Evidence for diet partitioning among three coexisting native freshwater
fishes in South Africa’s Cape Fold Ecoregion
JM Shelton1,2* , MS Bird3 and SM Marr4,5,6
1 Freshwater Research Centre (FRC), Scarborough, South Africa 2 Centre for Invasion Biology, Department of Conservation Ecology and Entomology, Stellenbosch University, South Africa 3 Department of Zoology, University of Johannesburg, Auckland Park, Johannesburg, South Africa 4 South African Institute for Aquatic Biodiversity (SAIAB), Grahamstown, South Africa
5 Centre for Invasion Biology, SAIAB, Grahamstown, South Africa 6 DST/NRF Research Chair in Inland Fisheries and Freshwater Ecology, SAIAB, Grahamstown, South Africa
ABSTRACT
The partitioning of limited resources commonly explains how different species can coexist within the same ecological community. In this 2010 study, the diets of three coexisting freshwater fishes (Cape galaxias Galaxias zebratus, n = 27; Cape kurper Sandelia capensis, n = 60; Breede River redfin Pseudobarbus burchelli, n = 77) were characterised and compared in three headwater streams in South Africa’s Cape Fold Ecoregion using gut contents and stable isotope analyses. These data were analysed to ascertain whether the three species exploit distinct trophic niches. Both approaches provided evidence that these species occupy different trophic niches, though with some overlap. However, dietary differences among sites were not consistent and were probably influenced by site-specific factors like resource availability. Pseudobarbus burchelli had a broader niche breadth at Tierkloof Stream than the other two species, but not at Waaihoek or Tierstel Streams. Our results also suggest that P. burchelli consumed a more omnivorous diet than do the other two species, whereas S. capensis occupied a higher trophic position than the other two species and consumed vertebrates. Our findings suggest that these species
occupy non-equivalent feeding niches in Cape Fold Ecoregion headwater streams, and that diet partitioning might facilitate their coexistence in these systems.
Keywords: gut contents, headwater stream, resource partitioning, stable isotopes, trophic niche overlap
Reproductive strategies of smooth-head catfish Clarias liocephalus (Boulenger,
1898), in the Rwizi-Rufuha wetland system, south-western Uganda
J Yatuha1*, J Rutaisire2, L Chapman3, J Kang’ombe4 and D Sikawa4
1 Biology Department, Mbarara University of Science and Technology, Mbarara, Uganda; 2 National Agricultural Research Organization, Entebbe, Uganda; 3 Department of Biology, McGill University, Montreal, QC, Canada; 4 Bunda College of Agriculture, University of Malawi, Lilongwe, Malawi
ABSTRACT
The reproduction of the smooth-head catfish (Clarias liocephalus), a heavily exploited wetland fish in Uganda, in a data-deficient fishery, was studied from January to December 2011. Analyses were based on a sample of 854 fish specimens obtained from a chain of wetlands that fringe the Rwizi River, a tributary of the Nile River. Samples were collected monthly from four sites. Fecundity, gonadosomatic index, size at sexual maturity, condition factor and growth patterns were used to describe the reproduction of the species. Mean female fecundity was 2 484.03 ± 1 289.90 (range 266–3 474). Females attained sexual maturity at a smaller size (12.0 cm TL) than males (13.79 cm TL), but were in better condition than males. Gonadosomatic index peaked in the wettest months of the study period, with highest proportion of mature ova occurring during July to November. Although C. liocephalus seems less fecund than other known clariids and is therefore prone to adverse effects from overexploitation, knowledge of its spawning periodicity and its size at sexual maturity could be useful in the management of the fishery in wetlands where it is still abundant.
Keywords: condition factor, fecundity, gonadosomatic index, size at maturity
Can the presence of curved forms of the diatom Aulacoseira ambigua in
the Nile (Egypt) and Vaal (South Africa) Rivers be ascribed to similar water
quality conditions?
