Coral Reefs – What is a coral reef? Habitat forming scleractinians Different types of reef – Symbiosis – Biogeography Controls on Biogeography – The value of reefs 29 April 2008 OCN 621 – Biological Oceanography

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

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 What is a coral reef?

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 – 3 rd 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

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

Island erosion Island sinking Reef accretion Atoll Formation

Spur and groove formation Reef Zones

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

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

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 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 ?

Modified from Spalding, M. et al 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

Veron, 1995 Biogeography

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