Masters Degrees (Marine Biology)

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Accretion versus bioerosion on the Maputaland reefs in South Africa - The major processes.
(2011) Grimmer, Ashley.; Schleyer, Michael H.; Glassom, David.
The development of coral reefs is largely restricted to areas within the tropics where favourable conditions for both coral and reef growth prevail. There is, however, a continuum from these typical, accretive reefs in the tropics to marginal, non-accretive, coral-dominated reef communities which occur at higher latitudes. High-latitude reefs function similarly in many regards to their tropical counterparts and are regulated by similar processes to a varying degree. In this study, the major biological and physico-chemical processes were assessed which directly or indirectly prevent the continued persistence of reefal frameworks and thus hinder reef accretion on high-latitude reefs in the iSimangaliso Wetland Park. These reefs have a high diversity of hard and soft corals with significant reef coverage, yet little evidence of any biogenic accretion has been observed. The scleractinian coral, Acropora austera, is one of the few corals which may be responsible for reef framework production. It exhibits a gregarious growth pattern, forming large, monospecific stands with an interlocking framework characteristic of the early stages of reef accretion. The framebuilding potential of A. austera and the continued persistence of such frameworks were thus determined by in situ monitoring of coral growth, mortality, bioerosion and several physico-chemical parameters. Growth rate and mortality of A. austera branches were measured at three sites of differing stand size and apparent age. This was achieved by repeated image analysis and by staining branches with the vital stain, Alizarin Red S. Both measures of growth yielded a similar linear extension rate of 24.5 mm/yr (n = 467), comparable to related species at similar latitudes. Mean branch mortality was as high as 50%, with clear differences manifested between each A. austera stand. Branch extension rates and branch mortality were inversely related between sites. Small, young stands exhibited significantly faster coral growth rates, lower mortality and a net increase in overall branch length over the study period, whilst the opposite was true of larger, more developed stands. In addition, bioerosion was determined at each site to assess its potential for carbonate removal and its destabilizing effect on reef frameworks. Bioerosion intensity was recorded as “percentage area damage” within cross-sections and “frequency of occurrence” of bioeroding organisms in coral rubble fragments (n = 120). The level of bioerosion was found to be substantial (up to 11.5% loss in weight of coral fragments over the 12-month study period) and was found to decrease significantly with a reduction in size of each A. austera stand. Aragonite saturation state is considered a major factor that limits the geographical range of coral reefs globally. Although previously thought to be limiting in Maputaland, mean ΩArag values of 4.40±0.29 were measured on the reefs in summer and 4.33±0.21 in winter and thus would not have limited reef development. Past studies have noted the turbulence on South African east coast reefs and its adverse effect on reef development. This was corroborated in this study with the measurement of considerable sediment re-suspension (0.17 g cm⁻² day⁻¹) and regular damage to both living coral and the reef framework caused by large swells. These results lead to the theory that Acropora austera stands senesce with increasing size and age. Although large coral frameworks are found on the Maputaland reefs, they do not persist in the long term. High rates of sediment re-suspension prevent infilling of the interstitial spaces and eventual cementation, while high levels of bioerosion lead to framework instability over time. Rough seas further hamper accretion by physical removal of both living coral and the coral-derived framework, thus removing recent growth. This process is suspected to cause an imbalance in the carbonate budget of these marginal reefs, ultimately favoring carbonate removal over carbonate deposition.
Age and growth of the Queen Mackerel (Scomberomorus plurilineatus) and Seventy-four (Polysteganus undulosus) of KwaZulu Natal, South Africa.
(1996) Chale-Matsau, Jacobeth R.; Beckley, Lynnath E.; Govender, Anesh.
This study provides information on the age and growth of two important Iinefish species, Scomberomorus pluriline~tus and Polysteganus undulosus. Age determination for both species was carried out using otoliths and growth was modelled using age- and length-based methods. For the age-based method various growth models were evaluated to determine which growth function best described the age-length data, whilst Shepherd's Length Composition Analysis was used to estimate growth parameters from length-frequency data. Preliminary stock assessments, based on limited catch data, were also attempted for both species. Age estimates for the pelagic migrant S. plurilineatus, derived from reading whole otoliths, ranged from 0 + to 6 + years. As validation by marginal increment analysis was inconclusive because of the seasonal occurrence of this species in KwaZulu-Natal waters, it was assumed that a single opaque band was laid down in the otolith annually. Reproducibility of age estimates evaluated using the average percentage error (APE) technique was good (9.4%). Von Bertalanffy growth parameters were poorly estimated from length-frequency data because multiple maxima were encountered on the fitting surface. However, from the age-length data, growth was adequately modelled by the von Bertalanffy growth equation: L t =9 3 5mmFL (l-e -0. 583yr-1 (t+o. 991yr) ) S. p!urilineatus are fully recruited to the fishery at the age of 1 + year and the ageiv at-50% maturity is 2 + years. Preliminary per-recruit analyses indicated that the spawner biomass of S. plurilineatus is at 50% of its unfished level. Polysteganus undulosus is an endemic, reef-dwelling sparid and large catches weremade earlier in the century. Age determination was carried out using sectioned otoliths collected in 1962 and 1963 before the collapse of the fishery. Age estimates ranged from 3 + to 20 + years. Marginal increment analysis indicated that active deposition of opaque bands occurred during winter but, because of the seasonal occurrence of P. undulosus in KwaZulu-Natal, validation was inconclusive. Reproducibility of the age estimates was low (APE = 18.2%) because of difficulties with band interpretation as a result of stacking on otolith margins in old fish. Von Bertalanffy growth parameters could not be adequately estimated from length frequency data because of the slow growth and longevity of this species. However, from the age-length data, no difference in growth rate between the sexes was observed, and growth for the combined sexes is described by the following logistic equation: L = 942mmTL t 1+e-O.277yr-l(t-S.178yrs) The age at full recruitment was found to be 12 + years and the age-at-50% maturity was 8.8 years. A preliminary stock assessment revealed that the spawner biomass of P. undulosus was already at 25% of its unfished level in the early 1960s.
Artisanal fishery in socio-economic development of rural communities in Malawi : a case study of enclave villages of Lake Malawi National Park.
(1998) Kumchedwa, Brighton Kalembeni.; Breen, Charles Mackie.
