OpenUCT :: Browsing by Author "Griffiths, Charles L"

Browsing by Author "Griffiths, Charles L"

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Open Access
Abundance and mortality of anchovy eggs caused by cannibalism and intraguild predation, and the potential effect on anchovy recruitment and clupeoid fluctuations
(1991) Szeinfeld, Edy Sylvia Valdes; Griffiths, Charles L
This thesis is structured in the form of five main chapters, each written in the form of an independent paper and supported by a general conclusion and one previously published paper on the same general theme. The central theme is the dynamics, ecology and evolution of intraspecific and intraguild predation - specifically the determination of an interacting mechanism between the guild fish species Engraulis capensis and Sardinops ocellatus and its significance for future fisheries management.
Open Access
An analysis of factors controlling the distribution of zooplankton in the Knysna estuary, South Africa
(1987) Veldhuis, Helen Anne; Griffiths, Charles L
The Knysna estuary system, on the south coast of South Africa, was sampled for zooplankton over period of one year. All species were recorded and an attempt was made at relating the distribution of populations to physical factors within the estuary. Over 50 species were identified. Pseudodiaptomus hessei, Acartia(Paracartia) longipatella and A.(Acartiella) natalensis were the dominant copepods in the upper estuary. Paracalanus spp. were dominant near the mouth. Zooplankton distribution was found to be related to tidal exchange. The zooplankton displayed a seasonal cycle of abundance, with maximum numbers occuring during summer. P. hessei displayed no pronounced seasonal cycle in abundance. Its abundance was strongly related to freshwater inflow. Seasonal succession was evident between A. natalensis, the summer dominant, and A. longipatella, the winter dominant. The controlling factors for this cyclical dominance were not clear. Diel vertical migration behaviour was shown to various degrees by virtually all zooplankton populations. The stimulus for this behaviour could not be definitely identified.
Open Access
Aspects of the biology and population dynamics of the deep-water commercially exploited crabs off South West Africa/Namibia
(1987) Melville-Smith, Roy; Griffiths, Charles L
Two crab species have been exploited on the South West African/ Namibian continental slope since 1973. The deep-sea red crab Geryon maritae forms >99 percent of the catch made by traps, the balance being a by-catch of stone crab Lithodes tropicalis. Historical information dating back to the late 1970's has been examined, but most of the data analysed in this study have been collected since 1980. Most of the research has been conducted on red crab. Four aspects of its biology have been examined in some detail, namely its reproduction, growth, movements and causes of its specific dep t h zonation off Namibia. These (particularly the first two) aspects have been used, together with information from commercial sampling and catch statistics, to examine possible changes in the yield-per-recruit should the age at first capture be increased, or fishing effort reduced. On the basis of these results, some management options are presented. Several techniques (photography, trawling, effective fishing area and tag-recapture) have been used to examine the abundance and density of red crab off Namibia, and are critically compared . Research on the stone crab has been largely restricted to an analysis of commercial catch data, though an unusual symbiotic relationship with a liparid fish has been identified and discussed.
Open Access
Aspects of the biology of, and fishery for, the Hottentot, Pachymetopon blochii (Val.) (Sparidae), in the Western and Southwestern Cape
(1987) Pulfrich, Andrea Christine; Griffiths, Charles L
Data extracted from historic records have been used together with information collected during a survey of major fishing centres in the west and southwest Cape, from Port Nolloth to Struis Bay, to document the development of the handline fishery, with special reference to the fishery for hottentot Pachymetopon blochii (Val.). The fishing communities are described and social conditions are compared with those reported in earlier surveys. Changes in the fishing vessels and tackle used in the handline fishery are described and the economic status of the fishery evaluated. The distribution and availability of P. blochii are assessed in relation to the various tackle types and catch methods in different areas and the contribution by this species to the total annual linefish catch is estimated. Total fishing effort expended in the commercial linefishery is used to calculate catch-per-unit-effort indices for the hottentot fishery and the seasonal and long-term trends in these indices are evaluated in relation to past and present constraints on the marketing of this species.
