Browsing by Author "Pitcher, Grant C"

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    Comparative laboratory study of photoacclimation in selected dinoflagellate and diatom species of the Benguela ecosystem
    (2010) Balarin, Marianne G; Field, John G; Barlow, RG; Pitcher, Grant C
    In their natural environment the diatoms (mixers) are exposed to fluctuations in incident irradiance due to vertical displacements in the water column induced by turbulence whereas the dinoflagellates (migrators and layer-formers) tend to control their vertical positions. In these two groups of phytoplankton physiological acclimation to these fluctuations results in the variation of a number of measurable photosynthetic parameters and variables which can be evaluated in controlled laboratory experiments. The processes can be expressed in time scales from seconds to hours e.g. carbon to chlorophyll ratio changes over several hours. Photoacclimative responses in five species of dinoflagellates (Alexandrium catenella, Protoceratium reticulatum, Prorocentrum micans, Prorocentrum triestinum, Gymnodinium zeta) and three diatom species (Chaetoceros sp., C. capense, C. cf. pendulus) were investigated with respect to parameters of P versus E curves (P*m, α* and Ek) and variability in chemical composition (C and N), photosynthetic capacity, pigment ratios, maximum quantum yield and chlorophyll to carbon ratio. These species were grown at irradiances of 33 (LL), 178 (ML) and 647 μmol quanta . m-2 . s-1 (HL) at a 12:12h day: night length at 17 ºC. The photosynthetic parameters, pigment concentration and Chl a-specific absorption were mostly affected by photoacclimational status. Species-specific differences were observed at the three different light levels in P versus E curves, pigment concentrations, absorption, carbon to chlorophyll a ratios and quantum yield. Photoprotective carotenoids (diadinoxanthin and diatoxanthin) were significantly different relative to Chl a in eight species of dinoflagellates and diatoms.
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    Experimental cultivation of the South African scallop Pecten sulcicostatus
    (2015) Arendse, Dale Cheryle; Griffiths, Charles L; Pitcher, Grant C
    Although scallops have a high economic value, they have yet to be commercially harvested or farmed in South Africa. Of the 29 Pectinid species recorded on the southern African coastline, Pecten sulcicostatus is the only species considered suitable for aquaculture, due to its large size. An investigation of the suitability of P. sulcicostatus for farming in South Africa forms the basis of this study. The successful cultivation of P. sulcicostatus will depend on successful rearing from fertilized egg to market size, and achieving a growth rate comparable to that of other commercial scallop species. This study aimed to examine the reproductive life cycle, in order to establish whether this species can be artificially conditioned to produce ripe gametes throughout the year and to investigate the various stages of cultivation, in order to determine whether this species is viable for farming. This thesis therefore describes the reproductive cycle of P. sulcicostatus and also reports on the first assessment of broodstock conditioning, larval rearing and the grow-out of spat. The reproductive study was undertaken by monthly collection of scallops in their natural habitat in False Bay from August 2004 - October 2005 and again from August 2010 - August 2011. The reproductive cycle was assessed by means of both gonadosomatic index (GSI) and qualitative and quantitative histological investigation. Environmental parameters were also monitored to determine any linkage to the reproductive cycle. The reproductive cycle was seasonal, with a peak spawning period in winter. A resting period appeared absent, as individuals started producing new gametes immediately after spawning, indicating a possible lack of synchronicity.
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    Scales of variability of phytoplankton composition and biomass in Algoa Bay, South Africa
    (2014) Mbambo, Sifiso Walter; Moloney, Coleen; Pitcher, Grant C; Jackson, Sue
    This study investigated the variability of environmental drivers of phytoplankton communities and biomass at different time scales in Algoa Bay. This research was motivated by Pacific oyster culturing at an Algoa Bay oyster farm. Time series of winds, sea surface temperatures (SSTs) and fluorescence were presented for the period from September/October 2010 to May/June 2012. The time series showed strong seasonal and interannual variability in the winds and SSTs. SSTs ranged from 12.5–25.5°C with a mean (±S.D.) of 18.4 ± 2.3°C. The dominance of south-easterly and south-westerly winds in summer of 2010/11 resulted in cooler temperatures and higher chlorophyll-a concentrations than were found in 2011/12. The summer of 2011/12 had non-persistent south-westerly winds that lead to warm temperatures and low chlorophyll-a concentrations. Two short field trips in early summer 2011 and early autumn 2012 sampled physical, chemical and biological variables. There was minor variability in the winds during these sampling periods and little spatial variability in SST. However, there were spatial differences in nutrient concentrations and chlorophyll-a distributions. The sampling trip in early summer 2011 found a strong thermocline at a depth of approximately 15 m, and SST ranged between 13.5 and 21°C. In early autumn 2012, deep water mixing was evident when the thermocline dropped to about 30 m, with a range of SSTs from 16.5–21°C. Temperature and nutrient values were significantly correlated (at p < 0.001) for NO3, PO4, and SiO4 in both field trips. Phytoplankton community structure in early summer 2011 showed a 30% level of similarity in grouping of species for stations closest to the shore, which had depleted NO3 concentrations. There was a dominance of dinoflagellates of Gonyaulax polygramma and other species, which are known for creating hypoxic conditions in the water column, leading to shellfish mortalities. In early autumn 2012 there was a strong grouping of samples at a 50% level of similarity alongshore, at stations with high NO3 concentrations. In this period pennate diatoms of Pseudo-nitzschia sp. were abundant; this genus has been reported to produce the neurotoxin, domoic acid. Variable environmental conditions with low chlorophyll-a concentrations at Algoa Bay’s marine culture site indicate unsuitable conditions for Pacific oyster production.
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    Taxonomy, distribution and toxicity of dinoflagellate species in the southern Benguela current, South Africa
    (2003) Botes, Lizeth; Hedderson, Terry A; Cook, Peter A; Pitcher, Grant C
    The threat of harmful algal blooms with their attendant problems, exists throughout the Benguela region. In the southern Benguela upwelling system, water discolorations, referred to as 'red tides', are common and usually attributed to dinoflagellate species. The first aim of the thesis was to investigate the taxonomy of gymnodinioid species in the southern Benguela current. In order to investigate the morphology of the southern Benguela isolates, a simple and rapid scanning electron microscope preparative technique was developed. In the course of these studies, a new genus and new species were identified and described.
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    Toxigenic phytoplankton and concomitant toxicity in the mussel Choromytilus meridionalis off the west coast of South Africa in the autumn of 2007
    (2010) Hubbart, Bernadette; Pitcher, Grant C; Bolton, John J
    Harmful algal blooms are prevalent off the west coast of South Africa in the summer and autumn months, and have a detrimental impact on human activities along the coast. Some harmful algal blooms are dominated by phytoplankton which produce toxins that can cause shellfish poisoning syndromes. The relationship between the abundance and toxicity of toxigenic phytoplankton, and the concentrations and composition of toxins in the filter-feeding mussel Choromytilus meridionalis, was investigated. Several different methods were used to determine toxin concentations in the mussel.