Larval fish dynamics within the coastal nearshore of the Eastern Cape, South Africa
- Authors: Sotshongaye, Oko
- Date: 2021-04
- Subjects: Fishes -- Larvae -- South Africa -- Eastern Cape , Fishes -- Larvae -- Development -- South Africa -- Eastern Cape , Fishes -- Larvae -- Ecology -- South Africa -- Eastern Cape , Coastal ecology -- South Africa -- Eastern Cape , Fishes -- Larvae -- Dispersal -- South Africa -- Eastern Cape
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/176977 , vital:42776
- Description: The coastal nearshore is important for the early development of fishes as it is used for spawning and/or as a nursery. One of the central concerns in coastal ecology is understanding the role of the nearshore for larvae, ultimately providing key knowledge on population dynamics and hence helping in making decisions pertaining to conservation and resource management. The aim of this study was to investigate the alongshore and cross-shore distribution of larval fishes and the links to the physio-chemical conditions (including prevailing winds) and hydrodynamics in the region of Algoa Bay, situated on the south east coast in the warm temperate region of South Africa. Fish larvae were sampled at nine sites for the first component of the study (January 2016 –March 2017) and at four sites for the second component (November 2019), near the surface and bottom (15-50 m) of the water column as well as at two different distances from shore (~400 m/~3 km) using a set of bongo plankton nets towed behind a boat. Environmental data were simultaneously collected using and acoustic Doppler current profiler (ADCP) and conductivity, temperature, depth (CTD) profiler. Larval fish abundance generally decreased with increasing distance from the shore, however, this varied in space and time, with some larval species recorded in high abundances offshore. Close inshore the larvae of coastal fish species producing benthic eggs (CBE) including the Blenniidae and Gobiesocidae mostly dominated, while offshore the larvae of coastal fish species producing pelagic eggs (CPE) i.e. Sparidae and Cynoglossidae, as well as pelagic fish species producing pelagic eggs (PPE) i.e. Clupeidae and Engraulidae mostly dominated. Vertical distribution of larvae differed according to taxon, with the Callionymidae (CPE), Cynoglossidae and Gobiesocidae occurring at high densities at the bottom of the water column, while the Blenniidae dominated near the surface. Fluorescence, temperature and salinity varied with depth (surface/bottom), being particularly high at the surface; currents moved faster at the surface than the bottom of the water column. Increased abundances of larval fishes were evident after upwelling events (associated with easterly winds) in the Bay, while during downwelling (associated with westerly winds), low densities were generally recorded, except for the sites situated near headlands/capes where there were higher densities of fish larvae during downwelling events. Overall, the results of this study suggest that spawning mode of the adults, oceanography and environmental conditions coupled with what is known of the behaviour of fish larvae, were important in shaping the larval fish community of the Algoa Bay region. These results highlight the importance of incorporating multiple biological (developmental stage, reproductive mode, species) and physical (currents, fluorescence, wind-driven up/down-welling) factors when addressing the mechanims of transport of larval fish in the coastal nearshore. , Thesis (MSc) -- Faculty of Science, Department of Zoology and Entomology, 2021
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- Date Issued: 2021-04
Combination ecosystem green engineering and early life history processes to enhance the intertidal biodiversity in the Port of East London
- Authors: Mafanya, Sandisiwer
- Date: 2020
- Subjects: Biotic communities -- South Africa -- East London , Perna -- Ecology --South Africa -- South Africa-- East London , Mexilhao mussel -- Ecology -- South Africa -- East London , Habitat (Ecology) -- Modification -- South Africa -- East London , Benthic animals -- Effect of habitat modification on -- South Africa -- East London , Harbors -- Environmental aspects -- South Africa -- East London
