The observed and estimated species pools underestimate the true regional taxon richness, because accurate enumeration and identification of some algae is not possible by light microscopy, and some taxa can only be detected in live samples (Cloern and Dufford,2005). Therefore, the estimates of taxonomic diversity are constrained to those taxa that are well preserved and identifiable by light microscopy. Not surprisingly, the most common taxa, as well
as the most species rich taxa across all the coastal communities were diatoms, followed by dinoflagellates as the second most taxon rich algal class. Diatoms are among the most common types of phytoplankton in the coastal ocean, and are responsible for about one fifth of the primary production on Earth (Armbrust, 2009). Centric diatoms of unclear identity were present in almost 60% of the coastal samples, followed by unidentified cells, which could not be assigned to any taxonomic group in ca 50% of the samples. It may be seen as a limitation of light microscopy that the identity of the commonest taxa is poorly resolved.