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Coral Reef Ecosystems. Coral biology Reproduction: sexual and asexual Production and symbiosis Reef formation and habitats Factors affecting coral reef distribution Physical Zoogeographic Corals and sponges as biodiversity and habitat Diversity in fishes Reproduction and larval dispersal
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Coral Reef Ecosystems • Coral biology • Reproduction: sexual and asexual • Production and symbiosis • Reef formation and habitats • Factors affecting coral reef distribution • Physical • Zoogeographic • Corals and sponges as biodiversity and habitat • Diversity in fishes • Reproduction and larval dispersal • Diel activity rhythms and migrations
Basic biology of corals • Corals are cnidarians in the class Anthozoa (including anemones and gorgonians); other classes are Scyphozoa (jellyfish) and Hydrozoa (hydroids, fire coral, etc.) • May be colonial or solitary, reef-building (hermatypic) or non-reef building • Most hermatypic corals are colonial but some (e.g., mushroom coral) are not • Reproduce asexually (by budding)and sexually • Sexual reproduction: can be hermaphroditic or dioecious. Sperm are released into the water, taken in by polyps, fertilization occurs in the female’s gastrovascular cavity, and planula larvae are released, often synchronously.
Symbiosis • The coral animal lives symbiotically with zooxanthellae: dinoflagellates. Coral polyps feed at night on plankton but meet only a fraction of their nutritional requirements. Zooxanthellae provide the balance of the coral’s nutrition by photosynthesis and transfer to the coral. Corals kept in the dark feed but do not grow whereas those not fed but in the light can grow. Tropical marine waters are very unproductive (18-50 g C/m /yr) but the reefs can be very productive because the primary production is linked to the coral. 2
Physical Factors Affecting Hermatypic (reef-building) coral • Temperature: ~ 18-30 • Depth: Light needed for symbiotic algae < 25 m (some to 70 m) • Salinity ~ 32-35 ppt (to 42 in Persian Gulf) • Sediment: smother coral and block light • Wave-action: oxygenates, supplies plankton, removes sediment • Air: prolonged exposure kills coral
Global distribution of corals Tropic of Cancer 23.5 o N Tropic of Capricorn 23.5oS Coral zone
Global diversity of reef building coral species Number of Species 300 200 100 50 10
Coral Biology Reproduction Feeding
Coral Reef Habitats 1 • Supratidal pools • Intertidal pools • Grass beds • Patch reefs • Back reef flats, channels • Reef crest – breaker zone • Buttress zone • Fore-reefs • Drop-off 2 6 4 3 5 7 8 9 Micro-habitats: Coral , sponges Temporal Structure: Day-Night Larval Dispersal – Recruitment
In addition to corals, sponges constitute both a major part of the biodiversity of coral reef systems but they also join with corals to provide much of the three-dimensional structure in reefs. As such they provide critical habitat for many fish and invertebrate species. Brittle star on an azure vase sponge
Families of Coral Reef Fishes Labridae - Wrasses Chaetodontidae - Butterflyfishes Scaridae - Parrotfishes Carcharhinidae
Families of Coral Reef Fishes Muraenidae Lutjanidae Carangidae Pomadasyidae Serranidae Aulostomidae
Families of Coral Reef Fishes Balistidae – Triggerfishes and Filefishes Acanthuridae Acanthuridae
Families of Coral Reef Fishes Pomacentridae - Damselfishes Diodontidae - Porcupinefishes Tetraodontidae - Puffers Ostraciontidae - Boxfishes
Reproduction and larval dispersal Bluehead wrasse Many coral reef fishes are sequential (often protogynous rather than protandrous) or even simultaneous hermaphrodites. In addition to this consideration, species may broadcast planktonic eggs or deposit them in nests. The dispersal patterns are important for recruitment. Nassau grouper
Coral Reef Ecosystems Larvae from pelagic eggs Larvae from non-pelagic eggs Relative abundance (%) 0 20 40 60 80 100 Bay channel 0-5 5-2 2-8 10-12 12 km Distance from Hawaiian Island of Oahu Leis in Sale (ed.) 1991
Coral Microhabitat Day Night
Coral Microhabitat Day Night