S Janse van Vuuren1*, AA Saber2, A Swanepoel3 and M Cantonati4
1 Unit for Environmental Sciences and Management, North-West University, Potchefstroom, 2520, South Africa; 2 Botany Department, Faculty of Science, Ain Shams University, Abbassia Square - 11566, Cairo, Egypt; 3 Rand Water, Scientific Services, PO Box 3526, Vereeniging 1930, South Africa; 4 MUSE-Museo delle Scienze, Limnology and Phycology Section, Corso del Lavoro e della Scienza 3, I-38123 Trento, Italy
ABSTRACT
Spiral colonies of the diatom Aulacoseira ambigua were assigned the rank of forma (Aulacoseira ambigua f. japonica). This spiral-shaped, colonial, centric diatom has limited geographical distribution and is currently reported to occur in only a few countries in the world. In Africa this species was described for the first time from the Vaal River, South Africa, but recent research on the Nile River also revealed its presence in Egypt. Physical and chemical data on water quality in these two river systems were compared to determine whether the presence of this uncommon ‘phenoecodeme’ could be ascribed to similar environmental conditions. Results indicate that the rivers are dissimilar with regard to many variables, but both rivers provide turbid, warm and eutrophic waters with medium to high mineral content and it was concluded that these factors favour and sustain the growth of this curved form.
Keywords: Bioassessment, eutrophic, environmental variables, first record, physicochemistry, spiral diatom
Cyanotoxins in small artificial dams in Kenya utilised for cage fish farming –
a threat to local people?
MN Kaggwa*, N Straubinger-Gansberger and M Schagerl
Department of Limnology and Oceanography, University of Vienna, 1 090 Vienna, Austria
ABSTRACT
Nine small artificial dams located in different climatic regions of Kenya were studied. The local communities use the stored water for various purposes, such as irrigation, domestic use, watering of livestock and cage fish farming. Such intense use is commonly accompanied by eutrophication, including fast growth of cyanobacteria, which at times produce cyanotoxins threatening human and animal life. We studied the pelagic community, analysed abiotic variables and identified microcystins by means of high performance liquid chromatography and ELISA kits at monthly intervals over a period of one year. Mass spectrometry (MALDI-TOF MS) was used to identify structural variants of microcystins by their protonated masses (M + H). Three dams contained microcystins, with the highly
toxic Microcystin-LR being identified as the most prominent substance. Cell content of the toxin varied from 7.2 to 686.7 fg cell−1. Basic limnological variables that indicate the probability of toxin presence were also recorded. Non-parametric Mann–Whitney U-test revealed significant differences in soluble reactive phosphorous, nitrate-N, water depth, total hardness and post-Nauplii stages sampled between toxin-producing and non-toxin-producing dams. Although most of the samples did not contain high amounts of cyanobacteria, the cyanotoxin-problem was evident, suggesting the need for regular cyanotoxin monitoring programs.
Keywords: aquaculture, cyanoprokaryotes, microcystin, Microcystis, phytoplankton
Biodiversity and ecology of epilithic diatoms in the Agnéby River, Ivory Coast
KR N’Guessan1*, BRD Aboua1, J Tison-Rosebery3, A Ouattara2 and EP Kouamelan1
ABSTRACT
The ecology and taxonomy of the epilithic diatom flora of the Agnéby River, Ivory Coast were studied in 2012. Tensites were investigated and diatoms were sampled on glass slides immersed for a period of 30 days during the wet and dry seasons. Physico-chemical parameters were measured at each site while sampling diatoms. Five taxa were largely dominant: Planothidium comperei CE Wetzel, N’Guessan and Tison-Rosebery, Eolimna minima (Grunow) Lange-Bertalot, Planothidium piaficum (JR Carter and Denny) CE Wetzel and Ector, Cocconeis schroederi Foged and Cocconeis scutellum var. parva (Grunow in Van Heurck) Cleve. Electrical conductivity, temperature, dissolved oxygen, nitrite and phosphorus were found to influence the distribution of taxa.
