LAUSR

Simple Summary Despite a long research history of fish parasites in the Azov–Black Sea region, the helminth community structure among fish populations remains poorly understood. Until recently, only a few articles considering the helminth communities of mullet fish from this region have been published. In the present paper, the data on the species diversity and the structure of the helminth communities of 12 common fish species are presented for coastal waters off Crimea. These communities are characterized by low species richness and relatively low diversity indices. Component communities are more diverse than infracommunities. Although these parameters correspond to unbalanced, immature communities, the modern helminth communities of Crimean marine fish are well-aggregated and follow a “core–satellite” distribution, indicating their balanced structure. There are no negative inter-specific relationships in most of the component communities. Obtained data expand the current knowledge regarding the organization of parasite communities in the region and may have important implications for the further monitoring and proper management of local fish stocks. Abstract In this paper, we analyzed the diversity and structure of helminth communities of 12 common fish species from the coastal zone of Crimea. A total of 53 helminth species were found. The total number of parasite species per host fish ranged from 3 to 18. Species richness at the infracommunity and component community levels were from 1.4–4.2 to 1.7–7, respectively. The Brillouin index for the infracommunites was 0.1–1, while the Shannon index for the component communities was 0.3–1.2. Component communities demonstrated a bi- or tri-modal distribution of the parasite prevalence and positive correlations between the prevalence and log-transformed abundance indices, thus following the “core–satellite” conception. Overall, the prevalence and abundance index of the dominant parasite in the component communities ranged from 18 to 80% and from 0.6 to 61.5 ind. per fish, respectively. The structure of the helminth component communities demonstrated good accordance with the nestedness mode where the rarest species occurred in the most diverse infracommunities, while the poorest infracommunities were composed of a few dominating species. More than two-thirds of the studied helminth species had an aggregated distribution indicating well-structured and developed communities. Our data provide a basis for further research and may be used for fish resource monitoring and management.