Environmental tolerances of resting stages of plumatellid bryozoans at Southern Reservoir, Dunedin, New Zealand

Abstract

Freshwater bryozoans grow at Southern Reservoir, a water treatment station in Dunedin, New Zealand fouling surfaces in the microstrainer hall and requiring expensive and time consuming maintenance. Preventing or minimising germination is a potentially useful way to control bryozoan infestation. Germination trials were conducted to assess the effect of temperature, dry storage, and various chemicals on floatoblast germination.

Plumatella vaihiriae is newly described from Southern Reservoir. A second, as yet unidentified, Plumatellid species was discovered through the presence of floatoblasts (Plumatella n. sp.). Storing dry floatoblasts of Plumatella n. sp. decreased germination. Storing dry floatoblasts of P. vaihiriae for 63 days or more prevented germination entirely. Sodium hydroxide, acid clean in place (CIP) and sulphuric acid were most successful of those chemical treatments tested in preventing germination of P. vaihiriae floatoblasts. Exposure to alkaline CIP and a combination of CIP solutions decreased germination of P. vaihiriae floatoblasts. Pre-heating acid CIP to 35°C prevented germination of P. vaihiriae floatoblasts. Exposure to alkaline CIP solutions at temperatures of 35°C and 50°C increased germination of P. vaihiriae and Plumatella n. sp. floatoblasts. The zooid wall provided protection for floatoblasts of P. vaihiriae from exposure to acid CIP.

On initial release from the zooid P. vaihiriae floatoblasts produced in winter and early summer are obligate dormants entering a diapausal state for at least three weeks. As summer approaches P. vaihiriae floatoblasts become thermos-quiescent and germinate once temperatures increase.

Dunedin City Council (DCC) water department staff must adhere to strict cleaning policies when moving both people and equipment between Southern Water Treatment Station and other water treatment stations and reservoirs. P. vaihiriae and Plumatella n. sp. floatoblasts could better sustain the effects of an acid environment during transport within a vector such as a water bird more so if eaten whilst within the zooid and remaining within the zooid walls during transport.