Coral reef ecosystems Coral reefs What are corals, what are reefs? Ecology Human stresses History of climate and human stresses Why are reefs important? Biodiversity Shoreline protection Nurse juvenile fish and other valuable food species Tourism Coastal ecosystems and ecosystem services Ecosystem services = services (not goods, resources) provided by an ecosystem Can be evaluated in monetary terms Coastal ecosystems are disproportionately valuable (Costanza et al. 1997) 6% of world area, 43% of ecosystem value Services include: Nutrient cycling Water storage and purification Recreation Coastal protection Fish nurseries 1
Reef ecosystem services (!!! '!!! &!!! %!!! $!!! #!!! "!!!! Coral Reefs Tropical Forests Temperate Forests What is a reef? a resistant structure that produces a relatively shallow area in the ocean generally made by an organism, but artificial reefs can also provide space for organisms and protect coastlines. Modern ocean: corals provide most of the framework; other organisms (calcifying algae, bivalves, etc.) contribute Average Global Value of Ecosystem Services ($/HA/YR), from Costanza et al.; figure from http://www.wri.org/wri/ reefsatrisk The latest in artificial reefs Eternal Reefs - an environmental legacy for your loved one s remains! Who else contributes to building reefs? Calcifying algae O6en the dominant producer of calcium carbonate! THE dominant reefbuilders in earliest geologic times Sponges Mollusks: Bivalves - especially in earlier geologic periods Gastropods Photo credits http://www.coralreefnetwork.com/stender /diving/japan/yawatano.htm http://www.huronscuba.com/travel/domin ica_photos.htm http://www.richardseaman.com/underwater/australia/giant Clams/ 2
Where are reefs found? In ocean waters that are: Shallow Warm (tropical) Nutrient-poor Clear (low sediment) Normal salinity http://wri.igc.org/reefsatrisk/ phylum Cnidaria Calcium carbonate skeleton (massive or branching) Some live in deep water, but the reefbuilders are only found in shallow waters, because Symbiotic with algae - provide nutrition and help with skeletal construction What is a coral? calcium carbonate skeleton - either massive or branching Many corals are colonial, made up of many single polyps Connected at base Feed independently (predatory! In addition to food from symbioticc algae) Sexually reproduce at the same time: mass spawning helps gametes find each other Also reproduce asexually (budding) 3
Polyps in: Polyps out: Polyps in: Polyps out: Reef-building corals have symbiotic algae Symbiosis: 2 species closely interacting in a mutually beneficial way dinoflagellate that lives in the coral tissue Photosynthesizes: corals with symbionts must live in well-lit water Coral benefit: algae change internal chemistry to aid in building a strong skeleton rapidly; also provide nutrition Algae benefit: they have a safe place to live Coral reefs and biodiversity Reefs and biodiversity Most major marine organism groups are represented on reefs! The most diverse marine habitat Nursery for juvenile fish = support fisheries Space for sessile benthic organisms Places for mobile organisms to hide Food! 4
Coral reef food web Types and development of reefs 5
Australia s Great Barrier Reef Barrier reef morphology Barrier reef, patch reefs, lagoon Atolls - sequence Reefs at risk 10% of coral reefs are damaged beyond recovery 58% are at moderate or high risk now What are the critical threats? How can we mitigate them? 6
Natural causes of reef damage: Science, 2002 Large-scale decline of coral reef ecosystems Demise of W. Antarctic Ice Sheet Shutdown of ocean s thermohaline circulation Natural predators - Acanthaster (crown of thorns starfish) Cyclones naturally damage reefs Strong El Niño events can damage corals Climate changes can alter where reefs can grow. Reefs have been remarkably resilient in the face of change in the geological history of the earth! Natural threats: predation Parrotfish Recent signs of stress Coral bleaching Fleshy algae overgrowth New and more coral diseases Loss of ecosystem diversity Coral death Crown of thorns starfish 7
Coral bleaching A response to stress by the coral organism, in which it expels its symbionts and growth slows. Coral turns white O6en linked to warmer temperatures, e.g. during El Niño events Coral can recover, if stress is short-lived Coral may die, if it never recovers symbionts or if other organisms colonize it while it is less able to defend itself. Large animals abundant Diverse, resilient ecosystem Complex physical architecture Water quality high Science, 2005 Few/no large animals Low diversity; boom and bust Rubble, seaweed, slime Water quality poor Recommendations Pandolfi et al. 2005 Science, 2003 Decline across Caribbean region Attribute to local/regional factors acting in synchrony Ecological, climatic, and anthropogenic sources 8
