Coral Reef Fishes

What is a ‘coral reef’? Coral Reef Fishes I. • complex structures formed by reef-building corals, algae, mollusks, and sponges Introduction to coral reefs II. Characteristics of coral reef fishes III. Maintenance of diversity • result from a balance between constructive and destructive processes • external framework provides habitat, refuge from predators, and food • distribution is limited by light, temperature, and hard substrate for initial colonization (between 30o N and 30o S latitude) Physical structure of coral skeletons (cracks and crevices) provides refuge from predators Distribution Diversity of corals and fishes highest in central Indo-Pacific • worldwide in tropical seas • lower abundance on western margins continents, where upwelling occurs (cooler & murkier) www.noaa.gov 1 Reef Zones Coral Morphology – variety of colony skeletal structures • reef flat (& lagoon) • reef crest • reef slope Primary Productivity is very high on coral reefs Production (kg Carbon per m2 per year) Average Oceanic areas Rainforest Kelp forest Coral Reef 0.1 kg 2 kg 2 kg 1.5-5 kg • ocean waters where coral occur are very nutrient poor (“oligotrophic”) Dynamics: coral reefs change over time 1. Physical disturbances • storms hurricanes, cyclones (affect fast-growing branching corals most) • sedimentation • heating (coral bleaching) 2. Biological disturbances • disease • predation • high productivity possible because of tight recycling of nutrients, photosynthetic fixation of carbon (by corals and algae) and nitrogen (by blue-green algae) II. Coral reef fishes A. Taxonomy: dominated by perciforms Summary of coral reef attributes • high structural complexity provides habitats for fishes • high productivity provides food • many different habitat types (e.g., zones) • dynamic (though not as much as kelp forests!) • in Micronesia, for example, 51 of 103 Families are Perciforms • 17 of the 20 most speciose families Perciforms B. Morphology (general characteristics): Generally: • laterally compressed • physoclistous swim bladders • highly modified jaw and pharyngeal apparatus (provides powerful and efficient feeding mechanisms) • pectoral fin locomotion common (MPF rowing) but very high morphological diversity (though dominated by families with small species) C. Diversity: extremely high • approximately 1/3rd to 1/2 of all fishes live on coral reefs (i.e., 10,000+ species) 2 D. Vision especially important (apparent in diversity of coloration) E. strong Habitat Associations F. Life-history characteristics Major Families of Coral Reef Fishes • mostly egg layers (oviparous) -- broadcast or demersal spawners • 95%+ have pelagic larval stage & sedentary adult stage (bipartite life cycle) 1. The Labroids • many species associate with particular features of the reef • may remain tightly associated with particular site for entire life 1. The Labroids a. Labridae (wrasses) 2. Pomacentridae (damselfishes) a. Labridae (wrasses) b. Scaridae (parrotfishes) 3 3. The Acanthuroids (mostly herbivores) a. Acanthuridae (surgeonfishes) 3. The Acanthuroids a. Acanthuridae b. Siganidae (rabbitfishes ) -- Indo-Pacific only 3. The Acanthuroids a. Acanthuridae 4. The Chaetodontoids a. Chaetodontidae (butterflyfishes) b. Siganidae c. Zanclidae (moorish idol) -- Indo-Pacific only 4. The Chaetodontoids 5. Haemulidae (Grunts) a. Chaetodontidae b. Pomacanthidae (angelfishes) 4 6. Gobiidae (gobies) 7. Blenniidae (blennies) 8. Synodontidae (lizardfishes) 9. Mullidae (goatfishes) Nocturnal Families Nocturnal Families 1. Apogonidae (cardinalfishes) 1. Apogonidae 2. Holocentridae (squirrelfishes) 5 Nocturnal Families The highly evolved: 1. Apogonidae 1. Ostraciidae (boxfishes) 2. Holocentridae 3. Muraenidae (moray eels) The highly evolved: The highly evolved: 1. Ostraciidae 1. Ostraciidae 2. Tetraodontidae (pufferfishes) 2. Tetraodontidae 3. Diodontidae (pocupinefishes) 3. Diodontidae 4. Balistidae (triggerfish) The large predators: The large predators: 1. Serranidae (groupers) 1. Serranidae 2. Lutjanidae (snappers) 6 The large predators: The large predators: 1. Serranidae 1. Serranidae 2. Lutjanidae 2. Lutjanidae 3. Lethrinidae (emperors) 3. Lethrinidae 4. Carangidae (jacks) Hypotheses to explain high diversity: III. Diversity -- What allows so many species to coexist without some being outcompeted? (e.g., thousands of species on Philippine reefs) A. Resource partitioning • reef fishes have obvious trophic specializations: specialized feeding behavior, territoriality (may be defense of food), and modified mouths • basic ecological theory: species that share resources should compete and eventually a competitive dominant excludes all other species, causing low species diversity Hypotheses to explain high diversity: A. Resource partitioning • reef fishes have obvious trophic specializations: specialized feeding behavior, territoriality (may be defense of food), and modified mouths • but is there evidence of current competition? – most species have overlapping resource use – experimental studies give mixed results B. Does predation keep fish populations below carrying capacity? • evidence that predation is potent force affecting reef assemblages: – high abundance of piscivores; tremendous losses in many fishes just after settlement – defensive structures, colors, & toxins – behavioral defenses: schooling, twilight changeover behavior 7 C. Is settlement of larvae too low to reach carrying capacity (Recruitment limitation hypothesis) Summary of evidence for mechanisms that allow species coexistence in high diversity coral reef fish communities Evidence: • removal of adults does not increase recruitment rate • after total removal of adults, can take several years to return to original numbers Competition may not cause competitive exclusion because… • species use resources in different ways • predators keep densities low • limited return of planktonic larvae to reef keeps densities low • recruitment pulses are sporadic & unrelated to reproductive output 8