Population Dynamics of Crustacean Zooplankton in a Mesotrophic Lake, with Emphasis on Boeckella hamata BREHM (Copepoda: Calanoida)

Abstract

The crustacean zooplankton in Lake Mahinerangi, a polymictic, mesotrophic reservoir, were studied for 19 months. The cladocerans, Bosmina meridionalis and Ceriodaphnia dubia, had unimodal patterns of abundance with peak densities in summer; cyclopoids had a single peak of maximum abundance in autumn and Daphnia carinara showed a bimodal pattern with peak densities in early summer and early winter. The strong seasonality in abundance of zooplankton in Lake Mahinerangi distinguishes this lake from other temperate lakes in New Zealand and may reflect its cool winter temperatures (< 5 "C for 2 months). A calanoid, Boeckella hamata, bred throughout the year and was the dominant species numerically. Instar analysis indicated that there were at least three, and possibly four, generations per year. Instantaneous birth and death rates were low with annual mean values (0.036 and 0.057, respectively) that were 2-3.5 times less than those recorded in a population of the same species in Lake Pounui, but within the range of those recorded in calanoid populations elsewhere in New Zealand. The Boeckella population in Lake Mahinerangi appears to be controlled largely by temperature, parasitism and food, with predation having no, or a negligible, effect.

Polymorphism and Food Limitation in Three Daphnia carinata Populations

“…Large numbers of very young instars were present in Taieri Pond in mid-November when sampling ceased. GEDDES, 1984) and New Zealand (MITCHELL, 1975;BURNS, 1992;BURNS and MITCHELL, 1980). However MITCHELL (1978) described marked morphological changes in populations of D. carinafa in two South Australian sewage ponds.…”

“…A water mite, Piona, preys on small cladocerans in summer but is rarely abundant (BUTLER and BURNS, 1991); the impact of predation by notonectids on pond-dwelling cladocerans in New Zealand has not been studied. Severe food limitation in populations of New Zealand zooplankton, particularly calanoid copepods, has been well documented, however (CHAPMAN and GREEN, 1987;BURNS, 1991BURNS, ,1992.…”

Disrupted seasonal clockwork in the population dynamics of a freshwater copepod by climate warming

“…Growth and development of these key planktonic taxa are subject to periodic (seasonal) and stochastic environmental variation, and their populations undergo extensive cyclic fluctuations both within and among years (Burns 1992;Twombly et al 1998). Copepods have distinct reproductive pulses and recurring population oscillations produced through endogenous and exogenous drivers.…”

The role of trematode parasites as a nutritional food source for higher trophic level consumers

“…Cercarial production can remain more or less constant once these temperaturethresholds are exceeded. In contrast, zooplankton populations typically show a spring bloom in spring months prior to the cercarial threshold temperature, before declining (Burns 1992). As such, cercariae may serve as an especially important food source at particular time points throughout the late spring, summer and eaerly autumn months.…”