Natural habitats and their biodiversity are usually associated with protected areas, incompatible with direct anthropogenic influence. Is there a biodiversity in urban environment, what is the role of peri-urban areas to the provision of species richness and is their potential being properly utilized? These are current issues that deserve the attention of decision-makers because the human's need of natural environment in cities is expressed more intensely than in any previous period in history. Green and blue infrastructure elements, being part of the larger system of urban ecosystems, provide an essential and proven benefits to the city dwellers, like health improvement, opportunities for nature-based daily outdoor recreation, strengthening sense of place etc. The main objective of this research is to assess this part of the landscape elements in urban and peri-urban environment, which are most supportive to the maintenance of habitats and their biodiversity. Selected Functional urban area with center city of Burgas is choosen for a case study. The urban ecosystems are assessed in GIS environment with unified indicator (based on City Biodiversity Index approach) according to 5 criteria: hemeroby index, share of protected areas, fragmentation index, presence of water and species richness. The assessment is performed on two spatial levels: within Functional urban area by Urban Atlas spatial units and within urban core – by grid cells (local climate zones). The final higher scores identify areas that provide the greatest extent the maintenance of habitats and their biodiversity. The results could support the urban planning and help to optimize the link between the natural elements within the Functional urban areas, providing ecological, economic and social benefits to the regions through the enhancement of the urban ecosystem’s functions and their services.