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A survey of marine fungi present on dead proproots of Rhizophora mucronata (Lam) was conducted in the Kosi system. Durban Bayhead and Mtata River The survey revealed 38 species of fungi, including 30 Ascomycotina, 1 Basidiomycotina and 7 mitosporic fungi Kallichroma spp and Phoma spp were present in high numbers at all three estuaries. Leptosphaeria australiensis and Swampomyces triseptatus occurred frequently at Kosi and Mtata. while Dactylospora hahotrepha was common at Bayhead and Mtata Species diversity was lower than recorded for most comprehensive surveys in tropical S E Asia However, the percentage colonization and frequencies of occurrence of fungi on wood indicate that marine fungi have an important ecological role to play in local mangrove communities More information is required not only from South Africa but also from the tropical African east coast

Results of an investigation into the fungi associated with submerged wood in the Palmiet River, Durban, South Africa are reported. Fifty eight fungi were identified including 28 Ascomycetes and 30 Hyphomycetes. Three are species new to science, including Annulatascus palmietensis K.D. Hyde, Goh & T.D. Steinke, Endophragmiella bitriseptata Goh, K.D. Hyde & T.D. Steinke, and Phialogeniculata africana Goh, K.D. Hyde & T.D, Steinke, and are described in this paper. The percentage occurrence of the fungi on wood is given and this is compared with other studies.

Nawawia dendroidea is described and illustrated based on a specimen collected on dead Phragmites in a stream in South Africa. The species produces parallel-indeterminate synnemata with dark-brown stipes and white, glistening conidial masses. Phialides are produced terminally on diverging conidiophores, and these produce round-tetrahedral to pyramidal conidia with 3-setulae. The species is compared with the two previously described Nawawia species and species in the similar genera Chalarodes and Phialosporostilbe .

Maculatifrondis aequatoriensis gen. et sp. nov. is described from living leaves of an unidentified palm in Cuyabeno, Ecuador. The species has unusual ascospores early deliquescing asci and a Cyclodomus anamorph and its taxonomic relationships are unknown, although it may belong in the Phyllachoraceae. Myelosperma parasitica sp. nov. causes leaf spots on Phoenix reclinata in South Africa. Both species are described and illustrated with differential interference micrographs.

A total of 93 species of marine fungi were identified from three habitats: mangroves, intertidal rocky shores and sandy beaches. The highest number (55 species) were obtained from mangrove wood, while 12 species and 19 species were collected from intertidal wood and sandy beaches, respectively. The high numbers obtained from the mangroves at Beachwood and on wood of Avicennia marina (Forssk.) Vierh. probably reflect the high intensity of sampling. Although some of the marine fungi can be regarded as cosmopolitan, the majority have affinities with tropical/subtropical areas. The high numbers of marine fungi obtained in this survey suggest that these organisms have a significant role to play in our estuarine and marine ecosystems.

Seasonal variation in nitrogen fixation of blue-green algae associated with Avicennia marina (Forssk.) Vierh. pneumatophores and wet and dry surface sediments were investigated in the Beachwood Mangrove Nature Reserve by means of the acetylene reduction technique. The blue-green algae identified were all non-heterocystous and have been reported to fix nitrogen. The dominant blue-green algae were Lyngbya confervoides C.Ag. ex Gomont, Oscillatoria limosa Ag. ex Gomont and Microcoleus chthonoplastes Thuret ex Gomont in the pneumatophore, wet and dry surface habitats, respectively. A marked seasonal variation in ARA (acetylene reduction activity) was apparent, with summer maxima being recorded. This coincided with maximum nitrogen-fixing blue-green algal numbers, temperature, light intensity and day length. Seasonal variations in organic carbon, inorganic nitrogen, salinity, percentage moisture and bacterial numbers are discussed. It was estimated that nitrogen fixation by blue-green algal communities supplies 24.3% of the annual nitrogen requirements of the mangrove swamp.