Open Access
Aspects of the biology, ecology and fishery of the beaked clam Eumarcia paupercula (Holten, 1802), in Maputo Bay
(2016) Mugabe, Eulália D.; Griffiths, Charles L; Macia, Adriano
Clam populations globally have declined, or been depleted, with one of the major causes being uncontrolled human exploitation. This thesis investigates the population structure, growth, reproduction and exploitation of the beaked clam Eumarcia paupercula in Maputo Bay. The substantial commercial harvesting of this clam may lead to overexploitation of the resource. In this regard, some fundamental knowledge is necessary for the management of future exploitation. The data collection was based on an 18-months (November 2012 - April 2014) sampling for population structure across a tidal flat. The growth analysis was performed on FiSAT II, using mark-recapture experiments and length-frequency data. Monthly reproduction analysis was based on the fluctuation of body weight and gonad smear analysis. Furthermore, interviews were used to ascertain the importance of the resources for collectors and estimate landings of E. paupercula. The von Bertalanffy growth function and length-frequency analysis revealed that E. paupercula has a fast growth rate and a short life span. Eumarcia paupercula is a year-round spawner with higher peaks in the summer; recruitment follows a similar pattern, occurring over the year and after the spawning peaks. The clam collectors, the majority of whom are women, have experienced an increase in the effort required to collect clams, resulting in a decline of catches over the season. This study highlights that temporal population dynamics are influenced by collection and reproductive patterns, and that single environmental parameters do not explain the patterns of growth, reproductive cycles and spatial distribution. Findings of this study have relevance and application for the livelihood of the collectors, as well as the sustainability of the Eumarcia paupercula stock, by providing a basis for fishery governance. While recommendations are presented for the management of E. paupercula collection, the Ministry of Fishery in Mozambique also has to consider collecting data on bivalves, as they are an important source of income for artisanal fishers. Future research should include monitoring of a less exploited population, so as to understand better how collection impacts on the population dynamics of E. paupercula. Furthermore, laboratory studies of the larval cycle are necessary to gain thorough understanding of the species life cycle.
Open Access
Behavioural ecology of white sharks carcharodon carcharias in False Bay, South Africa: towards improved management and conservation of a threatened apex predator
(2014) Kock, Alison Ann; O'Riain, Justin; Griffiths, Charles L; Mauff, Katya
The coastal waters off South Africa support a significant proportion of the global white shark population, with at least four well-established coastal aggregation sites. How critical these sites are to the southern African and hence global white shark population depends to a large extent, on their levels of residency a nd site fidelity, in relation to potential threats. Here, I attempt to provide such data by studying the annual and seasonal presence of white sharks in False Bay. From 1 April 2004 - 31 December 2007, a total of 68 (46 female, 22 male) sharks, ranging in length from 1.7 to 5 m, were tagged with acoustic transmitters and monitored on an array of 30 receivers, distributed along the Inshore region of False Bay and at Seal Island, for a maximum of 1349 days. I used generalized linear mixed effects models to investigate the effects of season, habitat type, sex, size and time of day on shark presence. Most tagged sharks were immature animals, some of which were detected in the Bay in all months and across all years. In autumn and winter, males and females aggregated around Seal Island, where they fed predominantly on young-of-the-year seals. Sharks, regardless of sex or size, over-dispersed on the South side of the Island at sunrise, where the probability of encountering predator-naïve seals was highest. Shark presence at Seal Island mirrored the spatial distribution of predation around the Island, which was highest on the South side within 400 m of the Island, and at sunrise. In spring and summer, there was marked sexual segregation in presence, with females frequenting the Inshore areas and males seldom being detected in the Bay . Within the Inshore region, female white sharks showed a preference for beach, compared to rocky, mixed and harbour habitats. The preference for beach habitat likely reflects a combination of high prey availability, in addition to an open habitat suitable for detecting and securing prey. Overall, the results confirm False Bay as a critical area for white shark conservation as both sexes, across a range of sizes, show high levels of fidelity to the Bay.
Open Access
Biogeographical patterns of southern African marine invertebrates
(2009) Scott, Robyn; Griffiths, Charles L
Biogeography is defined as the study of life, in a spatial and temporal context, with respect to the analysis and explanation of patterns for a given area. The tendency for species richness and diversity to increases towards the equator, where both peak, is a much debated and tested pattern. Underlying mechanisms thought to cause this pattern are: gradients in temperature, stress, productivity, competition, predation, stability, effective evolutionary time, niche breadth, range size and area of occupancy. Evidence exists that both supports and negates most of these mechanisms. In addition to the richness gradient, a latitudinal gradient in geographical range size exists, whereby species range sizes decrease with latitude, referred to as Rapoport's Rule. This has been linked to species ability to tolerate changes in climate. The latitudinal gradient in species richness is thought to be a by-product of Rapoport's Rule and the "Rescue Effect".
