This thesis aims to increase our understanding of mechanisms that influence larval dispersal in marine benthic invertebrates, particularly in the absence of strong oceanographic features (e.g. estuarine plumes, upwelling events, or markedly different water masses). Laboratory experiments identified behavioural mechanisms that regulate the vertical distribution of larvae in response to thermal stratification, and field studies in St. George’s Bay, Nova Scotia (NS), Canada, examined the relationship between larval abundance and physical variables (temperature, salinity, fluorescence, etc) and identified mechanisms that regulate larval distributions in situ. In the laboratory, I demonstrated that thermal stratification affects the vertical distribution of larvae by acting as a barrier to migration, or through temperature-dependent vertical swimming velocities. I also developed a random walk based model which highlighted that the key to successfully simulating larval response to temperature was 1) determining the temperature-dependent distribution of vertical swimming velocities and 2) the temporal autocorrelation in these velocities. In the field, the most striking pattern was that the larval distributions for species with similar swimming abilities were significantly correlated to one another at all scales (0.5 to 40 km). This suggests a common mechanism, related to larval swimming ability, which greatly influences the horizontal larval distribution. I found that the spatial scale of variability in larval distributions (~ 3 km) matches that in both the environmental variables and of coherent structures in current velocities (i.e. the tidal excursion). Results from an aggregation-diffusion model suggest that horizontal larval swimming could not be responsible for the observed level of aggregation in the larval horizontal distributions. I suggest that these horizontal patterns are the result of 1) an aggregative process (i.e. larvae swimming against a vertical current and maintaining their vertical position) and 2) a diffusive process which scales the aggregations to the scale of the coherent structures in current velocity (i.e. tidal excursion). In conclusion, this thesis increases our understanding of larval behaviour and its effects on larval dispersal. The results will be particularly useful to those who are interested in mechanisms regulate population connectivity, particularly those using bio-physical models to model dispersal trajectories.

Large marine vertebrate species can exhibit vast movements, both horizontally and vertically, which challenges our ability to observe their behaviours at extended time-scales. There is a growing need to understand the intra- and inter-annual movements of mobile marine species of conservation concern in order to develop effective management strategies. The basking shark (Cetorhinus maximus) is the world's second largest fish species, however, a comprehensive understanding of this species’ ecology, biology and spatial behaviour in the north-east Atlantic is currently lacking. This thesis seeks to investigate the movement ecology of basking sharks using a suite of technologies to integrate biologging, biotelemetry, remotely sensed data, and ecological modelling techniques. I use satellite telemetry data from basking sharks tracked in 2012, 2013 and 2014 to quantify movements in coastal waters off the west coast of Scotland within the Sea of the Hebrides proposed MPA. Sharks exhibited seasonal residency to the proposed MPA, with three long-term tracked basking sharks demonstrating inter-annual site fidelity, returning to the same coastal waters in the year following tag deployment (Chapter 2). I reveal that sharks tracked into winter months exhibit one of three migration strategies spanning nine geo-political zones and the High Seas, demonstrating the need for multi-national cooperation in the management of this species across its range (Chapter 3). I examine the vertical space-use of basking sharks to improve an understanding of the processes that influence movements in all dimensions. Basking sharks exhibit seasonality in depth-use, conduct deep dives to over 1000 m, and alter their depth-use behaviour in order to remain within thermal niche of between 8 and 16 oC (Chapter 4). Finally, I combine contemporaneous data recorded by deployed satellite tags with remotely sensed environmental data to employ novel ecological modelling techniques to predict suitable habitat for basking sharks throughout the Atlantic Ocean (Chapter 5).

