Chondrichthyans are threatened worldwide due to their life-history traits combined with a plethora of anthropogenic impacts that are causing populations to collapse. Marine Protected Areas (MPAs) are a conservation option, but their efficacy for chondrichthyans is still unclear. Conservation efforts might be challenging especially in developing countries, due to a lack of resources and monitoring and limited data and stakeholder support. Here Baited Remote Underwater Stereo-Video systems (stereo-BRUVs) were deployed inside and outside a small partially protected MPA (Robberg MPA, Western Cape, South Africa) to assess the status of cartilaginous fishes’ assemblages and to investigate the potential benefits derived from the presence of a marine reserve. Overall, 19 chondrichthyan species in 11 different families were observed. Chondrichthyans were observed in 78.5% of the sites and, of these, 89.7% of the MPA sites showed at least one chondrichthyan, while only in the 67.5% of surrounding exploited sites a cartilaginous fish was sighted. The presence of the MPA had a significant effect on the relative abundance of batoids, threatened species and local endemics, with more observations inside the MPA than outside, indicating the potential benefit of marine reserves on species that are more vulnerable to fishing pressure. Relative abundance was generally higher inside the bay than in the exposed area, and both relative abundance and species richness decreased significantly with depth. The analysis of the body length showed that the 35.5% of species had an average body length below maturity length, indicating that the area might be used as nursery ground for different species. This study provides evidence that MPAs, even though small and partially protected, can provide benefits for chondrichthyans, specifically to threatened species, endemic species and lesser-known species. Importantly, different environmental parameters must be considered to maximize the benefits an MPA can provide.
The Republic of Seychelles is one of six African Small Island Developing States (SIDS) and has a marine-based economy reliant on fisheries and international tourism. Seychelles has been flagged by the United Nations as highly vulnerable to climate change. Climatic threats are compounded with population declines of key fishery species. A progressive national stance towards ocean sustainability and an emerging economy partially driven by tourists are two of several factors that make Seychelles a good candidate for a sustainable seafood labelling and consumption programme, which would provide market-based incentives for fishery harvesters, regulators, buyers and consumers to improve sustainable practices. To address the feasibility of such a programme, we conducted a pilot study, surveying 33 artisanal fishers and mapping supply chain structure to examine incentives and challenges. Questions addressed fishers' years of experience, reliance on fishing for income, and flexibility in gear type and species targeted. Of the total number of respondents, 64% would like to see a programme implemented but only 34% thought it would be successful. Participants identified several barriers and benefits that primarily spanned socioeconomic and regulatory themes. Our pilot results indicate the sociocultural and economic impacts of sustainability programmes in Seychelles are as important as environmental considerations, a finding pertinent to anyone undertaking similar research efforts in other SIDS. We advocate for the necessity of thorough, location-based research and in-depth stakeholder consultation to elucidate economic, societal, behavioural and cultural factors that will affect the success of designing and implementing seafood labelling programmes in SIDS.
Wetlands physical and biological processes are fundamental to the distribution and structuring of organic matter in sediments. This study investigated spatial and temporal changes in organic matter sources in sediments within the Nylsvley Wetland, South Africa across two seasons, five sites and three wetland zones and identified pertinent contributors to sediment organic matter. Results showed distributions were uneven throughout the wetlands, with the seasonal zone having slightly high sediment organic matter in the cool-dry season and the permanent zone had high sediment organic matter in the hot-wet season, whereas the temporary zone had low SOM concentrations. Significant differences in nutrient concentrations were observed across wetland zones and seasons for Phosphorous, Potassium, Calcium and Magnesium, with the seasonal zone tending to be the most nutrient-rich in the cool-dry season, and with permanent zone nutrient levels rising substantially in the hot-wet season. Sediment δ13C differed significantly among wetland zones, whereas δ15N was statistically similar. Autochthonous plants were the main sources of organic matter in sediments overall across sites and zones. This study’s findings help to better understand the distribution of organic matter in wetland ecosystems and the role wetland zones play in the seasonal provisioning of allochthonous inputs.
