Hydrobiologia

doi: 10.1007/BF00008198pmid: N/A

Semesi, Adelaida K.

doi: 10.1007/BF00008199pmid: N/A

Abstract The mangroves of Tanzania are currently not being managed although they are legally gazetted as forest reserves. The management of this overexploited and under estimated natural resource rests with the Forest and Beekeeping Division in the Ministry of Natural Resources and Tourism. It is the Division's intention to conserve the mangroves of Tanzania, therefore steps are being taken to reach that goal. So far the Division, through its established mangrove project, has done an inventory of all the mangroves of mainland Tanzania with the assistance of NORAD. Aerial photography and ground checks were used to assess the state of all the mangrove reserves in the country. Literature search and a socio-economic study was also undertaken. The inventory revealed that the area covered by mangrove vegetation is 115 901 ha while the previous records indicate about 80 000 ha. If the bare saline areas, water bodies, and salt pans which are part of the mangrove reserves are included, the area amounts to 172 879 ha for the Tanzania mainland. The mangrove reserves have already been mapped in 30 sheets. Some sheets are mapped using a scale of 1:25 000 while others are mapped in 1:50 000 scale. The maps show the vegetation types, the area of each vegetation type, and the stand density and height of each compartment. The paper therefore presents the current status of the mangroves of Tanzania in respect to area, distribution and vegetation types. Included are the strategies being used to develop the mangrove management plans for Tanzania.

Azariah, Jayapaul;Azariah, Hilda;Gunasekaran, S.;Selvam, V.

doi: 10.1007/BF00008200pmid: N/A

Abstract Coringa mangrove forest is located in the Godavari delta, Andhra Pradesh, India. The mangrove community consisted of more than 13 species of mangrove and other plants in the present study area. The following three dominant mangrove plants,Avicennia marina, Excoecaria agallocha andSonneratia apetala were found to be present on the banks of a major channel of the Godavari river running through the forest. The structure and species distribution of mangrove, in the Channel Nagathana Kalaya has been described. The area behind the belt consisting ofAcanthus ilicifolius andMyriostachya wightiana is generally colonized byE. agallocha andA. marina. The zone has been called theAvicennia andExcoecaria zone. Adjacent to this zone species likeAegiceras corniculatum andA. officinalis were the common species. In the flat clayey soil,Suaeda maritima was found to grow. In areas of high elevation, devoid of inundation of tidal seawater during the high tidal period, species such asM. wightiana andAcanthus were found to colonize both the banks of the channels. An analysis of species diversity, indicated a definite trend in the distribution of mangrove from the mouth of the estuarine region to the inland waters. The levels of atmospheric pollutants such as sulphur dioxide (SO2), oxides of nitrogen (NOx), ammonia (NH3) and suspended particle matter (SPM) were within the legal limits.

Amarasinghe, M. D.;Balasubramaniam, S.

doi: 10.1007/BF00008201pmid: N/A

Abstract Mangrove stands in Puttalam lagoon and Dutch bay, two interconnected lagoons situated on the northwestern coast of Sri Lanka have been classified broadly into two groups, i.e., estuarine and island/mainland-fringing stands. Structural diversity of six mangrove stands, representing the two types was studied in terms of floristic composition, density, basal area, mean stand diameter, tree height, standing above-ground biomass and leaf-area index.Rhizophora mucronata andAvicennia marina were the dominant species. Higher mean stand diameters for the mangrove stands in Puttalam lagoon indicated greater maturity than the estuarine mangrove stands in Dutch bay. Nevertheless, estuarine stands in Dutch bay were structurally more complex (complexity indices 8.11–22.7) than the island/mainland-fringing mangrove stands (complexity indices 1.38–6.78). Higher number of species present in the estuarine mangrove stands is the major element that contributes to the higher values for the complexity indices for those stands. This appears to mask the contribution of stand-age to the complexity of a mangrove stand. Therefore complexity indices alone may not be used to explain adequately the structural diversity among mangrove stands.

Gang, P. O.;Agatsiva, J. L.

doi: 10.1007/BF00008202pmid: N/A

Abstract Mangroves form a unique ecosystem of limited extent covering an area of about 53 000 ha along the Kenyan coast which need protection from overexploitation. Background information on the areal extent and status of these mangroves is limited and makes their protection and management difficult. A model study has been carried out on the Mida Creek mangroves based on a double sampling approach starting with SPOT multispectral satellite imagery followed by ground checks to provide information on species composition, density and distribution of mangroves. The utilization of mangroves and uses around and within the mangroves were determined. During this study, seven mangrove species were identified in Mida Creek, namely:Avicennia marina, Bruguiera gymnorrhiza, Ceriops tagal, Rhizophora mucronata, Sonneratia alba, Xylocarpus granatum andLumnitzera racemosa. This report briefly outlines the present utilisation of mangrove species. It is recommended that a multidisciplinary management plan be developed in order to conserve and manage the mangroves of Kenya on a sustainable yield basis.

