Ivan Nagelkerken

Department of Animal Ecology and Ecophysiology
Radboud University Nijmegen
Toernooiveld 1, 6525 ED Nijmegen

The Netherlands

 

Room:  HG 01.018

Telephone:  31-24-3652471

Fax:  31-24-3652409

E-mail:  i.nagelkerken at science.ru.nl

 

Background and research interest

 

I did my M.Sc. on aquatic ecology (University of Nijmegen) and on marine biology (University Groningen) in the Netherlands. After finishing I moved back to Curaçao (Netherlands Antilles), where I worked at the Carmabi Ecological Institute as a marine ecologist and assistant marine park manager. During these years my main focus was on coral ecology and marine conservation ecology. I studied a variety of marine animals and subjects, including coral reef diseases (sponges, corals, sea fans, urchins), coral rehabilitation, coral regeneration, coral bleaching, sea turtle migration, oil pollution, marine debris, and coastal resource use. I did my Ph.D. on habitat utilisation by juvenile fish in tropical shallow-water habitats. Currently I am working as an assistant professor at the Radboud University Nijmegen in the Netherlands, and as a visiting professor at the Free University of Brussels in Belgium. At the latter university I teach management of tropical coastal habitats. My current research focus is on connectivity between mangroves, seagrass beds and coral reefs by fishes, and on sensory ecology of juvenile fishes. At this moment my research group consists of 5 Ph.D. students and about 15 M.Sc. and B.Sc. students, which work in the western Indian Ocean (Tanzania), Indonesia, and in the Caribbean (Curaçao and Aruba).

 

 

Scientific publications

 

 

BOOKS

  1. Nagelkerken I, editor (2009) Ecological connectivity among tropical coastal ecosystems. Springer Science and Business Media, Dordrecht, the Netherlands, 615 pp.

 

BOOK CHAPTERS

  1. van der Velde G, Nagelkerken I, Rajagopal S & bij de Vaate A (2002) Invasions by alien species in inland freshwater bodies in western Europe: the Rhine delta. In: Leppäkoski E, Gollasch S, Olenin S (eds). Invasive aquatic species of Europe - distributions, impacts and management. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 360-372

  2. van der Velde G, Leuven RSEW & Nagelkerken I (2004) Types of riverine ecosystems. In: Dooge JCI (ed) Fresh surface water. Encyclopedia of life support systems (EOLSS). Volume 1. UNESCO, EOLSS Publishers, Oxford, UK, pp. 365-397. [http://www.eolss.net]

  3. Nagelkerken I (2009) Evaluation of the nursery function of mangroves and seagrass beds for reef fishes and decapods: patterns and underlying mechanisms. In: Nagelkerken I (ed) Ecological connectivity among tropical coastal ecosystems. Springer Science and Business Media, Dordrecht, the Netherlands, pp. 357-399

  4. Nagelkerken I (2009) Introduction. In: Nagelkerken I (ed) Ecological connectivity among tropical coastal ecosystems. Springer Science and Business Media, Dordrecht, the Netherlands, pp. 1-6

 

PUBLICATIONS IN INTERNATIONAL SCIENTIFIC JOURNALS

  1. Nagelkerken IA & Debrot AO (1995) Mollusc communities of tropical rubble shores of Curaçao: long-term (7+ years) impacts of oil pollution. Marine Pollution Bulletin 30: 592-598

  2. Smith GW, Ives LD, Nagelkerken IA & Ritchie KB (1996) Caribbean sea fan mortalities. Nature 383: 487

  3. Nagelkerken I, van der Velde G & van Avesaath PH (1997) A description of the skeletal development pattern of the temperate coral Caryophyllia smithi based on internal growth lines. Journal of the Marine Biological Association of the United Kingdom 77: 375-387

  4. CARICOMP: Zieman J, Penchaszadeh P, Ramirez JR, Perez D, Bone D, Herrera-Silveira J, Sanchez-Arguelles RD, Zuniza D, Martinez B, Bonair K, Alcolado P, Laydoo R, Garcia JR, Garzón-Ferreira J, Diaz G, Gayle P, Gerace DT, Smith G, Oxenford H, Parker C, Pors LPJJ, Nagelkerken IA, van Tussenbroek B, Smith SR, Varela R, Koltes K & Tschirky J (1997) Variation in ecological parameters of Thalassia testudinum across the CARICOMP network. Proceedings of the 8th International Coral Reef Symposium 1: 663-668

