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Calcareous Algae of a Tropical Lagoon: Primary Productivity, Calcification and Carbonate Production
Stockholm University, Faculty of Science, Department of Botany.
Responsible organisation
2005 (English)Doctoral thesis, monograph (Other academic)
Abstract [en]

The green algae of the genus Halimeda Lamouroux (Chlorophyta, Bryopsidales) and the encrusting loose-lying red coralline algae (Rhodophyta, Corallinales) known as rhodoliths are abundant and widespread in all oceans. They significantly contribute to primary productivity while alive and production of CaCO3 rich sediment materials on death and decay. Carbonate rich sediments are important components in the formation of Coral Reefs and as sources of inorganic carbon (influx) in tropical and subtropical marine environments. This study was initiated to attempt to assess their ecological significance with regard to the above mentioned roles in a tropical lagoon system, Chwaka bay (Indian Ocean), and to address some specific objectives on the genus Halimeda (Chlorophyta, Bryopsidales) and the loose-lying coralline algae (rhodoliths).

Four Halimeda species were taxonomically identified in the area. The species identified are the most common inhabitants of the world’s tropical and subtropical marine environments, and no new species were encountered. Using Satellite remote sensing technique in combination with the percentage cover data obtained from ground-truthing field work conducted in the area using quadrants, the spatial and seasonal changes of Submerged Aquatic Macrophytes (SAV) were evaluated. SAV percentage cover through ground-truthing was; 24.4% seagrass, 16% mixed Halimeda spp., 5.3% other macroalgae species while 54.3% remained unvegetated. No significant changes in SAV cover was observed for the period investigated, except in some smaller regions where both loss and gains occurred. The structural complexity of SAV (shoot density, above-ground biomass and canopy height) for most common seagrass communities from six meadows, dominated by Thalassia hemprichii, Enhalus acoroides and Thalassodendron ciliatum, as well as mixed meadows, were estimated and evaluated. Relative growth of Halimeda species was up to 1 segment tip-1 day-1. The number of segments produced was highest in hot season. Differences between the numbers of segments produced were insignificant between the two sites investigated. The C/N ratios obtained probably shows that Halimeda species experience nitrogen limitation in the area and may be a factor among others responsible for the varying growth of species obtained. However, this can be a normal ratio for calcified algae due to high CaCO3 content in their tissues. Standing biomass of mixed Halimeda species averaged between 500-600 g dw m-2 over the bay, while the mean cover in Halimeda meadows was about 1560 g dw m-2. Carbonate production in Halimeda beds varied between 17-57 g CaCO3 m-2 day-1 and for H. macroloba between 12-91 g CaCO3 m-2 day-1. This indicates a high annual input of carbonate in the area. Decomposition of Halimeda using litter bag experiments at site I and II gave a decomposition rate (k) of 0.0064 and k = 0.0091 day-1 ash-free dry weight (AFDW) respectively. Hence it would take 76-103 days for 50% of the materials to decompose.

Adding inhibitors or varying the pH significantly reduced inorganic carbon uptake, and demonstrated that the two photosynthesis and calcification were linked. Addition of TRIS strongly inhibited photosynthesis but not calcification, suggesting the involvement of proton pumps in the localized low pH acid zones and high pH basic zones. The high pH zones were maintained by the proton pumps maintaining high calcification, while TRIS was competing for proton uptake from acid zones causing photosynthesis to drop. Rhodoliths were found to maintain high productivity at a temperature of 34oC, and even at 37oC. It is therefore concluded that, rhodoliths are well adapted to high temperatures and excess light, a behaviour which enables them to thrive even in intertidal areas.

Place, publisher, year, edition, pages
Stockholm: Botaniska institutionen , 2005. , 47 p.
National Category
Botany
Identifiers
URN: urn:nbn:se:su:diva-784ISBN: 91-7155-187-5 (print)OAI: oai:DiVA.org:su-784DiVA: diva2:199141
Public defence
2006-01-27, föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 13:00
Opponent
Supervisors
Available from: 2005-12-27 Created: 2005-12-27Bibliographically approved
List of papers
1. Assessment of vegetation changes in seagrass communities of tropical Chwaka Bay (Zanzibar) using satellite remote sensing
Open this publication in new window or tab >>Assessment of vegetation changes in seagrass communities of tropical Chwaka Bay (Zanzibar) using satellite remote sensing
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2006 (English)In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 67, no 3, 399-408 p.Article in journal (Refereed) Published
Abstract [en]

Spatial and temporal dynamics of submerged aquatic vegetation (SAV) cover were studied in the relatively pristine and seagrass-dominated area of Chwaka Bay, Zanzibar (Tanzania) by using satellite remote sensing. Through complementary field work the potential of the technique for change detection was verified. The general changes in SAV cover were examined using Landsat images from 1986, 1987, 1998, 2001 and 2003. Two of these images, from 1987 (Landsat TM) and 2003 (Landsat ETM+), were specifically analysed to create a map of the change in SAV cover. Overall, the general distribution of SAV stayed fairly stable over the period investigated, but the result also showed regions where significant alterations, both losses and gains, had occurred between the two years. Based on our findings and anecdotal information from local fishermen and seaweed farmers potential causative factors are discussed. It was concluded that a repeated mapping with satellite remote sensing is a suitable tool to monitor changes of seagrass and seaweed distribution in shallow tropical environments.

Keyword
vegetation changes; seagrass satellite remote sensing; landsat; Chwaka Bay; Zanzibar; East African region
Identifiers
urn:nbn:se:su:diva-25207 (URN)10.1016/j.ecss.2005.11.020 (DOI)
Note
Part of urn:nbn:se:su:diva-784Available from: 2005-12-27 Created: 2005-12-27 Last updated: 2017-12-13Bibliographically approved
2. Growth and standing biomass of Halimeda (Bryopsidales) species and their contribution to sediment production in a tropical bay
Open this publication in new window or tab >>Growth and standing biomass of Halimeda (Bryopsidales) species and their contribution to sediment production in a tropical bay
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-25208 (URN)
Note
Part of urn:nbn:se:su:diva-784Available from: 2005-12-27 Created: 2005-12-27 Last updated: 2010-01-13Bibliographically approved
3. Inorganic carbon uptake into photosynthesis and calcification in two common Halimeda species
Open this publication in new window or tab >>Inorganic carbon uptake into photosynthesis and calcification in two common Halimeda species
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-25209 (URN)
Note
Part of urn:nbn:se:su:diva-784Available from: 2005-12-27 Created: 2005-12-27 Last updated: 2010-01-13Bibliographically approved
4. Temperature effects on photosynthesis and calcification at varying light levels in rhodoliths from a tropical lagoon
Open this publication in new window or tab >>Temperature effects on photosynthesis and calcification at varying light levels in rhodoliths from a tropical lagoon
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-25210 (URN)
Note
Part of urn:nbn:se:su:diva-784Available from: 2005-12-27 Created: 2005-12-27 Last updated: 2010-01-13Bibliographically approved

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