Vitamin D content in Alaskan Arctic zooplankton, fishes, and marine mammals

摘要

We postulated that dietary ingestion of vitamin D may be used by some Alaskan Arctic marine mammal species in addition to, or instead of, cutaneous production to meet nutritional requirements. Zooplankton (n=5) sampled near Kaktovik, Alaska, contained no measurable vitamin D_2 or D_3, but did contain provitamin D (7-dehydrocholesterol), the cutaneous precursor for previtamin D3 in mammals. Fillets and livers from five fish species were sampled near Barrow, Alaska, and evaluated for vitamin D_3 content (no vitamin D_2 was detected). Differences in vitamin D_3 content appeared significant (P≤0.10) among fish livers (Kruskal-Wallis [H test]=8.25, df=4, P=0.08) and among fish fillets (H=7.80, df=4, P=0.01). We also found significant differences in several pairwise comparisons (Mann-Whitney U-test) of vitamin D3 levels in fillets and livers. Blubber from six species of marine mammals had no detectable vitamin D_2. The H test results for blubber vitamin D_3 concentration were highly significant: 28.12, df=5, P<0.001. There were also significant differences in vitamin D3 content from blubber in pairwise comparisons of primarily invertebrate feeders (bowhead whale (Balaena mysticetus) [mean=4.20 SD±1.10 ng/g], and Pacific walrus (Odobenus rosmarus divergens) [5.43±2.82 ng/g]) vs. primarily piscivorous feeders (ringed seal (Phoca hispida) [746.57±493.00 ng/g] and beluga whale (Delphinapterus leucas) [426.00±174.92 ng/g]) and a semiaquatic terrestrial carnivore (polar bear (Ursus maritimus) [406.17±311.70 ng/g]). The bearded seal (Erignathus barbatus) had intermediate blubber vitamin D3 concentration (156.83±139.25 ng/g), which may reflect an intermediate-type feeding strategy or an artifact of the small sample size.