Laboratory study of the survival and attachment of Didymosphenia geminata (Bacillariophyceae) in water sourced from rivers throughout New Zealand

Abstract

:Didymosphenia geminata is a freshwater diatom that can form extensive nuisance mats in rivers and streams. First detected in New Zealand in 2004, D. geminata has been found in over 150 rivers throughout the South Island. The diatom exhibited interesting distribution patterns in New Zealand, where it has remained absent from several apparently suitable habitats. The aim of this study was to investigate the role of New Zealand river water chemistry in the establishment of D. geminata. Water was collected from 16 North Island and four South Island rivers, and four South Island groundwater-fed creeks where D. geminata was absent, and from seven South Island rivers with low to medium levels of D. geminata and six South Island rivers with high levels of D. geminata. Water chemistry parameters were measured for these sites. The survival and attachment of D. geminata cells to the surface of culture plates were monitored in the laboratory under controlled conditions. Cells survived, attached and underwent cell division in waters with a wide range of chemistries, including water where D. geminata was absent. No correlation was found between cell survival, attachment, or division and any of the individual elements, compounds, or nutrient ratios tested. Findings in this study suggested that water chemistry, in isolation of other environmental parameters, was unlikely to be the sole variable responsible for D. geminata distribution in New Zealand. The attachment of free D. geminata cells to a substrate was a prerequisite for cell division, indicating that substrate composition may play an important role in D. geminata establishment.