Characteristics of sublittoral vegetation at the northwestern coast of the Japan Sea based on the concept of adaptive zone

On materials of the diving survey conducted in 2010, using additional data obtained from 1999 to 2023, sublittoral vegetation at the northwestern coast of the Japan Sea is described. Basing on the concept of adaptive zone, 16 associations are identified (Ulvetum fenestratae, Saccharinetum japonicae, S. cichorioidae, Kjellmanielletum crassifoliae, Costarietum costariae, Agaretum clathratae, Desmarestetum viridae, Sargassetum miyabeae, S. pallidae, Stephanocystetum crassipae, Bossielletum compressae, Ptilotetum asplenioidae, Odonthalietum corymbiferae, Zosteretum marinae, Z. asiaticae, Phyllospadicetum iwatensis) and a group of communities of encrusting calcareous algae. These associations are not abstract classification units, but mosaics of homogeneous adaptive zones of their main dominants considered as elementary Petersen-type communities where on average 58 % of bottom cover and 53 % of biomass are formed by the main dominant species. The associations of the upper layer can be identified visually, with assessing the projective coverage of main dominants and subdominants for each of them using underwater drones. Visual identifying for subordinate species is less available, as well as quantitative assessment of their coverage. The total area occupied by the vegetation associations is 217 km2 , i.e. about 2/3 of the total vegetation belt. The total biomass of vegetation within the associations is estimated as 1248 . 103 t, of which the biomass of the main dominants is 709 . 103 t. Commercial and potentially commercial resources of macrophytes are generally confined to their associations, that allows to estimate the total stock in 324 . 103 t, including 94 . 103 t of the only commercially used species Saccharina japonica. These stock values have no statistically significant difference from earlier estimations (p = 0.79), that approves using the concept of adaptive zone for assessment of commercial resources of subtidal vegetation.