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/166376 , vital:41357
- Description: Marine coastal ecosystems are highly impacted by anthropogenic activities, including the development of, and practices within, harbours and/or ports. Artificial structures associated with harbours have a different chemical composition, texture and orientation than that of the natural benthic habitats they have replaced, and are therefore not generally favourable for the settlement and occurrence of indigenous species. Attempts are being made to identify what structures and materials can be used to aid in the rehabilitation of native species within harbours. The aim of this study was to investigate the effects of utilising environmentally-friendly artificial structures (tiles) with varying complexity (crevices and ridges with different depths) with ecological engineers (the indigenous bivalve Perna perna), on the associated benthic biodiversity within an international port in South Africa (Port of East London). The objectives of the study were to test the effects of artificial habitat complexity and the presence of bivalves on 1) the growth, mortality and biomass of a selected model species of ecosystem engineer (P. perna), and 2) the associated intertidal biodiversity. Tiles seeded with bivalves (P. perna) were deployed at two sites in the Port of East London and monitored monthly over a period of 12 months (November 2016-October 2017) to assess survival, growth and associated biodiversity. Environmental variables were also measured every month. The results of the three-way repeated measures ANOVAs indicated that tile treatment (especially high complexity of 2.5 and 5 cm) had an effect on the diversity of mobile species, length, height and biomass of the bivalves used as model ecosystem engineer, indicating the potentials for protection from wave dislodgement and refuge provision. Treatment (especially flat tiles) also had an effect on sessile/sedentary species diversity, indicating the greater proportion of space provided by these non-complex tiles. In addition, month had an effect on the mortality, height and biomass of the bivalves. Mortality was highest in October 2017, while the growth in height and biomass of P. perna were largest in January and October 2017 respectively. The use of artificial tiles also had a positive effect on the survival, growth, and biomass of bivalves (especially the length, weight and dry weight in 2.5 cm and 5 cm complexity). Additionally, this research investigated patterns of settlement and recruitment of the local bivalve population (P. perna) in the Port of East London and adjacent natural coastline to understand the early life history temporal and spatial dynamics of this model ecosystem engineer species. Settlement and recruitment were assessed every month by deploying and replacing artificial collectors for a total period of 19 months (November 2016-May 2018). The results of the two-way ANOVAs indicated that month and site (port vs natural) had an effect on settlement and recruitment of bivalves. Settlement and recruitment of bivalves were highest in July 2017 (port) and March 2018 (natural rocky shore). This study has highlighted that the use of artificial concrete tiles with increased complexity, as well as the investigation of the early stages of mussel populations could be important to consider in a framework of rehabilitation of urban coastal environments such as the Port of East London. Ecological engineering (in terms of increased complexity and heterogeneity) has indeed the potentials to be incorporated in South African programmes aiming at improving natural biodiversity in coastal urban environments. Nonetheless, the spatio-temporal variability of early driver of mussel populations (settlement and recruitment) is also an important feature to be closely monitored if biodiversity in South African coastal armouring is to be enhanced effectively and in the long term.
