African Journals OnLine
South African Journal of Botany

VOLUME 67 ISSUE 3 (2001)

South African Journal of Botany 67 (7) 2001, 383–389
©2001 NISC Pty Ltd, www.nisc.co.za

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Restoration and management of mangrove systems — a lesson for and from the East African region

JG Kairo^{1, 2}*, F Dahdouh-Guebas², J Bosire^{1, 2} and N Koedam²

¹ Kenyan Marine and Fisheries Research Institute, PO Box 81651, Mombasa, Kenya

² Laboratory of General Botany and Nature Management, Mangrove Management Group, Vrije Universiteit Brussels, Pleinlaan 2, B-1050 Brussels, Belgium, [email protected] , [email protected] 

* Corresponding author, e-mail: [email protected] 

Received 2 February 2001, accepted in revised form 15 April 2001

The restoration of mangroves has received a lot of attention world wide for several reasons. Firstly, the long ignored ecological and environmental values of mangrove forests have been documented for many mangrove areas in the world. Secondly, there is a high subsistence dependence on natural resources from mangrove forests. In addition, large losses of mangroves have occurred throughout the world leading to coastal erosion, decline of fishery resources and other environmental consequences, some of which in need of urgent attention. Finally, governments throughout the world are showing commitments towards sustainable use of mangrove areas. This paper outlines the activities of mangrove restoration and management around the world with particular emphasis on Eastern Africa. As noted here, extensive research has been carried out on the ecology, structure and functioning of the mangrove ecosystem. However, the findings have not been interpreted in a management framework, thus mangrove forests around the world continue to be over-exploited, converted to aquaculture ponds, and polluted. We strongly argue that links between research and sustainable management of mangrove ecosystems should be established.

South African Journal of Botany 67 (7) 2001, 390–392
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Marine photosynthetic research in Zanzibar

S Beer

Department of Plant Sciences, Tel Aviv University, Tel Aviv 69978, Israel

* Corresponding author, e-mail: [email protected]  

Received 1 January 2001, accepted in revised form 5 May 2001

The species richness of marine macroalgae and, especially, seagrasses in Eastern Africa, in combination with its variable (e.g. high-amplitude intertidal) environments, provides an excellent background for basic functional studies of marine macrophytes. Such studies have so far contributed significantly to the understanding of seagrass photosynthesis (both inorganic carbon uptake mechanisms and adaptations to environmental factors such as irradiance), productivity and desiccation physiology. A recent, yet unpublished, study has also highlighted the importance of photosymbiotic associations with invertebrates in the area. This paper reviews works carried out in Zanzibar this far, and suggests topics for future research in the region.

South African Journal of Botany 67 (7) 2001, 393–398
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Status and distribution of mangroves in Mozambique

FMA Barbosa¹*, CC Cuambe² and SO Bandeira¹

¹ Department of Biological Sciences, Eduardo Mondlane University, PO Box 257, Maputo, Mozambique

² Forest Inventory Unit, Ministry of Agriculture and Rural Development, PO Box 1406, Maputo, Mozambique

* Corresponding author, e-mail: [email protected]  

Received 9 March 2001, accepted in revised form 5 May 2001

The status of mangrove forests in Mozambique is presented. Mangroves in Mozambique cover an area of approximately 396 080 hectares and occur mostly in sheltered shorelines and river estuaries. The highest concentrations of mangroves occur in central Mozambique, in the deltas and estuaries of large rivers. There are nine mangrove species in Mozambique. The major use is in building and as firewood. Major threats to mangroves include over exploitation for firewood and clearing of mangroves for solar salt production. Potential threats are oil pollution, uncontrolled coastal migration and industrial development along the coast. The rate of mangrove deforestation is estimated as 1 821 hectares year^-1, and is highest in Maputo and Beira. Conservation and management of mangroves in Mozambique falls under the Forests and Land Legislation Act, which envisages community participation in the protection of natural resources. Proposals are still under way for a national mangrove management plan.

South African Journal of Botany 67 (7) 2001, 399–410
©2001 NISC Pty Ltd, www.nisc.co.za

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Coastal microbial mats: the physiology of a small-scale ecosystem

LJ Stal

Netherlands Institute of Ecology, Centre for Estuarine and Marine Ecology, Department of Marine Microbiology, PO Box 140, NL-4400 AC Yerseke, Netherlands

* Corresponding author, e-mail: [email protected]  

Received 10 May 2001

Coastal inter-tidal sandy sediments, salt marshes and mangrove forests often support the development of microbial mats. Microbial mats are complex associations of one or several functional groups of microorganisms and their formation usually starts with the growth of a cyanobacterial population on a solid substrate. They are considered as analogues of fossil Precambrian stromatolites. Primary production by the cyanobacteria fuels the metabolism of sulfate reducing bacteria and the sulfide that they produce is oxidised by anoxygenic phototrophic bacteria and by colorless sulfur bacteria. Growth and metabolism of these microorganisms result in markedly fluctuating vertical gradients of oxygen and sulfide that shift during a day-night cycle. This review discusses the metabolic contributions of the different functional groups of microorganisms and how their joint effort results in the formation of the mat.

