Response of instream animal communities to a short-term extreme event and to longer-term cumulative impacts in a strategic water resource area,South Africa

Disturbance plays an integral part in generating heterogeneity required for ecosystem persistence, but the increased amplitude and duration of disturbances linked to drivers of global change could result in ecosystem shifts or collapse. Biomonitoring over time provides insights into trajectories of ecosystem change. The responses of two instream animal taxa to two contrasting disturbance events, a major flood event and the long-term cumulative effects of land-use changes, were assessed in 1999–2012 by quantifying variation and change in abundance of functional groups based on flow rate sensitivity, water quality and metrics of ecological condition. All metrics recovered to pre-flood conditions within seven months after the flood event. Similarly, cumulative impacts of land use effected significant decreases in some but not all metrics. Indices that did not change, including SASS total score and ASPT, were the result of insufficient consideration of the decrease in the abundance of sensitive taxa specifically, and the abundance of all taxa in general. The decrease in abundance of sensitive taxa could signal imminent collapse in certain metrics. Evidence is also provided for a shift in the structure of fish assemblages linked to the decrease and loss of taxa sensitive to ecosystem degradation caused by the longer-term impacts of land-use change.     

Health assessment of freshwater fish species from Albasini Dam,outside a DDT-sprayed area in Limpopo province,South Africa: a preliminary study

During 2006 to 2008, the water, sediment and fish in Albasini Dam, used as a reference site outside a DDT-sprayed area, had been found to be as affected as those in the nearby DDT-sprayed area were. Accordingly, the aim of the current study, conducted in 2014, was to determine the health status of fish from Albasini Dam by means of a histology-based fish health assessment protocol. High levels of nitrates, as well as the organochlorine pesticides aldrin, dieldrin, chlordane and methoxychlor, were found in the water. Fish muscle tissue contained pesticides, including methoxychlor. A semi-quantitative histological assessment on Clarias gariepinus, Coptodon rendalli and Oreochromis mossambicus showed diverse histopathology in selected target organs, with the gills being most affected. Notably, the testis tissue of one C. rendalli was filled with eosinophilic liquid, characteristic of necrosis. Microscopic intersex was found in two of the nine O. mossambicus sampled. This is the second time that intersex as microscopic testicular oocytes has been reported in O. mossambicus in South Africa. This finding perhaps indicates that reproduction may be compromised and this will be investigated further. The presence of intersex and other histopathology in organs could be early warning signs of the declining water quality in this dam.     

The biomass and yield of the dominant fish species in Hartbeespoort Dam,South Africa

The standing stocks of the three dominant fish species in Hartbeespoort Dam, O. mossambicus, C. gariepinus and C. carpio, were determined by mark and recapture experiments and Leslie's method of fishing success. The biomass of O. mossambicus increased from 279 t in 1982 to 521 t in 1983, following good recruitment to the population after a year's mild winter mortality. Only one reliable estimate of each of the other two species could be made, C. gariepinus (293 t) and C. carpio (581 t). The fish community was heavily utilised by recreational anglers and the estimated mean annual yields were O. mossambicus (144 t), C. gariepinus (102 t) and C. carpio (449 t). These yields are probably higher than the longer term mean harvest as a result of low water levels during the study period, which increased catchability. The high standing stocks and yields are ascribed to high nutrient concentrations and primary production.     

Relevance of elephant herbivory as a threat to Important Plants in the Addo Elephant National Park, South Africa

Although elephants are recognized as keystone species, the mechanisms of their impacts on biodiversity and community structure are rarely identified. In the Addo Elephant National Park (AENP), South Africa, elephant Loxodonta africana herbivory is apparently responsible for a significant reduction in plant richness, especially among the regionally rare and endemic small succulent shrubs and geophytes (Important Plants). We used faecal analysis to investigate the utilization of Important Plants in elephant diet in the AENP. Ninety plant species were identified in the diet. Only 14 of the 77 ( c . 18%) Important Plants previously thought particularly vulnerable to elephant browsing occurred in the diet, while at least 6% of species for which there are data were avoided. This refutes the generally held belief that elephant herbivory is the major driver of decline among Important Plants, and emphasizes the likely contribution of other mechanisms (e.g. knock-on effects, trampling, zoochory, etc.) to this phenomenon. The accurate prediction of impacts caused by elephants in the AENP and elsewhere, therefore requires an understanding of these previously marginalized mechanisms. By demonstrating appropriate cause-and-effect relationships between elephants and ecosystem change, we will be able to move beyond assuming that all the observed changes are due to elephant herbivory.     

