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When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g. AUTHOR (year of submission) "Full thesis title", University of Southampton, name of the University School or Department, PhD Thesis, pagination http://eprints.soton.ac.uk UNIVERSITY OF SOUTHAMPTON FACULTY OF SCIENCE SCHOOL OF OCEAN AND EARTH SCIENCE Ecological Controls on Density, Diversity and Community Structure of Polar Megabenthos By Daniel Oliver Brée Jones Thesis for the degree of Doctor of Philosophy December 2005 UNIVERSITY OF SOUTHAMPTON FACULTY OF SCIENCE SCHOOL OF OCEAN AND EARTH SCIENCE Doctor of Philosophy Ecological Controls on Density, Diversity and Community Structure of Polar Megabenthos By Daniel Oliver Brée Jones ABSTRACT Polar deep water environments are poorly studied. This thesis investigates fundamental questions as to the nature of controlling factors on megabenthic communities as well as the diversity, densities and distributions of organisms present. The deep (1000-1660m) Faroe-Shetland Channel harbours an Arctic fauna owing to cold deep- water intrusions from the Norwegian Sea. Despite the relatively low species richness of the megabenthos, variation in faunal composition with depth is apparent. Two distinct communities were identified in the north and south of the channel. Epibenthic megafauna in the south are dominantly filter feeders and in the north deposit feeders. Megabenthic diversity and density decreased to the northeast of the channel. Lebensspuren number and area increase northwards in the Channel. The increase in bioturbation and deposit feeder abundance is concurrent with an increase in fine sediment quantity. The response of a deep, Arctic benthic community to physical disturbance was investigated in the Faroe-Shetland Channel. High levels of physical disturbance, characterised by smothering of the seabed resulted in significant but variable reductions in megafaunal abundance (up to 92.3%). Reductions in diversity, particularly in species richness, were apparent between disturbed (ES(500) = 12.9) and undisturbed areas (ES(500) = 20.6). The implications of selective removal of taxa on ecosystem function and recovery are discussed. Low level disturbance had comparatively little effect on the communities. The effects varied in nature depending on motility and functional group (e.g. motile scavenger abundances were maximal at intermediate distances from disturbance). Effects of physical factors on the megabenthos of Kangerdlugssuaq Fjord mouth in Arctic Greenland were investigated. Large reductions in faunal density (1881 to 60,132 individuals ha-1) and increases in diversity (H´ = 0.93-2.54), through increases in richness (ES(220) = 7.6-18.8) and reductions in dominance (Berger-Parker Index = 0.77-0.38), were found from 270 to 720m depth. Distinct shallow, intermediate and deep communities were identified. Shallower stations had high levels of iceberg disturbance, directly reducing diversity and creating a complex, patchy environment. Responses to disturbance were taxa specific (e.g. mobile suspension feeders aggregate on disturbed areas), but the shallow area has higher densities of suspension feeding epifauna. Deeper areas experience small scale disturbance from deposition of drop stones but its relatively low frequency and magnitude allows increased diversity. Deposit feeding epifaunal and infaunal taxa increase with depth indicated by increased Lebensspuren. Density decreases result from decreased food supply with depth. Benthic megafauna were investigated from the NE Weddell Sea (250 to 500m depth), close to the Fimbul Ice Shelf. Faunal density decreased with depth; diversity was variable but not related to depth. Two distinct communities were found, a shallow community with dense patches of suspension feeders in undisturbed areas and a deep community where these were not present. Disturbance from icebergs was very important in controlling faunal distribution. In shallow waters direct effects of disturbance were observed. In deeper waters habitat changes, caused by past disturbance, controlled faunal distributions. Ice ploughing created a mosaic landscape of fine and coarse sediments. Megafaunal density was highest in coarse sediment and diversity highest in intermediate areas. Quantitative data on benthic megafaunal abundance and diversity obtained using the same method allowed valid comparisons to be made between these polar areas. Megafaunal abundance was comparable between