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Epifytische wieren (Bostrychietum) in de mangrove van Gazi Bay (Kenia) = Epiphytic algae (Bostrychietum) in the mangroves of Gazi Bay (Kenya)
De Schryver, T. (1990). Epifytische wieren (Bostrychietum) in de mangrove van Gazi Bay (Kenia) = Epiphytic algae (Bostrychietum) in the mangroves of Gazi Bay (Kenya). MSc Thesis. Rijksuniversiteit Gent. Faculteit Wetenschappen: Gent. 99, appendix pp.

Thesis info:

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Documenttype: Doctoraat/Thesis/Eindwerk

Trefwoorden
    Algen; Mangroves; Pneumatophores; Boodleopsis pusilla (Collins) W.R.Taylor, A.B.Joly & Bernatowicz, 1953 [WoRMS]; Bostrychia radicans (Montagne) Montagne, 1842 [WoRMS]; Bostrychia tenella (J.V.Lamouroux) J.Agardh, 1863 [WoRMS]; Brachytrichia quoyi Bornet & Flahault, 1886 [WoRMS]; Caloglossa leprieurii (Montagne) G.Martens, 1869 [WoRMS]; Catenella caespitosa (Withering) L.M.Irvine, 1976 [WoRMS]; Caulerpa fastigiata Montagne, 1837 [WoRMS]; Ceramium maryae Weber-van Bosse, 1923 [WoRMS]; Chaetomorpha crassa (C.Agardh) Kützing, 1845 [WoRMS]; Chaetomorpha gracilis Kützing, 1845 [WoRMS]; Chaetomorpha minima F.S.Collins & Hervey, 1917 [WoRMS]; Chlorophyta [WoRMS]; Dictyota adnata Zanardini, 1878 [WoRMS]; Ectocarpaceae C. Agardh, 1828 [WoRMS]; Enteromorpha clathrata (Roth) Greville, 1830 [WoRMS]; Enteromorpha kylinii Bliding, 1948 [WoRMS]; Enteromorpha multiramosa Bliding, 1960 [WoRMS]; Enteromorpha ramulosa (Smith) Carmichael, 1833 [WoRMS]; Gelidiella myriocladia (Borgesen) Feldmann & Hamel [WoRMS]; Gracilaria salicornia (C.Agardh) E.Y.Dawson, 1954 [WoRMS]; Herposiphonia tenella (C.Agardh) Ambronn, 1880 [WoRMS]; Hypnea valentiae (Turner) Montagne, 1841 [WoRMS]; Laurencia perforata (Bory de Saint-Vincent) Montagne, 1840 [WoRMS]; Lophosiphonia reptabunda (Suhr) Kylin, 1956 [WoRMS]; Lophosiphonia subadunca (Kützing) Falkenberg, 1901 [WoRMS]; Murrayella periclados (C.Agardh) F.Schmitz, 1893 [WoRMS]; Platysiphonia miniata (C.Agardh) Børgesen, 1931 [WoRMS]; Polysiphonia scopulorum Harvey, 1855 [WoRMS]; Rhizoclonium africanum Kützing, 1853 [WoRMS]; Stictosiphonia tangatensis (Post) R.J.King & Puttock, 1989 [WoRMS]; Ulvaria oxysperma (Kützing) Bliding, 1969 [WoRMS]; ISW, Kenia, Gazi Bay [Marine Regions]; Marien

