The direct contribution of fish to lake phosphorus cycles

Abstract

Un resumen en españ ol se incluye detrás del texto principal de este artículo. IntroductionFish affect lacustrine nutrient dynamics directly and indirectly. Direct effects occur by the regeneration (excretion and egestion), sequestration and translocation of nutrients (Vanni 2002) while indirect effects result from feeding activities that alter community structure, e.g., differential predation effects on zooplankton composition or zoobenthic biomass. Considerable uncertainty exists over the importance of direct fish effects, relative to other biota, in the internal nutrient cycling of lakes. Fish excretion rates have been shown to be relatively large in some lakes (Kraft 1993;Schindler et al. 1993;Persson 1997) and small in others (Nakashima & Leggett 1980;Boers et al. 1991;Helminen & Sarvala 1997;Gido 2002) but there has been no systematic evaluation of their contribution across lakes.From an analysis of bioenergetic models, Schindler & Eby (1997) showed that phosphorus excretion rates for individual fish were functions of fish mass, the phosphorus content of their prey and the environmental temperature. They showed that the phosphorus content of prey items increased with predator size, due to the ontogenetic dietary shift to more phosphorusrich benthic invertebrate and fish prey items. Sterner & Elser (2002) demonstrate that the contribution of consumers to nutrient recycling depends on the difference between the nutrient content of the consumer and its food. They pointed out that Schindler & Eby (1997) made no allowance for differences in the nutrient requirements of the (predominantly predatory) fish species they considered and that Vanni et al. (2002) have shown that the phosphorus content of food influences phosphorus excretion rates when algivorous/detritivorous fish are included in analyses. I ignore this more sophisticated stoichiometric view because relatively few species in glaciated regions of Europe and North America are specialist feeders on algae/detritus (D. Griffiths, unpublished data) and because the fish assemblages analysed here come mainly from these regions and contain a variety of trophic levels. Consequently, I assume that the impact of phosphorus regeneration by fish at the ecosystem level will depend largely on how their biomass, size and diet change with ecosystem productivity. Abstract -Published data are synthesised to assess the direct contribution of fish to the recycling of phosphorus across a lake productivity gradient. Phosphorus excretion rates by fish assemblages are more or less directly proportional to fish biomass, despite changes in mean body mass, species composition and diet with increasing lake productivity. Piecewise linear regression of published data shows for the first time that lacustrine fish biomass increases with total phosphorus (TP) concentration in the water column up to around 140 lgAETPAEl )1 but levels off above that value, suggesting that fish contribute less to nutrient recycling as lake productivity increases. The results confirm previous findings that ...

Phosphorus flux by macrobenthic invertebrates in a shallow eutrophic lake Donghu: spatial change

“…Inverse relationships between SRP excreted rate and body mass of organisms are confirmed in this study as well as by other empirical data for different taxa: fish, zooplanktonic and benthic organisms (Johannes, 1964;Gutelmakher, 1977;Oude and Gulati, 1988;Schindler and Eby, 1997;Griffiths, 2006). We find interspecies differences in individual SRP excretion rates within family Chironomidae (Table V) 32.8 ± 9.9 0.002 ± 0.001 2.1 ± 0.8 11.6 ± 3. of dry body mass) from central sites (20 ºC).…”

“…Phosphorus can be released from sediments through a variety of mechanisms, including activities of benthic animals. A lot of studies have confirmed important regulating role of benthic invertebrates in nutrient cycling by different mechanisms such as bioturbation, vertical migration and direct excretion (Andersson et al, 1988;Vanni, 2002;Griffiths, 2006). According to Vanni (2002), aquatic animals excrete phosphorus directly by egestion, releasing particulate phosphorus with feces and dissolved phosphorus with urine.…”

Introduced lake trout alter nitrogen cycling beyond Yellowstone Lake

“…Others concluded that fish were sinks of nutrients (Griffiths 2006, Sereda et al 2007). However, fish can sometimes supply most nutrients demanded by microbes.…”

“…For example, animal fluxes can depend on the animal's density, biomass, and size distribution ). Higher densities or biomass of fish generally means higher excretion fluxes in lakes (Griffiths 2006) and streams (McIntyre et al 2008). High densities (43,000 fish/ha) of grey snapper (Lutjanus griseus) in the Bahamas excreted large amounts of N and P reducing nutrient limitation (Layman et al 2011).…”

“…We assumed that 11% of dry mass is equal to the mass of N in cutthroat trout (Griffiths 2006). We estimated NH 4 þ fluxes at 100-m intervals by solving the differential equation using the Euler method…”