Browsing by Author "Pillay, Deena"

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    Aspects of the spatial and behavioural ecology of Hippopotamus amphibious in the Saint Lucia Estuary, KwaZulu-Natal, South Africa
    (2016) Prinsloo, Alexa Simone; Pillay, Deena; O'Riain, M Justin
    The common hippopotamus (Hippopotamus amphibius) is endemic to Africa but threatened by range restriction, exploitation and competition with humans and domestic livestock for access to critical resources such as fresh water and grazing. Collectively these impacts have resulted in population declines throughout most of their range with the consequence that hippos are classified as Vulnerable on the IUCN Red list. Despite these threats to their persistence and their important ecological role as ecosystem engineers there have been surprisingly few studies concerning factors that influence their current distribution and habitat use. Such research is important for developing effective conservation and management plans to improve the protection of vulnerable and ecologically important species such as hippo. South Africa is home to one of a few growing hippo populations and one of the last persisting in an estuarine habitat. The St Lucia Estuary, one of three Ramsar Wetlands of International Importance located in the iSimangaliso Wetland Park (itself a UNESCO World Heritage site), in northern KwaZulu-Natal is not only the largest estuarine system in Africa, but is also home to one of South Africa's largest hippo populations. In this study I explore aspects of the spatial and behavioural ecology of hippo within the St Lucia Estuary. More specifically, I investigate select abiotic and biotic predictors of hippo presence and the frequency with which they return to their diurnal lie-up sites. I used binary logistic regression models to evaluate the effects of the selected habitat features on hippo occurrence at two spatial scales (broad and fine). I used a negative binomial with log-link model to evaluate the effects of the selected habitat features on the frequency of use of sites (hippo persistence) in the fine-scale study. In addition, I employed both instantaneous scan sampling and continuous sampling methods in an attempt to determine the diurnal activity budgets and social interactions of a single group near the mouth of the St Lucia Estuary. I used non-parametric tests to evaluate differences in behaviour with daytime and across sampling days with a view to an improved understanding of how the environment influences the behaviour of hippo in an environment subject to ongoing human modification.
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    Benthic metrics as indicators of human disturbance in a marine-dominated lagoon
    (2018) Jones, Amy M; Pillay, Deena
    Expanding anthropogenic developments along with the added stress of climate change, are negatively influencing coastal ecosystems. Because of their many benefits to mankind, it is important to identify key bioindicators that can detect disturbance-induced ecosystem change. Benthic metrics are an excellent example of disturbance indicators in soft sediment based aquatic systems, and are directly applicable to one of South Africa’s most economically and ecologically significant marine-dominated lagoons; Langebaan lagoon. This lagoon is managed through the designation of three zones (A, B and C) with contrasting human presence. Public access, recreation and bait-collecting is permitted in A, but no bait colleting is permitted in B. Human presence is completely restricted in Zone C. This study thus aimed to test the level of impact of human disturbance on two zones of the lagoon (A and C), using benthic metrics as bioindicators. Macrofaunal community metrics (abundance, species richness, Shannon-Weiner diversity, evenness, and community structure), performance of a key ecosystem engineer (sandprawn abundance and condition factor), organic matter content and microphytobenthic biomass were compared between the two sites, comprising multiple subsites. Results showed minimal differences between disturbed and undisturbed sites, with the exception of organic matter content and Shannon-Weiner diversity comparisons, which were greater in undisturbed subsites. There was however, a general trend of increasing dominance by sandprawns (Callichirus kraussi) from undisturbed to disturbed subsites, whilst the undisturbed subsites were numerically dominated by a several codominant polychaetes (Euclymene spp., Notomastus latericeus and Marphysa sanguinea). Interestingly, there were more significant differences at the subsite level, suggesting that localized conditions are more important in shaping macrobenthic communities than disturbance impacts, as supported by previous literature. Despite limitations, this study does provide important baseline data relevant to optimizing sampling designs for detecting human disturbance impacts in Langebaan Lagoon. Key Words: Benthic metrics, bioindicator, macrobenthos, disturbance, trampling, coastal lagoon.
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    Drivers of burrow symbiont distribution in a softsediment system: host abundance or burrow trophic environment?
    (2013) Wright, Amy G; Pillay, Deena
    The Langebaan Lagoon sandflats are dominated by the burrowing activities of thalassinid shrimps. Their burrows are home to various burrow symbionts including a commensal shrimp (Betaeus jucundus), a six-legged crab (Spiroplax spiralis) and a scaleworm (Antinoe lactea). Little work has been conducted on these burrow symbionts, and the mechanisms influencing their abundance and distribution are unknown. To test whether host abundance or the burrow trophic environment (i.e. food availability) is the dominant force shaping patterns of burrow symbiont distribution, samples of host and symbiont abundances as well as chlorophyll-a and extracellular polymeric substance (EPS) measurements were taken from three sites in Langebaan Lagoon over spring and autumn. Clear signals emerged in contradiction of the hypothesis that burrow symbiont abundances peak in areas associated with high abundances of hosts. Host abundances peaked at Bottelary (10.18 counts/site ± 1.02 SE), a site where recreational activities and thalassinid shrimp bait collection are prohibited. In contrast, peak B. jucundus abundance (6.56 counts/site ± 0.37 SE) occurred at Oesterval during September – the muddy sediment of the site resulted in high sedimentary food retention and the September spring phytoplankton bloom resulted in peak chlorophylla (234.12 mg chl-a/g sediment ± 42.74 SE) and EPS (0.13 mg EPS/g sediment ± 0.008 SE) concentrations. Regression analyses confirmed that food availability was the best explanation of the patterns observed in B. jucundus distributions, over and above that of host distributions. S. spiralis and A. lactea did not show this pattern, the result of the low counts of these species in the collected samples or their reliance on food sources different to those depended on by B. jucundus. These results are of consequence in changing the way we think about symbiont distributions relative to that of the hosts, in that the two may not be linked directly, but rather influenced by larger scale trophic changes such as the availability of food within the burrow.