  5. CARICOMP: Wiebe WJ, Gerace DT, Flowers L, Johnson L, Ward C, Oxenford H, Parker C, Tschirky J, Smith SR, Ellison J, De Meyer K, Bush P, Garzón-Ferreira J, Nivia J, Pors LPJJ, Nagelkerken IA, Geraldes FX, Ramirez J, Herrera-Silveira J, Sanchez-Arguelles RD, Garcia JR, Alleng G, Bonair K, Laydoo R, Varela R, Klein E, Bone D, Perez D & Linton D (1997) Structure and productivity of mangrove forests in the greater Caribbean region. Proceedings of the 8th International Coral Reef Symposium 1: 669-672

  6. CARICOMP: Woodley JD, Bone D, Buchan K, Bush P, De Meyer K, Garzón-Ferreira J, Gayle P, Gerace DT, Grober L, Klein E, Koltes K, Losada F, McField MD, McGrath T, Mendes JM, Nagelkerken I, Ostrander G, Pors LPJJ, Rodríguez A, Rodríguez R, Ruiz-Renteria F, Smith G, Tschirky J, Alcolado P, Bonair K, Garcia JR, Geraldes FX, Guzman H, Parker C & Smith SR (1997) Studies on Caribbean coral bleaching, 1995-96. Proceedings of the 8th International Coral Reef Symposium 1: 673-678

  7. Cervino J, Goreau T, Smith G, DeMeyer K, Nagelkerken I & Hayes R (1997) Fast spreading new Caribbean coral disease. Reef Encounter 22: 16-18

  8. Nagelkerken I, Buchan K, Smith GW, Bonair K, Bush P, Garzón-Ferreira J, Botero L, Gayle P, Heberer C, Petrovic C, Pors L & Yoshioka P (1997) Widespread disease in Caribbean sea fans: I. Spreading and general characteristics. Proceedings of the 8th International Coral Reef Symposium 1: 679-682

  9. Nagelkerken I, Buchan K, Smith GW, Bonair K, Bush P, Garzón-Ferreira J, Botero L, Gayle P, Harvell CD, Heberer C, Kim K, Petrovic C, Pors L & Yoshioka P (1997) Widespread disease in Caribbean sea fans: II. Patterns of infection and tissue loss. Marine Ecology Progress Series 160: 255-263

  10. Goreau TJ, Bruckner AW, Cervino J, Hayes RL, Nagelkerken I, Porter JW, Porter KG, Richardson LL, Santavy DL, Smith GW & Williams EH (1997) Assessing coral reef health. Science 277: 165-166

  11. Debrot AO & Nagelkerken I (1997) A rare mass recruitment of the balloonfish (Diodon holocanthus L.) in the leeward Dutch Antilles, 1994. Caribbean Journal of Science 33: 284-286

  12. Nagelkerken I & Bak RPM (1998) Differential regeneration of artificial lesions among sympatric morphs of the Caribbean corals Porites astreoides and Stephanocoenia michelinii. Marine Ecology Progress Series 163: 279-283

  13. Cervino JM, Goreau TJ, Hayes RL, Kaufman L, Nagelkerken I, Patterson K, Porter JW, Smith GW & Quirolo C (1998) Coral disease. Science 280: 499-500

  14. Goreau TJ, Cervino J, Goreau M, Hayes R., Hayes M, Richardson L, Smith G, DeMeyer K, Nagelkerken I, Garzon-Ferreira J, Gil D, Peters EC, Garrison G, Williams EH, Bunkley-Williams L, Quirolo C, Patterson K, Porter JW & Porter K (1998) Rapid spread of diseases in Caribbean coral reefs. Revista de Biologia Tropical 46, Supplement 5: 157-171

  15. Nagelkerken I, Meesters EH & Bak RPM (1999) Depth-related variation in regeneration of artificial lesions in the Caribbean corals Porites astreoides and Stephanocoenia michelinii. Journal of Experimental Marine Biology and Ecology 234: 29-39

  16. Nagelkerken I, Smith GW, Snelder E, Karel M & James S (1999) Sea urchin Meoma ventricosa die-off in Curaçao (Netherlands Antilles) associated with a pathogenic bacterium. Diseases of Aquatic Organisms 38: 71-74