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- Date Issued: 2020
Combining DNA barcoding and morphology to identify larval fishes from the nearshore environment off the south-east coast of South Africa
- Authors: Somana, Zinzi Sinazo
- Date: 2020
- Subjects: Fishes -- Larvae -- South Africa -- Identification , Fishes -- Genetics -- Research -- Technique , Fishes -- South Africa -- Classification , Genetic markers
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144605 , vital:38362
- Description: The early life history stages of most marine fish species are undescribed. The problem is, most of these fishes have pelagic larvae which are minute, delicate forms. Linking the larval stage to an adult counterpart is extremely challenging as larvae are morphologically different from the adults. Historically, larval fish identification relied solely on distinguishing morphological characteristics and meristic measurements, which has resulted in taxonomic confusion and misidentification. The introduction of the deoxyribonucleic acid (DNA) barcoding technique as an alternative approach has been successful in positively identifying larval fishes. The correct identification of larval specimens is the key to a better understanding of larval ecology, which underpins the success of any adult fish population. This study aimed to positively identify larval fishes of the south-east coast of South Africa using morphological characteristics and DNA barcoding. Larval and eggs specimens for this study were collected from the shallow nearshore waters of the south-east coast of South Africa. A total of 177 larval specimens were used for morphological analysis. Body shape, gut shape, pigmentation and morphometric measurements (such as body depth, preanal length and total body length) were used to identify each specimen to the family level. In addition, a fragment of mitochondrial cytochrome c oxidase subunit 1 gene (COI) was adopted for sequencing to identify larval fish specimens and fish eggs. Sequences generated from this study were compared to those in the Barcode of Life Database (BOLD). When there were no close matches to a sequence, the GenBank nucleic acid sequence database, maintained by the National Center for Biotechnology Information (NCBI), was used as an alternative. A total of 18 different families were identified through morphology. Seventy-seven of the 177 larval specimens were not subjected to morphological identification due to physical damage. The majority of larvae identified using morphological characteristics belonged to either the Sparidae, Tripterygiidae or Gobiesocidae fish families. Through DNA barcoding, 12 fish families, 16 genera and 18 different species were identified. Ten DNA barcodes (categorised as ‘no match’) from 10 different larval specimens were not identified through any of the online databases. Therefore, the 2% threshold value was used to identify members of the same species. The K2P genetic distance relationships were calculated among the no match sequences and downloaded probability matches from NCBI. This resulted in two unknown specimens assigned to the Blenniidae and Gobiidae. All other taxa were identified to species level, except specimens representing the Gobiidae and Tripterygiidae families. Based on the K2P genetic distances Gobiidae representatives were categorised as members of the Caffrogobius genus. Twenty-eight barcodes represented specimens from the Tripterygiidae. DNA barcode data from COI was analysed using the standard phylogenetic procedures in MEGA6 to examine relationships and differentiation among sequences. These could not be identified to the lowest taxonomic rank due to limited sequence data to compare them with. The sequence data from these specimens gave different results in the two online databases. BOLD results were to family level (Tripterygiidae) and NCBI to the species level (Clinidae: Pavoclinus profundus). Results in this study confirmed the efficiency of the DNA barcoding technique in species level identification of fish larvae. The evidence from genetic barcodes of the Tripterygiidae specimens, supported by morphological characteristics, suggests the need for thorough research to identify the individuals to the species level. The fact that this study identified taxonomically problematic Gobiidae and Tripterygiidae specimens suggests that studies similar to this may highlight additional diversity and help to resolve the taxonomy of other species in these families. However, the lack of reference sequence data from the adult specimens, and especially those with cryptic diversity, were both shortcomings for the positive identification of larvae. With that being said, it shows the necessity for more research to be conducted on barcoding of larvae in general as to accommodate all kinds of species from biodiversity to economic perspectives.
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- Date Issued: 2020
Environmental drivers of the composition and distribution of larval fish assemblages off the south coast of South Africa
- Authors: Trassierra, Jaqueline Anne
- Date: 2019
- Subjects: Fishes -- Larvae -- South Africa -- Eastern Cape , Fishes -- Larvae -- Migration -- South Africa -- Eastern Cape , Fishes -- Larvae -- Dispersal -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/68154 , vital:29207
- Description: The species composition, distribution and patterns of vertical migration of larval fish assemblages were investigated in March and in September 2013 within two adjacent log spiral bays, Algoa Bay and St Francis Bay, on the south coast of South Africa. Fish larvae were collected by means of a boat towed bongo net (57 cm diameter; mesh aperture 500 μm). An onshore (2 km) and an offshore (3 km) station were each sampled twice during the daytime (06:00 – 18:00) with two horizontal tows: near the surface (0.5 m) and close to the bottom (12 m). Tows were repeated at night (18:00 – 23:00) for onshore sites. Larval catches included 16 fish families and 40 species. A multivariate analysis indicated that the species composition was significantly different between Algoa Bay and St Francis Bay, with Engraulidae, Blenniidae, Sparidae, Soleidae and Cynoglossidae making important contributions to the larval fish catch in Algoa Bay, while Blenniidae, Engraulidae, Tripterygiidae, Sparidae and Gobiesocidae contributed significantly in St Francis Bay. Differences in assemblage composition were noted between the Spring (September–October) and Autumn (March-April) months. The species composition of larval fish assemblages was related to wind speed, wave height, cloud cover, sea water temperature, depth, average current speed and direction. Wind speed, wave height, temperature and depth significantly contributed to the variation in larval fish densities. Abundances of larval fishes were greater offshore than onshore, larvae from pelagic eggs dominated catches offshore, while larvae from demersal eggs dominated onshore catches. Habitat structure strongly influenced the composition of larval fishes between the bays and abundances were significantly greater at night than during the day. Most larval fishes displayed a reverse diel vertical migration pattern and were most influenced by predators, wind speed and cloud cover. This study shows that larval fish assemblages are highly complex and patchy. Spawning mode, individual species behaviour, diel vertical migration, current structure, depth, temperature, wind speed, cloud cover and type of habitat substratum all influence larval fish composition and distribution in the nearshore waters of South Africa.