Two experiments were conducted in the laboratory to determine leaching losses from submerged mangrove leaves: the first, on freshly-picked and air-dried senescent Avicennia marina (Forrsk.) Vierh. leaves submerged in water of different salinities (16 and 32‰) for up to 14 days; the second, on freshly-picked senescent leaves of A. marina and Bruguiera gymnorrhiza (L.) Lam. submerged in water of 16‰ for up to 7 days. In both experiments, loss of dry mass and changes in nitrogen, phosphorus, potassium and tannins of the leaves were monitored. In the initial experiment there was a mean loss in dry mass of 24.6% after 14 days. The chemical analyses revealed that, although there was no significant decline in nitrogen concentration, there were sharp decreases in the other constituents. The greatest total loss relative to the amount initially present in the litter was in potassium (83 – 95%), while the losses for phosphorus and tannins were 57 – 87% and 74 – 85%, respectively. In general, losses were greater at 16‰ than at 32‰, and air-dried leaves showed greater initial losses than fresh leaves. In the second experiment, trends in leaching losses of both species were similar to those of the first experiment. With the exception of nitrogen, the concentrations of phosphorus and potassium (expressed as percentage oven-dry mass) had decreased significantly after 6 h in both species, while the concentrations of tannins showed a significant decrease only after 24 and 48 h in A. marina and B. gymnorrhiza, respectively. This work has confirmed that significant losses take place in the leaf litter as a result of leaching. It is suggested that those losses could have important consequences for the estuarine ecosystem.

Nitrogen fixation of decomposing Avicennia marina (Forssk.) Vierh. leaves was studied over a period of 16 weeks under exposed and submerged conditions. Rates of acetylene reduction activity (ARA) were highest under exposed conditions and reached a maximum after three to four weeks. Percentage total nitrogen increased during decomposition, the increase being greatest under submerged conditions, but this was not directly related to nitrogen fixation. Bacteria were considered to be the main agents of nitrogen fixation. Rates of decomposition were highest under exposed conditions. The contribution of nitrogen fixation to the nitrogen budget is significant.

Successive fungal colonization of leaves of Bruguiera gymnorrhiza (L.) Lam. was investigated at Beachwood Mangrove Nature Reserve, Durban, using a litterbag technique. Bags of two different mesh sizes were used (1.0 × 0.5 mm and 2.5 × 5 mm), but no significant differences in mass loss were observed over a period of 18 weeks. Fusarium spp., Penicillium spp., Trichoderma sp., Verticillium sp. and Phoma sp., amongst others, colonized the leaves prior to and after submergence. The phylloplane fungi did not break down leaf components whilst the leaf was living. After submergence, microbial colonization increased. Cellulolytic assay demonstrated that all of the isolated fungi, except Mucor sp., were able to degrade cellulose. The C:N ratio of the litter decreased from 143.6:1 to 28.4:1, indicating an increase in nutrient value with decomposition. This work revealed the presence of some fungal taxa, most of which possess in vitro cellulolytic activity.

Leaves of Bruguiera gymnorrhiza (L.) Lam. growing at Beachwood Mangrove Nature Reserve (Durban) were removed just prior to leaf fall, placed in mesh litterbags and submerged in the creek of the swamp. At the time of collection the leaves were colonized by phylloplane fungi. The degree of decomposition of leaf material was studied over a period of 18 weeks by means of SEM and LM techniques. After a week’s submergence, the leaves appeared to be devoid of phenolic deposits and microbial colonization intensified. SEM studies indicated that fungi may have degraded the cuticular waxes but the cuticle was still intact at the end of the study. Degradation of the internal tissues was shown to be associated with fungal activities.

Respiration and net photosynthesis of discs excised from cotyledons of Avicennia marina (Forssk.) Vierh. were measured at temperatures of 17, 21 and 25 °C in a Gilson Respirometer. Cotyledonary material was also analysed for TNC (total non-structural carbohydrates). Rates of respiration and net photosynthesis were significantly different at the three temperatures, with the lowest rates recorded in each case at 17 °C and the highest at 25 °C. TNC values revealed an initial decrease, followed by a small increase, and thereafter a drop to fairly constant low levels. While seedlings at 25 °C grew well, very little growth was recorded at 17 °C. Growth at the different temperatures was related to the relative excess of photosynthesis over respiration. The ecological implications of these results are discussed.