O presente estudo foi realizado ao longo de uma linha de costa, incluindo duas enseadas em Ubatuba-SP, Brasil. Os objetivos principais foram: (1) Examinar, em seis costões rochosos, séries temporais de assentamento larval de decápodos, afim de entender forçantes físicas associadas ao transporte em direção à costa, (2) Localizar agregações larvais no plâncton neustônico costeiro, para inferir a natureza das agregações e verificar a ocorrência de migração vertical em decápodos, (3) testar a relação entre suprimento e assentamento larval, a diferentes escalas espaciais. O papel da competência larval foi discutido à luz de evidências obtidas através amostragem planctônica em diferentes áreas dentro das enseadas e comparações inter e intra-taxonômicas. Entre maio e agosto de 2005, foram realizadas coletas, a cada dois dias, para estimar a taxa de assentamento larval de grupos de decápodes em coletores artificiais. Durante dois períodos de maior assentamento de Pachygrapsus transversus, a ocorrência nictemeral neustônica, desta e de outras espécies de decápodes foi avaliada. Sub-amostras de megalopas de brachyura foram separadas para mensuração do nível de competência larval, através do cultivo de larvas, obtendo estimativas do tempo decorrido até a muda, e através do estágio de muda de indivíduos previamente fixados. Modelos Log-lineares foram utilizados para testar o efeito do vento e da maré na taxa de assentamento, e os resultados foram confrontados com cenários de correntes superficiais fornecidos pelo modelo hidrodinâmico de circulação. Amostras planctônicas revelaram que agregações larvais são coincidentes com zonas de convergência, provavelmente causadas pela formação de ondas internas. Um conjunto de espécies de camarão sofre migração vertical típica, enquanto um padrão de migração reversa foi encontrado para grapsídeos, ix o que pode auxiliar no transporte em direção à costa para as áreas de assentamento devido a brisas marinhas. Portunídeos não apresentaram tendência de migração vertical. A competência parece ser melhor estimada através do método de cultivo. Em áreas dentro das enseadas, megalopas de portunídeos parecem ser mais competentes ao assentamento que as de grapsídeos, provavelmente por estarem mais próximas aos locais de assentamento. Megalopas neustônicas de P. transversus coletadas dentro das enseadas são menos competentes que as obtidas em coletores artificiais. O estágio transicional não foi capturado, sugerindo que a transição para o bentos e o desenvolvimento até estágios competentes são mais complexos do que normalmente assumido. Não foi encontrada correlação significativa entre o suprimento de megalopas e a taxa de assentamento. A taxa de assentamento de decápodes, que habitam a região entre-marés de costões rochosos, é aparentemente dependente da interação das forçantes de vento, maré e comportamento larval. As taxas de assentamento de grapsídeos e palemonídeos seguem o ritmo semi-lunar, com ocorrência máxima próximo às marés de quadratura, corroborando a hipótese de que ondas internas geradas pela maré são também responsáveis pelo transporte de decápodos costeiros. Ventos em direção à costa foram identificados como agentes chave, apesar de dependentes do regime de marés, enquanto que ventos de nordeste provavelmente trazem larvas de locais de produção. Padrões de circulação costeira e contrastes de assentamento consistentes espacialmente indicam que a Enseada do Flamengo é uma importante área de deposição de larvas. / The present study was carried out along a coastline including two bays in Ubatuba, SP, Brazil. The main objectives were (1) examine, at six different rocky shores, the time series of decapod larval settlement in order to understand the physical forcing associated to onshore transport, (2) locate neustonic plankton larval aggregations over the diel cycle to infer on the nature of patchiness and to verify the occurrence of vertical migration in the decapod species examined, and (3) test the relationship between larval supply and settlement, at different spatial scales. The role of larval competency was discussed based on evidence obtained by sampling the plankton at distinct within-bay areas and comparing the results both within and between taxa. From May to August 2005, samples were carried out every other day to estimate the larval settlement rate of two different decapod assemblages in artificial collectors. During two settlement pulses recorded for the megalopae of Pachygrapsus transversus, the nycthemeral neustonic occurrence of that and other decapod stages was assessed. Subsamples of brachyuran megalopae were separated to measure their competency level, by means of both larval rearing, thus obtaining time-to-moult estimates, and microscopic moult-staging of readily fixed individuals. Log-linear models were used to test the effect of wind and tide range on settlement rate, and results were confronted to possible scenarios of surface currents provided by hydrodynamic numerical modeling. Planktonic samples revealed that patches of larvae are coincident to slick fringes, probably caused by the formation of internal waves. A suite of shrimp species undertakes a typical diel vertical migration, while a reversed pattern was found for grapsids, which may assist the final onshore transport to settlement grounds due to marine breezes. Swimming crabs did not show any vertical xi migration trend. Competency is suggested to be better estimated using the larval rearing method. In within-bay areas, portunid megalopae appeared to be more competent to settle than those of grapsids, probably because the former are closer to settlement substrates than the latter, which should be first advected to the nearshore. Within-taxon comparisons revealed that neustonic megalopae of P. transversus collected in within-bay areas are less competent than those obtained from benthic collectors. A transitional stage was missing, suggesting that the transition to the benthos and the development into competent stages are more complex than usually assumed. Significant correlations between megalopae supply and settlement rate were not found. The settlement rate of decapods inhabiting the intertidal region of the rocky coast sampled is apparently dependent on the interaction of wind and tide forcing coupled with larval behaviour. Settlement rate of both grapsids and palaemonids follows a semilunar rhythm, with maxima occurring near neap tides, corroborating the hypothesis that tidally-driven internal motions are also responsible for onshore larval transport coastal decapods. Onshore wind-forcing was found to be the key agent, although dependent on the tide regime, while winds blowing from northeast are suggested to bring larvae from source sites. Coastal circulation patterns and spatially-consistent settlement contrasts indicate that Flamengo Bay is an important area of larval deposition.

