29 April 2008 OCN 621 Biological Oceanography Coral
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, 2600 km • Belize Barrier Reef – Second largest in the world • New Caledonia Barrier Reef – Second longest double barrier reef – 1500 km • Andros Barrier Reef – 3 rd largest barrier reef, 167 km long and 64 km wide • Red Sea Coral Reef – Egypt & Saudi Arabia • Pulley Ridge – Florida, Deepest photosynthetic coral reef, 60 m 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, French Polynesia
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 – ~30 m • 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 (Ca. CO 3) saturation state – Competition with temperate fauna Kleypas, 1999, Grigg, 2006
Biogeography • Distinct fauna between Atlantic and Indo. Pacific • 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 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 $$ Value • Found in over 100 countries – Over 500 million people worldwide rely on coral reefs • Major source of food – Poorer countries – Fish and invertebrates • Conch, bivalves, octopus, squid…. • Food for pelagic fish species • Limestone – Building materials, breakwaters, cement • Jewelry • Aquarium trade • Tourists – $6 -10 billion US tourist industry • Beach protection – Wave breaks
Conclusions • Majority of coral reefs are shallow, warm tropical, made from carbonate accreting species • Majority have photosynthetic algae • A reef can be in many different forms • Limited in latitude and depth • Higher diversity in the Indo Pacific • Reefs are worth $$s
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