A taxonomic review ofXenotilapia sima andX. boulengeri (Cichlidae; Perciformes) from Lake Tanganyika

Two cichlid fishes from Lake Tanganyika,Xenotilapia sima Boulenger, 1899 andX. boulengeri (Poll, 1942) are often confused owing to insufficient information on the diagnostic morphological characters for each species. Morphological and morphometric analyses showed thatX. sima differs fromX. boulengeri in having a greater number of teeth and anal and pectoral fin soft rays, thicker caudal peduncle, larger eyes, and a shorter snout and anal fin base.     

Phylogenetic analysis of Cyprichromini (Perciformes: Cichlidae) endemic to Lake Tanganyika and validation of the genus <Emphasis Type="Italic">Paracyprichromis</Emphasis>

The phylogenetic relationships among two Paracyprichromis and five Cyprichromis species, included in the Tanganyikan cichlid tribe Cyprichromini, were investigated using morphological features. The previously proposed diagnostic characters of Paracyprichromis are not synapomorphies, because the nonelongated swim bladder is plesiomorphic, the numbers of dorsal and anal fin rays and scales on longitudinal line and around the caudal peduncle overlap with those of Cyprichromis, and these counts and number of vertebrae are all included within the ranges of other Tanganyikan cichlids. The monophyly of Paracyprichromis is supported by a unique condition of infraorbitals to this genus. Additionally, the monophyly of Cyprichromis was reconfirmed by one of the previously proposed diagnostic characters, the presence of an elongated swim bladder.     

Ecology and conservation status of endemic freshwater crabs in Lake Tanganyika, Africa

Sedimentation resulting from riparian deforestation has a wide range of detrimental effects on aquatic biodiversity, but predicting the full consequences of such disturbances requires an understanding of the ecosystem’s key functional components. We investigated the ecology and response to sedimentation of the diverse, endemic freshwater crabs of Lake Tanganyika, which may occupy important positions in littoral foodwebs. Our surveys revealed crab distribution patterns to be patchy, and that crabs can be locally abundant (0–28 individuals m⁻²). Crab densities decreased with depth and the dry mass of crab assemblages ranged from 0.0 to 117.7 g m⁻². Comparisons among sites revealed significant effects of sedimentation on crab assemblage evenness, but provided no evidence that sedimentation has altered densities, incidence or species richness. The resilience of crabs to sedimentation might be related to their intraspecific dietary breadth. Stable isotope data (δ¹³C and δ¹⁵N) from crabs and their potential food resources indicated differences in trophic roles among endemic crab species. Overall, crabs occupy higher trophic positions than most other invertebrates, and they draw upon both benthic and planktonic energy pathways. The high biomass and top-predator status of some crab species suggests the potential for cascading effects on organisms lower in the food web.     

Limnological variability and pelagic fish abundance (Stolothrissa tanganicae and Lates stappersii) in Lake Tanganyika

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.

Seasonal patterns of sediment loading and benthic invertebrate community dynamics in Lake Tanganyika, Africa

1. This study investigated the spatiotemporal dynamics of benthic invertebrate communities located close to the mouths of the Kalambo and Lunzua Rivers, at the southern end of Lake Tanganyika, and subject to varying degrees of sediment load. 2. Metrics of exposure to riverine sediments were associated inversely with abundance and diversity of benthic organisms at sampling locations adjacent to both river mouths, indicating a major effect of riverine sediments on the structure of near‐shore benthic communities. 3. A lower abundance of benthos was found at the mouth of the Lunzua River, which exports significantly higher sediment loads than the Kalambo. 4. Seasonal cycles of abundance and diversity in the benthos varied with distance from river mouths. This has important implications for monitoring programmes investigating benthic communities close to the mouths of rivers. 5. Our findings suggest that recent increases in the sediment loading of Lake Tanganyika, owing to anthropogenic catchment disturbance, impact significantly on biological diversity throughout the lake littoral, which provides habitat for the majority of species in the lake.     

