Supplemental effects of diet mixing on absorption of ingested organic carbon in the marine copepod Acartia tonsa

We investigated increased carbon absorption efficiencies (AEs) as a possible cause for positive effects of diet mixing on copepod egg production rates (EPRs) and hatching success (EHS). Female Acartia tonsa were fed super(14)C/ super(51)Cr dual-labelled Dunaliella tertiolecta (Dun), Amphidinium carterae (Amp), Phaeocystis globosa (Pha), and 3 pairwise 1:1 mixes of the 3 diets. AEs, derived from the ratios of labels in algae and copepod faecal pellets, were 44% on Dun, 37% on Amp, and 49% on Pha, but increased significantly to 61% on Dun + Amp. As a result, EPRs remained low in all tested diets except for Dun + Amp, where it was twice that in the individual diets. Linear multiple regression analysis revealed that EPRs were strongly dependent on the ingestion and absorption of the fatty acids 18:3(n-3) and 22:6(n-3) so that the simultaneous ingestion and absorption of 18:3(n-3) from Dun and 22:6(n-3) from Amp enhanced EPR in the Dun + Amp diet. EHS was low with the Dun diet, which was devoid of 20:5(n-3) and 22:6(n-3). Multiple regression analysis showed that EHS depended on 16:1(n- 7) and any or all of 22:6(n-3), 20:5(n-3), or 18:5(n-3).