ECO-ETHOLOGY OF SHELL-DWELLING CICHLIDS IN LAKE TANGANYIKA THESIS Submitted in Fulfilment of the Requirements for the Degree of MASTER OF SCIENCE of Rhodes University by IAN ROGER BILLS February 1996 'The more we get to know about the two greatest of the African Rift Valley Lakes, Tanganyika and Malawi, the more interesting and exciting they become.' L.C. Beadle (1974). A male Lamprologus ocel/alus displaying at a heterospecific intruder. ACKNOWLEDGMENTS The field work for this study was conducted part time whilst gworking for Chris and Jeane Blignaut, Cape Kachese Fisheries, Zambia. I am indebted to them for allowing me time off from work, fuel, boats, diving staff and equipment and their friendship through out this period. This study could not have been occured without their support. I also thank all the members of Cape Kachese Fisheries who helped with field work, in particular: Lackson Kachali, Hanold Musonda, Evans Chingambo, Luka Musonda, Whichway Mazimba, Rogers Mazimba and Mathew Chama. Chris and Jeane Blignaut provided funds for travel to South Africa and partially supported my work in Grahamstown. The permit for fish collection was granted by the Director of Fisheries, Mr. H.D.Mudenda. Many discussions were held with Mr. Martin Pearce, then the Chief Fisheries Officer at Mpulungu, my thanks to them both. The staff of the JLB Smith Institute and DIFS (Rhodes University) are thanked for help in many fields: Ms. Daksha Naran helped with computing and organisation of many tables and graphs; Mrs. S.E. Radloff (Statistics Department, Rhodes University) and Dr. Horst Kaiser gave advice on statistics; Mrs Nikki Kohly, Mrs Elaine Heemstra and Mr. Dave Voorvelt produced the numerous excellent illustrations; Mrs. G. Armstrong (Geography Department, Rhodes University) conducted sediment grain size analysis; Ms Cindy Kulongowski, Dr Eva Hert, Ms Vanessa Twentyman-Jones, Mr Ofer Gon, Dr Paul Skelton and Dr M. Villet made comments on various parts of this thesis; Mr Ofer Gon and Dr Paul Skelton are thanked for numerous valuable discussions on many aspects throughout this study. Dr Martin Villet ran the phylogenetic data on Hennig86. Dr Martin Villet also read through the penultimate draft of the thesis and made value comments, he is sincerely thanked for all his help. Sincere thanks to my tutors Dr Tony Ribbink and the late Dr Humphry Greenwood for advice, guidance and patience during the course of my studies at Rhodes University. I was partially supported by a studentship from Dr Tony Ribbink. A huge thanks to Dakha Naran who has been a great friend and an enormous help over the past two years. Finally thanks and love to my parents who have supported me in so many ways for many years. ABSTRACT Observations of habitats are reported. A series of underwater experiments were conducted in natural habitats to answer questions concerning a) why Lamprologus ocellatus and Lamprologus ornatipinnis bury gastropod shells refuges into the substrate, and b) to examine interspecies differences in shell-using behaviours. Some behaviour patterns were analysed using phylogenetic methods. Lamprologus ocellatus and L. omatipinnis responded to new shells in a variety of ways, shells were moved, buried (and used) or hidden (buried and not used). How shells are utilised seems to be dependant on a complex of factors such as the size and quality of new the shell and the number already in the territory. Shell use may also be affected by neighbour species, sex, size and predation levels. There are interspecific differences in the size of shells used and the methods of shell use. The latter results in species-characteristic shell orientations, vertical burial in L. oeellatus and horizontal burial in L. ornatipinnis. Shell orientation does affect other species/use of shells. Shell movement and vertical orientation appear to be apomorphic while shell while shell hiding and burial are pleisiomorphic within the genus Lampr%gus. Numerous cues are involved in stimulating shell burial. Most of these cues are actively sought by the fish by external and internal inspections. Shell burial therefore appears to be a method of reducing the information gathering ability of potential shell-dwelling competitors. Shell burial can therefore be regarded as an investment process which enhances the residents ability to defend its territory. Males can also control the distribution of open shells within teritories and thus control mate access to shells. This behaviour could be a significant factor in the evolutin of marked sexual dichromatism exhibited within the genus. ii CONTENTS CHAPTER 1 INTRODUCTION .............•..•............•.................. 1 SHELL-DWELLERS ....•.................•....................... 2 In Lake Tanganyika ..•...........•...........•.............. 