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The distribution of Nassarius reticulatus around Anglesey (North Wales, UK) revealed well established populations along the west coast, smaller populations along the north coast and a complete absence of this gastropod from the east and south coast. Nassarius reticulatus is well adapted to varying degrees of wave exposure and prefers fine sand sediments, with <0.5% organic and < 2% silt content. New recruits appear in the population at a size of 7-8.9 mm between February and April one year after hatching. Mortality was higher in an intertidal lagoon than in a subtidal beach in Rhosneigr, especially during summer. Whelks from the intertidal lagoon had a higher L,,, and a lower K value than whelks from the subtidal beach in Rhosneigr. Nassarius reticulatus forms taller and thicker shells when inhabiting sheltered areas, which are more resistant to predation pressure. Growth rate increased with increasing seawater temperature. Smaller individuals allocated more energy to growth, while larger whelks invested more energy in reproduction. Shell growth rate was similar between males, females and imposex-affected females. Limitations in food availability suppressed shell growth and reproductive output. Length frequency analysis overestimated the shell growth of N. reticulatus, due to overlapping older size-classes. Estimation of the age and growth of N. reticulalus from statolith growth rings was a more reliable method than length frequency analysis. The first prominent statolith ring is formed during larval settlement and subsequent rings are formed annually. Spawning of N. reticulatus in the laboratory occurred throughout the year, with a peak during July. Breeding size classes of N. reticulatus have a shell length >_ 21 mm. Nassarius reliculatus produced smaller egg capsules containing smaller eggs, which had a shortened embryonic development and produced smaller larvae during the summer. Hatching occurred successfully over a range of seawater temperatures (8.5-20°C), however, larvae only metamorphosed at temperatures > 16.3°C. Lack of a suitable substrate for settlement reduced the growth rate of the larvae and delayed metamorphosis. Imposex examination in sympatric populations of N. reticulatus and Nucella lapillus indicated that both gastropod species were highly affected by TBT pollution in areas adjacent to commercial ports and small marinas.

Patellid limpets are harvested around the world and many stocks are currently overexploited. This study investigated the influence of environment and harvesting upon the biology of target species (Patella spp.) and upon the macro-community structure of non-target species. A broad-scale survey of Patella spp. across the British Isles and Portugal revealed that non-exploited Patella vulgata populations from England had traits indirectly associated with protandry. Females predominated in larger size classes; cumulative frequency distributions of males and females were different; sex ratios were biased towards the first sex and smallest sizes of males were smaller than the smallest sizes of females. In Portugal, P. vulgata populations did not show these patterns, suggesting that protandry was not occurring in those P. vulgata populations, although alternative explanations include the influence of low recruitment leading to fewer small males. In the England Patella depressa appeared to be gonochorist with a sex ratio of 1:1. In Portugal, however, P. depressa also showed some patterns indicating the possibility of slight protandry. In a manipulative experiment to simulate size-selective harvesting of limpets by humans, changes in sex ratio of P. vulgata in the south-west of England were monitored over an 18-month period of repeated removal of bigger limpets. There was strong evidence that the size at sex change decreased in response to the exploitation treatment, emphasizing its plasticity. Sex change occurred at a bigger size than expected from the overlap in male and female size classes. The limpet exploitation led to establishment of Fucus spp. At the end of the experiment, control plots had lower percentage cover of Fucus spp. than both low- and high-exploitation plots. Univariate and multivariate analyses confirmed that the communities on the two shores responded differently to the same source of disturbance. A comparative survey of populations across a gradient of exploitation in the Canary Islands indicated that the abundance of Patella aspera decreased from 1992 to 1999, while for Patella candei crenata no differences were detected, suggesting that P. aspera was under a higher harvest pressure during that period. The observed differences in catches between islands in 1999 indicated that overexploitation of limpet stocks at that time was not yet evident. The results of the field surveys and the manipulative experiment are discussed with respect to the role of ecological experimentation and aquaculture in resource management, and suggestions are made for key issues in future research and conservation.

