The co-occurrence of Artemia parthenogenetica and Branchinella spinosa (Branchiopoda: Anostraca) in a saline pond of south eastern Italy

The co-occurrence of Artemia parthenogenetica Bowen & Sterling, 1978 and Branchinella spinosa Milne-Edwards, 1840, was previously only supposed, on the basis of finding their cysts in the same lagoon, but active stages were never recorded together. In a saline lake in south eastern Italy, populations of the two species were observed for two years. A. parthenogenetica was typical of the early wet season (October–January), while B. spinosa, even if it was present before, developed in the late part of the wet season (February–May). Adult A. parthenogenetica were recorded only in the season 1999–2000. The seasonal distribution of A. parthenogenetica is probably controlled by abiotic conditions (i.e., photoperiod, temperature, conductivity, and rainfall); however, competition between specimens of similar body size (e.g., adults of A. parthenogenetica, and juveniles of B. spinosa) could explain the lower numbers of B. spinosa population in winter. The discovery of cysts of both species deep in the sediment of the lake suggests a long-lasting co-occurrence of these two Anostraca.