Showing papers by "University of Port Elizabeth published in 1979"
TL;DR: Significant correlation coefficients between different body components enabled calculation of regression equations by which biologically important parameters, such as protein, fat, ash and energy, can be estimated from a relatively simple moisture determination.
76 citations
TL;DR: The large wedge clam, Donax serra, shows no tidal migrations but does show a semilunar rhythm of movement from just above mean tide level (MTL) during springs to the low tide level during neap tides.
Abstract: All epifaunal and shallow-burrowing, intertidal macrofauna on an exposed sandy beach appear to undergo tidal migrations which vary in extent but are all upshore on the incoming tide and downshore on the outgoing tide during day and night. In the crustaceans this is probably endogenous rhythmic behaviour and they show increased activity at night. In the molluscs this movement is not synchronised by an intrinsic mechanism but results from behavioural responses to changing physical conditions. The large wedge clam, Donax serra, shows no tidal migrations but does show a semilunar rhythm of movement from just above mean tide level (MTL) during springs to the low tide level during neap tides.
69 citations
TL;DR: Donax serra ROding (Pelecypoda) isalarges and mussel which forms vast populations on some East Cape shores and should be able to penetrate river mouths, but is limited by restricted swash action.
Abstract: Donax serra ROding (Pelecypoda) isalargesand mussel which forms vast populations on some East Cape shores. It is most abundant on exposed beaches where the sand is not too coarse and phytoplankton production is high. Adultsoccupy 1 zonejust above the mean level of spring tide. Spat settle subtidally and move upshore as they grow. Growth is initially rapid, to about 32 mmatoneyearand48 mmattwoyears. Thereafter growth is very slow and most adult productions goesinto reproduction, with a small summerspawning and a large winterspawning each year. Somatic production is low, as large adults totally dominate the population and have low growth and low mortality. Reproductive production is relatively high and P/B values of 0,2 and 0,5 are suggested for growth and reproduction. D. serra was found to be very tolerant of fluctuating salinitiesforupto four days and should be able to penetrate river mouths, but is limited by restricted swash action. Total dry-tissue mass, energy and biochemical constituents showed some...
68 citations
Journal Article•
TL;DR: In this paper, the authors measured volumes of sea water flushed through the interstitial spaces of exposed sandy beaches by swash action and found that the percolation is important in draining particulate and dissolved organic matter into the beaches where decomposition by interstitial fauna recycles the nutrients.
Abstract: Volumes of sea water flushed through the interstitial spaces of exposed sandy beaches by swash action have been measured. They are found to depend on beach profile, sand particle size, type of tide, and degree of wave action. This percolation is important in draining particulate and dissolved organic matter into the beaches where decomposition by the interstitial fauna recycles the nutrients.
37 citations
TL;DR: Meiofauna and protozoan numbers correlated with oxygen tensions and redox values and with each other, and it is suggested that small protozoans are an important food source for the meioFauna.
Abstract: Vertical profiles of oxygenation and fauna were measured in two exposed sandy beaches. At the less exposed site the whole upper metre of sediment was oxidized although the redox potential discontinuity started at 85 cm. Meiofauna were concentrated in the upper 40 cm and protozoa in the upper 55 cm, but bacteria showed no distinct vertical drop-off in numbers. On a more exposed beach the upper 1,3 m was highly oxidized, with meiofauna concentrated in the upper 80 cm and protozoa in the upper 115 cm. Meiofauna and protozoan numbers correlated with oxygen tensions and redox values and with each other. It is suggested that small protozoans are an important food source for the meiofauna. Vertikale profiele van suurstofkonsentrasie en fauna is in twee oop sandstrande bepaal. By die meer beskutte strand was die hele boonste meter sediment geoksideer alhoewel die redokspotensiaal-diskontinu'rteit by 85 cm begin het. Meiofauna was in die boonste 40 cm gekonsentreer en protozoa in die boonste 55 cm, maar daar was nie 'n duidelike - afname in bakteriegetalie op dieper vlakke nie. In die geval van die meer blootgestelde strand was die boonste 1,3 m hoogs geoksideer. Meiofauna was in die boonste 80 cm en protozoa in die boonste 1,15 m gekonsentreer. Meiofauna- en protozoa- getalle het met suurstofkonsentrasies en redokswaardes sowel as met mekaar gekorreleer. Daar word voorgestel dat klein protozoa 'n belangrike voedselbron vir die meiofauna is.
28 citations
TL;DR: Populations of a gastropod, Bullia rhodostoma, and a bivalve, Donax sordidus, were monitored quantitatively over one year on an exposed sandy beach which supports a rich macrofauna and values for both species are compared to those obtained on a nearby sheltered beach which has a poor Macrofauna.
