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Nutrient Stoichiometry in Benthic Food Webs – Interactions Between Algae, Herbivores and Fish
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för ekologi och evolution.
2006 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The aim of this thesis was to identify general structuring mechanisms in benthic food webs within the framework of ecological stoichiometry theory. Ecological stoichiometry is defined as the balance of multiple chemical substances in ecological interactions and explicitly considers the combined dynamics of key elements such as carbon (C), nitrogen (N) and phosphorus (P). Ecological stoichiometry theory was developed for pelagic environments, thus it must be tested whether the same mechanisms are applicable to benthic environments.

In this thesis, ecological stoichiometry theory was used as a framework to investigate nutrient pathways in benthic littoral ecosystems. I conducted one invertebrate field sampling and six experiments. In the experiments, factors such as grazing, light, nutrients and fish presence were manipulated.

The results showed that stoichiometric variability in consumers could mostly be explained by taxa. However, there was some stoichiometric variability due to sampling season, site, and nutrient enrichment.

Grazing mostly increased periphyton N and P content, although nutrient recycling effects were dependent on grazer stoichiometry. Grazing changed benthic algal community composition by increasing the proportion of grazing resistant algae species. Additionally, grazing decreased algal diversity, especially under nutrient poor conditions. The manipulation of fish presence revealed that fish affected primary producer biomass and stoichiometry through nutrient recycling.

The manipulation of abiotic factors, such as light and nutrient addition could affect periphyton nutrient content, biomass and benthic algal chlorophyll a content. The separate addition of N or P led to an increase of the added nutrient in the periphyton. Increased light intensities led to a decreased cellular chlorophyll a content and increased C:nutrient ratios.

This thesis arrives at the conclusion that periphyton-grazer-predator interactions in the benthic are bound by stoichiometric constraints. Nutrient recycling by benthic invertebrates and fish are important mechanism in benthic littoral ecosystems.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis , 2006. , s. 44
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 197
Nyckelord [en]
Ecology, ecologial stoichiometry, periphyton, grazer, benthos, trophic interactions, nutrient, algae
Nyckelord [sv]
Ekologi
Identifikatorer
URN: urn:nbn:se:uu:diva-6933ISBN: 91-554-6592-7 (tryckt)OAI: oai:DiVA.org:uu-6933DiVA, id: diva2:168534
Disputation
2006-09-08, Friessalen, Kärnhuset, EBC, Norbyvägen 18, 752 36 Uppsala, 10:00
Opponent
Handledare
Tillgänglig från: 2006-05-24 Skapad: 2006-05-24 Senast uppdaterad: 2011-06-28Bibliografiskt granskad
Delarbeten
1. Stoichiometric variation in C:N, C:P and N:P ratios of littoral benthic invertebrates
Öppna denna publikation i ny flik eller fönster >>Stoichiometric variation in C:N, C:P and N:P ratios of littoral benthic invertebrates
2005 (Engelska)Ingår i: Journal of The North American Benthological Society, ISSN 0887-3593, E-ISSN 1937-237X, Vol. 24, s. 256-269Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Nutritional constraints on herbivores are important factors structuring food webs. Our study presents field data on the nutrient content of benthic invertebrates from Lake Erken (Sweden). The most abundant benthic invertebrates of the littoral community were sampled in 3 seasons at 5 sites to examine the influence of spatial and temporal variation of abiotic conditions on invertebrate C:N:P stoichiometry. The relationships between nutrient ratios and dry mass (DM) of invertebrates were evaluated using regression analysis. Nutrient ratios of periphyton, sampled in an earlier study, were compared to those of benthic invertebrates. C:N, C:P, and N:P ratios differed among invertebrate taxa. Coleoptera had relatively high C:N, C:P, and N:P ratios, whereas Isopoda had low C:N, C:P, and N:P ratios. Nutrient ratios differed with respect to season and location. C:P and N:P ratios were significantly lower and C:N ratios were significantly higher in autumn than in spring and summer. C:P and N:P ratios increased as a functions of invertebrate DM when all taxa were analyzed together. C:N and C:P ratios of periphyton were higher than those of benthic invertebrates, but N:P ratios were similar. Our results suggested that benthic invertebrates have taxon-specific C:N and C:P ratios, but the seasonal variability in ratios indicated that littoral invertebrates were rheostatic rather than homeostatic with respect to nutrient stoichiometry. The temporal and spatial variation in grazer nutrient content must be taken into account when applying stoichiometric theory to benthic food webs.

Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:uu:diva-94623 (URN)10.1899/04-015.1 (DOI)
Tillgänglig från: 2006-05-24 Skapad: 2006-05-24 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
2. Effects of macrograzers and light on periphyton stoichiometry
Öppna denna publikation i ny flik eller fönster >>Effects of macrograzers and light on periphyton stoichiometry
2004 (Engelska)Ingår i: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 106, nr 1, s. 93-104Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Ecological stoichiometry describes the biochemical constraints of trophic interactions emerging from the different nutrient content and nutrient demand of producers and consumers, respectively. Most research on this topic originates from well-mixed pelagic food webs, whereas the idea has received far less attention in spatially structured habitats. Here, we test how light as well as grazing and nutrient regeneration by consumers affects growth and biomass of benthic primary producers. In the first laboratory experiment, we manipulated grazer presence (two different snail species plus ungrazed control), in the second experiment we factorially combined manipulation of grazer presence and light intensity. We monitored snail and periphyton biomass as well as dissolved and particulate nutrients (nitrogen and phosphorus) over time. Grazers significantly reduced algal biomass in both experiments. Grazers affected periphyton nutrient content depending on the prevailing nutrient limitation and their own body stoichiometry. In the nitrogen (N-) limited first experiment, grazers increased N both in the periphyton and in the water column. The effect was stronger for grazers with lower N-content. In the phosphorus (P-) limited second experiment, grazers increased the P-content of the periphyton, but the grazer with lower N-content had additionally positive effects on algal N. Light reduction did not affect periphyton biomass, but increased chlorophyll-, N- and P-content of the periphyton. These experiments revealed that the indirect effects of grazers on periphyton were bound by stoichiometric constraints of nutrient incorporation and excretion.

Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:uu:diva-94624 (URN)10.1111/j.0030-1299.2004.13166.x (DOI)
Tillgänglig från: 2006-05-24 Skapad: 2006-05-24 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
3. Role of nutrient supply in grazer-periphyton interactions: Reciprocal influences of periphyton and grazer nutrient stoichiometry
Öppna denna publikation i ny flik eller fönster >>Role of nutrient supply in grazer-periphyton interactions: Reciprocal influences of periphyton and grazer nutrient stoichiometry
2006 (Engelska)Ingår i: Journal of The North American Benthological Society, ISSN 0887-3593, E-ISSN 1937-237X, Vol. 25, nr 3, s. 632-642Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Grazer-periphyton interactions are shaped, in part, by indirect effects of nutrient regeneration. They are an important model system with which to test predictions of ecological stoichiometry and the Growth Rate Hypothesis. We conducted a laboratory experiment to test how nutrient enrichment and grazer identity interact to regulate the nutrient content and stoichiometry of both periphyton and consumers. We considered a situation in which P concentration in the water column was high, in contrast to previous experiments in which P was the limiting nutrient. We added N and P, alone and in combination, to the water in experimental aquaria that contained periphyton communities on clay tiles and grazers (1 of 3 snail species) or no grazers (ungrazed control). Benthic algae incorporated nutrients in close proportion to their availability in each nutrient treatment. Algal biomass increased significantly with +N+P enrichment, but not with +N or +P enrichment alone. Grazers had no effect on periphyton C:N ratios and positive effects on periphyton C:P and N:P ratios. P content of grazers (% dry mass) increased and C:P and N:P molar ratios of grazers decreased in response to N enrichment of the water. Grazer P content increased in response to N enrichment, probably because of increased grazer growth rates. We hypothesize that the addition of N under N-limiting conditions led to increased P uptake or retention by grazers because of high growth rates and RNA production, consistent with the Growth Rate Hypothesis.