Surirella sparsipunctata Hustedt and S. sparsipunctata var. laevis Hustedt (Bacillariophyceae), a light and electron microscopical study

Hydrobiologia - Three populations of S. sparsipunctata from the eastern coast of Lake Tanganyika were studied by light and electron microscopy. We found no distinct differences between the type...     

Phytoplankton production and growth rate in Lake Tanganyika: evidence of a decline in primary productivity in recent decades

1. This study focused on phytoplankton production in Lake Tanganyika. We provide new estimates of daily and annual primary production, as well as growth rates of phytoplankton, and we compare them with values published in former studies.
2. Chlorophyll- a (chl- a ) in the mixed layer ranged from 5 to 120 mg chl- a  m⁻² and varied significantly between rainy and dry seasons. Particulate organic carbon concentrations were significantly higher in the south basin (with 196 and 166 mg C m⁻³ in the dry and the rainy season, respectively) than in the north basin (112 and 109 mg C m⁻³, respectively).
3. Carbon : phosphorus (C : P) ratios varied according to season. Phosphorus limitation seemed to occur more frequently than nitrogen limitation, especially during the rainy season. Severe P deficiencies were rare.
4. Measured particulate daily primary production ranged from 110 to 1410 mg C m⁻² day⁻¹; seasonal contrasts were well marked in the north basin, but less in the south basin, where primary production peaks occurred also in the rainy season. Estimates of annual primary production, based on daily primary production calculated from chl- a and water transparency, gave values lower than those reported in previous studies. Picophytoplankton accounted on average for 56% of total particulate production in the south basin during the wet season of 2003.
5. Phytoplankton growth rates, calculated from primary production, ranged from 0.055 to 0.282 day⁻¹; these are lower than previously published values for Lake Tanganyika.     

Abundance,distribution, and territory areas of rock-dwelling Lake Tanganyika cichlid fish species

Lake Tanganyika, the second-oldest and second-deepest lake in the world, harbors an impressive cichlid fish fauna counting about 250 endemic species that are characterized by a great level of ecological, morphological, and behavioral specialization. This study describes and compares cichlid fish communities at two rocky shores with differential human impact in the south of Lake Tanganyika. Species inventories and depth-dependent abundances were elaborated. About 41 and 46 sympatric cichlid species were recorded in the two study sites, respectively. Variabilichromis moorii was the most abundant species (29–60% of total number of fishes), followed by Aulonocranus dewindti (3–19%), Tropheus moorii (12%), Ophthalmotilapia ventralis (4–10%), Eretmodus cyanostictus (6–11%), and Cyathopharynx furcifer (0.01–9%). All other species had abundances below 5%. It further emerged that large cichlids such as Petrochromis species, Cyathopharynx furcifer, and Lobochilotes labiatus were very rare at one location, with frequencies of 0.55% or less. Territorial sizes of three particularly abundant species, Variabilichromis moorii, Aulonocranus dewindti, and Tropheus moorii, were assessed by behavioral observations. We distinguished between territorial core areas and total defended area, yielding average core areas between 0.4 (V. moorii) and 1.6 m² (T. moorii), and total defended areas averaging for each species between 1.6 (V. moorii) and 5.0 m² (A. dewindti) with no significant differences between the two study sites. The data on individual densities are also relevant for evolutionary studies, in that they allow more accurate calculations of effective population sizes.     

Genetic population structure as indirect measure of dispersal ability in a Lake Tanganyika cichlid

Diversification and speciation processes are influenced by intrinsic (ecological specialization, dispersal) and extrinsic (habitat structure and instability) factors, but the effect of ecological characteristics on dispersal is difficult to assess. This study uses mitochondrial control region sequences to investigate the population structure and demographic history of the endemic Lake Tanganyika cichlid Neolamprologus caudopunctatus with a preference for the rock-sand interface along two stretches of continuous, rocky shoreline, and across a sandy bay representing a potential dispersal barrier. Populations along uninterrupted habitat were not differentiated; whereas, the sandy bay separated two reciprocally monophyletic clades. The split between the two clades between 170,000 and 260,000 years BP coincides with a period of rising water level following a major lowstand, and indicates that clades remained isolated throughout subsequent lake level fluctuations. Low long-term effective population sizes were inferred from modest genetic diversity estimates, and may be due to recent population expansions starting from small population sizes 45,000–60,000 years BP. Comparisons with available data from specialized rock-dwelling species of the␣same area suggest that habitat structure and lake level fluctuations determine phylogeographic patterns on large scales, while fine-scale population structure and demography are modulated by species-specific ecologies.     

