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Parasites have deleterious effects on their hosts, often resulting in altered host behavior or increased energy expenditure. When organisms are exposed to suboptimal environments, parasite loading may increase. Microbialite pools along the warm temperate South African coastline have been hypothesized as refugia for Epaulette gobies (Coryogalops sordidus, Gobiidae) when they are outside of their previously known subtropical distribution. The aim of this study was to determine if C. sordidus individuals infected with metacercarial cysts display higher metabolic rates or different swimming behavior compared to noninfected individuals. We measured each goby's swimming performance using a critical station-holding speed (Ucrit) test (n = 60) and visually scored their swimming behavior (n = 52) during these measurements. Also, we measured the metabolic rate of gobies using an intermittent flow respirometer system to determine standard metabolic rate (SMR) and maximum metabolic rate (MMR) from gobies at 21°C before and after swimming trials. Metacercarial load carried by infected gobies seemingly had no impact on the host's energetics (SMR or MMR), swimming ability (as repeated Ucrit tests), or swimming behavior compared to noninfected gobies. Thus, the metacercarial intensity observed in gobies in the current study appeared to have no impact on host swimming performance or behavior. Furthermore, the swimming capacity observed for C. sordidus, in general, suggests that this goby is a poor swimmer compared to other gobiid species.
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Perciformes , Natación , Humanos , Animales , Metabolismo Energético , AmbienteRESUMEN
A focused diagnosis of ecosystem health in two South African estuaries (Kromme and Gamtoos) was conducted. Four pollution indices were used, i.e., geoaccumulation (Igeo), ecological risk (RI), contamination factor (CF) and pollution load index (PLI), to assess toxicity levels of metal contaminants in relation to background values. The Igeo results (11.1 %) can be classified as contaminated, with Cd, the only element with high values in both estuaries. Likely sources (herbicides, pesticides) of Cd are used in the agricultural dominated catchments. There was a high concentration of Mn (13.4 ± 2.51 and 12.3 ± 1.13 µg·g-1) and Fe (1289 ± 243 and 1291 ± 130 µg·g-1) at site 4 for Gamtoos and Kromme estuary respectively compared to the other metal elements. Although results indicate low metal contamination, with increasing global anthropogenic pressure, continuous monitoring should be prioritised to assist in managing estuarine systems that support a wide range of socio-economic and ecosystem services.
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Drought prone, arid and semi-arid ecosystems are challenging to restore once degraded due to low levels of natural recruitment and survival of reintroduced plants. This is evident in the restoration of degraded succulent thicket habitats in the Albany Subtropical Thicket Biome located in South Africa. The current restoration practice for this ecosystem focuses predominantly on reintroducing Portulacaria afra L. Jacq., which is naturally dominant in terms of cover and biomass, but largely absent in regions degraded by domestic livestock. This has been achieved by planting unrooted cuttings with limited consideration of soil water availability in a drought-prone ecosystem. This study tests the effects of the timing of water availability after planting on the root development of P. afra cuttings. Cuttings were harvested from seven individual plants and grown in a glasshouse setting. Eighty four cuttings were taken from each individual, twelve for each of the seven watering treatments per individual plant. The treatments represented a time-staggered initial watering after planting, including: on the day of planting, 4 days, 7 days, 14 days, 21 days, and 28 days after planting. After 32 days, all treatments were watered on a bi-weekly basis for two weeks; a control treatment with no watering throughout the experiment was included. The proportion of rooted cuttings per treatment and dry root mass were determined at the end of the experimental period (day 42). The early onset of watering was associated with a higher percentage of rooting (X2(5) = 11.352, p = 0.045) and had a weak, but non-significant, impact on the final dry root mass (F5,36 = 2.109, p = 0.0631). Importantly, no clear rooting window within 28 days was detected as the majority of cuttings exhibited root development (greater than 50% of cuttings rooted for each individual parent-plant); this suggests that watering at the time of planting P. afra cuttings in-field for restoration may not be necessary. An unexpected, but important, result was that parent-plant identity had a strong interaction with the accumulation of root mass (F36,460 = 5.026, p < 0.001; LR7 = 122.99, p < 0.001). The control treatment, which had no water throughout the experiment, had no root development. These findings suggest that water availability is required for the onset of rooting in P. afra cutting. However, the duration of the experiment was insufficient to detect the point at which P. afra cuttings could no longer initiate rooting once exposed to soil moisture, and thus no rooting window could be defined. Despite harvesting material from the same source population, parent-plant identity strongly impacted root development. Further work is required to characterise the rooting window, and to explore the effect of parent-plant condition on in-field and experimental restoration results; we urge that experiments using P. afra closely track the parent-source at the individual level as this may be a factor that may have a major impact on results.
