Widespread Kelp-Derived Carbon in Pelagic and Benthic Nearshore Fishes

We examined the use of multiple energy pathways in ecologically and economically valuable nearshore food webs.  To explore the relative proportion of phytoplankton- and kelp-derived carbon sources in nearshore marine fish predators, we measured carbon isotope values (δ¹³C) in muscle sampled from benthic-foraging kelp greenling (Hexagrammos decagrammus) and pelagic-foraging black rockfish (Sebastes melanops) at eight sites from the California Current (upwelling) to Alaska Coastal Current (downwelling) in the Pacific Ocean.  The δ¹³C values were higher in benthic-feeding kelp greenling than in pelagic-feeding black rockfish at seven of eight sites, indicating more kelp-derived carbon in greenling. The proportion of kelp-derived carbon varied by location ranging from 51-98% in kelp greenling and 54-80% in black rockfish.  Kelp-derived carbon generally increased with latitude in kelp greenling and mirrored known patterns in phytoplankton availability in black rockfish, with more kelp-derived carbon in rockfish at sites with lower phytoplankton.  We conclude that these two nearshore fishes routinely derive carbon from kelp and phytoplankton channels across coastal upwelling and downwelling systems.  Dual-channel carbon use, taken together with findings from other studies, may reflect a pervasive mechanism that could foster resilience of nearshore marine foodwebs to disturbance and indicates strong benthic-pelagic coupling.