Intestinal coiling pattern in the epilithic algal-feeding cichlids (Pisces, Teleostei) of Lake Tanganyika, and its phylogenetic significance

This paper suggests that, on the basis of ontogenetic change in intestinal coiling pattern, four types and four subtypes could be recognized within 20 species of epilithic algal-feeding cichlids in Lake Tanganyika. The phylogenetically useful anatomical features characterizing each type are as follows. Petrochromis type: torsion of the intestinal tract generally occurs at Stage 5 Intersecting Point (IP), and the haplochromine loop and a two-loop coiling system are observable. Cyathopharynx type: the value of IP becomes 7 before torsion occurs, and the coiling system changes qualitatively from one-loop to two-loop types. Asprotilapia type: torsion occurs at Stage 5 IP, and a one-loop coiling system is retained throughout ontogeny. Telmatochromis type: no torsion occurs, and a one-loop coiling system is retained throughout ontogeny. Within the Petrochromis type, each of the four subtypes is characterized by the following features. Petrochromis subtype: the rostrally directed haplochromine loop has its rostral part situated to the right side of the stomach in the adult stage. Pseudosimochromis subtype: a circular haplochromine loop is present. Eretmodus subtype: the haplochromine loop tends to be prolonged and bends through 90 or 180 further counter-clockwise. Tropheus subtype: torsion occurs at Stage 7 IP.     

Abundance and production of bacteria, and relationship to phytoplankton production, in a large tropical lake (Lake Tanganyika)

1. Abundance and bacterial production (BP) of heterotrophic bacteria (HBact) were measured in the north and south basins of Lake Tanganyika, East Africa, during seasonal sampling series between 2002 and 2007. The major objective of the study was to assess whether BP can supplement phytoplankton particulate primary production (particulate PP) in the pelagic waters, and whether BP and particulate PP are related in this large lake. HBact were enumerated in the 0–100 m surface layer by epifluorescence microscopy and flow cytometry; BP was quantified using ³H‐thymidine incorporation, usually in three mixolimnion layers (0–40, 40–60 and 60–100 m). 2. Flow cytometry allowed three subpopulations to be distinguished: low nucleic acid content bacteria (LNA), high nucleic acid content bacteria (HNA) and Synechococcus‐like picocyanobacteria (PCya). The proportion of HNA was on average 67% of total bacterial abundance, and tended to increase with depth. HBact abundance was between 1.2 × 10⁵ and 4.8 × 10⁶ cells mL⁻¹, and was maximal in the 0–40 m layer (i.e. roughly, the euphotic layer). Using a single conversion factor of 15 fg C cell⁻¹, estimated from biovolume measurements, average HBact biomass (integrated over a 100‐m water column depth) was 1.89 ± 1.05 g C m⁻². 3. Significant differences in BP appeared between seasons, especially in the south basin. The range of BP integrated over the 0–100 m layer was 93–735 mg C m⁻² day⁻¹, and overlapped with the range of particulate PP (150–1687 mg C m⁻² day⁻¹) measured in the same period of time at the same sites. 4. Depth‐integrated BP was significantly correlated to particulate PP and chlorophyll‐a, and BP in the euphotic layer was on average 25% of PP. 5. These results suggest that HBact contribute substantially to the particulate organic carbon available to consumers in Lake Tanganyika, and that BP may be sustained by phytoplankton‐derived organic carbon in the pelagic waters.     