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- Date Issued: 2019
Mesoscale alongshore and cross-shore transport and settlement of invertebrate larvae on the south east coast of South Africa
- Authors: Dyantyi, Siphelele Buntu
- Date: 2019
- Subjects: Marine invertebrates -- Larvae -- Dispersal -- South Africa -- Eastern Cape , Benthic animals -- Larvae -- Dispersal -- South Africa -- Eastern Cape , Mexilhao mussel -- Larvae -- Dispersal -- South Africa -- Eastern Cape , Mytilus galloprovincialis -- Larvae -- Dispersal -- South Africa -- Eastern Cape , Oysters -- Larvae -- Dispersal -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/97007 , vital:31386
- Description: Pelagic larval stages of most marine benthic species are important in maintaining coastal populations of adults. Several physio-chemical factors such as currents, winds, larval behaviour and time have an influence on the dispersal and transport of larvae to the adult habitat but their role is however still poorly understood. The aim of this study was to investigate the alongshore and cross-shore transport and temporal delivery of invertebrate larvae at four sites (Kenton on Sea, Cannon Rocks, Schoenmakerskop and Cape St Francis) along the south east coast of Eastern Cape, South Africa. Larval distribution of several taxa was determined during two sampling periods, by collecting water samples at nearshore line transects (3 distances: 900m, 1500m and 2400m – perpendicular to the shore) and at three depths (surface, thermocline/middle, bottom), which ranged from 15m (inshore) to 50m (offshore). Physical properties (current speed and direction, dissolved oxygen, fluorescence, turbidity, temperature, salinity, pH, pressure, density and conductivity) were measured and coupled in order to further understand larval distribution. The larvae were analysed as both total abundance and separately as the abundances of a variety of taxa which were: Perna perna, Mytilus galloprovincialis, oysters, early and late nauplii and cyprids. Larval settlement and recruitment on the rocky shores were measured by monthly deployment and collection of 20 (10 each for barnacles and mussels) artificial collectors at each site, which were preserved in ethanol or frozen for further processing. Multiple Permutational Multivariate Analysis of Variance (PERMANOVA) analyses were used to test the effects of site, depth and distance from the shore for the nearshore larvae (taxa analysed separately). In addition, a distance based linear model (distLM) was performed to analyse the relationship between the total larval abundance and the above mentioned physical variables. Multiple two-way analyses of variance (ANOVA) were performed to test the effects of months and sites on the settlement and recruitment of the larvae (P. perna, M. galloprovincialis, other bivalves, cyprids and juvenile barnacles) arriving on the shore. For the nearshore larval distribution, results from the PERMANOVAs revealed that most taxa showed a significant site and depth interactions with the exception of ‘early nauplii’ taxon. Also nearly all taxa were found within the thermocline, besides ‘oyster’ and ‘cyprids’ which were located at thermocline or bottom. Larvae were also located at variable distances from the shore, with most occurring at the offshore stations. Furthermore, there was a geographical separation of larval abundance according to sites, with most larvae located at Cannon Rocks and Kenton on Sea and least at Schoenmakerskop and Cape St Francis. For the settlement and recruitment, most taxa showed a seasonal trend, with the highest abundance of settlers and recruits expectedly appearing during the summer months of the sampling period. Additionally there was a site effect for most taxa (P. perna, M. galloprovincialis, other bivalves and juvenile barnacles), where settlers and recruits were mostly found at Cannon Rocks. Significant differences in abundance of settlers and recruits amongst the four sites indicate spatial and temporal variability for the targeted 180km stretch of coast. Overall for this study, taxon and ontogenetic stage of larvae were important in the distribution and abundance of larvae. Throughout the time frame of nearshore and intertidal sampling, Cannon Rocks consistently resulted as a ‘hot spot’ for larval abundance, settlement and recruitment, while a broad west to east separation was also observed. These results hence highlight that within this stretch of c.180km coast, time, taxon, ontogeny and post-settlement factors influence early dynamics of benthic populations.
