The calanoid copepod Acartia italica Steuer, phenomenon in the small saline Lake Rogoznica (Eastern Adriatic coast)

Abstract

Lake Rogoznica, near Sibenik, Croatia, is a salt coastal lake with a maximum depth of about 15 m. During most of the year, this small, naturally eutrophied lake is highly stratified, with hypoxia/anoxia occurring in the bottom layer. Total anoxia, with the presence of hydrogen sulphide, was recorded on September 27, 1997. At that moment, massive mortality of all planktonic and benthic organisms was observed. After the anoxia, Acartia italica, the only planktonic copepod species of the lake, re-established quickly. Before anoxia, the population dynamics of the A.italica population depended primarily on predator/prey relationships. However, in the post-anoxic period, nutrient-phytoplankton-copepod relationships became more important, as there was no longer any predation pressure. From all accounts, it would appear that only A.italica is adapted to the extreme conditions which appear from time to time in the lake, and that this species has an important role in the functioning of the lake ecosystem. Acartia italica was very important for the gradual normalization of life in the lake after total anoxia.