Abstract: Populations of a gastropod, Bullia rhodostoma, and a bivalve, Donax sordidus, were monitored quantitatively over one year on an exposed sandy beach which supports a rich macrofauna. B. rhodostoma had a single reproductive season with copulation in early summer. Growth was slow and is described by a Von Bertalanffy growth curve. The annual mortality rate was very low, - 0,34. Production was estimated and a P/B ratio of 0,94 obtained. A minimum estimate for production by reproduction gave a PR/B of 0,06. The average calorific value was 19,34 kJg D. sordidus appeared to have two spawning seasons and settlements in late winter and late summer. Growth was rapid and mortality moderate - 0,72. Steady state P/B was estimated to be 1,78. The mean calorific value was 18,84 kJg All of these values for both species are compared to those obtained on a nearby sheltered beach shich has a poor macrofauna.
26 citations
TL;DR: The plough shell, Bullia rhodostoma, has been studied on an open sandy beach where it is a common scavenger and samples taken over a year indicate hatching of young individuals from December to February.
Abstract: The plough shell, Bullia rhodostoma (Mollusca: Gastropoda), has been studied on an open sandy beach where it is a common scavenger. Samples taken over a year indicate hatching of young individuals from December to February. They reach a length of about 10 mm after 1 year and 40 mm after 10 years. The von Bertalanffy growth equation is L t = 47 (1 - e -0,19(t+0,23) ) and the annual mortality rate is 0,79. Mean decalcified dry biomass is 209 mg m -2 and production by growth 189 mg m -2 y -1 giving a P/B of 0,9. Most production by adults (>15 mm shell length) goes into reproduction, particularly In the females which grow larger than the males. Production by reproduction is estimated to be about 135 mg m -2 y -1 . Average calorific values are 19,04 kJ g -1 dry tissue Die ploegskulp, Bullia rhodostoma (Mollusca: Gastropoda), is op 'n oop sandstrand bestudeer waar dit 'n algemeen teenwoordige aasvreter is. Monsters wat oor 'n jaar geneem is, dui aan dat die jong individue tussen Desember en Februarie uitbroei. Hulle bereik 'n lengte van ongeveer 10 mm na 1 jaar en 40 mm na 10 jaar. Die Von Bertalanffy groeivergelyking is L t = 47 (1 - e -0,19(t+0,23) )) en die jaarlikse mortaliteitstempo is 0,79. Gemiddelde kalklose drofi biomassa is 209 mg m -2 y -1 wat 'n P/B van 0,9 gee. Die meeste volwasse (>15 mm skulplengte) produksie is in die vorm van voortplanting, veral in die wyfies wat groter as die mannetjies word. Produksie deur voortplanting is omtrent 135 mg m -2 y -1 Gemiddelde kaloriewaardes is 19,04 kJ g -1 droe weefsel.
23 citations
22 citations
TL;DR: Randall et al. as discussed by the authors found that guano harvests are not good indicators of gannet population trends on Bird Island, primarily because of harvesting methods and environmental conditions.
Abstract: Summary Randall, R. and Ross, G. J. B. 1979. Increasing population of Cape Gannets on Bird Island, Algoa Bay, and observations on breeding success. Ostrich 50:168-175. The South African Gannet Sula capensis on Bird Island has doubled in numbers between 1956 and 1974 and the process is continuing. The increase is similar to that of the two closely related species S. serrator and S. bassana. We estimated from the colony surface area and nest density that the number of birds with nests in 1974/5 was approximately 77 000. Making allowance for non-breeders, there were about 100 000 adults in 1974/5. Guano harvests from 1938–75 show considerable annual fluctuations with an overall downward trend. Poor agreement was found when relating guano harvests to population estimates, when the latter are gauged by colony surface area. We suggest that guano harvests are not good indicators of gannet population trends on Bird Island, primarily because of harvesting methods and environmental conditions. The number of chicks ...
21 citations
TL;DR: A population of Donax sordidus (Mollusca, Pelecypoda) has been studied for two years on an open sandy beach, with growth was rapid, the animals reaching 20 mm length within one year.
Abstract: A population of Donax sordidus (Mollusca, Pelecypoda) has been studied for two years on an open sandy beach. There were summer and winter settlements each year with the former being larger. Growth was rapid, the animals reaching 20 mm length within one year. Few live longer than 17 months. Production averaged 168,7 mg dry matter m-2y-1 and the steady state P¯/B¯ was 1,30y-1. Energy values averaged 17,84 kJg-1dry tissue and had a seasonal cycle with maximum values before spawning.