Litter fall was measured in a mixed mangrove community in which Avicennia marina (Forssk.) Vierh. was dominant over Bruguiera gymnorrhiza (L.) Lam. Mean litter production was 1.24 g dry matter m - 2 day - 1 or 4.51 tons ha - 1 yr - 1 over a 3-year period. Mean annual leaf yield comprised approximately 72% of total litter. Generally greater leaf fall occurred in the summer than in the winter. In both A. marina and B. gymnorrhiza propagule production was variable from year to year. In both species, reproductive material was present on the trees almost throughout the year. This behaviour and the low litter yields appeared to indicate that the community is approaching its southern limits. From the 14 ha of mangroves in the estuary it is calculated that total litter production is 50.7 tons yr - 1 , of which approximately 36.8 tons yr - 1 is leaf litter. The total litter production of the larger stands of mangroves in Transkei’s estuaries was calculated. Mangrove litter is considered to provide a significant input to these systems.

An autecological study of Cassia mimosoides L., which invades mismanaged Dohne Sourveld, was initiated at the Agricultural Research Institute, Dohne. A study of the growth characteristics revealed that the nature of the root distribution enabled the plant to take up moisture from superficial as well as deeper soil layers, while the position of the crown buds at or below soil level offered protection from fire damage. These characteristics plus the unpalatability of the plant to sheep and cattle placed it in a favourable position in competition with grasses. However, the relatively low‐growing C. mimosoides plants appeared to be at a disadvantage in rested veld. Although seeds were dormant when released, germination took place and seeds retained their viability over a long period. Under natural conditions the germination of non‐dormant seeds was controlled largely by temperature and moisture. Few seedlings established themselves in rested veld. It was suggested that a long rest period for the veld, followe...

Over a period of 4 years sampling was carried out for biomass determinations of algae epiphytic on pneumatophores of Avicennia marina (Forssk.) Vierh. The biomass showed trends towards high values in the warmer months and low values in the cooler period of the year. These trends were disrupted by abnormally high silt loads on the pneumatophores and by cyclones Domoina and Imboa. The cyclones did not appear to have altered the species composition of the algal community which was dominated by Bostrychia radicans (Mont.) Mont. B. radicans and B. moritziana (Sonder) J. Agardh provided the greatest biomass in the sampling area throughout the year, although the relative proportion of Caloglossa leprieurii (Mont.) J. Ag. showed an increase in late spring/early summer. There is evidence that epiphytic algae can provide a mean annual input of approximately 10.05 tons of litter which is considered significant for this system.

Leaves of Avicennia marina (Forssk.) Vierh. and Bruguiera gymnorrhiza (L.) Lam. were placed in litter bags and allowed to decompose in situ before collection at 7, 14, 21, 42, 64 and 85 days. Material from each collection was examined for structural changes using light microscopy and SEM. Samples of each collection were also cultured for fungi and bacteria. Examination of senescent leaves still attached to the trees revealed the presence of phylloplane micro-organisms. Decomposition in both species followed a similar pattern although the leaves of A. marina decomposed more rapidly than those of B. gymnorrhiza. By day 7 there were no obvious changes in leaf structure, initial decomposition of the leaf base was the only apparent change in structure on day 14; by day 21 portions of the cuticular layer had separated from the leaf tissue; on day 42 most of the leaves were split longitudinally, separating the adaxial and abaxial surfaces; in the day-63 material, fragmentation of the leaves was evident; further fragmentation and ‘skeletonization’ of leaves was observed after 85 days of decomposition. Both bacteria and fungi were important in the decomposition process. Leaves of both mangroves were found to harbour 20–25 species of fungi. This work appeared to confirm the significance of micro-organisms in the estuarine food web.

A new species ofPhaeosphaeria is described from mangroves in South Africa. InPhaeosphaeria capensis ascospores are 29–36×7–8 μm, cylindric-fusiform or somewhat clavate, widest at the middle, narrow at the base and rounded at the apex, (6-)7-septate, light brown or brown, minutely verruculose and surrounded by a spreading, mucilaginous sheath. It is compared withP. luctuosa andP. berlesei from grasses.

A new species ofGloniella from dead intertidal wood attached to trees ofAvicennia marina is described. It differs from previously reportedGloniella species in having relatively large clavate ascospores.