Local threats Mining coral material for construction Destructive fishing (using dynamite, cyanide, or nets that drag) Overfishing that alters local ecology Unregulated tourism Regional threats Coastal development Enhanced sedimentation from changing land use practices Nutrient discharges (agricultural, sewage) Toxic pollution from industry, petroleum, mining Reefs and nutrients: Reefs are found mainly in low-nutrient waters Coral reefs recycle nutrients within the ecosystem - when organisms die and decay, nutrients are rapidly reused if nutrients get high, algae overgrow corals killing them breaking down the reef structure Sedimentation 9
Global threats Climate warming Changing ocean chemistry (rising CO 2 ) Changing El Niño and other climate patterns Windblown dust Rising sea level? -4 C -2 C 0 C 2 C 4 C El Niño effect compared to other impacts Region Pre-1998 destruction Destruction in 1998 (El Niño) Arabia 2% 33% Indian Ocean 13% 46% Australia, 1% 3% Papua New Guinea South, East Asia 16% 18% Pacific Ocean 4% 5% Caribbean 21% 1% GLOBAL TOTAL 11% 16% (note that 1998 was not just an El Niño year, but the warmest year on record at that time) Global warming = tropical ocean warming Prediction of temperature change ca. 2090 (680ppm CO2) Tropical oceans warm by 1.5-2.5 C Meehl, 2005, Science Changing ocean chemistry = coral stress Modeled change in surface ocean ph in 2100 Colored lines = ph at different greenhouse emissions scenarios (550-810 ppm by 2100) (Caldeira and Wickett, 2005 JGR) Increased atmospheric CO 2 = Increased ocean CO 2 Ocean ph becomes more acidic and carbonate ions (needed for coral skeleton formation) are less available Effect on reef calcification for 2 X CO 2 : 20-40% decline (this happens regardless of any climate change caused by CO 2 ) 10
Reefs feel the impact of environmental changes that occur 1000 s of miles away! How can we gain a long-term perspective on reef health? Dust from the Sahel carries Aspergillis fungi across the Atlantic and infects Caribbean corals. A6er Shinn et al. 2000, GRL Corals preserve a record of their environment, along with annual growth bands, in their skeletons Case study: East Africa 1997-98 El Niño event Kenya Tanz. Moz. Rapid population growth Coastal development, incl. large cities and ports Subsistence livelihood depends on reef resources Tourism Sedimentation Climate variability linked to ENSO Reefs threatened! Impact of El Niño on East African reefs has intensified due to warming and land-use change 11
Sedimentation on East African reefs Ba/Ca and fluorescence indicate seasonal peaks in terrestrial runoff Intensifying land use Brighter bands = increases erosion and higher river sediment content Ba/Ca peaks A major risk factor for E. African reefs 0 20 40 60 80 100 120 140 160 180 200 Banding pattern replicates from core to core Ba/Ca * 10 5 mole rati0 0.0 1.0 2.0 Barium is high in river waters, so coral Ba reflects runoff Rise in Ba/Ca and its variance coincides with intensified cultivation and grazing under colonial rule Correlation with ENSO is significant only a6er ~1930. 1.E-05 9.E-06 8.E-06 7.E-06 6.E-06 5.E-06 4.E-06 Evidence of increased sedimentation on the reef Coral Ba/Ca Coral Ba/Ca variance Early 20th century increase 1800 1840 1880 1920 1960 2000 Year AD Great Barrier Reef, Australia: Sediment rise following colonial settlement From McCulloch et al. 2003 12
Malindi coral X-radiograph and UVfluorescence image, showing unambiguous annual banding X-radiograph UV-Fluorescence 1996 1994 1992 1990 1988 1986 1984 1982 1980-4.0-4.5-5.0 Coral d 18 O -5.5-5.0-4.9 Seychelles coral δ 18 O -4.8-4.7-4.6-4.5-4.4-4.3-4.2-4.1 Malindi coral δ 18 O Indian Ocean coral records of SST 1800 1820 1840 1860 1880 1900 1920 1940 1960 1980 2000 Year Corals use O from seawater (CO3) to build their skeletons When it is cooler, they use more of a rare isotope of O, 18 O; when its warmer, they use less of this rare form. Lower d 18 O values indicate warmer/wetter conditions, and higher values indicate cooler/drier conditions d 18 O ( ) -4.8-4.6-4.4-4.2-4.0 How have stresses on coral reefs changed? Temperature Sedimentation 1.4E-05 1.2E-05 1.0E-05 8.0E-06 6.0E-06-3.8 4.0E-06 1800 1840 1880 1920 1960 2000 Since early 20th century: enhanced sedimentation, with highest values during El Niño years Since ~1975: warmer temperatures, especially during El Niño events Ba/Ca Coral reefs in the 21 st century They face multiple interacting stresses Land use change and climate warming are exacerbating natural, formerly tolerable, stresses on reefs Parks and reserves offer no protection against these changes Costs of protecting reefs is not trivial, but the cost of losing them is likely to be even greater 13