Why Do Dinoflagellates Have Lower Growth Rates?¹

Dinoflagellates have substantially lower growth rates than other taxa of similar size. These low growth rates have been suggested to reflect the lower chlorophyll a to carbon ratio (Chl a: C) in dinoflagellates, but that speculation has never been widely tested. This study tests if the variations in growth rates among taxa are related to differences in Chl a: C using published data. I collected 92 data entries from the literature representing 31 species, mostly from two divisions (Chrysophyta and Pyrrophyta), and found a significant relation (r 2 = 0.39) between growth and Chl a: C. Since Chl a: C is almost independent of C content, I also developed a growth model using both C and Chl a: C. Together, the two variables explain 68% of variation in algal growth. However, a further 6.4% of the variance in growth can still be attributed to phyletic differences. Low Chl a: C is only a partial explanation for the low growth rates of the dinoflagellates.