Open Access
Biological structure of an Agulhas Bank subtidal reef community and consumption estimation for a dominant species
(1988) Duvenage, Ian R; Griffiths, Charles L
This thesis reports on an investigation into some aspects affecting and contributing to the flow of organic matter through a subtidal reef environment. In particular, the contribution of Porifera to the organic matter pool in terms of biomass and the consumption of organic matter by a dominant Porifera species are assessed. Further, reef fauna biomass and community structure, as well as Porifera respiration, the subsurface temperature regime above the subtidal reef and the amount of organic matter available for utilization are examined.
Open Access
The biology, distribution and ecology of Lampanyctodes hectoris and Maurolicus muelleri along the South-African coast
(1986) Prosch, Richardt Murray; Griffiths, Charles L
Lampanyctodes hectoris, commonly called lanternfish, is a myctophid and was first recorded in the South African pelagic catches in 1969. The average annual landings since then have been approximately 4% of the pelagic catch, the largest being 42 560 metric tons in 1973 (10,45% of the total landing). Maurolicus muelleri, commonly called lightfish, is a sternoptychid, and is not taken commercially. An attempt was made to document the basic biology of these two species before possible commercial fishing pressure brings about a change in these parameters. Samples of L. hectoris taken from commercial catches and research cruises, and samples of M. muelleri obtained from research cruises were analysed to obtain the biological parameters. L. hectoris spawning in the southern Benguela Current System occurs throughout the year, but mainly during the late winter to early spring with a peak in spring. M. muelleri spawning occurs throughout the year with a peak in spring/early summer and a smaller peak in winter. Maturity analysis show the same pattern, and also indicate that M. muelleri spawning has both a vertical and a horizontal dimension and its eggs were found in the temperature range 14 to 11°c.
Open Access
Brooding behaviour in Ophioderma wahlbergii, a shallow-water brittle star from South Africa
(2014) Landschoff, Jannes; Griffiths, Charles L
The brooding behaviour and brooded young are described for Ophioderma wahlbergii Müller & Troschel 1842, a large, common brittle star from the coastal waters of South Africa. Twenty specimens were collected each month from June 2013 – May 2014 (n = 240). The species was found to be gonochoric.
Open Access
Catch, effort and socio-economic characteristics of the gill and beach-seine net fisheries in the Western Cape, South Africa
(2000) Hutchings, Kenneth; Griffiths, Charles L; Lamberth, S J
This study was conducted with the overall objective of providing scientific infonnation relevant to the management of the gill and beach-seine net fisheries, particularly with respect to decisions about increased participation in the fisheries. Its primary aims were to provide quantitative estimates of total catch and effort, to assess the current and potential future importance of by-catch in the fisheries, to describe the socio-economic status of participants and to evaluate the management measures currently in effect.
Open Access
Climate and Bioinvasives drivers of change on South African Rocky shores?
(2011) Mead, Angela; Griffiths, Charles L
The overall aims of the thesis were to assess spatio-temporal change in macro species assemblages at sites located around the South African coast. Detected changes were considered in parallel with regional patterns of bioinvasion and climate change driven shifts in temperature trends over comparable time scales.
Open Access
The commercial fishery for sharks in the South-Western Cape, with an analysis of the biology of the two principal target species, Callorhinchus Capensis Dumeril and Galeorhinus Galeus Linn
(1992) Freer, David Walter Leacroft; Griffiths, Charles L
The South African shark fishery began in World War 2, based on a demand for shark liver oil. The initial landings are estimated at 3750 tons per annum, but have since declined to approximately 820 tons of shark, principally Galeorhinus galeus, with an additional 800 tons of Callorhjncbus capensis. The fishery for the later species has largely only developed since 1980. The fisheries for both of the principal species are dependent for their commercial success on fishing schools of breeding aggregations and in both cases the catch is mainly taken in breeding and nursery areas. G. galeus is a largely ichthyophagous species, which forms schools of fish of similar size. After sexual maturity, which is reached at a minimum TL of 1 278 mm (8,5y) for males, and a minimum TL of 1 371 mm (9,9y) for females, these schools further assort to include only mature fish of one sex. They are highly mobile and may be migratory. Fecundity is low in newly sexually mature fish but gradually increases with increasing size, although a mathematical relationship for this could not be established. The maximum number of pups recorded in this study was 20.