  17. Ritchie KB, Nagelkerken I, James S & Smith GW (2000) A tetrodotoxin-producing marine pathogen. Nature 404: 354

  18. Nagelkerken I, Bouma S, van den Akker S & Bak RPM (2000) Growth and survival of unattached Madracis mirabilis fragments transplanted to different reef sites, and the implication for reef rehabilitation. Bulletin of Marine Science 66: 497-505

  19. Nagelkerken I, Dorenbosch M, Verberk WCEP, Cocheret de la Morinière E & van der Velde G (2000) Day-night shifts of fishes between shallow-water biotopes of a Caribbean bay, with emphasis on the nocturnal feeding of Haemulidae and Lutjanidae. Marine Ecology Progress Series 194: 55-64

  20. Nagelkerken I, Dorenbosch M, Verberk WCEP, Cocheret de la Morinière E & van der Velde G (2000) Importance of shallow-water biotopes of a Caribbean bay for juvenile coral reef fishes: patterns in biotope association, community structure and spatial distribution. Marine Ecology Progress Series 202: 175-192  

  21. Nagelkerken I, van der Velde G, Gorissen MW, Meijer GJ, van‘t Hof T & den Hartog C (2000) Importance of mangroves, seagrass beds and the shallow coral reef as a nursery for important coral reef fishes, using a visual census technique. Estuarine, Coastal and Shelf Science 51: 31-44  

  22. Debrot AO & Nagelkerken I (2000) User perceptions on coastal resource state and management options in Curaçao. Revista de Biologia Tropical 48, Supplement 1: 95-106

  23. Nagelkerken I, Aerts L & Pors L (2000) Barrel sponge bows out. Reef Encounter 28: 14-15 

  24. Nagelkerken I, Kleijnen S, Klop T, van den Brand RACJ, Cocheret de la Morinière E & van der Velde G (2001) Dependence of Caribbean reef fishes on mangroves and seagrass beds as nursery habitats: a comparison of fish faunas between bays with and without mangroves/seagrass beds. Marine Ecology Progress Series 214: 225-235  

  25. Nagelkerken I, van der Velde G & Cocheret de la Morinière E (2001) Fish feeding guilds along a gradient of bay biotopes and coral reef depth zones. Aquatic Ecology 35: 73-86 

  26. Nagelkerken I, Wiltjer GAMT, Debrot AO & Pors LPJJ (2001) Baseline study of submerged marine debris at beaches in Curaçao, West Indies. Marine Pollution Bulletin 42: 786-789

  27. Cervino J, Goreau TJ, Nagelkerken I, Smith GW & Hayes R (2001) Yellow band and dark spot syndromes in Caribbean corals: distribution, rate of spread, cytology, and effects on abundance and division rates of zooxanthellae. Hydrobiologia 460: 53-63

  28. Cocheret de la Morinière E, Pollux BJA, Nagelkerken I & van der Velde G (2002) Post-settlement life cycle migration patterns and habitat preference of coral reef fish that use seagrass and mangrove habitats as nurseries. Estuarine, Coastal and Shelf Science 55: 309-321

  29. Nagelkerken I, Roberts CM, van der Velde G, Dorenbosch M, van Riel MC, Cocheret de la Morinière E & Nienhuis PH (2002) How important are mangroves and seagrass beds for coral-reef fish? The nursery hypothesis tested on an island scale. Marine Ecology Progress Series 244: 299-305

  30. Nagelkerken I & van der Velde G (2002) Do non-estuarine mangroves harbour higher densities of juvenile fish than adjacent shallow-water and coral reef habitats in Curaçao (Netherlands Antilles)? Marine Ecology Progress Series 245: 191-204

  31. Cocheret de la Morinière E, Pollux BJA, Nagelkerken I, Hemminga MA, Huiskes AL & van der Velde G (2003) Ontogenetic dietary changes of coral reef fishes in the mangrove-seagrass-reef continuum: stable isotopes and gut contents analysis. Marine Ecology Progress Series 246: 279-289

  32. Nagelkerken I & van der Velde G (2003) Connectivity between coastal habitats of two oceanic Caribbean islands as inferred from ontogenetic shifts by coral reef fishes. Gulf and Caribbean Research 14: 43-59