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    Ecological role of mining ponds in Southern Coastal Mines, Namibia
    (2020) Maritz, Liezl; Branch, George Meredith; Pillay, Deena
    Targeting marine diamondiferous deposits along the south-western Namibian coastline has involved the construction of seawall berms to advance the coastline and permit mining in previously subtidal areas. Large areas are mined out to bedrock level by the removal of overburden (sand and gravel), and after mining is complete, areas behind the seawalls fill with seawater, creating a series of coastal marine ponds that have the potential to function as saline wetlands corresponding to closed estuaries. The study site lies north of the Orange River mouth, within the Tsau//Khaeb (Sperrgebiet) National Park, to which the public has restricted access due to diamond mining in the area. Consequently, there is a focus on biodiversity conservation and the overall objective of this thesis was to determine the ecological value of the mining ponds by investigating whether they harbour sufficient biodiversity to qualify as a viable alternative ecological habitat, rather than restoring them to their original state as backfilled, revegetated dune areas. The study area, approximately 75 kilometres in length, was divided into north, middle and south sections, according to the age and status of mining activities, and I first assessed whether ponds in these three areas differed in their physical properties (Chapter 1). To determine whether the ponds serve as a useful ecological role worth preserving, I then investigated the diversity and amount of saltmarsh vegetation (Chapter 2), bird species (Chapter 3) and fish (Chapter 4) currently benefiting from these mining ponds. Ponds in the north are older and hypersaline whereas the south and middle ponds are younger and closely approach physical conditions in the sea. Diurnal fluctuations in oxygen concentration took place, but oxygen levels never dropped below 80% and were thus not limiting. After about 15 years, ponds developed salinities in excess of 80‰, which is likely to set limits on their ecological viability. Most ponds supported saltmarshes, but only a single species, Salicornia natalensis, grew around them. Its abundance was greatest around old ponds, but its health decreased with salinity. Wind emerged as a likely means of dispersal among ponds. The ponds supported a rich avifauna, averaging 11028 birds per count for all ponds combined; 36 species were recorded, ten being endemics, and five being listed in Namibia's Red Data Book. Numbers were highest for ponds that were being ‘dewatered' to remove water prior to mining, as this exposed a rich benthic epifaunal source of food. Blacknecked Grebe, Cape Cormorant, Greater and Lesser Flamingos, Kelp Gull and Common Tern were the most abundant birds. Salinity did not limit bird numbers or diversity, so the northern high-salinity ponds may continue to serve as bird habitat for periods of time much greater than the 15 years after which they become hypersaline. In comparison with nine other wetlands in the region, the ponds had great numbers, diversity, densities, and numbers of threatened species than about half of these wetlands, many of which are considered Important Bird Areas (IBAs). In many cases, they also supported more species that had numbers in excess of 1% of the southern African population than these IBAs. Only two species of fish commonly occurred in the ponds, the west coast steenbras Lithognathus auratus and the southern mullet Chelon richardsonii, although small numbers of two other marine species were recorded. The diversity of marine fish was thus low, even by the impoverished standards of west-coast estuaries. Unexpectedly, there were no significant differences between the ichthyofauna of ponds in the north, middle and south, nor was there any relationship between total fish numbers and salinity. Body condition of steenbras was lowest in the hypersaline north ponds, and their stomach contents contained a low diversity of food items there. The presence of recruits and the range of gonadal states suggested that both species bred in the ponds. Steenbras proved to be protandrous, with females dominating larger size classes. Growth rates of both species were faster in the ponds than in the adjacent sea, and mullet achieved substantially greater sizes in ponds. Thus, the ponds do serve as viable ecosystems, albeit with a limited range of saltmarsh and fish species, and support an impressively diverse avifauna. Their long-term viability will, however, become limited by rising salinity as their age increases.
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    Ecology and behaviour of burrowing prawns and their burrow symbionts
    (2014) Moyo, Ropafadzo Kelebuhile; Pillay, Deena
    Ecosystem engineers play important roles as determinants of community dynamics by modulating resource availability for other species. Marine soft-sediment ecosystems are dominated by burrowing engineers which indirectly create biogenic structures that often attract other species, often leading to the evolution of symbiotic relationships. Engineered structures provide non-trophic (e.g. refuge) and trophic functions (e.g. food) for burrow symbionts, however, the relative importance of these functions for symbionts is poorly understood. The behavioural interactions between burrowing engineers and their burrow symbionts are also poorly understood, mainly due to the difficulty in conducting behavioural observations in situ. This study aimed to enhance our understanding of the ecological processes and behavioural interactions underlying symbiotic relationships between a dominant South African ecosystem engineer (Callianassa kraussi) and its burrow symbiont (Betaeus jucundus) in soft sediment systems in Langebaan Lagoon. The study specifically quantified the relative importance of host abundance (a proxy for non-trophic functions) and food availability (trophic functions) provided by burrows of C. kraussi in influencing the abundance and distribution of B. jucundus. The second aim was to quantify behavioural changes of C. kraussi in the presence and absence of the symbiont B. jucundus and determine if the sex of C. kraussi influences its behavioural response to B. jucundus. Results indicate that at a patch scale, trophic functions (food availability) provided by burrows was more important than non-trophic functions in determining symbiont abundance and distribution. However, at an ecosystem scale, non-trophic functions could be a very important determinant of symbiont abundance and distribution. In terms of behavioural interactions, the presence of B. jucundus elicited three distinct behavioural responses from C. kraussi: intolerance, semitolerance and tolerance. In the absence of B. jucundus, there was no difference between male and female C. kraussi behaviour but this pattern changed in the presence of B. jucundus. Overall, the study has contributed to increasing our understanding of ecological processes that determine the abundance and distribution of burrow symbionts in marine soft-sediments as well as behavioural interactions between burrowers and their symbionts.
