Dispersal and colonization success of monoraphid vs. biraphid diatoms (Bacillariophyta).

Abstract

Monoraphid diatoms (Bacillariophyta) evolved more recently than biraphid diatoms. Monoraphids initially support two raphes, but seal the second raphe during the valve construction process. I studied the change in relative abundance sizes of biraphid and monoraphid diatoms colonizing artificial substrates to determine if the monoraphid condition was advantageous to early colonists. Three monoraphid species (Cocconeis placentula, Achnanthidium minutissimum, and Eucocconeis flexella) and three biraphid species (Mastogloia smithii, Navicula cryptotenella, and Sellaphora pupula) were examined. Original diatom collections were made from artificial substrates in three northern Michigan lakes over the course of 21 days in 1975. Monoraphid and biraphid relative abundances were counted on days 1, 3, 6, 15, and 21. The hypothesis that monoraphids would initially out-compete biraphids as pioneer colonists had mixed support. Because both groups' relative abundances tended to increase over time and the site of collection had no effect on relative abundance, results suggest that both monoraphid and biraphid diatoms were colonizing the artificial substrate. There was no difference in relative abundance size across all lakes and all days. However, the monoraphid relative abundance increased faster than the biraphid relative abundance. Further research is necessary to determine why monoraphids have higher relative abundance growth rates.