New Zealand Journal of Marine and Freshwater Research abstracts
The Lake Okaro ecosystem
2. Production of the chironomid Polypedilum pavidus
and its role as food for two fish species
DONAL J. FORSYTH MARK R. JAMES
Taupo Research Laboratory
Department of Scientific and Industrial Research
P. O. Box 415, Taupo, New Zealand
Abstract
Lake Okaro, a nutrient-rich lake on the central volcanic plateau of the North Island, New Zealand, supported a maximum littoral population of the chironomid
Polypedilum pavidus Hut-ton of 309 000 larvae m~
2 in 1983/84. This population depended for food on the shoreward drift of cyanobacteria (blue-green algae). The larvae were an important food source for the benthic bully
Gobiomorphus cotidianus McDowall from January to June. From June to December the cla-doceran
Ceriodaphnia dubia Richard was prominent in the diet when the fish moved towards the open water of the lake. The bully removed up to 128% of chironomid production only when population density of the larvae was low. At other times fish predation had little impact on the larvae. Most larvae were eaten by bullies during the day. Bullies caught at night were on average larger and preferred to eat small individuals of their own species. The smslt
Retropinna retropinna (Richardson) played a minor predatory role in the lake. It ate
P. pavidus larvae at all times but favoured
C. dubia in winter and small bullies in autumn. In Lake Okaro cyanobacterial food supply was of overriding importance to the chironomid population but fish predation was a minor influence. Both fish species were opportunistic feeders switching seasonally to the most readily available prey.
Keywords Chironomidae; cyanobacteria; Gobiomorphus cotidianus; Lake Okaro; Polypedilum pavidus; predation; production; Retropinna retropinna
Received ,? May 1987; accepted 2 October 1987
New Zealand Journal of Marine and Freshwater Research, 1988, Vol. 22: 327-335 Crown copyright 1988Received 8 May 1987; accepted 2 October 1987
PDF file of entire paper: medium quality (639K); (scanned from paper original: notes about this process)
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