THE ECOLOGY OF BENTHIC FORAMINIFERA OF THE PERU OXYGEN MINIMUM ZONE

Oxygen minimum zones (OMZ) are widespread features in the most productive regions of the world ocean that strongly influence the distribution and diversity of planktonic and benthic marine communities. In particular, the Peru margin is characterized by one of the world's most pronounced OMZ, which extends from approximately 170 to 700 m of water depth. This study examines the effect of oxygen and organic matter availability associated with the Peru OMZ on the distribution of living (Rose Bengal stained) benthic foraminifera. Four stations along a water depth transect were sampled with a multicorer off Callao, Peru (~12 ºS, 305 m; 562 m; 830 m and, 1210 m). Within the upper 5 cm of sediment, most benthic foraminifera were found in the top 1.5 cm. Total abundances, species composition and vertical distribution patterns, however, changed with water depth. Maximum foraminiferal densities occurred in the heart of the OMZ (305 m), where bottom-water concentration was lowest (0.02 ml/L) and sediment labile organic matter was greatest. Calcareous foraminifera dominated water depths from 305 m to 830 m (bottom-water oxygen concentrations ranging from 0.02 to 0.84 ml/L), whereas agglutinated taxa were predominant at 1210 m with the highest content of bottom-water oxygen (1.78 ml/L). This suggests that calcareous foraminiferal assemblages thrive under low-oxygen and organic-rich conditions and that agglutinated assemblages can more easily prevail under conditions of greater oxygenation. These results are consistent with previous studies in the Arabian Sea and along the California margin. A better understanding of the ecology of modern benthic foraminifera within OMZs is important for reconstructions of changes in paleoproductivity and paleoclimate-related variations in OMZ intensity.