Transcript 29 April 2008 OCN 621 – Biological Oceanography • Coral Reefs – What is a coral reef? • Habitat forming scleractinians • Different types of.

29 April 2008
OCN 621 – Biological Oceanography
• Coral Reefs
– What is a coral reef?
• Habitat forming scleractinians
• Different types of reef
– Symbiosis
– Biogeography
• Controls on Biogeography
– The value of reefs
What is a coral reef?
• “Reef”
– Feature lying beneath the surface of the water
with which a boat could get stuck on
• Typically diverse assemblage of habitat
forming scleractinians
• Mainly Shallow
– But……not always……
• Important engineers
– Biodiversity
• “Rain forests of the ocean”
• Cover less than 1/10% of ocean floor
• Habitat for 25% of all marine species
What is a coral reef?
• Scleractinians (primarily)
– Other organisms also produce calcium carbonate
structures
– Forminifera, cocolithophores, pteropods,
halimeda, red algae, soft coral spicules, sponge
spicules
• Reef structure is cemented together by
calcareous red algae or by lithification
• Organisms creating non-carbonate skeletons
– Chitin, silica, gorgonin
– Octocorals, sponges
Coral Reefs of the World
• Great Barrier Reef, Australia
– Largest coral reef in the world, 2600km
• Belize Barrier Reef
– Second largest in the world
• New Caledonia Barrier Reef
– Second longest double barrier reef – 1500km
• Andros Barrier Reef
– 3rd largest barrier reef, 167km long and 64km wide
• Red Sea Coral Reef
– Egypt & Saudi Arabia
• Pulley Ridge
– Florida, Deepest photosynthetic coral reef, 60m deep
Scleractinian morphology
• Branching
– Often fast growing
• Plate-like
– Often found in deeper environments
• Massive/lobed
– Generally slower growing, k-selected
• Encrusting
– Sometimes parasitic
Branching
Plate Like
Massive, Lobed
Encrusting
Types of Reef
• 4 Main types of reef
– Fringing, Barrier, Patch and Atoll
– Also – Apron, Bank, Ribbon & Table
• Fringing reef
– a reef that is directly attached to a shore or
borders it with an intervening shallow channel or
lagoon
– Bora Bora, French Polynesia
Bora Bora
Types of Reef
• Barrier Reef
– a reef separated from a mainland or island shore
by a deep lagoon
– Great Barrier Reef - Australia
Great Barrier Reef, Australia
Types of Reef
• Patch Reef
– an isolated, often circular reef, usually within a
lagoon or embayment
– Outer edge of each patch reef is surrounded by a
halo of sand that extends out to adjacent seagrass
beds.
– The width of this ring of sand is determined by the
distance that herbivorous fish feel is within safe
foraging range from the reef.
– Florida
Types of Reef
• Atoll Reef
– a more or less circular or continuous barrier reef
extending all the way around a lagoon without a
central island
– Midway, Hawaiian Islands
Midway
Maldives
Atoll Formation
• Island erosion
• Island sinking
• Reef accretion
Reef Zones
Spur and groove formation
Symbiosis
• Photosynthetic algal endosymbionts
– Dinoflagellates
– Algae located in gastrodermis
– Carbohydrates and lipids excreted by the algae
– Protection and nitrogenous waste provided by
host
• Other marine taxa also engage in similar
symbiosis
– Sea anemones, jellyfish, sponges, clams, forams
• Can provide up to 90% of corals energy
Symbiosis
Symbiosis
• Genus Symbiodinium
– Different species live in different corals
– Controversial
• Ingested by corals
– But not digested
• Reproduce by budding
• 3 Life Stages
– Vegatative
– Cyst
– Motile
Shallow water coral biogeography
• Warm tropical climates
– Low latitudes (30ºN to 30ºS)
– High solar insolation
– Warm water currents
• Clear shallow waters
– good light penetration
– ~30m
• low sedimentation and turbidity
– Oligotrophic waters
– nutrient poor but not exclusively
• Hard substrata
Annual Pattern of Daily Solar Insolation
Biogeography
Biogeography
• What limits shallow coral reefs?
– High latitude and depth
– Temperature, chronic low temperature stress
– Light irradiance, insufficient solar insolation
– Aragonite (CaCO3) saturation state
– Competition with temperate fauna
Kleypas, 1999, Grigg, 2006
Biogeography
• Distinct fauna between Atlantic and IndoPacific
• Lower diversity in the Atlantic
– Younger, smaller ocean basin with less thermal
capacity
– North-south mountain ranges did not impede
glacial advances during ice ages
– More extinction events
– But older coral genera ~60 mya ?
Biogeography
Indo-West
Pacific
Eastern
Pacific
Western
Atlantic &
Caribbean
Scleractinian corals
genera
species
80
719
n/a
34
28
62
16
52
Alcyonarian corals
Sponges
Bivalves
Echinoderms
Fish
Seagrasses
Mangroves
690+
244
2,000
1,200
4,000
34
59
0
6
117
378
148
1,400
9
11
4
Taxonomic Group
564
208
650
7
13
Hawaii
Modified from Spalding, M. et al. 2001
Biogeography
• Higher diversity in the Indo-Pacific
– Older ocean basin with more stability through
geological time
– Larger body of water with more thermal capacity
– East-west mountain ranges limited glacial advances
during ice ages
– But younger coral genera ~30 mya ?
• Center of diversity in the Indo-Australian
Archipelago (IAA)
– Diversity gradient as radial distance from center
increases
Biogeography
Veron, 1995
Reef $$ Value
• Found in over 100 countries
– Over 500 million people worldwide rely on coral reefs
• Major source of food
– Poorer countries
– Fish and invertebrates
• Conch, bivalves, octopus, squid….
• Food for pelagic fish species
• Limestone
– Building materials, breakwaters, cement
• Jewelry
• Aquarium trade
• Tourists
– $6-10billion US tourist industry
• Beach protection
– Wave breaks
Conclusions
• Majority of coral reefs are shallow, warm
tropical, made from carbonate accreting
species
• Majority have photosynthetic algae
• A reef can be in many different forms
• Limited in latitude and depth
• Higher diversity in the Indo Pacific
• Reefs are worth $$s