Extracting growth rates from the non-laminated coralline sponge Astrosclera willeyana using "bomb" radiocarbon

Coralline sponges have the potential to fill in gaps in our understanding of subsurface oceanographic variability. However, one disadvantage they have compared to hermatypic reef building coral proxies is that they do not have annual density bands and need to be radiometrically dated for an age determination. To elucidate growth rate variability we have measured radiocarbon in 1 mm increments from Astrosclera willeyana sponges collected off the Central and Northern Great Barrier Reef (GBR) and from Truk in the Caroline Islands and compared these radiocarbon profiles to independently dated coral radiocarbon records. Growth rates of the GBR sponges average 1.2 {+-} 0.3 and 1.0 {+-} 0.3 mm yr{sup -1}, north and central respectively but can vary by a factor of two. The growth rate of the Truk sponge averages 1.2 {+-} 0.1 mm yr{sup -1}. These growth rates are significantly faster to those measured for other GBR Astrosclera willeyana sponges (0.2 mm yr{sup -1}) by Calcein staining (Woerheide 1988)