ii Table of Contents ................................................................................................................. ii List of Figure ....................................................................................................................... iv List of Tables ....................................................................................................................... vi Acknowledgements.............................................................................................................. ix Summary ........................................................................................................................... xi Chapter 1: General Introduction........................................................................................ 1 1.1 Estuaries as systems…………………………………………………………………………………..1 1.2 Literature review as background to this study……………………………………………………….4 1.2.1 Soft-sediment fauna...................................................................................................................4 1.2.1.1 Salinity & Hydrology .............................................................................................................5 1.2.1.2 Sediment particle size.............................................................................................................8 1.2.1.3 Larval settlement and recruitment ..........................................................................................9 1.2.2 Bivalve molluscs as study organisms .....................................................................................10 1.3 Hypotheses, Objectives & Aims of this study………………………………………………………..12 Chapter 2: Study Area & General Methodology ............................................................ 17 2.1 The Hopkins River…………………………………………………………………………………...17 2.2 The Hopkins River estuary…………………………………………………………………………..17 2.3 Study sites……………………………………………………………………………………………19 2.4 The study organism - Soletellina alba (Bivalvia: Psammobiidae)…………………………………24 2.5 General Methodology……………………………………………………………………………….26 2.5.1 Abundance estimates...............................................................................................................26 2.5.2 Measurements of length & mass ............................................................................................27 2.5.3 Monitoring of growth..............................................................................................................28 2.6 Data Analyses………………………………………………………………………………………..28 Chapter 3: Hydrology, river discharge & the physico-chemical environment ............ 63 3.1 Introduction………………………………………………………………………………………….63 3.2 Methods………………………………………………………………………………………………64 3.2.1 Hydrology & river discharge..................................................................................................64 3.2.2 Salinity......................................................................................................................................64 3.2.3 Dissolved oxygen......................................................................................................................67 3.2.4 Statistical Analysis...................................................................................................................68 3.2.4.1 River discharge......................................................................................................................68 3.2.4.2 Salinity ..................................................................................................................................68 3.3 Results………………………………………………………………………………………………..68 3.3.1 Hydrology & river discharge..................................................................................................68 3.3.2 Salinity......................................................................................................................................69 3.3.3 Dissolved oxygen......................................................................................................................72 3.4 Discussion……………………………………………………………………………………………72 Chapter 4: The population dynamics of S. alba ............................................................ 100 4.1 Introduction………………………………………………………………………………………...100 4.2 Methods……………………………………………………………………………………………..103 4.2.1 Distribution & abundance ....................................................................................................103 4.2.2 Recruitment of juveniles .......................................................................................................106 4.2.3 Data Analysis .........................................................................................................................108 4.2.3.1 Distribution & abundance ...................................................................................................108 iii 4.2.3.2 Length-frequency data.........................................................................................................109 4.2.3.3 Recruitment of juveniles......................................................................................................110 4.3 Results………………………………………………………………………………………………112 4.3.1 Distribution & abundance ....................................................................................................112 4.3.2 Length-frequency data..........................................................................................................114 4.3.3 Recruitment of juveniles .......................................................................................................115 4.4 Discussion…………………………………………………………………………………………..118 4.4.1 Abundance and distribution.................................................................................................118 4.4.2 Length-frequency data..........................................................................................................120 4.4.3 Recruitment of juveniles. ......................................................................................................122 Chapter 5: Growth........................................................................................................... 171 5.1 Introduction………………………………………………………………………………………..171 5.2 Methods…………………………………………………………………………………………….172 5.3 Data Analysis………………………………………………………………………………………176 5.4 Results………………………………………………………………………………………………178 5.4.1 Pilot cage experiments, 1996-1997 .......................................................................................178 5.4.1 Caged and uncaged bivalves, 1997-1998..............................................................................179 5.5 Discussion…………………………………………………………………………………………..181 Chapter 6: Response to fluctuations in salinity............................................................. 216 6.1 Introduction………………………………………………………………………………………...216 6.2 Methods…………………………………………………………………………………………….219 6.2.1 Abundance and condition in relation to channel elevation................................................219 6.2.2 Growth, condition & mortality of caged bivalves at two channel elevations ...................222 6.2.3 Salinity tolerance experiment...............................................................................................223 6.3 Data Analyses………………………………………………………………………………………225 6.3.1 Abundance and condition in relation to channel elevation................................................225 6.3.2 Growth, condition & mortality of caged bivalves at two channel elevations ...................225 6.3.3 Salinity tolerance experiment...............................................................................................226 6.4 Results………………………………………………………………………………………………227 6.4.1 Abundance and condition in relation to channel elevation................................................227 6.4.2 Growth, condition & mortality of caged bivalves at two channel elevations ...................229 6.4.3 Salinity tolerance experiment...............................................................................................229 6.5 Discussion…………………………………………………………………………………………..230 6.2.1 Abundance and condition in relation to channel elevation................................................230 6.3.2 Growth, condition & mortality of caged bivalves at two channel elevations ...................232 6.2.3 Salinity tolerance experiment...............................................................................................232 Chapter 7: General Discussion ....................................................................................... 266 7.1 Hydrology and physico-chemical conditions during the study period……………………………266 7.2 Understanding S. alba in terms of its size, abundance, distribution & life history - is it like other estuarine bivalves?……………………………………………………………….267 7.3 Modelling the interaction of the physico-chemical environment and the population dynamics of S. alba - future prospects………………………………………………………………………..270 7.3.1 Potential physico-chemical models.......................................................................................270 7.3.2 Physiological Models .............................................................................................................271 7.4. Peculiarities of population dynamics in estuaries that alternately flood & close - a new regional versus global perspective needed?………………………………………………...274 7.5 Returning to the initial hypotheses and aims of this study………………………………………..276