Anthropogenic activities have increasingly subjected freshwater ecosystems globally to various pressures. Increasing land use activities have been highly linked to deteriorating freshwater ecosystems and dwindling biodiversity. For sound management and conservation policies to be implemented, relations between land use, environmental, and biotic components need to be widely documented. To evaluate the impacts of land use on biotic components, this study analyzed the diatom and macroinvertebrate community composition of the Eastern Highlands (Zimbabwe) streams to assess the main spatial diatom and macroinvertebrate community variances and how environmental variables and spatial factors influence community composition. Diatom and macroinvertebrate sampling was done in 16 streams in protected areas (national parks) and impacted sites (timber plantation and communal areas). Water (pH, phosphorus, and ammonium) and sediment (nitrogen, phosphorus, calcium, magnesium, manganese, and zinc) and habitat (substrate embeddedness, and habitat) variables differed significantly with land use. Principal Component Analysis (PCA) showed that the protected area had the best water quality, particularly marked by high pH levels and low phosphorus concentrations among environment types. Heavy metals were high in the communal areas although mercury was higher in the national park. Significant differences were observed in diatom metrics, specifically dominance and evenness, with no significant differences being observed in macroinvertebrate metrics across land uses. Diatoms differed in terms of composition in response to land use. Results provide an important scientific reference for land use optimization and guidance for the formulation of policies to protect freshwater resources in African Highland streams. Management and conservation initiatives in the Eastern Highlands are further recommended as this study detected high levels of mercury in the protected area, implying high levels of illegal mining.
To support sustainable growth of ocean-based economies, many countries are engaging in marine spatial planning (MSP) processes, which require robust decision-support tools. Systematic conservation planning (SCP) is commonly used in decision-making to guide spatially efficient protected area expansion. Here we contend that SCP can also be used to streamline MSP negotiations by developing a coherent, integrated portfolio of sites for multiple sectors that depend on biodiversity being maintained in a good state, as a counterpoint to spatial priorities for those commercial and industrial activities that have negative environmental impacts. We demonstrate this in Algoa Bay, South Africa, given the social-ecological complexity of the bay, and its central location in the first national MSP process. In anticipation of this national process, a civil-society-led Community of Practice was established with a core team to lead stakeholder engagement, data acquisition and management, and SCP analyses. More than 500 stakeholders participated in the project and many contributed spatial data or engaged in expert-based participatory mapping. Spatial products were supplemented with existing, published datasets. Altogether, conservation targets were set for 115 biodiversity features and 22 nature-based activities, with the cost layer built from data on 10 commercial and industrial activities, cumulative pressures (n = 31) on ecosystems, and planning-unit area. All targets were met in 15% of the study area, of which only a third (4%) was outside of marine protected areas, demonstrating that it is possible to align multi-sector priorities for intact biodiversity. This approach can be widely applied in MSP to support sustainable ocean economies.
As a first step in stock identification of estuarine round‐herring Gilchristella aestuaria, a morphometric analysis of multiple standardised traits and body condition was conducted on samples from sites across the distribution range of the species, including freshwater and estuarine populations. Multivariate analyses, including a principal components analysis (PCA), revealed that sites on the same river system and sites in close geographic proximity, tend to share morphometric traits. Most of the variation in PCA was due to caudal fin length. Single traits were analysed with generalised additive models with river system location as the smooth term. Caudal fin length was strongly related to river systems, and to a lesser extent salinity and turbidity. Unlike previous local‐scale studies, this broad‐scale study did not support the notion of ecotypes based on eye diameter. Condition indices like body depth and relative weight were related to climatic conditions, salinity and turbidity, more than to river system. The findings agree with previous studies on phylogenetic history and limited gene flow in G. aestuaria, and suggest variation in environmental productivity that affect body condition in different populations. Subsequent research should examine temporal changes in traits like caudal fin length and body condition based on long‐term seasonal sampling. Safeguarding this potential resource may be enabled by adopting appropriate management methods based on delineation of stocks with different levels of productivity and connectivity, before widespread fishing of this species is promoted.