Application of a direct toxicity assessment approach to assess the hazard of potential pesticide exposure at selected sites on the Crocodile and Magalies rivers,South Africa

The potentially hazardous effects of agricultural pesticide usage in the Crocodile (west) Marico catchment were evaluated using the Danio rerio and Daphnia pulex lethality, Selenastrum capricornutum growth inhibition and the Ames mutagenicity plate incorporation assays. Hazard assessment categories are proposed to standardise the output of the different toxicity assessments. Sites were categorised according to the toxicity hazard indicated and were related to the gradients of agricultural land-use intensity at each site. Intensive agricultural sites showed the highest effects to all tested biota. Receiving water at urban sites associated with increased nutrients and lowest pesticide usage showed few adverse effects, while the relatively unimpacted site indicated no hazard to any organism, and only a slight stimulation to algal growth. Weighted hazard scores indicated that the unimpacted sites were least hazardous, falling within a B category, the urban sites were moderately hazardous (C category), and the agricultural sites (D category) had the highest potential impacts on aquatic organisms. This study demonstrated the usefulness of using the hazard assessment approach and the role it could play in assessing site-specific potential toxicity hazards of river water impacted by agrochemicals. It can be used together with other assessment methods, such as biological indices, in a tiered approach.     

Fish sampling in the marine-dominated Kariega Estuary,South Africa,using a demersal otter trawl: day/night effects

Very few demersal fish assemblage studies using otter trawls in estuaries have been done in South Africa and none of these have tested for the effects of diel period. This study aimed to test whether diel period affects otter trawl catches in the clear, permanently open Kariega Estuary in terms of both species composition and abundance. Fish were sampled by day and night from 30 October to 1 November 2007 at 15 sites using an otter trawl. More species were collected at night, when there were higher catch rates for all key species, with the exception of Rhabdosargus holubi, which was more abundant during the day. Overall assemblages collected by day and by night were similar, with six species accounting for over 90% of the catch in both day and night samples. Both day and night samples reflected differences related to region, with the highest mean CPUE during day and night sampling being recorded in the head region.     

The marine microalgaChlorella stigmatophora as a potential source of single cell protein: Enhancement of the protein content in response to nutrient enrichment

Summary Mass cultures ofChlorella stigmatophora were carried out in order to obtain maximum protein production and to study the chemical variations in function of the nutrient concentration. Cultures reached maximum cellular densities of 2.2·10⁸ cells/ml, with a growth velocity between 0.49 and 0.55 doublings/day. Carbohydrate content in the stationary phase ranged between 2.23 and 2.74 pg/cell, RNA between 0.78 and 1.36 pg/cell and DNA between 0.013 and 0.016 pg/cell. The maximum value for chlorophylla was 0.13 pg/cell. Maximum protein content was obtained with a nutrient concentration of 16 mM of NaNO₃, giving 4.85 pg/cell and a protein concentration of 0.7 g/l. The protein content can be manipulated by changes in the nutrient concentration, showing differences up to a 9.2-fold increase. This characteristic makesChlorella stigmatophora a suitable source of single cell protein.     

Hide, rest or die: a light-mediated diapause response in Daphnia magna to the threat of fish predation

1. In a laboratory batch culture experiment, a diapause response of Daphnia magna to a simulated threat of fish predation was tested at various light intensities, which under natural conditions determine potential vulnerability of Daphnia to visual planktivorous fish. 2. Under moderate light intensity (1.4 μmol m^?2 s^?1) that allows effective predation by fish, the proportion of females producing dormant eggs was significantly higher than under dim light conditions (0.001 μmol m^?2 s^?1) that are not favourable for visual detection of prey. Production of dormant eggs was not observed in complete darkness or in treatments missing fish kairomones, irrespective of tested light conditions. 3. The observed phenomenon is interpreted as a flexible response of prey to the conditional risk of predation assessed by Daphnia according to the presence of fish‐derived cues on the one hand and the presence of dark refugia on the other. Irrespective of the presence of fish kairomones, Daphnia may not produce resting eggs as long as a safe, dark, bottom zone is accessible.     

Macrocystis (Laminariales,Phaeophyceae) in South Africa: potential for cultivation through holdfast fragmentation and use as feed for the aquacultured abalone,Haliotis midae

Journal of Applied Phycology - Macrocystis pyrifera (Linnaeus) C. Agardh, known in some regions as ‘giant kelp’, occurs along temperate coastal rocky reefs throughout the southern...     

