Meiofauna assemblages in and around the Aleutian Trench, with focus on Harpacticoida (Copepoda)

• Ectinosomatidae are the most abundant harpacticoid family. • Pseudotachidius is the most abundant genus in the Bering Sea, despite the comparatively small sample size compared to the other sampling sites. • In addition to water depth, the Chl- a also contributes to the variation within the harpacticoid communities. The aim of this study was to investigate and compare the composition of meiofaunal organisms in and around the Aleutian Trench, with a detailed focus on Harpacticoida. Overall, Nematoda were the most abundant Taxon (88.5 – 86.6%) followed by Copepoda (4.8 – 3.8%). The highest concentrations of these two taxa were observed in the northern rim of the trench and the Bering Sea, while Loricifera demonstrated higher abundances in the southern rim. Furthermore, a greater number of harpacticoid families were identified in samples from the northern rim and the Bering Sea compared to the other sampling sites. A total of 16 different harpacticoid families were identified, with Ectinosomatidae being the most abundant. Samples from the Aleutian trench exhibited low diversity and the lowest number of encountered families. The distribution and composition of meiofaunal organisms were found to be influenced by water depth, silt and clay content, and TOC. For the harpacticoid families, the most influential factors were water depth and Chl- a . The families Ectinosomatidae and Pseudotachidiidae contribute the most to Bray-Curtis dissimilarities. Out of seven selected harpacticoid genera, no genera showed a significant high abundance in the Aleutian trench, while Pseudotachidius showed a higher abundance in the Bering Sea compared to the northern rim of the trench and within the trench, and Zosime showed a higher abundance in the Bering Sea and in the northern rim compared to the southern rim of the trench.