  33. Nagelkerken I, Pors LPJJ & Hoetjes P (2003) Swimming behaviour, dispersal patterns, and orientation cues in released captive-reared loggerhead turtles (Caretta caretta L.). Aquatic Ecology 37: 183-190

  34. Cocheret de la Morinière E, Pollux BJA, Nagelkerken I & van der Velde G (in press) Diet shifts of Caribbean grunts (Haemulidae) and snappers (Lutjanidae) and the relation with nursery-to-coral reef migrations. Estuarine, Coastal and Shelf Science 57: 1079-1089

  35. Cocheret de la Morinière E, Nagelkerken I, van der Meij H & van der Velde G (2004) What attracts juvenile coral reef fish to mangroves: habitat complexity or shade? Marine Biology 144: 139-145 37

  36. Dorenbosch M, van Riel MC, Nagelkerken I, van der Velde G (2004) The relationship of reef fish densities to the proximity of mangrove and seagrass nurseries. Estuarine, Coastal and Shelf Science 60: 37-48

  37. Nagelkerken I & Nagelkerken WP (2004) Loss of coral cover and biodiversity on shallow Acropora and Millepora reefs after 31 years on Curaçao, Netherlands Antilles. Bulletin of Marine Science 74: 213-223

  38. Nagelkerken I & van der Velde G (2004) Are Caribbean mangroves important feeding grounds for juvenile reef fish from adjacent seagrass beds? Marine Ecology Progress Series 274: 143-151

  39. Nagelkerken I & van der Velde G (2004) Relative importance of interlinked mangroves and seagrass beds as feeding habitats for juvenile reef fish on a Caribbean island. Marine Ecology Progress Series 274: 143-151

  40. Dorenbosch M, Verweij MC, Nagelkerken I, Jiddawi N, van der Velde G (2004) Homing and daytime tidal movements of juvenile snappers (Lutjanidae) between shallow-water nursery habitats in Zanzibar, western Indian Ocean. Environmental Biology of Fishes 70: 203-209

  41. Nagelkerken I & van der Velde G (2004) A comparison of fish communities of subtidal seagrass beds and sandy seabeds in 13 marine embayments of a Caribbean island, based on species, families, size distribution and functional groups. Journal of Sea Research 52: 127-147

  42. Nagelkerken I, Vermonden K, Moraes OCC, Debrot AO & Nagelkerken WP (2005) Changes in coral reef communities and an associated reef fish species, Cephalopholis cruentata (Lacépède), after 30 years on Curaçao (Netherlands Antilles). Hydrobiologia 549: 145-154

  43. Lugendo BR, Pronker A, Cornelissen I, de Groene A, Nagelkerken I, Dorenbosch M, van der Velde G, Mgaya YD (2005) Habitat utilisation by juveniles of commercially important fish species in a marine embayment in Zanzibar, Tanzania. Aquatic Living Resources 18: 149-158  

  44. Dorenbosch M, Grol MGG, Nagelkerken I & van der Velde G (2005) Distribution of coral reef fishes along a coral reef – seagrass gradient: edge effects and habitat segregation. Marine Ecology Progress Series 299: 277-288

  45. Dorenbosch M, Grol MGG, Christianen MJA, Nagelkerken I & van der Velde G (2005) Indo-Pacific seagrass beds and mangroves contribute to fish density and diversity on adajacent coral reefs. Marine Ecology Progress Series 302: 63-76

  46. Verweij MC, Nagelkerken I, de Graaff D, Peeters M, Bakker EJ, van der Velde G (2006) Structure, food and shade attract juvenile coral reef fish to mangrove and seagrass habitats: a field experiment. Marine Ecology Progress Series 306: 257-268

  47. Dorenbosch M, Grol MGG, Nagelkerken I & van der Velde G (2006) Seagrass beds and mangroves as potential nurseries for the threatened Indo-Pacific humphead wrasse, Cheilinus undulatus and Caribbean rainbow parrotfish, Scarus guacamaia. Biological Conservation 129: 277-282

  48. Nagelkerken I, Verberk WCEP, Dorenbosch M & van der Velde G (2006) Segregation along multiple resource axes in a tropical seagrass fish community. Marine Ecology Progress Series 308: 79-89

