Ursula M. Scharler

University of KwaZulu-Natal | ukzn · School of Life Sciences

Anthropogenic pressures are increasing in coastal ecosystems globally, yet identifying robust indicators of change and managing coastal resources can be complicated by phenotypic plasticity and differential life-history responses of key organisms. We illustrate this using biogeochemical and sandprawn (Kraussillichirus kraussi) response metrics alon...

Biodiversity is essential for estuarine ecosystems' functioning, resilience, and persistence. While biodiversity assessments provide some insight into the ecosystem state, they cannot quantify every aspect of ecosystem-level function. We assessed aspects of estuarine ecosystem function and pinpointed taxa of interest that fulfil specific roles in e...

Capturing ecological data variability in food web models is an important step for improving model representation of empirical systems. One approach is to use linear inverse modelling and Markov Chain Monte Carlo (LIM-MCMC) techniques to set up an inverse LIM problem using empirical data constraints, and then sample multiple plausible food webs from...

Ecosystems are often modelled as food webs or ecological networks, which map energy flows between species or functional groups. While there are multiple sources of uncertainty in ecological network models, a fundamental difficulty is quantifying the uncertainty of flow magnitudes, even if derived from field data, limiting the degree to which the mo...

The foundation of a healthy marine environment is central to the ecosystem-based management approach and is recommended for achieving sustainable development outcomes in marine spatial planning. Algoa Bay, South Africa, features a metropolitan area, protected natural area and hosts a range of uses that are closely interconnected with the health of...

Globally estuaries are under increasing pressure from human development impacts as well as the growing effects of climate change that is already, and increasingly so, causing major changes in events such as droughts. Although droughts are regular occurrences and are projected to become progressively more significant in many parts of the world, thei...

Network analysis of complex systems is a rapidly growing field. Both theoretical and empirical network studies have permeated many different ecological, biological, social, and economic fields, investigating the interrelationships between nodes as structural and functional attributes in static, time-dynamic, or spatially explicit formats. We consid...

Background: Pollution – unwanted waste released to air, water, and land by human activity – is the largest environmental cause of disease in the world today. It is responsible for an estimated nine million premature deaths per year, enormous economic losses, erosion of human capital, and degradation of ecosystems. Ocean pollution is an important, b...

Background: Pollution – unwanted waste released to air, water, and land by human activity – is the largest environmental cause of disease in the world today. It is responsible for an estimated nine million premature deaths per year, enormous economic losses, erosion of human capital, and degradation of ecosystems. Ocean pollution is an important, b...

Pollution – unwanted waste released to air, water, and land by human activity – is the largest environmental cause of disease in the world today. It is responsible for an estimated nine million premature deaths per year, enormous economic losses, erosion of human capital, and degradation of ecosystems.Ocean pollution is an important, but insufficie...

Freshwater availability is a major topic in scientific literature and the public domain. Estuaries are complex and dynamic ecosystems that depend on freshwater inflow from their catchments and exchange with the marine environment. Catchment forcings are subject to shifts in frequency and intensity due to regional hydrological variability over time....

Prolonged mouth closure in estuaries is often associated with hypersalinity, mainly as a result of reduced freshwater inflow. However, on the KwaZulu-Natal coast, South Africa, temporarily open/closed estuaries have a tendency towards hyposalinity during closed mouth conditions, primarily because of their perched nature reducing saltwater intrusion...

Ecological Network Analysis (ENA) has provided insights into the structure, function, and transformation of ecosystems for more than forty years. Key insights from ENA focus on how the patterns of directed weighted transactions among system components (e.g., species, functional groups, economic sectors) create emergent and often unexpected relation...

Zooplankton community composition, biomass and metabolism can vary drastically over space and time in subtropical estuaries. Changing environmental conditions can affect communities differently, depending on the characteristics of the species involved. In the present study, we compared the rates of oxygen consumption of the dominant zooplankton tax...

Sediment grain size and organic matter influences the distribution of macrozoobenthic fauna. These parameters also influence bioavailability and toxicity of contaminants in aquatic systems, because sediment is the sink and source for most contaminants. These sediment parameters therefore potentially confound sediment toxicity results when using ina...

In this paper, we identified seven ecological network analysis (ENA) metrics that, in our opinion, have high potential to provide useful and practical information for environmental decision-makers and stakeholders. Measurement and quantification of the network indicators requires that an ecosystem level assessment is implemented. The ENA metrics co...

