elevation of 2320 meters. It is Mexico's deepest natural lake, with a maximum depth of 64 meters, and a mean depth of 38.6 meters. The lake has an area of 1.81 square kilometers. It is both saline and alkaline (pH 8.7-9.2). Lake Alchichica is ecologically unique, with
stromatolite deposits and a high degree of endemism. The biota has adapted to extreme conditions characterized by high ionic concentrations of water and poor nutrient content. The dominant stromatolite species are the spongy type
Enthophysalis atrata,
Enthophysalis sp.
Calothrix cf.
Parletina and
Calothrix sp. and the columnar stromatolites
Enthophysalis lithophyla and
Nitzschia sp. In the deep parts of the lake, abundant
cladophores develop on the spongy stromatolites, with many
cyanobacterial
epiphytes Chamaesiphon halophilus,
Heteroleibleinia profunda,
Mantellum rubrum and
Xenococcus candelariae. 23 genera of phytoplankton have been found: fourteen genera of
Chrysophyta, five of
Cyanophyta and four of
Chlorophyta. The dominant species throughout the year are
Agmenellum sp.,
Amphora sp.,
Chaetoceros similis,
Coscinodiscus sp.,
Cyclotella striata,
Nodularia spumigena,
Stephanodiscus niagarae and
Synechocystis sp. The best represented species best of vascular plants in the
axalpazcos are rooted emergent
hydrophytes
Eleocharis montevidensis,
Juncus andicola,
J. balticus subsp. mexicanus (syn.
J. mexicanus),
Phragmites australis,
Scirpus californicus and
Typha domingensis, the submerged rooted hydrophytes
Cyperus laevigatus,
Potamogeton pectinatus and
Ruppia maritima, and the free-floating hydrophyte
Lemna gibba. Animals endemic to Lake Alchichica include the
Taylor's Salamander (Ambystoma taylori), the fish
Poblana alchichica (Alchichica silverside, Charal de Alchichica), and the
isopod Caecidotea williamsi. ==References==