Coral Reefs & Climate Change PDF

Global Change Science CORAL REEFS & CLIMATE CHANGE Heidi Burdett Outline ✓ What is a coral? ✓ Coral morphology ✓ Coral reef distribution ✓ Coral reef development ✓ Coral reefs aren’t just corals ✓ Threats to coral reefs ✓ The future of coral reefs Coral reefs in numbers Corals have been ar...

Global Change Science CORAL REEFS & CLIMATE CHANGE Heidi Burdett Outline ✓ What is a coral? ✓ Coral morphology ✓ Coral reef distribution ✓ Coral reef development ✓ Coral reefs aren’t just corals ✓ Threats to coral reefs ✓ The future of coral reefs Coral reefs in numbers Corals have been around for hundreds of millions of years Cover 600,000 square miles ~90,000 species found on coral reefs 25% of all fish species Half the calcium that enters the ocean ends up in reef systems The value of coral reefs Ecosystem services are worth £65 billion per year WHAT ARE THOSE SERVICES? 500 million people directly benefit from reefs 30 million people completely rely on reefs for their livelihood What is a coral? What is a coral? Coral reproduction Coral reproduction Sexually: Most broadcast spawners Many hermaphroditic (75%), some have separate sexes Some brooders Produce eggs and sperm internally to form planula larvae Coral reproduction Asexually: fragmentation Coral reproduction What do these strategies mean for connectivity? Are polyps all the same? Is one colony one organism? Hybrids are common: ‘species’ definition is blurred Coral carbonate skeleton Coral skeleton = CaCO3 as aragonite in crystalline form → WHAT IMPLICATIONS DOES THIS HAVE FOR SUSCEPTIBILITY TO ACIDIFICATION / DISSOLUTION? Process of calcification releases CO2 → ARE CORALS A NET SOURCE OR SINK OF CARBON?  Coral taxonomy Kingdom: Animalia Phylum: Cnidaria Class: Anthozoa Subclasses Alcyonaria (Octocorals) Zoantharia/Hexacorallia Alcyonacea Antipatharia Zoanthidea Helioporacea Corallimorpharia Scleractinia Coral morphology Corals have a varied morphology This determines their resilience to environmental conditions (e.g. wave action) Different morphologies suit different parts of the reef Can be a critical part of their life-history strategy Acropora spp. Table coral  Brain coral: Colpophyllia sp. Massive coral Staghorn coral: Acropora cervicornis Branching coral Fire coral: Millepora sp. Blade-like coral Pavona clavus Columnar coral Orbicella sp. Astreopora randalli Plate-like and foliose coral  x Fungia sp. Porities lutea Free-living corals The making of reefs Not all corals can create reefs Hermatypic corals: reef-building and contain zooxanthellae Ahermatypic corals: NOT reef-building and tend not to contain zooxanthellae Tropical coral reefs Reef structure extensive Fast growth rates Up to 1 cm per month Support diverse & productive communities Centennial-scale climate archives Under threat from human disturbance Limited distribution of tropical coral reefs Source: NOAA WHY? Reef distribution Reef structure Reefs occur in different sizes and shapes due partly to Hydrological conditions Geological conditions Can be grouped into 4 general categories Atolls Barrier reefs Fringing reefs Patch reefs / coral bommies Atolls Darwin’s subsidence theory First suggested by Charles Darwin following his Beagle voyage 1831-1836 http://www.oceanservice.noaa.gov/education/kits/corals/media/supp_coral04a.html Darwin’s subsidence theory Deep sea volcano erupts ↓ Volcanic island ↓ Fringing reef develops ↓ Land subsides ↓ Barrier reef ↓ Inner reef heavily sedimented ↓ Atoll Barrier and fringing reefs Barrier / fringing reefs Atolls are very old structures, e.g. Enewetok Atoll is 60 million years old Fringing/Barrier reefs are much younger, generally