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|Title:||Effects of habitat loss on waders (Aves, Charadrii) in the Mondego estuary (Portugal)||Other Titles:||Consequências da perda de habitat para as limícolas (aves, charadrii) do estuário do Mondego (Portugal)||Authors:||Santos, Tiago Múrias dos||Orientador:||Marques, João Carlos||Keywords:||Ecologia; Biologia||Issue Date:||29-Mar-1998||Citation:||SANTOS, Tiago Ferrand Almeida Múrias dos - Effects of habitat loss on waders (Aves, Charadrii) in the Mondego estuary (Portugal). Coimbra : [s.n.], 1997. Tese de doutoramento. Disponível na WWW em: http://hdl.handle.net/10316/2140.||Abstract:||A perda de habitat é uma das principais causas que podem afectar a sobrevivência das limícolas (Aves: Charadrii) em muitos estuários da Europa. O principal objectivo deste estudo foi investigar os efeitos de alterações nos habitats das limícolas decorrentes da acção humana directa - a destruição de habitats supra-mareais (as salinas) - e indirecta - as exuberâncias ("blooms") periódicas de macroalgas nas vaseiras inter-mareais, consequência do processo de eutrofização em curso - num estuário submetido a intenso "stress ambiental", o estuário do Mondego.Desde 1984 que as salinas têm vindo a ser progressivamente abandonadas ou destruídas. Este estudo sugere que o desaparecimento deste habitat poderá representar uma sobrecarga de até 45% no número de horas de alimentação.aves-1 nas zonas de alimentação inter-mareais, que poderão revelar-se incapazes de albergar as aves para aí deslocados, especialmente se os níveis actuais de competição intra-específica forem já elevados. Esse efeito será amplificado se a alimentação nas áreas intermareais for afectada pelos "blooms" algais. O presente estudo não evidenciou níveis de competição intra-específicos suficientemente elevados para conduzir a um decréscimo das densidades de aves na zona inter-mareal; por outro lado não ficou demonstrado que as algas repelissem de alguma forma a alimentação das limícolas nas zonas por elas colonizadas.
Como principal conclusão, pode inferir-se que, apesar da intensa pressão humana, a sobrevivência das populações de limícolas do estuário do Mondego não parece estar em risco imediato. Porém, a médio prazo, a destruição das salinas pode vir a afectar muitas espécies, devido à perda efectiva de tempo de alimentação, e a situação pode piorar ainda mais se for acompanhada por uma deterioração das condições alimentares nas vaseiras inter-mareais em virtude do crescimento incontrolável das áreas periodicamente afectadas pelos "blooms" algais, como consequência do processo de eutrofização acelerado que actualmente se verifica.
Habitat loss is a major factor that can potentially affect the survival of wader populations (Aves: Charadrii) in many estuaries of Europe. A number of studies have been made on this subject in northern Europe, in the last two decades, but there is a lack of data regarding the southern half of the continent. The main objective of this thesis was to investigate what could be the short to medium–term effects on waders of changes in the estuarine habitats as a consequence of two important factors directly or indirectly attributable to human action in the Mondego estuary (west Portugal): the loss of supra–tidal habitats (mainly salinas) and the increase of eutrophication in the mudflats, expressed as periodic ‘blooms’ of green macroalgae. The salinas are being abandoned and converted into fish-farms, which can not be used as feeding grounds by waders, at an alarming rate (5.2 ha.year -1in the the period 1984–94). Of about 305 ha of salinas in the estuary, 35% have been deserted or drained, 23% have been converted into fish-farms and only 42% were still producing during the course of this study. The Mondego estuary still hold a numerous and diversified wader assemblage, which was particularly important in winter and during the spring and autumn migratory passages. It includes one species (Avocet, Recurvirostra avosetta) of international importance, according to the criterion of the Ramsar Convention (>1% of the flyway population in winter) and at least 8 species of national importance (>1% of the national winter numbers). Part of the birds that used the estuary throughout the year remained in the salinas both at low-tide (30%) and at high-tide (58%), and most of them feed there. The active salinas were clearly more used for feeding than the inactive ones, but these could still hold a number of birds for a long time (up to 20 years) after they have been abandoned, depending on the particular environmental conditions of each salina. An hypothetical destruction of the salinas would mean that the feeding would subsequently be restricted to the mudflats. According to the calculations developed in this study, such increase could reach up to 45% of the birds–feeding hours that presently occur in the mudflats. However, not all species were likely to be affected in the same way by the loss of feeding opportunities in case the salinas were lost. Little Stint, Calidris minuta, Redshank Tringa totanus and Common Sandpiper Actitis hipoleucos would be the species more affected by the loss of space, while Turnstone Arenaria interpres and Dunlin Calidris alpina would be those more affected by the loss of feeding time at high–water. The predicted increase in the birds feeding–hours that would occur in the mudflats, if the salinas were to be destroyed, could be potentially detrimental for the survival of the estuarine populations of many species if the levels of inter-specific competition in the flats (which ultimately determine the carrying capacity of an area) were already high. The two tests used to assess the occurrence of interspecific competition (feeding interference among birds and depletion of the prey resources) suggested that the phenomenon was probably too weak to be perceived in the Mondego, at least with the methodology used. Thus, at present, the mudflats are probably still able to buffer the potential effects of the loss of space if the salinas were lost. However, the displaced birds would also lose feeding time, and this could not be recovered in the mudflats. The increasing process of eutrophication in the area may represent a direct threat to the mudflats, while feeding grounds for waders, through changes in the composition of the invertebrate communities and in the abundances of the main prey species. The present study did not present any evidence that the algae repelled the birds. Indeed, some species (e.g. Dunlin) may even have benefited of a surplus of food provided by the mats when they first appear, in early spring, but not in autumn, after the algal crash. This suggests that, at present, the occurrence of the algae on the flats do not represent an immediate threat to the waders’ feeding in the Mondego. Nevertheless, the situation can change in the long-term if the eutrophication process can not be reduced. The main conclusion of this study is that, in spite of the heavy human pressure in the estuary, the survival of the wader populations seems not to be threatened in the short–term. However, in the medium–term, the destruction of the salinas could seriously affect the survival of some species, and the situation could still become worse if it was accompanied by a global change in the composition of the prey communities caused by an increase of the eutrophication process in the estuary. Nevertheless, both these drastic alterations can still be prevented. Possible ways of achieving that in the salinas could be to find sustainable ways of keeping them actively producing, tomanage inactive ones in order tomake them suitable for waders, to carefully control the establishment of new fish-farms in old salinas, and to improve the design of the fish–ponds in order to provide waders with alternative feeding places to the destroyed salinas. As to the eutrophication process, any action to reduce it would have to be taken at a regional level, and would take more time. In any case, a long–term monitoring of the process at all levels of the trophic chain would be greatly welcome.
|Description:||Tese de doutoramento em Biologia (Ecologia) apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra||URI:||http://hdl.handle.net/10316/2140||Rights:||openAccess|
|Appears in Collections:||FCTUC Ciências da Vida - Teses de Doutoramento|
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