Spirulina (Arthrospira platensis) Influences Nutritional Characteristics and the Relative GC–MS Chemical Profile of Aquaponically Cultivated Celery (Apium graveolens)

Aquaponic cultivation provides a resource-efficient approach to crop production, while plant biostimulants may improve crop performance and nutritional quality. This study evaluated the effects of Arthrospira platensis (Spirulina) supplementation on celery (Apium graveolens) cultivated under aquaponic conditions. Aquaponic celery supplemented with 2, 4, or 8 g L−1 of Spirulina (CAS2, CAS4, and CAS8, respectively) was evaluated over three weeks. Untreated aquaponic celery (CA) was included as a week-3 endpoint reference, while soil-grown celery (CS) was included as a descriptive week-3 reference. Growth, biomass, protein, total lipids, crude fiber, mineral composition (Na, K, Ca, P, and Fe), and aflatoxin occurrence were assessed, and specialized metabolite profiles were characterized descriptively by gas chromatography–mass spectrometry (GC–MS). Among the supplemented groups, Spirulina dose was associated with changes in growth, biomass, nutritional composition, and mineral accumulation, with the magnitude of several responses varying across the three-week cultivation period. Because CA was sampled only at week 3, the longitudinal analyses evaluated dose-associated responses among CAS2, CAS4, and CAS8 and did not constitute a longitudinal comparison between Spirulina supplementation and the untreated control. At week 3, several growth and nutritional responses were higher in Spirulina-supplemented celery than in CA, with the greatest values for several responses generally observed at 8 g L−1. Potassium showed a non-monotonic response, with the highest week-3 value observed at 4 g L−1, whereas sodium increased markedly at higher supplementation levels. Descriptive GC–MS profiling showed differences in the relative representation of detected chemical classes among the analyzed samples; however, these profiles were obtained from representative samples without independent biological replication and were therefore used for descriptive chemical characterization rather than inferential testing. No aflatoxins were detected. Overall, Spirulina supplementation was associated with dose- and time-dependent differences in growth and selected nutritional and mineral characteristics among the supplemented aquaponic celery groups, while week-3 comparisons indicated higher values for several responses relative to untreated aquaponic celery. The GC–MS analysis provided descriptive evidence of differences in the relative chemical profiles of the analyzed samples.