UWCScholar :: Browsing by Author "Smit, Albertus J."

Browsing by Author "Smit, Albertus J."

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An assessment of the influence of host species, age, and thallus part on kelp-associated diatoms
(MDPI, 2020) Mayombo, Ntambwe Albert Serge; Majewska, R.; Smit, Albertus J.
Diatom community composition and abundances on different thallus parts of adult and juvenile specimens of Ecklonia maxima and Laminaria pallida were examined in False Bay, South Africa, using light and scanning electron microscopy. Altogether, 288 thallus portions were analysed. Diatom abundances ranged from 0 to 404 cells mm−2 and were generally higher on E. maxima and juvenile thalli than L. pallida and adult specimens. Moreover, diatom abundances differed between the various thallus parts, being highest on the upper blade and lowest on the primary blade. A total of 48 diatom taxa belonging to 28 genera were found. Gomphoseptatum Medlin, Nagumoea Witkowski and Kociolek, Cocconeis Ehrenberg, and Navicula Bory were the most frequently occurring genera, being present in 84%, 65%, 62.5%, and 45% of the analysed samples, respectively. Among these, Cocconeis and Gomphoseptatum were the most abundant, contributing 50% and 27% of total diatom cells counted collectively across all samples.
A blueprint for integrating scientific approaches and international communities to assess basin-wide ocean ecosystem status
(Nature Research, 2023) Roberts, J. Murray; Devey, Colin W.; Smit, Albertus J.
Ocean ecosystems are at the forefront of the climate and biodiversity crises, yet we lack a unified approach to assess their state and inform sustainable policies. This blueprint is designed around research capabilities and cross-sectoral partnerships. We highlight priorities including integrating basin-scale observation, modelling and genomic approaches to understand Atlantic oceanography and ecosystem connectivity; improving ecosystem mapping; identifying potential tipping points in deep and open ocean ecosystems; understanding compound impacts of multiple stressors including warming, acidification and deoxygenation; enhancing spatial and temporal management and protection. We argue that these goals are best achieved through partnerships with policy-makers and community stakeholders, and promoting research groups from the South Atlantic through investment and engagement. Given the high costs of such research (€800k to €1.7M per expedition and €30–40M for a basin-scale programme), international cooperation and funding are integral to supporting science-led policies to conserve ocean ecosystems that transcend jurisdictional borders.
Climate change in coastal waters: Time series properties affecting trend estimation
(AMS, 2016) Schlegel, Robert W.; Smit, Albertus J.
In South Africa, 129 in situ temperature time series of up to 43 years are used for investigations of the thermal characteristics of coastal seawater. They are collected with handheld thermometers or underwater temperature recorders (UTRs) and are recorded at precisions from 0.58 to 0.0018C. Using the natural range of seasonal signals and variability for 84 of these time series, their length, decadal trend, and data precision were systematically varied before fitting generalized least squares (GLS) models to study the effect these variables have on trend detection. The variables that contributed most to accurate trend detection, in decreasing order, were time series length, decadal trend, variance, percentage of missing data (% NA), and measurement precision. Time series greater than 30 years in length are preferred and although larger decadal trends are modeled more accurately, modeled significance (p value) is largely affected by the variance present. The risk of committing both type-1 and type-2 errors increases when $5% NA is present. There is no appreciable effect on model accuracy between measurement precision of 0.18–0.0018C. Measurement precisions of 0.58C require longer time series to give equally accurate model results. The implication is that the thermometer time series in this dataset, and others around the world, must be at least two years longer than their UTR counterparts to be useful for decadal-scale climate change studies. Furthermore, adding older lower-precision UTR data to newer higher-precision UTR data within the same time series will increase their usefulness for this purpose.
Epiphytic diatom assemblages associated with South African kelps: Ecklonia maxima and Laminaria pallida
(University of Western Cape, 2020) Mayombo, Ntambwe Albert Serge; Smit, Albertus J.; Majewska, Roksana
Kelp forests are dynamic and productive ecosystems which host large biodiversity of sessile fauna and flora, including diatoms. These microalgae occur at the base of coastal marine food webs and contribute substantially to the productivity of marine ecosystems. Diatoms constitute one of the most common and species-rich groups of both phytoplankton and phytobenthos. Possessing a unique silica cell wall, diatoms play a key role in the global carbon and silicon cycles. As the changes in species composition of diatom communities are a direct reaction to the combination of environmental factors prevailing in their ecosystems, diatom analysis is widely and successfully used in biomonitoring of various environmental conditions and paleoecological reconstructions.
A novel approach to quantify metrics of upwelling intensity, frequency, and duration
(Public Library of Science, 2021) Abrahams, Amieroh; Schlegel, Robert W.; Smit, Albertus J.
The importance of coastal upwelling systems is widely recognized. However, several aspects of the current and future behaviors of these systems remain uncertain. Fluctuations in temperature because of anthropogenic climate change are hypothesized to affect upwelling-favorable winds and coastal upwelling is expected to intensify across all Eastern Boundary Upwelling Systems. To better understand how upwelling may change in the future, it is necessary to develop a more rigorous method of quantifying this phenomenon. In this paper, we use SST data and wind data in a novel method of detecting upwelling signals and quantifying metrics of upwelling intensity, duration, and frequency at four sites within the Benguela Upwelling System. We found that indicators of upwelling are uniformly detected across five SST products for each of the four sites and that the duration of those signals is longer in SST products with higher spatial resolutions. Moreover, the high-resolution SST products are significantly more likely to display upwelling signals at 25 km away from the coast when signals were also detected at the coast.
