Browsing by Author "Hawkins, Stephen J."
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- Conectividade em populações de lapas nas ilhas da Macaronésia (Atlântico-NE): uma abordagem multidisciplinarPublication . Faria, João; Ribeiro, Pedro; Hawkins, Stephen J.; Neto, Ana I.De uma forma geral, é consensual que a sobre-exploração de um dado recurso natural exerce um impacto profundo na respectiva comunidade, sobretudo quando se trata de uma espécie chave para o ecossistema. Por exemplo, as lapas que têm tradicionalmente sido exploradas para consumo humano em todos os arquipélagos da Macaronésia e, particularmente nos Açores, viram o seu efectivo populacional reduzido nas últimas décadas na grande maioria das ilhas. Alguns trabalhos recentes sugerem que a legislação existente para a sua captura tem sido ineficaz na protecção das suas populações, com óbvias implicações para a sustentabilidade das comunidades costeiras das quais fazem parte. Para fins de conservação é necessário determinar o grau de conectividade existente entre populações de lapas distribuídas ao longo de um sistema dispersivo como seja a regi.o da Macaronésia. Neste sentido, torna-se fundamental o estudo da variabilidade genética, conectividade, e resiliência das populações de lapas na Macaronésia, com especial ênfase para o arquipélago dos Açores. A conjugação de dados genéticos, biológicos, ecológicos e oceanográficos poderá contribuir de forma significativa para compreender a dinâmica populacional destes organismos, permitindo testar hipóteses relativas aos padrões de dispersão larvar, recrutamento, conectividade entre populações, diversidade genética e equilíbrio populacional. Esta abordagem multidisciplinar permitirá gerar informação teórico-prática relevante que pode ser utilizada para desenvolver estratégias de conservação capazes de promover a exploração sustentável de lapas na região da Macaronésia, em particular no arquipélago dos Açores.
- Conservation of limpet populations: a heavily exploited resource in Azores, NE-AtlanticPublication . Faria, João; Ribeiro, Pedro; Martins, Gustavo M.; Rivas, Manuel; Hawkins, Stephen J.; Presa, Pablo; Neto, Ana I.Limpet harvesting in Azores (NE Atlantic) has been taking place probably since the islands were first colonized in the XV century. Limpet species are highly exploited and populations from most islands have declined steadily bringing about catastrophic effects on coastal communities. Despite their economic importance limpets are also ecologically key species and require prioritizing conservation strategies. Patellid limpets are broadcast spawners which go through a planktonic larval stage in their life cycle. They are benthic as adults and the larva is the only phase during their life-cycle which has the ability to disperse over assumed large spatial distances. However, there is now mounting evidence that gene flow between islands and mainlands can be low, even for species with a relatively long planktonic larval stage. Low levels of larval exchange may thus limit the success of conservation objectives expected upon migration and recruitment. In dispersive isolated oceanic islands such as the Macaronesian Islands, the Azores Archipelago in particular, is not clear whether limpet populations from different islands form a single meta-population or, in contrast, populations on each island are isolated from the rest. Knowledge on this scenario is crucial for the management and conservation of exploited populations of limpets. Here we have developed and described species-specific multiplexed microsatellite markers for the limpets Patella candei and Patella aspera using whole genome shotgun 454 sequencing. These genetic tools have allowed the study of the population genetic structure and evolutionary history of patellid species in the archipelago of Azores. Genetic studies, alongside with biological, ecological and oceanographic information, represent an important contribution for the understanding of population dynamics by allowing testing hypothesis about larval dispersal patterns, recruitment and life history traits, population connectivity, genetic diversity, and population equilibrium.
