ВІЛЬНОЖИВУЧІ МОРСЬКІ НЕМАТОДИ ПРИБЕРЕЖНОЇ ЗОНИ О. ЗМІЇНИЙ УКРАЇНСЬКОГО ШЕЛЬФУ ЧОРНОГО МОРЯ

The species diversity, quantitative parameters and spatial distribution of the free-living marine nematodes in the meiobenthic community of the coastal zone area near the Snake Island, Black Sea, Ukraine shelf, have been studied for the first time. In total of 47 species from 5 orders, 14 families and 31 genera were registered. The representatives of orders Monhysterida and Enoplida were most abundant. The results of the comparative analysis of nematode assemblage in dependence of the substrate type are described. The percentage of nematodes in total meiobenthos in piers fouling consisted of 16% only, but on silt bottoms it reached 60.8%. The species diversity also increases on silt bottoms. Four nematode species are registered in piers fouling, but 36 on silts. The omnivores-carnivores consisted of 50% of the nematode assemblage in piers fouling. On silts, the percentage of non-selective deposit feeders reached 47%, but epistrate feeders decreased up to 14%.

Nematodes down under: State of knowledge and future trends

Nematodes inhabit most environments that address their need of water, carbon, and energy. They also play an important role in epigean food webs by occupying different trophic levels, while providing essential ecosystem services such as regulating decomposition and nutrient mineralization. Conversely, little is known about the role that nematodes play in subterranean ecosystems. For this reason, an in-depth review was undertaken in order to concatenate data from existing literature and provide a baseline for future studies. A total of 41 surveyed scientific works, published over a time period of 138 years, reported 295 unique taxa from 78 different cave systems. Although an increase in scientific outputs was recorded from the late 1990s, there is a considerable lack of information on cave-dwelling nematodes from Asia, South America, and North America. Also, only seven true cave-dwelling (troglobitic) species have been discovered, which may indicate a lack of comprehensive taxonomic efforts. From an ecological perspective, very few works have reported on the importance of nematode assemblages associated with cave ecosystems. This has resulted in the causal factors leading to population resilience processes, as well as trophic interactions, remaining mostly speculative. Nonetheless, the isolated cave-dwelling nematode assemblage associated with Movile Cave, including the true cave-dwelling species Chronogaster troglodytes, fulfills an important role by feeding on microbial mats and in turn serving as a food source for predators. This example of a cave nematode assemblage providing ecosystem services has inspired the undertaking of the Gcwihaba Caves Research Project, which aims at studying artificially opened caves in Ngamiland, Botswana. Compared to other caves in the area with natural openings, the artificially opened systems present different food source pathways, atmospheric conditions, and community assemblage structures. This provides a unique opportunity to study isolated cave communities, including nematode assemblages, as well as their ecological importance.

THE INFLUENCE OF TIDAL AND RAINFALL CYCLES ON INTERTIDAL NEMATODES: A CASE STUDY IN A TROPICAL SANDY BEACH

The present study describes the nematode assemblage of the bay of Tamandaré (Brazil), a tropical sandy beach, during the low, flood, high and ebb tides of two consecutive tidal cycles in four different months of the year (May, July, September and November). The nematode assemblage was dominated by Metachromadora and Perepsilonema and varied significantly between months and tides. Densities were lower in July, and changes in assemblage structure occurred during the transitional periods between rainy and dry months, which showed the influence of rainfall. Flood and ebb tides appeared to exercise the greatest influences over the tidal cycle, although the patterns were not very clear. Identification at genera/species level is recommended for future studies, to better understand the patterns of nematode assemblages during tidal cycles.

Spatial patterns of distribution of meiofaunal and nematode assemblages in the Huvadhoo lagoon (Maldives, Indian Ocean)

Huvadhoo Atoll is a little-known and generally uncontaminated atoll of the southern Maldives, although the human pressure is increasing. This study represents the first attempt to characterize the meiofaunal and nematode assemblages of its lagoon both from a taxonomic and functional point of view. The nematode assemblage was made up of a total of 131 genera in 33 families. Desmodoridae, Chromadoridae and Xyalidae represented the richest and most abundant families, followed in terms of abundance by Selachinematidae and Comesomatidae. The nematode richness was overall higher than that reported in the previous studies carried out in the Central part of the archipelago. The diversity patterns revealed higher values than those reported for the back-reefs platforms, so confirming the positive influence of the water depth on the biodiversity of the nematode assemblage. The statistical analysis highlighted a significant taxonomic difference of the assemblages between the stations characterized by fine and medium-coarse sands, respectively, in line with the auto-ecological preferences of the taxa detected. The use of some nematode descriptors for assessing the ecological quality status (EQS) of the lagoon has revealed a slight disturbance in the station close to Viligili, one of the most urbanized islands. However, the summarization of all the descriptors used allows the highlighting of the good EQS of the Huvadhoo lagoon. Thus, the results of this study may be taken as the starting point for the future monitoring of the potential and real impact of the anthropogenic activity on the area over time.