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Caryophyllales , Ecosistema , Biomasa , Suelo , SudáfricaRESUMEN
Microbialites are formed through two processes, the trapping and binding of sediment grains and mineral precipitation. Sediment trapping and binding result in coarse sandy textures, whereas fine micritic textures are produced by mineral precipitation. Although well-studied modern microbialites (e.g. Bahamas and Shark Bay) are formed through the former process, purely trapped-and-bound examples are rare throughout the geologic record and limited to shallow-marine environments. Through the use of conventional microscopy and 3D micro-computed tomography (µ-CT) scanning, this study found that South African coastal microbialites have a primarily mineral precipitated texture, although detrital material is included sporadically. Furthermore, these modern microbialites exhibit both micritic and fibrous layering with high porosity. The novel use of 3D microtomography rotational scans has revealed that microbialites are extensively burrowed by metazoan activity and was also able to distinguish the occurrence and distribution of heavy minerals and detrital shell material in the samples. Some of the detrital grains appeared to be accidental/random inclusions, while in other cases the metazoan burrows provided space for the accumulation of sediment once abandoned. In both cases, sediment was incorporated as a product of intermittent accumulation, rather than systematic trapping and binding. The microfabric texture of South African microbialites is therefore a function of both biological (e.g. microbially mediated precipitation) and environmental (e.g. sporadic sediment deposition and inorganic cementation) influence. Overall, the findings presented here highlight the importance of these systems regarding microbialite formation, ichnology and taphonomy.
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Sedimentos Geológicos , Microscopía , Animales , Bahamas , Minerales , Microtomografía por Rayos XRESUMEN
Functional drivers of phytoplankton that can potentially form harmful algal blooms (HABs) are important to understand given the increased prevalence of anthropogenic modification and pressure on coastal habitats. However, teasing these drivers apart from other influences is problematic in natural systems, while laboratory assessments often fail to replicate relevant natural conditions. One such potential bloom-forming species complex highlighted globally is Mesodinium cf. rubrum, a planktonic ciliate. This species occurs persistently in the Sundays Estuary in South Africa yet has never been observed to "bloom" (> 1,000 cell.ml-1). Modified by artificial nutrient-rich baseflow conditions, the Sundays Estuary provides a unique Southern Hemisphere case study to identify the autecological drivers of this ciliate due to artificial seasonally "controlled" abiotic environmental conditions. This study utilised a three-year monitoring dataset (899 samples) to assess the drivers of M. cf. rubrum using a generalised modelling approach. Key abiotic variables that influenced population abundance were season and salinity, with M. cf. rubrum populations peaking in summer and spring and preferring polyhaline salinity regions (>18) with pronounced water column salinity stratification, especially in warmer months. This was reflected in the diel vertical migration (DVM) behaviour of this species, demonstrating its ability to utilise the optimal daylight photosynthetic surface conditions and high-nutrient bottom waters at night. The only phytoplankton groups clearly associated with M. cf. rubrum were Raphidophyceae and Cryptophyceae. Although M. cf. rubrum reflects a niche overlap with the dominant HAB-forming phytoplankton in the estuary (the raphidophyte, Heterosigma akashiwo), its reduced competitive abilities restrict its abundance. In contrast, the mixotrophic foraging behaviour of M. cf. rubrum exerts a top-down control on cryptophyte prey abundance, yet, the limited availability of these prey resources (mean < 300 cells ml-1) seemingly inhibits the formation of red-water accumulations. Hydrodynamic variability is necessary to ensure that no single phytoplankton HAB-forming taxa outcompetes the rest. These results confirm aspects of the autecology of M. cf. rubrum related to salinity associations and DVM behaviour and contribute to a global understanding of managing HABs in estuaries.
