Le suivi de la contamination côtière par les métaux, au moyen de bivalves du genre Mytilus, est de pratique courante dans de nombreux programmes de surveillance à travers le monde. La bioaccumulation résulte d'une interaction entre facteurs physiologiques (croissance, perte de poids, absorption, stockage), chimiques (transferts métaux, spéciation, biodisponibilité) et environnementaux (température, MES, chlorophylle). L'étude et la modélisation de ces interactions est d'un intérêt considérable pour la compréhension des phénomènes et l'interprétation de la bioaccumulation des métaux traces chez la moule. Compte tenu des objectifs de l'étude, afin d'intégrer l'effet de l'état physiologique de l'organisme bioindicateur, le modèle de bioaccumulation choisi suit le concept d'un modèle cinétique à base énergétique, par un couplage d'un modèle de croissance (modèle DEB : à budget énergétique dynamique) à un modèle simple d'accumulation. Afin de le paramétrer et de le calibrer, une étude cinétique d'accumulation (6 mois) et de décontamination (3 mois) a été réalisée pour cinq métaux (Hg, Cd, Pb, Cu et Zn), par la technique des transplants, sur trois sites d'étude aux potentiels trophiques et chimiques différents (Baie du Lazaret, Etang de Bages et l'île de Port-Cros). En plus de traiter de l'accumulation des métaux traces à partir de la voie dissoute et particulaire, le modèle tient compte de la biologie de l'individu et permet de quantifier l'effet de la croissance et des changements environnementaux, tant chimiques que nutritifs, sur la bioaccumulation. L'accumulation des métaux traces se fait à partir de l'eau et/ou de la nourriture alors que l'élimination se fait lors d'étapes physiologiques telles que la reproduction ou directement par excrétion dans le milieu. La contribution de la physiologie de l'organisme détermine des variables d'état tels que le soma, les réserves et le compartiment reproductif, dont les variations dans le temps influencent les cinétiques de capture et d'élimination au sein de l'organisme. Reliant par une méthode explicative les concentrations dans l'organisme à celle du milieu, le modèle permet d'évaluer la contamination effective des sites en s'affranchissant des différences physiologiques dues au trophisme. Cette application a été réalisée sur le réseau de surveillance français RINBIO par analyse inverse.

Mytilus galloprovincialis is invasive on rocky shores on the west coast of South Africa where it has become the dominant intertidal mussel. The success of this species on the west coast and its superior competitive abilities, have led to concern that it may become invasive on the south coast at the expense of the indigenous mussel Perna perna. On shores where these species co-occur, there appears to be habitat segregation among zones occupied by mussels. M.galloprovincialis dominates the high-shore and P.perna the low-shore, with a mixed zone at mid-shore level. This study examined the factors responsible for these differences in distribution and abundance. The study was conducted in Plettenberg Bay and Tsitsikamma (70km apart) on the south coast of South Africa. Each site included two randomly selected locations (300-400m apart). A third mussel species, Choromytilus meridionalis, is found in large numbers at the sand/rock interface at one location in Plettenberg Bay. Aspects of settlement, recruitment, growth and mortality of juvenile and adult mussels were examined at different tidal heights at each site. Quantitative analysis of mussel population structure at these sites supported the initial observation of vertical habitat segregation. Post-larvae were identified to species and this was confirmed using hinge morphology and mitochondrial DNA analysis. Size at settlement was determined for each species to differentiate between primary and secondary settlement. Adult distribution of C.meridionalis was primarily determined by settlement, which was highly selective in this species. Settlement, recruitment and growth of P.perna decreased with increasing tidal height, while post-settlement mortality and adult mortality increased higher upshore. Thus all aspects of P.perna’s life history contribute to the adult distribution of this species. Presumably, the abundance of P.perna on the high-shore is initially limited by recruitment while those that survive remain prone to elimination throughout adulthood. M.galloprovincialis displayed the same patterns of settlement and recruitment as P.perna. However, post-settlement mortality in this species was consistently low in the low and high zones. Juvenile growth also decreased upshore, suggesting that M.galloprovincialis may be able to maintain high densities on the high-shore through the persistence of successive settlements of slow-growing individuals. The low cover of M.galloprovincialis on the lowshore appeared to be determined by adult interactions. M.galloprovincialis experienced significantly higher adult mortality rates than P.perna in this zone. There were seasonal variations in the competitive advantages enjoyed by each species through growth, recruitment or mortality on the low-shore. In summer, P.perna had higher recruitment rates, faster growth and lower mortality rates, while M.galloprovincialis had slightly higher recruitment rates and faster growth rates in winter. P.perna is a warm water species while M.galloprovincialis thrives on the cold-temperate west coast of South Africa. Therefore both species appear to be at the edge of their optimal temperature regimes on the south coast, which may explain the seasonal advantages of each. Nevertheless, P.perna has maintained spatial dominance on the low-shore suggesting that it may ultimately be the winner in competition between these species. M.galloprovincialis appears to have a refuge from competition with P.perna on the high-shore due to its greater tolerance of desiccation stress, while being competitively excluded from the low-shore. Warm water temperatures coupled with poor recruitment rates at most sites may limit the success of M.galloprovincialis on this coast.