Keywords: diversity, environmental parameters, seasonal variability, tropical rivers, West Africa
Evaluation of satellite retrievals of water quality parameters for Lake Victoria
in East Africa
A Gidudu1*, R Mugo2, L Letaru1, J Wanjohi2, R Nakibule1, E Adams3, A Flores3, B Page3 and W Okello4
ABSTRACT
Lake Victoria in East Africa is a major ecosystem, whose size and importance has warranted the exploration of MODIS imagery to provide continuous and accurate water quality information. To this effect, two sea expeditions (in November 2014 and February 2015) were carried out to collect in situ lake surface temperature (LST), chlorophyll a (Chl) and Secchi disk depth (SDD) to compare with the corresponding satellite derived variables. Comparisons were made based on the following error matrices: coefficient of correlation (r), mean square error (MSE), root mean square error (RMSE), mean absolute deviation (MAD) and mean absolute percent error (MAPE). In general the results showed that satellite derived LST gives a good estimate of in situ LST. Conversely, the error matrices indicated that satellite derived Chl yielded more uncertainty when compared with in situ Chl. This could be because of the fact that the MODIS Chl product algorithm was designed for oceans and may not be appropriate for inland lakes. Satellite derived SDD compared fairly well with in situ SDD. From these results it is evident that with more in situ observations and improved algorithms, MODIS can be useful to improve how water quality is monitored on Lake Victoria.
Keywords: chlorophyll a, inland lake, MODIS, monitoring, Secchi depth, temperature
Suppression of the aquatic weed Hydrilla verticillata (L.f.) Royle
(Hydrocharitaceae) by a leaf-cutting moth Parapoynx diminutalis Snellen
(Lepidoptera: Crambidae) in Jozini Dam, South Africa
A Bownes1,2
ABSTRACT
A classical biological control programme against Hydrilla verticillata (L.f.) Royle (Hydrocharitaceae) was initiated in South Africa following the discovery of extensive mats in Jozini Dam in northern KwaZulu-Natal (KZN) in 2006. However, in mid-2008, high densities of a phytophagous insect, Parapoynx diminutalis Snellen (Lepidoptera: Crambidae) were discovered on the H. verticillata infestation, causing high levels of defoliation and dieback of the weed. In order to quantify the impact of the moth and to assess the long-term threat of H. verticillata to South African water bodies, a monitoring programme was initiated in 2013. Although P. diminutalis did not demonstrate a preference for H. verticillata over a native aquatic plant, Potamogeton schweinfurthii A. Bennett (Potamogetonaceae), moth populations followed a cyclical pattern of abundance, with rapid population increases coinciding with increases in the abundance of H. verticillata. High damage levels to H. verticillata were associated with high densities of immature P. diminutalis, which consistently led to population crashes of H. verticillata. Parapoynx diminutalis appears to have great potential to contribute to the management of H. verticillata in South Africa. However, the moth’s oligophagous habits will probably preclude its intentional introduction into water
bodies with H. verticillata where it does not already occur.
Keywords: biological control, cyclical pattern of abundance, insect herbivory, plant-herbivore interactions
Effect of drift sampler exposure time and net mesh size on invertebrate
drift density in the Njoro River, Kenya
PW Mureithi1, JG Mbaka2*, CM M’Erimba1 and JM Mathooko1
ABSTRACT
Although invertebrate drift is an important ecological process in lotic ecosystems, very little is known about it in Kenyan rivers. The primary aim of this study was to investigate the effect of driftnet mesh size and exposure duration on drift density in 2017. Drift samples were dominated by Chironomidae, Baetidae, Simuliidae, Caenidae and Culicidae. The 100 µm mesh driftnet had the highest mean invertebrate density, followed by the 250 µm and 500µm nets. Invertebrate drift densities decreased with increased exposure time. This study demonstrates that sampler mesh size and exposure time should be taken into account when characterising invertebrate drift in streams. Future studies should consider sampling different biotopes and during different seasons.
