African Journal of Aquatic Science

A review of the reported and future potential ecological impacts of the invasive freshwater snail Tarebia granifera in South Africa

J.J. Pearson — 2024-11-27

The Southeast Asian gastropod Tarebia granifera is an invasive freshwater snail across several continents. Our review summarises the impacts of this invasive snail on invaded aquatic ecosystems. The most important impacts are those related to their ability to reproduce quickly and reach high densities within invaded ecosystems. The snail has reportedly caused declines and local extinctions in native snail populations globally. They can further significantly reduce algal standing stocks and may have severe impacts on benthic biomass, resulting in decreased benthic biodiversity and disturbances in aquatic ecosystem function. These invasive snails also cause bioturbation that can lead to changes in the nutrient cycles of invaded aquatic ecosystems and affect food web dynamics, with unknown implications for ecosystem function. Furthermore, T. granifera is well known to harbour a diverse range of parasitic species of medical and veterinary importance both within and outside their native ranges. The effective control of invasive T. granifera remains challenging as they are not easily preyed upon, and potential control methods may have unintentional side effects on native biota. This review provides evidence that there is a need to control this invader to avoid further degradation of freshwater habitats and aquatic biodiversity.

Perceptions and knowledge about the use of biological indicators in freshwater ecosystem monitoring in Rwanda

A. Nzarora — 2024-11-27

The use of biological monitoring (biomonitoring) to assess water quality is recognised alongside the use of chemical and physicochemical parameters due to its ability and efficiency in providing information about both current and long-term changes. Indeed, biomonitoring is applied in several developed and developing countries. Nevertheless, some developing countries, such as Rwanda, are yet to adopt such a monitoring system. This paper presents results of an assessment of the knowledge and perceptions by water resource managers about the use of biomonitoring and bioindicators, and challenges to their integration into existing routine water quality monitoring systems in Rwanda. Qualitative research, using semistructured interviews, was conducted with nine water resource practitioners from six water governance institutions between August and November 2021. The results show that participants are aware that macroinvertebrates, algae and fish are bioindicators that have potential applications in Rwanda to complement the chemical and physicochemical parameters already being collected in the country’s water monitoring system. The main challenges for integration of biological indicators, as indicated by participants, include the need for equipment, funding, technical skills and taxonomic knowledge. Training in the use of bioindicators and taxonomy are needed to raise the awareness and skills of staff from the institutions involved in freshwater ecosystem management in Rwanda, and to encourage integration of biomonitoring results into national water monitoring frameworks.

Comparative analysis of habitat structure and macroinvertebrate assemblages in headwater streams of Odzi sub-catchment, Chimanimani District, Zimbabwe, post Cyclone Idai-induced flooding

Brian Mamvura — 2024-11-27

Flooding results in short and long-term modifications of aquatic ecosystem structure and biodiversity. Cyclone Idai, which ravaged through Zimbabwe in 2019, had devastating consequences on aquatic ecosystems. However, the extent of habitat modification and consequent biodiversity shifts are unknown. This study focuses on the comparative analysis of (i) habitat structure and (ii) macroinvertebrate assemblages in headwater streams of the Odzi sub-catchment, Chimanimani District, Zimbabwe, specifically examining the conditions post-Cyclone Idai-induced flooding. Field sampling was conducted in the dry season (September−November) 2019 and wet season (January−March) 2020. Headwater streams of the Murare (first order), Umvumvumvu (first and second order) and Nyanyadzi (first and second order) rivers were sampled. Habitat assessment was done following the Benthic Macroinvertebrate Monitoring Protocol Implementation Plan. Selected water variables were measured using appropriate probes. Macroinvertebrate assemblage data were collected using the South African Scoring System (SASS 5) protocol. Spatiotemporal variations in water quality, habitat structure and macroinvertebrate metrics were assessed using two-way ANOVA, ANOSIM and SIMPER. Significant spatiotemporal heterogeneity (p < 0.05) was detected in temperature, turbidity, conductivity and total dissolved solids, velocity and depth regimes, channel flow status, sediment deposition, channel alteration and frequency of riffles for the three rivers. Habitat quality ascending hierarchical order was: Umvumvumvu > Murare > Nyanyadzi after Cyclone Idai induced flooding. The highest macroinvertebrate composition diversity was detected in Murare River, the least flood-affected stream. The largest dissimilarity (ANOSIM, 75.3%) was between the Umvumvumvu and Nyanyadzi rivers. Macroinvertebrate community structure differed significantly because of species uniqueness and heterogenous tolerance to changes in environmental conditions after flooding. Flooding intensity and duration induces dissimilar environmental tolerances and persistent macroinvertebrates communities in lotic systems across local catchment scales. Long- term assessment of water quality impairment, resilient functional feeder groups and rifflescale physical habitat structure are imperative for optimised micro-scale conservation of macroinvertebrates in headwater streams prone to flash flooding.