Despite its consequences for ecological processes and population dynamics, intra-specific variability is frequently overlooked in animal movement studies. Consequently, the necessary resolution to reveal drivers of individual movement decisions is often lost as animal movement data are aggregated to infer average or population patterns. Thus, an empirical understanding of why a given movement pattern occurs remains patchy for many taxa, especially in marine systems. Nonetheless, movement is often rationalized as being driven by basic life history requirements, such as acquiring energy (feeding), reproduction, predator-avoidance, and remaining in suitable environmental conditions. However, these life history requirements are central to every individual within a species and thus do not sufficiently account for the high intra-specific variability in movement behavior and hence fail to fully explain the occurrence of multiple movement strategies within a species. Animal movement appears highly context dependent as, for example, within the same location, the behavior of both resident and migratory individuals is driven by life history requirements, such as feeding or reproduction , however different movement strategies are utilized to fulfill them. A systematic taxa-wide approach that, instead of averaging population patterns, incorporates and utilizes intra-specific variability to enable predictions as to which movement patterns can be expected under a certain context, is needed. Here, we use intra-specific variability in elasmobranchs as a case study to introduce a stepwise approach for studying animal movement drivers that is based on a context-dependence framework. We examine relevant literature to illustrate how this context-focused approach can aid in reliably identifying drivers of a specific movement pattern. Ultimately, incorporating behavioral variability in the study of movement drivers can assist in making predictions about behavioral responses to environmental change, overcoming tagging biases, and establishing more efficient conservation measures.
This paper examines the efficacy of diatoms as bioindicators of water quality in the upper reaches of the Great Fish River following a period of reduced flow from drought conditions. Of the five sites, three were sampled three times in an 18 month period while the remaining two were sampled once. As a comparison, one headwater site within Mountain Zebra National Park, situated in the same district, was sampled. A total of 166 diatom taxa belonging to 29 genera were identified. Dominant taxa for the Great Fish River were identified as Amphora pediculus; Epithemia sorex; Nitzschia frustulum; Navicula veneta and Craticula buderi. These species, indicative of high nutrient concentrations and moderately saline to brackish conditions can tolerate low flow conditions. The Generic Diatom Index (GDI), the Specific Pollution sensitivity Index (SPI) the Biological Diatom Index (BDI) and the% Pollution Tolerant Valves (%PTV) – part of the UK Trophic Diatom Index (TDI) were used for interpretation of the results. The indices showed that this river is in poor condition. By comparison the headwater site in the Mountain Zebra National Park had Cocconeis placentula var. euglypta, Achnanthidium minutissimum and Cocconeis placentula var. lineata as dominant species and, using the same indices, the river was classified as in moderate to good condition with respect to water quality. When compared to a previous study (2010 – 2012), these sites showed a shift in dominant species indicating a change in water flow conditions and quality.
