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Trophic ecology of meiofauna: Response to sedimentation of phytoplankton blooms in the Baltic Sea
Stockholm University, Faculty of Science, Department of Systems Ecology. (Marine Ecology)
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Marine soft sediments are the second largest habitat on Earth. How animal communities in this habitat are structured is a central issue in marine ecology. Food is an important limiting factor for many benthic populations, and settling organic matter from phytoplankton blooms is of vital importance to them. This thesis discusses the effects of settling phytoplankton blooms on benthic meiofaunal populations in the Baltic Sea and how species interactions affect the fate of settled organic matter. Eutrophication in the Baltic Sea has altered phytoplankton community dynamics, with indications that toxin-producing cyanobacterial blooms may reach the benthos in greater quantity than previously. Paper I found that meiofauna feed on settled cyanobacteria, yet suffer no increase in mortality. However, growth of meiofauna is significantly slower on a diet of cyanobacteria than when fed spring bloom diatoms, indicating that the studied cyanobacteria are nutritionally poor (Paper II). In Paper III we found that the presence of macrofauna reduces the access of meiofauna to settled organic matter, presumably through interference competition that increases when several macrofauna species are present. We also found that meiofaunal populations influence the provision of ecosystem services by benthic microbes. Paper IV shows that when meiofauna is abundant, mineralization of organic matter is positively affected, presumably through facilitation mechanisms. In contrast, paper V reports that degradation of the contaminant naphtalene decreases significantly at high meiofauna abundance.

In conclusion, this thesis shows that type and quality of organic matter available, as well as competition from macrofauna, affect how meiofauna grow and incorporate nutrients. Furthermore we found meiofauna to be an important functional component of the benthic ecosystem, with marked effects on ecosystem processes such as nutrient regeneration and contaminant degradation.

Place, publisher, year, edition, pages
Stockholm: Department of Systems Ecology, Stockholm University , 2010.
Keyword [en]
Meiofauna, Cyanobacteria, competition, facilitation, ecosystems processes
National Category
Ecology
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-38809ISBN: 978-91-7447-083-3 (print)OAI: oai:DiVA.org:su-38809DiVA: diva2:315444
Public defence
2010-05-27, Högbomsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 09:30 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: In press.

Available from: 2010-05-05 Created: 2010-04-29 Last updated: 2017-10-04Bibliographically approved
List of papers
1. Settling blooms of filamentous cyanobacteria as food for meiofauna assemblages.
Open this publication in new window or tab >>Settling blooms of filamentous cyanobacteria as food for meiofauna assemblages.
2008 (English)In: Limnology and Oceanography, ISSN 0024-3590, Vol. 53, no 6, 2636-2643 p.Article in journal (Refereed) Published
Abstract [en]

Summer blooms of filamentous nitrogen-fixing cyanobacteria in the Baltic Sea are normally dominated by Aphanizomenon sp. and the toxin-producing Nodularia spumigena. In a 2-week laboratory experiment, we followed the uptake by representative benthic meiofauna species of C-14-labeled organic carbon from blooms, each dominated by one of these cyanobacteria. Natural bloom material was collected and labeled by incubation with (NaHCO3)-C-14. Uptake of cyanobacterial carbon was recorded for the major meiofauna taxa living in the first-centimeter layer, namely ostracods, harpacticoids, and nematodes. The uptake rates were within the range found for diatoms in other studies, indicating that cyanobacteria may be an important food resource for the meiobenthos. The uptake of cyanobacterial carbon varied significantly among species, even within the same class. The ostracod Candona neglecta showed the highest uptake values, whereas two other ostracod species took up very little of the label. There was no significant difference in utilization of carbon from Aphanizomenon sp. and N. spumigena and no reduction in the abundance of the meiofaunal taxa analyzed compared to unexposed controls, indicating that Baltic meiofaunal assemblages in general experience no mortality when exposed to settled cyanobacteria, even the hepatotoxic N. spumigena.

National Category
Ecology
Identifiers
urn:nbn:se:su:diva-15617 (URN)000261355500025 ()
Available from: 2008-12-07 Created: 2008-12-07 Last updated: 2010-04-29Bibliographically approved
2. Settling cyanobacterial blooms do not improve growth conditions for soft bottom meiofauna
Open this publication in new window or tab >>Settling cyanobacterial blooms do not improve growth conditions for soft bottom meiofauna
2009 (English)In: Journal of Experimental Marine Biology and Ecology, ISSN 0022-0981, E-ISSN 1879-1697, Vol. 368, 138-146 p.Article in journal (Refereed) Published
Abstract [en]

Summer blooms of the toxin-producing cyanobacteria Nodularia spumigena are frequent in the Baltic Sea and recent findings suggest that they may be an important food source for the benthos below the euphotic zone. To investigate the effects of settling spring and summer phytoplankton blooms on meiofaunal growth, we assayed concentrations of nucleic acids in three ostracod species (Candona neglecta; Heterocyprideis sorbyana and Paracyprideis fennica) and one genus of nematodes (Paracanthonchus spp.) after incubation in sediments with the one of the following food additions: (1) diatoms, (2) the cyanobacterium Nodularia spumigena, (3) Tetraphyll® as a known high-quality food source, (4) lignin as a refractory artificial food, and (5) control (no added organic matter). The ribosomal ribonucleic acid (RNA) content and RNA:DNA ratios of the tested organisms were lower in the cyanobacteria treatment than in the diatom treatment, with the difference in RNA:DNA ratios being statistically significant for all species except C. neglecta. Moreover, individuals incubated with N. spumigena showed RNA:DNA levels similar to those found in the lignin and control treatments. Furthermore, N. spumigena had lower concentrations of both enzymatically hydrolysable amino acids (EHAA) and eicosapentaenoic acid (EPA) than diatoms suggesting lower nutritional quality for consumers. These results indicate that recently settled summer blooms of N. spumigena are nutritionally poor and do not improve conditions for meiofaunal growth in Baltic sediments. In contrast, input of diatoms to the sediments during spring is crucial for meiofaunal growth.