Fishing, and artisanal fishing in particular, plays a key role in the provision of rural employment and more importantly, household food security in the developing nations. The importance of artisanal fishery is shown in Malawi where artisanal fishery produces between 85-95% of the total fish production, and about 70% of the animal protein in human consumption comes from fish. About 43,000 people are employed directly in artisanal fisheries and approximately 100,000150,000 are indirectly employed within the artisanal fishery. Owing to increasing human population in the developing countries coupled with the common property, open-access nature of the fish resource, the resource has not been able to cope with the ever-increasing socio-economic demand placed on it. The resource is so degraded that it is has started to decline beyond capacity to sustain itself. This study was an attempt to examine and understand the artisanal fishery as it contributes to the socio-economic well being of the rural population particularly, the enclave communities of Lake Malawi National Park. The present study used structured interviews, focus group interviews, key informant interviews and personal observation to collect socio-economic information of the fishery. These research tools revealed that among the enclave communities income levels are low and unsustainable due to declining productivity of fishing. The decline may be a result of increasing human population, weak community-based institutions, limited agriculture, poor infrastructure with regard to processing and marketing of fish, limited supplementary and alternatives economic activities, and the fishing methods. Documentary information was used to contextualize artisanal fishery, to examine and understand the common-property and open-access nature of the fish resource as it relates to the exploitation Of fish among the enclave communities. Integrated development that brings together conservation and socio-economic development is the only option that will increase the income of the enclave communities to sustainable levels and achieve the Park's conservation objectives. The socio-economic intervention options should include provision of basic social facilities such as education, health, safe water etc, increase the economic power of the enclave communities through irrigation, adding more value to the fishery, engaging in aquarium trade, community-based eco-tourism and beekeeping. These options would lead to socio-economic sustainability among the enclave communities and would bring about the conservation objectives of the Park.
An assessment of abundance trends and biology of langoustines (Metanephrops mozambicus) and pink prawns (Haliporoides triarthrus) from the deep-water trawl fishery off eastern South Africa.
(2013) Robey, James.; Groeneveld, Johan Conrad.; Fennessy, Sean Thomas.
Deep-water trawling (>200 m deep) for crustaceans in the South West Indian Ocean (SWIO) yields catches of several species, including prawns (Haliporoides triarthrus, Aristaeomorpha foliacea, Aristeus antennatus and Aristeus virilis), langoustine (Metanephrops mozambicus), spiny lobster (Palinurus delagoae) and geryonid crab (Chaceon macphersoni). Infrequent deep-water trawling takes place off Tanzania, Kenya and Madagascar; however, well-established fisheries operate off Mozambique and South Africa. Regular trawling off South Africa started in the 1970’s, mainly targeting M .mozambicus and H. triarthrus. Catch and effort data for the South African fishery were regularly recorded in skipper logbooks over a 23 year period (1988 – 2010); this database was obtained from the Department of Agriculture, Forestry and Fisheries (DAFF) in order to assess abundance trends of M. mozambicus and H. triarthrus. Generalized linear models (GLM) were used to quantify the effects of year, month, depth and vessel on catch per unit effort (CPUE). By year, the standardized CPUE of M. mozambicus increased, and three factors (or a combination of them) could explain the trend: reduced effort saturation, improved gear and technology, or an increase in abundance. By month, CPUE peaked in July and was highest between depths of 300 and 399 m. The standardized CPUE of H. triarthrus fluctuated more by year than for M. mozambicus, possibly because it is a shorter-lived and faster growing species. The monthly CPUE peaked in March, and was highest between depths of 400 and 499 m. Totals of 2 033 M. mozambicus (1 041 males and 992 females) and 5 927 H. triarthrus (2 938 males and 2 989 females) were sampled at sea between December 2010 and March 2012, during quarterly trips on-board a fishing trawler. A GLM framework was used to explore their size composition, sex ratio variability, size at maturity and reproductive cycles. Male and female M. mozambicus size distributions were similar, but varied by month and decreased as depth increased. Female H. triarthrus were significant larger than males; size structure varied by month, but showed no change over depth. The sex ratio of M. mozambicus favoured males (1 : 0.89), but was close to parity in all months, except November when males predominated. H. triarthrus exhibited parity (1 : 1.002) with no significant variations in sex ratios by month. The proportion of egg-bearing M. mozambicus in the population declined between March and August (hatching period) and then increased until December (spawning period). The L₅₀ (length at 50% maturity) of M. mozambicus was estimated to be 49.4 mm carapace length (CL), and the smallest and largest observed egg-bearing females were 33.5 and 68.6 mm, respectively. No reproductively active female H. triarthrus were recorded during the sampling period. Growth parameter estimates for M. mozambicus (male and female combined) using Fabens method were K = 0.48 yearˉ¹ and L∞ = 76.4 mm CL. Estimates for the von Bertalanffy growth formula (VBGF) were: K = 0.45 yearˉ¹ and L∞ = 76.4 mm CL. H. triarthrus male and female growth parameter were estimated separately. For males they were K = 0.5 yearˉ¹ and L∞ = 46.6 mm CL using Fabens method, and K = 0.76 yearˉ¹ and L∞ = 46.6 mm CL using the VBGF. For females they were K = 0.3 yearˉ¹ and L∞ = 62.9 mm CL using Fabens method, and K = 0.47 yearˉ¹ and L∞ = 62.9 mm CL using the VBGF. CL to total weight regressions were calculated for both species; no significant differences were found between male and female M. mozambicus, although H. triarthrus females became larger and heavier than males. Comparisons with three earlier studies (Berry, 1969; Berry et al., 1975; Tomalin et al., 1997) revealed no major changes in the biology of either species off eastern South Africa. Stocks appear to be stable at current levels of fishing pressure, although some factors are not yet fully understood. Disturbance caused by continual trawling over a spatially limited fishing ground may affect distribution and abundance patterns, especially in M. mozambicus, which was less abundant in the depth range trawled most frequently. The absence of reproductive H. triarthrus in samples suggests that they occur elsewhere, and there is some evidence of a possible spawning migration northwards to Mozambique; this suggests that H. triarthrus is a shared stock between South Africa and Mozambique. The results from this thesis will add to the knowledge of M. mozambicus and H. triarthrus in the SWIO, and provide a basis for developing sustainable management strategies for the deep-water crustacean trawl fishery off eastern South Africa.
An assessment of changes in the Ichthyofaunal bycatch of the Tugela Bank prawn trawlers in KwaZulu-Natal.
(2006) Mkhize, Mbali.; Fennessy, Sean Thomas.; Van der Elst, Rudy P.
Bycatch refers to the portion of the catch that is captured incidentally to the target species and is one of many growing problems facing the world's marine fisheries in recent years. Prawn trawling is one of the world's most lucrative marine fisheries, contributing about 3% to the total annual production of the world's marine fisheries. It is also one the most wasteful because it is associated with large quantities of bycatch. This is because of the high diversity and abundance of other organisms in areas where prawn trawling occurs, and the non-selective nature of the otter trawl used to land prawns. The South African shallow water prawn trawl fishery is typical of penaeid fisheries, and operates on the Tugela Bank off northern KwaZulu-Natal. The bycatch of penaeid prawn trawlers operating on the Tugela Bank was analysed between March 2003-July 2004 as a follow up to an initial study between May 1989-June 1992. The aim of this study was to determine if there has been any change in bycatch species composition over the 13-years and to determine the impacts of trawling on the environment. Catch composition data were recorded from 168 trawls processed onboard trawlers and on-shore. A total of 122 species was identified with teleosts contributing more than 60% to relative abundance by number. Comparison between the 1989-1992 and 2003-2004 data sets showed that although the species compositions were similar, there was an increase in the relative abundance of pelagic species. It is not clear if the change is due to trawling impacts or due to fluctuations in recruitment of these taxa. The annual discarded bycatch was estimated at 88 tonnes in 2003 and the prawn catch was estimated at 1 1 tonnes, both substantially lower than in 1 989-1992. There was no difference in discard rate between trawls from shallow and medium depths. However, there were significant differences in discard rates between large and medium gears, and warm (December-April) and cool (May- November) seasons. Kolmogorov-Smirnov tests revealed that there were significant differences between the 1990s and 2000s length frequency distributions of three sciaenid species (Otolithes ruber, Johnius dorsalis and J. fuscolineatus), which all showed an increase in fish size for the 2003- 2004 data. This assessment, however, is confounded by a gear effect as mesh size differs between the two sample periods. Based on the results of the study, management recommendations were made to improve the management of the Tugela Bank prawn trawl fishery by reducing bycatch. It was recommended that the observer programme continue for further investigation into the changes in species dynamics. Further research on BRDs (Bycatch Reducing Devices) and gear types that reduce bycatch is also recommended.