Use of15N/14N rations to evaluate the food source of the mysid,Neomysis intermedia Czerniawsky,in a eutrophic lake in Japan

The stable isotope ratios of nitrogen were measured in the mysid,Neomysis intermedia, together with various biogenic materials in a eutrophic lake, Lake Kasumigaura, in Japan throughout a year of 1984/85. The mysid, particulate organic matter (POM, mostly phytoplankton), and zooplankton showed a clear seasonal change in ¹⁵N with high values in spring and fall, but the surface bottom mud did not. A year to year variation as well as seasonal change in ¹⁵N was found in the mysid. The annual averages of ¹⁵N of each material collected in 1984/85 are as follows: surface bottom mud, 6.3 (range: 5.7–6.9); POM, 7.9 (5.8–11.8); large sized mysid, 11.6 (7.7–14.3); zooplankton, 12.5 (10.0–16.4); prawn, 13.2 (9.9–15.4); goby, 15.1 (13.8–16.7). The degree of¹⁵N enrichment by the mysid was determined as 3.2 by the laboratory rearing experiments. The apparent parallel relationship between the POM and the mysid in the temporal patterns of ¹⁵N with about 3 difference suggests the POM (mostly phytoplankton) as a possible food source ofN. intermedia in this lake through the year.     

Similarity in parasite communities of the teleost fish Pinguipes brasilianus in the southwestern Atlantic: Infracommunities as a tool to detect geographical patterns

Patterns of distance decay in similarity among communities of the fish Pinguipes brasilianus (Teleostei: Pinguipedidae) from five areas in the southwestern Atlantic were investigated to determine whether the rate of decay varied depending on the community level or the parasite guild analyzed (ectoparasites, adult endoparasites and larval endoparasites). Similarities in species composition were computed at both the component community and infracommunity levels. Similarity indices were calculated between all possible pairs of assemblages from different zones. Infracommunity similarity values between and within host populations were averaged. Significance of linear regressions for similarity values against distance was assessed using randomization tests. Different patterns were observed for each guild, and similarity among infracommunities within host populations varied accordingly. Decay in similarity over distance was recorded for most communities. The slopes differed significantly between infracommunities and component communities in all cases, and stronger decay was always observed for infracommunities. Different geographical patterns in parasite communities were a consequence of variability in parasite availability in the different regions, modulated by oceanographic conditions, as well as variation among species in terms of host specificity and life-cycles strategies. Infracommunities showed a stronger effect of distance than component communities, probably due to the influence of short term and local variability of oceanographic conditions.     

Effects of Phe-to-Trp mutation and fluorotryptophan incorporation on the solution structure of cardiac troponin C, and analysis of its suitability as a potential probe for in situ NMR studies

19F NMR spectroscopy is potentially a powerful tool for probing protein properties in situ. However, results obtained using this technique are relevant only if the 19F probe offers minimal perturbation to the surrounding environment. In this paper, we examine the effect of 5-fluorotryptophan (5fW) incorporation on the three-dimensional structure of cardiac troponin-C (cTnC), with the intention of developing a 19F-labeled TnC for use in in situ 19FNMR. We find that, in general, 5fW does not perturb the structure of the protein significantly. Replacement of residue Phe 153 with 5fW produces no noticeable change in protein conformation. However, replacement of residue Phe 104 with 5fW produces a folding behavior that is dependent on the Escherichia coli strain used to express the mutant. The orientations of the indole rings in these mutants are such that the Trp residue adopts a chi2 of approximately 90 degrees in the F104W mutant and approximately -100 degrees in the F153W mutant. Using results from 19F-1H heteronuclear NOE experiment, we show the replacement of L-Trp with 5fW at these positions does not change the orientation of the indole ring and the spread of the 5fW side-chain dihedral angles increases moderately for the F104(5fW) mutant and not at all for the F153(5fW) mutant. Based on these structures, we conclude that the substitution of Phe by 5fW at these two positions has minimal effects on the structure of cTnC and that the 5fW indole rings in both mutants have well defined orientation, making the two mutants viable candidates for use in in situ 19F NMR spectroscopy.     