Plastic ingestion by estuarine mullet Mugil cephalus (Mugilidae) in an urban harbour, KwaZulu-Natal, South Africa
(National Inquiry Services Centre (NISC), 2016) Naidoo, T.; Glassom, D.; Smit, Albertus J.
Coastal urban environments have high plastic pollution levels, and hence interactions between plastic debris and marine life are frequent. We report on plastic ingestion by mullet Mugil cephalus in Durban Harbour, KwaZulu-Natal, South Africa. Of 70 mullet (13.0–19.5 cm total length), 73% had plastic particles in their guts, with a mean of 3.8 particles per fish (SD 4.7). Plastic ingestion showed no relation to digestive tract content or fish length. White and clear plastic fibres were ingested most commonly. This urban population of M. cephalus had a higher incidence of plastic ingestion than has been reported in studies on fish from other coastal areas or the oceanic environment.
Riverine dominance of a nearshore marine demersal food web: evidence from stable isotope and C/N ratio analysis
(National Inquiry Services Centre (NISC), 2016) de Lecea, A.M.; Smit, Albertus J.; Fennessy, S.T.
The Thukela Bank, KwaZulu-Natal, supports a diverse ecosystem and South Africa’s only prawn fishery. Oceanographic studies suggest riverine input is not important for the biology of this system, whereas biological studies suggest the contrary, with prawn catches increasing with increased fluvial run-off. The aim of this study was to determine (i) the importance of riverine and marine organic matter for the Thukela Bank food web; and (ii) whether there are seasonal changes in the Thukela River stable isotope values, and, if so, whether these are reflected in the isotope values of demersal organisms. Estuarine organic matter, sediments and demersal organisms were collected from several sites across the bank in the wet and dry seasons of 2008, 2009 and 2010. Marine particulate organic matter was also collected in 2010 and analysed for δ13C and δ15N, as well as C/N ratios. There were strong seasonal changes in isotopic values of organic matter and fauna, especially faunal δ13C. There was an apparent time-lag in organisms assimilating riverine organic matter isotopic values, with the isotopic signature of demersal organisms reflecting that of riverine organic matter from the previous season, which is likely the result of tissue turnover time. In 2010, Thukela Bank sediment organic matter was of riverine origin and this maintained the demersal food web. We conclude that Thukela River organic matter is an important input to the food web of the Thukela Bank, indicating that any future damming of the catchment area could have serious consequences for this ecosystem.
Seaweeds in two oceans: beta-diversity
(Frontiers Media, 2017) Smit, Albertus J.; Bolton, John J.; Anderson, Robert J.
Several species assembly mechanisms have been proposed to structure ecological communities. We assess the biogeography of seaweeds along 2,900 km of South Africa’s coastline in relation to a thermal gradient produced by the Agulhas Current, and contrast this with the environmental structure created by the Benguela Current. We subdivided the coastline into “bioregions” to examine the regional patterning. To investigate the assembly mechanisms, we decomposed Sørensen’s b-diversity into “turnover” (bsim) and “nestedness-resultant” (bsne) dissimilarities, and used distance-based redundancy analysis (db-RDA) to relate them to the Euclidean thermal difference, dE, and geographical distance. Moran’s eigenvector maps (MEM) were used as an additional set of spatial constraints. Variation partitioning was then used to find the relative strengths of thermal and spatially-structured thermal drivers. Spatial and environmental predictors explained 97.9% of the total variation in bsim and the thermal gradient accounted for 84.2% of this combined pool. bsim was the major component of overall b-diversity in the Agulhas Current region, suggesting niche influences (environmental sorting) as dominant assembly process there. The much weaker thermal gradient in the Benguela Current-influenced region resulted in a high amount of bsne that could indicate neutral assembly processes. The intensification of upwelling during the mid-Pliocene 4.6–3.2 Ma (i.e., historical factors) were likely responsible for setting up the strong disjunction between the species-poor west coast and species-rich south and east coast floras, and this separation continues to maintain two systems of community structuring mechanisms in the Atlantic and Indian Ocean influenced sides of South Africa.
Winter is coming: A southern hemisphere perspective of the environmental drivers of sars-cov-2 and the potential seasonality of covid-19
(MPDI, 2020) Smit, Albertus J.; Fitchett, Jennifer M.; Engelbrecht, Francois A.
SARS-CoV-2 virus infections in humans were first reported in December 2019, the boreal winter. The resulting COVID-19 pandemic was declared by the WHO in March 2020. By July 2020, COVID-19 was present in 213 countries and territories, with over 12 million confirmed cases and over half a million attributed deaths. Knowledge of other viral respiratory diseases suggests that the transmission of SARS-CoV-2 could be modulated by seasonally varying environmental factors such as temperature and humidity. Many studies on the environmental sensitivity of COVID-19 are appearing online, and some have been published in peer-reviewed journals. Initially, these studies raised the hypothesis that climatic conditions would subdue the viral transmission rate in places entering the boreal summer, and that southern hemisphere countries would experience enhanced disease spread. For the latter, the COVID-19 peak would coincide with the peak of the influenza season, increasing misdiagnosis and placing an additional burden on health systems. In this review, we assess the evidence that environmental drivers are a significant factor in the trajectory of the COVID-19 pandemic, globally and regionally. We critically assessed 42 peer-reviewed and 80 preprint publications that met qualifying criteria.

Browsing by Author "Smit, Albertus J."

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