An assessment of the shore-based and offshore boat-based linefisheries of KwaZulu-Natal, South Africa.
(2011) Dunlop, Stuart William.; Mann, Bruce Quintin.; Van der Elst, Rudy P.
The purpose of this study was to evaluate the current management effectiveness of the KwaZulu-Natal linefishery (i.e. the shore linefishery and the offshore boat-based linefishery). Methods used included a stratified-random creel sampling technique and an associated questionnaire survey for the shore-based linefishery and a random access-point technique and associated questionnaire survey for the offshore boat-based linefishery. Additional catch and effort data for the offshore boat-based linefishery was also obtained from Marine and Coastal Management’s (MCM) Linefish Observer Programme. The study was undertaken between February 2009 and April 2010. Total participation within the two linefisheries ranged between 41283-68200 shore-anglers and 21220-28857 boat-fishers (2001-4445 boats). Excluding the increase in the number of boat-fishers that fish off charter vessels (i.e. charter clients), it seems that there have been relatively few new entrants into the marine linefishery of KZN since 1994-96. In contrast, total angler effort in both the shore (779382-1287548 angler-days.annum-1) and offshore (39664 boat outings annum-1) linefisheries has decreased substantially in the past 12 years. Overall catch per unit effort (CPUE) for the KZN shore linefishery amounted to 0.18 ±0.3 fish.angler-1.hour-1 or 0.07 ±0.13 kg.angler-1.hour-1. Eighty-four fish species, belonging to 39 families were recorded in catches of shore-anglers during the study period. Only five species accounted for 75% of the catch recorded along the coast (Sarpa salpa 34.8%, Pomatomus saltatrix 14.7%, Diplodus capensis 14.5%, Pomadasys olivaceum 6.5% and Rhabdosargus holubi 4.9%). The total annual catch for the KZN shore linefishery was estimated between 249.2 and 276.7 metric tonnes (mt).annum-1 (636589 - 706995 fish.annum-1). Overall CPUE was significantly different between the various sectors of the KZN offshore boatbased linefishery. The commercial boat sector had the highest CPUE both numerically (p < 0.05; 307.4 fish.outing-1) and by weight (p < 0.05; 235.6 kg.outing-1). Contrastingly, the recreational boat sector had the lowest CPUE both numerically (p < 0.05, 8.6 fish.outing-1) and by weight (p < 0.05, 15.0 kg.outing-1). The charter boat sector (p < 0.05, 26.6 fish.outing-1 or 41.6 kg.outing-1), although far lower than commercials, had a CPUE slightly higher than the recreational boat sector. In total, 86 fish species, belonging to 27 families were recorded in catches of boat-fishers (all sectors) during the study period. The top five species that comprised the bulk of the commercial catch numerically included Chrysoblephus puniceus (66.0%), Cheimerius nufar (22.4%), Lethrinus nebulosus (4.6%), Pachymetopon aeneum (1.9%) and Chrysoblephus anglicus (0.9%). Similarly, recreational catch composition was dominated by C. iii puniceus (33. 9%), L. nebulosus (9.0%), Thunnus albacares (7.4%), Scomber japonicus (5.3%) and C. anglicus (4.4%). The top five species in charter boat-fishers’ catches comprised C. puniceus (34.4%), L. nebulosus (16.7%), T. albacares (13.1%), C. anglicus (8.1%) and P. aeneum (4.6%). The socio-economic characteristics of the KZN shore and offshore linefisheries have changed very little since the last national linefish assessment conducted during 1994-96. Recreational (both shore and boat-based) and charter anglers generally agree with most of the linefishery regulations, with exception of the beach vehicle ban. However, knowledge and compliance with the current fishery regulations by recreational and charter anglers was limited. Commercial fishers had good knowledge of all the fishery regulations, but did not agree with the minimum legal size and daily bag limits that are in place on certain fish species. Subsequently, the majority of commercial skippers interviewed stated that they disobeyed these two regulations frequently. General policing of the KZN linefishery by EKZNW seems to be more focused on permit requirements rather than enforcing species-specific linefish regulations. Comparison of the catch and effort results of this study with the long-term monitoring data stored on the NMLS showed that while the NMLS data is limited by a number of biases, it still provides a valuable system for monitoring long-term trends in the KZN linefishery. Analysis of overall CPUE, catch composition and total catch in both the shore and offshore linefisheries of KZN suggested that both fisheries are currently in a relatively stable condition and that little change has occurred in the past 12 years. However, comparisons of speciesspecific CPUE values from this study with recent literature suggest that some species (i.e. Argyrosomus thorpei and Scomberomorus commerson) are severely overexploited. Furthermore, in relation to the catches recorded throughout most of the 20th century, current catch trends suggest that linefish resources have been fished to very low levels which are only ‘superficially’ sustainable at current levels of fishing effort.
Association of juveniles of four fish species with sandbanks in Durban Bay, KwaZulu Natal.
(1994) Graham, M. A.; Forbes, Anthony Tonks.; Cyrus, Digby Paul.
Estuaries in South Africa are important nursery areas for the juveniles of many fish species. The condition of many of these systems has, however, deteriorated as a result of degradation caused by urban, industrial and agricultural development. An assessment of the role of harbours, particularly in KwaZulu Natal, as nursery grounds has therefore become an important issue. Durban Bay has undergone considerable changes since the mid-1800s and further developments are proposed. If these developments continue, they will result in the loss of large areas of the sandbanks, but Portnet has recognised the need to integrate environmental considerations into future port developments and operations. It was the overall aim of this study to establish the nature of the association of the juveniles of four common fish species viz. Pomadasys commersonnii, Gerres filamentosus, Liza dumerilii and Leiognathus equula with these sandbanks and, thereby assess the impact of their removal. It was found that all species were abundant on the sandbanks and that the diets of P. commersonnii, G. fiiamentosus and L. equuia were very similar, consisting primarily of bivalve siphon tips, benthic crustaceans and polychaetes. The respective contributions of each food type to the diet varied with species. The diet of L. dumerilii differed from that of the other three species, consisting primarily of benthic floc, foraminiferans, ostracods and sponge spicules. Despite differences in selectivity, it was concluded, from studies of the benthos in the harbour, that all four species, irrespective of size, were feeding on these sandbanks, as opposed to in the channels, throughout the year. Removal of the sandbanks for the construction of a new pier would, thus, result in the elimination of important feeding grounds for the juveniles of these four species.