South African Journal of Botany 67 (7) 2001, 411–419
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Challenges for marine botanical research in East Africa: Results of a bibliometric survey

PLA Erftemeijer*, AK Semesi and CA Ochieng

Department of Botany, University of Dar es Salaam, PO Box 35060, Dar es Salaam, Tanzania

* Corresponding author, e-mail: [email protected] 

Received 7 January 2001, accepted in revised form 5 June 2001

A bibliometric review was made of published and grey literature on marine botanical research in the Western Indian Ocean (1950–2000) to evaluate the current status of marine botanical research in the East African region. All literature references indexed in Aquatic Sciences and Fisheries Abstracts, Life Sciences Collection, and other computerised databases, as well as annual reports, bibliographies, web-sites, review articles, cross-references, papers and reports published in grey literature — obtained from various institutions and libraries operating in this region — were systematically analysed to provide a diagnosis of strengths and weaknesses in the marine botanical research in the region to date. The results of the analysis are discussed in order to identify the main challenges to be faced as a solid basis for future research efforts in marine botany in the East African region.

South African Journal of Botany 67 (7) 2001, 420–425
©2001 NISC Pty Ltd, www.nisc.co.za

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Seagrass research in the eastern Africa region: emphasis on diversity, ecology and ecophysiology

SO Bandeira¹* and M Björk²

¹ Department of Biological Sciences, Eduardo Mondlane University, PO Box 257, Maputo, Mozambique

² Botany Department, Stockholm University, 10691, Stockholm, Sweden

* Corresponding author, e-mail: [email protected] 

Received 7 April 2001, accepted in revised form 8 June 2001

This paper presents a brief review of seagrass research in the eastern African region, including Somalia, Kenya, Tanzania, Mozambique, eastern South Africa, Seychelles, Comoros, Madagascar, Reunion and Mauritius. Only about 60 references have been published from this region since the 1930's, covering mainly seagrass diversity and ecology, and only about 30 of these have been published during the last 10 years in international journals. These covered mainly ecology, ecophysiology and anatomy/histochemistry. Considering this and the fact that eastern Africa with its 12 species is a region of high diversity of seagrasses, seagrass research in the region appears to be in its infancy. Apart from the need for continued survey and mapping activities, future research has to focus on the significance of seagrass beds in the region, their role in the coastal ecosystem and how they are affected by various anthropogenic changes.

South African Journal of Botany 67 (7) 2001, 426–432
©2001 NISC Pty Ltd, www.nisc.co.za

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Nitrogen-fixing cyanobacteria in tropical oceans, with emphasis on the Western Indian Ocean

B Bergman

Department of Botany, Stockholm University, SE-106 91, Stockholm, Sweden

* Corresponding author, e-mail: [email protected]  

Received 22 May 2001, accepted 12 June 2001

It is now widely recognised that cyanobacteria in the marine environment are represented by unicellular, filamentous as well as filamentous heterocystous taxa. The unicellular pico-cyanobacteria contribute substantially to primary production, while the larger planktonic non-heterocystous genus Trichodesmium appear to be the most potent provider of new nitrogen to oceans. Although there have been rather few studies in the Indian Ocean, recent surveys suggest a rich diversity among benthic cyanobacteria along the east African coast and many of the taxa identified are known to fix or are potential nitrogen fixers. The northeastern monsoon promotes large surface blooms of Trichodesmium, and besides some unicellular nitrogen-fixers such as Gloeocapsa sp., heterocystous cyanobacteria of the genus Richelia, living in symbiosis with certain diatoms, are particularly common in the area. Other potential cyanobacterial nitrogen-fixers are discussed as are factors known to regulate marine nitrogen fixation.

