POTENTIAL TOOLS FOR TRACKING OCEAN CLIMATE: VARIABILITY IN STABLE ISOTOPES IN LIVING CORALLINE ALGAE

Abstract

Our ability to track long term climate change in coastal regions is limited in temperate and polar regions. Physical oceanographic dynamics in temperature and upwelling events can be recorded as carbon and oxygen stable isotope signals in carbonate producing organisms. Because coralline algae photosynthesize, produce calcium carbonate and are widely distributed, they may provide a new tool for detecting short‐term change. However, little is known about how coralline algae incorporate stable isotopes into their calcite thallus structure. The objectives of this study were to determine if growth and isotopic signature differ in articulated coralline algae grown in different oceanographic regimes in Monterey Bay. The articulated alga Calliarthron cheiliospororioides was outplanted at three locations varying in seawater temperature and upwelling strength. New algal growth was measured by staining the algae with Alizarin Red and enumerating the amount of accumulated material at the branch tips. Growth rates varied seasonally and spatially. Low‐upwelling daily growth rates averaged 0.044–0.056 mm day−1, while high‐upwelling growth rates were 0.083 mm day−1. Isotope ratios were obtained by analyzing microsampled portions of the alga in a mass spectrometer. Changes in the 18O/16O and 13C/12C ratios appear to reflect change in seawater temperature and upwelling strength, respectively.