Biodiversity of soft sediment macrobenthic fauna of the KwaZulu-Natal Bight midshelf.
(2013) Hein, Liesel.; Mackay, Christine Fiona.
The KwaZulu-Natal Bight is influenced by various nutrient inputs from the Thukela River and particular oceanographic features of the shelf such as the St Lucia upwelling cell and the Durban lee eddy that are in turn associated with Agulhas Current behaviour. Little is known about KZN Bight community dynamics of most faunal groups and so knowledge about the ecological functioning of this system as a whole is lacking. To address this, a large multidisciplinary project on the Bight was conducted through the African Coelacanth Ecosystem Programme. One aim of the programme was to establish whether nutrient inputs have significant impacts on this oligotrophic shelf and if so, how? This study looked at the macrobenthic compartment to examine variations in diversity across the KZN Bight in the midshelf habitat only. Changes in diversity were explained in relation to important habitat and/or process drivers. Replicated biological and sediment samples were collected in and between the three focus areas of high nutrient input along the Bight spanning an area from Durban to just south of the St Lucia Estuary mouth. Samples were collected twice at the same stations, once during a wet period (February 2010) and once during a dry period (August 2010). These periods were selected to represent high and low outflow and thus potentially higher and lower nutrient inputs to the Bight, respectively. Macrobenthos collected by 0.2m2 Van Veen grab were identified to the lowest possible taxonomic level and resulting data were analysed using combinations of univariate and multivariate statistical procedures. Diversity was described using well-published techniques that related to community Alpha () and Beta (β) diversity and including several newer methods such as Taxonomic Diversity indices (Taxonomic Distinctness (Δ*), Average Taxonomic Distinctness (Δ+), Variation in Taxonomic Distinctness (Λ+)) to determine the taxonomic relatedness of macrobenthic communities within the study area. Midshelf macrobenthic community  and β diversity was highly variable across the shelf with no distinct patterns related to focus area. Diversity values were however similar to values obtained in what are considered highly diverse tropical and high latitude shelves. Diversity was then related to hydrographic parameters measured on the Bight to understand the possible indirect or direct roles the Agulhas Current and Thukela River have in maintaining the macrobenthos. Findings were that diversity was only weakly related to measured environmental variables suggesting far more complex interactions in the biophysical environment of the Bight. This was highlighted by the finding that alpha and beta diversity measures had complimentary relationships as an inverse trend was found between these measures along the KZN Bight. Thus, more detailed systematic studies on the Bight are needed to fully understand the role and supply of nutrients on specific communities and how these pertain to the ecological function of the whole shelf ecosystem.
Biology and population dynamics of the King Mackerel (Scombereomorous commerson, Lacepede, 1800) off the coast of Natal .
(1992) Govender, Anesh.; De Freitas, A. J.; Van der Elst, Rudy P.
This thesis provides a study on aspects of the biology and population dynamics of Scomberomorus commerson off the south east coast of southern Africa. This is necessary for the evaluation of the current management policies and for the selection of the "best" management strategy for this species off the coast of Natal. The current status of S. commerson off the Natal coast was assessed in terms of yield-per-recruit and spawning biomass-per-recruit analyses. Input parameters to these per-recruit models include growth and mortality rates and basic biological data. Estimates of these parameters and the methods employed are detailed in the thesis . S. commerson has a protracted spawn ing period rang ing from November to March. The principal spawning area is Mozambique. Fifty percent sexual maturity is attained at 1096mm and 706mm(FL) for females and males, respectively. The, ratio of males to females in the sampled catches is approximately 1:2 with females attaining a significantly larger mean size: females (926mm,FL) and males (898mm , FL). The masslength relationsh ip for both sexes can be described by the following equation: Ma s s ( g ) = O.1353X10-5 • [FL(mm) J3.25 15 Growth parameter estimates for the combined sexes were estimated from a lengthbased as well as an age-based method. An objective technique was utilised to determine which growth function best describes the age-length data of S. commerson. Age data were obtained from otolith readings. The precision of otolith readings was described by an index. This index, the average percent error, which is equal to 20.25%, is higher than that recorded in other studies. Two opaque bands are laid down annually. This was validated by marginal increment analyses as well as from tagging data. The age-length relationship , assuming biannual periodicity of the opaque band, is best described by a Von Bertalanffy growth function: L age(mm, FL) = 134 4mm (l-e ...{).292 yr-'Cage-+2.999 yrs») The instantaneous natural mortality rate (M) was estimated using two different techniques: the Pauly equation and the Rihkter and Efanov equation. The former equation was very sensitive to changes in the mean environmental temperature and both techniques produced different estimates. The average of both methods was, therefore, taken as an estimate of M which is 0.5 yr'. The instantaneous fishing mortality rate (F) is currently estimated to be 0.25 vt", This estimate is, however, positively biased as the effects of emigration have not been taken into account. The per-recru it analyses were conducted for three different growth equations for the same values of F and M, age-at-maturity and age-at-first-capture. For all growth equations the yield-per-recruit increased with increased fishing with maximum yield-perrecruit attained either at infinite F or at very high values of F (> 5 yr'), FO.1 was attained between 0.6 and 0.8 v' for all growth equations. The Von Bertalanffy growth function, assuming annual periodicity of the opaque band, was the most unrealistic. It predicted a virtual collapse of the fishery When F=M and a reduction of the spawning biomass to 50% of its unfished level at F=0.1 yr'. The length based derived growth equation and the Von Bertalanffy growth function, assuming biannual periodicity of the opaque band, predicted that spawning biomass dropped to 50% of the pristine level at F=0.19 and 0.16 vr' . respectively. It is believed that the current restrictions on sport catches of 10 fish/person/day offers adequate protection for the Natal king mackerel stock. These restrictions should be maintained in Natal. However, if fishing effort on this species continues to increase (as is anticipated in an open access fishery) or if there is increased commercial interest or if there is renewed fishing in Mozambique, a minimum size is recommended to adequately protect the spawning stock. Such a minimum size should be implemented in Mozambique which is the principal spawning area for king mackerel. Setting a minimum size in Natal, above the size-at-50% maturity may substantially reduce catches in the short and medium term because at least 90% of the catch currently taken will be inaccessible to fishermen. Restrictions of king mackerel catches in Natal, alone, is not considered a viable management option as Natal's commercial and to a certain extent recreational fishermen may turn to Mozambican waters to harvest king mackerel. Management options should be implemented and enforced both in Natal and Mozambique.
Biology and stock assessment of the coastal fish, Sarpa Salpa (Sparidae), off the KwaZulu-Natal coast, South Africa.