Maurolicus é um gênero representado por peixes mesopelágicos, com elevada biomassa na Zona Econômica Exclusiva sudeste sul brasileira. O material deste estudo provém de arrastos com rede de meia água efetuados com o N/Oc. Atlântico Sul, entre as isóbatas de 100 e 1500 m e entre as latitudes 22° e 35° S, realizados no inverno de 1996; outono de 1997 e primavera de 1997. A análise das características merísticas e morfológicas de 120 exemplares, coletados em 4 pontos distintos, indicou que na região ocorre M. stehmanni Parin & Kobyliansky, 1993. Através da análise da distribuição vertical e horizontal das capturas, verificou-se que a espécie está associada à região de quebra de plataforma continental, permanecendo em profundidades maiores que 200 metros durante o dia, migrando para camadas superiores a noite, com a diminuição da intensidade luminosa. Pela distribuição de freqüência de comprimento e proporção entre jovens e adultos constatou-se que ocorreu recrutamento em todos os períodos estudados. A partir da análise da proporção entre peixes jovens e adultos por comprimento estimou-se o L50médio em 32 mm. As análises da relação gonadossomática, da freqüência dos estádios de maturidade gonadal e do ∆K (diferença entre o fator de condição total e somático) indicaram que a espécie apresentou atividade reprodutiva em todas as áreas e épocas analisadas. A relação entre o raio do otólito e o tamanho dos indivíduos é linear, porém não foi possível identificar a periodicidade de formação dos anéis, impossibilitando estimativas adequadas dos parâmetros de crescimento. Aplicando-se a rotina ELEFAN I, do pacote computacional FISAT, aos dados de freqüência de comprimento foi estimado o L∞ em 53 mm e k em 0,9 ano-1, indicando que a espécie atinge o tamanho médio da 1 a maturação gonadal em torno do 1º ano de vida. / Maurolicus is a genus of mesopelagic fish very abundant in the south-eastern and south Brazilian Economic Exclusive Zone. The material of this study was sampled by mid water trawl during cruises of R/V Atlântico Sul in winter of 1996, autumn of 1997 and spring of 1997, between 100 and 1500 meters depth, from latitudes of 22° to 35° S. The meristic and morphological analysis of 120 specimens collected in 4 distinctive points, has indicated the occurrence of M. stehmanni Parin & Kobyliansky, 1993 in the area. Through the vertical and horizontal distribution of the catches it was verified that this species is associated with the shelf break, staying in depths higher than 200 m during the day, migrating to lower depths at night as the luminous intensity falls. The length frequency and the proportion between youngs and adults showed that the recruitment occured during the periods surveyed. By means of young-adult proportion by length a value of L50 about 32 mm was estimated. The study of gonadossomatic relationship, gonadal maturity frequency and ∆K (difference between total and somatic condition factor) indicated that M. stehmanni presented reproductive activity in the area during all the sampled seasons. There is a linear relationship between the standard length and the otolith radius, however the periodicity of the zone formation was not identified, which did not permit appropriate estimates of the growth parameters. The L∞ of 53 mm and k of 0,9 year–1 were estimated using ELEFAN I routine (FISAT) based on length frequency data, indicating that M. stehmanni attains maturity around its first year of life.

