Stable isotope analysis of micronekton around Hawaii reveals suspended particles are an important nutritional source in the lower mesopelagic and upper bathypelagic zones

Abstract

AbstractSeveral studies have found that the respiratory demand for carbon by the mesopelagic community exceeds carbon supply through the particulate sinking flux by up to two to three orders of magnitude, suggesting that mesopelagic communities rely on additional overlooked carbon sources. Suspended particles (defined as 0.7–53 μm) have been suggested as one of these sources but few studies have evaluated their contribution to the mesopelagic food web. We use amino acid compound‐specific nitrogen isotope analysis to investigate whether suspended particles are an important nutritional source to fish, cephalopod, and crustacean micronekton species in the central North Pacific. Our results suggest that micronekton feed from food webs fueled by a variety of nutritional sources including surface dwelling phytoplankton and bacteria, sinking particles, and suspended particles, with micronekton becoming more reliant on suspended particles with increasing habitat depth. Several species were identified as feeding from a primarily suspended particle‐based food web including the fishes Cyema atrum, Cyclothone pallida, Melanocetus johnsonii, Serrivomer sector, and the pelagic octopod Japetella diaphana. We also found that micronekton species feeding from a suspended particle food web cannot be identified using bulk tissue δ15N values. Our data support the notion that suspended particles are an important nutritional source in the lower mesopelagic and upper bathypelagic and they should be accounted for when estimating carbon supply for these communities.