Place, publisher, year, edition, pages
Elsevier B.V, 2009
Keyword
Benthic-pelagic coupling, Cyanobacteria, Meiofauna, Organic matter quality
Identifiers
urn:nbn:se:su:diva-32584 (URN)10.1016/j.jembe.2008.09.014 (DOI)000262796300005 ()
Available from: 2009-12-14 Created: 2009-12-14 Last updated: 2017-12-12Bibliographically approved
3. Diversity of larger consumers enhances interference competition effects on smaller competitors
Open this publication in new window or tab >>Diversity of larger consumers enhances interference competition effects on smaller competitors
2011 (English)In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 166, no 2, 337-347 p.Article in journal (Refereed) Published
Abstract [en]

Competition between large and small species for the same food is common in a number of ecosystems including aquatic ones. How diversity of larger consumers affects the access of smaller competitors to a limiting resource is not well understood. We tested experimentally how species richness (0-3 spp.) of benthic deposit-feeding macrofauna changes meiofaunal ostracods' incorporation of fresh organic matter from a stable-isotope-labeled cyanobacterial bloom, using fauna from the species-poor Baltic Sea. Presence of macrofauna mostly decreased meiofaunal incorporation of bloom material, depending on the macrofauna species present. As expected, the species identity of macrofauna influenced the incorporation of organic matter by meiofauna. Interestingly, our results show that, in addition, species richness of the macrofauna significantly reduced meiofauna incorporation of freshly settled nitrogen and carbon. With more than one macrofauna species, the reduction was always greater than expected from the single-species treatments. Field data from the Baltic Sea showed a negative correlation between macrofauna diversity and meiofaunal ostracod abundance, as expected from the experimental results. We argue that this is caused by interference competition, due to spatial niche differentiation between macrofauna species reducing the sediment volume in which ostracods can feed undisturbed by larger competitors. Interference from macrofauna significantly reduces organic matter incorporation by meiofauna, indicating that diversity of larger consumers is an important factor controlling the access of smaller competitors to a limiting food resource.

Keyword
Asymmetrical competition, Biodiversity, Complementarity, Resource partitioning, Species richness
National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-68116 (URN)10.1007/s00442-010-1865-0 (DOI)000290587600005 ()
Note
authorCount :4Available from: 2012-01-03 Created: 2012-01-03 Last updated: 2017-12-08Bibliographically approved
4. Meiofauna enhances organic matter mineralization in soft sediment ecosystems
Open this publication in new window or tab >>Meiofauna enhances organic matter mineralization in soft sediment ecosystems
2010 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Organic matter mineralization in soft sediments is a key process mediated by benthic fauna and bacteria that is crucial for sustaining primary production in aquatic systems. Few studies have examined the effect of meiofauna on the degradation of labile organic matter in soft sediments. Here we investigated the influence of meiofauna on the benthic decomposition of a radiolabelled diatom bloom by measuring the production of 14CO2 in a laboratory microcosm. Mineralization of the diatom bloom material was significantly enhanced when meiofauna was present in higher abundances, with cumulative mineralization values after 17 days being on average 50% greater in the treatment with high meiofauna abundance compared to sediments with low meiofauna abundance. Our experiment shows that meiofauna can enhance the mineralization of organic matter, probably by stimulating the activity of sediment bacterial community, indicating that positive biological interactions such as facilitation from meiofauna are important for ecosystem processes in soft sediments.

National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-38803 (URN)
Available from: 2010-04-29 Created: 2010-04-29 Last updated: 2010-04-29Bibliographically approved
5. Meiofauna reduces bacterial mineralization of naphthalene in marine sediment
Open this publication in new window or tab >>Meiofauna reduces bacterial mineralization of naphthalene in marine sediment
2010 (English)In: The ISME journal, ISSN 1751-7362, no 4, 1421-1430 p.Article in journal (Refereed) Published
Abstract [en]

The role of sediment-living meiofauna, benthic invertebrates smaller than 1000lm, such as nematodes and ostracods, on the mineralization of naphthalene, a common polycyclic aromatic hydrocarbon (PAH), in marine sediment was studied in microcosms using radiorespirometry. A method to extract live meiofauna was developed and used in order to experimentally manipulate meiofauna abundance and group diversity. Higher abundances of meiofauna were found to significantly decrease naphthalene mineralization. Furthermore, a change in the bacterial community composition (studied using terminal restriction fragment length polymorphism) was also observed in presence of higher meiofauna abundance, as well as a lower number of cultivable naphthalene-degrading bacteria. The reduced mineralization of naphthalene and the altered bacterial community composition in the presence of increased meiofauna abundance is likely the result of top-down control by meiofauna. This study shows that higher abundances of meiofauna can significantly decrease the microbial mineralization of PAHs such as naphthalene and also significantly modify the bacterial community composition in natural marine sediments.

Place, publisher, year, edition, pages
International Society for Microbial Ecology, 2010
Keyword
biodegradation; predation; polycyclic aromatic hydrocarbons; trophic interactions; top-down control; live meiofauna extraction; T
National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-38802 (URN)10.1038/ismej.2010.63 (DOI)
Available from: 2010-04-29 Created: 2010-04-29 Last updated: 2011-01-10Bibliographically approved

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