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.

Recruitment of planktonic larvae into sedentary benthic populations regulates the population dynamics of marine invertebrates. The processes controlling recruitment, however, are poorly understood, and recruitment remains largely unpredictable, which complicates management of exploited shellfish resources. The mussels Perna perna, Choromytilus meridionalis and Mytilus galloprovincialis, found on the south coast of southern Africa, have planktonic larvae and sedentary adult stages. This thesis examines dispersal, settlement and early post-settlement growth and mortality, and their effect on recruitment and demography of intertidal mussel populations in the region of Algoa Bay on the south coast of southern Africa. Temporal and spatial variation in the body mass, density and size structure of mussels, the distribution of bivalve larvae on plankton grids in the nearshore zone and the distribution of a recently introduced invasive mussel, Mytilus galloprovincialis, were examined between 1989 and 1992. Furthermore, data on hourly or daily changes in wind strength and direction, air and sea surface temperatures and low and high tide levels in the study region, were obtained. There were 3-4 peaks in spawning (characterised by an abrupt decline in weight) and settlement activity annually. These peaks varied in exact timing, intensity and duration between sites and over time. However, at a site, spawning was followed by settlement 4-8 weeks later, and there was a significant (P < 0.05) direct correlation between spawning intensity prior to the appearance of a new cohort and the cohort density (settlement intensity). The stochastic spatial and temporal variation in breeding activity was superimposed on a more general pattern of a higher intensity of spawning and settlement in Algoa Bay than on the open coast, and a higher settlement intensity on coastal sandstone shores than on dune rock shores. Spawning was more frequent in winter and spring, and the probability of spawning and settlement peaked around the spring and autumn equinox, if temperature and wind conditions were suitable. Larval behaviour had little effect on their dispersal in the well-mixed nearshore region. Larvae were passively dispersed by currents, and their dispersal range and direction depended on prevailing winds and local topography. The sharp decline in density of recruit and adult M. galloprovincialis with increasing distance from the point of introduction, showed that some larvae were carried by wind generated currents over moderately long distances (-100 km). However, since most (76 %) M. galloprovincialis recruited within 4 km of the parent population, it is possible that larvae become trapped in small gullies and crevices around rocky shores, and have a limited dispersal range. This could explain the link between local patterns of spawning and settlement. The distribution and abundance of settlers on the shore was influenced by larval behaviour and the availability of settlement, substrata. Larvae preferred to settle primarily on foliose coralline algae and migrate to the adult mussel bed when they were larger (0.60-7 mm), but larvae also settled directly on adult mussels, possibly because the amount of coralline algae was limited. Both direct and secondary settlement were considered to be important in maintaining mussel populations since the rate of settlement was low(generally < 60 000.m-2). Cohort analyses showed that prior to maturity post-settlement growth (- 30 mm in 10 months) and mortality rates (60-100%) were high, but varied. When settlement intensity was low this variability uncoupled the relationship between spawning and recruitment intensity. Multiple regression analysis showed that together reproductive effort (gamete output), settlement intensity, growth and mortality prior to maturity, accounted for 76 % of the variance in recruitment into mature adult populations. The low settlement rate coupled with the short life span of mussels « 3 years), meant that populations underwent marked spatial and temporal variations in structure and abundance as settlement intensity varied, but there were consistent general differences between mussel populations on dune rock and sandstone shores in Algoa Bay and on the open coast. It was concluded from these results that, spawning intensity and post-settlement growth and mortality, rather than dispersal, regulated recruitment and the structure and abundance of intertidal P. perna and C. meridionalis populations along the south coast of southern Africa. On the basis of these results it is recommended that species with limited dispersal, variable recruitment and high natural mortality, such as P. perna, should be conserved by protecting a small part of the population in reserves, and controlling utilisation outside reserves to minimize disturbance to local brood stocks. Furthermore, since the potential for reseeding adjacent exploited areas is limited, several small reserves placed at regular intervals along the coast would be more effective than a single large reserve.

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.