Occasional egg-eating by the scale-eater Plecodus straeleni (Cichlidae) of Lake Tanganyika

Synopsis Of 23 males and 39 females of Plecodus straeleni observed for one hour each, 2 males and 14 females searched for the mouthbrooder Cyathopharynx furcifer under courtship display near or in the bower to get eggs, besides foraging for other prey to ripe off scales and skin. After finding a courting C. furcifer, they quietly waited on the substrate near the bower until it spawned. Immediately after spawning, the waiting P. straeleni dashed upon the female of C. furcifer and quickly collected the eggs. This egg-eating was achieved 5 times by 3 females who spent most of their time searching and waiting.     

Restriction fragment length polymorphism and molecular taxonomy in Vitis vinifera L.

Forty-six accessions of grapevine (V. vinifera L.) were compared by restriction fragment length polmorphism (RFLP) analysis, and 111 informative or unique restriction fragments were found that revealed an important level of polymorphism. RFLP patterns were compared in two ways: by calculating electrophoretic similarity degree values further analyzed by principal component analysis and by studying the distribution of rare restriction fragments. Six taxonomic groups could be defined, which partially confirmed relationships derived from ampelographical data. Our data support the existence of ecogeographical groups.     

Vertical distributions of stable isotopic compositions and bacteriochlorophyll homologues in suspended particulate matter in saline meromictic Lake Abashiri

We determined chloropigment composition as well as stable carbon and nitrogen isotopic compositions of dissolved and particulate species in saline meromictic Lake Abashiri. We observed a sharp peak of bacteriochlorophyll e in a narrow redox boundary zone and the upper monimolimnion, indicating a dense population of brown-colored strains of green sulfur bacteria around the chemocline. Nitrogen isotopic records of particulate nitrogen and dissolved ammonium suggested that the green sulfur bacteria in the redox boundary zone assimilated either ammonium or dinitrogen through the nitrogen fixation pathway. In the anoxic monimolimnion, several lines of evidence suggest that a major portion of particulate organic matter originated from the overlying mixolimnion and redox boundary zone.     

Recolonization and possible recovery of Burrowing Mayflies (Ephemeroptera: Ephemeridae: Hexagenia spp.) in Lake Erie of the Laurentian Great Lakes

Burrowing mayflies of the genus Hexagenia spp. were widely distributed (ca. 80% of sites) and abundant (ca. 160 nymphs/m²) in the western basin of Lake Erie of the Laurentian Great Lakes in 1929–1930, prior to a period of anoxia in the mid 1950s. Nymphs were absent or rare in the basin between 1961 and 1973–1975. In 1979–1991, nymphs were infrequently found (13–46% of sites) in low abundance (3–40 nymphs/m²) near shore (<7.5 km from shore), but were absent or rare offshore (0–7% of sites at 0–1 nymphs/m²). Increased abundance occurred offshore between 1991 (0% of sites) and 1993 (52% of sites at 7/m²). Annual sampling, beginning in 1995, indicates that nymphs increased in both nearshore and offshore waters. By 1997, nymphs were found throughout the lake (88% of sites) at a mean density 40-fold greater (392/m²) than that observed in 1993 (11/m²). In 1998, the distribution of nymphs remained the same as 1997 (88% of sites) but density declined 3-fold (392 to 134/m²). These data indicate that mayflies have recolonized sediments of western Lake Erie and that their abundance may be similar to levels observed before their disappearance in the mid 1950s. However, prior to the mid 1950s, densities were greater in offshore than nearshore waters, but between 1979 and 1998 greater densities occurred near shore than offshore. In addition, there were two areas in the 1990s where low densities consistently occurred. Therefore, recovery of nymphs in western Lake Erie may not have been complete in 1998. At present we do not know the cause for the sudden recolonization of nymphs in large portions of western Lake Erie. Undoubtedly, pollution-abatement programs contributed to improved conditions that would have ultimately led to mayfly recovery in the future. However, the explosive growth of the exotic zebra mussel, Dreissena polymorpha, undoubtedly diverted plankton foods to bottom substrates which could have increased the speed at which Hexagenia spp. nymphs recolonized sediments in western Lake Erie in the 1990s.     

