Carbon biomass, production rates and export flux of copepods fecal pellets in the Changjiang (Yangtze) River estuary

Abstract

Copepod fecal pellets are ubiquitous throughout the oceans. Their production and export can represent a highly efficient pathway of carbon export. However, the role these fecal pellets play in carbon export in the Changjiang (Yangtze) River estuary is not well known. Two cruises were carried out in the Changjiang estuary in the spring and summer of 2013, during which time carbon biomass, production, and export of copepod fecal pellets were studied. Spring and summer fecal pellet carbon biomass ranged 0.30–1.01 mg C/m3 (mean=0.56±0.20 mg C/m3 ) and 0.31–1.18 mg C/m3 (mean=0.64±0.24 mg C/m3), respectively, significantly lower than phytoplankton. At most stations, fecal pellet carbon biomass was higher in surface or subsurface layers than deeper layers. Production rates ranged 0.65–1.49 pellets/(ind.∙h) (mean=1.02±0.27 pellets/(ind.∙h)) in spring and 0.62–1.34 pellets/(ind.∙h) (mean=0.98±0.22 pellets/(ind.∙h)) in summer, within the range reported in previous studies. Higher production rates of fecal pellets occurred at stations with higher chlorophyll a concentrations, and production rates of copepods of size 500–1 000 μm greater than copepods >1 000 μm during both cruises. The potential export flux of fecal pellets was slightly higher in summer (mean=68.95±14.37 mg C/(m2 ∙d)) than spring (mean=52.08±11.33 mg C/(m2 ∙d)) owing to higher summer copepod abundances. To our knowledge, this study is the first of its kind in the Changjiang estuary, and it confirms the significant role of copepod fecal pellets in local carbon export.