An autecological study of Cassia mimosoides L., which invades mismanaged Dohne Sourveld, was initiated at the Agricultural Research Institute, Dohne. A study of growth characteristics revealed that the nature of the root distribution enabled the plant to take up moisture from superficial as well as deeper soil layers, while the position of the crown buds at or below soil level offered protection from fire damage. These characteristics plus the unpalatability of the plant to sheep and cattle placed it in a favourable position in competition with grasses. However, the relatively low-growing C. mimosoides plants appeared to be at a disadvantage in rested veld. Although seeds were dormant when released, germination took place and seeds retained their viability over a long period. Under natural conditions the germination of non-dormant seeds was controlled largely by temperature and moisture. Few seedlings established themselves in rested veld. It was suggested that a long rest period for the veld, followed by a spring burn, would be most effective in controlling the establishment of seedlings.Keywords: cassia mimosoides; cattle; competition; disturbance history; dohne sourveld; establishment; fire; germination; grasses; grassland; invasive plants; moisture; plants; root distribution; seed germination; seedlings; seeds; sheep; viability

This paper describes taxa of the Class Cyanophyceae which are inconspicuous within a turf-like Bostrychietum that coats plant, mud and rock in the mangrove-associated estuaries of southern Africa. The pneumatophores of the white mangrove Avicennia marina, support the richest flora. Of the 27 taxa recorded Microcoleus chthonoplastes has the widest biogeographical range and was common on most substrata. Non-heterocystous were more prevalent than heterocystous Cyanophyceae and four other taxa occurred epiphytic only on the dominant macroalgal species of Bostrychia, Caloglossa, Enteromorpha and Rhizoclonium. Preliminary explanations, based on related studies, are offered on the recycling of nitrogen by Cyanophyceae within the mangrove ecosystem.

Litter fall was measured in two mangrove communities: one dominated by Avicennia marina (Forsk.) Vierh. and the other comprising an almost pure stand of Bruguiera gymnorrhiza (L.) Lam. Mean litter production for the A. marina community was 1,91 g dry matter m− 2day− 1 or 6,98 tons ha− 1year− 1 over a 3-year period, while the values for the B. gymnorrhiza stand were 2,26 g dry matter m− 2day− 1 or 8,24 tons ha− 1year− 1 over 4 years. Highest litter values in both communities were obtained when seedlings were shed in autumn. The A. marina community produced extremely variable yields of litter components and total litter from year to year, whereas the yields from B. gymnorrhiza were more consistent. Mean annual leaf yield comprised 59,0% and 62,5% of the total litter in the A. marina and B. gymnorrhiza communities respectively. In the B. gymnorrhiza stand stem material constituted only 6,0% of the total litter yields, while in the A. marina community the contribution was 17,8%. From the 44 ha occupied by mangroves it is calculated that total litter production is 334,2 tons year− 1, of which approximately 200 tons year− 1 is leaf litter. This is considered to provide a significant input to this system.

The development of wall ingrowths in leaf blade epidermal cells of the marine angiospermZostera capensis was studied by electron microscopy. Prior to the appearance of ingrowths long profiles of endoplasmic reticulum cisternae become arranged peripherally closely following the contours of the walls. The plasmalemma assumes a wavy appearance and in regions where wall ingrowths first start forming (i.e., along the radial, inner tangential and transverse walls) the plasmalemma becomes separated from the walls by an undulating extracytoplasmic space. Small, irregular projections of secondary wall material make their appearance here. Paramural bodies, dictyosomes, endoplasmic reticulum (ER) and possibly also microtubules seem to be closely associated with the initiation and subsequent development of wall projections. As the cells mature, new ingrowths arise in a centrifugal direction along the radial and transverse walls. When wall ingrowths reach a certain stage of their development, mitochondria become strongly polarized towards them and become closely associated with the plasmalemma which ensheaths the ingrowths. There is often also a close association between ER cisternae and the involuted plasmalemma of the wall projections. Initially ingrowths are slender, curved structures, but become more complex as the cells mature. Ingrowths are most extensively developed along the inner tangential and transverse walls. As epidermal cells age there is a loss of wall material from the ingrowths. The probable significance of the formation of wall ingrowths in the epidermal cells is also discussed.