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    Ecology and ecophysiology of Zostera capensis: responses and acclimation to temperature
    (2020) Lawrence, Cloverley Mercia; Pillay, Deena; Jarre, Astrid; Bolton, John
    This study aimed to understand the ecology of the threatened, habitat-forming seagrass, Zostera capensis in Langebaan Lagoon, a marine protected area that forms part of the West Coast national park, South Africa; and the physiological strategies that allow this habitat to persist in sub- and supra-optimal temperatures. First, the environmental drivers responsible for spatial and temporal variability in Zostera and its associated macro-epifauna were determined. Secondly, the effects of temperature and the role of algal grazing in maintaining seagrass performance under temperature stress were investigated. Seasonal field collections of seagrasses and their associated macro-epifauna were undertaken, along with regular measurements of key environmental variables. Thereafter, mesocosm experiments were performed to measure the responses of Zostera to thermal stress and grazing using morphometry, fluorometry, chromatography and biochemistry. Significant seasonal variability in seagrass distributions with severe diebacks in summer were found, which influenced associated macro-epifauna communities. Populations responded to environmental stress by changing their growth form producing small-leaves in high densities in the high intertidal, while those in low intertidal and subtidal areas produced sparse, large-leaved populations. These distinct populations supported unique faunal diversities, which were dominated by grazing invertebrates. Temperature was a consistent driver of seagrass density and leaf size, while turbidity and exposure were key environmental factors that influenced macro-epifaunal patterns. Macro-epifaunal abundances were highly positively correlated with seagrass leaf width and biomass. Different growth forms displayed different responses to thermal stress, including a higher photosynthetic rate, and accumulations of carbon and nitrogen as phenolic compounds, in small- compared to large-leaved plants. This implies that large-leaved populations are more vulnerable to stress from fouling, which was evident in their larger epiphyte loads, compared to small-leaved populations. In addition, grazers were ineffectual at regulating epiphyte growth which increased under warming conditions. These findings suggest differences in resilience between sub-populations of Zostera, and attest to their capacity to recover from environmental stress. They further emphasise the significance of identifying characteristics and acclimation strategies that allow habitats to persist under climate change, and thus sustain biodiversity and productivity, as well as continue to provide important ecosystem services.
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    Effects of burrowing sandprawns (Callichirus kraussi) on urban estuarine water quality
    (2019) Venter, Olivia; Pillay, Deena
    Eutrophication, one of the leading global water pollution challenges, can be addressed with nature-based solutions (NBSs). NBSs use or mimic natural processes (ecosystem services) to improve water quality, for example microorganisms, plants and filter feeders have already been shown to mitigate eutrophication. However, burrowing endobenthic organisms have not yet been considered as a NBS, despite their potential to greatly impact water quality. Therefore, the purpose of this study was to determine whether these endobenthic organisms could be effective as NBSs, more specifically whether the activities of the common sandprawn (Callichirus kraussi) can improve water quality in terms of pelagic nutrient, microalgal and suspended solids concentrations. C. kraussi is a benthic ecosystem engineer that, like other endobenthic crustaceans, affects water flow, sediment biogeochemistry and benthic-pelagic fluxes through bioturbation and bioirrigation. Their elaborate burrow systems may act as biological filters for pelagic microalgae, but they may also be a source of nutrient-rich excrement inputs into the water column. To determine the effects of C. kraussi on water quality, a laboratory mesocosm experiment and comparative in situ analysis were used in this study. In the mesocosm experiment, water quality at 3 increasing C. kraussi densities (0 [control], 100 and 200 individuals·m-2 ) were compared. At the end of the experiment, the water column NH4 + concentration in the high density C. kraussi treatment was 2.6 times greater compared to the controls. Despite this increase in the NH4 + concentration, the water column chl-a concentrations were 42.8% (50% density treatment) and 44.3% (100% density treatment) lower compared to the controls. Additionally, microalgal biomasses in the sediment were less concentrated on burrow mounds created by C. kraussi compared to the adjacent sediment between mounds and within the burrows. However, the overall chl-a concentrations in the sediment did not differ between treatments. This suggests that C. kraussi has the effect of breaking up microalgal mats on the sediment surface with their burrow mounds without changing the overall sediment surface chl-a concentration, thereby maintaining benthic-pelagic coupling. C. kraussi did not affect suspended solids concentrations in the water column over the 12-day study period. For the in situ component, water quality was compared at sites where C. kraussi was present and the adjacent sections where it was absent in the Zandvlei Estuary Nature Reserve. The findings from the mesocosm experiment were reflected in situ: Chl-a concentrations in C. kraussi habitats were reduced by 43.1% from upstream areas without C. kraussi, and again increased by 32.9% from C. kraussi habitats to downstream canalised areas without C. kraussi. Differences in suspended solids concentrations were also not explained by C. kraussi presence in situ. The conclusion from this study is that ecosystem engineering by C. kraussi has an overall positive effect on water quality in urban estuaries, principally by reducing chl-a concentrations in the water column and maintaining benthic-pelagic coupling. Therefore, C. kraussi should be conserved for its water purification ecosystem services. This can be achieved by maintaining soft sediments in estuaries, rather than constructing concrete canals in which C. kraussi cannot burrow. Regulation of C. kraussi extraction for fishing bait is also necessary to prevent the loss of their filtration function. Furthermore, this study supports the use of C. kraussi as a NBS to eutrophication and encourages the consideration of similar endobenthic organisms for this purpose. Endobenthic ecosystem engineering should not be underestimated in addressing the global challenge of eutrophication.
