[Show abstract][Hide abstract] ABSTRACT: Actinellopsis murphyi gen. et spec. nov.: A new small celled freshwater diatom (Bacillariophyta, Abstract In this paper we describe Actinellopsis murphyi gen. et spec. nov. a small heteropolar and dorsiventral diatom from a seep habitat in Zambia. This novel taxon has the chief distinguishing characteristic, along with its cell symmetry, of having the raphe positioned wholly in the valve face and not extending onto the mantle. It is further placed within the Peroniaceae as it possesses a straight raphe on the valve face and rimoportulae, and the frustules are heteropolar with regard to the length of the raphe. We also transfer the fossil diatom Actinella giraffensis to Actinellopsis as the morphological characteristics of this taxon are consistent with those of the generitype.
[Show abstract][Hide abstract] ABSTRACT: Diploneis fenestrata sp. nov. (Bacillariophyta), a new aerophilic diatom species from Zambia, Africa Abstract Diploneis fenestrata, a new aerophilic diatom is described from Lumangwe falls, Zambia. This novel species occurs as an epiphyte on the roots and stems of trees located within the spray zone of the falls. Its morphology was examined with both light and scanning electron microscopy. Diploneis fenestrata is distinguished from other taxa in the genus Diploneis by its prominent square openings ranging in number from 4-14 occurring within the area of the longitudinal canal only at the outer cell wall. The occurrence of these characteristic square openings found in the genus Diploneis is further discussed.
[Show abstract][Hide abstract] ABSTRACT: A study was made of the type material of Achnanthidium exiguum (Grunow) Czarnecki. This often encountered and apparently ubiquitous species was originally described as Stauroneis exilis by Kützing from the island of Trinidad and later re–named as Achnanthes exigua by Grunow. The type material for this taxon (Kützing sample 397), housed in the Van Heurck collection at the National Botanic Garden of Belgium, Meise was investigated and the ultrastructure of this taxon was documented using both LM and SEM observations. A new Antarctic taxon, formerly identified as A. exigua, was described as a new species, Achnanthidium australexiguum sp. nov. The position of both taxa within the genus Achnanthidium is briefly discussed.
Journal of the Czech Phycological Society 02/2014; 14(1):43–51. · 1.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Stenopterobia cataractarum sp. nov. (Bacillariophyta), a new benthic diatom from a waterfall in Zambia, Africa Abstract Rivers, streams and associated habitats have been sampled for diatoms in the relatively understudied Congo and Zambezi sister basins. The primary purpose of the sampling effort was to collect samples for biological monitoring purposes and the establishment of a diatom-based monitoring programme. However, a large number of possibly endemic and novel taxa have been encountered in this region making the application of diatom-based indices at a species level difficult. In this paper we describe a new species of Stenopterobia from the Ntumbachushi Falls in the Luapula Province of Zambia. This taxon is closely related to Stenopterobia delicatissima but chiefly differentiated by a lower number of striae, a well-defined unornamented lanceolate axial area and shortened ribs which do not fuse with the fenestrae. This taxon also shows some similarity to Stenopterobia delicatissima var. ghanaensis but the valves are consistently narrower.
[Show abstract][Hide abstract] ABSTRACT: We studied the distribution of long-chain alkenes (n-C23 to n-C31) in well-dated sediments from Lake Challa, a deep crater lake near Mt. Kilimanjaro in equatorial East Africa, to reveal signatures of palaeo-environmental and palaeo-climatic changes affecting the production of these compounds during the last 25 kyr. The apolar fractions of organic sediment extracts dated to the last 16 kyr showed an unusual dominance of δ13C-depleted n-C25:1 and n-C27:1 alk-1-enes. These alkenes were not detected in soil and litter from near the shoreline and from the inner rim of the crater, pointing to an autochtonous, aquatic source. Analysis of suspended particulate matter indicated that the n-alk-1-enes are produced in the well-oxygenated upper 30 m of the water column, indicating a phytoplanktonic origin. Sedimenting particles collected monthly from December 2006 to November 2007 showed increased fluxes of n-alk-1-enes following the locally prominent short rain season in November - December. Green algae and/or cyanobacteria were identified as candidate sources of these alkenes. Production of the n-C25:1 and n-C27:1 alkenes in Lake Challa was much reduced during the Last Glacial Maximum and early late-glacial period, suggesting a temperature or CO2 effect on habitat suitability. We explored the potential of n-alk-1-ene accumulation rates, and of a derived Alkene Index [n-C27:1]/([n-C25:1]+[n-C27:1]), to record longer-term climatic changes. The Alkene Index record of Lake Challa over the past 25 kyr shows clear periodicity with a dominant frequency of ∼2.3 kyr, potentially indicative of monsoon variability directly or indirectly forced by variation in solar radiation.