Space and spatially structured environmental variables account for variation in blackfly and mayfly communities in sub-tropical South African rivers

P.A. Ramulifho — 2024-11-27

Using aquatic invertebrate assemblages for bioassessment of streams and rivers is a fast and cost-effective approach to studying the impact of environmental stressors in aquatic ecosystems. The use of aquatic invertebrates is premised on their predictable responses to environmental stressors. Assemblage structure is not, however, only influenced by environment, but also neutral processes and temporal variation. This study quantified the relative roles of the environment (niche processes), space (neutral processes) and temporal factors in structuring mayfly and blackfly assemblages at family and species levels. Asymmetric eigenvector maps in conjunction with canonical redundancy analysis and variation partitioning were used to explore the relative roles of these three factors in structuring macroinvertebrate assemblages. At a species level, flow and water temperature were more important in explaining assemblage structure than at the family level. At the family level, space was more important than temporal and environmental factors. Unexplained variation at species and family level was more than 50%. This suggests (i) caution in using family-level rapid assessments to infer the role of the environment in structuring aquatic macroinvertebrate assemblages, as neutral processes are also dominant; and (ii) that the importance of stochastic processes, such as dispersal, should not be underestimated in rapid assessments.

Per-recruit analysis and proposed sustainable harvest strategy for rednose labeo Labeo rosae and Mosambique tilapia Oreochromis mossambicus in Flag Boshielo Dam, Olifants River, South Africa

S.M. Marr — 2024-11-27

Inland fisheries development in South Africa has been proposed to improve rural livelihoods and food security. However, inland fisheries are susceptible to collapse through overfishing. Therefore, establishing biological reference points for these fisheries is essential for long- term sustainability. Here, spawner-biomass-per-recruit (SBR) analysis was used to set biological reference points for a gillnet fishery targeting the rednose labeo Labeo rosae and Mozambique tilapia Oreochromis mossambicus at Flag Boshielo Dam on the Oliphants River in Limpopo Province, South Africa. Both species are currently exploited at the impoundment by subsistence fishers that keep their entire catch. The current yields are estimated at 59 and 172 g yr−1 for L. rosae and O. mossambicus, respectively. The per-recruit analysis showed that age-at-first-capture for both species should be 4 years, at minimum lengths of 280 mm TL and 250 mm TL for L. rosae and O. mossambicus, respectively, with fishers using a minimum mesh size of 100 mm to reduce the risk of stock collapse. To maintain a SBR value greater than 25% of a pristine population, the L. rosae yield could be increased to 98 g yr−1, while the O. mossambicus yield could be increased to 176 g yr−1, following implementation of the recommended mesh size and size limits. A per-recruit analysis for O. mossambicus that includes recruitment variability and error to accurately calculate the biological reference points is recommended.

Life-history of invasive common carp, Cyprinus carpio, within a natural lake (Groenvlei), South Africa

D.L. Mukhari — 2024-11-27

Common carp, Cyprinus carpio, is a global invasive species illegally introduced into the Groenvlei system, South Africa, in the 1990s for recreational angling. To manage this population effectively, basic information is needed on its biology including growth and reproduction. This study examined the growth trends of C. carpio using otolith growth zone deposition rates which were validated using a chemical mark–recapture experiment (n =16). From a total of 140 C. carpio, length-at-age was best described using the Von Bertalanffy growth model for males and females. The average lengths-at-50% maturity were estimated at 314 mm FL (males) and 262 mm FL
(females). Compared with other South African C. carpio populations, the Groenvlei population is relatively fast growing and long lived, with the oldest female aged 20 years and the oldest male aged 18 years, likely facilitated by relatively favourable environmental conditions at Groenvlei. Data from this study provide a baseline at the commencement of C. carpio management interventions at Groenvlei and an opportunity to monitor changes in population dynamics facilitated by these efforts.

