Temporal variability in, and impact of food availability on vanadium and iron concentrations in Ciona intestinalis tissues (Tunicata, Ascidiacea)

Ascidians accumulate high levels of iron and/or vanadium in their tissues, the function of which is unknown. There is little directed study of the ecophysiological variation in the trait. We examined the variation in vanadium and iron levels in the hemocytes, body wall and tunic of the ascidian Ciona intestinalis over several seasons, including the spring bloom period. There were significant peaks in the vanadium and iron levels in the hemocytes and tunic, (up to four to five-fold higher) in March and August. The activity of G6PDH, an enzyme of a proposed reductive mechanism for vanadium, was higher in March as well. A feeding experiment showed few differences between high and low food groups in vanadium or iron levels. The season to season changes in metal levels and the differences between laboratory held animals and animals sampled directly from Woods Hole suggest that low loss rates may maintain high vanadium and iron levels, even when dissolved levels in sea water are low. This work is the first to show that vanadium and iron levels in ascidian tissues varies from season to season.