Geochimica et Cosmochimica Acta 01/2014; · 3.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background: The first records of Protosteloid Amoebae in the Democratic Republic of the Congo are discussed in the present paper. This survey on Protosteloid Amoebae is the first from Central African; the previous records for the African continent were restricted to Egypt, Kenya, Malawi, Tanzania and Uganda.
Methods: Aerial litter samples, collected in 2010 during the “Boyekoli Ebale Congo” expedition in the Congo River basin between the cities of Kisangani and Bumba, were put into culture on wMY medium, a weak malt yeast nutrient agar medium.
Results: The aerial litter cultures revealed 23 species representing 70 % of the total number of species described worldwide. Two of these taxa, Schizoplasmodiopsis reticulata and Schizoplasmodium seychellarum, are new records for the African continent. The isolate LHI05 was observed for the first time on a substrate collected outside Hawai’i. In addition, 5 unknown taxa were observed. A selection of micrographs is presented of the new recorded species, the unknown taxa and all their related species observed in this study.
Conclusion: The high species diversity observed on a limited number of samples suggests that the investigated region is, together with Hawai’i, one of the world’s tropical hotspots for Protosteloid Amoebae.
Plant Ecology and Evolution 01/2014; 147:85-92. · 1.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Microscope slides containing material from Sierra Leone used by Woodhead and Tweed to describe eight new Surirellaceae taxa in the mid-twentieth century were reinvestigated. Only two taxa were found on the original slides, Surirella approximata Woodhead & Tweed and S. engleri [var. constricta] f. minor Woodhead & Tweed. The valve variability of S. engleri O. Müller includes valves of S. engleri [var. constricta] f. minor which is now regarded as a synonym. As no holotypes were indicated by the authors, types are given here. Comments on S. rudis var. sierra-leonensis Woodhead & Tweed, S. rudis [var. sierra-leonensis] f. constricta Woodhead & Tweed and S. esamangensis Foged are also given. Valves resembling Stenopterobia recta Woodhead & Tweed, Surirella asperrima f. rokuprensis Woodhead & Tweed, S. engleri f. sierra-leonensis Woodhead & Tweed and S. rokuprensis Woodhead & Tweed could not be found on the Woodhead and Tweed original slides.
Diatom Research 01/2013; 28(2):121-129. · 0.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cavinula lilandae, a small new diatom from the Congo Basin in Central Africa, was observed in acid riverine habitats in an almost pristine tropical rain forest. It occurred in a periphytic diatom community dominated by Eunotia spp. and Fragilariforma strangulata (Zanon) Williams & Round. Beside the type locality in the Baomba Stream, and the closely located Lilanda River, in the Democratic Republic of Congo, this taxon was also observed in a small river in Zambia, north of the Bangweulu swamps. Cavinula lilandae is distinguished from other taxa within the genus Cavinula D.G. Mann & A.J. Stickle by the following characteristics: uniseriate striae becoming irregularly biseriate near the poles; irregularly formed areolae; and irregular depressions in the valve face close to the axial area which are not perforating the valve face.
Diatom Research 01/2013; 28(2). · 0.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A revision of taxa from the genus Surirella from the Antarctic region resulted in the description of three new taxa: S. subantarctica Van de Vijver & Cocquyt sp. nov., S. heardensis Van de Vijver & Cocquyt sp. nov. and S. australovisurgis Van de Vijver, Cocquyt, Zidarova & Kopalová sp. nov. Detailed light (LM) and scanning electron microscope (SEM) observations are used to characterize these three new taxa. Comparisons with similar taxa and the ecological preferences of each species are added. The morphological characteristics of a fourth Antarctic Surirella taxon, S. kerguelensis Grunow are illustrated as this taxon was only known from a few hand drawings and LM pictures. Finally, a fifth taxon, S. lapponica A. Cleve was found on South Georgia and likewise illustrated. The revision of these species made clear that the genus Surirella showed similar biogeographical trends as other, previously revised genera indicating that a distinct Antarctic diatom flora exists.
