The Benthic Ecology of Some Ria Formosa Lagoons, With
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The benthic ecology of some Ria Formosa lagoons, with reference to the potential for production of the gilthead seabream (Sparus aurata L.) Sofia Gamilo Universidade do Algarve 1994 TESES SD The benthic ecology of some Ria Formosa lagoons, with reference to the potential for production of the gilthead seabream (Sparus aurata L.) Sofia Gamito (Maria Sofia Júdice Gamito Pires) Assistente da Universidade do Algarve Dissertação apresentada à Universidade do Algarve para obtenção do grau de Doutor em Ciências Biológicas, especialidade de Ecologia Unidade de Ciências e Tecnologias dos Recursos Aquáticos 1994 i «i. ■mp.'» ' T-r^CÃO s>Vir ElV * íleyi Contents: Acknowledgements Abstract Resumo List of figures List of tables Some definitions Chapter I - INTRODUCTION AND AIMS 1.1 Introduction 1.1.1 The Ria Fonnosa 1.1.2 The climate in the Algarve 1.1.3 Extensive aquaculture 1.1.4 The biology oíSpanis aurata 1.1.5 Feeding habits oíSparus aurata 1.2 Aims Chapter II - ENVIRONMENTAL CONDITIONS Physical and Chemical water data Summary 1 u 2.1 Methods ' ' 2.1.1 Selection and location of sampling sites 11 2.1.2 Water analysis methodology 13 2.2 Results and discussion í 4 2.2.1 Climatic conditions during the period of study 14 2.2.2 Temperature 16 2.2.3 Salinity 18 2.2.4 Dissolved Oxygen 20 2.2.5 Biochemical Oxygen Demand 25 2.2.6 pH 27 2.2.7 Suspended matter 27 2.2.8 Nutrients - Silicate, phosphate, nitrate and nitrite 30 2.2.9 Chlorophyll a and phaeopigments 3 8 2.3 Conclusions 43 Chapter III - MACROFAUNA - DENSITY AND SPECIES DISTRIBUTIONS. Relationshíps with the environmental data Summary 45 3.1 Methods 46 3.1.1 Sediment 46 3.1.2 Vegetation 47 3.1.3 Macrofauna 47 3.1.4 Data analysis 48 3.1.4.1 Ordination of stations 48 3.1.4.2 Density 48 3.1.4.3 Diversity 49 3.1.4.4 Rank abundance curves 49 3.1.4.5 Taxa associations 49 3.1.4.6 Relationshíps with the environmental data 50 3.2 Results and Discussion 52 3.2.1 Sediment 52 3.2.2 Vegetation 54 3.2.3 Macrofauna 56 3.2.3.1 Ordination of stations 56 3.2.3.2 Density 59 3.2.3.2.1 Polychaetes 62 3.2.3.2.2 Molluscs 64 3.2.3.2.3 Crustaceans 67 3.2.3.2.4 Other taxonomic groups 70 3.2.3.3 Diversity 71 3.2.3.4 Rank abundance curves 74 3.2.3.5 Taxa associations 78 3.2.3.6 Relationshíps with the environmental data 83 3.3 Conclusions 91 Chapter IV - MACROFAUNA PRODUCTION Relationshíps with the environmental data Summary 94 4.1 Methods 95 4.1.1 Biomass determination 95 4.1.2 Production determination 98 4.1.3 Data analysis 98 4.2 Results and discussion ^ 4.2.1 Mean individual weights and conversion factors 99 4.2.2 Variation in mean annual biomass 192 4.2.3 Annual Production 1°^ 4.2.4 Relationships with the environmental data 199 4.3 Conclusions ' 5 Chapter V - FEEDING SELECTIVITY of Sparus aurata 114 Summary 5.1 Methods 115 5.1.1 Experimental design 11 ^ 5.1.2 Data analysis 117 • 11X 5.2 Results and Discussion 110 5.2.1 Preparation of gilthead groups 118 5.2.2 Gilthead capture 1^9 5.2.3 Condition of fish l20 5.2.4 Benthic invertebrates l22 5.2.5 Fish gut contents l25 - * i^l 5.2.6 Selectivity Índices 5.2.7 Fish predation on Cerithium vulgatum 132 5 2 8 Effects of físh predation on the benthos 135 ■ . 1-37 5.3 Conclusions Chapter VI - POTENTIAL PRODUCTION of Sparus aurata Summary 6.1 Introduction 6.2 Conceptual model ^9 6.3 Sparus aurata growth 1 ^ 6.4 Sparus aurata food consumption 151 6.5 Benthic production 1^ 6.6 Environmental factors 192 6.7 Final model ^99 6.8 Sensitivity analysis l8^ 6.9 Conclusions / Final remarks 189 GENERAL CONCLUSIONS 191 REFERENCES 195 APPENDICES: Al. Physical-Chemical data Al - 212 A2. Macrofauna species list A2 - 219 A3. Macrofauna data A3 - 224 A4. Models A4 - 244 ACKNOWLEDGEMENTS A work of this kind implies always the help and advice of several people, from technicians to specialists in taxonomy and in data analysis. It will be difficult to thank ali of them individually. Firstly, my special thanks to Prof. Jefífey Wallace and Dr. David Raffaelli who encouraged and helped me throughout the last stages of the experimental work, and in the structuring of the present manuscript. Without their enthusiasm and dedication this work would never have been possible. I am grateful to Dr. Helena Barahona Fernandes and Dr. Sadat Muzavor who guided the fírst stages of my research. I would specially like to thank the Centro de Investigação Marítima do Sul - Delegação de Olhão (from the Instituto Português de Investigação Marítima), where 1 began my research. Special thanks to Dr. Costa Monteiro, for ali the facilities he made available, to Manuela Falcão, who did some of the physical-chemical water analyses, and to