South African Journal of Botany 67 (7) 2001, 433–438
©2001 NISC Pty Ltd, www.nisc.co.za

The progression of a mangrove forest over a newly formed delta in the Umhlatuze Estuary, South Africa

T Bedin

Department of Biology and Nature Conservation, Agricultural University of Norway, PO Box 5014, N-1432 Ås, Norway

* Corresponding author, e-mail: [email protected] 

Received 18 January 2001, accepted in revised form 5 March 2001

Different age groups were recognised in a mangrove forest that progressed over a delta forming after the construction of a harbour in the Umhlatuze Estuary, South Africa in 1976. The rate of progress was high during the first period, varying from 20 to 55ha year ^-1 until 1982. Thereafter there was a small decrease in the total area, whereas the rate has been 5.4ha year ^-1 over the last 13 years. Diameter at breast height (dbh) and densities of trees and seedlings were investigated in the field in the different age groups recognised from the aerial photo record covering the area. The youngest stands (1–6 years old trees) had a significantly lower mean dbh compared to the older stands (>6 years). The difference was also clear when it came to stem densities, where significantly higher densities were found in the youngest stands. The mean density of live seedlings was high in the youngest stands, being significantly lower in the older stands. When it came to the mean density of dead seedlings, the number from the youngest stand was lower than the ones obtained for older groups. The oldest group had however a very low density. It is suggested that the mangrove progression has slowed down, thus indicating that the system is settling down.

South African Journal of Botany 67 (7) 2001, 439–442
©2001 NISC Pty Ltd, www.nisc.co.za

Biomass distribution and leaf nutrient concentrations and resorption of Thalassia hemprichii at Inhaca Island, Mozambique

ARO Martins* and SO Bandeira

Department of Biological Sciences, Eduardo Mondlane University, PO Box 257, Maputo, Mozambique

* Corresponding author, e-mail: [email protected] 

Received 9 March 2001, accepted in revised form 25 April 2001

Biomass and nutrients (C, N and P) of the seagrass Thalassia hemprichii were compared for the Northern Bay (NB) and Southern Bay (SB) of Inhaca Island, southern Mozambique. T. hemprichii is one of the most dominant seagrass species in the Indian Ocean, although still poorly documented in Africa. Its mean biomass varied between 787.4 ± 233.8gDWm^-2 and 1876.8 ± 389.4gDWm^-2 for NB and SB, respectively. For the associated seagrass species, Cymodocea rotundata, Halodule wrightii, Halophila ovalis and Zostera capensis, they corresponded up to 8.8% of the T. hemprichii biomass. Leaf nutrient concentrations showed a clear gradual decrease with age. This varied from 3.03% to 1.7% for N, 0.25% to 0.07% for P in NB and from 3.3% to 1.7% for N, 0.27% to 0.1% for P in SB. Mean C:N:P ratios, normalised for biomass, were 545:35:1 and 509:35:1 for NB and SB, respectively. The leaf resorption efficiencies, were 9.5% and 63.9% for nitrogen and 44.4% and 63.2% for phosphorus in NB and SB, respectively.

South African Journal of Botany 67 (7) 2001, 443–449
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Litter production in three mangrove stands of Mida Creek, Kenya

P Gwada¹* and JG Kairo²

¹ Marine Ecological & Environmental Research Programme, Kenya Marine & Fisheries Research Institute (KMFRI), PO Box 81651, Mombassa, Kenya

² Laboratory of Botany and Nature Management, Mangrove Management Group, Free University of Brussels, Pleinlaan 2, B–1050, Brussels, Belgium

* Corresponding author, e-mail: [email protected] 

Received 13 February 2001, accepted in revised form 10 May 2001

The assessment of mangrove litter productivity by litter-traps for the year 1996–97 was obtained from three dominant mangrove stands in Mida Creek: Rhizophora mucronata (L.), Ceriops tagal (Perr.) C. B. Robinson and Avicennia marina (Forsks). Two Monsoon-related climatic conditions occur in the area: wet period (Southeast monsoons, March–July) and dry season (Northeast monsoons, October–January). The three stands showed variations in productions between morphological parts and between seasons. Community average total production during the period was 4.36g dry m^-2 day^-1 with 6.57 and 2.65g dry m^-2 day^-1 produced in wet and dry periods respectively. Species average total productions for the period were 4.49, 6.22 and 2.35g dry m^-2 day^-1 for Rhizophora, Ceriops and Avicennia stands respectively. Species average seasonal productions were 6.13, 11.00, and 2.55g dry m^-2 day^-1 for wet periods, and 2.91, 2.80 and 2.25g dry m^-2 day^-1 for dry periods for Rhizophora, Ceriops and Avicennia stands respectively. Peak litterfall in Rhizophora and Ceriops occurred during the wet season, while peak litterfall for Avicennia occurred during the dry season. Leaves dominated outflow throughout the observation period, with staggered peaks for the different species and seasons. The reproductive units also showed staggered peaks between the different species and seasons. The staggered production pattern in litter quality and quantity amongst the different species is discussed in relation with their phenological spreads and prevailing unique hydrological conditions.

