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Photosynthetic performance, epiphyte biomass and nutrient content of two seagrass species in two areas with different level of nutrients along the Dar es Salaam coast
Stockholm University, Faculty of Science, Department of Botany.
Dar es Salaam Institute of Technology, Department of Sciences and Laboratory Technology.
(English)In: Aquatic conservation, ISSN 1052-7613, E-ISSN 1099-0755Article in journal (Refereed) Submitted
Abstract [en]

Heavy nutrient loads in coastal waters often lead to excessive growth of micro- and macroalgal epiphytes on seagrass leaves, with varying effects on the underlying seagrasses. This study evaluates the photosynthetic performance, epiphytic biomass, and tissue nutrient content of two common tropical seagrasses, Cymodocea serrulata and Thalassia hemprichii, in two intertidal areas along the Dar es Salaam coast in the Indian ocean; Ocean Road (near the city centre, nutrient-rich) and Mjimwema (south of the centre, nutrient-poor). Epiphyte biomass was significantly higher at the nutrient-rich site, and epiphytes were associated with reduced photosynthetic performance in both seagrass species at both sites. Likewise, nitrogen and phosphorus tissue content was higher in both species at the nutrient-rich site than at the nutrient-poor site, further illustrating the documented difference in nutrients between the two areas. Epiphytic species composition on the seagrass leaves varied between seagrass species and between sites. Cymodocea serrulata had a higher number of epiphytic species at Mjimwema than at Ocean Road, while Thalassia hemprichii had more epiphytic species at Ocean Road than at Mjimwema. Our results indicate that seagrass photosynthetic performance, epiphytic biomass and nutrient content of the seagrass are influenced by nutrient gradients in the water.

National Category
Botany
Research subject
Plant Physiology
Identifiers
URN: urn:nbn:se:su:diva-55839OAI: oai:DiVA.org:su-55839DiVA: diva2:408771
Available from: 2011-04-06 Created: 2011-03-29 Last updated: 2017-12-11Bibliographically 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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