- Diel fluctuations of a sandy beach fish assemblage at Porto Pim, Faial Island, AzoresPublication . Nash, Richard D.; Santos, Ricardo S.; Hawkins, Stephen J.Os peixes da praia de areia de Porto Pim, Açores foram amostrados através de arrastos de rede (chinchorro) a intervalos de três horas durante um período de 24 horas nos meses de Agosto, Setembro e Outubro de 1989. A associação de peixes era dominada, em cada um dos meses, por três a quatro espécies (90-97% dos indivíduos). A maioria das espécies estavam representadas por formas juvenis. A variação entre meses do padrão diário pode explicar-se primariamente pelas mudanças no padrão de abundância das espécies dominantes. Ao longo dos três meses as variações na estrutura da associação implicaram mudanças no padrão diário. Muitas das espécies tinham um padrão de abundância definido, primariamente por ser ou diurno ou nocturno. Encontrou-se também um padrão de maré na estrutura da associação de peixes caracterizado por uma maior diversidade na maré baixa.
- Enhancing stocks of the exploited limpet Patella candei d'Orbigny via modifications in coastal engineeringPublication . Martins, Gustavo M.; Thompson, Richard C.; Neto, Ana I.; Hawkins, Stephen J.; Jenkins, Stuart R.It is widely recognised that microhabitats are important for a variety of marine organisms, yet this knowledge has rarely been applied in the construction of engineered structures as a means of enhancing biodiversity or populations of species at risk. Here we examined the influence of microhabitats on the distribution and survival of the exploited limpet Patella candei on natural shores before determining the effect of introducing such habitats to an artificial seawall. On natural shores individuals were associated with pits (a natural feature of volcanic rocky shores). Animals inhabiting pits showed reduced mortality and were smaller than those on open rock. Microhabitat utilisation was similar over the vertical range of distribution of P. candei. Following observation of natural patterns, we applied this knowledge by experimentally drilling pits at varying densities and sizes in a seawall that had been constructed with simple topographical complexity. Overall, the number of animals increased in areas with experimentally increased microhabitat area. There was evidence that this was the result of immigration (larger animals) but also of increased recruitment. This study demonstrates one cost-effective way of conciliating the need to protect our coastlines while promoting the conservation and stock enhancement of over-exploited species.
- Evidence of long-term changes in the distribution of key intertidal speciesPublication . Vale, Maria; Neto, Ana I.; Martins, Gustavo M.; Hawkins, Stephen J.Globally, changes are occurring in the biogeochemistry and ecology of the oceans, which may influence the physiology, phenology, and species distribution. Biological communities are reacting to climate change through changes in the abundance and phenology of the organisms and through the poleward shift in species distribution. Rocky shores are relatively simple ecosystems, which makes them an excellent model system for the understanding of the consequences of climate change. This study aims to examine the evidence of long-term changes on the distribution of key intertidal species in the Azores. Grey literature and unpublished data collected in the late 1980’s by Stephen J. Hawkins and his colleagues in the island of São Miguel (Azores) was compared to data collected in 2012. Whilst most taxa sampled in 1988 were still present during 2012, there were changes in species distribution. In general, there was an overall decrease in the abundance of organisms that was more pronounced on the sheltered area. In addition, there was generally a shift upwards of the vertical distribution of taxa that was more pronounced on the exposed area. These changes are temptatively interpreted as a consequence of increased temperatures and wave action (both predicted by climate change scenarios). This study also suggests that there may be interactive effects between environmental processes affecting species distributions. In addition, there was evidence that processes operating at large temporal scales may indirectly influence the distribution of species via changes in the abundance of their competitors.
- Expedition Azores 1989 : Ecology and taxonomy of the fauna and flora of the marine littoral. An introductionPublication . Martins, Helen R.; Santos, Ricardo S.; Hawkins, Stephen J.; Nash, Richard D.No Verão de 1989, o Departamento de Oceanografia e Pescas da Universidade dos Açores, Horta, e o Port Erin Marine Laboratory, University of Liverpool, Isle of Man, levaram a cabo um programa de investigação (Expedição Açores 1989) tendo em vista estudar a fauna e flora do litoral marinho das ilhas do Faial e Pico, no arquipélago dos Açores. A reserva marinha natural do Monte da Guia foi estudada com particular detalhe. Neste local, foram efectuados 10 perfis com o objectivo de descrever as comunidades botânicas e faunísticas e organizar com espécimens recolhidos, colecções de referência. Com base nestes trabalhos foram até à data publicados 5 artigos, 6 novos artigos são incluídos neste número da revista Arquipélago. Outros artigos serão publicados em volumes posteriores e noutras revistas científicas.