(1995) Van Der Walt, Bryan Anthony.; Govender, Anesh.; Beckley, Lynnath E.
This study investigated aspects of the biology of Sarpa salpa, such as reproduction, age and growth, and mortality, which are necessary for an assessment of the status of this species off the KwaZulu-Natal (KZN) Coast. The importance of S. salpa to the shore-based fishery in KZN was evaluated using Natal Parks Board shore patrol data. These data were validated by analysing preliminary results of an independent shore-angling survey along the KZN Coast. Despite differences in the catch composition and catch rates between the two analyses, both data sources highlighted the importance of S. salpa to the shore-based fishery in KZN. Shore-based catches were markedly seasonal coinciding with the breeding season of the species. The species in KZN is targeted primarily to provide a supplementary source of animal protein. An investigation of the reproductive biology of S. salpa indicated a protracted spawning period for the species. Size at 50 percent maturity for combined sexes was attained at 145 mm fork length. The sex ratio in shore-based catches was 1:1.6 in favour of males. A frequency distribution by size indicated that males dominated the smaller size classes while females dominated the larger size classes. Detailed histological examination of gonadal development showed that S. salpa has the potential for protandrous sex change. An age and growth study based on the examination of whole otoliths indicated that S. salpa was relatively fast-growing and a maximum age of six years was recorded for the species. One opaque band was laid down per year. This was validated by marginal increment analysis and by an oxytetracycline labelling experiment using captive fish. Growth in S. salpa was described by a Von Bertalanffy growth function: Lage (mm FL) = 224mm(1 -e-o.55 year-1(age+o.51years)) The natural mortality rate (M = 0.6 year-1) was derived using Pauly's equation and the current fishing mortality (F) rate was estimated at 0.8 year-1. The current status of S. salpa in the shore-based fishery was assessed by determining the effects of F and age-at-capture on the yield- and spawner biomass-per-recruit. Current levels of fishing pressure on S. salpa appeared to be appropriate for utilisation of the stock off the KZN South Coast. In terms of management, S. salpa appears to be in no need of any restrictive measures at present.
Chemical cue interactions between alien invasive and native aquatic gastropods in the iSimangaliso Wetland Park, South Africa.
(2013) Raw, Jacqueline Leoni.; Perissinotto, Renzo.; Miranda, Nelson Augusto Feranandes.
The importance of chemical cues in mediating interactions among individuals and structuring communities is being increasingly recognized in aquatic environments. Chemical cues have been shown to drive predator-prey interactions in which behavioural responses in terms of movement have been reported. The role of chemical cues in mediating interactions between heterospecific competitors, in which there is an observed behavioural response, has not been previously investigated. This research project has used the biological invasion of Tarebia granifera, a caenogastropod endemic to south-east Asia, to determine the role of chemical cues in driving displacement interactions with native gastropods within coastal lakes and estuarine environments of the iSimangaliso Wetland Park, in northern KwaZulu-Natal, South Africa. An experimental approach was used to measure behavioural responses of gastropods to chemical cue treatments by quantifying components of movement. Responses of three dominant native gastropods within Lake St Lucia were tested in a preliminary in situ experiment. The mean Displacement, mean Number of Steps and grand mean Turning Angle were determined from recorded pathways of individual gastropods using image-processing software. Responses to chemical cues released by T. granifera were significantly different and negative in comparison to the control and conspecific chemical cue treatments. Following these results, the experiment was repeated and refined to include responses between native heterospecific gastropods from populations within the larger geographical range of the iSimangaliso Wetland Park. Additionally, the case of whether the observed responses could be attributed to build up of metabolic waste products was also investigated. The results confirmed those of the preliminary in situ study. Negative responses were only reported for gastropods which did not have a shared evolutionary history with T. granifera, irrespective of metabolic waste concentrations Native gastropods moved away from chemical cues released by T. granifera using a directed orientation mechanism. Interestingly, native gastropods did not exhibit this behavioural response to chemical cues of other heterospecifics. This suggests that T. granifera has developed chemical cues under evolutionary pressure, which act as deterrent on naïve gastropods. The implications for these responses are considered within the framework of Movement Ecology with contributions to Chemical Ecology. The potential of this interaction as a mechanism of invasion to be included within spread models is discussed.
The commercial and recreational marine skiboat linefisheries in Richards Bay, KwaZulu-Natal.
(2005) Jairam, Sureka.; Van der Elst, Rudy P.
In order to assess and improve their management, a survey of the commercial and recreational marine linefisheries in Richards Bay was conducted from June 2002 to July 2004. The ultimate aim of this survey was to develop a sound management framework for the commercial and recreational marine Iinefisheries in Richards Bay. Skippers on both commercial and recreational skiboats were all white males in their mid-40s whom were fairly experienced. There were twice as many crew on commercial than recreational skiboats. The crew on commercial skiboats were mostly black males while on recreational skiboats, crew were mostly white males. Slinger was the most important species caught by commercial fishermen off Richards Bay, accounting for the vast majority of catches by number and mass. The total contribution by sparids to commercial catches amounts to approximately 93 % by number and 81 % by mass. Recreational catches comprised a greater variety of species (73 recreational species versus 54 commercial species), signifying a less focussed targeting approach compared to commercial skiboat fishermen. Although slinger also numerically dominated recreational linefish catches, catface rockcod were most important by mass. Although there were five times more recreational outings during the study, total catch by commercial skiboat fishermen was five times higher than that of recreational fishermen. This was expected, as the average duration of each commercial outing is more than twice that of recreational outings and the crew numbers are higher. Commercial skiboat fishermen in Richards Bay are also more effective, as the average number of fish caught per man per hour on commercial skiboats was approximately 4 times greater than that on recreational skiboats. Total estimated catch for the commercial sector was 28 tonnes and 173 tonnes for the recreational sector. Comparison of data between this survey and commercial data available on NMLS showed similar species composition, although the dominance of slinger was 20 % higher in this survey compared to data. Similarly, within the recreational sector, there was a close similarity in catch composition between this survey and that catch inspections. The profit (excluding the costs of fixed assets) that each commercial fisherman earns per month was estimated to be in the region ofR8 500. However, if one examines the value of the commercial linefishery as a whole, it appears that there is a net loss of R90 000 per year, excluding the costs of fixed assets. The discrepancy stems from the disparity between the recorded number of launches and the number reported by skippers. Most of the commercially caught fish are not sold in Richards Bay, but are exported to Gauteng. The average monthly Iinefish catch by commercial fishermen was less than half the average estimated consumption of Iinefish in Richards Bay, and the difference appears to be made up from recreational catches, with many consumers indicating that they either caught their own fish or were given it. Knowledge of and compliance with fishing regulations by commercial and recreational skiboat fishermen in Richards Bay was reasonably good. The main recommendations emanating from this study include continuous monitoring of the Richards Bay commercial and recreational line fishery in order to determine the efficacy of the new regulations, the development of area-based commercial linefishing permits and the possible introduction of restrictions on the sale of fish outside of the Richards Bay area.