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    The effects of the macroalga Gracilaria gracilis and increasing temperatures on the performance of the endemic Cape eelgrass Zostera capensis
    (2017) Beltrand, Maeva Mereana Marion; Pillay, Deena
    Rising temperature caused by global warming alters physiology, phenology and/or distribution in a wide array of plant and animal species, which has dramatic knock-on effects at different levels of organisation. This study investigates the individual and interactive effects of temperature (18áµ’C, 22áµ’C and 30áµ’C) and additions of the macroalga Gracilaria gracilis (high and low) on the performance of the seagrass Zostera capensis, which occurs in Langebaan Lagoon, South Africa over a seven-week period. Results from the laboratory experiment revealed that G. gracilis did not significantly affect the performance of Z. capensis although temperature did result in greater leaf width, fouling and senescent biomass, as well as marginally greater leaf area and lower below-ground biomass at 30áµ’C. Increasing temperature also increased G. gracilis biomass, percent cover and fouling by microalgae. In addition, there was no interaction between temperature and the additions of Gracilaria. The overall findings of this study indicate that Z. capensis abundance is likely to decrease while G. gracilis will conversely increase in abundance in response to warming. Changes in abundance of those two ecosystem engineers highlight the possibility of a phase shift from a seagrass- to macroalgal-dominated state in Langebaan Lagoon.
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    Endobenthic Ecosystem Engineering: influence of sandprawns (Callichirus kraussi) on zooplankton assemblages
    (2022) Oyatoye, Abioye E; Pillay, Deena
    Ecosystem engineering activities of the burrowing Southern Africa sandprawn (Callichirus kraussi), were shown in recent research to influence bentho-pelagic coupling in soft sediment estuarine ecosystems through reducing phytoplankton biomass in the overlaying water. The phytoplankton reduction mechanism was hypothesized to be driven by their adsorption along sandprawn burrow walls during irrigation. However, given that phytoplankton is a major trophic resource for filter feeders, any effect of sandprawns in reducing phytoplankton biomass may generate possible indirect effects on filter feeders such as zooplankton assemblages. To date, there has been no known research addressing questions on density of sandprawns and associated effects on zooplankton assemblages. This study therefore aimed to address this knowledge gap and quantify the influence of ecosystem engineering by C. kraussi on two size categories of zooplankton assemblages; mesozooplankton and microzooplankton, based on the premise that water pumping activities would lead to a decline in abundance of phytoplankton (adsorption onto burrow walls), thereby, resulting in negative bottom-up effects on zooplankton assemblages. This aim was accomplished using an 18-days mesocosms laboratory experiment, with each experimental mesocosm being each half-filled with sediment and water collected from the Zandvlei Estuary and divided into 3 treatments of varying C. kraussi densities (0% (control), 50% and 100% natural sandprawn density, n = 3). At the end of the experiment, increases in C. kraussi densities from controls to 100% treatments resulted in declines in abundance of total phytoplankton cells, nanophytoplankton, and picophytoplankton. However, sandprawn density had no significant effect on zooplankton assemblages, which were dominated by hyperbenthic taxa. There were discernible trends in dominance at the taxon level in microzooplankton and mesozooplankton assemblages. The copepod order Hapacticoida became increasingly dominant in both assemblages from control to 100% treatment with percentage contributions increasing from 79.23% to 95.93% in the microzooplankton assemblage and 43.07% to 92.28% in the mesozooplankton assemblage. Increasing dominance in both microzooplankton and mesozooplankton assemblages with increasing sandprawn density were confirmed using dominance plots. In conclusion, the main findings in this experiment suggest that endobenthic ecosystem engineering effects may not be confined to the sedimentary components of estuarine ecosystems but may extend to generate subtle effects on zooplankton taxa, mainly by way of increasing dominance. This study is the first direct evidence of the bentho-pelagic coupling effects of endobenthic ecosystem engineers on pelagic zooplankton assemblages that are dominated by hyperbenthic taxa and lays the foundation for subsequent research into understanding consequences of endobenthic ecosystem engineering on pelagic ecosystems.
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    Environmental determinants of greater flamingo foraging behaviour in an estuarine intertidal sandflat
    (2014) Liang, Andrea Yankee; Pillay, Deena
    The impact of flamingo predation on the benthic community has been well researched through the use of caging and exclusion experiments. However, there is still very little known about flamingo spatial foraging preferences and the environmental cues that determine them. The purpose of this study was to investigate the foraging distributions of non-breeding Greater Flamingos (Phoenicopterus ruber roseus) within one of their southern African overwintering grounds, the Heuningnes Estuary. This was achieved by comparing spatial level differences in the abundance and size of flamingo foraging pits across sites and shore positions, and by examining the effects of soil moisture content and sediment profile as environmental cues driving flamingo foraging behaviour. Pit abundance was obtained as a total count per quadrat, and pit size was measured from photographs taken in the field. Sediment cores provided soil moisture content measurements, while sediment profile was measured as the angle of elevation from each shore position to the high water mark. It was found that flamingos fed homogeneously across all four sites, but restricted their foraging to the high shore and upper mid shore regions of the intertidal. Soil moisture content was not a significant driver of flamingo foraging behaviour, but sediment profile was significant. It was proposed that flamingo foraging preference for the high shore and upper mid shore regions was because: (1) the sediment profiles were flatter, (2) the macrofaunal prey densities were greater and (3) these shore positions coincided with the required depth for stamp-feeding, which was linked to the high tide and the time of day at which foraging occurred. This study provides novel information regarding the environmental drivers of Greater Flamingo foraging behaviour and the spatial use of the intertidal sandflats of the Heuningnes Estuary. Furthermore, this knowledge could be useful for the management of flamingo foraging grounds of the De Mond Nature Reserve.