The Kosi System, the most northern estuarine system in the Republic of South Africa, supports five species of mangroves: Avicennia marina (Forssk.) Vierh., Bruguiera gymnorrhiza (L.) Lam., Ceriops tagal (Perr.) C.B. Robinson, Lumnitzera racemosa Willd. and Rhizophora mucronata Lam. All populations, particulary those of A. marina, C. tagal and R. mucronata, were severely set back due to large numbers having been killed in 1965/1966. Recolonization by all is taking place, although growth is slow relative to that in many other estuaries in Natal and, further, the recovery has been hindered by biotic disturbance. Nevertheless the situation in April 1985 was one of active growth with, generally, dense stands of relatively short individuals in almost all parts occupied by mangroves prior to 1965, as well as a spread into places not previously recorded as having been occupied by mangroves. This distribution is shown on maps. Data, recorded periodically since 1972, are presented to illustrate structure of stands and changes in sizes of individuals in selected sites.

Litter fall was measured in two mangrove communities at St Lucia and at Richards Bay. At St Lucia one community comprised almost pure Avicennia marina (Forssk.) Vierh. while the other was dominated by Bruguiera gymnorrhiza (L.) Lam. At Richards Bay one community consisted almost entirely of A. marina while the other was dominated by Rhizophora mucronata Lam. Mean litter production by the A. marina community was 2,78 g dry matter m − 2 d − 1 and 2,89 g dry matter m − 2 d − 1 for St Lucia and Richards Bay respectively, while for the B. gymnorrhiza and R. mucronata communities, mean production was 2,00 and 2,66 g dry matter m − 2 d − 1 respectively. Higher litter values were generally obtained during the warmer, wetter months. Mean annual leaf yields comprised 44,1 % of the total litter in the older A. marina community at St Lucia compared with 73,3% in the young, vigorous community at Richards Bay. Reproductive material made an important contribution to litter (mean value 41,1 %) in the former community. In the B. gymnorrhiza and R. mucronata communities the mean contribution of leaves to total litter was 48,8% and 52,3% respectively. In the B. gymnorrhiza community the most variable major component of litter was the propagules. In all communities stem material generally made a small contribution to total litter. From a calculation of the area occupied by mangroves in each estuary it was estimated that total litter production was 1322,7 and 4684,1 t yr − 1 at St Lucia and Richards Bay respectively. It is suggested that this provides a significant input of litter to these systems.

Rates of degradation of leaves of Avicennia marina (Forssk.) Vierh. and Bruguiera gymnorrhiza (L.) Lam. were investigated in St Lucia Estuary in the warm and cool seasons at three positions on the shore, viz. where leaves were constantly submerged, where they were exposed only at low spring tides and where they were inundated only at high spring tides. Degradation occurred more rapidly in A. marina than in B. gymnorrhiza and leaves constantly submerged decomposed at a faster rate than those exposed for most of the time. Decomposition rates were consistently lower in the cool season. The concentration of nitrogen in all leaves increased over the decomposition period, although there was a decrease in total nitrogen content with rapid decomposition. While under certain conditions degradation proceeds at a rapid rate, because of the lower additions of nitrogen to the system from decomposing leaves, there do not appear to be significant ecological advantages from this rapid decomposition. There were sharp decreases in the phosphorus and potassium contents of the leaves, presumably largely due to leaching. This work has emphasized the importance of mangrove leaf litter as a source of, and substrate for, nutrient release.

Summary The ultrastructural morphology of cavities in the outer walls of leaf blade epidermal cells of the marine angiosperm Zostera capensis is described. The cavities usually occur beneath the cuticle and are generally spherical to ovoid in shape. They are not bounded by a membrane although their margins are occasionally more electron-dense than the wall that surrounds them. In young epidermal cells the subcuticular cavities penetrate partially into the overlying cuticle. In more mature cells, flask-shaped extensions of the cavities penetrate through the cuticle. The actual opening through the cuticle appears to be slit-like. It is extremely small and is filled with an electron-dense material. While the cavities in the youngest epidermal cells examined generally lack contents, those of more mature cells contain mainly fibrillar material. In addition to fibrillar material, electron-dense amorphous or crystalline-like material maybe present within the cavities. The occurrence of the latter types of material on the cuticle surface, as well as within the wall below the cavities, suggests that these materials are probably excreted from the epidermal cells via the cavities. Structural similarities between the subcuticular cavities and the subcuticular spaces in the outermost secretory cells of salt glands on the leaves of certain halophytes are pointed out, and some suggestions are offered as to the nature of the material apparently being excreted from the cavities.