Keywords: lotic ecosystems, macroinvertebrates, Nakuru County, riffle habitats
Trophic state and nutrient limitation in Lake Baringo, Kenya
EO Okech1*, N Kitaka1, SO Oduor1 and D Verschuren2
ABSTRACT
The trophic state of Lake Baringo and factors that could be limiting the development of algal biomass in it were investigated during one wet/dry hydrological cycle in 2014–2015. Water samples were analysed for dissolved inorganic nutrients, including NH +4, NO2− and NO3−, total phosphorus and Chlorophyll a. Light attenuation was estimated using Secchi depth. The trophic state was determined using Carlson trophic state indices (CTSI). Deviations in CTSI, nutrient ratios and ambient nutrient concentrations were used to identify factors limiting phytoplankton growth. The mean values measured for Secchi depth, nitrate, total phosphorus and Chlorophyll a showed significant seasonal variation (p < 0.05). Based on the Carlson trophic state index, the results show that Lake Baringo is eutrophic. However, the lake is also experiencing phosphorus limitation and poor light penetration, because of high turbidity, which is more pronounced during the wet season.
Keywords: algal biomass, eutrophic state, light attenuation, phosphorus limitation
First records of Atyoida serrata (CS Bate, 1888) from South Africa (Crustacea:
Caridea: Atyidae)
M Coke
ABSTRACT
Collections of Atyoida serrata (CS Bate, 1888) are reported from KwaZulu-Natal, South Africa for the first time. This species is currently known only from the lower reaches of the Mgeni, Vungu and Mtamvuna river systems where it occupies rocky cascades and rock crevices in torrential habitats.
Keywords: distribution range, first African records, KwaZulu-Natal, Molweni River, Vungu River
A mass mortality of fishes caused by receding water levels in the vegetated
littoral zone of the West Kleinemonde Estuary, South Africa
AK Whitfield* and PD Cowley
ABSTRACT
On 15 November 2017 the mouth of the West Kleinemonde Estuary breached following heavy catchment rains and increased river flow. The water level in the estuary following mouth opening decreased by 1.65 m within 24 h, resulting in an almost complete draining of the littoral zone where large beds of the aquatic macrophyte Ruppia cirrhosa and mats of the associated filamentous algae were present. As the water depth within the plant beds decreased, the macrophytes, together with the algal filaments, created an increasingly dense mat, trapping fish that were resident, foraging or passing through the littoral zone. By 16 November 2017 large numbers of fishes belonging to at least 20 species were trapped in pools and depressions within the littoral, as well as within the R. cirrhosa beds and filamentous algal mats in the lower reaches of this system. Other affected taxa included crustaceans, especially isopods, and large numbers of small bivalves attached to macrophyte vegetation. Beneficiaries of the fish kill, in terms of unexpected food availability, included a variety of piscivorous bird species and the Cape clawless otter Aonyx capensis. This is the first documented account of a diverse species fish kill
associated with estuary mouth breaching.
Record of Blue tilapia Oreochromis aureus (Steindachner, 1864) in the
Eerste River catchment, Western Cape province, South Africa
SM Marr1,2,3* , G Gouws1, S Avlijas4, D Khosa1,5, ND Impson6, M van der Westhuizen7 and OLF Weyl1,2,3
ABSTRACT
Oreochromis aureus was imported from Israel into South Africa in 1959 but data on its current status in South Africa are
lacking. Genomic DNA was extracted and the COI gene amplified at the South African Institute for Aquatic Biodiversity.
The identity of the sequences and specimens was determined using the Barcode of Life Data Systems and GenBank.
Morphological and genetic assessment demonstrated that 11 specimens collected from two farm dams in the Eerste
River System, Western Cape province, were Oreochromis aureus. A MaxEnt model compiled using global distribution,
rainfall and temperature data predicted that large areas of southern Africa were climatically suitable for this species,
indicating considerable invasion debt in southern Africa. As a result, surveys to assess for the extent of the invasion in
South Africa and eradication of existing populations, if feasible, are recommended management actions.
Keywords: COI gene, DNA barcoding, invasion risk, Israeli tilapia, MaxEnt, mitochondrial DNA