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    Flamingo foraging activity as a driver of spatial heterogeneity in Langebaan Lagoon, South Africa
    (2013) Payne, Robyn; Pillay, Deena
    Numerous studies have attempted to quantify the effect of epifaunal predation and its co-occurring disturbance on macrofaunal communities with the aid of exclosure experiments. However, no attention has been paid to the possible impacts of different foraging methods used by flamingos on benthic communities. Multivariate and univariate analyses were carried out in order to determine the effects of two different flamingo feeding strategies (pit and channel foraging) on sediment penetrability and macrofaunal community structure in Langebaan Lagoon. The two foraging strategies appear only to differ with regards to prey removal and recolonisation. The more energy intensive, pitforming foraging enables the flamingo to obtain higher quantities of Urothoe grimaldii in addition to bivalves, while promoting recolonisation by opportunists. On the other hand, channel-foraging enables the attainment of various polychaete and nematode species. These small-scale differences, as well as the spatial (and possibly temporal) variation in structures generate habitat complexity. Thus, this preliminary study supports the notion that flamingo foraging activity is a key driver of spatial heterogeneity in Langebaan Lagoon and highlights the need for further research.
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    Flamingo foraging plasticity: ecological drivers and impacts
    (2017) Gihwala, Kirti Narendra; Pillay, Deena; Varughese, Melvin
    The consequences of predation have become a central focus of marine ecological research. Numerous studies have emphasized the importance of apex predators in structuring assemblages at various organisational levels and in determining how ecosystems function. However, less appreciated currently is the fact that predators display multiple foraging behaviours, thereby allowing them to overcome problems associated with unpredictability of food resources in space and time. The primary goal of this dissertation is to contribute to growing understanding of the ecological causes and consequences of foraging plasticity displayed by Greater Flamingo Phoenicopterus ruber roseus in intertidal sandflat ecosystems in Langebaan Lagoon, South Africa. P. roseus feeds by either (1) creating pits, which involves flamingos stirring up deep sediments with their feet or (2) creating channels, in which their inverted bills are swept from side-to-side on the sediment surface. The first objective of the study was to quantify the ecological drivers of decisions made by flamingos to feed, and to implement either pit- or channel-foraging strategies. The latter was achieved through RandomForest modelling techniques that identified the prominent ecological drivers from a suite of biotic and abiotic variables. Results indicate that biotic variables, i.e. those associated with flamingo prey assemblages, were key in driving choices made by flamingos to forage and to implement either pit- or channel-foraging strategies. The second aim of this dissertation was to quantify the repercussions of the two different foraging behaviours on benthic assemblages. Comparisons of benthic assemblages in flamingo foraging structures (pits and channels) with adjacent non-foraged sediments (controls) indicated differential effects of both flamingo foraging methods on benthic communities, with channel-foraging eliciting a greater negative impact compared to pit-foraging, for which impacts were negligible. Abundance of macrofauna and surface-dwelling taxa such as micro-algae and the amphipod Urothoe grimaldii were all negatively impacted by channel-foraging. Sizes of channels constructed by flamingos were inversely related to their impacts, with impacts on macrofaunal abundance being greater in smaller channels. Overall, this study has shed light on the differential effects of foraging plasticity on prey assemblages and its importance in enhancing spatio-temporal heterogeneity in intertidal sandflats. The study also emphasizes the need to incorporate foraging plasticity into current thinking and conceptual models of predation in marine soft sediments, in order to appreciate the full spectrum of predation effects on assemblages.
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    Flamingo predation impacts on benthic communities: effects of spatial gradients
    (2014) Gihwala, Kirti Narendra; Pillay, Deena
    Biological disturbances on marine soft sediment ecosystems have been well researched. However, little attention has been paid to the potential ecological role that iconic shore bird predators may have on marine ecosystems. This paper tests the effects of spatial gradients on Greater Flamingo (Phoenicopterus ruber) predation impacts on the benthic macrofaunal community structure in an intertidal sandflat ecosystem in South Africa. P. ruber is a benthic filter-feeder known to feed on benthic dwelling invertebrates through pit formation, where deep sediments are stirred up by trampling their feet. Macrofaunal community structure between flamingo pit foraging structures and adjacent non-foraged sediments (controls) yielded insignificant spatial differences. However, subtle positive and negative effects of flamingo predation on macrofaunal abundance were noted at specific sites. Flamingos in this study were not targeting a specific prey group. Thus of the 19 macrofaunal prey items identified, none were significantly impacted across treatments, except for an unidentified polychaete. However, this was once again site specific. The results suggested this polychaete is generally abundant within the area sampled. Furthermore, its distribution is perhaps affected by the level of intensity employed in pit-foraging, rather than being preyed upon. Greater polychaete abundance in pits relative to controls may be attributed to vigorous flamingo feeding efforts. Pit foraging appears to be an expensive strategy to employ, but the energy investment may be reduced through the use of sophisticated sensory organs to detect accessible prey deep within the sediment. Overall, the study has shown that the impact of flamingo predation on a spatial gradient is small and site specific. However, the study highlights the need for further research on quantifying the ecological role flamingos play as predators on marine ecosystems.