Diatom Research 01/2013; 28(1). · 0.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper presents an illustrated guide to the identification of non-pollen palynomorphs (NPPs) preserved in lake-sediment archives from equatorial East Africa. Modern NPPs were recovered from recently deposited surface sediment in 20 small crater lakes in western Uganda, located along environmental gradients of vegetation (moist evergreen and semi-deciduous forest, wooded and open grass savannah), land use (pastoralism, crop agriculture, plantations) and lake characteristics (basin morphometry, water chemistry and aquatic production). We analyzed 9700 NPP specimens, which could be assigned to 265 distinct morphotypes, of which 239 belong to six major taxonomic groups: spores and other remains of fungi (198 morphotypes), spores of ferns and mosses (19 morphotypes), microscopic zoological remains (14 morphotypes), colonies, coenobia or zygo-/aplanospores produced by filamentous algae (7 morphotypes) and microscopic aquatic plant remains (1 morphotype). The remaining 26 morphotypes could not be assigned to a specific taxonomic category. Using primary taxonomic and molecular phylogenetic literature, 73 (28%) of the recovered morphotypes could be identified at the species, genus or family level, thereby conferring ecological indicator value to them. This study may facilitate the use of fossil NPPs to help reconstruct past climatic and anthropogenic impacts on African ecosystems, as already broadly established in other study regions outside Africa.Research Highlights► Illustrated guide of 187 non-pollen palynomorphs from East African lake sediments. ► 28 % of the recovered 265 morphotypes are identified and ecologically classified. ► NPPs may shed light on past climatic and human impacts on African ecosystems.
Review of Palaeobotany and Palynology 01/2011; 164:143-173. · 1.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Multiproxy analysis of a well-dated 25 ka lake sediment sequence from Lake Challa, on the eastern flank of Mount Kilimanjaro (East Africa), reveals the climatic controls that govern both the lake's paleohydrology and the climate-proxy record contained in the mountain's receding ice cap. The oxygen isotope record extracted from diatom silica (δ18Odiatom) in Lake Challa sediments captured dry conditions during the last glacial period and a wet late-glacial transition to the Holocene interrupted by Younger Dryas drought. Further, it faithfully traced gradual weakening of the southeastern monsoon during the Holocene. Overall, δ18Odiatom matches the branched isoprenoid tetraether (BIT) index of rainfall-induced soil runoff, except during 25–22 ka and the past 5 k.y. when insolation forcing due to orbital precession enhanced the northeastern monsoon. This pattern arises because during these two periods, a weakened southeastern monsoon reduced the amount of rainfall during the long rainy season and enhanced
[Show abstract][Hide abstract] ABSTRACT: Background and aims - With a depth of at least 220 m, Lake Kyaninga is the deepest known maar crater lake in western Uganda. We studied its limnology and phytoplankton community to determine how the frequency and depth of water-column mixing influences nutrient cycling and seasonality in this aquatic ecosystem.Methods - Water-column temperature was measured continuously during a full annual cycle between August 2007 and August 2008. Other physical and chemical variables as well as diatom and other phytoplankton communities were investigated on three occasions, namely during the dry season in August of 2007 and 2008, and during the main wet season in April 2009.Key results and conclusions - The water column of Lake Kyaninga is permanently stratified (meromictic) below ∼ 100 m depth. Above this depth, mixing frequency varies from daily (down to 8-12 m depth) over at least once per year (down to 39-47 m depth), to once in several years or decades (between 39-47 and ∼ 100 m depth). Nutrient and chlorophyll concentrations as well as phytoplankton data classify the lake as low in aquatic productivity (oligotrophic). Its pelagic, open-water phytoplankton community is dominated by Cyanobacteria (blue-green algae) and Chlorophyta (green algae). Bacillariophyta (diatoms) contribute only a minor part of total phytoplankton biomass in both wet and dry seasons, and are characterized by an assemblage of small Nitzschia species. Epiphytic and epipelic diatoms are relatively few, because steep rocky crater slopes limit the littoral zone even though water-column transparency is high. The composition of recently deposited diatom assemblages preserved in offshore surface sediments gives a good, annually integrated representation of the present-day pelagic diatom community. The documented species richness of the diatom flora of Lake Kyaninga is moderate with about 150 taxa. Only ∼ 17% of these are biogeographically restricted to tropical Africa; and most of these belong to the genus Nitzschia.