Dispersal and connectivity of patellid limpets (Patella spp.) in the eastern North Atlantic have been examined by addressing reproductive biology, larval development, population genetics and physical modelling of dispersal. The reproductive cycles of four limpet species were assessed on the northern and central Portugese coast, to determine spawning periods. This information was incorporated into dispersal models. The results showed that P. depressa and P. ulyssiponensis have almost year-round breeding, with a brief resting phase in the early summer. Conversely, the two other species displayed much shorter spawning periods, with gamete release taking place between December and March in P. vulgata and between September and December in P. rustica. The relationship between temperature and planktonic periods in P. depressa, P. ulyssiponensis, and P. vulgata was investigated with laboratory rearing experiments. Average duration of precompetent periods varied inversely with temperature, ranging between 3.7-14.0 days in P. depressa, 2.8-13.7 days in P. ulyssiponensis and 5.7-14.6 days in P. vulgata, whilst delay periods ranged between 15.8-25.4 days in P. depressa, 14.5-27 days in P. ulyssiponensis and 16.5-25 days in P. vulgata. Population genetic structure was examined on a range-wide scale in P. depressa and along the Iberian coast in P. rustica using microsatellite markers, plus one mtDNA locus in P. rustica. Results suggested high levels of gene flow throughout the study area and widespread lack of population differentiation in both species. A biophysical model of dispersal has been developed to assess the degree of demographic connectivity over ecological and evolutionary time frames, and to identify possible barriers to dispersal for P. depressa and P. rustica. The model predicted high levels of connectivity through most of the study area in both species, but in P. depressa simulations identified two large extensions of adult habitat discontinuity as barriers to larval dispersal. The model also showed that despite the potential for long-distance dispersal, most of the larvae released at one given location settle within much shorter distances. These results illustrate the need to view the study of marine dispersal as a multidisciplinary task, and suggest that relying on just one line of evidence may produce misleading results.

Le développement de l’halioticulture est récent et a été très rapide au niveau mondial. Il s’explique par une demande supérieure à l’offre et par un épuisement des stocks dans le milieu naturel. Pour soutenir leur développement, la plupart des filières de production halioticole ont récemment mis en place des programmes de sélection génétique. En France, la filière ormeaux peine à se développer. Cette thèse CIFRE, cofinancée par France Haliotis, seule écloserie d’ormeau en France, a donc été initiée afin de définir les bases d’un programme de sélection pour améliorer la rentabilité de son élevage. La thèse s’est déroulée en deux étapes : l’étude des effets du processus de domestication observés sur les ormeaux issus de cette écloserie, et l’estimation de paramètres génétiques dans son système de production. Deux expérimentations comparant une population sauvage et une population d’élevage ont permis de montrer que les ormeaux produits sur l’élevage jusqu’en 2013 présentaient des performances égales à celles des ormeaux sauvages. A l’âge adulte, les ormeaux d’élevage ont néanmoins montré une moins grande sensibilité aux manipulations d’élevage et un comportement d’évitement des prédateurs produit par rapport aux ormeaux sauvages. L’estimation de paramètres génétiques a pu être effectuée grâce à la constitution d’un jeu de 123 marqueurs SNP permettant la reconstruction du pedigree de familles élevées en mélange pendant 4 ans. L’estimation de l’héritabilité de différents caractères associés à la croissance montre que des progrès importants pourraient être obtenus par sélection sur le poids à 42 mois. En revanche, les caractères comportementaux et physiologiques étudiés dans cette thèse n’apparaissent pas ou peu héritable. Un programme de sélection adapté au système de France Haliotis a donc été proposé pour améliorer le poids des animaux à 4 ans. L’analyse des corrélations génétiques suggère qu’une sélection multicritères pour améliorer conjointement la croissance, le taux de chair et contrôler l’évolution du développement gonadique, pourrait également être envisagée. / In the context of an increasing demand and a declining supply from fisheries, worldwide aquaculture production of abalone has greatly increased in the last decades. Selective breeding has been initiated to improve growth in major abalone species. In France, the abalone production was initiated 30 years ago and struggles to develop. This CIFRE PhD co-financed by France Haliotis, the only French hatchery in activity, was initiated to study early domestication process of farmed abalone population and to provide knowledge required to design a selective breeding program adapted to this company. Wild and farmed populations were compared, showing that, until 2013, farmed and wild abalone presented similar performances. However, lower physiological and behavioural responses to farm stressor were observed, as well as less response to predator contact.Estimations of genetic parameters were performed using a novel set of 123 SNP markers in order to successfully assign parentage in a single cohort resulting from the reproduction of 40 broodstock reared under common conditions over 4 years. Heritability estimates were obtained for a large number of production traits, indicating that individual selection of live weight when 42-month-old would lead to significant gains. A selective breeding program suitable for France Haliotis production system has been proposed to improve the weight at 4 years. The analysis of genetic correlations suggest that a multi-criteria and selective breeding program to improve growth, meat yield and to control reproductive allocation could also be established, but would be more complex to implement

Copies of author's previously published articles inserted. / Bibliography: p. 377-400. / xiv, 400, [20] p., [5] leaves of plates : ill. (some col.), maps ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Zoology, 1995