Community dynamics of meiofauna during a wet phase in the St Lucia estuarine system, South Africa.
(2015) Naidoo, Bryaleen Leesa.; Perissinotto, Renzo.; Bownes, Sarah Jane.
Meiofauna are an important component within the benthic environment of any aquatic habitat. Despite their significance and ubiquitous nature, these organisms are relatively poorly studied in Africa. Following a decade long drought period, the St Lucia Estuary experienced higher than average amounts of rainfall at the end of 2010. These heavy rainfall events replenished the freshwater capacity of the system, raising the water level and subsequently reducing salinity throughout the estuarine lake, thus marking the start of a two year long wet phase. Meiofauna community dynamics were assessed to determine their response to a wet phase and to the disturbance brought on by intense rainfall. Diversity indices and a host of multivariate analyses were used to gain an understanding of the meiofaunal communities of the system during this wet phase. Meiofaunal density and richness tended to be higher during the first year of the wet phase. Meiofauna communities within each site became more homogenous in the second year of the wet phase, indicating a more established community adjusted to wet conditions. Following a flood disturbance in early January 2011, meiofaunal communities at each site differed in terms of primary and secondary colonisers. Over time, communities increased in dissimilarity, suggesting succession at some level. A successional pattern was observed as the taxonomic composition of the communities shifted over time. The lack of a climax community in St Lucia in the medium term was likely due to the uneven impact that the lake experienced with the onset of the disturbance, with the northern reaches experiencing a greater degree of impact than the southern reaches. The continuity in disturbance occurrences also caused the system to move back to a previous successional state. The meiofauna of St Lucia are therefore able to recover after disturbances related to a wet phase and maintain some form of resilience. In the long term, meiofaunal communities may require a longer time period, than the one considered in this study, to reach the levels of abundance previously recorded.
Community structure and function of macrobenthos in three feature areas of the Natal Bight, South Africa.
(2013) Untiedt, Candice Bobby.; Mackay, Christine Fiona.
The Natal Bight off the east coast of South Africa is a unique shelf habitat, exhibiting high secondary productivity and supporting high diversity. Ecosystem attributes are influenced by local oceanographic features and outwelling via one of the largest rivers in the country. This study forms part of a larger, multi-institutional, multi-disciplinary study under the second phase of the African Coelacanth Ecosystem Programme (ACEP II) Natal Bight Project, investigating how material sources, posited to be derived from these features, shape the ecological structure and functioning of the region. Macrobenthic samples were collected along cross shelf transects off Richard’s Bay, Durban and the Thukela River mouth during two cruises, corresponding with periods of variable rainfall. Macrobenthic communities were classified taxonomically, to the lowest level possible, and functionally. Community patterns were investigated within and between feature areas and related to measurable environmental factors in order to determine environmental drivers and assess the importance of identified oceanographic features. Environmental parameters measured included sedimentary characteristics as well as physico-chemical conditions in the surrounding pelagic milieu. A total of 38 215 individuals belonging to 826 taxa were recorded from the three feature areas, of which the majority were Polychaeta and Crustacea. An in-depth investigation of the polychaete component has shown that this group can be used as a proxy for the whole macrobenthic community which has important implications for future studies. Facultative feeding modes dominated the trophic functioning macrobenthic communities sampled on the Natal Bight. Primary community metrics of abundance and numbers of macrobenthic taxa were reduced from the high to low rainfall period but differences were not significant, probably due to the lack of temporal repetition. The Thukela feature area was found to support the most abundant and taxon rich macrobenthic community. Mid-shelf stations sampled along the Thukela and Durban transects were in close proximity to the coarse paleo-dune cordon, running along the 60 m isobath and supported a diverse assemblage. Despite the lack of temporal repetition in the present study, there were significant short-term changes in the structure and functioning of macrobenthic communities on the Thukela shelf. This suggests that Thukela River outflow has a significant effect on the functioning of the Natal Bight ecosystem. This was surprising given the importance which has previously been placed on the Cape St. Lucia upwelling cell in terms of contributing nutrients and sustaining biological productivity and diversity on the Natal Bight.
Coral propagation for aquarium specimens.
(2001) Jordan, Ingrid Elizabeth.; Schleyer, Michael H.
Coral reefs are being destroyed and degraded by natural and anthropogenic processes. Live corals are becoming increasingly popular as marine aquarium specimens, in both the commercial and private sectors, leading to the degradation of coral reefs. This often has serious economic implications for the fishing, aquarium and tourist industries. It is clear that there is a need for the management and protection of these fragile ecosystems. The artificial propagation of coral is desirable as it will alleviate the demand for wild coral specimens, and will also provide a stock for the rehabilitation of damaged reefs. Although corals are being propagated worldwide by hobbyists, reports on their work are mainly anecdotal and there is little in the scientific literature on the specific requirements for optimal growth rates and survival in suitable coral species. This study thus focused on developing techniques to propagate a range of appropriate coral species and to promote their optimal growth. The results revealed that different morphological groups of scleractinian corals require specialised techniques of fragmentation and attachment to ensure survival. The corals were broken using a hammer and chisel. Attachment techniques varied from the use of superglue (which is widely used in the United States), to thermoplastic glue. The mean mortality using superglue was 73% (n=120, ±0.167), using epoxy, 62% (n=120, ±0.127) and with thermoplastic glue it was 11% (n=120, ±0.108) Superglue was extremely difficult to work with and proved ineffective, especially when attempting to glue uneven surfaces. Certain species did not survive using this adhesive due to exposure of the coral to air. The most effective method of rapid attachment was the use of thermoplastic glue that set rapidly underwater. The use of electrolysis to promote the attachment of coral nubbins was tested as an alternative to the various adhesives. This method increased the survival of the nubbins and eliminated exposure to air. It has proven suitable for both coral propagation and in situ reef rehabilitation. Growth experiments revealed that the manipulation of current flow, light and the addition of different feeds had different effects on the growth rates of selected candidate species. A suite of optima was thus developed for each species. The majority of species grew best in a bi-directional current flow, with yeast as feed, under actinic blue light. An experiment that combined the optimal current flow, feed and light conditions, revealed that the majority of species grew best under mixed light with yeast as feed. The trade in corals is sensitive in terms of their handling, transportation and CITES (Convention on International Trade in Endangered Species) status. Having established the viability of their propagation, consideration was given to appropriate regulatory and marketing procedures to accommodate this sensitivity of the cultivated material.
Coral recruitment on a high-latitude reef at Sodwana Bay, South Africa: research methods and dynamics.
(2011) Hart, Justin Richard.; Glassom, David.; Schleyer, Michael Henry.