- Exploitation of intertidal grazers as a driver of community divergencePublication . Martins, Gustavo M.; Thompson, Richard C.; Neto, Ana I.; Hawkins, Stephen J.; Jenkins, Stuart R.1. The possibility that different assemblages of species may represent alternative stable states has been the subject of much theoretical and empirical work. Alternative stable states may in theory arise froma perturbation of sufficient magnitude that pushes an assemblage from one stable equilibrium point to another. Overfishing is one such disturbance that can lead to cascading community level effects. Yet, whether these different assemblages represent alternative stable states or are the consequence of chronic disturbance from fishing is still a matter of debate. Understanding the mechanisms that drive community stability is fundamental if we are to assess the consequences of anthropogenic impacts on the structure and function of ecosystems to better inform management of disturbed habitats. 2. To investigate the extent to which present-day community state is stable versus being maintained by chronic exploitation, we manipulated the time and intensity of physical disturbance and grazing by limpets in a system where over-harvesting of limpets has led to a regional-scale shift in community structure to one in which algal turfs have replaced barnacles as the primary space occupier in the mid-intertidal. 3. After a 1-year period since disturbance was applied, assemblages in disturbed areas were significantly different from undisturbed areas, but the timing of disturbance and its intensity had little effect on the outcome of succession. Undisturbed areas were highly resistant to new colonization and persisted unchanged throughout the study period. 4. Manipulation of limpet abundance in disturbed patches showed that, where present, limpets successfully prevented the recolonization of space by algal turfs. Moreover, there was evidence that grazing by limpets at the turf ⁄open-rock boundary effectively pushed the turfs back, extending the area of open-rock. 5. Synthesis and applications. Our findings provide evidence that in this system the dominance by algal turfs does not represent an alternative stable state but that chronic exploitation of limpets leads to the persistence of this community. Conservation strategies aimed at protecting or enhancing limpet abundances (e.g. no-take marine reserves) should allow the gradual restoration of this community to its pre-disturbed state.
- Exploitation of keystone species: population and community-level effectsPublication . Martins, Gustavo M.; Thompson, Richard C.; Hawkins, Stephen J.; Neto, Ana I.; Jenkins, Stuart R.
- The exploitation of patellid limpets in the Azores.Publication . Martins, Gustavo M.; Jenkins, Stuart R.; Hawkins, Stephen J.; Neto, Ana I.; Thompson, Richard C.
- Exploitation of rocky intertidal grazers : population status and potential impacts on community structure and functioningPublication . Martins, Gustavo M.; Jenkins, Stuart R.; Hawkins, Stephen J.; Neto, Ana I.; Thompson, Richard C.A wide range of anthropogenic activities are impacting the ecology of coastal areas. Exploitation of marine resources is one such activity, which, through cascading trophic effects, can have influences well beyond that of the target species. We investigated the mid-rocky-shore community structure of the Azores archipelago, a seldom-studied habitat, where there is a local tradition of exploiting limpets, the main intertidal grazers. The limpet population structure differed among islands, and there was an inverse relationship between the abundance of larger limpets and the human population per coastal perimeter, but not the associated catch data. At small scales of resolution (quadrats), there was a negative relationship between the cover of algae and limpets and a positive relationship between barnacles and limpets. These relationships were also apparent at the larger scale of islands as a function of the gradient of exploitation. Our results show how natural habitat fragmentation may be useful where the experimental testing of a hypothesis is not possible, and provide evidence for the trophic cascading effects of limpet exploitation at landscape scales.