Seasonal and spatial variations of food sources of krill Euphausia pacifica in Yellow Sea using fatty acids analysis

Abstract

Krill, Euphausia pacifica, is known as a key species in the Yellow Sea ecosystem but their feeding ecology has not been sufficiently studied over conditions observed during high seasonal variability of food quality and quantity. In order to understand the seasonal and spatial variations of their food sources, we sampled E. pacifica and particulate organic matter (POM) during the spring (April) and summer (August) in 2012 and 2013 and analyzed their dietary lipid markers. Lipids of E. pacifica in the Yellow Sea, mainly comprised of phospholipid (41-86% of total lipids), showed seasonal (spring > summer) and regional (spring: north > south summer: north < south) variation. These may be related to various factors (e.g., water temperature, spawning, and diet composition) as part of their survival strategy. Fatty acids (FAs) of E. pacifica were dominated by saturated FAs (SAFAs) 16:0 and polyunsaturated FAs (PUFAs) 20:5(n-3) and 22:6(n-3), known to be from diatoms and dinoflagellates, respectively. Their FA composition also showed significant regional differences (offshore vs. inshore) based on principal component analysis (PCA) of FA abundance. In spring, samples (krill and POM) from inshore had high abundance of allochthonous FAs (e.g., 16:1(n-9), 24:1(n-9)), whereas samples from offshore had many autochthonous FAs (e.g., 18:1(n-7), 20:5(n-3), BrFA)). Especially, FA composition of E. pacifica in summer was very similto understand the seasonal and spatial variations of their food sources, we sampled E. pacifica and particulate organic matter (POM) during the spring (April) and summer (August) in 2012 and 2013 and analyzed their dietary lipid markers. Lipids of E. pacifica in the Yellow Sea, mainly comprised of phospholipid (41-86% of total lipids), showed seasonal (spring > summer) and regional (spring: north > south summer: north < south) variation. These may be related to various factors (e.g., water temperature, spawning, and diet composition) as part of their survival strategy. Fatty acids (FAs) of E. pacifica were dominated by saturated FAs (SAFAs) 16:0 and polyunsaturated FAs (PUFAs) 20:5(n-3) and 22:6(n-3), known to be from diatoms and dinoflagellates, respectively. Their FA composition also showed significant regional differences (offshore vs. inshore) based on principal component analysis (PCA) of FA abundance. In spring, samples (krill and POM) from inshore had high abundance of allochthonous FAs (e.g., 16:1(n-9), 24:1(n-9)), whereas samples from offshore had many autochthonous FAs (e.g., 18:1(n-7), 20:5(n-3), BrFA)). Especially, FA composition of E. pacifica in summer was very simil