Award: OCE-1949119

Overview:We investigated the diet of cold water corals that live in the deep ocean in order to understand the nitrogen isotope signature that is preserved through time in the calcium carbonate skeleton of cold water corals. This isotope signature that can be measured in fossil coral skeletons provides information on conditions in past oceans provided we understand how it is modulated by what corals eat. Because deep water corals are difficult to access, the main components of their diets remain unresolved. Intellectual Merit:We maintained a cold water coral species,Balanophyllia elegans, for many months in laboratory tanks and fed it a controlled diet with a known nitrogen isotopic signature, and established that corals have a normal isotopic signature in their tissue relative to their diet, similar to that of other animals. FromB. eleganscoral specimens collected near Friday Harbor, WA, we determined that the isotope signature preserved in the coral skeletons matches closely that of their soft tissue. From an investigation of the isotope signature of all potential components ofB. elegansdiet at Friday Harbor, we concluded that zooplankton 0.5 mm comprise the dominant component of their diet rather than phytoplankton-derived particles which have otherwise been hypothesized to be an important part of cold water coral diets. We measured the nitrogen isotopic signature of coral skeleton specimens obtained from the Smithsonian collection; Specimens were comprised of 4 different cold water species were recovered from a range of depth in the ocean at three different locations: near Hawaii, off the California coast, and near the Azores. The coral skeletons showed an increase in their isotope composition with depth, suggesting the isotope signature of their diet increases with depth. Specimens from larger species from a given depth had higher isotopic signatures, suggesting that bigger specimens eat bigger prey and are thus more carnivorous. Finally, we looked at how quickly dietary nitrogen is deposited in the coral skeleton after feeding, and where in the skeleton. Dietary nitrogen appeared in the skeleton within a few hours of feeding and was deposited in discrete bands, providing insights on timescales and spatial distribution of processes recorded in the coral skeleton. Broader Impacts:Funding contributed to the training of a graduate student at the University of Connecticut, and of 5 undergraduate interns at St-Olaf College and Pomona College. Last Modified: 07/19/2024 Submitted by: JulieGranger