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Nutrient enrichment affects the seagrass Cymodocea serrulata and induces changes to its epiphytic cyanobacterial community
University of Dodoma, School of Natural Sciences and Mathematics.
Stockholm University, Faculty of Science, Department of Botany.
University of Dar es Salaam, Department of Molecular Biology and Biotechnology.
Dar es Salaam Institute of Technology, Department of Sciences and Laboratory Technology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

To better understand how elevated water column nutrient levels affect the performance of the seagrass Cymodocea serrulata as well as the composition and density of its associated epiphytes, two sets of experiments were carried out where nutrient concentration were manipulated in a flow though system containing seagrasses. The photosynthetic performance, growth characteristics and nutrient content (N:P) were followed for C. serrulata. Simultaneously the biomass, species composition for the epiphytic cyanobacteria, in particular diazotrophs was monitored. The photosynthetic capacity of seagrasses decreased with increase in nutrient concentrations and exposure time. Nutrient contents of seagrass leaves and epiphytes decreased after nutrient addition. A higher diversity of both heterocystous and non-heterocystous cyanobacteria was observed in the experimental seagrasses as compared with natural field samples. Many of the cyanobacterial sequences retrieved represented uncultured and potentially novel diazotrophic phylotypes. Diel nitrogenase activity measurements verified the presence of a distinct proportion of diazotrophs, which was negatively affected by moderate nutrient levels. These results demonstrate that seagrasses were physiologically stressed by the increased nutrient level as revealed by low maximum quantum yields, although the effect was not instant. In contrast the epiphytes whose response was apparent during the short term exposure to moderate nutrient concentration which also promoted rapid change in their composition.

Keyword [en]
Cymodocea serrulata, diazotrophy, epiphyte, cyanobacteria, nutrient enrichment; photosynthesis, seagrasses
National Category
Botany
Research subject
Plant Physiology
Identifiers
URN: urn:nbn:se:su:diva-55868OAI: oai:DiVA.org:su-55868DiVA: diva2:408781
Available from: 2011-04-06 Created: 2011-03-30 Last updated: 2011-04-13Bibliographically approved
In thesis
1. Seagrasses and Eutrophication: Interactions between seagrass photosynthesis, epiphytes, macroalgae and mussels
Open this publication in new window or tab >>Seagrasses and Eutrophication: Interactions between seagrass photosynthesis, epiphytes, macroalgae and mussels
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Seagrass meadows are highly productive, ecologically and economically valuable ecosystems. However, increased human activities along the coastal areas leading to processes such as eutrophication have resulted in the rapid loss and deterioration of seagrass ecosystems worldwide. This thesis focuses on the responses of seagrasses to increases in nutrients, subsequent increases in ephemeral algae, and changes in the physical-chemical properties of seawater induced by interaction with other marine biota. Both in situ and laboratory experiments conducted on the tropical seagrasses Cymodocea serrulata and Thalassia hemprichii revealed that increased concentrations of water column nutrients negatively affected seagrass photosynthesis by stimulating the growth of the epiphytic biomass on the seagrass leaves. Interaction between seagrasses and other marine organisms induced different responses in seagrass photosynthesis. Ulva intestinalis negatively affected the photosynthetic performance of the temperate seagrass Zostera marina both by reducing the light and by increasing the pH of the surrounding water. On the other hand, the coexistence of mussels Pinna muricata and seagrass Thalassia hemprichii enhanced the photosynthetic activity of the seagrass, but no effect on the mussels' calcification was recorded. This study demonstrates that seagrass productivity is affected by a multitude of indirect effects induced by nutrient over-enrichment, which act singly or in concert with each other. Understanding the responsive mechanisms involved is imperative to safeguard the ecosystem by providing knowledge and proposing measures to halt nutrient loading and to predict the future performance of seagrasses in response to increasing natural and human perturbations. 

Place, publisher, year, edition, pages
Stockholm: Department of Botany, Stockholm University, 2011. 44 p.
Keyword
CO2, epiphytes, eutrophication, mussels, pH, Photosynthetic activities, seagrasses, Ulva
National Category
Botany
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-55808 (URN)978-91-7447-250-9 (ISBN)
Public defence
2011-05-06, Föresläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 13:00 (English)
Opponent
Supervisors
Projects
Swedish Agency for Research Cooperation (Sida/SAREC) marine bilateral programme
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Papers 1, 3 and 4: Submitted. Paper 2: Manuscript.Available from: 2011-04-14 Created: 2011-03-29 Last updated: 2011-04-13Bibliographically approved

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