Community Composition of Deep Sea Meiofauna in the Atacama Trench and Pacific Seamounts

In February of 2019, seven stations were sampled between Valparaiso, Chile and Tahiti, French Polynesia at water depths ranging from 2895 – 7742 m. Our stations included a site at the bottom of the Atacama Trench, five seamounts along the Easter Seamount Chain, and a site off the coast of Easter Island. Samples were taken from the base of the seamounts with a multicorer. One from each station was used for meiofauna analysis, and separated into five 1 cm slices down to 5 cm sediment depth and preserved in DESS. The meiofauna density for each core sample ranged from 18 to 171 individuals per 10 cm², and a total of 7 higher taxa were observed (nematodes, copepods, polychaetes, tardigrades, gastrotrichs, kinorhynchs, and hydrozoans). Only metazoan meiofauna were counted. ANOVA revealed a significant difference in meiofauna density (ind./cm²) across all sediment depths (p=0.0046), and a Tukey’s HSD post-hoc test showed a significant difference between the first centimeter and the 3^rd, 4^th, and 5^th centimeters. Compared to previous studies in the literature, the total meiofauna densities in our samples was noticeably much lower than expected. Thus, we decided to re-centrifuge the residue of all samples with a LUDOX-HS40 dilution of approximately 1.21 specific gravity, as opposed the original dilution of approximately 1.15. Re-centrifugation resulted in approximately 30% increase in specimens found than was originally the case. While these results are obviously tentative, we suggest using a LUDOX dilution of 1.21 when isolating meiofauna specimens to obtain maximum extraction efficiency. Storage in DESS may affect total abundance of meiofauna in quantitative studies, as it is not known how DESS compares to formal with regards to long term storage of meiofauna specimens. Future studies should include obtaining replicates and preserving specimens in both DESS and formalin.