Most of the detailed studies on periphyton in New Zealand rivers and streams have focused on diatoms. Despite the recent rise of interest in potentially toxic cyanobacterial mats, knowledge of the diversity and ecology of these and other macroscopic growth forms is incomplete.
A taxonomic survey was made on periphytic cyanobacteria at 100 locations along Kaituna River and a 1st to 3rd order tributary stream. Samples were taken from runs, riffles and pools in shaded and unshaded locations and from varied substrata from January to December 2011. Descriptions were made of all macroscopic growths. Fifty-six morphospecies were identified of which 29 are new records for New Zealand. Crust components were the most diverse with 23 morphospecies followed by mats (16), gelatinous colonies (5) and epiphytes (7). Five appeared only after growth in enrichment cultures.
Twelve morphospecies were isolated into cultures for use in polyphasic assessment. In 16S rDNA phylogenies, Placoma regulare and Heteroleibleinia fontana did not cluster with other members of their traditional families. Nostoc sp. 2 was positioned distant from other Nostoc strains. Comparison of 16S – 23S rRNA internal transcribed spacer compositions for seven mat-forming oscillatorialean morphospecies confirmed their recognition as distinct morphospecies. Amplified fragment length polymorphisms were used to investigate genetic diversity of Nostoc verrucosum in relation to dispersal. This indicated that local dispersal is dominant while cross-catchment dispersal is probably infrequent.
Light intensity, substratum type and water conductivity were significant factors influencing spatial patterns of distribution. Higher diversity of crusts, mats and gelatinous colonies was recorded in unshaded locations. Mats and gelatinous colonies were most diverse in Kaituna River and crusts in second to third order streams. Morphospecies in water with high conductivity were restricted to those locations. Spates had a major effect on temporal distribution. An increase in frequency and intensity of spates in spring and winter resulted in greater reduction in cover. Smaller spates caused partial removal followed by rapid regrowth within a week. Major spates caused complete removal of visible cover with re-colonization occurring within three to four weeks. This study has provided a first detailed account of cyanobacterial diversity and ecology in a New Zealand catchment. It provides a basis for long-term monitoring at this site of the effects of changes in climate and in human activities in the catchment.