South African Journal of Botany 67 (7) 2001, 450–459
©2001 NISC Pty Ltd, www.nisc.co.za

New records of the Chlorophyta from South Africa, with the emphasis on the marine benthic flora of KwaZulu-Natal

F Leliaert¹*, O De Clerck¹, JJ Bolton² and E Coppejans¹

¹ Research Group Phycology, Department of Biology, Ghent University, KL Ledeganckstraat 35, 9000, Ghent, Belgium

² Botany Department, University of Cape Town, Private Bag, Rondebosch 7700, South Africa

* Corresponding author, e-mail: [email protected] 

Received 30 April 2001, accepted in revised form 29 May 2001

Eleven species of marine Chlorophyta that have not previously been reported for South Africa have been found on the coast of Kwazulu-Natal: Avrainvillea cf. riukiuensis Yamada; Boodleopsis pusilla (Collins) W.R. Taylor, Joly & Bernatowicz; Bornetella nitida Sonder; Caulerpa serrulata (Forsskål) J. Agardh; C. taxifolia (Vahl) C. Agardh; Chaetomorpha spiralis Okamura; Cladophoropsis sundanensis Reinbold; Halimeda gracilis Harvey ex J. Agardh; Neomeris annulata Dickie; Neomeris bilimbata Koster; Udotea indica A. Gepp & E. Gepp. Three of the above genera (Avrainvillea, Boodleopsis and Bornetella) are new for South Africa. Descriptions and illustrations are provided for each species. Furthermore the species are compared with other similar species in the area and their ecology and biogeography are briefly discussed.

South African Journal of Botany 67 (7) 2001, 460–464
©2001 NISC Pty Ltd, www.nisc.co.za

Evaluation of Padina boergesenii (Phaeophyceae) as a bioindicator of heavy metals: some preliminary results from Mauritius

R Dulymamode*, N Sukhoo, I Bhugun

Faculty of Science, University of Mauritius, Reduit, Mauritius

* Corresponding author, e-mail: [email protected] 

Received 16 May 2001, accepted in revised form 3 June 2001

The suitability of the brown macroalga Padina boergesenii was assessed as an indicator of eight heavy metals (Fe, Mn, Zn, Cd, Cr, Pb, Ni and Cu) at 5 stations around Mauritius. The results were compared with metal concentrations in seawater. Iron and Manganese were found in greater concentrations, the highest ones being recorded at Baie du Cap and Bambous Virieux. Chromium, Nickel and Copper occurred as traces in most regions. The concentration factor in the alga for Fe and Mn at each site was 10²–10³ fold. In-vitro studies of metal uptake showed some evidence of a synergistic mechanism underlying Cd/Zn absorption in P. boergesenii. The results of these studies confirm the suitability of P. boergesenii as a bioindicator of heavy metals.

South African Journal of Botany 67 (7) 2001, 465–474
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Possible introduction of alien phytoplankton via shipping ballast water: A South African perspective

C Marangoni*, RN Pienaar and SD Sym

School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Private Bag 3, WITS 2050, Johannesburg, South Africa

* Corresponding author, e-mail: [email protected] 

Received 13 May 2001, accepted in revised form 5 June 2001

Saldanha Bay is one of a few sites along the South African coast that is suitable for both shipping and mariculture. Ships visiting Saldanha Bay carry ballast water which, although essential, has been implicated in the transport of alien organisms. This study investigates the possible introduction of alien phytoplankton into Saldanha Bay by ballast water. The phytoplankton composition of Saldanha Bay was determined by collecting seasonal samples. Most of the 173 taxa encountered belonged to the Bacillariophyta (diatoms) and Dinophyta (dinoflagellates). The greatest species diversity in the water column was encountered during summer and autumn, but the greatest diversity of encysted organisms in the bottom sediment was encountered during winter. A catalogue of all organisms encountered was prepared to serve as a baseline for future investigations in the area. Ballast water samples, collected from 36 ships, were dominated by diatoms (64 species). Only 9 cosmopolitan species were found to be common to both the ballast waters and Saldanha Bay samples implying that the ballast water discharged into the area is not introducing any foreign organisms capable of establishing new populations. To obtain a more accurate assessment of this threat to South Africa, the methods of sampling ballast waters needs to be re-examined. Other ports also need to be investigated, especially Richards Bay, South Africa's busiest port. Ballast water introductions of phytoplankton, seaweeds or animals into this species rich area could have damaging ecological and economic consequences.