the Arctic and Antarctic stations, although in both areas abundance decreased with increased depth. Diversity was higher in the Antarctic stations, but species richness and evenness in both areas changed with depth. Iceberg disturbance was found to be very important in structuring megabenthic communities, particularly in the Antarctic. The results of this study are used to assess the utility of towed camera sleds, remotely operated vehicles and autonomous underwater vehicles as a method for obtaining ecological information in remote environments. Contents CONTENTS Chapter 1 – General Introduction History of deep-sea polar exploration 1 The deep ocean environment 2 Topography 2 Circulation and temperature 3 The deep benthic environment 5 Deep-sea community measures 6 Faunal density in the deep sea 6 Species diversity in the deep sea 7 Physical controls on deep-water communities 11 Depth 12 Habitat 13 Food supply 14 Currents 15 Disturbance 16 Measuring Diversity 19 Species diversity 19 Species Richness 19 Evenness 20 Measuring species richness 20 Disentangling metrics of species diversity in gradients of abundance 24 Measuring evenness 25 Combined diversity measures 25 Measurement of diversity between habitats 27 Megafauna 29 Deep-sea sampling 32 Traditional methods 32 Photography 33 History of use 33 Photographic techniques 34 Work in the Polar Regions using deep-sea photography 39 Sites of Interest 40 The polar environment 40 Arctic 40 Arctic bathymetry 40 Arctic benthic environment 41 Arctic primary production 43 Arctic seawater characteristics 43 Arctic ice 43 Antarctic 44 Antarctic bathymetry 44 Antarctic benthic environment 47 Antarctic primary production 49 Antarctic ice 49 Faroe-Shetland Channel 51 FSC bathymetry 51 FSC hydrographic regime 52 FSC benthic environment 54 Polar megabenthos 55 Arctic megabenthos 55 Species richness and biodiversity 55 Distribution and zonation 56 Contents Faunal densities and biomass 57 Antarctic megabenthos 58 Species richness and biodiversity 59 Distributions and zonation patterns 61 Faunal densities, biomass and productivity 61 The fauna under ice 63 Aims 64 Chapter 2 – Materials and Methods Data collection 65 WASP 65 Remotely Operated Vehicle 66 Autosub vehicle 68 Collection Devices 71 ROV Suction Sampler 71 Agassiz Trawl 72 Rock Dredge 73 Image analysis 75 Chapter 3 – Ecology of the Deep Faroe-Shetland Channel Introduction 76 Materials and Methods 79 Field Sampling 79 Photo Analysis 80 Data Analysis 80 Results 83 Environment and physical setting 83 Megafaunal density 85 Size and biomass 86 Diversity 88 Community analysis 89 Lebensspuren 95 Discussion 99 Abundance and biomass 99 Diversity 100 Species distribution patterns 103 Lebensspuren 105 Chapter 4 – Effects of disturbance on cold-water Faroe-Shetland Channel Communities Introduction 107 Materials and Methods 109 Study area 109 Data collection 113 Data analysis 114 Results 116 Discussion 127 Contents Chapter 5 – Ecology of the Kangerdlugssuaq Fjord Mouth, East Greenland Introduction 135 Materials and Methods 137 Study area 137 Field sampling 139 Photo analysis 141 Data analysis 142 Results 144 Environment and physical setting 144 Density 146 Diversity 148 Community composition 148 Small-scale patchiness 151 Traces 153 Discussion 156 Density 156 Diversity 158 Community patterns 160 Traces 163 Chapter 6 – Ecology of benthic megafaunal communities in the Fimbul Ice Shelf region, Weddell Sea, Antarctica Introduction 165 Materials and Methods 167 Study area 167 Field sampling 170 Photo analysis 171 Classification of disturbance 172 Data analysis 173 Results 175 Seabed environment 175 Density 176 Diversity 181 Community patterns 184 Discussion 186 Characterisation of the seabed environment 186 Density 188 Diversity 189 Community composition 191 Chapter 7 – Conclusions Biological conclusions Introduction 195 Methods 198 Data analysis 199 Analysis 199 Common fauna 199 Changes in densities 201 Contents Changes in diversity 202 Changes in the physical environment between regions and the effects on the 207 communities Discussion 210 Common fauna between regions 210 Faunal density between regions 211 Diversity between regions 211 Changes between the poles in relation to physical factors 212 Sufficiency of sampling 219 Methodological conclusions Introduction 221 Methods 225 Photographic technique 225 Comparison of vehicles 228 Analysis 229 Photographic technique 229 Comparison of vehicles 232 Discussion 233 Photographic technique 233 Comparison