Meiobenthos (or meiofauna) are microscopic invertebrates that inhabit biofilms and interstitial spaces in rivers. They are diverse and extremely abundant, and they perform essential ecological functions by linking microbial production to higher trophic levels (e.g. macrobenthic invertebrates and fishes). However, meiobenthic communities remain poorly studied in Africa. Here, we sampled meio- and macrobenthic invertebrate communities associated with biofilms and sediments across an upstream–downstream gradient along the Olifants, Sabie and Crocodile rivers flowing through the Kruger National Park (KNP). We expected to link differences in community structure to environmental gradients as those rivers show different degrees of anthropogenic stress as they enter the park. Both meio- and macrobenthic communities differed across rivers and also structured along an upstream–downstream gradient. The upstream sites, which were the closest to the park borders, consistently showed a lower diversity in all three rivers. There, the invasive snail Tarebia granifera strongly dominated (making up 73% – 87% of the macrobenthos), crowding hard substrates, while concomitantly the abundances of biofilm-dwelling meiobenthos like nematodes and rotifers were substantially reduced. Nevertheless, the diversity and evenness of communities then tended to increase as water flowed downstream through the park, suggesting a beneficial effect of protected river reaches on benthic invertebrate diversity. However, for the Crocodile River, which makes up the southern border of the park, this trend was less conspicuous, suggesting that this river may experience the greatest threats. More generally, benthic invertebrate communities were driven by the concentrations of phosphates, sulphates, ammonium and organic matter and by substrate characteristics. Conservation implications: Meiobenthic organisms are very abundant in KNP rivers and react to environmental gradients; thus, they should be more considered for bio-monitoring or conservation of comprehensive assemblages of animals. Interestingly, protected reaches tended to show a reduced dominance of the invasive T. granifera and a higher diversity of benthic invertebrates.
Changes in behaviour and physiology are the primary responses of fishes to anthropogenic impacts such as climate change and over-fishing. Behavioural changes (such as a shift in distribution or changes in phenology) can ensure that a species remains in an environment suited for its optimal physiological performance. However, if fishes are unable to shift their distribution, they are reliant on physiological acclimatization (either by broadening their metabolic curves to tolerate a range of stressors, or by shifting their metabolic curves to maximize their performance at extreme stressors). However, since there are links between fish physiology and behaviour, changes to either of these trait groups may have reciprocal interactions. This paper reviews the current knowledge of the links between the behaviour and aerobic metabolic physiology of fishes, discusses these in the context of exploitation and climate change and makes recommendations for future research needs. The review revealed that our understanding of the links between fish behaviour and metabolic physiology is rudimentary. However, both are hypothesized to be linked to stress responses along the hypothalamic pituitary axis. The link between metabolic physiological capacity and behaviour is particularly important as both determine the response of an individual to a changing climate and are under selection by fisheries. While, it appears that all types of capture fisheries are likely to reduce the adaptive potential of fished populations to climate stressors, angling, which is primarily associated with recreational fishing, may induce the separation of natural populations by removing individuals with bold behavioural traits and potentially the physiological traits required to facilitate behavioural change. Future research should focus on assessing how the links between metabolic physiological capacity and behaviour influence catchability, the response to climate change drivers and post-release recovery. The plasticity of phenotypic traits should be examined under a range of stressors of differing intensity, in several species and life history stages. Future studies should also assess plasticity (fission or fusion) in the phenotypic structuring of social hierarchy and how this influences habitat selection. Ultimately, to fully understand how physiology is influenced by the selective processes driven by fisheries, long-term monitoring of the physiological and behavioural structure of fished populations, their fitness and catch rates are required. This will provide information that can be used by managers to retain behavioural and physiological trait diversity, which will be necessary to improve the resilience of fished populations to the impacts of climate change and safeguard the provision of resources for future generations.
The Nile Tilapia, Oreochromis niloticus, is a freshwater cichlid indigenous to the tropical and subtropical parts of the eastern and western Africa and is being cultured in the Lake Malawi catchment on the Tanzanian side. Historically, the Nile Tilapia has been successful in dispersing once it has been introduced into a catchment area. The probability of the Nile Tilapia successfully colonizing Lake Malawi is enhanced by many of its life history attributes including its fast growth rate, large size relative to native Oreochromis spp., and its diverse repertoire of feeding options. Where introduced, Nile Tilapia has had devastating impacts through competition or hybridization with native congenerics. We contend that the Nile Tilapia is a significant threat to the native fishes of Lake Malawi. With Lake Malawi harboring more species of fishes than any other freshwater lake in the world, a loss of species diversity due to the introduction of Nile Tilapia would be catastrophic for this unique system. Native fishes that in recent years provided 70% of the animal protein consumed in the country would be threatened by the colonization of the Nile Tilapia. We are convinced that should the Nile Tilapia become established in Lake Malawi it would (1) Cause the extirpation/extinction of native fishes, (2) Hybridize with endemic Oreochromis spp., and (3) Damage the livelihoods of existing artisanal fishermen.
