Occurrence
The most abundant growth of Euglena acus occurred in the sludge lagoons at Mangere and Papakura. The organism was also seen frequently in the Mangere oxidation and polishing ponds but was not present in high numbers. Other euglenoids, mainly Phacus tortus (Lemm.) Skvortzow and Trachelomonas volvocina Ehrenb., were also seen here at times. Surprisingly, in the similar oxidation pond at Manurewa, sampled regularly for seven years, Euglena acus
was never found but Euglena polymorpha Dang. and Lepocinclis texta (Dujard.) Lemm. were abundant. Of other ponds that were sampled less frequently E. acus
was found in the Pukekohe raw sewage lagoon and in small numbers in polluted rain pools at Papatoetoe and Albany. It was not found in the North Shore Drainage Board polishing pond at Albany, where rare specimens of E. poly- morpha were the only euglenoids seen.
In the Mangere sludge lagoons, E. acus was by far the most abundant euglenoid flagellate and at times the most abundant photosynthetic organism present. Other euglenoids found at rare intervals in these lagoons were E. agilis
Carter, E. minuta Prescott and a very few specimens of E. oxyuris Schmarda. The sludge lagoons at Papakura supported floras dominated by a variety of
Euglena species. The most abundant of these were E. acus during 1964 and E.
sanguinea Ehrenb. and E. agilis from 1965 onwards. Species of Chlorococcales and other algae were very rare in these lagoons compared with the Mangere sludge lagoons.
There was no clearly defined seasonal variation of E. acus but it was often less abundant during the summer and autumn (December-March) (Fig. 2) and in previous years between February and May (Haughey, 1965). The most signifi- cant correlation seemed to be with the free ammonia concentration (Fig. 2). However, in the Mangere sludge lagoons there were periods (e.g., Mangere Lagoon No. 1, June-August 1964 and August 1965-March 1966) when very high numbers of small-celled species of Chlorococcales were present (mainly
Selenastrum minutum (Naeg.) Collins and Chlorella spp.) and at these times E.
acus did not become abundant even though the ammonia levels were high. During calm, sunny weather vertical migration toward the bottom was noted
in the Papakura sludge lagoons. This phenomenon was the cause of the isolated low count during August 1964. A comparison of the counts in the two Papakura lagoons toward the end of November 1964 shows the effect of a gentle breeze when this vertical migration had taken place. The sample from the No. 1 lagoon was collected from the upwind side of the lagoon where gentle upwelling was occurring to replace the clearer top water that was being moved downwind. The correspondingly lower count in the sample from the No. 2 lagoon was
taken on the downwind side.