20 citations
TL;DR: The effect of disturbance on sediment cores was investigated and it was found that oxygen demand in disturbed cores increased by up to 60%, due mainly to an increase in bacterial activity.
Abstract: Measurements of biological oxygen demand in a sandy beach using conventional in situ techniques are compared with laboratory measurements of interstitial oxygen changes in intact cores. Oxygen uptake as measured in the laboratory was approximately three times that measured in the field despite the fact that the cores were undisturbed. In addition, the effect of disturbance on sediment cores was investigated and it was found that oxygen demand in disturbed cores increased by up to 60%, due mainly to an increase in bacterial activity. This effect was still evident after 24 hours of incubation. The applicability of conventional respirometer techniques to well-drained systems such as open sandy beaches is questioned and an alternative approach suggested.
TL;DR: In this paper, the primary settlement of mussels on seaweed should be taken into consideration when drawing up management programs, for seaweed harvesting, where other seaweeds provide more easily accessible substrate for primary settlement.
Abstract: Monthly samples of Gelidium pristoides were collected and all the P. perna in these samples were counted and measured. Samples from a sheltered site had on average more P. perna juveniles (10/g dry mass G. pristoides ) than samples from exposed sites (2/g dry mass G. pristoides ), where other seaweeds provide more easily accessible substrate for primary settlement. It is suggested that primary settlement of mussels on seaweed should be taken into consideration when drawing up management programmes, for seaweed harvesting.
TL;DR: Summer respiration rates in Donax serra and D. sordidus were significantly higher than winter rates and the value of the exponent b in the mass/metabolism equation was significantly affected by seasonal temperature acclimation.
TL;DR: In this article, lines of diffraction contrast have been observed near the interfaces of epitaxial layers of III-V compounds in transmission electron microscope samples cut perpendicular to the growth plane.
TL;DR: A rapid method for the quantitative estimation of protozoa populations in sand is described and compared with the seawater-ice technique, which involves the gentle shaking of sand samples in filtered seawater and staining with Acridine Orange for counting under a fluorescence microscope.
TL;DR: The intertidal distribution and abundance of sand and mud-flat meiofauna at the mouth and the middle reaches of Mngazana estuary were monitored and the data compared with those from other South African estuaries.
Abstract: The intertidal distribution and abundance of sand and mud-flat meiofauna at the mouth and the middle reaches of Mngazana estuary were monitored over a period of 15 months from April 1977 to July 1978 and the data compared with those from other South African estuaries.
TL;DR: In this article, it was shown that a ring R is (right) strongly prime if every nonzero two-sided ideal contains a finite set whose right annihilator is zero, and the strongly prime radical s(R)G = s(W) for certain classes of groups.
Abstract: A ring R is (right) strongly prime (SP) if every nonzero two sided ideal contains a finite set whose right annihilator is zero, SP rings have been studied by Handelman and Lawrence who raised the problem of characterizing SP group algebras. They showed that if R is SP and G is torsion free Abelian, then the group ring RG is SP. The aim of this note is to determine some more group rings which are SP. For a ring R we also define the strongly prime radical s(R). We then show that s(R)G = s(W) for certain classes of groups.
01 Jan 1979
TL;DR: It is suggested that primary settlement of mussels on seaweed should be taken into consideration when drawing up management programmes, for seaweed harvesting.
Abstract: Monthly samples of Gelidium pristoides were collected and all the P. perna in these samples were counted and measured. Samples from a sheltered site had on average more P. perna juveniles (10/g dry mass G. pristoides ) than samples from exposed sites (2/g dry mass G. pristoides ), where other seaweeds provide more easily accessible substrate for primary settlement. It is suggested that primary settlement of mussels on seaweed should be taken into consideration when drawing up management programmes, for seaweed harvesting.
TL;DR: In this paper, the authors considered dislocation generation by means of the nucleation of dislocation half-loops in the Peierls troughs of the crystal and developed a theory developed for semicircular dislocation loops.
Abstract: Misfit dislocation generation by means of the nucleation of dislocation half-loops is considered. The theory developed for semicircular dislocation loops is extended to half-loops lying in the Peierls troughs of the crystal. Contour plots of dislocation energy versus dislocation dimensions are produced from which the non-equlibrium behaviour of the loops can be deduced.
Es wird die Bildung von Misfit-Versetzungen durch die Keimbildung von Versetzungshalbschleifen untersucht. Die fur halb-zirkulare Versetzungsschleifen entwickelte Theorie wird auf Halb-Ver-setzungen, die in den Peierlstrogen des Kristalls liegen, angewendet. Die Konturbilder der Versetzungsenergie uber der Versetzungsdimension werden aufgezeichnet, aus denen sich das Nicht-gleichgewichtsverhalten der Schleifen ableiten last.
