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Larval fish assemblages are crucial indicators for monitoring marine ecosystem dynamics and the recruitment potential of fishery stocks. This study investigates the spatiotemporal dynamics of larval fish assemblages in the central Southern Black Sea (Sinop) and the environmental parameters shaping these patterns. An intra-annual monthly sampling survey identified 35 species across 20 families; the assemblage structure was dominated by Engraulis encrasicolus, Gobius niger, Sprattus sprattus, Mullus barbatus and Trachurus mediterraneus. Multivariate analyses revealed a clear temporal structuring of larval fish assemblages due to intra-annual variation. However, no significant spatial separation was observed among the stations. Distance-based Linear Models (DistLM) indicated that assemblage variability was primarily associated with salinity, chlorophyll a and temperature, as well as light transmission and current velocity. Species-specific responses of dominant taxa to environmental variables were examined using Generalized Additive Models (GAMs), revealing distinct environmental partitioning among species. Model results indicated that E. encrasicolus abundance was primarily associated with chlorophyll a and low salinity gradients, whereas G. niger exhibited a response to multiple variables, including low salinity, low light transmission, and a wide thermal range. Conversely, the distribution of S. sprattus was strictly limited by low temperatures and specific ranges of light transmission. These findings suggest that larval fish assemblages in the Southern Black Sea are structured by a complex combination of physical forcing (such as mesoscale hydrological features) and biological interactions, in which differentiated environmental responses facilitate species coexistence.

This study investigated the temporal and spatial variability of mesozooplankton community structure, abundance, biomass, and species composition in Hamsilos Bay, located in the southern Black Sea, during the summer of 2024. Zooplankton samples were collected monthly from six stations distributed throughout the bay between June and August 2024. Mesozooplankton abundance and biomass exhibited pronounced temporal and spatial variability, with generally higher values recorded at shallow inner-bay stations. Copepoda and meroplankton constituted the dominant components of the mesozooplankton community throughout the study period. In terms of abundance, Paracalanus parvus, Oithona similis, and Acartia clausi were the dominant species in June 2024, whereas a marked increase in the abundance of Oithona davisae was observed during July 2024 and August 2024. In addition, copepod early life stages represented a substantial proportion of the mesozooplankton community throughout the sampling period. Biomass distribution differed from abundance patterns and was mainly influenced by the contribution of meroplanktonic larvae and relatively large-bodied organisms. Multivariate analyses revealed significant differences in mesozooplankton community structure among sampling periods and stations. Overall, the results indicate that the summer mesozooplankton community structure in Hamsilos Bay was associated with temporal shifts in dominant species and local environmental conditions. Furthermore, the findings highlight the importance of evaluating both abundance and biomass together to achieve a more comprehensive assessment of mesozooplankton community structure.

The Strait of Istanbul (Bosphorus, SoI) system, which serves as a biological corridor between the Black Sea and the Sea of Marmara, plays a critical role in the transport of fish during their early life stages. This study examined the structure, distribution, and relationship with environmental factors of the surface ichthyoplankton assemblage in the transition zone between the Strait of Istanbul and the Northern Marmara Sea, beginning at the Black Sea entrance. The research was conducted at 13 stations determined between 22 and 29 July 2023, representing the summer period. Sampling was performed using a WP2 plankton net, while hydrographic data (temperature, salinity and current velocity) were obtained in high resolution from the Copernicus Marine Service (CMEMS) satellite database. A total of 21 taxa were identified in the assemblage, with Engraulis encrasicolus (European anchovy) and Trachurus mediterraneus (Mediterranean horse mackerel) identified as the dominant species in the upper layer. The results of the Distance-Based Linear Model (DistLM) and dbRDA analyses indicate that temperature and salinity gradients are the main explanatory variables for variation in species composition. Additionally, the observed spatial patterns and the model's sensitivity to current velocity suggest that the Strait of Istanbul surface current system could potentially act as a supportive mechanism for the localized transport of E. encrasicolus early life stages. In turn, this transport process is thought to have potential implications for the local recruitment dynamics of the species in the Sea of Marmara.

This study was conducted to determine species diversity, abundance dynamics, and variation in the summer ichthyoplankton assemblage along the Gümüldür coast (İzmir), a significant coastal habitat of the Aegean Sea. Sampling was conducted at five stations in a shallow coastal area characterized by Posidonia oceanica seagrass meadows during July and August 2024. As a result of the study, 27 taxa belonging to 18 families were identified. Among the identified taxa, 22 were represented as eggs and 9 as larvae. The taxa dominant in the plankton community were identified as Labridae (70.7%), Engraulidae (7.8%) and Sparidae (5.3%), respectively. The mean abundance was calculated as 7189 ind‧1000 m-³ for fish eggs and 351 ind‧1000 m-³ for larvae throughout the study period. The highest mean abundance was recorded for Coris julis eggs with 2544 ind‧1000 m-³ larvae with 78 ind‧1000 m-³. Engraulis encrasicolus eggs with 558 ind‧1000 m-³ and larvae with 13 ind‧1000 m-³. Among the sampling periods, species diversity reached its peak in the first half of July (Smax=13, J'max= 0.96, H'max=2.39). In contrast, during the first half of August, species diversity decreased as the Labridae species became increasingly dominant, even as total abundance peaked. A decline in spawning activity was observed in the second half of August. As the first ichthyoplankton study conducted in Gümüldür, this research emphasizes the importance of the regional seagrass meadows, particularly for ecologically significant demersal fish taxa.

This study was conducted using monthly data collected between July 2015 and June 2016 in the marine area of Hamsilos Nature Park, located in Sinop, Southern Black Sea. The primary objectives were to determine the diversity of ichthyoplankton assemblages, examine seasonal variations, assess spatial differences between the inner and outer parts of Hamsilos Bay, and highlight the ecological relationships of the predominant species with environmental factors. The comprehensive collection during the study resulted in a mean abundance of 2217 eggs.10 m² and 2743 larvae.10 m², with 28 species belonging to 21 families identified. Specifically, Engraulis encrasicolus is the most abundant in spring and summer, Gaidropsarus mediterraneus is the most abundant in autumn, and Sprattus sprattus is the most abundant in winter. A temporal analysis revealed the highest abundances in August, September, and July, with the lowest in April, May, and February. Significant seasonal differences in abundance and diversity were detected. No spatial differences were found between the inner and outer areas of Hamsilos Bay. Small pelagic species dominated the ichthyoplankton community, while demersal species, though diverse, were less abundant. According to the results of the DistLM analysis, the structure of the ichthyoplankton community is influenced by temperature and salinity. During the study, the water temperature ranged from 8.35 °C in February to 25.50 °C in August, and the salinity varied from 17.67 psu in September to 19.04 psu in May.

Sebastes schlegelii Hilgendorf, 1880 is an Indo-Pacific species with a widespread distribution in the coastal waters of the Far Eastern region. This study represents the first documentation of S. schlegelii off Sinop coast from the Southern Black Sea. The four specimens collected on 28 May 2023 and 18 June 2023 from rocky habitat at a depth of about 6 meters off Sinop coast had a total length range of 226 to 237 mm and weights ranging from 197.57 to 254.98 g. The spread of this species to the southern Black Sea coast is attributed to the transportation of early life stage individuals from the northern coast of the Black Sea to the southern coast via the cyclonic Rim Current.