ANOXIA AND ITS IMPACTS ON THE VERTICAL DISTRIBUTION OF COPEPODS IN A DEEP MEDITERRANEAN COASTAL LAKE

摘要

The present study investigates the vertical distribution of the copepods found in a deep and anoxic Mediterra nean coastal lake during a two-year period. The numeri cally most important adult copepods were the calanoids Paracartia latisetosa (66.9 %) and Calanipeda aquaedul cis (27.4 %), while the harpacticoids Euterpina acuti frons, Harpacticus gracilis, Tisbe sp. and Microsetella sp. along with the cyclopoid Oithona nana accounted on average for 5.7 %. The copepod nauplii (not distinguished to species) were found year-round and outnumbered the community. For all species, greater abundance values were found in late spring and in summer while lowest in win ter. Along the vertical axis, over 90 % of the abundance of the two most important species and nauplii was recorded in the surface 0-5 m layer, except in winter and early spring when considerable proportions were also recorded in deeper layers. The percentage contribution of the harpacticoids and cyclopoid species within the copepod's community showed an increase with depth, from 5.4 % in the surface to 39.5 % in the deepest layer. An exponential increase in the average percentage of copepod carcasses with depth was also noticed. In the well oxygenated surface layer, the most important parameter influencing the seasonal cycles of all species was temperature. The depletion of oxygen and the increase of hydrogen sulphide with depth were restrict ing factors for the vertical distribution of calanoid cope pods. However, they seemed to have affected less the pres ence of harpacticoid and cyclopoid species which seemed to be more tolerant to anoxia.