Can feeding of fish on terrestrial insects subsidize the nutrient pool of lakes?
Mehner, Thomas, Jan Ihlau, Hendrik Dörner, and Franz Hölker
Limnol. Oceanogr., 50(6), 2005, 2022–2031

We estimated consumption and excretion rates of terrestrial-borne phosphorus by a population of the insectfeeding fish species bleak (Alburnus alburnus) in a 0.12-km² mesotrophic lake of the German lowlands. Fish abundance, growth rates, and diet composition were determined, and consumption and nutrient metabolism were calculated by a bioenergetics model. Mean bleak abundance was about 77,000 ind. km^-2. About 84% of bleak consumption consisted of terrestrial insects. Annual consumption of lake-external phosphorus (P) by bleak was 432 g, representing ~2.1% of the lake internal P-pool. Annual excretion of terrestrial-derived phosphorus by bleak was equivalent to ~11% of the mean epilimnetic SRP concentration. A substantial subsidy of lake nutrient pools by insectivorous fish is more likely in lakes <0.03 km² owing to the increasing perimeter-to-area ratio between donor and recipient habitats. Terrestrial nutrient subsidy by fish feeding may be important only in small oligotrophic lakes in forested areas.