A survey was conducted to determine some effects of termite mounds on the veld. Termitaria were found to occupy approximately 0,4% of the area of the paddock under investigation. Growth of grasses immediately surrounding intact termitaria increased as shown by the higher number of tillers and a high percentage of reproductive tillers. Although the plant species composition surrounding intact termitaria did not appear to differ very much from the adjacent veld, weathered termitaria revealed a change in species more typical of disturbed conditions. Nitrogen content was highest in soil from the centre of intact termitaria, but there were no significant differences in the surface soil from the edge of termitaria, from weathered mounds, or from undisturbed veld. Runoff from termitaria caused increased moisture penetration surrounding the mounds. The significance of an infestation of termite mounds on the veld is discussed.

Summary Preliminary findings on the fine structure of the leaf epidermis of Zostera capensis are described. The epidermal cells have transfer cell characteristics. Wall ingrowths, ensheathed by the plasmalemma, are particularly well-developed along the inner tangential cell walls. Numerous mitochondria, with prominent cristae, are clustered around the ingrowths. The cells have dense cytoplasmic contents with a large population of vesicles and many profiles of smooth ER. Dictyosomes and microbodies are relatively sparse while chloroplasts, with well-developed grana systems, fill the cells. A thin but distinct cuticle covers the outer surface of the leaf. The outer tangential cell wall is about twice as thick as the other walls and has an interesting ultrastructure: the innermost part of this wall has staining characteristics which differ from the rest of the wall; wall striations, adjacent to this intenselystaining region, are more prominent here than in the other walls; and unusual sub-cuticular cavities which appear to contain some fibrillar material are present in the outermost portion of the wall. The possible physiological significance of the enlarged plasmalemma, the intensely staining inner region of the outer cell wall and the subcuticular cavities, are suggested.

Propagules of A. marina (Forssk.) Vierh. were shown to be either ‘sinkers’, i.e. sink on shedding their pericarp, or ‘floaters’ i.e. remain buoyant after shedding their pericarp. While propagules from different estuaries showed big variations in buoyancy, generally mangroves in the north produced a high proportion of ‘floaters’ while those in the south produced mainly ‘sinkers’. The buoyancy of propagules appeared to be determined by the relative densities of the different parts of the cotyledons. Anatomical sections revealed that there was little difference between the different parts of ‘sinkers’, whereas in ‘floaters’ parts which were buoyant had a high proportion of intercellular air spaces and those which sank had closely- packed cells high in reserves. Some of the ‘sinkers’ were found to become buoyant after a period of submersion, although propagules from all estuaries did not behave in this way. Apparently those propagules which had a density close to that of sea water tended to become buoyant later and it was suggested that utilization of reserves reduced the original density to a level which enabled these propagules to float. The implications of variations in buoyancy of A. marina propagules for the further distribution of this mangrove along the southeast Cape coast are discussed.

Growth of Scaevola plumieri (L.) Vahl, a coastal dune pioneer species, showed seasonal variations in leaf appearance and abscission. Generally more leaves were produced and shed in the warmer months than in the cooler months. However, rate of leaf appearance exceeded rate of leaf abscission in summer, while in winter the reverse applied. Leaves produced in winter showed greater longevity than summer leaves. Flowering commenced in October and all ripe fruits had been shed by March. Maximum seed germination appears to take place during December/January.

Nitrogen fixation of blue-green algae (cyanobacteria) associated with Avicennia marina (Forssk.) Vierh. pneumatophores and wet and dry surface sediments was investigated in the Beachwood Mangrove Nature Reserve by means of the acetylene reduction technique. Studies revealed percentage moisture and temperature to be the prime factors influencing ARA (acetylene reduction activity) in these habitats and rates were highest under submerged conditions and at 22°C. High concentrations of inorganic nitrogen (between 1 and 5 mg l−1) significantly depressed ARA in all habitats. Increases in ARA occurred with increase in light intensity up to 40 μE m−2 s−1, with negligible dark rates being recorded in association with the wet and dry surface sediments. Significant dark rates of ARA and stimulation of ARA by sucrose in association with the pneumatophores indicated that bacteria may also be contributing to ARA in this habitat. No organic carbon stimulation was noted in the other sites. Salinity had little effect on ARA over the range generally experienced in each habitat.