South African Journal of Botany 67 (7) 2001, 475–482
©2001 NISC Pty Ltd, www.nisc.co.za

The distribution of epiphytic algae on three Kenyan seagrass species

J Uku^{1, 2}* and M Björk²

¹ Kenya Marine and Fisheries Research Institute, PO Box 81651, Mombasa, Kenya

² Botany Department, Stockholm University, S-10691, Stockholm, Sweden

* Corresponding author, email: [email protected] 

Received 15 January 2001, accepted in revised form 11 June 2001

A survey of epiphytic algae attached on the leaves of the seagrasses Cymodocea rotundata Ehrenberg and Hemprich ex Ascherson, Thalassia hemprichii (Ehrenberg) Ascherson and Thalassodendron ciliatum (Forsskål) den Hartog was conducted in intertidal seagrass beds located in Vipingo and Nyali along the Kenyan coast. The aim of the survey was to determine the differences in epiphytic loading on these seagrass species between areas that have different nutrient levels. The study revealed a significant difference in the levels of nitrates, ammonia and phosphates in the water column at the two sites with Vipingo having lower levels of all nutrients. The biomass of T. hemprichii and T. ciliatum and their associated epiphytic algae was higher in Nyali. However the biomass of the C. rotundata was lower in Nyali, though the epiphytic biomass remained the same when the two sites were compared. Rhodophytes dominated in both sites and there were more cyanophytes found on the seagrasses of Vipingo. The data presented in this paper shows that nutrient loading has an influence on the composition and biomass of epiphytic algae growing on these intertidal seagrasses. Vipingo, which had a lower level of nutrient loading, had higher numbers of cyanobacteria while in Nyali, where nutrient loading was higher, there were fewer species of epiphytes seen on the seagrasses.

South African Journal of Botany 67 (7) 2001, 483–487
©2001 NISC Pty Ltd, www.nisc.co.za

Short Communication

The impacts of a river effluent on the coastal seagrass habitats of Mahé, Seychelles

JC Ingram and TP Dawson*

Environmental Change Institute, University of Oxford, 1A Mansfield Road, Oxford OX1 3TB, United Kingdom

* Corresponding author, e-mail: [email protected] 

Received 2 January 2001, accepted in revised form 5 May 2001

A survey was conducted investigating the composition, distribution and abundance of seagrass in the vicinity of an untreated river effluent on the island of Mahé, Seychelles. This is a highly populated region of the island with a high concentration of human activity occurring within the river catchment. Results indicated that sedimentation, salinity and water quality resulting from the effluent discharge appears to be the dominant factor in inhibiting seagrass growth immediately adjacent to and north of the effluent mouth resulting from sea currents driven by south-easterly winds.

South African Journal of Botany 67 (7) 2001, 488–491
©2001 NISC Pty Ltd, www.nisc.co.za

Short Communication

The effect of seasons on yield and quality of carrageenan from Tanzanian red alga Eucheuma denticulatum (Gigartinales, Rhodophyta)

AS Buriyo¹*, AK Semesi and MSP Mtolera²

¹ Botany Department, University of Dar es Salaam, PO Box 35060, Dar es Salaam, Tanzania

² Institute of Marine Sciences, University of Dar es Salaam, PO Box 668, Zanzibar, Tanzania

* Corresponding author, e-mail: [email protected] , [email protected] 

Received 26 January 2000, accepted in revised form 5 May 2001

Samples were collected monthly from Oyster Bay, Dar es Salaam. Light, temperature, salinity, pH, seawater nitrogen and phosphorus were determined on each sampling period. Mean carrageenan yield was significantly higher during the SE monsoon period (t = 6.15, P<0.05). Gel strength was significantly higher during NE monsoon period (t = 2.61, P<0.05) and lower during the start of the rainy season particularly in March.

South African Journal of Botany 67 (7) 2001, 492-496
©2001 NISC Pty Ltd, www.nisc.co.za

Short Communication

A taxonomic listing, including new distribution records, for benthic, intertidal seaweeds from Mecúfi, northern Mozambique

SO Bandeira¹*, CM António² and AT Critchley³

¹ Department of Biological Sciences, Universidade Eduardo Mondlane, PO Box 257, Maputo, Mozambique

² Provincial Directorate for Environmental Coordination, Pemba, Mozambique

³ Multidisciplinary Research and Consultancy Centre, University of Namibia, Private Bag 13301, Windhoek, Namibia

* Corresponding author, email: [email protected] 

Received 21 February 2001, accepted in revised form 5 May 2001

The intertidal seaweed flora of Mecúfi District is presented. A total of 125 species records are reported (46 Chlorophyta, 22 Phaeophyta and 57 Rhodophyta). Fifty eight percent (72) of these records are new for Mozambique, this adds significantly to information on the seaweed flora of the country.