Collectors are similar to a plankton net with a conical polyester net (used for silk screen) with 200 pm and length/mouth diameter ratio 2/1.
Sexually reproducing animals were found, with the exception of June, only during autumn and early winter with a time lag between the first occurrence of males and ephippial
The mortality of individuals was higher at the site most influenced by the petrochemical complex, followed by the station located upstream from this area, while the formation of ephippial
eggs was uniform at all stations (Vargas, Migliavacca, Horn, & Terra, 2008).
falcatus Zacharias, 1898 x Synchaetidae Synchaeta pectinata Ehrenberg 1832 Polyarthra vulgaris Carlin, 1943 Cladocerans Total of ephippial
6 28 34 Bosminidae Bosminopsis deitersi Richard, 1895 x Chydoridae Alona poppei Richard, 1897 x Ephemeroporus tridentatus (Bergamin, 1932) Chydorus sp.
Although individual species vary, temperatures above 29-31 C have been shown to cause increased ephippial
egg production (Threlkeld, 1979) and mortality in cladocerans (Carlson, 1973), resulting in an overall decline in community abundance.
It was no possible to find males and ephippial
females, because the conditions in Yucatan Peninsula are quite stable, with a mild winter, and permanent water sources, with a moderate to high precipitation rates most of the year.
Hence, to convert ephippial
densities to daily production rates I divided the number of ephippia per female by the length of the molt cycle (Edmondson 1968, Paloheimo 1974, Braner 1988).
eggs hatch when conditions turn favorable again, and the ex-ephippial generation starts to reproduce parthenogenetically.
Although abundant in the samples (S1, S3), females, males and ephippial
females, this species did not appear in the cultures.
As mentioned earlier, Jarnefelt (1956) found ephippial
Alonella excisa females in Lake Tuusulanjarvi in southern Finland in early June.
eggs are resistant to harsh environmental conditions (Schwartz and Hebert 1987); they can even pass intact through predators' intestines (Mellors 1975).