Open Access
Comparative ecology and physiology of four South African mussel species with notes on culture potential
(1991) Van Erkom Schurink, Corine; Griffiths, Charles L
The objective of this study was to compare the distribution patterns, reproductive cycles, growth rates and physiological processes in four species of South African marine mussels - Aulacomya ater, Choromytilus meridionalis, Mytilus galloprovincialis and Perna perna. The first chapter is a preliminary account of the introduction of the invasive M. galloprovincialis, and its ecological effects. Its rate of invasion is estimated by monitoring changes in the diet of oystercatchers, as well as comparing its resistance to silt and dessication, and its reproductive and its growth strategies with those of other intertidal mussel species. It appears that although presently mainly confined to cool water of the west and south coasts, M. galloprovincialis will soon colonize in the near future the warmer waters of the east coasts. The second chapter consists of a survey revealing the distribution patterns and standing stock of the four species around the South African coasts. The cool upwelled waters of the west coast support the major populations of A. ater, C. meridionalis and M. galloprovincialis, while the warm east coast is mainly colonized by the brown mussel P. perna. The Transkei and Natal coasts are intensively exploited by subsistence gatherers with an annual rate of removal approaching or even exceeding standing stock. The overall wild crop is ca > 1000 metric tons, while aquaculture output is estimated at 800 tons per annum. The third chapter looks at the timing and the intensity of spawning of the four species. Gamete build up and release results in marked variation in flesh yield. The dry flesh weight of M. galloprovincialis can vary three-fold between ripe and spawned conditions at a length of 65mm. Equivalent figures for C. meridionalis, A. ater and P. perna are respectively 2.8, 2.3 and 2.2-fold. It appears that A. ater shows the greatest gamete output with three annual spawnings, followed by M. galloprovincialis and C. meridionalis with two protracted spawnings. The fourth chapter deals with growth performance of the four species under different environmental conditions. A. ater consistently grows much slower than other species, is intolerant to aerial exposure or silt load and grows best in cold waters. C. meridionalis also likes cool water conditions, but is the most tolerant of silt load. M. galloprovincialis and P. perna are the least affected by tidal exposure and both grow faster in warm water conditions. In terms of aquaculture development, M. galloprovincialis is the most appropriate species to grow on the west and south coasts, while P. perna will be the candidate for the east coasts of South Africa. The fifth chapter compares rates of filtration, respiration and ammonia excretion, as well as absorption efficiencies and subsequent scope for growth in the four mussel species. All species maintain a relatively steady scope for growth over the ration levels 1-7 mg 1- . However, rates are the highest in M. galloprovincialis (254 J h-1 at 7 mg 1-1 ration) followed by C. meridionalis and P. perna at 117 and 70 J h-1 and finally A. ater, with only 23 J h-1. Scope for growth in M. galloprovincialis is high at all temperatures (1 o-20Â°c) while that of A. ater is low and declines rapidly with temperature. The scope for growth of P. perna and C. meridionalis is intermediate, but while C. meridionalis becomes less efficient at higher temperatures P. perna show a rapid increase with increasing temperature. These physiological measures are correlated to the observed distribution pattern and growth rates in the field.