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Cilióforos , Estramenopilos , Estuarios , Floraciones de Algas Nocivas , FitoplanctonRESUMEN
Whereas the anthropogenic impact on marine biodiversity is undebated, the quantification and prediction of this change are not trivial. Simple traditional measures of biodiversity (e.g. richness, diversity indices) do not capture the magnitude and direction of changes in species or functional composition. In this paper, we apply recently developed methods for measuring biodiversity turnover to time-series data of four broad taxonomic groups from two coastal regions: the southern North Sea (Germany) and the South African coast. Both areas share geomorphological features and ecosystem types, allowing for a critical assessment of the most informative metrics of biodiversity change across organism groups. We found little evidence for directional trends in univariate metrics of diversity for either the effective number of taxa or the amount of richness change. However, turnover in composition was high (on average nearly 30% of identities when addressing presence or absence of species) and even higher when taking the relative dominance of species into account. This turnover accumulated over time at similar rates across regions and organism groups. We conclude that biodiversity metrics responsive to turnover provide a more accurate reflection of community change relative to conventional metrics (absolute richness or relative abundance) and are spatially broadly applicable. This article is part of the theme issue 'Integrative research perspectives on marine conservation'.
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Biodiversidad , Invertebrados/fisiología , Fitoplancton/fisiología , Vertebrados/fisiología , Zooplancton/fisiología , Animales , Océano Atlántico , Ecosistema , Alemania , Océano Índico , Mar del Norte , SudáfricaRESUMEN
Upstream anthropogenic perturbations can dramatically affect estuarine water quality, especially in small systems where water retention times are high. Management of these modified ecosystems often requires direct interventions to prevent detrimental long-term effects. The heavily urbanized and temporarily closed Zandvlei Estuary in South Africa has a long history of anthropogenic manipulation, and therefore acts as an ideal case-study to gauge reactive management practices. Continued deterioration of estuarine water quality and ecological functioning prompted the adoption of an adaptive management approach. Subsequent management interventions to increase salinity variability and nutrient removal included the (1) adoption of a mouth management plan, (2) regular harvesting of submerged vegetation, and (3) removal of flow obstructions. Physico-chemical and nutrient monitoring data (2010-2018) were assessed to document the response of phytoplankton to these interventions. Time-series analysis indicated an upward trend in salinity throughout the estuary. This corresponded with a temporal decline in phytoplankton biomass levels and was supported by model results that highlighted a strongly inverse relationship with salinity. The frequency of high-biomass events (>80⯵gâ¯Chl-aâ¯l-1) also declined in each of the designated estuarine zones. In April 2012, an extensive harmful algal bloom (HAB) of Prymnesium parvum (Prymnesiophyceae) was recorded (~530⯵gâ¯Chl-aâ¯l-1) in the estuary, culminating in hypoxic conditions (O2â¯<â¯2â¯mgâ¯l-1) and fish kills. However, the subsequent mechanical breaching of the mouth has prevented reoccurrences of P. parvum. Similarly, more saline conditions arising from increased marine connectivity reduced the abundance of the previously dominant Bacillariophyceae and Chlorophyceae classes. The overall improvement in water quality validates the efficacy of management interventions aimed at restoring and conserving ecosystem functionality. Yet, these efforts are a deviation from natural estuarine functioning and thus a 'catchment to coast' approach that incorporates upstream nutrient mitigation measures is needed to achieve sustainable long-term management objectives.
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Conservación de los Recursos Naturales/métodos , Monitoreo del Ambiente , Estuarios , Eutrofización , Fitoplancton/fisiologíaRESUMEN
Hydrological regimes are key in shaping the structure of phytoplankton communities in estuaries. Because anthropogenic disturbances often alter the quantity and quality of riverine inputs, this research focused on investigating phytoplankton dynamics in the St. Lucia Estuary, since being reconnected to the Mfolozi River. Due to the closed mouth state of the estuary, the input from the river resulted in oligohaline (≥5) conditions and the characteristic reverse salinity gradient to persist throughout the study (i.e. one year). Model results indicated that phytoplankton communities were structured by rainfall, light transmittance and depth, while shifts between dominant groups were driven by salinity and flow season. The persistence of chlorophytes and euglenophytes as the co-dominant functional group indicates the freshening and nutrient-enriched nature of the river. This study provides the first detailed account documenting the response of the phytoplankton community to recent restoration efforts in the St Lucia Estuary, a Ramsar Site.
