Distribution of acid and vanadium in Rhopalaea birkelandi Tokioka

The distribution of acidity, vanadium, and fouling in Rhopalaea birkelandi Tokioka, a solitary ascidian common on the Pacific coast of Central America, was investigated. The tunic around the siphons released acid (pH ?2) when slightly bruised and was not fouled. However, the basal parts of the tunic, which were non-acidic, were fouled. Whole R. birkelandi has ≈610 ppm vanadium dry wt; the zooid with the tunic removed has ≈ 1956 ppm and the tunic has ≈ 500 ppm vanadium dry wt. Vanadocytes were present. These data are discussed in reference to previous work on the roles of vanadium and acid in benthic ascidians.