Open Access
Contributions to the taxonomy of South African hermit crabs (Crustacea: Decapoda: Paguroidea) – integrating microCT scanning and barcoding
(2018) Landschoff, Jannes; Griffiths, Charles L
Hermit crabs form an important component of the marine benthos and globally more than 1,200 species have been described. In the unique bioregion of South Africa, hermit crabs are poorly known, and the last taxonomic revision of the group was that of K. H. Barnard in 1950, who recorded only 32 species. This study combines morphological taxonomy, threedimensional (3D) micro-computed tomography (µCT) visualisations, and molecular barcoding to add to, revise, and provide an updated listing of, the regional fauna. The first section of the thesis comprises four chapters, each giving a detailed account of a species either new to science, or to the region. The pagurid hermit crab Goreopagurus poorei, a new species and genus record to the country, is reported and described from deep sea habitats along the Agulhas Shelf, extending the distribution by >10,000 km across the Indian Ocean. Furthermore, three species are described as new to science, one each from the three most common families. The first of these, a deep-water species from a genus of the family Parapaguridae that was previously unknown to South Africa, Paragiopagurus atkinsonae n. sp., is fully described and illustrated, and compared with two other parapagurids that each play a dominant role in the regional benthic offshore invertebrate community. The other two species new to science, Diogenes n. sp. from the family Diogenidae, and Pagurus n. sp. from the family Paguridae, inhabit coastal reefs in subtidal waters off southern KwaZulu-Natal. For the first time in crustacean taxonomy, species descriptions, particularly the one of Pagurus n. sp., are informed by, or based on, µCT imagery of calcified body parts. Following on this technique, Chapter 6 is a short presentation of the 3D raw dataset of seven µCT scans of types and rare museum specimens used in this thesis, which is made publicly available for download. The taxonomic use of the scanning method, with disseminating volumetric data of hermit crabs, is discussed briefly. The final section investigates the fauna as a whole. In Chapter 7, 194 cytochrome c oxidase subunit I gene segments (COI ‘barcodes’) of 43 nominal species plus 12 additional putative species (n = 55 species-like units) were used to validate morphological identifications. Testing this dataset revealed high barcoding efficacy, with nearly 99% identification success rates, and with the best Kimura 2-parameter distance to safely delimit species of hermit crabs of about 3.5%. Chapter 8 updates the regional fauna and provides taxonomic accounts for 62 nominal species which have either been added subsequent to the previous monographic review, or which have undergone taxonomic revision since that time. Of these, 12 are added for the first time here, increasing the number of known South African hermit crab species to 72, an expansion of 56% since Barnard, and about 20% since a recent species list published by W. Emmerson in 2016. Because colour images are provided for 51 out of 72 species, Chapter 8 can also be used as a preliminary guide. However, this study has shown that the hermit crabs of South Africa are by far more diverse than originally thought, and the summary, which includes only the 72 nominal taxa and none of the additional 10 putative species included in the barcoding dataset, is speculated to be only 60–70% complete. Future taxonomic work, especially in the genera Diogenes and Paguristes, will most likely result in many more species descriptions. Therefore, this current study is to be seen as important step towards a fully illustrated taxonomic catalogue on the South African hermit crabs to be produced in the near future.
Open Access
Deep water parapagurid hermit crabs: their distribution, abundance, population structure and associations in the Southern Benguela
(2017) Wright, Amy Grace; Griffiths, Charles L
The parapagurids Sympagurus dimorphus (Studer, 1883) and Parapagurus bouvieri (Stebbing, 1910) dominate South African deeper-water benthic invertebrate communities. Samples from the 2016 DAFF bi-annual hake demersal research trawl surveys provided data on population structure and morphology. Since these species forego the use of "traditional" gastropod shells in favour of symbiotically-associated Epizoanthus pseudoshells, these data were also used to investigate parameters of pseudoshell association. S. dimorphus to have a female-biased sex ratio of 1:1.5, and P. bouvieri of 1:1. The proportion of males in both species increased with cephalothoracic shield (CL) length. S. dimorphus males had positive allometric major right chelipeds, while P. bouvieri cheliped lengths were positively allometric in males, and negatively allometric in females. All collected P. bouvieri occurred in pseudoshells, but S. dimorphus showed a real shell occupancy rate of 3.39% (n = 38). A positive relationship was found between CL size and real shell occupation frequency (r2 = 0.96). S. dimorphus pseudoshell zoanthid polyps increased in number as a function of both total shell volume (R2 = 0.73) and colony height (R2 = 0.61), with polyps present on every available part of the shell. No such relationship was found for P. bouvieri, presumably because the polyps are distributed in a linear pattern around the back and outside of the pseudoshell. Juvenile parapagurids appear to select for Naticidae original shells, with Euspira napus being the dominant original shell species for both S. dimorphus (45.45 %) and P. bouvieri (39.00 %). Questions are raised about whether these hermits exist along an evolutionary continuum of traditional shell reliance, whereby the species utilise their pseudoshells differently - P. bouvieri appears to show a stronger mutualistic symbiosis with its exclusive pseudoshell species than S. dimorphus, and may have lost the ability to change shelters entirely, utilising the pseudoshell as a brood pouch covering only the abdomen, rather than as a shell in which to retract to escape predation. Data from 1987 - 2014 surveys were used to map the distribution patterns and densities of these species in the southern Benguela, and to investigate changes in the populations over time. As it stands, no correction factor need be applied to South African parapagurid catches as a result of the 2003-2004 change in survey gear. However, further work is needed. S. dimorphus occurred at a significantly greater mean sample mass (287.88 kg.km⁻²) than P. bouvieri (31.37 kg.km⁻²). The bulk of sample mass occurred within the West Coast Benguela upwelling region, with very few parapagurids caught over the Agulhas Bank, which may be too shallow for either species, given that S. dimorphus showed a preferential depth range of 200 - 299 m (range 30 - 814 m) and P. bouvieri of 400 - 499 m (range 62 - 700 m). The highest mean sample masses occurred on muddy sand (61.00 kg.km⁻²) and sandy sediments (45.68 kg.km⁻²). Overall catchability (mean = 43.35%) has remained constant over the 23 years (R2 = 0.13) with a slight trend towards increasing catchability over time, which may correspond to a change in survey design.
