Phosphorus Excretion by Zooplankton

Abstract

The cxcrction of dissolved inorganic and organic phosphorus by scvcrnl species of marinc crustaceans and a planktonic rotifer was measured under laboratory conditions. The rate of excretion decrcascd as bacterial activity and duration of cxperimcnts increasctl and was directly related to tempcraturc and salinity. Excretion rates were higher in early evening than at other times of day.The claily phosphorus r&miremcnts of the phytoplankton, calculated from 14C mcasurcd rates of production and an assunrcd C : P ratio of 40 : 1, were compared with phosphorus released by zooplankton.The rates of excretion and the abundance of zooplankton were used to calculate an average daily adclition of inorganic phosphorus to the photic zone. Jn Bras d'Or Lake, zooplankton released twice the average daily phytoplankton phosphorus requirement; in Morrison's Pond, only one-fifth was supplied by animal excretion. Microzooplankton excretion (not considered in this study) may explain the discrepancy between phytoplankton rcquiremcnts and rcgencrntion rate in Morrison's Pond. Phosphorus supplied from the hypolimnion by eddy diEfusion in Bras d'Or Lake was one-tenth that rcgenerated by the-zooplankton--

Plankton-toxin interaction with a variable input nutrient

“…This is probably because the effect is upon the higher food chain level, which has less effect to the system. When toxin has a negative effect on the growth rate of phytoplankton, inequality (15) implies that toxin will always remain in the system. As a result, we cannot use σ 0 to predict the system dynamics as we do for system (1) since σ 0 is the average net growth rate of phytoplankton when toxin is absent.…”

“…As a result, we cannot use σ 0 to predict the system dynamics as we do for system (1) since σ 0 is the average net growth rate of phytoplankton when toxin is absent. At the other extreme, ρ 0 is the average net growth rate of phytoplankton when the toxin is at its maximal level S 0 [inequality (15)]. …”

“…Since the effects of inhibition is upon the higher trophic level, the analysis of model (23) is very similar to system (1). In particular, S(t) satisfies inequality (15). All solutions of Equation (23) remain nonnegative and are bounded, and Equation (23) has the following limiting system: (24) where N * (t) is the positive τ -periodic solution of Equation (2).…”

“…Beside these active migrations of zooplankton triggering the pulsed nutrient input passive accumulation of zooplankton by periodically tidal currents are known [20,43] generating identical effects of pulsed nutrient enrichments. Some diatoms or cyanobacteria are able to actively regulate their buoyancy and hence can vertically migrate [11,15,25]. In contrast to the zooplankton these organisms perform diel vertical migrations to gather nutrients in the deeper water at night-time [1,38,40].…”

The role of particulate matter in the productivity of surface waters

“…While many marine organisms have been shown to return simple inorganic nutrients to the oceans (Pomeroy et al, 1963;Johannes, 1964Johannes, , 1965Barlow & Bishop, 1965;Hargrave & Geen, 1968;Jawed, 1969;Whitledge & Packard, 1971;McCarthy & Whitledge, 1972;Yoshida & Kimata, 1972), in the long run bacterial activity must be the most important factor in nutrient regeneration. The larger organisms, no matter how effective they may be at breaking down organic nitrogen and phosphorus compounds to their simplest inorganic forms, can attack only those materials present in particulate form; many larger organisms have been shown to absorb some organic compounds directly from solution, but in only a few genera does this mechanism supply any major part of the nutritional needs of the animals (Wangersky,3977).…”