  49. Dahlgren CP, Kellison GT, Adams AJ, Gillanders BM, Kendall MS, Layman CA, Ley JA, Nagelkerken I, Serafy JE (2006) Marine nurseries and effective juvenile habitats: concepts and applications. Marine Ecology Progress Series 312: 291-295

  50. Dorenbosch M, Grol MGG, Nagelkerken I, van der Velde G (2006) Different surrounding landscapes may result in different fish assemblages in east African seagrass beds. Hydrobiologia 563: 45-60

  51. Dorenbosch M, Pollux BJA, Pustjens AZ, Rajagopal S, Nagelkerken I, van der Velde G & Moon-van der Staay SY (2006) Population structure of the Dory snapper, Lutjanus fulviflamma, in the western Indian Ocean revealed by means of AFLP fingerprinting. Hydrobiologia 568: 43-53

  52. Adams AJ, Dahlgren CP, Kellison GT, Kendall MS, Layman CA, Ley JA, Nagelkerken I & Serafy JE (2006) Nursery function of tropical back-reef systems. Marine Ecology Progress Series 318: 287-301

  53. Layman CA, Dahlgren CP, Kellison GT, Adams AJ, Gillanders BM, Kendall MS, Ley JA, Nagelkerken I, Serafy JE (2006) Marine nurseries and effective juvenile habitats. Marine Ecology Progress Series 318: 307-308

  54. Verweij MC, Nagelkerken I, Wartenbergh SLJ, Pen I, van der Velde G (2006) Caribbean mangroves and seagrass beds as daytime feeding habitats for juvenile French grunts, Haemulon flavolineatum. Marine Biology 149: 1291-1299

  55. Debrot AO & Nagelkerken I (2006) Recovery of the long-spined sea urchin Diadema antillarum in Curaçao (Netherlands Antilles) linked to lagoonal and wave sheltered shallow rocky habitats. Bulletin of Marine Science 79: 415-424

  56. Lugendo BR, Nagelkerken I, van der Velde G & Mgaya YD (2006) The importance of mangroves, mud and sand flats, and seagrass beds as feeding areas for juvenile fishes in Chwaka Bay, Zanzibar: gut content and stable isotope analysis. Journal of Fish Biology 69: 1639-1661

  57. Williams EH Jr, Bunkley-Williams L, Kruitwagen G & Nagelkerken I (2007) A new host and locality record: Gnathia sp. (Isopoda: Gnathiidae) on the Barred Mudskipper, Periophthalmus argentilineatus Valenciennes, 1837 (Perciformes: Gobiidae), from Tanzania. Journal of the Egyptian Society of Parasitology 37: 851-852

  58. Pollux BJA, Verberk WCEP, Dorenbosch M, Cocheret de la Morinière E, Nagelkerken I & van der Velde G (2007) Habitat selection during settlement of three Caribbean coral reef fishes: Indications for directed settlement to seagrass beds and mangroves. Limnology and Oceanography 52: 903-907

  59. Dorenbosch M, Verberk WCEP, Nagelkerken I & van der Velde G (2007) Influence of habitat configuration on connectivity between fish assemblages of Caribbean seagrass beds, mangroves and coral reefs. Marine Ecology Progress Series 334: 103-116

  60. Nagelkerken I (2007) Relationship between anthropogenic impacts and bleaching-associated tissue mortality of corals in Curaçao (Netherlands Antilles). Revista de Biologia Tropical 54 (Suppl. 3): 31-44

  61. Nugues MM & Nagelkerken I (2007) Status of aspergillosis and sea fan populations in Curaçao ten years after the 1995 Caribbean epizootic. Revista de Biologia Tropical 54 (Suppl. 3): 153-160

  62. Lugendo BR, de Groene A, Cornelissen I, Pronker A, Nagelkerken I, van der Velde G & Mgaya YD (2007) Spatial and temporal variation in fish community structure of a marine embayment in Zanzibar, Tanzania. Hydrobiologia 586: 1-16

  63. Kruitwagen G, Nagelkerken I, Lugendo BR, Pratap HB & Wendelaar Bonga SE (2007) Influence of morphology and amphibious life-style on the feeding ecology of the mudskipper Periophthalmus argentilineatus. Journal of Fish Biology 71: 39-52

  64. Lugendo BR, Nagelkerken I, Kruitwagen G, van der Velde G & Mgaya YD (2007) Relative importance of mangroves as feeding habitat for fish: a comparison between mangrove habitats with different settings. Bulletin of Marine Science 80: 497-512