Nearshore marine ecosystems can benefit from their interaction with adjacent ecosystems, especially if they alleviate nutrient limitations in nutrient poor areas. This was the case in our oligo- to mesotrophic study area, the KwaZulu-Natal Bight on the South African subtropical east coast, which is bordered by the Agulhas current. We built stoichio...

Input data for Ecopath Carbon networks of the DE, TM and RB susbsystems. P/B = Production/ Biomass, Q/B = Consumption/Biomass, EE = Ecotrophic Efficiency. EE and flows to detritus are proportions. (DOCX)

Diet compositions used in initial unbalanced Ecopath carbon networks. Group numbers refer to those in Table 4.1. Rows represent prey and columns represent predators. Groups 1 and 2 refer to primary producers and therefore do not require a predator column. I = imports. The first value in the column for group 28 was used in the DE networks and the se...

Demersal functional groups and representative species of each sub-region where known. (DOCX)

C:N and C:P ratios used to construct nitrogen and phosphorus networks. DE = Durban Eddy, TM = Thukela Mouth, RB = Richards Bay. (DOCX)

Carbon, nitrogen and phosphorus biomasses (g m-2) of groups in each network. Bold values represent biomasses estimated by Ecopath. (DOCX)

Nutrient limitations calculated from ascendency analysis, and turnover times in a node. DE: Durban Eddy, TM: Thukela Mouth, RB: Richard Bay. S: summer, w: winter. LN: Limiting Nutrient. C: carbon, N: nitrogen, P: phosphorus. (DOCX)

From 25th until 27th of September 2017, the Landesbetrieb für Küstenschutz, Nationalpark und Meeresschutz Schleswig Holstein (NPV) and the Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung (AWI) organized a workshop on food web metrics and indices and its applicability to assess the functioning of food webs and status in a ho...

Background and Significance of the topic: This chapter contributes to the documentation of novel network-based resilience concepts to socio-ecological systems. Although the resilience concept has been studied in depth in ecological systems, it surely has relevance outside this area and in recent years has been a main domain of study for socioeconom...

Estuarine carbon fluxes constitute a significant component of coastal CO2 emissions and nutrients recycling, but high uncertainty is still present due to the heterogeneity of these areas. Although South Africa has nearly 300 estuaries, very little is known about their contribution to carbon emissions or sequestration. This study aims to provide a f...

Temperature is one of the more important factors affecting metabolism and fitness of aquatic ectothermic animals. The present study aimed, therefore, at quantifying and comparing the oxygen consumption rates of several subtropical macrobenthos organisms living in two South African estuarine systems. Oxygen fluxes were measured in the laboratory at...

Anthropogenic intervention along with natural variability can both influence and compromise continued ecosystem functioning. Ecological network analysis (ENA) was used to explore ecosystem functioning following disturbances to food web networks of a South African estuary, Mdloti, under different seasons. Keystone species, in particular, play an imp...

The importance of fluctuations in rainfall and riverine flow on ecosystem functioning in a permanently open estuary (POE), the Mlalazi, and 2 temporarily open/closed estuaries (TOCEs), the East Kleinemonde and Mpenjati, were investigated. These systems, located on the east coast of South Africa, are strongly influenced by seasonal changes in rainfa...

Poster detailing and describing bacterial ecology with regards to bacterial numbers, biomass and productivity along the KZN Bight during the sampling period undertaken for the ACEP II project.

Important drivers of woody cover in African savannas are rainfall, soil and nutrients, and disturbance factors, such as fire and herbivory. However, very little is known about how these drivers influence woody cover at specific height classes. The main aim of this study was to identify which of these drivers are the best predictors of woody cover a...

The KwaZulu-Natal Bight is a shallow indentation of the eastern seaboard of South Africa, characterised by a narrow (45 km wide) extension of the continental shelf, with a shelf break at about 100 m. It has a complex hydrography: the waters of the bight are derived from the fast-flowing, southward-trending Agulhas Current, which is fed mostly by th...

Riverine influences on nearshore oceanic habitats often have detrimental consequences leading to algal blooms and hypoxia. In oligo- to mesotrophic systems, however, nutrient delivery via rivers may stimulate production and even be a vital source of nutrients, as may nutrient supplements from upwelling. We investigated the nutrient content (C, N, P...

Nearshore marine environments are influenced by an array of variables that can either be land-derived or of marine origin, and nearshore phytoplankton communities may differ in their taxonomic composition and biomass in response to such variables. The KwaZulu-Natal Bight (hereafter referred to as ‘the bight’) is an oligo-mesotrophic, nearshore ocea...