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Monitoreo del Ambiente/métodos , Estuarios , Fitoplancton/crecimiento & desarrollo , Ríos/química , Ciclo Hidrológico , Chlorophyta/crecimiento & desarrollo , Euglénidos/crecimiento & desarrollo , Dinámica Poblacional , Salinidad , Estaciones del Año , Sudáfrica , Movimientos del AguaRESUMEN
Consumer responses to altered resource conditions can vary depending on dietary preference, resource characteristics and secondary resource features such as shelter. These can have cascading effects, especially if the consumed resource impacts on overall ecological functioning. In this study, we assessed the dietary composition of grazer communities following seasonal changes in the characteristics of their staple food-source (macroalgae). This was conducted in the living stromatolite pools growing along the coast of South Africa. Stable isotope mixing models suggested that following macroalgal bleaching in summer, metazoan consumers shifted their diet from predominantly macroalgae to a generalist composition. This has important implications for the integrity of the stromatolite matrix and its layered deposition. Where previously in winter stromatolite microalgae comprised a minor component of metazoan consumer diets, in summer, following a change in the resource conditions of macroalgae, microalgae featured more prominently in grazer diets. This seasonal grazing pressure on stromatolite-related resources probably promotes the pattern of annual layering observed in the stromatolite accretion. It also demonstrates a mechanism whereby grazer dietary shifts following a change in their preferred food resource can affect the ecosystem structure of their environment, specifically the stromatolite layering process which responds to microalgal growth or grazing conditions.
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Grazing and burrowing organisms usually homogenise microalgal mats that form on benthic sediments of many aquatic ecosystems. In the absence of this disruption, microalgal mats can accrete laminated deposits (stromatolites). Stromatolites are rare in modern coastal ecosystems, but persist at locations where metazoans are largely excluded. This study aimed to assess the trophic structure at stromatolite locations where metazoans co-occur, to determine the grazing influence exerted by the metazoans on the stromatolite-forming microalgae (cyanobacteria and diatoms). Stable isotope signatures (δ13C and δ15N) were used as food-web tracers and dietary composition of consumers was calculated using source mixing models. Results clearly demonstrate that the dominant macrofaunal grazers do not utilise stromatolite material as a food resource, but rather subsist on autochthonous macroalgae. For instance, the mean (±SD) dietary composition of two of the most abundant grazers, Melita zeylanica (Amphipoda) and Composetia cf. keiskama (Polychaeta), consisted of 80 ± 11% and 91 ± 7% macroalgae, respectively. This suggests that the stromatolite-forming benthic microalgae are not disrupted significantly by grazing pressures, allowing for the layered mineralisation process to perpetuate. Additionally, grazers likely have a restrictive influence on pool macroalgae, maintaining the competitive balance between micro- and macroalgal groups.
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Organismos Acuáticos , Cadena Alimentaria , Animales , Carbono/metabolismo , Cianobacterias , Diatomeas , Ecosistema , Microalgas , Nitrógeno/metabolismoRESUMEN
Microbialites, bioaccretionary structures formed during the growth and metabolism of microorganisms (principally cyanobacteria) were the dominant lifeform in shallow late-Archean and Proterozoic oceans. During the Cambrian radiation of metazoan life, which began ~540 Mya, microbialite abundance and diversity further declined following a peak in the Mesoproterozoic. Notwithstanding contention, grazing and bioturbation effects of metazoans have been hypothesized as the dominant driver of modern microbialite scarcity. However, this metazoan-microbialite exclusion has not been fully explored in the few extant microbialites. Here we provide further evidence showing that living marine layered microbialites (stromatolites) coexist with a persistent assemblage of benthic macro-invertebrates, as has previously been demonstrated in some thrombolitic (clotted) microbialites. Surprisingly, these metazoans have active habits, such as burrowing, which should be expected to disrupt the layered matrix. As other studies have shown, through a network of burrows, metazoans can exploit local diurnal oxygen refugia within microbialites as well as escape predation. Our results, therefore, add novel evidence in support of the hypotheses that geologically, metazoans are not always incompatible with stromatolites, while ecologically, microbialites may act as micro-refugia for modern metazoans and historically have performed a similar inferred role in past ecosystems.
