Potential effects of different salinities on the survival of the mangrove crab, Uca urvillei and its associated chemoautotrophic bacterial symbionts

The ability of natural populations to maintain fitness is important to their long-term persistence and has further relevance in the light of climate change scenarios. Fitness is however also influenced strongly by interactions with other species of the community. It is, therefore, important to focus on how environmental change can alter key biological interactions. The present study aimed to investigate the effects of different salinity levels on one species of mangrove crab, Uca urvillei and the associated chemoautotrophic bacterial symbionts, from the Mngazana estuary, South Africa. To examine the influence of different salinities over time on the symbiotic bacterial community, salinity experiments were set up, choosing three salinity exposures (5, 20 and 35percent) and four time exposures (3, 7, 14 and 21 days). The results showed that microbial community associated with U. urvillei was generally stable throughout the three salinity treatments, while the survival of the host (crab), was influenced by high salinities, particularly after day 14. Overall, the results of this study suggest that over time, environmental salinity (35percent) has the potential to affect significantly the physiology of U. urvillei, but this might not necessarily be the case for the associated microbial communities. The modes at which the significant symbionts are transferred from mother to offspring were also investigated by analysing the bacterial profiles from eggs, ovigerous and non-ovigerous females, along with mud. The results were fairly complex, but with significant differences in the bacterial communities of eggs from mud and females. These differences were driven mostly by two dominant phyla: Actinobacteria and Proteobacteria. The presence of both these phyla throughout the categories (even though in different percentages) suggest that U. urvillei might employ a mixed mode strategy of acquiring and maintaining the bacterial symbionts. Overall, this study contributes to further understand the dynamic and complex effects of environmental Abstract ii change on symbiotic communities, with overall potential cascading repercussions to the persistence of mangrove systems.Thesis (MSc) (Zoology) -- Faculty of Science and Agriculture, 201

Potential effects of different salinities on the survival of the mangrove crab, Uca urvillei and its associated chemoautotrophic bacterial symbionts

The ability of natural populations to maintain fitness is important to their long-term persistence and has further relevance in the light of climate change scenarios. Fitness is however also influenced strongly by interactions with other species of the community. It is, therefore, important to focus on how environmental change can alter key biological interactions. The present study aimed to investigate the effects of different salinity levels on one species of mangrove crab, Uca urvillei and the associated chemoautotrophic bacterial symbionts, from the Mngazana estuary, South Africa. To examine the influence of different salinities over time on the symbiotic bacterial community, salinity experiments were set up, choosing three salinity exposures (5, 20 and 35percent) and four time exposures (3, 7, 14 and 21 days). The results showed that microbial community associated with U. urvillei was generally stable throughout the three salinity treatments, while the survival of the host (crab), was influenced by high salinities, particularly after day 14. Overall, the results of this study suggest that over time, environmental salinity (35percent) has the potential to affect significantly the physiology of U. urvillei, but this might not necessarily be the case for the associated microbial communities. The modes at which the significant symbionts are transferred from mother to offspring were also investigated by analysing the bacterial profiles from eggs, ovigerous and non-ovigerous females, along with mud. The results were fairly complex, but with significant differences in the bacterial communities of eggs from mud and females. These differences were driven mostly by two dominant phyla: Actinobacteria and Proteobacteria. The presence of both these phyla throughout the categories (even though in different percentages) suggest that U. urvillei might employ a mixed mode strategy of acquiring and maintaining the bacterial symbionts. Overall, this study contributes to further understand the dynamic and complex effects of environmental Abstract ii change on symbiotic communities, with overall potential cascading repercussions to the persistence of mangrove systems.Thesis (MSc) (Zoology) -- Faculty of Science and Agriculture, 201

Fiddler crab bioturbation determines consistent changes in bacterial communities across contrasting environmental conditions

Ecosystem functions are regulated by compositional and functional traits of bacterial communities, shaped by stochastic and deterministic processes. Biogeographical studies have revealed microbial community taxonomy in a given ecosystem to change alongside varying environmental characteristics. Considering that stable functional traits are essential for community stability, we hypothesize that contrasting environmental conditions affect microbial taxonomy rather than function in a model system, testing this in three geographically distinct mangrove forests subjected to intense animal bioturbation (a shared deterministic force). Using a metabarcoding approach combined with sediment microprofiling and biochemistry, we examined vertical and radial sediment profiles of burrows belonging to the pantropical fiddler crab (subfamily Gelasiminae) in three contrasting mangrove environments across a broad latitudinal range (total samples?=?432). Each mangrove was environmentally distinct, reflected in taxonomically different bacterial communities, but communities consistently displayed the same spatial stratification (a halo effect) around the burrow which invariably determined the retention of similar inferred functional community traits independent of the local environment

Morphological characteristics and abundance of prokaryotes associated with gills in mangrove brachyuran crabs living along a tidal gradient