Nearshore water quality can be highly impacted by anthropogenic activities ongoing along the coast, the effects of which on natural environments can be permanent and irreversible, with consequences for ecosystem biodiversity and functioning, as well as for associated services. Benthic filter feeders (e.g., mussels) provide several services for coastal regions, including improving water quality by reducing eutrophication, being a major source of food for humans, and as a habitat-forming species. Here, we seek to understand the role of benthic filter feeders in enhancing water quality in an urban coastal system in order to assess their role as ecosystem service providers and how they should be included in ecosystem-based evaluations. Using as a model False Bay, South Africa's largest natural bay and a socioeconomic hotspot, this multidisciplinary study was designed to identify possible pollution sources to a highly-urbanised coastal region, assess their effects on several biological and biogeochemical parameters, and evaluate the role of mussels in mitigating these anthropogenic inputs. We consider several sources of pollution, including nutrient loading from wastewater and river outflows, heavy metals, and aerosol deposition. We find that pollutant inputs are largely attenuated by the circulation of the bay and by the presence of filter feeders that bioaccumulate contaminants, thereby removing them from coastal waters. Our work thus emphasizes the potential for mussels and natural abiotic processes to ameliorate anthropogenic impacts, although these mitigation strategies are not without environmental risk. We recommend that such information should be included in national assessments used to develop appropriate strategies and policies for coastal environmental management and conservation.
Bioturbation is one of the most important processes that governs sediment biocenosis in intertidal systems. By facilitating oxygen penetration into anoxic layers, bioturbation alters the overall sediment biogeochemistry.
Global contamination of freshwater ecosystems by chemical compounds, such as pesticides, may exert high pressure on biologically-driven organic matter decomposition. These pollutants may also impair the quality of organic substrates for colonising invertebrates and reduce primary productivity by decreasing the abundance of phytoplankton. In southern Africa, increasing pesticide usage associated with macadamia plantations, in particular, presents a growing risk to freshwater ecosystems. Here, we examined macadamia (Macadamia integrifolia) leaf litter decomposition following exposure to three pesticides (i.e., Karate Zeon 10 CS (lambda-cyhalothrin), Mulan 20 AS (acetamiprid), Pyrinex 250 CS (chlorpyrifos)) used commonly in macadamia plantations, via an ex-situ microcosm approach. We examined mosquito colonisation of these microcosms as semi-aquatic macroinvertebrates which form a significant component of aquatic communities within standing waters. Macadamia leaf litter tended to decompose faster when exposed to Karate and Pyrinex pesticide treatments. Additionally, chlorophyll-a, conductivity, total dissolved solids, and pH differed among pesticide treatments and controls, with pesticides (Karate Zeon and Mulan) tending to reduce chlorophyll-a concentrations. Overall, pesticide treatments promoted mosquito (i.e., Culex spp.) and pupae abundances. In terms of dominant aquatic mosquito group abundances (i.e., Anopheles spp., Culex spp.), the effect of pesticides differed significantly among pesticide types, with Pyrinex and Mulan treatments having higher mosquito abundances in comparison to Karate Zeon and pesticide-free treatments. These findings collectively demonstrate that these pesticides used in the macadamia plantation may exert pressure on adjacent freshwater communities by shaping leaf-litter decomposition, semi-aquatic macroinvertebrate colonisation dynamics, and chlorophyll-a.