The KwaZulu-Natal Bight comprises the only sizeable shelf region on the eastern coast of South Africa, and is influenced by both the Agulhas Current on its seaward side and rivers and estuaries on its landward side. Established knowledge of the effect of the Agulhas Current includes the influence on nutrient concentrations in the bight of a semi-pe...

Ciliates play an important role in overall grazing rates, nutrient regeneration and secondary production in estuarine systems. We investigated the genera richness, abundance, cell volume and biomass of ciliates under different environmental conditions, including hypersalinity in an estuarine lake system (Lake St. Lucia, South Africa). A reverse sal...

This study aimed to determine the variability of carbon and nitrogen elemental content, stoichiometry and diet proportions of invertebrates in two sub-tropical estuaries in South Africa experiencing seasonal changes in rainfall and river inflow. The elemental ratios and stable isotopes of abiotic sources, zooplankton and macrozoobenthos taxa were a...

We propose that woody plant dynamics can be influenced both structurally and compositionally by long term exposure to disturbance (e.g. fire and herbivory).

Our study investigated the carbon:nitrogen:phosphorus (C:N:P) stoichiometry of mangrove island of the Mesoamerican Barrier Reef (Twin Cays, Belize). The C:N:P of abiotic and biotic components of this oligotrophic ecosystem was measured and served to build networks of nutrient flows for three distinct mangrove forest zones (tall seaward fringing for...

Robustness is a universal feature of ecological systems which promotes sustainability over time. Robustness of an aquatic ecosystem, specifically an estuarine system, is investigated here using indicators derived from ecological network analysis. Estuaries provide us with many ecosystem services and these are consequently prone to face anthropogeni...

The endemic amphipod Grandidierella lignorum is an organism potentially suited to the toxicity testing of coastal water and sediment in South Africa. The ranges of salinity and temperature at which G. lignorum can be used for toxicity testing were investigated under laboratory conditions, in order to avoid potential confounding effects induced by t...

Strongly varying water levels and turbidities are typical characteristics of the large shallow estuarine lake system of St. Lucia, one of the largest on the African continent. This theoretical study investigated the combined effects of variable water depth and turbidity on seasonal pelagic and benthic microalgae production using a mathematical mode...

Estuaries are considered stressed environments because of the high variability in their physico-chemical properties; however, estuarine biota are able to thrive in this perceived stressful environment. The environmental homeostasis hypothesis states that this natural stress provides estuarine communities with the ability to reach stability by compe...

Marine waters off the African east coast are generally oligotrophic, and localised fluvial and upwelling processes can be critical in driving marine food webs. The KwaZulu-Natal Bight in South Africa provides an example for investigating this, with nutrient inputs suggested to be provided by an upwelling cell and the second largest river in the cou...

Almost all the 258 estuarine systems of South Africa have been the subject of at least some physical, chemical and biological investigations, but the St Lucia system is arguably the best studied of these (Whitfield, 2000). This is due in part to its complexity and ecological importance, but also to its large size, equalling about 50% of all of Sout...

Penaeid prawns are targeted in the Thukela Bank shallow-water trawling grounds in south-eastern Africa. Based on previous studies, these targeted prawns are assumed to primarily use 2 large estuaries (St. Lucia and Richards Bay/Mhlathuze) as nurseries on the KwaZulu-Natal (KZN) coast, which comprise over 80% of the estuarine habitat in the region....

In this paper, we use data gathered from the Sylt–Rømø Bight Ecosystem in Germany to conduct an ecological network analysis. Specifically, we perform Network Environ Analysis to compare with results already published using EcoPath, which incorporates the ecological network analysis package NETWRK.We focus on the issue of model aggregation in that t...

ABSTRACT: Penaeid prawns are targeted in the Thukela Bank shallow-water trawling grounds in south-eastern Africa. Based on previous studies, these targeted prawns are assumed to primarily use 2 large estuaries (St. Lucia and Richards Bay/Mhlathuze) as nurseries on the KwaZulu-Natal (KZN) coast, which comprise over 80% of the estuarine habitat in th...

Whole food-web studies of mangrove ecosystems are rare. However, several components of the flora and fauna and selected linkages from primary food sources (primary producers and detritus) and between heterotrophs have been studied in detail. Considerable attention has been given to carbon imports and exports from mangrove ecosystems in the form of...

In this chapter, we provide an overview of the rise of ecological modeling as a problem-solving tool for environmental management including a review of some of the more important and widely used models. While there has been a great increase in the computing power available to simulate ecological systems, a few fundamental concepts, which were alrea...