  65. Nagelkerken I (2007) Are non-estuarine mangroves connected to coral reefs through fish migration? Bulletin of Marine Science 80: 595-607

  66. Verweij MC & Nagelkerken I (2007) Short and long-term movement and site fidelity of juvenile Haemulidae in back-reef habitats of a Caribbean embayment. Hydrobiologia 592: 257-27066

  67. Verweij MC, Nagelkerken I, Hol KEM, van den Beld AHJB & van der Velde G (2007) Space use of Lutjanus apodus including movement between a putative nursery and a coral reef. Bulletin of Marine Science 81: 127-138

  68. Nagelkerken I & Faunce CH (2007) Colonisation of artificial mangroves by reef fishes in a marine seascape. Estuarine, Coastal and Shelf Science 75: 417-422

  69. Lugendo BR, Nagelkerken I, Jiddawi NS, Mgaya YD & van der Velde G (2007) Fish community composition of a tropical non-estuarine embayment in Zanzibar (Tanzania). Fisheries Science 73: 1213-1223

  70. Huijbers CM, Mollee EM & Nagelkerken I (2008) Post-larval French grunts (Haemulon flavolineatum) distinguish between seagrass, mangrove and coral reef water: Implications for recognition of potential nursery habitats. Journal of Experimental Marine Biology and Ecology 357: 134-139

  71. Nagelkerken I, Blaber SJM, Bouillon S, Green P, Haywood M, Kirton LG, Meynecke J-O, Pawlik J, Penrose HM, Sasekumar A & Somerfield PJ (2008) The habitat function of mangroves for terrestrial and marine fauna: a review. Aquatic Botany 89: 155-185

  72. Huijbers CM, Grol MGG & Nagelkerken I (2008) Shallow patch reefs as alternative habitats for early juveniles of some mangrove/seagrass-associated fish species in Bermuda. Revista de Biologia Tropical 56 (Suppl. 1): 161-169

  73. Verweij MC, Nagelkerken I, Hans I, Ruseler SM & Mason PRD (2008) Seagrass nurseries contribute to coral reef fish populations. Limnology and Oceanography 53: 1540-1547

  74. Nagelkerken I & Faunce CH (2008) What makes mangroves attractive to fish? Use of artificial units to test the influence of water depth, cross-shelf location, and presence of root structure. Estuarine, Coastal and Shelf Science 79: 559-565

  75. Grol MGG, Dorenbosch M, Kokkelmans EMG & Nagelkerken I (2008) Mangroves and seagrass beds do not enhance growth of early juveniles of a coral reef fish. Marine Ecology Progress Series

    76. 366: 137-146

  76. Nagelkerken I, Bothwell J, Nemeth RS, Pitt JM & van der Velde G (2008) Interlinkage between Caribbean coral reefs and seagrass beds through feeding migrations by grunts (Haemulidae) depends on habitat accessibility. Marine Ecology Progress Series 368: 155-164

  77. Paddack MJ, Reynolds JD, Aguilar C, Appeldoorn RS, Beets J, Burkett EW, Chittaro PM, Clarke K, Esteves R, Fonseca AC, Forrester GE, Friedlander AM, García-Sais J, González-Sansón G, Jordan LKB, McClellan DB, Miller MW, Molloy PP, Mumby PJ, Nagelkerken I, Nemeth M, Navas-Camacho R, Pitt J, Polunin NVC, Reyes-Nivia MC, Robertson DR, Rodríguez-Ramírez A, Salas E, Smith SR, Spieler RE, Steele MA, Williams ID, Wormald CL, Watkinson AR & Côté IM (2009) Recent region-wide declines in Caribbean reef fish abundance. Current Biology 19: 590-595

  78. Dorenbosch M, Grol MGG, de Groene A, van der Velde G & Nagelkerken I (2009). Piscivore assemblages and predation pressure affect relative safety of some back-reef habitats for juvenile fish in a Caribbean bay. Marine Ecology Progress Series 379: 181-196

  79. Nagelkerken I, van der Velde G, Wartenbergh SLJ, Nugues MM & Pratchett MS (2009) Cryptic dietary components reduce dietary overlap among sympatric butterflyfishes (Chaetodontidae). Journal of Fish Biology 75: 1123-1143