Impacto da herbivoria no sucesso do estabelecimento de novas pradarias de ervas marinhas

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.