Vertical export of particulate organic matter and fecal pellets off central Peru (Callao, 12°S) during the early 2023 El Niño event

Total mass flux (TMF) represents the export of all particulate material, both organic and inorganic, through the water column and plays a key role in biogeochemical cycling. The objective of this work was to quantify the TMF and assess the contribution of fecal pellets in Callao Bay (12°S, Peru) during the early 2023 El Niño (EN) event. To this end, a mechanical sediment trap was deployed at 32 m depth, along with temperature sensors installed at 15, 20 and 25 m on a mooring line, operated from austral summer until autumn 2023 (179 days). TMF values ranged from 143 to 172 mg m-2day-1; which are lower than those typically reported for the region under normal seasonal conditions, indicating reduced particulate export during this warm-phase period. Fecal pellets derived from zooplankton and fish were identified. Zooplankton pellets presented two distinct shapes (cylindrical and ovoid) and showed a mean flux of 1.99 ± 0.40 mg m-2day-1, contributing 1.26 ± 0.09% to the TMF. Fish pellets displayed a single cylindrical shape and exhibited a flux of 9.68 mg m-2day-1, contributing 6.77% to the TMF. These differences reflect the larger size and volume of fish pellets relative to zooplankton pellets. Sinking velocities further highlighted these contrasts: zooplankton pellets sank more slowly (18.34 ± 16.25 m day-1), whereas fish pellets exhibit faster settling rates (668.53 ± 713.82 m day-1), indicating distinct sedimentation behaviors. Overall, the results reveal reduced TMF and low fecal pellet production during the early 2023 EN event, providing insight into how warm anomalies modulate particulate material export dynamics off the central Peruvian coast.