Meiofaunal Communities from Three Contrasting Habitats at the Lucky Strike Vent Field, Northern Mid-Atlantic Ridge

Meiofaunal community composition, with emphasis on nematode genera and their functional traits, collected within an induced-disturbance experiment at the Lucky Strike vent field (Northern Mid-Atlantic Ridge). This study builds on the disturbance experiment initiated in 2017 at the Montségur active edifice (Marticorena et al., 2021) during the Momarsat 2017, 2018, and 2019 cruises conducted within the framework of the MERCES H2020 European project. Twelve stainless-steel quadrats (50 × 50 cm) were deployed at the Montségur edifice in 2017 using the ROV Victor6000. Four quadrats (R0a, R0b, R1, R2) served as reference samples to characterize baseline meiofaunal assemblages and assess natural temporal variability. Eight experimental quadrats were subjected to induced faunal clearance to monitor recolonization dynamics. At the active site, four quadrats were defaunated in 2017 and sampled after one year (C1a, C1b; 2018) and two years (C2a, C2b; 2019) to evaluate recovery trajectories. In 2018, the experimental design was extended to two additional habitats: a sedimented peripheral area (P1, P2) located approximately 30 m from Montségur and a visually inactive sulfide structure (I1, I2) located approximately 400 m north of Montségur. At these habitats, quadrats were defaunated in 2018 and sampled after one year to assess recolonization patterns. Faunal removal and sampling were conducted using the mechanical arm and suction sampler of the ROV Victor6000 (2017–2018) and the Nautile submersible (2019). In contrast to previous studies focusing on macrofauna retained on a 300 µm sieve, this dataset targets the meiofaunal fraction retained on a 32 µm mesh (32 µm–1 mm). Meiofauna were extracted by Ludox centrifugation, sorted into major taxonomic groups, and fixed in 4% formalin. For nematodes, 150 individuals per sample were randomly subsampled, cleared, mounted on permanent slides, and identified to genus level using standard pictorial keys. The dataset includes meiofaunal abundances per quadrat, nematode genus-level composition, and genus-based functional trait assignments (feeding type, body shape, tail morphology, and maturity index based on the c–p scale), together with associated environmental variables. This dataset enables analyses of meiofaunal community structure, functional composition, and post-disturbance recolonization dynamics across active, peripheral, and inactive hydrothermal habitats.