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Cianobacterias , Invertebrados , Animales , EcosistemaRESUMEN
Extant marine stromatolites act as partial analogues of their Achaean counterparts, but are rare due to depleted ocean calcium carbonate levels and suppression by eukaryotic organisms. Unique, peritidal tufa stromatolites at the interface between marine and freshwater inputs were discovered in South Africa in the past decade. Our aim was to investigate the benthic microalgal community (green algae, diatoms and cyanobacteria) of these stromatolites to assess succession and dominance patterns using real-time, in situ measurements of algal concentrations and composition. These biological measurements were modelled using generalized linear modelling (GLM) multivariate statistics against water physical and chemical parameters measured at regular monthly intervals, from January to December 2014. Salinity peaked and temperature dipped in winter, with both correlated to microalgal community change (GLM: P < 0.01). Diatoms and cyanobacteria, which construct the stromatolites, were consistently the dominant groups within the algal community, with minimal green algae present throughout the year. Importantly, this demonstrates a unique, relatively stable microalgal stromatolite community as opposed to those of other marine stromatolites, which likely require seasonal and stochastic disturbance to persist. This has implications in terms of interpreting community succession and differential layering in modern and fossilized stromatolites respectively.
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Carbonato de Calcio/metabolismo , Cianobacterias/metabolismo , Diatomeas/metabolismo , Microalgas/metabolismo , Chlorophyta/metabolismo , Ambiente , Exposición a Riesgos Ambientales , Fósiles , Océanos y Mares , SalinidadRESUMEN
How animals respond to varying environmental conditions is fundamental to ecology and is a question that has gained impetus due to mounting evidence indicating negative effects of global change on biodiversity. Behavioural plasticity is one mechanism that enables individuals and species to deal with environmental changes, yet for many taxa information on behavioural parameters and their capacity to change are lacking or restricted to certain periods within the annual cycle. This is particularly true for seabirds where year-round behavioural information is intrinsically challenging to acquire due to their reliance on the marine environment where they are difficult to study. Using data from over 13,000 foraging trips throughout the annual cycle, acquired using new-generation automated VHF technology, we described sex-specific, year-round activity budgets in Cape gannets. Using these data we investigated the role of weather (wind and rain) on foraging activity and time allocated to nest attendance. Foraging activity was clearly influenced by wind speed, wind direction and rainfall during and outside the breeding season. Generally, strong wind conditions throughout the year resulted in relatively short foraging trips. Birds spent longer periods foraging when rainfall was moderate. Nest attendance, which was sex-specific outside of the breeding season, was also influenced by meteorological conditions. Large amounts of rainfall (> 2.5 mm per hour) and strong winds (> 13 m s-1) resulted in gannets spending shorter amounts of time at their nests. We discuss these findings in terms of life history strategies and implications for the use of seabirds as bio-indicators.
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Biodiversidad , Aves/fisiología , Ecología , Vuelo Animal/fisiología , Animales , Conducta Alimentaria , Océanos y Mares , Estaciones del Año , Tiempo (Meteorología) , VientoRESUMEN
During breeding, animal behaviour is particularly sensitive to environmental and food resource availability. Additionally, factors such as sex, body condition, and offspring developmental stage can influence behaviour. Amongst seabirds, behaviour is generally predictably affected by local foraging conditions and has therefore been suggested as a potentially useful proxy to indicate prey state. However, besides prey availability and distribution, a range of other variables also influence seabird behavior, and these need to be accounted for to increase the signal-to-noise ratio when assessing specific characteristics of the environment based on behavioural attributes. The aim of this study was to use continuous, fine-scale time-activity budget data from a pelagic seabird (Cape gannet, Morus capensis) to determine the influence of intrinsic (sex and body condition) and extrinsic (offspring and time) variables on parent behaviour during breeding. Foraging trip duration and chick provisioning rates were clearly sex-specific and associated with chick developmental stage. Females made fewer, longer foraging trips and spent less time at the nest during chick provisioning. These sex-specific differences became increasingly apparent with chick development. Additionally, parents in better body condition spent longer periods at their nests and those which returned later in the day had longer overall nest attendance bouts. Using recent technological advances, this study provides new insights into the foraging behaviour of breeding seabirds, particularly during the post-guarding phase. The biparental strategy of chick provisioning revealed in this study appears to be an example where the costs of egg development to the female are balanced by paternal-dominated chick provisioning particularly as the chick nears fledging.