Nyckelord
nutrient cycling, benthos, food web, C : N : P stoichiometry, gastropods, Growth Rate Hypothesis
Nationell ämneskategori
Ekologi
Identifikatorer
urn:nbn:se:uu:diva-94625 (URN)10.1899/0887-3593(2006)25[632:RONSIG]2.0.CO;2 (DOI)000239769000009 ()
Tillgänglig från: 2006-05-24 Skapad: 2006-05-24 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
4. Gastropod grazers and nutrients, but not light, interact in determining periphytic algal diversity
Öppna denna publikation i ny flik eller fönster >>Gastropod grazers and nutrients, but not light, interact in determining periphytic algal diversity
2007 (Engelska)Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 152, nr 1, s. 101-111Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The potential interactions of grazing, nutrients and light in influencing autotroph species diversity have not previously been considered. Earlier studies have shown that grazing and nutrients interact in determining autotroph species diversity, since grazing decreases species diversity when nutrients (i.e. N or P) limit autotroph growth, but increases it when nutrients are replete. We hypothesized that increased light intensities would intensify the interactions between grazing and nutrients on algal species diversity, resulting in even stronger reductions in algal species diversity through grazing under nutrient–poor conditions, and to even stronger increases of algal species diversity through grazing under nutrient-rich conditions. We studied the effects of grazing (absent, present), nutrients (ambient, N + P enriched) and light (low light, high light) on benthic algal diversity and periphyton C:nutrient ratios (which can indicate algal nutrient limitation) in a factorial laboratory experiment, using the gastropod grazer Viviparus viviparus. Grazing decreased algal biomass and algal diversity, but increased C:P and N:P ratios of periphyton. Grazing also affected periphyton species composition, by decreasing the proportion of Spirogyra sp. and increasing the proportion of species in the Chaetophorales. Grazing effects on diversity as well as on periphyton N:P ratios were weakened when nutrients were added (interaction between grazing and nutrients). Chlorophyll a (Chl a) per area increased with nutrient addition and decreased with high light intensities. Light did not increase the strength of the interaction between grazing and nutrients on periphytic algal diversity. This study shows that nutrient addition substantially reduced the negative effects of grazing on periphytic algal diversity, whereas light did not interact with grazing or nutrient enrichment in determining periphytic algal diversity.

Nyckelord
Benthos, Ecological stoichiometry, Nutrient ratios, Periphyton, Viviparus viviparus
Nationell ämneskategori
Biologiska vetenskaper
Identifikatorer
urn:nbn:se:uu:diva-94626 (URN)10.1007/s00442-006-0636-4 (DOI)000245808100010 ()17285319 (PubMedID)
Tillgänglig från: 2006-05-24 Skapad: 2006-05-24 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
5. Food web complexity affects stoichiometric and trophic interactions
Öppna denna publikation i ny flik eller fönster >>Food web complexity affects stoichiometric and trophic interactions
Visa övriga...
2006 (Engelska)Ingår i: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 114, nr 1, s. 117-125Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The stoichiometry of trophic interactions has mainly been studied in simple consumer–prey systems, whereas natural systems often harbour complex food webs with abundant indirect effects. We manipulated the complexity of trophic interactions by using simple laboratory food webs and complex field food webs in enclosures in Lake Erken. In the simple food web, one producer assemblage (periphyton) and its consumers (benthic snails) were amended by perch, which was externally fed by fish food. In the complex food web, two producer assemblages (periphyton and phytoplankton), their consumers (benthic invertebrates and zooplankton) and perch feeding on zooplankton were included. In the simple food web perch affected the stoichiometry of periphyton and increased periphyton biomass and the concentration of dissolved inorganic nitrogen. Grazers reduced periphyton biomass but increased its nutrient content. In the complex food web, in contrast to the simple food web, perch affected periphyton biomass negatively but increased phytoplankton abundance. Perch had no influence on benthic invertebrate density, zooplankton biomass or periphyton stoichiometry. Benthic grazers reduced periphyton biomass and nutrient content. The difference between the simple and the complex food web was presumably due to the increase of pelagic cyanobacteria (Gloeotrichia sp.) with fish presence in the complex food web, thus fish had indirect negative effects on periphyton biomass through nutrient competition and shading by cyanobacteria. We conclude that the higher food web complexity through the presence of pelagic primary producers (in this case Gloeotrichia sp.) influences the direction and strength of trophic and stoichiometric interactions.

Nationell ämneskategori
Ekologi
Identifikatorer
urn:nbn:se:uu:diva-94627 (URN)10.1111/j.2006.0030-1299.14517.x (DOI)000239563300012 ()
Tillgänglig från: 2010-11-11 Skapad: 2006-05-24 Senast uppdaterad: 2017-12-14Bibliografiskt granskad

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