Open Access
Demographics of a seasonal aggregation of white sharks at Seal Island, False Bay, South Africa
(2014) Hewitt, Adrian Michael; Griffiths, Charles L; Booth, Tony; Kock, Alison
White sharks (Carcharodon carcharias) are widely distributed, ecologically important marine apex predators that are considered to be vulnerable to extinction. Given their crucial roles in structuring marine ecosystems, their populations need to be effectively monitored. Photo-identification provides a standardised, non-lethal method of assessing the population dynamics of extant species and provides live-encounter mark-recapture and data that are essential for management and conversation. White sharks occur throughout South African coastal waters but their centre of abundance is the Western Cape, where large sharks predominate at aggregation sites like Seal Island, False Bay. This study documents inter- and intra-seasonal trends in mean sighting rates and sex ratios of white sharks at Seal Island, and provides mark-recapture data that are used to estimate proportions of "resident" and "transient" white sharks, their size-distribution and maturity composition.
Open Access
Development of a quality index method (QIM) scheme and its implementation in a shelf-life study of kingklip (Genypterus capensis)
(2003) Gebremariam, Thomas W; Graz, Michael; Griffiths, Charles L
In this study Quality Index Method (QIM) schemes for raw headed and gutted (H&G) fish and skinless fillets as well as cooked fillets of kingklip (Genypterus capensis) were developed in a shelf life study. The QIM schemes for raw H&G and skinless fillets are based on six and seven quality attributes respectively, with a scoring system from 1 to 6, where a score of six is best quality (perfect). For the case of cooked fillets the scheme is based on six attributes, with a scoring system from I to 5, where a score of five is best quality. Sensory analysis of cooked fillets was carried out parallel to sensory analysis of raw H&G and skinless fillets as well as microbial count study until 18 days of storage. These were used to decide the maximum storage time in ice and to observe how the different quality attributes of cooked fish, especially odour and flavour, deteriorated with storage time in ice, as they are the best symptoms of fish spoilage. However, the microbial count study alone was continued until 22 days in ice in order to follow the bacterial spoilage pattern with storage time.
Open Access
Dynamics and utilization of surf zone habitats by fish in the South-Western Cape, South Africa
(1997) Clark, Barry Malcolm; Griffiths, Charles L; Bennett, Bruce
The main objectives of this study were to examine, by means of beach seine netting, the composition, abundance and size structure of fish assemblages frequenting surf-zone habitats in the south-western Cape, South Africa, to investigate temporal and spatial variations in these assemblages in relation to physical environmental parameters, and to assess the importance of this habitat as a nursery and feeding ground for littoral fish. In all, 54 fish species from 29 families were recorded, with three species (Atherina breviceps, Liza richardsonii and Rhabdosargus globiceps) dominating numerically. Two separate surveys were designed to provide a comprehensive assessment of the factors influencing spatial variability in the composition abundance and community structure of the surf fish assemblages in this region. In the first, surf ichthyofaunal assemblages at 11 localities, selected to encompass as wide a range of physical parameters as possible, were sampled at monthly intervals for a period of two years. Results of this study indicated that the degree of wave exposure, the presence of emergent rock on the shore and turbidity were responsible for most of the spatial variability in abundance and community structure observed. In the second survey, samples were collected at eight localities spanning an exposure gradient from highly exposed, open ocean beaches to extremely sheltered marine sandy beaches, in order to isolate and carefully examine the influences of wave exposure on surf fish assemblages. Two important trends were evident in the abundance and community structure of teleost catches in this study. Overall abundance increased markedly as wave exposure decreased, while highest species richness and diversity, and lowest dominance were recorded at intermediate levels of exposure.
