Fighting a hard battle: Effects of hypoxia and temperature on euphausiids in the North
Pacific
Lingbo Li, Julie E. Keister and Mei Sato
University of Washington, Seattle, WA, USA. E-mail: lingboli.fish@gmail.com
Dead zones have been increasingly reported in recent years, especially among the most
productive ecosystems on the planet. Recent studies show that decreasing oxygen and increasing
temperature with global warming may threaten many marine organisms. Because Euphausia
pacifica is a key prey for fish, mammals, and seabirds, their responses to hypoxia and
environmental changes play a key role in both ecosystem functioning and fisheries. We studied
Hood Canal—a narrow, deep fjord in Washington State—as an example to investigate the
seasonal effects of hypoxia on abundance and distribution of euphausiids. Various techniques
and methods were applied including CTD, depth-stratified plankton tows, acoustics, and stable
isotopes analyses at four stations during summer through fall, 2012 & 2013. Notably, we
observed abundant juveniles and adult euphausiids in low dissolved oxygen waters in the Hood
Canal, e.g. <2mg O2/l. Their distributions were not significantly correlated with temperature,
dissolved oxygen, salinity, or fluorescence. We then examined their stress level during hypoxic
time periods by comparing their oxygen supply and demand across the environmental conditions
they experienced in the field. We extend our analysis to the western North Pacific to compare
spatial differences in their metabolic stress. We finally discuss the challenges of future
environmental change for euphausiids and as a consequence, the food webs of the temperate
coastal ecosystems.