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    Genetics and ecosystem effects of the invasive mussel Semimytilus algosus, on the West Coast of South Africa
    (2016) Zeeman, Susanna Catharina Franzina; Branch, George M; Pillay, Deena; Von der Heyden, Sophie
    Invasive species can radically affect community composition and ecosystem processes, and human traffic has accelerated their spread. On the South African coast, 86 invasive species have been recorded, although until recently only the Mediterranean mussel Mytilus galloprovincialis and the barnacle Balanus glandula have had significant ecosystem effects on a large geographic scale. Semimytilus algosus was first detected at Elands Bay in 2009 and by 2010 it occupied 500 km of the West Coast of South Africa from Groenriviermond to Bloubergstrand. Given the fact that it is an ecosystem engineer forming dense beds, it is likely to have marked community effects. My study aimed to determine: (A) the identity, genetic composition and origin of the population, and (B) potential interactions between M. galloprovincialis and S. algosus and their effects on community composition. I conducted surveys to assess the abundance and zonation of S. algosus, analysed its competitive abilities by comparing its life-history strategies to other mussel species on the West Coast, and conducted field experiments to examine survival and interactions between S. algosus and M. galloprovincialis at different shore heights. I confirmed the identity of this species and found that the South African population has comparable genetic variation to the Chilean and Namibian populations. It spread to South Africa, seemingly through larval dispersal from Namibia, and now ranges from Groenriviermond in the north to Hout Bay in the south, spreading southward. It is most abundant on the low shore, with M. galloprovincialis on the mid shore. Mixed beds co-exist in the transition zone. Biodiversity in S. algosus beds is similar to that in M. galloprovincialis beds. High recruitment rates of S. algosus on the low shore, and its high genetic variation at all sites, enable it to colonise rock quickly and become established in new areas. The competitive ability of Semimytilus algosus is strongly related to shore height. It cannot survive on the high shore due to intolerance to desiccation. On the low shore its high recruitment rate offsets its high mortality due to wave action and predation.
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    Human disturbance impact on shorebirds at Muizenberg Beach, South Africa, during and prior to the COVID-19 lockdown
    (2021) Lewis, Jemma Elizabeth; Pillay, Deena
    The impact of humans on the natural environment has been so extensive that the scientific community has defined a new geological era: the Anthropocene. Coastal ecosystems rank amongst the most threatened of global habitats due to high urban human population density and demand for socio-ecological services provided by the coast. Sandy beach ecosystems are prominent constituents of coastal regions and sought after for their recreational value, but these systems are understudied relative to more charismatic marine habitats such as coral reefs and kelp forests. Human disturbance has been identified as one of the most serious threats to sandy beach ecosystems, but several knowledge gaps prevail, including its effects on shorebirds. The 2020 global COVID-19 pandemic resulted in a period of abnormally limited human mobility that has been coined the ‘anthropause'. In South Africa, a national lockdown commenced on 27 March 2020 and consisted of five levels to combat the pandemic. Specifically, lockdown levels 5, 4, and 3 did not permit human presence in public areas, including beaches. The aim of this study was to understand the impact of human disturbance during and prior to the COVID-19 lockdown on shorebird abundance and community structure on Muizenberg Beach, South Africa (34°06.3′S 18°28.3′E), using two approaches. The first approach used photographic data to compare shorebird numbers across five lockdown levels in 2020 with equivalent periods in 2019 (prior to the pandemic) to determine the effects of contrasting levels of human abundance on shorebirds. Results from this component indicated that shorebird abundance was negatively related to human abundance and year, but positively associated with the lockdown levels. Most importantly, greatest shorebird abundance across the study were recorded under lockdown levels 5 and 4, when there were virtually no humans on the beach. Similarly, the lowest bird abundance was recorded under lockdown level 1, when human abundance was greatest for 2020. The second approach implemented in this study was based on in situ counts of shorebirds on Muizenberg Beach between lockdown levels 3 and 1 in 2020, to understand how intermediate to moderate levels of lockdown influenced shorebird community structure. PERMANOVA analysis indicated that while a significant difference in the shorebird community structure among lockdown levels was detected, it was secondary relative to zonal variation. SIMPER analysis showed Larus dominicanus (Kelp Gull) to be the dominant shorebird species, contributing the most to community structure within all three lockdown levels. Significant differences in community indices and L. dominicanus abundance were detected between zones but not lockdown levels, apart from the Shannon-Wiener diversity metric. In general, the minor effects of lockdown levels 3 to 1 on the shorebird community were attributed to high human numbers on the beach and low species variation across the respective lockdown levels. Overall, results indicate a strong negative relationship between shorebird and human abundance on Muizenberg Beach over a two-year period prior to, and including, periods of enforced lockdown. At intermediate to moderate levels, however, lockdown had minimal effects on community structure. In a global context, findings provide valuable information on human impacts on sandy beach shorebirds and suggest that closure for two months may positively impact bird communities within urban beach ecosystems.
