Effect of grazing and nutrient supply on periphyton biomass and nutrient stoichiometry in habitats of different productivity

Abstract

The impact of grazing and nutrient supply on epilithic periphyton was investigated in factorial field experiments in four seasons at three Swedish sites of different productivity and herbivore composition (Lake Limmaren, Lake Erken, and Väddö, a low salinity coastal site). Nutrient supply was enhanced by a granulose fertilizer containing nitrogen (N) and phosphorus (P), and grazer density was manipulated by exclusion cages. Algal biomass was increased by nutrient enrichment and reduced by grazer presence, but effects were highly variable between sites and seasons. Generally, grazers had stronger effects on algal biomass than nutrient enrichment, but there was no overriding effect of either grazing or nutrients. This indicated a simultaneous top-down and bottom-up control of algal biomass. Taxonomic composition of the periphyton was more affected by grazer presence than by nutrients. Internal nutrient ratios of the algae indicated N limitation at two of the sites. At all sites, the content of N and P in the periphytic assemblage was enhanced by the experimental nutrient enrichment, resulting in decreased C : N and C : P ratios. The presence of herbivores also increased periphytic nutrient content (decreased N : P and C : P ratios) in some experiments, suggesting an increase in algal P due to excretion. The effect strength of grazers and nutrients on periphyton was affected by different abiotic characteristics such as light availability, nutrient concentrations, and temperature. However, single environmental characteristics were not sufficient to explain the relative importance of grazing and nutrients.

Effects of the zebra mussel, an exotic freshwater species, on seston stoichiometry

“…We observed strongest effects of grazers on C : P and N : P ratios of seston, whereas the C : N ratios were less affected or unaffected, corroborating earlier findings from pelagic communities (Urabe 1995) and benthic communities (Hillebrand and Kahlert 2001). In our experiment ammonium was the main component of the DIN, congruent with most observations on benthic nitrogen regeneration (Prins and Small 1994;Gardner et al 1995).…”

“…In addition, the mismatch between the nutrient composition of primary producers and the nutrient demand of consumers has prominent implications for nutrient recycling by consumers (Elser and Urabe 1999;Vanni 2002;Hillebrand et al 2004). Nutrient excretion rate by an animal is positively correlated to the nutrient concentration in the food and negatively correlated to the nutrient content of body tissues (Vanni 2002).…”

The influence of substratum type and nutrient supply on biofilm organic matter utilization in streams

“…The C : N ratio has been demonstrated sensitive to be to the enhancement of nutrient supply (Peterson et al 1993;Hillebrand and Kahlert 2001). However, changing the nutrient conditions caused only a slight decrease in the C : N ratio (increase in N content) of Fuirosos biofilms.…”

“…Benthic autotrophs and heterotrophs respond differently to nutrient enrichment (Mulholland et al 1991;Hillebrand et al 2002) and depending on the substratum type (solid substratum vs. sediment; Blumenshine et al 1997). These differential responses to nutrient enrichment may be related to the nutrient status of the biofilm.…”

Disturbance-related patterns in unstable rocky benthic habitats of the north-eastern Baltic coast

“…Processes such as grazing and anthropogenic disturbance from nutrient addition are known to be important for the algae on tops of boulders (Hillebrand and Kahlert, 2001;Kotta et al, 2004;Kraufvelin et al, 2006;Korpinen and Jormalainen, 2008). In soft sediment habitats of the Baltic Sea, physical disturbance from sand movement is known to be important (Herkül et al, 2006;Torn et al, 2010).…”