- Full Text:
- Date Issued: 2019
Mesoscale mechanisms of larval transport and settlement in relation to physical factors off the south coast of South Africa: a topographic approach
- Authors: Mian, Shana Iva
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5947 , http://hdl.handle.net/10962/d1020844
- Description: The majority of benthic marine invertebrate life cycles include a meroplanktonic phase. Most marine biologists recognise that this stage could play an important role in dispersal, especially for sedentary or sessile organisms. Recent studies on larval dispersal have found that dispersal does not occur to the extent that was previously believed. Some larvae instead remain close to their natal populations through larval nearshore retention mechanisms, both active and passive. This study attempted to a) describe nearshore distribution patterns of several intertidal larvae in relation to nearshore hydrodynamics, b) infer whether larvae are active or passive in the water column and whether this differs among taxa and c) compare pelagic mussel larval abundance with settlement rates, at 2 bay and 2 open coast sites on the south coast of South Africa to note any topographical effects. At each of the four sites, pelagic samples were collected along 2 transects. Larvae and current speed data were collected at various depths (surface, mid-depth and bottom) at distances of 200, 400, 900 and 2400m offshore of the coast. Settlement samples were collected at sites that were onshore of the pelagic transects using plastic souring pads following previous studies. Pelagic larval distribution showed no effect of topography. Instead larval abundance was highly variable among sample periods and among different taxa. Slow swimming D-stage mussel larvae were found to be positively correlated with both upwelling and turbulence indices suggesting that they behave as passive particles in the water column. The abundances of larval taxa with faster swimming speeds than the D-larvae were negatively correlated with upwelling and did not correlate with turbulence. This suggests that these larvae are more active within the water column than the D-larvae which would theoretically allow them to maintain their position in the water column. Further analysis revealed that mean larval depth correlated with mean depth of shoreward moving water masses regardless of the state of upwelling. These results suggest that larvae were actively selecting the depth at which they were found presumably in order to associate themselves with shoreward moving currents. This interpretation was supported by ontogenetic patterns in the behaviour of barnacle larvae, the nauplii of which were found further offshore as they aged, and closer onshore again once they reach the faster swimming cyprid stage. Although there was no detectable effect of topography on the abundances of planktonic larvae, the settlement section of this study revealed an effect of topography, with higher settlement and recruitment rates at bay sites than at the open coast sites. Settlement rates were seen to be negatively correlated with turbulence at bay sites but not open coast sites. Recruitment rates for each sample event were positively correlated with upwelling at each site. This study found pelagic larvae to be generally active within the water column which allowed them to remain close to the shore regardless of topography and upwelling/turbulence regimes. Although meaningful correlation analyses between pelagic larval supply and settlement rates could not be conducted due to loss of settlement collectors, settlement rates were affected by local topography with higher settlement and recruitment in bay sites.