TL;DR: In this paper, a new phase in the Fe-(111) Au bicrystals was identified as face-centred cubic by tilting diffraction experiments and the lattice parameter of the structure was determined and was found to be a function of the overgrowth thickness.
TL;DR: The energy expression for threading dislocation in a single-layer heteroepitaxial structure which bows out under the influence of the coherency strain is derived in this article.
Abstract: The energy expression for a general threading dislocation in a single-layer heteroepitaxial structure which bows out under the influence of the coherency strain is derived. It is found that, whereas some threading dislocations begin to bow out only once the epilayer has attained a certain critical thickness, others commence the bowing-out process as soon as the epilayer starts to grow. The results of this work are applied to the special cases of (001) and (211) oriented GaAs-Ga0.7Al0.3As single-layer structures.
Der Energieausdruck fur eine allgemeine, sich durch eine einschichtige heteroepitaktische Struktur ziehende Versetzung, die sich unter dem Einflus der Koharenzspannung verbiegt, wird abgeleitet. Es wird gefunden, das, wahrend einige der sich durchziehenden Versetzungen erst dann anfangen sich zu verbiegen, wenn die Epitaxieschicht eine gewisse kritische Dicke erreicht hat, die anderen den Verbiegungsprozes beginnen, sobald die Epischicht zu wachsen beginnt. Die Ergebnisse dieser Arbeit werden auf den speziellen Fall von (001)- und (211)-orientierten GaAs-Ga0,7Al0,3As-Einschichichtstrukturen angewendet.
TL;DR: It is suggested that D. r.
Abstract: Derocheilocaris remanei katesae was described from Durban on the east coast of South Africa by Noodt (1954). He distinguished this subspecies on the basis of the shape of the anterior portion of the cephalon, the spines and seta of the anal operculum and the body shape. The work of Hessler ( 1972 ) on African mystacoca rids brought to light the extreme conservativeness of this subclass and the minute nature of differences sufficient to warrant species status. Forms from Angola and South West Africa, considered by Noodt to be D. remanei, were shown by Hessler to be distinct species and named D. angolensis and D. delamarei respectively. D. r. katesae thus became separated from the type D. remanei by at least two species and nearly 1000 km of coastline. A further species was then recorded from Algoa Bay on the south-eastern corner of Africa (McLachlan & Grindley, 1974) and named D. algoensis. At the time it was not certain whether D. r. katesae and D. algoensis were the same species or whether D. r. katesae was distinct and warranted species status. Noodt's (1954) description of D. r. katesae was not sufficiently detailed to decide this. Now as the result of a series of collections along the east coast of South Africa both north and south of Durban it is possible to clarify this. All specimens examined from these east coast collections are identical to D. algoensis. Three points of difference between Noodt's (1954) description and D. algoensis, namely (1) the antero-medial notch of antennulary portion of cephalon, (2) the constriction separating antennulary portion of cephalon from the rest of the cephalon and (3) the acute process on the supra anal process (anal operculum), were checked. In all cases these appeared as described for D. algoensis, namely (1) a U-shaped anteromedial notch in the cephalon, (2) the constriction in the cephalon had a distinct notch and (3) the supra anal process had two acute processes, a short stout vertral one and a slender, longer dorsal one. It must thus be concluded that D. r. katesae and D. algoensis are conspecific and the small differences in Noodt's description were due to distorted specimens. It is therefore suggested that D. r. katesae Noodt, 1954 be considered a senior synonym of D. algoensis McLachlan & Grindley, 1974. The recorded range of D. katesae is now extended from Algoa Bay up the east coast of South Africa to Sordwana Bay near the Mozambique border. REFERENCES
TL;DR: A 35 year old male suffering from obsessive-compulsive neurosis was referred to this examiner after 18 months of psycho-analysis and it was reported that marital, personal and social relations had improved as a result of his control over previous compulsive acts.
Abstract: A 35 year old male suffering from obsessive-compulsive neurosis was referred to this examiner after 18 months of psycho-analysis. The client's multiple obsessive-compulsive behaviour had decreased only slightly and further obsessions had subsequently manifested themselves. A seven-day baseline was initiated after which a multimodal behaviour therapy regimen was used over a 28-day period. After the 21st day the subject reported full control of his compulsions and on a six-week assessment he reported that marital, personal and social relations had improved as a result of his control over previous compulsive acts.