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The tidal flats of the Banc d'Arguin, Mauritania, are covered by vast beds of Zostera noltii. At low tide these seagrass beds appear to be interspersed with partly vegetated, circular pools of 5-25 in diameter. Between February and May 2001 we described these pools and studied their possible origin. Several hypotheses regarding the origin have been developed. The first group of hypotheses assumes that the pools result from erosion activity. Since human disturbance of seagrass beds at the Banc d'Arguin is virtually non-existent, causes should be found in natural bed disturbances and/or tide or wave action. Therefore, small gaps, simulating holes dug by the crab Callinectes marginatus, were made to see if they would further erode by tidal currents or waves. The experiments showed no erosion. Neither we found support for other hypotheses assuming erosion to be the cause of circular pools. The alternative group of hypotheses stated that sedimentation on the flats would be responsible. We conclude that accretion of creek remnants is the most likely process behind the development of the pools; this conclusion is based on both mapping of the pattern of pools, the sediment profile in and around the pools and the distribution of seagrass biomass. Also the disturbance experiments showed bed accretion rather than bed erosion and support this hypothesis. (c) 2005 Elsevier B.V. All rights reserved.

Se confirma la existencia de praderas de Zostera noltii Hor nem. (Zosteraceae) en Lanzarote (Islas Canarias). Se enuncian brevemente las características más importantes de las praderas submarinas y se realizan algunos comentarios fitosociológicos The occurrence of the seagrass Zostera noltii Hornem. (Zosteraceae) in Lanzarote (Canary Islands) is verified. The more signi-ficant characteristics and some phytosociological comments of the sea grass beds are briefly enunciated.

The marine angiosperm Zostera noltii (dwarf eelgrass), an important facilitator species and food source for invertebrates and waterfowl, predominantly inhabits intertidal habitats along eastern Atlantic shores from Mauritania to southern Norway/Kattegat Sea and throughout the Mediterranean, Black and Azov seas. We used 9 microsatellite loci to characterize population structure at a variety of spatial scales among 33 populations from 11 localities throughout the entire biogeographic range. Isolation by distance analysis suggested a panmictic genetic neighborhood of 100 to 150 km. At the global scale, a neighbor-joining tree based on Reynolds distances revealed strongly-supported groups corresponding to northern Europe, Mauritania and the Black/Azov Sea; separate Mediterranean and Atlantic-Iberian groups were poorly supported. Clones (genets with multiple ramets) were present in most populations but were generally small (ca.

Dissertação mest., Biologia Marinha, Universidade do Algarve, 2009 Direct fish herbivory is not a well studied subject in seagrass research. This work tried to focus that problem in transplanted and natural seagrass species in the Luiz Saldanha Marine Park and Sado estuary. The species studied were Cymodocea nodosa, Zostera marina and Zostera noltii and the herbivorous fish Sarpa salpa (salema). In transplanted and natural seagrass the intensity of herbivory was assessed through the analysis of length, percentage of leaves with bite marks and biomass. These variables were analysed for plants with protections against herbivores and plants without protections. The place of the leaf with higher percentage of bite marks was also assessed. Another factor analysed was if the placement of artificial seagrass in the middle of real ones would deter herbivores from feeding on the plants. In the laboratory the food preference of the salemas was tested using the three species used in the study site. The analysis allowed to conclude that the protections against herbivores work since the percentage of leaves with bite marks was lower. However, these protections prevent the normal development of seagrass because they get clogged up with algae and keep light and water flow from getting to the plants. The area of the leaf with higher percentage of bite marks is the tip, where there are, usually, more epiphytes. Placing artificial seagrass doesn’t deter herbivores from eating the real seagrass. The analysis of length (between protected and unprotected seagrass leaves) varies from experiment to experiment, in some they’re the same and others it’s clearly different. But it’s evident the difference between the initial and final length of the leaves. It wasn’t possible to determine which species salemas preferred. Herbivory plays a negative role in the establishment of transplanted seagrass meadows in Luiz Saldanha Marine Park.

Tese de doutoramento, Ciências do Mar, da Terra e do Ambiente, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2015 In this thesis I looked at different components of dispersal in the seagrass Zostera noltii, from the dispersal potential of both sexual and asexual propagules to indirect genetic estimation and landscape genetics analysis. My studies show that the dispersal biology of Z. noltii is very dependent on commonly underestimated asexual dispersal. This asexual LDD is the most parsimonious explanation for the wide distribution of clones in the lagoon and dramatically changes our view of the species’ life history. Furthermore, I propose that the observed lack of association between landscape features and spatial genetic structure is a consequence of this LDD of asexual propagules. The high dispersal capacity of Z. noltii combined with a tidal regime which homogenizes the otherwise complex lagoon habitat, are prevalent over any effects of landscape on gene flow caused by the lagoon complexity as shown by the landscape genetics analyses. Nevertheless, sexual reproduction also affects spatial genetic structure, as the positive kinship between clones within a 3 km range is a signature of restricted seed dispersal. Nesta tese, investiguei as diferentes componentes de dispersão da erva marinha Zostera noltii, desde o potencial de dispersão de propágulos assexuados e sexuados até à sua estimação indirecta através de métodos genéticos e análise de genética paisagistica. O meu estudo demonstra que a dispersão da Z. noltii possui um importante componente assexual, geralmente subestimada. A DLD assexual é a explicação mais parcimoniosa para a larga distribuição de clones na Ria Formosa e altera drasticamente a nossa visão do ciclo de vida da espécie. Para além disso, proponho que a falta de associação observada entre as características da paisagem e a estrutura genética espacial é uma consequência da DLD dos propágulos assexuados. Esta elevada capacidade de dispersão da Z. noltii combinada com o regime de marés que homogeneíza o de outra forma complexo habitat lagunar, predominam sobre quaisquer efeitos da paisagem no fluxo genético causado pela complexidade lagunar. No entanto, há também um efeito da reprodução sexuada na estrutura genética espacial, dado que o grau positivo de parentesco entre clones dentro de uma área de 3 km representa um sinal de dispersão restrita de sementes. FCT – Fundação para a Ciência e Tecnologia - SFRH/BD/68570/2010 A secção de trabalho mostrada no capítulo dois foi financiada pela infraestrutura europeia ASSEMBLE (acordo de subvenção n. 227799) concedidos para o projecto DISPERSE.