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  • De Schryver, T., meer

Abstract
    The present study deals with the epiphytic macroalgae vegetation on pneumatophores in the mangrove of Gazi Bay, situated on the south coast of Kenya. The purpose was to study the variation of the Bostrychietum along several environmental gradients present in the mangrove. Seven transects at right angles to the coastline and at increasing distance from the open sea were studied: two short transects on the left bank of the tide channel, two longer transects in the mixed mangrove vegetation of the right bank, and three transects near the inlet of the bay, at Gazi Beach. In total, 367 pneumatophores were collected. 36 algal species were found: 14 Chlorophyta, with as most important genera Boodleopsis, Chaetomorpha (4), Cladophora (2), Enteromorpha (4) and Ulva; 2 Phaeophyta, the most important species being Dictyota adnata; 18 Rodophyta, with as most important genera Bostrychia (2), Catenella, Caloglossa, Polysiphonia and Murayella. Relative cover estimates for all species were obtained using vertical zones of 5 cm. The resulting data matrix comprises 1092 relevés. The data were analyzed using 3 phytosociological computer programs: TWINSPAN, DCA and CCA. In addition, the standing crop of the epiphytes was studied on five locations with a dense cover. The four red algal genera, worldwide characterizing the Bostrychietum are also present in the mangrove system of Gazi Bay. Bostrychia tenella, Catenella caespitosa and Caloglossa leprieurii are the three most frequent taxa. Murayella periclados, another characterizing species, was found in all transects, though with lower abundances. Differences in emersion period, resulting from the increasing distance to open sea, are also reflected in floristic differences between the transects. Close to the open sea, the green algal species of the genera Chaetomorpha, Cladophora and Enteromorpha were frequently found, cover estimates however were low. The green alga Ulva oxysperma was uniquely found in these transects with a short emersion period. A second gradient in emersion period with increasing distance from the tidal channel was reflected in a strong decline of species diversity and total cover. This was only found in the longer transects from the mixed stands on the right bank. Epiphytic was generally maximal in the 5-15 cm zone. Above and below this zone a decline in cover was noted. This was also found in other mangrove systems. The zone of maximal cover tends to become lower on the pneumatophores with increasing distance from the open sea. Bostrychia tenella most clearly shows a zonation pattern. This species is characterized by its resistence to dessication. High covers were found even in the upper segments of the pneumatophores. Catenella caespitosa also shows a marked resistence to desiccation, though less than Bostrychia tenella. A strong exposure to direct sunlight is reflected in lower cover estimates. Especially among red algae this sciophilous character is prominent. The green alga Ulva oxysperma on the other hand was found with the highest relative covers in strongly sun-exposed regions. This was also observed in other studies. Most species showed no preference for a certain mangrove species except for Bostrychia tenella and Ulva oxysperma. The former species seems to prefer hard substrates like Rizophora and old Sonneratia pneumatophores. It is absent on young and on dead Sonneratia pneumatophores which are very soft. Ulva oxysperma on the other hand seems to prefer these soft substrates. Bostrychia tenella was absent on places with a fine sediment, probably as a result of the very high turbidity. This species however is very resistant to strong wave-action. Smaller red algal taxa are much less tolerant to wave-action. The mathematical analysis showed the importance of the distance to open sea as a main controlling factor for the epiphytic vegetation. Boodleopsis pusilla, Dictyota adnata, Stictosiphonia tangatensis and Bostrychia tenella seem to prefer localities further away from the open sea. Polysiphonia scopulorum is an indicator species for localities near the open sea. The above mentioned green algae were distinctly separated from the other taxa in the ordination diagrams. It is important to note however that our date are less suitable for ordination and TWINSPAN-analysis due to the strong heterogeneity in cover estimates, diversity and to the complexity of the environmental factors in the mangrove system. With respect to biomass the largest DM-values were found at Gazi Beach. The negative influence of sun-exposure on epiphytic growth was clearly reflected in a lower biomass. Biomass was comparable on both Avicennia and Sonneratia pneumatophores. A distinct trend emerged from analysis of the vertical distribution of biomass. Greatest biomass levels were found in the zone between 5 and 15 cm. Above this zone biomass declined gradually, below this zone biomass levels were also much mower. Especially in stations with fine sediment the latter trend was very marked. This again shows the negative influence of high turbidity on epiphytic growth.

Dataset
  • Epiphytic macroalgae vegetation on pneumatophores in the mangrove of Gazi Bay sampled between August and September 1989, meer

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