The current study presents data from research conducted in Mangalia military port, in the period November 2008 - February, March, and April 2009. An analysis of percentage composition of the invertebrates’ populations is done in the paper. Taxa belonging to at least 10 major groups were found, either on mobile substrata, either on rocky one, sometimes covered with macrophyte algae. The data were used in the evaluation of some synecological indices, as frequency (F %), average density (D avg ind. • m-²), for each of the studied stations. Correlation between variation of the number of taxa and density depending on type of substrata was done. The ecological significance index WD and its correlation with the rank was also calculated, showing that, in the studied area, oligochaetes, nematodes and harpacticoids are considered as characteristic groups, holding, in order, the first three ranks.