Publication: Wakame is a recorder of oceanographic conditions
The sea off Sanriku coast, northeastern Japan, is characterized by seasonal influence of the prevailing water of the Oyashio and the warm current waters. The Oyashio is depleted in radiocarbon content (Δ14C) of dissolved inorganic carbon (DIC) relative to the warm waters. We hypothesized that Δ14C of the large brown macroalga Undaria pinnatifida reflected the Δ14C-DIC in bay water during photosynthetic production, and can be used as an indicator of oceanographic conditions during algal growth. To test this hypothesis, we cultivated Undaria pinnatifida in Otsuchi Bay on the Sanriku Coast and examined the Δ14C variability among U. pinnatifida pinnae (leaflet-like structures arising sequentially along the vertical axis of the blade) reflect. During the cultivated period, the Oyashio intruded into the bay, accompanied by a decrease in bay water Δ14C-DIC. We found that the Δ14C of the pinnae reflected Δ14C-DIC, as pinnae that formed before the Oyashio intrusion had significantly higherΔ14C than those that formed after the Oyashio intrusion. Our results indicate that the Δ14C of U. pinnatifida pinnae can serve as a record of Oyashio intrusion into the bay during algal growth. This new method is potentially useful in understanding complicated relationships between oceanographic conditions and macroalgal physiology. (Naomi Satoh)