Assessing the extent to which African wetland inventories can report to the global targets on biodiversity, including Goal A of the Global Biodiversity Framework

M.M. Sadiki — 2024-11-27

Wetlands face global threats with estimates suggesting a loss ranging from 21% to 85% of their original extent. Africa’s wetlands, covering about 4.4% of the continent, provide crucial services to millions of people and harbour significant biodiversity. This study assesses African countries’ readiness for the Kunming−Montreal Global Biodiversity Framework (GBF) through wetland inventories. It examines the progress made under the Aichi Targets for 2020, revealing 39% of reporting African countries indicating being on track for Aichi Target 11. Subsequently, the study explores wetland inventorying trends from national reports made to the Ramsar Convention from COP07 (1999) to COP14 (2022), showcasing increased membership and progress in African countries. Notable patterns emerge, revealing challenges in maintaining accurate inventories. Despite varying responses, 67% of African countries reported having a comprehensive wetland inventory at one point in the past 23 years. However, the wetland inventories are out of date, and critical information is not easily accessible, hampering accurate reporting on the current state of wetlands, and hindering informed decision- making for conservation and protection initiatives. Global datasets have contributed to reporting on wetland ecosystems; however, biodiversity-focused wetland typology systems like the IUCN Global Ecosystem Typology are crucial for a comprehensive understanding of wetland ecosystems.

Occurrence of contaminants of emerging concern in the uMhlathuze and uThukela river systems, KwaZulu-Natal, South Africa

L.R. Nsibande — 2024-11-27

Contaminants of emerging concern (CECs), which include inorganic substances, exhibit potential adverse effects on aquatic life even though they commonly occur at very low concentrations in aquatic resources. The lack of data available about the risk of CECs to the environment is a hindrance to environmental protection.To this end, we examined the extent to which the uMhlathuze and uThukela rivers are exposed to selected CECs. Pharmaceuticals and lifestyle drugs (58 compounds), pesticides (27 compounds), microplastics (fibres and films), and inorganic metals (Al, Cr, Cu, Fe, Mn, Ni, Pb, Si, Ti and Zn) were detected in both river systems. Additionally, a bioaccumulation of metals was detected in Chiromantes eulimene. In both river systems, the highest frequency of CECs and concentration of microplastics and metals were detected downstream of the wastewater treatment plant’s (WWTP’s) effluent discharge points. The WWTPs’ effluent was a notable source of CECs and metals in the water resources. However, industrial and agricultural activities in the respective catchments were potential diffusers of the contaminants.

A rapid fishery assessment to collect biological information and life-history parameters for rednose labeo Labeo rosae and Mozambique tilapia Oreochromis mossambicus in Loskop Dam, Olifants River, South Africa

H.A. Hlungwani — 2024-11-27

A 2-week rapid fishery assessment using various sampling gears was conducted to collect life-history data on rednose labeo Labeo rosae and Mozambique tilapia Oreochromis mossambicus in Loskop Dam on the Olifants River, Mpumalanga Province, South Africa. These native species were the two most-abundant fish species caught in the impoundment during the study. Both species displayed a bimodal population size distribution comprised of recent recruits and large-sized individuals. Isometric growth (b value ~3), an asymptotic length (L∞) of 447 mm, and length at 50% sexual maturity (Lm50) of 198 mm were estimated for L. rosae. Isometric growth, L∞ of 451 mm, and Lm50 of 124 mm were estimated for O. mossambicus. This rapid assessment at Loskop Dam produced sets of life-history parameters comparable to those previously reported for these two species in Flag Boshielo Dam, ~80 km downstream.