Due to the chemico-physical differences between air and water, the transition from aquatic life to the land poses several challenges for animal evolution, necessitating morphological, physiological and behavioural adaptations. Microbial symbiosis is known to have played an important role in eukaryote evolution, favouring host adaptation under changing environmental conditions. We selected mangrove brachyuran crabs as a model group to investigate the prokaryotes associated with the gill of crabs dwelling at different tidal levels (subtidal, intertidal and supratidal). In these animals, the gill undergoes a high selective pressure, finely regulating multiple physiological functions during both animal submersion under and emersion from the periodical tidal events. We hypothesize that similarly to other marine animals, the gills of tidal crabs are consistently colonized by prokaryotes that may quantitatively change along the environmental gradient driven by the tides. Using electron microscopy techniques, we found a thick layer of prokaryotes over the gill surfaces of all of 12 crab species from the mangrove forests of Saudi Arabia, Kenya and South Africa. We consistently observed two distinct morphotypes (rod- and spherical-shaped), positioned horizontally and/or perpendicularly to the gill surface. The presence of replicating cells indicated that the prokaryote layer is actively growing on the gill surface. Quantitative analysis of scanning electron microscopy images and the quantification of the bacterial 16S rRNA gene by qPCR revealed a higher specific abundance of prokaryote cells per gill surface area in the subtidal species than those living in the supratidal zone. Our results revealed a correlation between prokaryote colonization of the gill surfaces and the host lifestyle. This finding indicates a possible role of prokaryote partnership within the crab gills, with potential effects on animal adaptation to different levels of the intertidal gradient present in the mangrove ecosystem

Bioturbation Intensity Modifies the Sediment Microbiome and Biochemistry and Supports Plant Growth in an Arid Mangrove System

In intertidal systems, the type and role of interactions among sediment microorganisms, animals, plants and abiotic factors are complex and not well understood. Such interactions are known to promote nutrient provision and cycling, and their dynamics and relationships may be of particular importance in arid microtidal systems characterized by minimal nutrient input. Focusing on an arid mangrove ecosystem on the central Red Sea coast, we investigated the effect of crab bioturbation intensity (comparing natural and manipulated high levels of bioturbation intensity) on biogeochemistry and bacterial communities of mangrove sediments, and on growth performance of Avicennia marina, over a period of 16 months. Along with pronounced seasonal patterns with harsh summer conditions, in which high sediment salinity, sulfate and temperature, and absence of tidal flooding occur, sediment bacterial diversity and composition, sediment physicochemical conditions, and plant performance were significantly affected by crab bioturbation intensity. For instance, bioturbation intensity influenced components of nitrogen, carbon, and phosphate cycling, bacterial relative abundance (i.e., Bacteroidia, Proteobacteria and Rhodothermi) and their predicted functionality (i.e., chemoheterotrophy), likely resulting from enhanced metabolic activity of aerobic bacteria. The complex interactions among bacteria, animals, and sediment chemistry in this arid mangrove positively impact plant growth. We show that a comprehensive approach targeting multiple biological levels provides useful information on the ecological status of mangrove forests.IMPORTANCE 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. Here, we investigate how high crab bioturbation intensity modifies the mangrove sediment bacterial community, which is the second largest component of mangrove sediment biomass and plays a significant role in major biogeochemical processes. We show that the increase in crab bioturbation intensity, by ameliorating the anoxic condition of mangrove sediment and promoting sediment bacterial diversity in favor of a beneficial bacterial microbiome, improves mangrove tree growth in arid environments. These findings have significant implications because they show how crabs, by farming the mangrove sediment, can enhance the overall capacity of the system to sustain mangrove growth, fighting climate change

Is invasion science moving towards agreed standards? The influence of selected frameworks

The need to understand and manage biological invasions has driven the development of frameworks to circumscribe, classify, and elucidate aspects of the phenomenon. But how influential have these frameworks really been? To test this, we evaluated the impact of a pathway classification framework, a framework focussing on the introduction-naturalisation-invasion continuum, and two papers that outline an impact classification framework. We analysed how these framework papers are cited and by whom, conducted a survey to determine why people have cited the frameworks, and explored the degree to which the frameworks are implemented. The four papers outlining these frameworks are amongst the most-cited in their respective journals, are highly regarded in the field, and are already seen as citation classics (although citations are overwhelmingly within the field of invasion science). The number of citations to the frameworks has increased over time, and, while a significant proportion of these are self-citations (20–40%), this rate is decreasing. The frameworks were cited by studies conducted and authored by researchers from across the world. However, relative to a previous citation analysis of invasion science as a whole, the frameworks are particularly used in Europe and South Africa and less so in North America. There is an increasing number of examples of uptake into invasion policy and management (e.g., the pathway classification framework has been adapted and adopted into EU legislation and CBD targets, and the impact classification framework has been adopted by the IUCN). However, we found that few of the citing papers (6–8%) specifically implemented or interrogated the frameworks; roughly half of all citations might be viewed as frivolous (“citation fluff”); there were several clear cases of erroneous citation; and some survey respondents felt that they have not been rigorously tested yet. Although our analyses suggest that invasion science is moving towards a more systematic and standardised approach to recording invasions and their impacts, it appears that the proposed standards are still not applied consistently. For this to be achieved, we argue that frameworks in invasion science need to be revised or adapted to particular contexts in response to the needs and experiences of users (e.g., so they are relevant to pathologists, plant ecologists, and practitioners), the standards should be easier to apply in practice (e.g., through the development of guidelines for management), and there should be incentives for their usage (e.g., recognition for completing an EICAT assessment).This paper emerged from a workshop on ‘Frameworks used in Invasion Science’ hosted by the DSI-NRF Centre of Excellence for Invasion Biology in Stellenbosch, South Africa, 11–13 November 2019, that was supported by the National Research Foundation of South Africa and Stellenbosch University.The South African Department of Forestry, Fisheries and the Environment, (DFFtE); Czech Science Foundation; Czech Academy of Sciences; the Oppenheimer Memorial Trust; the DSI-NRF Centre of Excellence for Invasion Biology (CIB) and National Research Foundation.http://www.pensoft.net/journals/neobiotaam2021Zoology and Entomolog