Pedro Pousão-Ferreira, for his comments, for the giltheads used in the experimental section, and also for allowing me to use one of his family salinas. Thanks also to ali the technicians, especially José Luís Sofia, José João Sá e Silva and Luís Francisco who helped me in the field work. Thanks are also due to the technicians of C1MS - Delegação de Faro, for doing some of the physical-chemical water analysis. I am grateful to Eugénio Júdice, director of Parque Natural da Ria Formosa at the time the field work was done, for his permission to carry out the sampling program at Caldeira de Moinho de Maré and at one salina. I am also grateful to Luis Filipe Mendonça for his permission to carry out the sampling program and also the experiment on feeding habits of the gilthead in his salina. Many thanks to Dr. João Carlos Marques, for ali the work in identifying and counting the amphipods, for providing access to SYSL and for ali the comments and advice he gave during this research. Thanks are also due to Prof. Gerard Bellan, Dr. Philippe Bouchet, Dr. Pierre Lozovet, Dr. Bernard Métivier, Dr. Rui Santos, Carlos Sousa Reis, António Monteiro, Ângelo Pereira, and Sandra Cruz for helping in the identification or confirmation of some of the species found and to Paula Nunes and v Victor Lourenço for their help in the field work, during the last years of research. Paula helped also in the sorting of some samples of benthos. Thanks are also due to Dr. Martin Sprung, for bis advice and discussions about the benthic data, and Dr. Karim Erzini and Emygdio Cadima for the valuable discussions conceming the elaboratíon of the model, and to other collegues of the University of Algarve, for their profítable assistance. This work would not have been possible without the initial financial support ffom the former Instituto Nacional de Investigação Científica. It has also been in part supported by Comissão de Coordenação da Região do Algarve, through the program PIDR (Plano Integrado de Desenvolvimento Regional) and by Junta Nacional de Investigação Científica through the project "Aquacultura no Algarve - Caracterização Bioeconómica". vi ABSTRACT Extensive aquaculture is traditional in the Algarve, being practised in lagoons (either in special aquaculture ponds or in water reservoirs of salinas as a supplement to salt production). The físh production can be increased, as a íirst step, by improving the water circulation, or by utihsmg additional areas in abandoned salinas. However, in order to do so it is desirable to know about the ecological conditions, for which no information presently exists for the Ria Formosa lagoons. A two-year sampling program was therefore carried out, in four lagoons subjected to different water renewal regimes, with the aim of determining the actual ecological conditions and relating these to the dynamics of water circulation. Ali the studied lagoons, situated near Olhão, in the Ria Formosa, received the same incoming water through the Marim channel. In one lagoon the water was partially renewed every day. In two other lagoons, the water was renewed according to salt-production requirements, and in the fourth lagoon the water was renewed only fortnightly, during the spring tides. These different water regimes created a gradient of increasing environmental stress. The most stressed lagoon experienced large environmental variations, mainly of salinity, which were reflected in the benthic populations, represented by a few, abundant and productive, small opportunistic species. In the least stressed lagoon, the benthic populations were more diverse, with organisms characteristic of estuanne or coastal areas, as well as of the Ria Formosa tidal channels. The secondary production in this lagoon was high, when compared with the other lagoons studied and with data from the Ria Formosa and other estuarine or coastal areas. The other two lagoons had intennediate characteristics. A second environmental gradient of increasing eutrophication was noticed between the least stressed lagoon and the intermediate lagoons, reflected by high biochemical oxygen demand leveis. In these lagoons excessive primary production can lead to a deterioration of the water quality and sometimes to depletion of dissolved oxygen, during the neap tides when water renewal is minimal. The benthic populations were less diverse. However, the secondary production in these lagoons can attain high values, comparable to that in the least stressed lagoon. vn The main físh species cultured in these lagoons is Spams aurata, a benthic feeder. A fíeld experíment was carried out in one of the lagoons of intermediate stress with the aim of studying possible selective feeding behaviour of the gilthead.