Spatial distribution and effects of temperature rise on coastal free-living nematode community in the South Caspian Sea

In the present study, the spatial distribution of coastal free-living nematodes was first investigated at six different stations. The highest density, number of species, and Shannon diversity were recorded at Sisangan station. Subsequently, Sisangan station was chosen for studying the responses of the coastal free-living nematode community to increased surface water temperature (Field control = 20 °C, Treatment 1 = 24 °C, Treatment 2 = 27 °C, and Treatment 3 = 30 °C) experimentally over a period of 50 days. A total of thirteen species from eleven genera were identified. The genus Daptonema and the species Daptonema karabugasensis being the most dominant in all treatments. The highest total density and total Shannon index were recorded in the T3 treatment. There were no significant differences in the total number of species and the evenness index among the treatments. Changes in temperature significantly affected the community structure, primarily due to the presence or absence of specific species. SIMPER analysis showed that some species like Daptonema karabugasensis, Tripyloides marinus and Adoncholaimus araelensis were dominant within the community, although their relative abundance declined at the T2 and T3 treatments. In contrast, the relative abundance of Chromadorella parapoecilosoma and Chromadorita tenuis increased with rising temperatures in these treatments. The number of gravid females and juveniles also rose with temperature, peaking in the T3 treatment. As the temperature rose, the proportion of predators/omnivores (2B) in the community gradually increased, although the epistrate feeders (1B) remained dominant across all communities.