Maurolicus é um gênero representado por peixes mesopelágicos, com elevada biomassa na Zona Econômica Exclusiva sudeste sul brasileira. O material deste estudo provém de arrastos com rede de meia água efetuados com o N/Oc. Atlântico Sul, entre as isóbatas de 100 e 1500 m e entre as latitudes 22° e 35° S, realizados no inverno de 1996; outono de 1997 e primavera de 1997. A análise das características merísticas e morfológicas de 120 exemplares, coletados em 4 pontos distintos, indicou que na região ocorre M. stehmanni Parin & Kobyliansky, 1993. Através da análise da distribuição vertical e horizontal das capturas, verificou-se que a espécie está associada à região de quebra de plataforma continental, permanecendo em profundidades maiores que 200 metros durante o dia, migrando para camadas superiores a noite, com a diminuição da intensidade luminosa. Pela distribuição de freqüência de comprimento e proporção entre jovens e adultos constatou-se que ocorreu recrutamento em todos os períodos estudados. A partir da análise da proporção entre peixes jovens e adultos por comprimento estimou-se o L50médio em 32 mm. As análises da relação gonadossomática, da freqüência dos estádios de maturidade gonadal e do ∆K (diferença entre o fator de condição total e somático) indicaram que a espécie apresentou atividade reprodutiva em todas as áreas e épocas analisadas. A relação entre o raio do otólito e o tamanho dos indivíduos é linear, porém não foi possível identificar a periodicidade de formação dos anéis, impossibilitando estimativas adequadas dos parâmetros de crescimento. Aplicando-se a rotina ELEFAN I, do pacote computacional FISAT, aos dados de freqüência de comprimento foi estimado o L∞ em 53 mm e k em 0,9 ano-1, indicando que a espécie atinge o tamanho médio da 1 a maturação gonadal em torno do 1º ano de vida. / Maurolicus is a genus of mesopelagic fish very abundant in the south-eastern and south Brazilian Economic Exclusive Zone. The material of this study was sampled by mid water trawl during cruises of R/V Atlântico Sul in winter of 1996, autumn of 1997 and spring of 1997, between 100 and 1500 meters depth, from latitudes of 22° to 35° S. The meristic and morphological analysis of 120 specimens collected in 4 distinctive points, has indicated the occurrence of M. stehmanni Parin & Kobyliansky, 1993 in the area. Through the vertical and horizontal distribution of the catches it was verified that this species is associated with the shelf break, staying in depths higher than 200 m during the day, migrating to lower depths at night as the luminous intensity falls. The length frequency and the proportion between youngs and adults showed that the recruitment occured during the periods surveyed. By means of young-adult proportion by length a value of L50 about 32 mm was estimated. The study of gonadossomatic relationship, gonadal maturity frequency and ∆K (difference between total and somatic condition factor) indicated that M. stehmanni presented reproductive activity in the area during all the sampled seasons. There is a linear relationship between the standard length and the otolith radius, however the periodicity of the zone formation was not identified, which did not permit appropriate estimates of the growth parameters. The L∞ of 53 mm and k of 0,9 year–1 were estimated using ELEFAN I routine (FISAT) based on length frequency data, indicating that M. stehmanni attains maturity around its first year of life.

Processes during the meroplanktonic phase regulate population dynamics for many marine benthic invertebrates. I examined changes in vertical distribution of different meroplanktonic larvae in a coastal embayment during a stable period, at high temporal frequencies and spatial resolutions. Plankton samples were collected at 6 depths (3, 6, 9, 12, 18, 24 m) using a pump, every 2-h over a 36- and a 25-h period, during a spring and neap tide, respectively, concurrently with measures of temperature, salinity, fluorescence and current velocity. For 10 gastropod taxa, larval vertical distribution was mostly related to the thermal structure of the water column. Each of 7 taxonomic groups was found either exclusively near the surface, associated with the fluorescence maximum, or showed diel changes in distribution. These larvae that occupy different depths in the water column exhibit different dispersal potentials. / Biogeographical data contained in this thesis will be submitted to the Oceanographic Biogeographic Information System (OBIS) and may be accessed on-line at http://www.iobis.org