Freeze-dried diatom cells as a viable dietary substitute in laboratory studies for benthic harpacticoid copepods

Feeding conditions can significantly influence physiological responses in marine copepods in experimental trials. For benthic harpacticoids, diatoms represent the dominant and ecologically relevant food source. However, maintaining live diatom cultures is labour-intensive and introduces variability across replicates and time, potentially compromising experimental consistency and reproducibility. This study evaluates whether freeze-dried diatom cells can serve as a standardised dietary substitute without altering the fatty acid composition of benthic harpacticoid copepods. Using Platychelipus littoralis as a model species, we show that copepods fed with either fresh or freeze-dried Nitzschia sp. cells showed similar fatty acid profiles. The relative proportions of essential fatty acids, including eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), remained consistent between these two feeding conditions. This suggests that the lyophilisation process preserves the nutritional quality of the diatom cells, specifically in terms of fatty acid concentration and composition. These findings confirm that freeze-dried diatom cells are a suitable alternative to fresh food during laboratory experiments with benthic harpacticoid copepods, offering standardised and low-maintenance feeding conditions. The use of freeze-dried diatoms enhances experimental reproducibility and reduces the logistical burden of using live algal cultures in benthic copepod research.