Author(s):
Conduto, Telma Lúcia Pereira dos Santos Coelho
Date: 2018
Persistent ID: http://hdl.handle.net/10400.1/10792
Origin: Sapientia - Universidade do Algarve
Project/scholarship:
info:eu-repo/grantAgreement/FCT/SFRH/SFRH%2FBD%2F44532%2F2008/PT;
info:eu-repo/grantAgreement/FCT/FARH/SFRH%2FBD%2F44532%2F2008/PT;
Subject(s): Rede trófica bentónica costeira; Estuário; Peixe; Octopus vulgaris; variabilidade na dieta; Marcadores tróficos; Ácidos gordos; Isótopos estáveis; Matéria orgânica terrestre; Fontes energéticas alócto; Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias
Description
The transfer of production along coastal habitats from migration of organisms and natural or anthropogenically caused environmental conditions create complex food webs between habitats. A species is rarely independent from the resources of other habitats as nutrients and food supply flow easily in the aquatic environment developing strong habitat connections between food webs. These multiple trophic interactions are very susceptible to variability in the environmental conditions of the habitat that supplies the energy source. All this justifies additional investigation on coastal habitat specific food webs interactions and key energetic connections that extent from primary producers to top consumers. Given the easy access and importance to achieve sustainability of species and their supporting habitats, explicitly for fisheries species that maintain local economy, this thesis aims to study energy sources, prey and consumers that transcend habitats in the eastern Algarve coastal area. A General Introduction highlights the functioning of coastal food webs and the flow of nutrients and food with the movement of organisms between distinct habitats in the coastal area. The constant changes in the coastal landscape and the variability in environmental conditions create a knowledge gap in the functional role of different habitats in the complex web of coastal trophic interactions and secondary production that support coastal fisheries. Temporal and spatial variability in trophodynamics of fisheries species was performed with trophic markers: fatty acids and stable isotopes. These biomarkers determine the importance of the outwelling of terrestrial organic matter in trophic webs of adjacent coastal habitats and if movement of consumers results in the transfer of energy sources between habitats. This introduction describes the most relevant aspects in trophic markers biochemistry and applications in ecology and detailed analytical procedures for the following chapters, as well as quality control of analysis. Applications in ecological studies are exemplified from the identification of energy sources, including terrestrial organic matter, microphytobenthos and different groups of phytoplankton that support the food webs of a wide variety of aquatic consumers. Chapter 2 demonstrates how the wide range of primary producers and energy sources is reflected in the diet of coastal fish, estuarine fish and offshore fish. The relative contribution of energy sources determined the importance of upriver foraging behavior of marine fish for the transport of marine production upriver and the importance of the estuarine environment as feeding ground for coastal fishes. Estuary primary producers and vascular plants were recognized as a potential source of energy for mid estuary fishes against marine phytoplankton and microphytobenthos for coastal fishes. Chapter 3 describes the role of terrestrial organic matter as energetic source for fish food webs in the estuary and adjacent coastal area. Organic detrital material of terrestrial origin flows in rivers towards coastal areas in a dynamic and continuous process but nevertheless it had a minor role in this connectivity between the estuarine and coastal trophic webs. Chapter 4 evaluates several tissues of a cephalopod from the benthic coastal environment to define inter-tissue comparisons. Tissues with the same function represented the trophic markers in similar proportions and were ineffective to determine temporal and spatial diet variability. Mantle and digestive gland were the chosen tissues for the sequent analyses. Chapter 5 demonstrates the main sources of nutrition in the diet of Octopus vulgaris from the coastal benthic environment. Here are described potential trophic pathways to other habitats, including the role of terrestrial production. This chapter explains the temporal variability in the contribution of the different production sources for the octopus food web in the area of the fishery and demonstrates octopuses depend mainly on local primary sources. The trophic markers supported a trophic web based in dinoflagellate production in the marine environment. Chapter 6 shows the feeding behavior of the cephalopod O. vulgaris towards the input of allochthonous prey and how human interactions create a trophic coupling between the benthic and pelagic environment. The opportunistic behavior of this cephalopod was demonstrated for a food resource absent from the natural diet. Chapter 7 is the general discussion from the overall results and conclusions of the case studies in this thesis under the subject of habitat trophic connectivity of coastal fishery species. Pros and cons of the chosen techniques are discussed as well as issues arising from the sample sizes and pooling of samples. Further research and techniques will improve studies on trophic dynamics and connectivity in these ecologically and economically important benthic habitats.
