Evaluation of carbon transfer efficiency from microalgae to Litopenaeus vannamei larvae using a laboratory scale rearing system

In recent years, understanding carbon footprints in aquaculture has become increasingly important and typically requires accounting for biological carbon flows, including the photosynthetic fixation, transfer, and retention of carbon within production systems. Among these flows, microalgae are particularly important because they fix inorganic carbon through photosynthesis and a part of the fixed carbon is transferred to higher trophic levels through feeding interactions. However, the transfer of carbon fixed by microalgae to aquaculture species remains poorly quantified. Here, we focused on Litopenaeus vannamei, a globally important farmed shrimp species with a larval stage during which they can be reared using microalgae as the single feed source. We established a laboratory-scale rearing system for this stage using the diatom Chaetoceros gracilis as the sole feed and quantified both the carbon contained in the microalgal feed and its transfer to shrimp biomass. Carbon transfer efficiencies differed between the two feeding densities tested, with the higher efficiency observed when C. gracilis was maintained at 100,000 cells/mL (33.0%). By extrapolating these laboratory-scale measurements to global production statistics for L. vannamei, we obtained a first-order estimate of global carbon retention during hatchery seed production of 9.2 tons of carbon (tC) per year. These findings provide a quantitative basis for incorporating microalgae-mediated biological carbon flows into assessments of aquaculture carbon footprints and improve our understanding of carbon retention in aquaculture systems.