Amarasinghe, M. D.;Balasubramaniam, S.

doi: 10.1007/BF00008203pmid: N/A

Abstract Productivity studies were carried out from September, 1985 to August, 1987 in two mangrove stands, i.e. estuarine and island fringing, in Dutch bay, a lagoon situated on the northwestern coast of Sri Lanka. Net above-ground primary productivity was measured by monitoring litterfall and above-ground biomass increment. The average annual rate of litterfall in the estuarine and island-fringing mangrove stands are 588.14 g m−2 (approximately 6 t ha−1) and 407.33 g m−2 (approximately 4 t ha−1) respectively. The average annual rates of above ground woody growth are 614.74 g m−2 (approximately 6 t ha−1) in the estuarine stands and 286.8 g m−2 (approximately 3 t ha−1) in the island-fringing mangrove stands. Hence estuarine mangrove stands record a higher annual rate of above-ground net primary production (NPP; 1207.88 g m−2 or approximately 12 t ha−1) than the fringing mangrove stands (694.22 g m−2); approximately 7 t ha−1). The annual rate of NPP in the water front zones of the stands (1300.47 g m−2 in the estuarine stands and 874.56 g m−2 in the fringing stands) are greater than those in the back-mangrove zones (115.28 g m−2 in the estuarine stands and 513.88 g m−2 in the island-fringing stands). These variations may be attributed to the differences in tidal flushing and influence of freshwater in the two localities.

Hatton, J. C.;Couto, A. L.

doi: 10.1007/BF00008204pmid: N/A

Abstract Changes in coastline configuration and sand movements on Portuguese Island, a small island lying close to Inhaca Island 35 km east of Maputo, Mozambique have resulted in large areas of the Island being eroded away and consequent restricted tidal recharge of the mangrove. Measurements made during 1989 show that flooding of the mangrove occurred on only three occasions. Percentage mortality of the dominant species,Ceriops tagal (Perr.) C. B. Robinson., is high. However, at the time of the study, the co-dominant,Bruguiera gymnorrhiza (L.) Lam., showed no signs of stress. Halophytic conditions are indicated by an invasive spread of salt-tolerant herbs. All species of crustaceans and molluscs have disappeared from the mangrove. Although mortality ofC. tagal is high, the regeneration status of this species is also high, comparable to that in a regularly recharged mangrove on Inhaca Island. It is suggested thatC. tagal propagules were shed under conditions when seedling establishment was favorable i.e. flooding. These seedlings may represent the last cohort which may also suffer stress and death unless tidal recharge is re-established.

Coppejans, Eric;Beeckman, Hans;De Wit, Mie

doi: 10.1007/BF00008205pmid: N/A

Abstract The seagrass and macroalgal vegetation of Gazi Bay (at approximately 50 km south of Mombasa) have been studied by means of 88 relevés along 7 transects. Correlation between the distribution of the seagrasses and some abiotic factors (particle size fractions, chemical composition of the substrate) is not well marked. Nevertheless a general zonation and succession of seagrasses could be established: 1. A transition zone between the mangal and the seagrass beds is covered byBoodleopsis pusilla; 2. the pioneer associationHalophila ovalis +Halodule wrightii forms low sandy bumps at the upper limit of the seagrass beds, but also occurs in the whole midlittoral where sandlayers have recently been accumulated (e.g. on coral platforms); 3. the climax vegetation of the intertidal zone seems to beThalassia hemprichii which sometimes is associated withCymodocea rotundata andC. serrulata, certainly in deeper pools and close to low water mark;Halimeda opuntia,Gracilaria salicornia andG. corticata are also frequent in this vegetation type; 4. from low water at neap tide downwards patches of monospecificEnhalus acoroides vegetation can also occur; 5. from mean low water down to approximately −1 m mixed meadows ofThalassia, C. serrulata, C rotundata andHalodule uninervis are well developed; the seaweedsHalimeda macrooloba andAvrainvillea obscura are also typical for this zone; locally patches ofSyringodium isoetifolium grow on small bumps andHalophila stipulacea grows as a pioneer on bare sand; 6. from −1 m downwards the whole lagoon is covered by homogeneous, monospecificThalassodendron ciliatum meadows, locally replaced byE. acoroides.

Kannan, L.;Vasantha, K.

doi: 10.1007/BF00008206pmid: N/A

Abstract Species richness of phytoplankton of the Pitchavaram mangals was high. There were 82 species constituted by 67 species of diatoms, 12 species of dinoflagellates and 3 species of bluegreen algae. The diatoms formed the bulk with 72% followed by the dinoflagellates with 15%, in which there were autochthonous (temporary and permanent) and allochthonous forms. Phytoplankton population density exhibited a wide seasonal fluctuation with the minimum during monsoon and the maximum during summer, suggesting the possible differential influence of various environmental factors.

Ellison, Aaron M.;Farnsworth, Elizabeth J.

doi: 10.1007/BF00008207pmid: N/A

Abstract The aerial prop roots of the neotropical red mangrove,Rhizophora mangle L., begin growing well above highest high water (HHW) and often extend well below lowest low water (LLW) before rooting in the benthic substratum. In Belize, Central America, prop roots growing below LLW are colonized by diverse assemblages of organisms, including macroalgae, hydrozoans, ascidians, sponges, anemones, hard corals, and isopod crustaceans. Mangroves, root-fouling epibionts, root herbivores, and benthic predators engage in complex interactions that are major determinants of mangrove growth and production. Species richness of root epibionts increases with distance from the mainland and with proximity to the barrier reef. Species richness decreases with variability in water temperature and salinity. Ascidians and sponges transplanted from Lark Cay into the coastal Placencia Lagoon failed to survive, but anemones from Lark Cay survived in Placencia Lagoon. Reciprocal transplants survived off-shore. The gastropod predator,Melongena melongena L., present only in mainland estuaries, reduced local barnacle abundance and epibiont species richness in Placencia Lagoon. Isopod species richness also increases with distance from shore, but the number of roots bored by these species decreases. These isopods can reduce root relative growth rate (RGRroot) by 55%. On off-shore cays, sponges and ascidians ameliorate negative effects of isopods. In mainland estuaries where epibionts are less common, isopod damage to roots is more severe. Experimental studies in mangrove swamps throughout the world would clarify the importance of plant-animal interactions in these widespread tropical ecosystems.