Thesis (MScConEcol)--UnStellenbosch University, 2011. / ENGLISH ABSTRACT: The privilege of utilising resources from the globe's marine ecosystems is threatened. Adequate regional and global conservation efforts are vital. Understanding species' distributions and the environmental variables influencing community structures are important for instigating optimum conservation plans. A major threat facing marine ecosystems is the introduction and proliferation of alien invasive species. The distribution and geographical expansion of marine alien invasive species, along with environmental variables driving their increase is also critical for drawing up conservation plans. In response to this point, this study addresses gaps in our knowledge regarding intertidal marine invertebrate species distributions particularly that of marine alien species in the Kogelberg Biosphere Reserve (KBR) and adjacent Betty's Bay Marine Protected Area (MPA) in the Western Cape of South Africa, a prime area for south-coast marine conservation. Species identifications were done in September 2010. Two marine alien invertebrate species were identified along the coastline. These were the invasive mytilid Mediterranean mussel Mytilus galloprovincialis and the bryozoan Watersipora subtorquata. A quantitative systematic survey of the intertidal region, consisting of seven rocky shore sites was then undertaken from October 2010 to December 2010. The abundance of all focal marine invertebrate species, within six selected habitat types was assessed. Environmental variables were also recorded. Statistical tests were done to investigate for significant interaction in mean abundance and mean species richness among intertidal zones and protection status (MPA and non-MPA), and among intertidal sampling units (SU‟s) and protection status. There was also investigated for significant difference in mean abundance and mean species richness across intertidal zones and habitat types where protection status was not taken into account, and to test for significant differences in mean abundance and mean species richness between the intertidal zones and habitat types. Correspondence analyses were used to illustrate relationships between species composition and the defined environmental variables. Tests were done to investigate for significant differences in mean abundance of the identified marine alien species between the MPA and non-MPA, study sites, SU's, and wave exposures. These results indicated that vertical and horizontal stress gradients along the shore mainly influence abundance and species richness. The significantly higher abundance of M. galloprovincialis outside the MPA is due to its preference for wave-exposed areas. The reason for the difference in the total abundance of W. subtorquata in the different habitats is not clear, although it appears that the higher abundance of this species in the MPA is because the sheltered nature of the MPA. M. galloprovincilais displaces indigenous species. W. subtorquata does not cause any significant harm along the coast of South Africa. This study indicates that the abundance of M. galloprovincialis and W. subtorquata in the MPA is relatively low. The MPA is therefore in good condition with regards to intertidal alien species. It is important that the MPA and adjacent KBR's coastline maintain its current pristine status. / AFRIKAANSE OPSOMMING: Die voorreg om mariene hulpbronne te benut, word bedreig. Voldoende nasionale en globale mariene bewaring is krities. 'n Deeglike kennis van spesies verspreiding en omgewingsveranderlikes wat gemeenskapstrukture beïnvloed is noodsaaklik vir optimale bewaringspogings. Mariene indringerspesies en verspreiding van indringerspesies bedreig mariene ekosisteme. Dit is belangrik om basiese kennis in te win oor die geografiese verspreiding van indringerspesies saam met die omgewingsveranderlikes wat hierdie verspreiding beïnvloed. Hierdie studie fokus dus daarop om die kennis met betrekking tot intergety ongewerwelde spesiesverspreiding, veral dié wat uitheems is langs die kus van die Kogelberg Biosfeer Reservaat (KBR) en aangrensende Bettys Baai Mariene Beskermde Gebied (MBG) in die Wes-Kaap in Suid-Afrika uit te brei. Hierdie streek word beskou as gesog vir mariene bewaring in Suid-Afrika. Identifikasie van spesies is in September 2010 gedoen. Twee intergety uitheemse ongewerwelde spesies is langs die kus geïdentifiseer; die indringer 'mytilid' Mediterreense mossel - Mytilus galloprovincialis en die 'bryozoa' Watersipora subtorquata. 'n Kwantitatiewe sistematiese oorsig van die intergety rotsagtige streek, bestaande uit sewe lokaliteite, is gedoen. Steekproefneming is vanaf Oktober 2010 tot Desember 2010 uitgevoer. Alle fokale intergety ongewerwelde spesies, in ses geselekteerde habitattipes is getel. Omgewingsveranderlikes is aangeteken. Daar is statisties getoets vir verskille in die talrykheid en spesiesrykheid tussen die intergety zones en beskermingsstatus (MBG en nie-MBG), en tussen die intergety habitattipes en beskermingsstatus. Daar is ook getoets vir verskille in talrykheid en spesiesrykheid tussen die intergety zones en habitattipes waar beskermingsstatus nie in ag geneem is nie. Ooreenstemmende analises is gedoen om die verhoudings tussen die spesiesamestelling en die gedefinieerde omgewingsveranderlikes te illustreer. Daar is statisties getoets vir verskille in die talrykheid van die geïdentifiseerde uitheemse spesies tussen die MBG en nie-MBG, die verskillende lokaliteite, die verskillende habitattipes en tussen die verskillende golf blootstellings. Hierdie studie dui aan dat vertikale en horisontale stresgradiënte die hoofoorsaak is wat talrykheid en spesiesrykheid beïnvloed. Die aansienlik hoër talrykheid van M. galloprovincialis buite die MBG is van die gebied se hoër golfblootstelling. Die beduidende verskil in talrykheid van W. subtorquata is onduidelik. Dit kan egter afgelei word dat die beskutte aard van die MBG 'n rol speel by die aansienlik hoër talrykheid van hierdie spesie binne die MBG. M. galloprovicialis verplaas inheemse spesies. Geen beskikbare bewys dui daarop dat W. subtorquata enige beduidende skade langs die kus van Suid-Afrika aanrig nie. Die lae talrykheid van beide hierdie spesies binne die MBG dui daarop dat hierdie unieke area steeds in goeie toestand ten opsigte van intergety uitheemse spesies is. Dit is noodsaaklik dat die huidige status van die MBG en aangrensende kuslyn gehandhaaf word.