Food sources of benthic communities at the Caiwei Guyot and Yap Trench, northwestern Pacific Ocean: inferences from carbon and nitrogen isotopes

To investigate nutritional resources for benthic communities at two sites in the northwestern Pacific Ocean (the Caiwei Guyot and the Yap Trench), stable isotopes of carbon and nitrogen (δ13C and δ15N) were measured in the tissues of megabenthic consumers (Porifera, Asteroidea, Crinoidea, Holothuroidea, Ophiuroidea, Gammaridea, and Actiniaria) as well as four potential food sources (suspended particles, sinking particles, zooplankton, and sedimentary organic matter, SOM). Fast-sinking particles are generally thought to be the primary food source for benthic consumers, but that paradigm does not seem to apply at these abyssal sites. Here, the δ13C and δ15N signatures of fast-sinking particles (as collected by sediment traps; δ13C = −24.1 to −22.6‰, δ15N = 1.4 to 5.4‰) were significantly lower than those of the megabenthos (δ13C = −20.1 to −16.1‰, δ15N = 10.2 to 17.9‰), indicating that these particles are not likely a direct food source for the animals. Buoyant particles (and slow-sinking particles), on the other hand, seem to be a significant direct food source for the megabenthos. Sedimentary organic matter and zooplankton are also important direct food sources. Trophic level analysis similarly indicates a diversity of food sources and suggests that for at least some animals, microbes (e.g., bacteria) may be a food source as well.