Sea cucumbers have an important role in the marine ecosystem by filtering sediment, stabilizing the bacterial community, and contributing to primary production through the conversion of detritus into nitrogen compounds. This research was focused on the adaptations of Holothuria tubulosa (Gmelin 1791.) to environmental conditions under the influence of intensive aquaculture, with special emphasis on the area below the fish farm in Lamjana bay on the island of Ugljan. As a research method, a circular transect with a diameter of 20 meters was chosen, in which individuals were counted and measured, and samples were taken from each transect for further chemical testing. The research was conducted on two occasions, once in July, before the intensive feeding of the fish, and once in November, after the feeding. The structure of the population in the zone of local and transitional influence of organic matter was compared with a reference point outside the zone of influence. Population density was significantly higher at the reference point compared to locations below and next to the cage. However, the average size of sea cucumbers under and next to the cage was 38-45 % larger than at the reference point. The results indicate that population density depends on the length of individuals (shorter length results in higher density and vice versa). This research lays the foundation for further analyzes of the life cycle of sea cucumbers H. tubulosa, especially in the context of the development of integrated multi-trophic aquaculture.