2 In Lake Malawi ...............•........................... 6 In marine habitats ........•................................ 6 SOFT SUBSTRATE SHELL-DWELLERS .....•.•......................... 8 DIAGNOSES OF THE SHELL DWELLERS STUDIED .••.................... 11 OBJECTIVES OF THIS STUDY ............................••....... 12 CHAPTER 2 FIELD OBSERVATIONS IN SOFT SUBSTRATE HABITATS OF LAKE TANGANYIKA •..•.........................•.... 13 INTRODUCTION ..........................................•.... 13 OBSERVATIONS, DESCRIPTIONS OF STUDY SITES AND METHODS ..............•........................... 15 RESULTS ........................•......................•.... 17 THE FISH COMMUNITY ......•..••...........•......•............ 17 Day-time ............................................... 17 Night-time . • . 1 7 OBSERVATIONS OF SHELL-DWELLING FISHES ....••.................•. 17 Abundance ............................................. 17 Social structure of shell-dwellers .............................. 20 Numbers of shells in territories ................................ 21 Inter-shell distances and shell distributions ....................... 24 Refuge use and fleeing behaviour - day-time ...................... 25 - night-time ....................•. 28 Oviposition sites. ........................................ 28 Feeding behaviour observations ............................... 29 MOLLUSC SHELL DEPOSITS .........•.•.......................... 30 iii Shells used by cichlids ..................................... 30 Shell occupancy .......................................... 31 DESCRIPTIONS OF STUDY AND COLLECTION SITES ..................... 34 Musende Rocks, Zambia .................................... 34 Mbita Island, Zambia ...................................... 36 ChezL Zambia ........................................... 39 Gitaza, Burundi .......................................... 39 SUBSTRATE GRAIN SIZES ........................................ 40 REMARI(S AND DISCUSSION ...................................... 42 Shell-dwelling fish abundance ................................ 42 Territory sizes of shell-dwellers ............................... 42 Refuge use ............................................. 42 Oviposition sites and female behaviour .......................... 43 Feeding ................................................ 44 CONCLUSIONS ................................................ 44 CHAPTER 3 SHELL BURIAL BEHAVIOUR BY UNDERWATER EXPERIMENTS IN NATURAL HABITATS ......................................... 46 INTRODUCTION ............................................... 46 MATERIAL AI\ID GEI\IERAL METHODS ................................ 49 Data analysis ............................................ 49 EXPERIMENTS AND RESULTS ..................................... 51 Experiment 1 (shell quality) .................................. 51 Methods ............................................... 51 Results ................................................ 52 Experiment 2 (varying shell size) .............................. 55 Methods ............................................... 55 Results ................................................ 56 Experiment 3 (shell abundance) ............................... 58 Methods ................................................ 58 Results ................................................ 59 iv Experiment 4 (shell abundance) ............................... 62 Methods ............................................... 62 Results ................................................ 62 Experiment 5 (shells not buried) ............................... 64 Methods ............................................... 64 Results ................................................ 64 DISCUSSION ................................................. 67 Can fish determine shell quality? .............................. 67 Do fish respond differently to varying sized shells? .............•.............................. 69 Does shell abundance affect fish behaviour? ...................... 69 Does shell abundance affect numbers of shell-dwelling communities? ................................. 70 What if shells are prevented from being buried? .................... 71 Why are shells buried? ..................................... 71 CHAPTER 4 INTERSPECIFIC COMPETITION FOR SHELL RESOURCES ................... 75 INTRODUCTION ............................................... 75 MATERIAL AND GENERAL METHODS ................................ 76 Experiment 1 (interspecific shell size) ........................... 76 Methods ............................................... 76 Results ................................................ 77 Experiment 2 (interspecific methods) .....•..................... 85 Methods ..............................................