Plankton community cycling and recovery after drought — dynamics in a basin on a flood plain

Abstract

Lake Merrimajeel, a shallow swamp, is part of the Murray-Darling, a flood plain river system with high plankton diversity. It fluctuates drastically in water level and often dries out. The dynamics and seasonality of zooplankton in the face of these fluctuations and the effects of a total drawdown and refilling were monitored between February 1977 and January 1980. During this period thirty species of rotifers, thirty four of microcrustacea and several other species were recorded. Despite erratic fluctuations in water level, temperature and turbidity a community cycle from dominance by rotifers in summer/autumn and crustacea in winter/spring was maintained. The drawdown disturbed this cycle but it was reestablished the following year. Diversity and density reached a maximum just before the drawdown, during hot, turbid conditions. During this drying phase the waters remained relatively fresh and well oxygenated. 'Phyllopods' were not recorded. The recovery phase was characterised by a group of rare species. It is postulated that these rare, colonising or successional species are dependent on a brief flush of rich organic material produced on flooding.The generally depressive effect of increased turbidity does not hold in this lake and many limnetic species were abundant during periods of high turbidity. It is suggested that turbidity may be tolerated or even be advantageous to some species, depending on the nature of the suspended material.The ability of species to lead a fugitive existence by temporarily colonising basins after drawdowns and refilling may be an important factor in producing the high diversity of plankton in flood plain river systems such as the Murray-Darling.

Australian waterbirds—products of the continent's ecology

“…Abundant food for waterbirds usually coincides with flooding patterns or rainfall, producing wetland habitat (Maher 1984;Maher and Carpenter 1984;Briggs et al 1985b;Crome and Carpenter 1988;Kingsford 1989b;Boulton and Lloyd 1992;Puckridge et al 2000). In contrast, food abundance is low during dry periods (Kingsford 1989a;Whitehead and Saalfeld 2000) and waterbirds may take whatever foods are available, disperse or die.…”

Density and distribution of potential prey for larval fish in the main channel of a floodplain river: pelagic versus epibenthic meiofauna

“…Whilst a number of studies in Australia have established that high densities of meiofauna can occur in floodplain habitats during both high and low flow conditions (e.g. Crome, 1986;Crome and Carpenter, 1988;Tan and Shiel, 1993), only a few studies have examined densities within the main channel of lowland rivers (Shiel et al, 1982;Shiel, 1985;Kobayashi et al, 1998). Shiel et al (1982) and Shiel (1985) found low average densities of zooplankton (<150 individuals l À1 ) in the pelagic zone across a number of seasons in the Murray and Darling Rivers, whereas average densities up to 803 individuals l À1 occurred in the tidal Hawkesbury-Nepean River system (Kobayashi et al, 1998).…”

Fitoplâncton em três lagoas marginais ao Rio Paranapanema e em sua desembocadura no Reservatório de Jurumirim (São Paulo, Brasil) durante um período prolongado de seca

“…No segundo período, as chuvas intensas propiciaram elevação do volume do reservatório e circulação da água, um processo de diluição foi detectado, em função do decréscimo nas concentrações de clorofila-a, matéria particulada e nutrientes, com maior número de espécies de algas constituídas por Crytophyceae e Cyanophyceae. Em relação ao zooplâncton, predador do fitoplâncton, Crome & Carpenter (1988) observaram aumento das densidades e de diversidade das espécies na fase final de um processo de seca quando as águas eram turvas em lago de planície de inundação na Austrália. Essas elevações foram atribuídas não ao efeito de concentração pela redução do volume do ambiente, mas à diminuição da pressão de predação, por alta taxa de mortalidade dos predadores.…”