Plant Ecology and Evolution 10/2010; 143(3):365-377. · 1.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Type microscope slides and material from Ghana from which Foged described nine new Surirella taxa in the 1960's were reinvestigated. Although these taxa have not been reported in the literature afterwards, the results of our study confirm the identity of six species: Surirella agonaensis, S. bonsaensis, S. esamangensis, S. nagbogensis, S. sorriensis and S. takoradiensis. They constitute an important element of the endemic diatom flora of West Africa. The study of Surirella takoradiensis var. suhinensis resulted in its proposed synonymy with the nominate variety. Surirella delicatissima var. ghanaensis is transferred to the genus Stenopterobia: Stenopterobia delicatissima var. ghanaensis (Foged) Cocquyt & Kusber comb. nov. Valves resembling Foged's drawing of Surirella dodowaensis could not be detected on the holotype slide; however, two observed frustules in girdle view are in agreement with the description of this taxon.The report of Surirella ventricosa, a diatom described from Sulawesi, in samples from Ghana could not to be justified. Valves similar in shape to S. ventricosa fall within the variability of the closely related S. nagbogensis, described from Ghana.
Nova Hedwigia 07/2010; 91(1-2):111-136. · 0.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The population of an unknown naviculoid diatom from Lake Vrana in Croatia was identified as Navicula hedinii, a species described in 1922 from a small lake in eastern Turkestan (China). This species has some similarities with Navicula pseudocrassirostris, a marine species found in European coastal waters. Based on the ultrastructure of the two species, they can no longer be included within the taxonomical concept of Navicula sensu stricto. Following a comparative morphological analysis of both species with genera bearing similar characters (Adlafia, Veigaludwigia, Kobayasiella, Cavinula, Stenoneis, Climaconeis, Berkeleya, Sellaphora, Cosmioneis), a new genus, Envekadea is proposed for the two species. The new genus is characterized by a sigmoid raphe course with golfclub-like terminal fissures deflected in opposite directions, the areolae covered by external porous hymenes and the presence of one chloroplast, H-shaped in valve view.
European Journal of Phycology 02/2009; 44(1):123-138. · 2.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Global studies of historical land use focusing on the large-scale landscape change that can potentially affect global climate (via effects on surface albedo, aerosols, and the carbon cycle) have concluded that the impact of pre-colonial East African cultures on regional ecosystems was limited, due to very low mean population density. This contrasts with the paradigm in East African archaeology and paleoecology that the onset of anthropogenic deforestation started at least 2500 years ago, following the introduction of iron metallurgy by Bantu immigrants. This conflict highlights the present lack of real data on historical climate-environment-human interactions in East Africa, which are eminently relevant to sustainable natural resource management and biodiversity conservation in a future of continued population growth and global climate change. CLANIMAE responds to the urgent need of a correct long-term perspective to today's climate-environment-human interactions in East Africa, by reconstructing simultaneously the histories of past climate change and of vegetation and water-quality changes over the last 2500 years, through multi-disciplinary analysis of dated lake-sediment records. The climate reconstructions integrate information on biological, geochemical and sedimentological indicators of past changes in the water balance of the study lakes, which cover the climatological gradient from (sub-)humid western Uganda to semi-arid eastern Kenya. Reconstruction of past terrestrial vegetation dynamics is based on analyses of fossil plant pollen and phytoliths, plus the fossil spores of fungi associated with the excrements of large domestic animals as indicators of lake use by pastoralists. The evolution of water quality through time is reconstructed using silicon isotopes in diatom algae as proxy indicator for past phytoplankton productivity, and paleoecological analyses of fossil diatoms and aquatic macrophytes, following calibration of diatom and macrophyte species distribution against lake trophic status and turbidity in the modern-day regional lake gradient. The integrated paleoecological research method of this project addresses the question of past climate-environment-human relationships at the time scale at which the relevant processes have actually occurred. This will allow us to 1) separate the influences of natural climate variability and human activity on East African ecosystems, 2) determine the exact timing and relative magnitude of indigenous (pre-20th century) anthropogenic land clearance compared to recent landscape alteration, 3) determine the severity of lake water-quality losses due to siltation and excess nutrient input directly linked to deforestation and agriculture, compared to those associated with natural ecosystem variability, and 4) assess the resilience of African ecosystems, and prospects for the restoration of disturbed ecosystems if human pressure were to be reversed.
