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Interactions between seagrasses and mussels: CO2, pH and calcification
University of Dar es Salaam, Department of Aquatic Sciences and Fisheries.
Stockholm University, Faculty of Science, Department of Botany.
Tel Aviv University, Department of Plant Sciences.
Institute of Marine Sciences, Zanzibar.
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(English)In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015Article in journal (Refereed) Submitted
Abstract [en]

Mussels and other bivalves commonly found in tropical seagrass meadows are thought to increase seagrass productivity, and seagrass photosynthesis, through raising the pH of the surrounding water, has been shown to increase rates of calcification in calcareous algae. The effects of seagrass-driven increases in pH on mussel calcification and possible feedback effects of mussel metabolism on seagrass photosynthesis were studied in a seagrass bed on the south-western coast of Zanzibar, Tanzania. Seagrasses and mussels (Pinna muricata) were enclosed, separately or together, in transparent plastic cylinders. The pH and photosynthesis were measured and seawater samples were taken from the experimental cylinders to determine total alkalinity and total inorganic carbon concentration. Cylinders containing only sediments were exposed to light and dark and used as controls. The results showed no effects of increased pH on calcification rates in the mussels. However, photosynthetic rates of the seagrass Thalassia hemprichii rose by up to 15% in the presence of mussels, possibly as a result of water stirring caused by the mussels’ filter feeding and/or CO2 released by their respiration.

Keyword [en]
Inorganic carbon, mussels, pH, photosynthesis, seagrasses
National Category
Botany
Research subject
Plant Physiology
Identifiers
URN: urn:nbn:se:su:diva-55866OAI: oai:DiVA.org:su-55866DiVA: diva2:408777
Available from: 2011-04-06 Created: 2011-03-30 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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