Prevalence and potential link between E. coli O157:H7 isolated from drinking water, meat and vegetables and stools of diarrhoeic confirmed and non-confirmed HIV/AIDS patients in the Amathole District - South Africa

Aim:  The current study investigated the prevalence and molecular relatedness between Escherichia coli O157:H7 isolated from water, meat and meat products and vegetables and from stools of confirmed and non-confirmed Human Immune Virus/Acquired Immunodeficiency Syndrome (HIV/AIDS) patients with diarrhoea.
Methods and Results:  Culture-based and polymerase chain reaction techniques were used to identify E . coli O157:H7. Thirty-five per cent of meat products, 25·5% of water, 21·7% of vegetables as well as 56·5% and 43·5% of stools of confirmed and non-confirmed HIV/AIDS patients, respectively, were presumptively positive with E . coli O157. Molecular results indicated that 10·3%, 8·6% and 7·8% of the vegetables, water and meat products examined carried E . coli O157:H7, which had homologous fliC _H7 , rfbE _O157 and eaeA genetic loci to the genes of some E . coli O157:H7 isolated from 12·2% and 8·8% of the stools of confirmed and non-confirmed HIV/AIDS patients, respectively.
Conclusions:  Water, meat and meat products and vegetables are potential sources of E . coli O157:H7 that are potentially capable of causing diarrhoea in humans especially HIV/AIDS patients.
Significance and Impact of the Study:  Great care should be exercised to ensure that water and foods consumed by HIV/AIDS patients are safe, as contaminated water and foods can cause secondary infections in these patients.     

Gonadal development in a giant threatened reef fish,the humphead wrasse Cheilinus undulatus,and its relationship to international trade

An opportunity arose to obtain humphead wrasse Cheilinus undulatus specimens between 2006 and 2009 from Indonesia, the major source and exporting country of this species, making study on its early gonad development possible for the first time. Protogynous hermaphroditism, previously proposed for this species, was confirmed in this study. Based on histological examination of 178 specimens, mainly <500 mm total length (L_T) and ranging from 208 to 1290 mm L_T (119·1 g to 43·0 kg whole body mass), the minimum body sizes for female and male sexual maturation were determined to be 650 and 845 mm L_T, respectively. Primary male development through juvenile sexual differentiation was not detected. A unique blind pouch, with a possible sperm storage function and associated with the testis, was reported for the first time in the Labridae. In Hong Kong retail markets, the global trading centre for this valuable species, live C. undulatus on sale for food were dominated by body sizes <500 mm L_T between 1995 and 2009, reflecting an international trade largely focused on juveniles. In consideration of these findings, and given the threatened status of this species, management for C. undulatus capture and trade nationally and internationally are discussed with recommendations for ensuring sufficient spawning biomass in exploited populations and for sustainable trade.     

Application of multivariate statistics and toxicity indices to evaluate the water quality suitability for fish of three rivers in the Kruger National Park,South Africa

The water quality of the Olifants, Letaba and Luvuvhu rivers within the Kruger National Park was assessed for their suitability to sustain fish populations. Since water quality assessments result in huge datasets, principal component analysis and an aquatic toxicity index (ATI) were employed to reduce these to more manageable indices. Water quality changed over time, with metal concentrations decreasing, and high flows resulted in increased concentrations of suspended metals. The ATI indicated that metals had no major effect on lowering index values in any of the rivers, and that these values were affected by turbidity in both the Olifants and Letaba rivers, whilst nutrients such as ammonium and orthophosphates negatively affected index scores in the Luvuvhu River. Water quality has improved from the 1990s to 2011.     

Physiological responses to folivory and phytopathogens in a riparian tree,Brabejum stellatifolium,native to the fynbos biome of South Africa

The canopies of many tree species sustain a large diversity of folivorous arthropods and phytopathogenic fungi. These organisms are thought to influence overall tree and stand productivity. Leaf diseases caused by Phyllosticta owaniana and Periconiella velutina, phytopathogenic fungi commonly found on the native riparian tree Brabejum stellatifolium (wild almond), like any other leaf disease, can potentially reduce a plant's photosynthetic efficiency. In addition to these two phytopathogens, the weevils Setapion provinciale and Setapion quantillum are abundant in wild almond canopies. Despite their pervasive occurrence, the impacts of these phytopathogens and arthropods on host tree leaf physiology have not been examined. The gas exchange response of wild almond leaves to phytopathogens and folivore damage was assessed. Leaf nitrogen, phosphorus and water content were also determined. Declines in photosynthetic rates and other physiological parameters were associated with increasing damage severity by weevils and phytopathogens in leaves of B. stellatifolium. Nitrogen and phosphorus contents were negatively associated with disease severity. Water and phosphorus contents were also negatively correlated with increased weevil damage, while nitrogen content was positively correlated with it. The observed responses of B. stellatifolium metabolic functioning to fungal pathogen and folivory indicate a possibility of suppressed wild populations of wild almond.     

