Distribution of Sprattus sprattus phalericus (Risso, 1827) and zooplankton near the Black Sea redoxcline

Understanding what environmental drivers influence marine predator-prey relationships can be key to managing and protecting ecosystems, especially in the face of future climate change risks. This is especially important in environments such as the Black Sea, where strong biogeochemical gradients can drive marine habitat partitioning and ecological interactions. We used underwater video recordings in the north-eastern Black Sea in November 2013 to observe the distribution and behaviour of the Black Sea sprat (Sprattus sprattus phalericus, Risso 1827) and its zooplankton prey. Video recordings have shown that the Black Sea sprat S. sprattus phalericus tolerates severely hypoxic waters near the redoxcline. The school was distributed in the 33-96 m layer [oxygen concentration (O₂ ) 277-84 μmol L^-1 ]. Some individuals were observed to leave the school and descended 20 m deeper for foraging on copepods in the 119-123 m layer (O₂ 12-10 μmol L^-1 ). Zooplankton appeared concentrated on the upper boundary of the suboxic zone (O₂ < 10 μmol L^-1 ). No zooplankton were observed below O₂ 6-7 μmol L^-1 (128 m). Understanding the ability of this species to tolerate low oxygen waters is crucial to predicting future responses to natural and anthropogenic changes in hypoxia.