This study aimed to determine a nutritionally adequate feeding protocol for Hippocampus hippocampus juveniles. In the experimental trial, seahorses were fed copepods from 0-7 days post-parturition (DPP) and, from 8-28 DPP, four dietary treatments: (copepods (control diet), microalgae-enriched Artemia with a DHA/EPA ratio of 2:1, microalgae-enriched Artemia with a DHA/EPA ratio of 2:1 along with 5% copepods, and with 10% copepods) were tested. Results showed that juvenile seahorses fed on copepods attained a significantly higher (P<0.05) growth performance (5.1 mg d-1) than fish-fed diets with 5% and 10% copepod inclusion, (3.09 and 3.07 mg d-1, respectively), and fish-fed enriched Artemia (1.83 mg d-1) which performed poorly. Data suggests that feeding copepods during the first 7 DPP promotes maturation of the digestive tract of juvenile seahorses, and the addition of a limited amount of copepods to the diet improves H. hippocampus juvenile growth performance when compared to the use of Artemia as a single diet due to the improvement of the essential fatty acid profile in the diets.

Zooplankton and ichthyoplankton community assessments depend on species diagnostics, yet morphological identifications are time consuming, require taxonomic expertise, and are hampered by lack of diagnostic characters –particularly for larval stages. Metabarcoding can identify multiple species in communities from short DNA sequences in comparison to reference databases. To evaluate species resolution across phylogenetic groups and food webs of zooplankton and ichthyoplankton, we compare five metabarcode mitochondrial (mt)DNA markers from gene regions of (a)cytochrome c oxidase subunit I, (b) cytochrome b, (c) 16S ribosomal RNA, and (d) 12S ribosomal RNA for DNA extracted from net tows in the Northeastern Pacific Ocean’s Salish Sea across seven sites and two seasons. Species resolved by metabarcoding are compared to invertebrate morphological identifications and biomass estimates. Results indicate that species resolution for different zooplankton and ichthyoplankton taxa can markedly vary among gene regions and markers, and in comparison to morphological identifications. Thus, researchers seeking “universal” metabarcoding should take caution that several markers and gene regions likely will be needed; all will miss some taxa and yield incomplete overlap. Species resolution requires careful attention to taxon marker selection and coverage in reference sequence repositories. In summary, combined multi-marker metabarcode and morphological approaches improve broadscale zooplankton diagnostics.