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- Date Issued: 2016
The epibiotic relationship between mussels and barnacles
- Authors: Bell, Caroline Margaret
- Date: 2014
- Subjects: Epibiosis , Mussels -- Ecology -- South Africa , Mussels -- Behavior -- South Africa , Mussels -- Habitat -- South Africa , Barnacles -- Ecology -- South Africa , Barnacles -- Behavior -- South Africa , Barnacles -- Habitat -- South Africa , Perna -- Behavior -- South Africa , Mytilus galloprovincialis -- Behavior -- South Africa , Marine biodiversity -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5847 , http://hdl.handle.net/10962/d1011460 , Epibiosis , Mussels -- Ecology -- South Africa , Mussels -- Behavior -- South Africa , Mussels -- Habitat -- South Africa , Barnacles -- Ecology -- South Africa , Barnacles -- Behavior -- South Africa , Barnacles -- Habitat -- South Africa , Perna -- Behavior -- South Africa , Mytilus galloprovincialis -- Behavior -- South Africa , Marine biodiversity -- South Africa
- Description: Epibiosis is an ecological relationship that has been described as one of the closest possible associations in marine ecosystems. In the space limited rocky intertidal, mussel beds provide important secondary space for barnacles. The epibiotic relationship between mussels and barnacles on the south-east coast of South Africa was considered at different scales, from large-scale, natural patterns of epibiosis on the rocky shore, to fine-scale settlement choices of barnacles and the effects on the condition and growth rates of individual mussels. Mussel and barnacle assemblages were generally stable over a 12-month period. The tracking of individual mussels with and without barnacle epibionts resulted in a significant increase in mortality rate of mussels with epibionts over 12 months (two-way ANOVA, p = 0.028). Barnacles on rocks, as well as on mussels, were also tracked with no significant effect of substratum on mortality of barnacles (two-way ANOVA, p = 0.119). Prevalence and intensity of barnacle infestations was also examined in relation to coastline topography on two co-occurring mussel species, the indigenous Perna perna and invasive Mytilus galloprovincialis. The results were complex, but bay status had significant effects on prevalence and intensity for both mussel species, depending on the time and zone. The effect of bay in relation to time was particularly relevant for M. galloprovincialis (four-way nested ANOVA, Season X Site(Bay): p = 0.0002), where summer prevalence was higher than that of winter in bays, regardless of zone, while in open coast sites, the effect of season was only significant in the mid zone. Patterns of intensity generally showed higher values in summer. Substratum preference by barnacles was investigated by recording settlement, survival and mortality of Chthamalus dentatus barnacles on various treatments. There was a strong preference for the rock-like plastic substratum by primary settlers (pair-wise tests of PERMANOVA: Dead < Rock mimic (p = 0.0001); Replica < Rock mimic (p = 0.019) and Live < Rock mimic (p = 0.0001)). This indicates that barnacles settle on mussel shells only as a secondary choice and that micro-topography is an important variable in barnacle settlement. The effect of barnacle epibiosis on condition index and growth of P. perna and M. galloprovincialis was also examined as a direct indication of the health of mussels subjected to the biological stress of epibiosis. Although not significant (PERMANOVA: P. perna: p(perm) = 0.890; M. galloprovincialis: p(perm) = 0.395), growth for both mussel species was slower for barnacle-infested individuals in summer, which is the main growing season for mussels in the region. Results from condition index calculations, however, showed no negative impacts of epibiotic barnacles (three-way ANCOVA: P. perna: p = 0.372; M. galloprovincialis: p = 0.762). Barnacle epibionts create a new interface between the mussel and its environment and this interaction can affect other members of the community. The possibility of the barnacle epibiont causing increased drag also needs further investigation. Biological processes operating within a wide range of physical stressors drive the interactions on the rocky shore, such as epibiosis. Overall, the results of this study suggest that the epibiotic relationship between mussels and barnacles on the south-east coast of South Africa does not significantly affect the mussel species present and that barnacles only use mussel shells as a secondary choice of substratum.