[Show abstract][Hide abstract] ABSTRACT: The abundance of two main pelagic fish species in Lake Tanganyika (Stolothrissa tanganicae and Lates stappersii) has always been observed to fluctuate considerably at different time scales. The inverse correlation between the abundance
of these species has often been interpreted as the consequence of predator−prey relations (avoidance behaviour by the prey).
However, currently the two species often appear spatially segregated in the lake, S. tanganicae dominating in the north while L. stappersii is generally abundant in the south where it feeds mostly on shrimps. A fluctuating abundance of the species is nevertheless
observed. As these fish species have a major importance for the fisheries, we investigated the limnological variability in
relation to the short-term variability of fish catches. The abundance of S. tanganicae was positively correlated to plankton biomass (r=0.65), while water transparency (r=0.56), depth of mixed layer (r=−0.70) and oxygenated water appeared important drivers for the abundance of L. stappersii. Alternating “mixing” and “stable” states of the epilimnion related to seasonal and internal waves variability are probably
determinant for the short-term variability in abundance of S. tanganicae and L. stappersii. In the framework of this study, remote sensing has shown a potentially interesting application for fisheries research at
Lake Tanganyika. We observed a close correspondence between phytoplankton blooms at the time of trade winds changes and increased
catches of S. tanganicae in the south. The anti-correlated abundance of S. tanganicae and L. stappersii probably mainly reflects the underlying fluctuating limnological environment. Fisheries studies need to integrate limnological
and planktonic monitoring to better understand large and complex ecosystems such as Lake Tanganyika.
[Show abstract][Hide abstract] ABSTRACT: A nearshore core (LT03-05) from the north basin of Lake Tanganyika provides diatom, pollen, and sedimentary time series covering the last ca. 3800 yr at 15–36 yr resolution. A chronology supported by 21 AMS dates on terrestrial and lacustrine materials allows us to account for ancient carbon effects on 14C ages and to propose refinements of the region's climatic history. Conditions drier than those of today were followed after ca. 3.30 ka by an overall wetting trend. Several century-scale climate variations were superimposed upon that trend, with exceptionally rainy conditions occurring 1.70–1.40 ka, 1.15–0.90 ka, 0.70–0.55 ka, and 0.35–0.20 ka. Around 0.55–0.35 ka, during the Spörer sunspot minimum, drier conditions developed in the northern Tanganyika basin while more humid conditions were registered at Lakes Victoria and Naivasha. This indicates significant variability in the nature and distribution of near-equatorial rainfall anomalies during much of the Little Ice Age.
Quaternary Research 01/2009; 72(1):47-56. · 2.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: During a preliminary survey of the diatoms from the Peruvian hot spring of La Calera (Colca Canyon, Peru), several new species were found: Navicula cadeei sp. nov., Ulnaria colcae sp. nov., Cymbella comperei sp. nov. and Denticula thermaloides sp. nov. Based on detailed light and scanning electron microscopic analysis, it is clear that these four species can distinctly be separated from other similar taxa. The paper presents morphologic details for the four new species and discusses their taxonomic position and characteristic features.
Diatom Research - DIATOM RES. 01/2009; 24(1):209-223.
[Show abstract][Hide abstract] ABSTRACT: Desiccation of the Sahara since the middle Holocene has eradicated all but a few natural archives recording its transition from a "green Sahara" to the present hyperarid desert. Our continuous 6000-year paleoenvironmental reconstruction from northern Chad shows progressive drying of the regional terrestrial ecosystem in response to weakening insolation forcing of the African monsoon and abrupt hydrological change in the local aquatic ecosystem controlled by site-specific thresholds. Strong reductions in tropical trees and then Sahelian grassland cover allowed large-scale dust mobilization from 4300 calendar years before the present (cal yr B.P.). Today's desert ecosystem and regional wind regime were established around 2700 cal yr B.P. This gradual rather than abrupt termination of the African Humid Period in the eastern Sahara suggests a relatively weak biogeophysical feedback on climate.