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    Impacts of burrowing sandprawns (Kraussillichirus kraussi) on water quality, phytoplankton and pelagic bacterial assemblages
    (2023) De Cerff, Carla; Pillay, Deena; Rocke Emma
    Coastal environments are among the most threatened ecosystems globally, with water quality degradation constituting a major scientific and management issue that requires addressing. Burrowing sandprawns (Kraussillichirus kraussi) have been shown in past research to improve water quality by removing microalgae from the water column. Their burrows are thought to act as biofiltration systems, with water-borne phytoplankton particles being adsorbed onto burrow walls during bi-directional water pumping. However, not much is known about ecological repercussions of this hypothesised mechanism and whether it indiscriminately impacts all microorganisms in the water column. This issue forms the foundation of my research, which aimed to experimentally determine whether potential filtration effects of sandprawns are consistent across pelagic bacterial and phytoplankton assemblages or whether there are any discriminatory responses. Findings demonstrated that increasing sandprawn density did not significantly reduce the abundance of bacterial water quality indicators (Escherichia coli and total heterotrophic bacteria). However, sandprawns were found to reduce the abundance of phytoplankton cells. At the end of the experiment, the relative abundance of phytoplankton in the controls were 1.9 times higher relative to the 100% treatment. Similarly, the concentrations of nitrite were 17.7 times higher in controls relative to 100% treatment at the end of the experiment. Furthermore, increasing sandprawn abundance induced a phytoplankton sizebased shift from pico- to nano dominance, with nanophytoplankton contributing 17.76% at the beginning of the experiment, but shifting to 58.07% at the end of the experiment in the maximum sandprawn density treatment. Additionally, sandprawn presence had no significant impact on cryptophytes or Prochlorococcus-like algal abundance. These results demonstrate that sandprawns disproportionately impact certain groups and influence phytoplankton assemblages beyond biomass decline. These findings are novel as such discriminatory effects on pelagic assemblages have previously not been attributed to endobenthic deposit-feeding ecosystem engineers. This study therefore provides novel insights into mechanisms by which these organisms may alter coastal ecosystems and influence bentho-pelagic coupling processes. This is especially significant when viewed in the context of global change, where understanding the factors that influence phytoplankton dynamics are important for predicting ecosystem functioning under projected climatic conditions. Given the overall top-down impact of sandprawns on phytoplankton, this study supports the idea of sandprawns being effective nature-based tools that can mitigate the global challenge of eutrophication in coastal ecosystems. The results of this study ultimately emphasises the need for protection and conservation of sandprawns (and functionally similar endobenthic engineers) and their habitats from threats such as habitat loss.
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    Influences of the abalone Haliotis midae on subtidal benthic communities
    (2010) Zeeman, Susanna Catharina Franzina; Branch, George M; Pillay, Deena; Jarre, Astrid
    The South African abalone Haliotis midae is a commercially exploited species that is seriously threatened by overfishing and poaching. This not only affects the species itself but also the integrity and functionng of the ecosystem through associated changes in community structure. I assessed the influence of abalone on the ecosystem by a combination of (a) dietary studies, (b) comparisons of communities living on shell versus surrounding rock substratum, and (c) removal experiments using field exclusion/inclusion plots.
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    Interaction between grazing by starfish (parvulastra exigua) and nutrient enrichment on intertidal soft-sediment communities.
    (2013) Qwabe, Welly; Pillay, Deena
    Top-down and bottom-up forces are important determinants of community structure, having significant control over diversity metrics. Bottom-up control is frequently represented by nutrient level, which determines ecosystem productivity. Top-down control includes consumer (e.g. grazers and predators) effects on lower trophic levels. Consumers determine community structure through 2 main interacting mechanisms viz. by creating physical disturbances to the habitat and by removing other species through consumption. Both of these mechanisms rely predominantly on the effectiveness of the consumer in terms of exerting dominance on members of lower trophic levels or in terms of generating physical disturbances to the ecosystem as well as the type of community being affected. Today, the pervasive overharvesting of important consumers and increased nutrient loading in coastal natural habitats are globally recognised as factors requiring urgent attention. Such activities can significantly modify the interaction between top-down and bottom-up forces and the consequent effects on communities. This dissertation presents results of a field experiment investigating the interactive effects of top-down (grazing) and bottom-up (nutrients) effects on intertidal soft-sediment communities on the West coast of South Africa. The herbivorous starfish (Parvulastra exigua) was the grazer used in the study, and manipulated to generate five levels of increasing starfish densities. Slow-release fertilizer (Plantacote N: P: K) was utilized to generate three levels of increasing nutrient levels effects. The experiment was undertaken based upon three central aims, the first of which was to examine if nutrient enhancement can interact with increasing starfish densities to structure communities of producers (microalgae) and consumers (macrofauna). The second aim was to examine if the interactive effects of nutrients and starfish densities can influence the microalgal biomass (Chl a) and extracellular polymeric substances (EPS) associated with the sediment. The third aim was to investigate if the interactive effects of nutrients and starfish densities can affect functional group composition of macrofauna. The findings did not show interactive effects of nutrients and starfish on microalgal and macrofaunal community assemblages. There was, however, a strong influence of nutrient enhancement on both communities. The responses of microalgal morphotypes and macrofaunal species to nutrient enhancement were limited. Seventeen of the 59 microalgal morphotypes which dominated community structure were affected by nutrient enhancement whereas two of the six dominant macrofaunal species were affected by nutrient enhancement. These results indicate that the effects of nutrients on both communities operate on a few taxa. Microalgal morphotypes showed varying responses to increasing nutrient levels including unimodal hump and U-shapes, and linear increases and decreases. The interactive effect of nutrient enrichment and starfish densities was only apparent for few microalgal morphotypes, macrofaunal species and EPS concentration. For diversity indices, only macrofaunal species diversity was influenced by nutrients but the response pattern was not graphically obvious. At the functional group level, increasing nutrient enhancement resulted in an increase in abundance of suspension feeders. Starfish density had a significant effect on EPS concentration, with a hump-shaped response to increasing starfish densities at the first level of nutrient enrichment. Microalgal species richness and diversity were also affected by starfish densities and responded in a U-shape manner against increasing starfish densities at the first and second levels of nutrient enrichment. Surface and burrowing predators/scavengers and suspension feeders were affected by starfish densities. Suspension feeders showed a hump-shaped response against increasing starfish densities at all nutrient levels. In conclusion, the top-down force exerted by P. exigua on producers and consumers was very limited in this study and the bottom-up effect of nutrients was much more important as a structuring agent of producer and consumer assemblages. The findings of the study are evaluated against the predictions of the grazer-reversal hypothesis, which predicts a promotive effect of grazing on diversity at high nutrient levels but a negative effect on diversity at low nutrient levels.