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- Date Issued: 2014
The effect of mussel bed structure on the associated infauna in South Africa and the interaction between mussel and epibiotic barnacles
- Authors: Jordaan, Tembisa Nomathamsanqa
- Date: 2011
- Subjects: Mytilidae -- South Africa , Mytilus galloprovincialis -- South Africa , Mussel culture -- South Africa , Shellfish culture -- South Africa , Perna -- South Africa , Barnacles -- South Africa , Mussels -- South Africa , Mussels -- Ecology , Barnacles -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5675 , http://hdl.handle.net/10962/d1005360 , Mytilidae -- South Africa , Mytilus galloprovincialis -- South Africa , Mussel culture -- South Africa , Shellfish culture -- South Africa , Perna -- South Africa , Barnacles -- South Africa , Mussels -- South Africa , Mussels -- Ecology , Barnacles -- Ecology
- Description: Mussels are important ecological engineers on intertidal rocks where they create habitat that contributes substantially to overall biodiversity. They provide secondary substratum for other free-living, infaunal or epifaunal organisms, and increase the surface area for settlement by densely packing together into complex multilayered beds. The introduction of the alien invasive mussel Mytilus galloprovincialis has extended the upper limit of mussels on the south coast of South Africa, potentially increasing habitat for associated fauna. The aim of this study was to describe the structure of mussel beds, the general biodiversity associated with multi- and monolayered mussel beds of indigenous Perna perna and alien M. galloprovincialis, and to determine the relationship between mussels and epibiotic barnacles. This was done to determine the community structure of associated macrofauna and the role of mussels as biological facilitators. Samples were collected in Plettenberg Bay, South Africa, where M. galloprovincialis dominates the high mussel zone and P. perna the low zone. Three 15 X 15 cm quadrats were scraped off the rock in the high and low zones, and in the mid zone where the two mussel species co-exist. The samples were collected on 3 occasions. In the laboratory mussel-size was measured and sediment trapped within the samples was separated through 75 μm, 1 mm and 5 mm mesh. The macrofauna was sorted from the 1 mm and 5 mm sieves and identified to species level where possible. The epibiotic relationship between mussels and barnacles was assessed by measuring the prevalence and intensity of barnacle infestation and the condition index of infested mussels. Multivariate analysis was used on the mean abundance data of the species for each treatment (Hierarchical clustering, multidimensional scaling, analysis of similarity and similarity of percentages) and ANOVA was used for most of the statistical analyses. Overall, the results showed that tidal height influences the species composition and abundance of associated fauna. While mussel bed layering influenced the accumulation of sediments; it had no significant effect on the associated fauna. Time of collection also had a strong effect. While there was an overlap of species among samples from January, May and March, the principal species contributing to similarity among the March samples were not found in the other two months. The outcomes of this study showed that low shore mussel beds not only supported a higher abundance and diversity of species, but were also the most structurally complex. Although the condition index of mussels did not correlate to the percentage cover of barnacle epibionts, it was also evident that low shore mussels had the highest prevalence. The levels of barnacle infestation (intensity) for each mussel species were highest where it was common and lowest where it was least abundant. This is viewed as a natural artefact of the distribution patterns of P. perna and M. galloprovincialis across the shore. Mussels are more efficient as facilitators on the low mussel zone than the high mussel zone possibly because they provide habitats that are more effective in protecting the associated macrofauna from the effects of competition and predation, than they are at eliminating the effects of physical stress on the high shore. Although mussels create less stressful habitats and protect organisms from the physical stress of the high shore, there are clear limitations in their ability to provide ideal habitats. The biological associations in an ecosystem can be made weak or strong depending on the external abiotic factors and the adaptability of the affected organisms.
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- Date Issued: 2011