Coral recruitment is a key process that contributes to the community structure and resilience of coral reefs. As such, quantification of this process is important to assist with the management of these threatened ecosystems. While coral recruitment has been the focus of numerous studies over the past 30 years, an understanding of this process on the high-latitude reefs of South Africa is limited. In addition, variations in methods used in recruitment studies make the results difficult to compare. A rapid in-situ method for universal application in the detection of early post-settled recruits would thus be useful. In this study, scleractinian coral recruitment was investigated at three study sites on Two-mile Reef, over two six-month sampling periods, covering summer and winter. Two components were investigated by attaching settlement tiles consisting of ceramic and marble tiles, and ceramic tiles conditioned with crustose coralline algae (CCA) onto the reef in a spatially structured experimental design. Firstly, coral recruitment was compared on the three different tile surfaces and fluorescence photography was investigated as a rapid in situ technique to detect early post-settled recruits. Fluorescence photography was then used to compare recruitment on tiles with the surrounding natural substrata. Secondly, the spatial and temporal variation in the abundance, composition and size of recruits was investigated. Additionally, the percentage cover of biota surrounding each recruit within three millimeters of its corallum was visually estimated to quantify the microhabitat surroundings of coral recruits. Overall recruitment on the three tile types differed, yet spatial variation in coral recruitment, regardless of tile surface, accounted for most of the variance in recruitment. While the highest recruitment occurred on CCA tiles, this was not significantly greater than ceramic tiles, indicating that the conditioning of ceramic tiles with Mesophyllum funafutiense CCA did not enhance coral settlement in this study. Although many recruits were not detected with fluorescent photography (73%), it proved useful to reveal recruits as small as 0.75 mm in corallum diameter, and indicated that recruitment on the tiles and natural substratum differ significantly. Spatially, the abundance and composition of coral recruits differed between study sites, within sites, and predominantly occurred on tile edges. Coral recruitment was lowest at shallower sites, and was dominated by pocilloporids regardless of study site. Additionally, the abundance and composition of recruits differed between the two sampling periods, with a 6.6-fold decrease in the mean abundance of recruits from summer to winter, with only pocilloporid settlement occurring in the latter season. The majority of recruits were <3 mm, and their microhabitat was dominated by bare substrata and crustose coralline algae. The results suggest that, while the choice of artificial settlement surface used in such studies can have a profound influence on the results, spatial variation in recruitment can be greater. The recovery of scleractinian coral taxa on Two-mile Reef in the event of a severe disturbance is expected to differ, with greatest recovery in areas of high levels of recruitment. The microhabitat surrounding recruits is described here for the first time, suggesting that further research into coral-crustose coralline algae interactions is warranted. Finally, while fluorescence photography has its limitations, it shows promise as a useful tool for rapid qualitative, but not quantitative, assessment of recruitment.
Dietary dynamics of two key fish species in the St Lucia estuarine system, South Africa.
(2014) Dyer, David Clifford.; Perissinotto, Renzo.; Carrasco, Nicola Kim.
Among the 155 species of fish recorded so far in the St Lucia estuarine lake, Oreochromis mossambicus and Ambassis ambassis are the two most prominent. Although originally endemic to southern Africa, O. mossambicus is now one of the most widely distributed exotic fish species worldwide. Together with A. ambassis, they have become the dominant fish species in the St Lucia estuarine lake since the closure of the mouth in 2002 and are, therefore, a crucial component of the food webs throughout the system. After a decade dominated by dry and hypersaline conditions, the St Lucia system has changed dramatically in terms of prevailing environmental conditions, as a result of higher than average rainfall at the end of 2011 and the onset of a new wet phase at the start of 2012. In response, A. ambassis, which prefers lower salinity regimes, has expanded its distribution range throughout the estuarine lake. Stable δ¹⁵N and δ¹³C isotope analysis was used in conjunction with gut content analysis to elucidate the diet of these species at sampling localities spanning the geographical range of the system and determine whether these species shift their diet in response to environmental or climatic shifts. From both studies it is evident that from a temporal and spatial scale these two species adopt similar, yet very different, dietary tactics. Oreochromis mossambicus was shown to adopt a generalist feeding strategy, opportunistically feeding on dietary items that are available thus allowing this species to alter its diet according to the environment that it inhabits. Trophic positioning of this species was found to be controlled by salinity in St Lucia as dietary composition differed greatly between sites. In contrast, Ambassis ambassis displayed a more specialist dietary composition, feeding predominantly on zooplankton. However, this species also opportunistically supplements its diet with additional sources when available. Trophic position of A. ambassis was higher in the dry season owing to the increased productivity of the system during the wet season. The success and dominance of both species in the St Lucia system can therefore be attributed to their dietary strategies. Under extreme environmental conditions, O. mossambicus has the added advantage of its wide tolerance of different environmental conditions, particularly salinity, thus allowing it to proliferate.
Diversity and distribution of subtidal soft-bottom macrofauna of the Isimangaliso Wetland Park, South Africa.
(2014) Harmer, Rogan Will.; Glassom, David.
There have been no previous studies describing the subtidal soft-bottom macrofaunal assemblages of the iSimangaliso Wetland Park or how they are influenced by the ecological and environmental processes associated with coral reef proximity. With South Africa having high wave energy the transportation of nutrients and organisms between the soft-bottom areas and reef habitats is probable. This transfer of resources may create ecological linkages which organisms depend on. The aim of this study was to document the species diversity, distribution and abundance of in- and epi-macrofauna in iSimangaliso Wetland Park and to relate these to depth, sediment grain size, location, reef proximity and protective status. Macrofauna were collected using an air-lift design suction sampler. The macrofauna were identified to the lowest possible taxonomic level, biomass estimates were calculated and sediment grain size was determined. A total of 5166 animals were collected and 121 macrofauna species were identified. Macrofaunal assemblages inhabiting the soft-bottom sedimentary habitat surrounding the reefs changed in species abundance and diversity with increasing distance from the reef. Lower abundances and diversity were found closest to the reefs strongly indicating that the macrofaunal assemblages were negatively affected by the reef proximity. Although reef proximity was indicated as influential, environmental gradients were found to be more important in defining community structure. Higher percentages of coarse sediments found closest to the reef edge coincided with lower abundances, biomass and species richness of macrofauna. Trends of higher abundances at the middle distance indicated hydrodynamic disturbance may be affecting near shore assemblages. Sediment grain size and hydrodynamic disturbance both appeared to be the main determinants of assemblage structure around reefs. Trophic interactions by reef associated predators were indicated by lower macrofaunal abundances recorded at close proximity to the reefs.There was no evidence for the presence of a latitudinal diversity gradient as localised environmental conditions were found to be more influential in determining soft-bottom macrofaunal community structure and distribution in the iSimangaliso Wetland Park. The presence of ecological linkages between soft-bottom macrofaunal communities and coral reefs gives insight into the important roles soft-bottom macrofauna play in the functioning of the iSimangaliso Wetland Park marine reserve. The documentation of the species diversity and distribution of macrofauna in the soft-bottom habitats will provide valuable baseline information for the future management strategies.
The dynamics of microphytobenthos in the Mdloti and Mhlanga estuaries, Kwazulu-Natal.
(2004) Iyer, Kogilam.; Perissinotto, Renzo.; Nozais, C.
