A global database of nitrogen and phosphorus excretion rates of aquatic animals.

Animals can be important in modulating ecosystem-level nutrient cycling, although their importance varies greatly among species and ecosystems. Nutrient cycling rates of individual animals represent valuable data for testing the predictions of important frameworks such as the Metabolic Theory of Ecology (MTE) and ecological stoichiometry (ES). They also represent an important set of functional traits that may reflect both environmental and phylogenetic influences. Over the past two decades, studies of animal-mediated nutrient cycling have increased dramatically, especially in aquatic ecosystems. Here we present a global compilation of aquatic animal nutrient excretion rates. The dataset includes 10,534 observations from freshwater and marine animals of N and/or P excretion rates. These observations represent 491 species, including most aquatic phyla. Coverage varies greatly among phyla and other taxonomic levels. The dataset includes information on animal body size, ambient temperature, taxonomic affiliations, and animal body N:P. This data set was used to test predictions of MTE and ES, as described in Vanni and McIntyre (2016; Ecology DOI: 10.1002/ecy.1582).

Extrinsic and intrinsic controls of zooplankton diversity in lakes.

Pelagic crustacean zooplankton were collected from 336 Norwegian lakes covering a wide range of latitude, altitude, lake area, mean depth, production (as chlorophyll a), and fish community structure. Mean zooplankton species richness during the ice-free season was generally low at high latitudes and altitudes. Further, lower species richness was recorded in western lakes, possibly reflecting constraints on migration and dispersal. However, despite obvious spatial limitations, geographic boundaries were only weak predictors of mean zooplankton richness. Similarly, lake surface area did not contribute positively to mean richness such as seen in other ecosystem surveys. Rather, intrinsic factors such as primary production and fish community (planktivore) structure were identified by regression analysis as the major predictors of zooplankton diversity, while a positive correlation was observed between species richness and total zooplankton biomass. However, in spite of a large number of variables included in this study, the predictive power of multiple regression models was modest (<50% variance explained), pointing to a major role for within-lake properties, as yet unidentified intrinsic forces, stochasticity, or dispersal as constraints on zooplankton diversity in these lakes.

Biological control of undesirable cyanobacteria in culturally eutrophic lakes.

The relationship between Oscillatoria agardhii and one of its natural grazers, the gymnostomid ciliate Nassula ornata was studied in laboratory experiments. Ingestion of Oscillatoria by Nassula increased exponentially over the temperature range 5-20°C, and the grazer was able to suppress Oscillatoria at all temperatures. Laboratory studies showed further that the predatory copepod Cyclops strenuus was able to suppress Nassula, and that juvenile roach (Rutilus rutilus) also fed on Nassula. In an enclosure experiment in an Oscillatoria-lake, Nassula reduced Oscillatoria concentration with more than 50% as compared to the control. The scarcity of Nassula in many Oscillatoria-lakes may be due to predation by cyclopoid copepods and juvenile fish; predominantly cyprinids. A proposed model describes well the population dynamics of Oscillatoria and Nassula in mixed cultures.