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

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 D-3 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 (Pless than or equal to0.10) 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 D-3 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 D-3 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 D-3 concentration (156.83 +/- 139.25 ng/g), which may reflect an intermediate-type feeding strategy or an artifact of the small sample size. (C) 2004 Wiley-Liss, Inc.