Ecosystem modelling allows for an understanding of the structure and functioning of data-limited ecosystems provided that models undergo extensive sensitivity analyses to explore the levels of uncertainty. We explored one such data-limited system, the KwaZulu-Natal (KZN) Bight, a river-influenced bight on the east coast of South Africa. Potential s...

This research compares two existing methodologies, mixed trophic impact analysis and utility analysis, which use network analysis to evaluate the direct, pair-wise, and indirect, holistic, ecological relations between ecosystem compartments. The two approaches have many similarities, but differ in some key assumptions which affect both the final re...

The construction of material and energy budgets within ecosystems has long been accomplished via manual calculation. Recently, optimization techniques have been adapted to automate the procedure, but these methods require assumptions that may not square with biological reality. Two algorithms are developed to construct ecosystem budgets under minim...

Information indices from Ecosystem Network Analysis (ENA) can be used to quantify the development of an ecosystem in terms of its size and organization. There are two types of indices, i.e. absolute indices that describe both the size and organization of ecosystem (Total System Throughput (TST)—system size, Ascendancy (A)—size of organized flows an...

Ecological network analysis (ENA) is a systems-oriented methodology to analyze within system interactions used to identify holistic properties that are otherwise not evident from the direct observations. Like any analysis technique, the accuracy of the results is as good as the data available, but the additional challenge is that the data need to c...

Four Eastern Cape estuaries, the Kromme, Gamtoos, Swartkops and Sundays Estuaries have a permanent connection to the adjacent ocean, but differ in the amount of freshwater inflows as well as in the land-use patterns in their respective catchment areas. The nutrient loading to the four estuaries in terms of phosphate, nitrate, nitrite and ammonia th...

Aquatic ecosystems worldwide provide important resources for human populations. Estuarine and marine habitats provide many essential ecosystem services, including climate regulation, yet currently these systems are impacted over large areas through over-exploitation and degradation. Moreover, aquatic ecosystems represent an integrative picture of e...

Ecological networks are quantitative, graph-based descriptions of ecosystems, consisting of compartments (trophospecies and nutrient pools) that exchange fluxes of nutrients or energy. Previous research pointed out how the model's design is a crucial task that can heavily influence analyses results, and how merging compartments for the purpose of c...

Carbon flow networks of the Kromme, Swartkops and Sundays estuaries, situated on the south coast of South Africa, were analysed using ecological network analysis. A major difference between the three estuaries is the freshwater inflow regimes: The Kromme Estuary receives very little freshwater (annual mean 0.07 m−3 s−1), the Swartkops Estuary recei...

Assessments of trophic structure through ecological network analysis (ENA) have been done in a wide variety of estuarine and coastal environments. For example, some have used it to compare trophic structures within ecosystems focusing on temporal conditions (Baird and Ulanowicz 1989; Baird et al. 1998) and among ecosystems focusing on spatial condi...

This book provides a synthesis of theoretical and empirical food web research. Whether they are binary systems or weighted networks, food webs are of particular interest to ecologists by providing a macroscopic view of ecosystems. They describe interactions between species and their environment, and subsequent advances in the understanding of their...

The response of mangrove ecosystems to environmental change can be examined with stable isotopic tracers of C and N. The δ13C and δ15N of a taphonomic series of Rhizophora mangle L. (Red mangrove) leaves were analyzed from Twin Cays, Belize, to facilitate reconstruction of past mangrove ecosystems. On Twin Cays, fresh leaves of dwarf R. mangle tree...

Three estuaries with differing catchment use and freshwater input were investigated in terms of their nutrient status, phytoplankton biomass, freshwater inflow and salinity between 1993 and 1995. The nutrients analysed include phosphate, nitrate, nitrite, ammonia and total particulate nitrogen. All the parameters were investigated for their relatio...

Ecological water reserves are part of the new water management philosophy in South Africa. The estuaries are threatened by excessive water abstraction from their rivers and the consequent reduction in freshwater input. This study was conducted to further improve our understanding of freshwater requirements in terms of nutrients for South African es...

The natural runoff from the Kromme River catchment area has been severely restricted by impoundments with storage capacities exceeding the mean annual runoff (MAR). As a consequence, freshwater input into the Kromme Estuary has been drastically reduced and the estuary itself has been labelled as 'freshwater-starved'. The annual allocation of storag...

The natural runoff from the Kromme River catchment area has been severely restricted by impoundments with storage capacities exceeding the mean annual runoff (MAR). As a consequence, freshwater input into the Kromme Estuary has been drastically reduced and the estuary itself has been labelled as 'freshwater-starved'. The annual allocation of storag...