Publicação
Intertidal benthic diatoms of the Tagus estuary : taxonomic composition and spatial-temporal variation
| Resumo: | The taxonomic composition of intertidal benthic diatom communities of many estuarine and coastal areas worldwide is still fairly unknown. In order to increase knowledge on the biodiversity and community structure of the intertidal benthic diatoms of the Tagus estuary, a two-year survey was carried out in 6 stations with distinct sediment structure. The main output of the study is the Identification Guide which is supplemented by 1019 micrographs (volume 2). This detailed systematic account of 185 diatom taxa observed includes: morphological descriptions and comparisons to similar species, as well as information on biogeography and autoecology. Moreover, the structure of the diatom communities was characterized by its diversity and other features related to community physiognomy, such as size-class or life-form distribution. Temporal patterns were clearly subordinate to spatial ones; mud content was found to be the environmental variable most correlated to the multivariate patterns of the biotic data. The level of physical disturbance of the sediment was found to be responsible for the structure of the diatom communities as it controls the interplay between two different functional groups composing the diatom assemblages: the epipelon and the epipsammon. The epipelon, a less diverse community, mainly composed of medium-sized species, shows a certain degree of seasonal variation. This community dominates sheltered areas and its occurrence can be predicted by the mud content of the sediment, a good indicator of the level of sediment exposure. The epipsammon, a very diverse community composed by minute species, does not show temporal patterns. Its occurrence is conditioned by the presence of the substrate (i.e. sandgrains) that is colonized by several types of life-forms. Alternatives to species-level identification were examined in order to bridge the gap between functional and structural ecological studies. The major multivariate patterns were mostly replicated but with unequal success. Species presence/absence and genus-level abundance data generated the best results. However, the temporal patterns were clouded by the decrease in taxonomical resolution or the loss of abundance data. The great intrinsic value of biodiversity assessment, even of microscopic organisms, is recognized and well established nowadays. Floristic studies made in conjunction with ecological-oriented research on microphytobenthos enhance our understanding of the structure and function of this important community and provide much needed data on the biogeography and autoecology of these microorganisms. Key words: diatoms, ecology, taxonomy, microphytobenthos, spatial-temporal distribution, diversity, epipelon, epipsammon, life-form, community, intertidal flat, estuary. |
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| Autores principais: | Ribeiro, Lourenço |
| Assunto: | Diatomáceas Biodiversidade Estuário do Tejo (Portugal) Teses de doutoramento - 2010 |
| Ano: | 2010 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | The taxonomic composition of intertidal benthic diatom communities of many estuarine and coastal areas worldwide is still fairly unknown. In order to increase knowledge on the biodiversity and community structure of the intertidal benthic diatoms of the Tagus estuary, a two-year survey was carried out in 6 stations with distinct sediment structure. The main output of the study is the Identification Guide which is supplemented by 1019 micrographs (volume 2). This detailed systematic account of 185 diatom taxa observed includes: morphological descriptions and comparisons to similar species, as well as information on biogeography and autoecology. Moreover, the structure of the diatom communities was characterized by its diversity and other features related to community physiognomy, such as size-class or life-form distribution. Temporal patterns were clearly subordinate to spatial ones; mud content was found to be the environmental variable most correlated to the multivariate patterns of the biotic data. The level of physical disturbance of the sediment was found to be responsible for the structure of the diatom communities as it controls the interplay between two different functional groups composing the diatom assemblages: the epipelon and the epipsammon. The epipelon, a less diverse community, mainly composed of medium-sized species, shows a certain degree of seasonal variation. This community dominates sheltered areas and its occurrence can be predicted by the mud content of the sediment, a good indicator of the level of sediment exposure. The epipsammon, a very diverse community composed by minute species, does not show temporal patterns. Its occurrence is conditioned by the presence of the substrate (i.e. sandgrains) that is colonized by several types of life-forms. Alternatives to species-level identification were examined in order to bridge the gap between functional and structural ecological studies. The major multivariate patterns were mostly replicated but with unequal success. Species presence/absence and genus-level abundance data generated the best results. However, the temporal patterns were clouded by the decrease in taxonomical resolution or the loss of abundance data. The great intrinsic value of biodiversity assessment, even of microscopic organisms, is recognized and well established nowadays. Floristic studies made in conjunction with ecological-oriented research on microphytobenthos enhance our understanding of the structure and function of this important community and provide much needed data on the biogeography and autoecology of these microorganisms. Key words: diatoms, ecology, taxonomy, microphytobenthos, spatial-temporal distribution, diversity, epipelon, epipsammon, life-form, community, intertidal flat, estuary. |
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