Factors influencing densities and distributions of Pontoporeia hoyi in Lake Ontario

The physical and chemical characteristics of the sediment-water interface greatly influence distributions of the bottom-feeding amphipod Pontoporeia hoyi which is a major component of the Great Lakes aquatic food-webs. Sediment-water interface samples from the Great Lakes indicate that Pontoporeia densities are positively correlated with sediment concentrations of organic carbon, particularly in the upper depth range of the species. Pontoporeia is not found in anoxic sediments. Growth rates and production of Pontoporeia are influenced by the quality of food supplies and there appears to be a seasonal response to the down-flux of plankton detritus. Comparisons of numerations and distribution patterns also revealed an apparent positive relationship between Pontoporeia and sediment-associated bacteria. Interlake comparisons of population densities provide no clear evidence of any large scale impact by contaminated sediment on this species. Depending upon the extent to which organic carbon (OC) is assimilated in the water column, bottom sediments may store and buffer the quantity of OC available to Pontoporeia. Thus, if the annual down-flux of OC remains generally constant, populations of Pontoporeia should also remain constant unless influenced by changes in predation intensity.Numerations of Pontoporeia revealed that populations of this amphipod are much larger in Lake Michigan than in Lake Ontario. We suggest that much of this difference can be accounted for by different forms of predator-prey interaction near the base of the benthic food-web. Commercial fisheries data tend to support this idea. We also speculate that differences in the concentration of dissolved silica may figure prominantly among factors that affect Pontoporeia population densities.Under proposed new taxonomy (Bousfield, 1989), Pontoporeia hoyi is now classified as Diporeia hoyi. However, for convenience, we have retained the commonly used genus Pontoporeia throughout this text.     

Restriction fragment length polymorphism diversity in soybean

Summary Fifty-eight soybean accessions from the genus Glycine, subgenus Soja, were surveyed with 17 restriction fragment length polymorphism (RFLP) genetic markers to assess the level of molecular diversity and to evaluate the usefulness of previously identified RFLP markers. In general, only low levels of molecular diversity were observed: 2 of the 17 markers exhibited three alleles per locus, whereas all others had only two alleles. Thirty-five percent of the markers had rare alleles present in only 1 or 2 of the 58 accessions. Molecular diversity was least among cultivated soybeans and greatest between accessions of different soybean species such as Glycine max (L.) Merr. and G. soja Sieb. and Zucc. Principal component analysis was useful in reducing the multidimensional genotype data set and identifying genetic relationships.     

Phylogenic status of a purple sulfur bacterium and its bloom in Lake Kaiike

Two bacterial species at the upper boundary of the H₂S-containing lower layer of Lake Kaiike, a purple sulfur bacterium and Macromonas sp., markedly changed their population densities in a single year (maximum cell numbers ranged between 10⁶ and <10³ cells ml^–1), although neither species ever entirely disappeared from the lake over at least the past 30 years. Genetic characteristics based on the sequence of the 16S rDNA of the purple sulfur bacterium showed it to be a new species of the Chromatiaceae family. This bloom of purple sulfur bacterium occurred when the H₂S layer was disturbed by an external intrusion of seawater.     

The recent palaeolimnology of Lake Nicholls,Mount Field National Park,Tasmania

Analyses were carried out for diatoms, spherical carbonaceous particles, and magnetic minerals on a short sediment core from a small cirque lake, Lake Nicholls, in the Mount Field National Park, south-west Tasmania.Catchment disturbance is not evident from the fairly constant sediment accumulation rates and magnetic analyses of the sediment record. However, there is evidence for a low level of atmospheric contamination during the industrial period, which reaches a maximum at the present time, but is less than in many areas of north-west Europe. Changes in the diatom assemblages recorded in the sediment core are likely to be related to factors, other than catchment change or atmospheric contamination, such as the response of within lake processes to climate change.Several diatom taxa found in the cores cannot presently be assigned to known species. Although some of these may later be identified following this preliminary study, it seems highly likely that freshwater lakes in south-west Tasmania contain a number of new and perhaps endemic taxa.