In intact plants C14‐assimilates were translocated from the treated leaf on the primary tiller to young leaves on that tiller, to secondary tillers, and also to the roots. Plants defoliated after l...

Decomposition of leaves of Bruguiera gymnorrhiza (L.) Lam. was studied over a period of 96 days under controlled conditions of temperature (16° and 24°C) and salinity (0‰, 15‰ and 30‰). During the experimental period leaves at 24°C and 0‰ showed the greatest loss of dry matter, while the slowest decrease was recorded at 16°C and 30‰. Nitrogen content of decomposing leaves increased during the experiment, while phosphorus and potassium contents showed a steady decrease. The phosphorus content of the water revealed an initial decrease, attributed to microbial activity, followed by a steady increase. Dissolved oxygen content of the water decreased to a constant low level, while pH values fell initially and then increased again. The rate of decomposition in this laboratory study was slower than values obtained in field studies where physical breakdown occurs in addition to microbial action.

Experiments were conducted to determine changes occurring during early growth of Avicennia marina (Forssk.) Vierh. seedlings after shedding of the pericarp. Treatments included growth in the field and in growth cabinets at 21° and 25°C; and in a second experiment in growth cabinets at 17° and 23°C. Cotyledons showed a decrease in dry mass, and the hypocotyl and epicotyl increased in length initially before reaching a constant length. Growth rates of the shoot showed significant differences: 17°C

Vegetative and floral phenological observations were conducted on Bruguiera gymnorrhiza (L.) Lam., Rhizophora mucronata (Lam.) and Avicennia marina (Forssk.) Vierh. in Mgeni Estuary. In shoots of B. gymnorrhiza in the sun, semi-shade and shade, leaf emergence showed high values in the warmer months with low values in the cooler period of the year. Although leaf abscission did not show clear trends as in the case of leaf emergence, values were generally lower during the cooler (and also dry) months. In all of the above light regimes the number of leaves/shoots showed a decrease over the 5-year period of the observations. However, longevity of leaves was influenced by exposure, with sun, semi-shade and shade leaves having a mean lifetime of 89,3; 103,1 and 141,8 weeks respectively. Highest numbers of propagules were borne on shoots in the sun, none was produced in the shade, while an intermediate number was found in semi-shade. In R. mucronata, data for leaf emergence and abscission showed similar trends to those obtained for B. gymnorrhiza. The number of leaves/shoots increased during the 4 years of observations. Leaf longevity averaged 99,4 weeks which was longer than obtained for Rhizophora spp. by previous workers. Observations had to be curtailed on A. marina which revealed a bimodal leaf emergence pattern with low figures for leaf abscission only in the winter months. Leaf longevity averaged 56,4 weeks which compared well with results from other workers. The significance of these results for litter production and degradation is considered.

Phenological observations were conducted on Ceriops tagal Perr. C.B. Robinson (vegetative and floral) and Lumnitzera racemosa Willd. (floral) in the Mgeni Estuary. Leaf emergence in C. tagal was unimodal with high initial values in early summer (December), followed by decreasing numbers of leaves for the remainder of the summer, with the last leaves making their appearance in June/July. Leaf abscision showed high values in August/September but, with the exception of smaller peaks in April, produced no other consistent trends, Leaf/shoot ratios revealed an undulating pattern with high values in summer and decreasing values in the cooler months. Mean longevity of leaves marked in the first two years of the study was approximately 30 and 32 months respectively, It was not possible to follow reproductive behaviour in C, tagal. In L. racemosa a period of 3–4 months was required for development from flowers to the abscission of propagules. The significance of these results for litter production is discussed.

