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Seagrass photosynthesis controls rates of calcification and photosynthesis of calcareous macroalgae in a tropical seagrass meadow

Semesi, Immaculate Sware (author)
Stockholms universitet,Botaniska institutionen,University of Dar es Salaam, Tanzania
Beer, Sven (author)
Tel Aviv University, Israel
Björk, Mats (author)
Stockholms universitet,Botaniska institutionen,University of Dar es Salaam, Tanzania
 (creator_code:org_t)
Inter-Research Science Center, 2009
2009
English.
In: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 382, s. 41-47
  • Journal article (peer-reviewed)
Abstract Subject headings
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  • Diel fluctuations in seawater pH can be >1 pH unit (7.9 to >8.9) in the seagrass meadows of Chwaka Bay (Zanzibar, Tanzania). The high daily pH values are generated by the photosynthetic activity of the bay’s submerged seagrasses and macroalgae, and maintained by the relatively low, tide-dominated, water exchange rate. Since pH in principle can affect rates of both calcification and photosynthesis, we investigated whether diel variations in pH caused by photosynthesis could affect rates of calcification and photosynthesis of the calcareous red (Hydrolithon sp. and Mesophyllum sp.) and green (Halimeda renschii) algae growing within these meadows. This was done by measuring rates of calcification and relative photosynthetic electron transport (rETR) of the algae in situ in open-bottom incubation cylinders either in the natural presence of the rooted seagrasses or after the leaves had been removed. The results showed that seagrass photosynthesis increased the seawater pH within the cylinders from 8.3–8.4 to 8.6–8.9 after 2.5 h (largely in conformity with that of the surrounding seawater), which, in turn, enhanced the rates of calcification 5.8-fold for Hydrolithon sp. and 1.6-fold for the other 2 species. The rETRs of all algae largely followed the irradiance throughout the day and were (in Mesophyllum sp.) significantly higher in the presence of seagrasses despite the higher pH values generated by the latter. We conclude that algal calcification within seagrass meadows such as those of Chwaka Bay is considerably enhanced by the photosynthetic activity of the seagrasses, which in turn increases the seawater pH.

Subject headings

NATURVETENSKAP  -- Biologi -- Botanik (hsv//swe)
NATURAL SCIENCES  -- Biological Sciences -- Botany (hsv//eng)

Keyword

calcareous algae
calcification
Halimeda sp.
Hydrolithon sp.
Mesophylum sp.
photosynthesis
Plant physiology
Växtfysiologi
Plant Physiology
växtfysiologi

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ref (subject category)
art (subject category)

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Semesi, Immacula ...
Beer, Sven
Björk, Mats
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NATURAL SCIENCES
NATURAL SCIENCES
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and Botany
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Marine Ecology P ...
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Stockholm University

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