Proposal of identification criteria for resting spores of Chaetoceros species (Bacillariophyceae) from a temperate coastal sea

Abstract

Chaetoceros is a large, ecologically important genus of marine planktonic diatoms. Many species of Chaetoceros form resting spores to survive environmental stress. Species identification based on morphological characteristics of resting spores is difficult. In the present study, we proposed a flow diagram for the identification of Chaetoceros species based on morphology. Resting spores of 18 Chaetoceros species were identified in water and sediment samples from southern Japan and the East China Sea based on morphological characteristics of resting spores and/or the vegetative cells containing them. A single ring of puncta was found to be the most important morphological feature of resting spores for species identification, by which the positions of primary and secondary valves were correctly determined. Other morphological characteristics such as features of the primary valve face, margins of the primary and secondary valve mantles, and secondary valve face are also useful for species identification. A combination of these morphological characteristics was used to construct a flow diagram for identification of the 18 Chaetoceros species found in our samples with light microscopy. This flow diagram is most applicable to Japanese waters, but the approach should be refined and improved to understand the biology and ecology of Chaetoceros species in any marine ecosystem.