Macroalgae associated with 19 mangrove estuaries from Kosi estuary to the Nahoon River have been studied. Twelve taxa of the Class Rhodophyceae are described with information on the nature of the substrata for settlement and the seasonal occurrence of fertile plants. Bostrychia moritziana (Sonder) J. Ag., B. radicans (Mont.) Mont. and Caloglossa leprieurii (Mont.) J. Ag. form the persistent components of the mangrove bostrychietum. Bostrychia tenella (Vahl) J. Ag., B. tangatensis Post and B. scorpioides (Gmelin) Mont. have restricted distributions. Polysiphonia subtilissima Mont. and Gelidium spp. are more common associates than Murrayella periclados Schm. and Catenella nipae Zanardini. A freshwater alga is also an associate of the bostrychietum. The findings are discussed and compared with mangrove bostrychieta from other countries, particularly Australia.

Net photosynthetic and respiratory rates of two estuarine algae, Bostrychia radicans Mont. and Caloglossa leprieurii (Mont.) J. Ag. collected from the Mgeni Estuary mangrove swamp, were studied. Both species are intertidal and common on Avicennia marina (Forssk.) Vierh. pneumatophores. Maximum photosynthetic rates of B. radicans were evident between 25% and 58% desiccation. Respiratory rates were constant up to 58% desiccation and decreased thereafter. C. leprieurii showed highest photosynthetic rates under submerged conditions, whilst respiratory rates were highest under saturated conditions. Both species showed increases in photosynthetic and respiratory rates with increase in temperature. Photosynthetic rates peaked at 32 °C to 37 °C, whilst respiratory rates peaked at 37 °C. With increases in light intensity, maximum photosynthetic rates of C. leprieurii and B. radicans occurred at 140 to 225 μE m− 2 s− 1 and 225 to 550 μE m− 2 s− 1 respectively. Both species were tolerant of a range of salinities. The ecological implications of these results are discussed.

Samples of algae epiphytic on the pneumatophores of Avicennia marina (Forssk.) Vierh. were collected at different seasons of the year. The distribution of this mangrove, which extends from the mouth of the estuary to Wankute island, approximately 6.5km upstream, covers a salinity range from 35‰ to 7‰ at its upper limits, and includes the Ukhalwe inlet in which the surface water of the upper reaches is 0‰. Thirty-six species of epiphytic algae were collected across this distribution range, of which there were 11 rhodophycean, 17 cyanophycean (cyanobacteria), 7 chlorophycean and 1 phaeophycean. Most of the red algae were restricted to the high (> 25‰) salinity areas, while the blue-green algae generally appeared to have a wider salinity and exposure tolerance. Six algal species were found to have a distribution covering the entire salinity range, 10 species were recorded in waters ranging from 35‰ to 7‰, 16 and 2 species were limited to high (> 25‰) and lower (5-18‰) salinity areas, respectively, while one species occurred only in freshwater. The ecological implications of these results are discussed. The need for additional collections from localities to the north is stressed to establish the affinities of this community with those in more tropical areas.

The occurrence of individual species, of which there are five in South Africa, and the approximate total area of mangroves in all known South African estuarine systems are presented for the first time for South Africa as a whole. Natural increase is occurring throughout the region although this is masked in many places by the direct destruction of the mangroves themselves or through adverse effects on their habitats. S. Afr. J. Bot . 1982, 1: 51-53

A survey was conducted to determine some effects of termite mounds on the veld. Termitaria were found to occupy approximately 0, 4% of the area of the paddock under investigation. Growth of grasses immediately surrounding intact termitaria increased as shown by the higher number of tillers and a high percentage of reproductive tillers. Although the plant species composition surrounding intact termitaria did not appear to differ very much from the adjacent veld, weathered termitaria revealed a change in species more typical of disturbed conditions. Nitrogen content was highest in soil from the centre of intact termitaria, but there were no significant differences in the surface soil from the edge of termitaria, from weathered mounds, or from undisturbed veld, runoff from termitaria caused increased moisture penetration surrounding the mounds. The significance of an infestation of termite mounds on the veld is discussed.Language: EnglishKeywords: botany; composition; dohne research station; eastern cape; effects; grass; grasses; Increased phytomass; moisture penetration; phytomass; plant species composition; runoff; soil nitrogen; Soil studies; south africa; species composition; termitaria; Termitaria counts; termite mounds; vegetation; Vegetation assessment