Gratiana boliviana, a potential biocontrol agent of Solanum viarum: Quarantine host-specificity testing in Florida and field surveys in South America

Host-specificity tests andfield surveys were conducted to determine thesuitability of the tortoise beetleGratiana boliviana Spaeth (Coleoptera:Chrysomelidae) from Argentina for classicalbiological control of Solanum viarumDunal (Solanaceae) in the USA. Thehost-specificity tests were conducted at theFlorida Department of Agriculture and ConsumerServices-Division of Plant Industry quarantinefacility in Gainesville, Florida (USA). Multiple-choice host-specificity tests wereconducted in small cages using 123 plantspecies in 35 families. Adults fedsignificantly (>41% of the leaf area offeredwas damaged) on the target weed(S. viarum), and fed lightly (<20%) onSolanum torvum Sw. (noxious weed native towest-Africa). Adults did some exploratoryfeeding (<5%) on eggplant, Solanummelongena L. (economic crop), Solanumelaeagnifolium Cav. (major agricultural weedin the western US), and on Solanumtampicense Dunal (weed of Central Americanorigin). No feeding was observed on any of theother 118 plant species that were testedincluding another 21 Solanum species.G. boliviana adults laid an average of 68eggs per female on S. viarum, 5 eggs perfemale on S. torvum, and an average of0.2 eggs on eggplant. No-choicehost-specificity tests were also conducted inwhich G. boliviana adults and neonatelarvae were exposed to 19 and 22 plant speciesrespectively. Tests with the neonatesindicated this insect was able to complete itsdevelopment only on S. viarum (67%reached the pupae stage). The no-choice testswith adults indicated that this insect fed,laid eggs, and completed development only onS. viarum. The unsprayed eggplant fieldsthat were surveyed in its natural range inArgentina, Brazil, Paraguay, and Uruguay fromJune 1997 to March 2000 indicated thatG. boliviana is not a pest of eggplants in SouthAmerica. Therefore, a petition for fieldrelease of G. boliviana for classicalbiological control of S. viarum in theUSA was submitted in April 2000.     

Biology and host range of the leafminer,Pseudonapomyza sp. (Diptera: Agromyzidae), a potential biological control agent for Tecoma stans (Bignoniaceae) in South Africa

Tecoma stans (Bignoniaceae), is an evergreen shrub that has a wide natural distribution in the tropical and subtropical parts of the western hemisphere. This shrub is native to Mexico and the southern regions of the USA. This weed is widely distributed in South Africa and neighbouring countries. As part of the biological control initiative, a leafmining fly, Pseudonapomyza sp. (Diptera: Agromyzidae), was imported into South Africa, and was subsequently studied as a potential biological control agent for T. stans. During no-choice tests involving 46 plant species in 16 families, Pseudonapomyza sp. only oviposited and developed on T. stans. Neither oviposition nor larval development was recorded on the closely related and indigenous plant species. When six plant species in the Bignoniaceae family were exposed to Pseudonapomyza sp. during multi-choice tests, oviposition and larval development only occurred on T. stans. It was concluded that Pseudonapomyza sp. was sufficiently host-specific to be released against T. stans in South Africa. Pseudonapomyza sp. also displayed very promising biological attributes that could enhance its effectiveness to control T. stans.     

Largest reported groups for the Indo‐Pacific bottlenose dolphin (Tursiops aduncus) found in Algoa Bay,South Africa: Trends and potential drivers

This study investigates how group size of Indo‐Pacific bottlenose dolphins (Tursiops aduncus) changes temporally, spatially, and/or with predominant behavior at two discreet sites along the Eastern Cape coastline of South Africa: Algoa Bay and the Wild Coast. The mean group size of bottlenose dolphins was large with an average of 52 animals. Significantly larger groups were observed in Algoa Bay ( = 60, range = 1–600) than off the Wild Coast ( = 32.9, range = 1–250). In Algoa Bay, the mean group size increased significantly over the study period, from an average 18 animals in 2008 to 76 animals in 2016. Additionally, the largest average and maximum group sizes ever reported both in South Africa and worldwide, were recorded in Algoa Bay (maximum group size = 600). Neither season nor behavior had a significant effect on mean group size at both sites. Similarly environmental variables such as the depth and substrate type also had no influence on group size. It remains unclear which ecological drivers, such as predation risk and food availability, are leading to the large groups observed in this area, and further research on abundance and distribution of both predators and prey is necessary.