New Zealand Freshwater and Brackish Diatom Types
The diatoms, or Bacillariophyceae, are an extremely diverse group of microalgae, with global estimates of species ranging from 10,000 to 100,000 or more. They exist as unicells or cell aggregates, and occur in both the oceans and freshwaters, with high ecological importance.
They are perhaps the best studied group of microalgae, largely due to one distinctive feature: their cells are enclosed within a rigid box of silica, termed a frustule. In the centric diatoms, this takes the shape (roughly) of a rounded hatbox, whereas in the pennate diatoms–the other major subdivision–it takes the form of a more elongate shoebox. Both types can be viewed on this website.
The diatom frustule has proven extremely useful for taxonomists, because it can be cleaned and preserved, and markings on the silica provide very detailed characters that can be used to classify species. These attributes are unusual among microalgae, which frequently cannot be archived in herbaria without losing most of the useful taxonomic features from the specimens, of which there may have been few to begin with!
Diatom taxonomy consequently has a rich history, with specialist journals, professional and amateur practitioners, and numerous specimen collections that remain as effective today as when they were first accessioned. Important applications of the discipline include the reconstruction of past environments from sediment cores, exploiting the persistence in sediments of frustules from ancient times and the fact that environmental tolerances of species are relatively well understood; another is the study of biogeography, or the spatial distribution of species. The painstaking examination of many historical and new collections has resulted in a view of Australasia as a centre of diatom endemism.
This website aims to make available images and associated information on the species of diatoms from brackish and freshwater habitats that were first described from New Zealand material.