Explorations of intertidal benthos in the area of Vitino Specialized Marine Port using usual hydrobiological methods have been carried out for more than ten years. Studies on the structure of intertidal communities by means of various statistics allow for a quasi-cyclic dynamics of their biomass to be revealed. The dynamics of the main features of an intertidal blue mussel bed at one of the sampling sites is demonstrated. In addition, some analytical approaches to an expert evaluation of the state of sea floor ecosystems for anthropogenic impacts' diagnostics are critically discussed. It is shown that a nonrecurrent evaluation cannot be reliable due to permanent quasi-cyclic processes occurring in intertidal communities, whereas the evaluation methods based on shifting the natural selection pressure along the K-, r-axis may only be used with great care. To obtain a safe evaluation, long-term monitoring is required, with the number of sampling repetitions at each point to be selected so as to level aggregated distributions of individual species.