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    Interactions between ecosystem engineering by burrowing sandprawns (Callichirus kraussi) and nutrients: consequences for benthic community structure and ecosystem functioning
    (2019) Qwabe, Welly; Pillay, Deena
    Non-trophic interactions are significant structuring agents of ecological communities. Knowledge of how this process drives ecosystem functioning and community structure either individually, or interactively with other processes, is however, limited, particularly in shallow soft- littoral ecosystems. At a local level, such systems are dominated by allogenic engineers such as the burrowing axiid sandprawn Callichirus kraussi Stebbing, which has important effects on macro- and meiobenthic assemblages. C. kraussi is distributed across the South African coastline, from the subtropical Mozambican border to the temperate west coast borders with Namibia. Bioturbation — the principal mechanism by which C. kraussi engineers influence associated biota in sedimentary systems, also has significant effects on sediment properties, biofilms, microalgal and microbial composition. However, theory suggests that ecosystem engineering effects are contextually dependent and contingent upon processes that are temporally and spatially variable. In South Africa, variations in background nutrient levels across the coastline is significant, with the West coast being dominated strong upwelling, which increases biological productivity. Within the west coast, upwelling is also seasonally variable, being strongest in summer. In view of this natural variability in nutrient levels across the coast, seasonal variability within the west coast and the fact that the sandprawn C. kraussi dominates across these conditions, the central focus of this PhD thesis was to investigate how ecosystem engineering by sandprawns C. kraussi and nutrient levels individually or interactively influence assemblages and ecological processes in coastal soft-sediment ecosystems. The study was carried out in Langebaan Lagoon, which is a marine lagoonal system on the west coast of South Africa that is dominated by sandprawns and subjected to seasonal upwelling that is a feature of the west coast. This thesis was based on the two principal approaches, viz. a field comparative study and in situ experiments. The field observational study investigated the responses of macroand meiofaunal communities to sandprawn bioturbation impacts between upwelling and non-upwelling seasons, with the aim of understanding how upwelling nutrient pulses modify these benthic assemblages. Benthic and water column chlorophyll-a (chl-a) levels were also measured, while meiofaunal communities were investigated within sandprawn burrows (burrow-walls) and at the sediment surface. It was hypothesized that chl-a levels, and community metrics would be lower in winter (non-upwelling) but increase in summer upwelling season due to nutrient pulses. It was also hypothesized that community metrics would be negatively correlated with sandprawn density due to bioturbatory effects (sediment turnover) in winter (non-upwelling) but this relationship would become neutral or positive increased in summer, due to increased productivity offsetting negative bioturbative effects. Clear, non-intuitive and ecologically interesting outcomes emerged from the field study. Firstly, benthic chl-a concentrations appeared to be lower in summer relative to winter in 2015, although, this pattern disappeared in 2016. In contrast, water column chl-a concentrations within the lagoon channel conformed to the posed hypothesis, being consistently greater in summer relative to winter. Even though both macro- and meiofaunal assemblages differed significantly between seasons, the hypothesis that community metrics would be greater in summer relative to winter season was not overwhelmingly supported by these findings. Pearson correlation analyses revealed that sandprawn effects were generally weaker within seasons but stronger when winter and summer data were combined and investigated per year. In terms of the latter, most community metrics and benthic chl-a levels were generally negatively correlated with sandprawn abundances, but this varied seasonally and spatially. Overall, results of the comparative study suggest that increases in water column chl-a levels do not necessarily translate into increases in benthic chl-a and community metric levels. One possible reason for this is that increasing bioturbation by C. kraussi overrides nutrient enrichment effects. This conclusion though is spatially dependent, given that results of correlation analyses were site-specific. The factorial field experiment employed in this dissertation manipulated nutrients (fertilizer capsules, Plantacote N: P: K) and sandprawns (C. kraussi densities) to investigate their individual and interactive effects on benthic assemblages. I hypothesized within the context of the grazer-reversal hypothesis of Proulx and Mazumder (1998) that, responses of diversity metrics should alter from a linear decrease at the ambient nutrient level to a unimodal hump-shaped response at the intermediate nutrient level and then to a linear increase at highest nutrients. Generally, emerging patterns for meiofaunal diversity metrics and individual morphotypes were inconsistent with the prediction of the grazer-reversal model. Instead, responses were of an increasing and decreasing nature. The outcomes of this investigation, however, revealed that meiofaunal community structure at the sediment surface was significantly affected by the main effect of sites and sandprawn densities, while within burrow-walls, the interaction between sites and nutrients, but also sandprawn densities alone, significantly affected meiofaunal community structure. Overall, meiofaunal results of this investigation showed limited support for the grazer-reversal hypothesis. Although the findings of this investigation also indicated limited support for the grazer-reversal hypothesis on the macrofauna community, interactive effects of nutrient enrichment and sandprawn densities emerged to influence the macrofaunal community structure and abundances of certain individual species/taxa. Generally, macrofaunal community metrics exhibited both increasing and decreasing patterns in response to experimental treatments, however, in some instances unimodal hump-shaped patterns emerged. There was evidence of macrofaunal functional groups (i.e. suspension feeders) conforming to the hypothesis posed, but this was site-specific. Overall, I conclude that an interplay between nutrients and sandprawns does not exert strong influences on the benthic communities of Langebaan Lagoon. However, sandprawn ecosystem engineering, mainly in the form of bioturbation overrides nutrient enrichment effects in regulating benthic assemblages.
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    The interactive effect of sandprawn (Callichirus kraussi) stebbing bioturbation and nutrients on macrofaunal communities
    (2011) Cooper, Rachel; Pillay, Deena; Branch, George M
    My thesis combined an observational study and field and laboratory experiments to investigate how nutrients and bioturbation by C. kraussi interact to structure macrofaunal communities and how ambient temperatures influence these factors.