As a result of the materials found in the 2019 monitoring studies, six new species of macroalgae were identified for the marine area of the Nature Reserve "Cape Martyan." They were located on the Southern Coast of Crimea (SCC): <i>Bolbocoleon piliferum</i> Pringsh., <i>Giraudia sphace-larioides</i> Derb&#232;s et Solier, <i>Myrionema balticum</i> (Reinke) Foslie, <i>Lithophyllum cystoseirae</i> (Hauck) Heydr., <i>Bonnemaisonia hamifera</i> Har., and <i>Choreonema thuretii</i> (Bornet) F. Schmitz (the latter two species were recorded for the hydrobotanical region "Southern Coast of Crimea" for the first time). Correspondingly, the list of marine macrophytes within the boundaries of the Nature Reserve now includes 160 species and intraspecific taxa at the species rank, which consist of &#126; 36&#37; of the total number of macrophytes identified in the Black Sea. Thus, the protected water area near the Cape Martyan continues to function as one of the key refugia for natural phytodiversity in the region. At the same time, <i>B. hamifera</i> is an invasive transforming species that has recently invaded the SCC region. This is a threat to the ecosystem of the Nature Reserve, and in the near future the invasion may cover the entire Northern Black Sea region. The results of this study expand the level of understanding of natural phytodiversity of the reserve, the hydrobotanical region and the region as a whole yet simultaneously indicating a developing problem of biological invasion, which, under the current conditions of the isolated Azov-Black Sea basin, can have catastrophic consequences.

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The data on the composition and distribution of macrophytobenthos of marine and lagoon water areas of the Black Sea coastal zone in the west of the Tarkhankut Peninsula in the summer season are presented. It is shown that the occurrence and general characteristics of the vegetation cover are determined by the type of substrate. In the sea (where hydrological conditions are relatively homogeneous), the ratio of ecological-floristic groups and the species composition change with distance from the coast and along with it, depending on the depth and geomorphological features of coastal zone fragments. In the lagoon, the ratio of such groups changes along the complex gradient of environmental factors, formed by the groundwater runoff of fresh and marine waters. Within the surveyed area, 91 species of macrophytes were registered: Tracheophyta – 1 species (1.1%), Chlorophyta – 23 (25.3%), Ochrophyta (Phaeophyceae) – 21 (23.1%), and Rhodophyta – 46 (50.5%). Of these, 87 species were recorded in the sea (including 44 in the pseudolittoral zone and 81 – in the sublittoral zone). The macrophytobenthos has a pronounced marine oligosaprobic character. Short-vegetation Rhodophyta dominate by the number of species, and perennial Phaeophyceae dominate by biomass, reaching 1 kg∙m-2 in the pseudolittoral and almost 7 kg∙m-2 in the sublittoral. In the lagoon, 18 species of macrophytes were registered (4 exclusively in the lagoon). Mesosaprobic short-vegetation Rhodophyta dominate by the number of species; marine and brackish-water macrophytes are equally represented. Polysaprobic perennial Tracheophyta, which belong to the marine group, dominate by biomass, which is ranging from 0.04 to 1.2 kg∙m-2. It was found that at the time of the research, the macrophytobenthos of the surveyed area was characterized by high productivity, high species, and coenotic diversity. There were taxa and biotopes, which are subject to special protection under regional and international programs. In general, the nature of the vegetation, the composition of the flora and the ratio of the main ecological-floristic indicators corresponded to those indicated for the Tarkhankut-Sevastopol hydrobotanical region of the Black Sea. Considering the sozological value, the aquatic component of the territorial-aquatic complex was recommended for conservation and inclusion in the ecological networks (incl. the Emerald Network). The increased anthropogenic pressure and the threat of the coastal zone transformation actualize the problem of its conservation as one of the key reserves of the floristic and biotopic diversity of coastal-marine areas in the Northern Black Sea region.

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