Ecology of meiofauna of the Atacama Trench – bathymetric variation and comparison with the less productive Kermadec Trench

Hadal regions are the deepest areas of the ocean (>6,000m depth). Particulate organic matter (POM) derived from the primary surface production is the main food supply for the hadal zone, although carrion falls and localized chemosynthetic production also provide resources for some hadal communities. POM flux to the trench floor varies in space and time depending on factors such as local surface primary production and proximity to the coast. Recent investigations of hadal environments have shown that the steep topography of trenches lead to a POM funneling effect resulting in high infauna abundance relative to the adjacent abyssal plain, however several trenches remain poorly sampled. The Atacama Trench is the most southern and deepest trench of the East Pacific Ocean; the first, and until now, only study of Atacama Trench meiofauna, based on core samples from a single station, observed an extraordinarily high density and biomass of meiofauna in comparison to other trenches and the adjacent bathyal region, which led to the “meiofauna hotspot hypothesis”. Here, we investigate the spatial variability of meiofauna in the Atacama Trench along the trench axis (six hadal stations classified in three sections: North, Central and South), and three shallower stations (<6000m, one in each section). We also compare the Atacama Trench meiofauna with the less productive Kermadec Trench meiofauna to further test the meiofauna hotspot hypothesis. Preliminary data show high variability of meiofauna density within the axis but not in the shallower stations. While the meiofauna density decreases toward deeper area in the North section, the South section shows an opposite trend. Ongoing analysis will clarify if the surface production controls the meiofauna community in Atacama Trench. Nevertheless, the hadal meiofauna density was not exceedingly high, and the new data not supports a meiofauna hotspot in Atacama Trench.