Nine egg capsules of the Rasptail Skate (Rostroraja velezi) were collected from their southernmost distributional range in northern Peruvian waters for their description. Egg capsules had a glossy black or dark brown color, with a subrectangular shape, slightly wider at posterior end than at anterior end. Egg capsules when observed under a stereoscope revealed a finely striated surface. Egg capsules ranged from 6.8 to 7.7 cm in length, 4.9 to 6.2 cm in maximum width, and 4.2 to 5.9 cm in minimum width. Anterior horn length was shorter than posterior horn length (0.29% vs. 0.58%). Differences in egg capsule surface and size were observed when compared to capsules of R. velezi from Baja California, Mexico, possibly due to differences in environmental conditions since individuals sampled belong to different marine provinces. Our results represent the second study to describe egg capsules for this species and the first in the Tropical Eastern Pacific marine province.
South Africa lacks research on the nutritional value of inland small fish species available to poor rural communities, despite the potential of such species to mitigate micronutrient deficiencies. Here we provide the first nutrient composition analysis for estuarine roundherring Gilchristella aestuaria, a widespread small fish species that is abundant in many estuarine and freshwater habitats. Protein, fat, calcium, iron, zinc and vitamin A content of G. aestuaria from five estuarine and two freshwater habitats were analysed. We found no difference in nutrient content between estuarine and freshwater habitats, and no significant correlation (Spearman’s test) between levels of each nutrient and variation in temperature, turbidity, pH, chlorophyll a, phosphates, nitrates and ammonia. Compared with other small fish species consumed in other countries, G. aestuaria has comparable iron, zinc, calcium, fat and protein, but very low levels of vitamin A. When considering the recommended dietary allowance of infants aged two or more, adult men and women, and pregnant and lactating women, we found that G. aestuaria is an excellent source of all these nutrients, except vitamin A.
Climate change, land cover change and the over–abstraction of groundwater threaten the existence of Groundwater-Dependent Ecosystems (GDE), despite these environments being regarded as biodiversity hotspots. The vegetation heterogeneity in GDEs requires routine monitoring in order to conserve and preserve the ecosystem services in these environments. However, the in–situ monitoring of vegetation heterogeneity in extensive, or transboundary, groundwater resources remain a challenge. Inherently, the Spectral Variation Hypothesis (SVH) and remotely-sensed data provide a unique way to monitor the response of GDEs to seasonal or intra–annual environmental stressors, which is the key for achieving the national and regional biodiversity targets. This study presents the first attempt at monitoring the intra–annual, spatio–temporal variations in vegetation heterogeneity in the Khakea–Bray Transboundary Aquifer, which is located between Botswana and South Africa, by using the coefficient of variation derived from the Landsat 8 OLI Operational Land Imager (OLI). The coefficient of variation was used to measure spectral heterogeneity, which is a function of environmental heterogeneity. Heterogenous environments are more diverse, compared to homogenous environments, and the vegetation heterogeneity can be inferred from the heterogeneity of a landscape. The coefficient of variation was used to calculate the α- and β measures of vegetation heterogeneity (the Shannon–Weiner Index and the Rao's Q, respectively), whilst the monotonic trends in the spatio–temporal variation (January–December) of vegetation heterogeneity were derived by using the Mann–Kendall non–parametric test. Lastly, to explain the spatio–temporal variations of vegetation heterogeneity, a set of environmental variables were used, along with a machine-learning algorithm (random forest). The vegetation heterogeneity was observed to be relatively high during the wet season and low during the dry season, and these changes were mainly driven by landcover- and climate–related variables. More specifically, significant changes in vegetation heterogeneity were observed around natural water pans, along roads and rivers, as well as in cropping areas. Furthermore, these changes were better predicted by the Rao's Q (MAE = 5.81, RMSE = 6.63 and %RMSE = 42.41), than by the Shannon–Weiner Index (MAE = 30.37, RMSE = 33.25 and %RMSE = 63.94). These observations on the drivers and changes in vegetation heterogeneity provide new insights into the possible effects of future landcover changes and climate variability on GDEs. This information is imperative, considering that these environments are biodiversity hotspots that are capable of supporting many livelihoods. More importantly, this work provides a spatially explicit framework on how GDEs can be monitored to achieve Sustainable Development Goal (SDG) Number 15.
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