Microphytobenthos (MPB) generally dominates total autotrophic biomass in temporarily open/closed estuaries (TOCEs) of South Africa. A comparative study of MPB biomass was undertaken in two KwaZulu-Natal TOCEs, the Mdloti and the Mhlanga. Both estuaries receive different volumes of treated sewage waters. The Mdloti receives 8 ML.d-1, while the Mhlanga receives 20 ML.d-1, resulting in a capping flow of 0.092 and 0.23 m3.s-1, respectively. Through these effluents, eutrophication is enhanced and periods of mouth opening are also increased and prolonged, particularly at the Mhlanga. The aim of this study was to investigate fluctuations in MPB biomass in the Mdloti and the Mhlanga systems, with emphasis on freshwater flow and the alternation of closed and open phases. Sediment samples for MPB biomass were collected on a monthly basis, between March 2002 and March 2003, in the lower (mouth), middle, and upper (head) reaches of the two estuaries. MPB biomass ranged from 1.33 to 391 mg chI a m-2 and from 1.7 to 313 mg chI a m-2 in the Mdloti and the Mhlanga, respectively. A I-way ANOVA revealed no significant differences in MPB chI a concentrations between the two estuaries for the entire data set (Fl, 76 =1.48, P > 0.05). At the Mdloti, MPB biomass varied considerably, with values ranging from 1.33 to 131 mg chI a m-2 during the open phase, and from 18 to 391 mg chI a m-2 during the closed phase. A Mann-Whitney U test confirmed the high significance of these differences between open and closed phases (U= 29, P < 0.001). At the Mhlanga, MPB biomass ranged from 7.0 to 313 mg chI a m-2 during the open phase, and from 1.7 to 267 mg chI a m-2 during the closed phase. Unlike what was observed at the Mdloti, the higher MPB values at the Mhlanga were not always associated with the closed mouth state. In relation to key physico-chemical and biological factors, grazing pressure exerted by the zooplankton community appeared to have played a major role in controlling MPB biomass. Zooplankton biomass was consistently and positively correlated to MPB biomass throughout the study period both at the Mdloti (r = 0040, P < 0.001) and at the Mhlanga (r = 0.33, p < 0.05). Unlike what was shown in previous studies, light attenuation was not significantly correlated with MPB biomass during the period ofthe study, either at the Mdloti or the Mhlanga. These results show that the opening and closing of the mouth play a key role on the MPB biomass of both estuaries. The Mdloti seems to function as a typical TOCE, with prolonged open and closed phases. The Mhlanga, on the other hand, lacks a prolonged closed phase. This, in turn, affects its entire trophic structure and functioning.
The dynamics of nano- and microplankton in the St. Lucia estuarine lake system, KwaZulu-Natal.
(2013) Fru Azinwi, Nche-Fambo.; Scharler, Ursula Michaela.; Tirok, Katrin.
St. Lucia estuarine lake system has a history of episodic droughts and floods leading to a high variability in physico-chemical characteristics which may influence the community structure of nano- and microplankton that are the main primary energy synthesisers in aquatic systems. Originally, the St. Lucia estuary and the Mfolozi River shared the same mouth with the Mfolozi River acting as the main source of fresh water to the system and as stabiliser of the common inlet. Due to prolonged mouth closure from 2001-2012 and high evaporation rates, severe extended droughts and high salinities were experienced in 2001-2012.This project aimed to characterise community composition and biomass of nano-and microplankton (autotrophic and heterotrophic) under the varying and extreme physico-chemical conditions in order to characterize the energy basis of the planktonic food web in St. Lucia. Its main objectives were to compare and add onto Johnson’s (1977) list of phytoplankton taxa in the system, to estimate the biomass (carbon) of nano- and microplankton from cell counts and biovolume measurements, and lastly to understand and establish trends in the change in community structure of these organisms with the varying physico-chemical characteristics. Nano- and microplankton samples were collected monthly from October 2010 to September 2011 at three different sites: Lister’s Point, Charters Creek and the mouth representing the lakes and estuary Channel. Chlorophyll a and physico-chemical parameters were also measured in situ during collection. In the lab, samples were settled using the Utermöhl method and species were identified to at least genus level, counted and cell measurements taken under an inverted microscope for biovolume calculations and biomass thereof. Abundance in cells per liter and biomass (carbon) in pg/L was then analyzed from the counts. The nano-and microplankton groups recorded in the system were cyanobacteria, chlorophytes, cryptophytes, dinoflagellates, ciliates and diatoms. Seventy eight phytoplankton taxa were identified composed of 56 diatoms, eight green algae, one cryptophyte, seven cyanobacteria and six dinoflagellate taxa. Nineteen ciliate taxa were also found. Only 12 of the diatom taxa identified in this study were listed by Johnson (1977), none of the taxa in the other phytoplankton groups was listed by Johnson (1977). The Johnson (1977) study conducted in the system from 1975-1977 listed the phytoplankton taxa occurring at that time. There was no significant difference in the community composition, biovolume and biomass between seasons hence no seasonal trend however, there were significant differences in the nano- and microplankton community composition, biovolume and biomass at the three different sites of the system. Cyanobacteria were the main taxa in the northern embayments dominating in abundance, biovolume and biomass (biological variables), green algae and cryptophytes dominated in abundance, biovolume and biomass in the Channels while in South Lake, green algae dominated in abundance but diatoms dominated in biovolume and biomass. Ciliate biological variables were higher in the northern regions than in the other parts of the estuary. The absence or limited grazing pressure of ciliate predators in the northern region due to their inability to cope with the extreme salinities compared to the other parts of the system explains why the northern embayments had the highest abundance, biovolume and biomass of ciliates. Ciliates and heterotrophic dinoflagellates were the heterotrophs in this study. Autotrophic:heterotrophic biomass ratio was lowest in the northern regions as heterotrophs had a higher biomass there. This ratio was higher in the South Lake and the Channel. The lack of stratification and generally high turbidity in the system made the system unfavourable for dinoflagellate growth. The higher presence of ciliate predators in the South Lake and Channel probably accounts for the low heterotrophic biomass hence high autotrophic:heterotrophic biomass ratio in South Lake and the Channel. Nutrients were not limiting during this study and salinity was the main physico-chemical characteristic accounting for the differences in nano- and microplankton biological variables. The Cyanothece bloom in the northern region was primarily due to high salinities (>150) which also indicated unfavourable conditions for other plankton types. The high diatom biomass in the southern lake was due to low salinities (<28) which favoured their growth, whereas chlorophytes and cryptophytes dominated in the Channel mainly due to low turbidity (median of 11.4NTU) and fresh water input from the Mfolozi lowering salinities (<5). The South Lake and Channel thus had the highest available energy for higher trophic level organism since 1) diatoms and green algae are the most favoured food source for phytoplankton grazers while the cyanobacteria though most abundant are the least favoured food source leaving the northern lake with smaller energy source for higher trophic level organisms and 2) The low autotrophic:heterotrophic biomass ratio in the northern region leaves the region with a lower net carbon biomass than the other parts of the system with a higher autotrophic: heterotrophic biomass.

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