Open Access
The ecology of three sandy beaches on the West Coast of South Africa
(1981) Bally, Roderick Peter Alexander; Brown, Alec C; Griffiths, Charles L
The ecology of three sandy beaches on the west coast of South Africa is examined in this thesis. The first chapter constitutes an introduction to the subject and presents a brief review of studies carried out on beaches in South Africa in order to place this thesis into its proper context. In the second chapter, methods of sampling sandy-beach macrofauna (in particular sampling strategies) are briefly reviewed and discussed. For this study it was decided to adopt a grid sampling strategy, and the value of this strategy was tested. In the third chapter the sedimentological characteristics of the beach were examined in considerable detail in order to determine whether these differed between beaches, between zones and seasons on individual beaches. Characteristic differences were found for all the above categories, and the reasons for these are discussed in detail. Two zonation classificatory schemes for intertidal sandy-beach fauna have been proposed: that of Dahl (1953) and that of Salvat (1964). The zonation of organisms on west coast beaches is described in chapter 4, and the results obtained are discussed in the light of the above zonation schemes. Using cluster analysis, ordination and information statistic techniques, Salvat's zonation scheme was found to best describe the situation on the west coast, and its advantages over Dahl's scheme are discussed. Chapter 5 deals with the biomass and densities of macrofauna and meiofauna on the three beaches studied and discusses these results in relation to season and results obtained on beaches elsewhere. On a very broad basis, it is found that the results from west coast beaches fall within the range of results obtained elsewhere, although they rank among the higher values. The results also show that mean individual mass of organisms is related to beach exposure - the mean mass increases with increasing exposure. The respiratory metabolisms of the three dominant isopod species are examined in chapter 6. Using multivariate analysis, the effects of mass, temperature and activity on respiratory rates were determined for each species. Analysis of the results showed that the activity potential of each species differed, and this was correlated with the degree of exposure of the zone inhabited by each species. Thus the species living at the top of the shore showed a high activity potential while that living at the bottom of the shore had the lowest activity potential. The results and the reason for these differences are discussed and related to the differences in the conditions pertaining in each species' environment. Traditionally, sandy beaches are investigated by means of one or two transects across the beach, and the results extrapolated to the remainder of the beach. The results obtained in chapter 2 show that there is considerable variation in biomass and density values along the beach, but a special study of this was made in chapter 7. This showed that all species in fact have an irregular distribution both along and across the beach. These distribution patches are described for all species on all three beaches in this chapter. In addition, interspecific competition and predator-prey relationships were investigated, to determine whether these had any influence on the distributions of the species concerned. Animal-sediment relationships are investigated in chapter 8 and two major types of relationship are described. The first or gross type occurs where species are excluded from a beach due to unfavourable grain size, or where the intertidal position of all the species is affected by the sediment coarseness. The second type is where species or size-classes within species select particular grades within a particular intertidal zone. Animal-sediment relationships are discussed for each species, although these were not detected in all cases. Â· In chapter 9 the biogeography of the sandy beach genera occurring on west coast beaches is investigated. It was found that genera generally made up of intertidal species consisted of fewer species, with generally larger distribution ranges, than genera that tended to consist mainly of sub-tidal species. Of the 15 genera investigated in this chapter, almost all had a greater percentage of species occurring tropically than in temperate and arctic and antarctic climatic zones. When these percentages were corrected for coastline length or oceanic area, however, the concentrations of species were found to be highest in temperate zones, in all cases. The reasons for these findings are discussed in the light of Bretsky and Lorenz's (1970) theory pertaining to genetic-adaptive strategies and mass extinctions. Finally, in chapter 10, the results of this thesis are synthesized and placed into the context of existing knowledge on sandy beach ecology. In addition, trends in sandy beach studies are discussed and future fields of research outlined.