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Mussel, Seagrass and Calcareous Algal Interactions: Influence of CO2 and pH on Photosynthesis and Calcification in a Tropical Bay
Stockholm University, Faculty of Science, Department of Botany.
University of Dar es Salaam, Botany Department.
Tel Aviv University.
Institute of Marine Sciences, Zanzibar.
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(English)Manuscript (Other academic)
Abstract [en]

Changes in seawater pH and thus, the inorganic carbon (Ci) composition brought about by photosynthetic carbon uptake have been shown to influence the productivity of marine plants. In this work, we enclosed different combinations of seagrasses Thalassia hemprichii, the mussel Pinna muricata and the calcareous coralline algae Amphiroa fragilissima in open plastic cylinders in a tropical seagrasses meadow at Fumba Bay, Zanzibar, Tanzania, while measuring pH and rates of photosynthesis and calcification. The results showed that the photosynthetic production of seagrasses increased in the presence of mussels (probably due to their supply of respiratory CO2) while the presence of seagrasses supported an increase in calcification of the coralline algae (probably by the higher pH generated by the former). Photosynthetic rates of the seagrasses and the coralline algae were ~20% and ~13% higher, respectively, in the presence of mussels than in their absence. Also, the rate of calcification of the coralline algae was significantly higher (by 11%) in the presence of seagrasses than when alone. Calcification by the mussels, on the other hand, was not affected by the presence of algae or seagrasses. These results illustrate how pH changes induced by fluxes in Ci can act as a factor controlling both productivity and calcification in densely populated shallow marine ecosystems.

Keyword [en]
Coralline algae, Calcification, Mussels, pH, Photosynthesis, Seagrasses
National Category
Botany
Research subject
Plant Physiology
Identifiers
URN: urn:nbn:se:su:diva-27478OAI: oai:DiVA.org:su-27478DiVA: diva2:214426
Available from: 2009-05-05 Created: 2009-05-05 Last updated: 2011-04-13Bibliographically approved
In thesis
1. Seawater pH as a Controlling Factor in Macroalgal Calcification and Photosynthesis
Open this publication in new window or tab >>Seawater pH as a Controlling Factor in Macroalgal Calcification and Photosynthesis
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Biological calcification and photosynthesis are important processes with a great influence on both structure and function of oceanic ecosystems. The pH of the seawater has a strong influence on both these processes and therefore the impacts of different pH levels on calcareous macroalgae were investigated in laboratory and field experiments at Chwaka and Fumba Bays in Zanzibar, Tanzania. The levels of pH were manipulated, first in the laboratory by adding HCl, NaOH or by bubbling seawater with CO2 enriched air. Secondly, pH was allowed to fluctuate naturally as a consequence of marine photosynthetic carbon uptake or release through respiration by mussels. The effects on both photosynthesis and calcification were then analyzed on a seagrass (Thalassia hemprichii), and the calcareous red and green algae Mesophyllum sp., Hydrolithon sp., Amphiroa fragilissima and Halimeda renschii, as well as on the mussel Pinna muricata. The laboratory studies revealed a significant decrease in calcification rates in Hydrolithon sp. with decreasing pH, while photosynthesis showed an opposite trend. Also, increased dissolved CO2 lowered pH from 8.1 to 7.8 and caused a ~20% decline in calcification rates. In the field, seagrasses raised pH to ~9, increasing calcification rates significantly in the calcareous algae while photosynthetic rates showed no significant differences with changes in pH expect in Mesophyllum sp., in which rates increased at elevated pH caused by the presence of seagrasses. Conversely, seagrass photosynthesis increased significantly in the presence of mussels. Based on these findings, we conclude that pH is important in shaping biological processes that determines ecological interactions within shallow tidal areas by modifying seawater carbon composition and, thus, influencing calcification and photosynthesis processes.

Place, publisher, year, edition, pages
Stockholm: Department of Botany, Stockholm University, 2009. 47 p.
Keyword
Calcareous macroalgae, CO2, mussels, pH, seagrasses, tropical lagoons
National Category
Botany
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-27479 (URN)978-91-7155-887-9 (ISBN)
Public defence
2009-06-04, föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 13:00 (English)
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Available from: 2009-05-14 Created: 2009-05-05 Last updated: 2009-05-05Bibliographically approved

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