Koseff - 1 February 6, 2009 Turbulent Times in our Coral Reef Systems Jeffrey R. Koseff Environmental Fluid Mechanics Laboratory, Stanford University Functioning of coral reefs • Coral reefs are comparable to terrestrial rain forests in terms of productivity and their immense diversity. • One of the most important geological and biological functions in the growth of coral reef ecosystems is the sedimentation and accretion of calcium carbonate (CaCO3). • The estimated annual global reef production of CaCO3 represents 11% of all marine carbonate production despite the fact that coral communities comprise <0.2% of the seafloor! Importance of corals and coral reefs • Corals remove and recycle carbon dioxide. Excessive amounts of CO2 contribute to global warming. • Reefs shelter land from harsh ocean storms and floods. • Reefs provide resources for fisheries. Food items include fishes, crustaceans, and molluscs. • Coral reefs attract millions of tourists every year. • The coral reef is an intricate ecosystem and contains a diverse collection of organisms. Without the reef, these organisms would die. • Evidence suggests that the coral reef could potentially provide important medicines, including anti-cancer drugs and a compound that blocks ultraviolet rays. • Coral skeletons are used as bone substitutes in reconstructive bone surgery. The pores and channels in certain corals resemble those found in human bone. Bone tissue and blood vessels gradually spread into the coral graft. Eventually, bone replaces most of the coral implant. • The coral reef provides a living laboratory. Both students and scientists can study the interrelationships of organisms and their environment. Threats to coral reef ecosystems Recent evidence indicates that coral reefs are deteriorating worldwide, and as much as 58% are in crisis. Symptoms include: • loss of hard corals • increased abundance of algae, and • a dramatic increase in bleaching episodes and disease outbreaks. Scientists and managers still lack critical information about the causes, but evidence suggests a variety of human forces: • population increases • shoreline development • increased sediments in the water • trampling by tourists and divers • ship groundings, pollution, overfishing • fishing with poisons and explosives that destroy coral habitat. Eutrophication Issue • Deteriorating water clarity • Lost diversity of corals (50%) • Decrease in coral cover (50%) • Low rates of larval settlement and recruitment • Decreased rates of reef calcification • Competition with macro-algae Coral Reef Paradox • light availability is paramountKoseff - 2 February 6, 2009 • therefore, productive reefs found in clear, oligotrophic waters (clarity enhanced by nutrient limitation) • despite this limitation coral reefs are extremely productive ecosystems The The ““Paradox of the ReefParadox of the Reef””::““BlueBlue”” OligotrophicOligotrophicwaters offshorewaters offshorevs.vs.Rich, Productive reef““leakageleakage””of N,Pof N,P2.5 mmolN m-2d-1ReefReefflatflatGPP:GPP:~ 0.5 ~ 0.5 gCgCmm--22dd--11GPP:GPP:55--10 10 gCgC mm--22dd--11 The Hetrotrophic Pathway Hypothesis • Nutrients are supplied via grazing and predation of plankton by reef heterotrophs. • Key links are fish predation on zooplankton and invertebrate grazing on phytoplankton • Nutrients excreted by these heterotrophs fertilize the reef and balance the “leakage” The Pacific Ocean 2020 Challenge: Rescuing an Ocean in Crisis Center for Ocean Solutions (http://www.centerforoceansolutions.org/) - Scientific Consensus Statement “The people from around the Pacific Ocean, from the Arctic to Antarctic, from countries populous and sparse, are witnessing a decline of the Pacific Ocean’s vast resources and in the ability of people to use those resources. Pollutants, nutrient and sediment run-off from land, overfishing, habitat destruction, and climate change emerge repeatedly as the major causes. Though this wide-spread similarity of threats across the Pacific Ocean is alarming, it also provides the opportunity to craft solutions that target pan-Pacific problems and therefore provide hope to hundreds of millions of people who rely on the Pacific Ocean and its ecosystems.” Control Volume ApproachControl Volume Approach––Experimental SetupExperimental SetupKoseff - 3 February 6, 2009 Ocean Acidification • Anthropogenic CO2 release has already caused the pH of the surface waters in the Atlantic and Pacific to fall from 8.2 to 8.1, and they will reach 7.8 by the end of the century. • Locally, effects will be intensified by climate-induced changes in ocean circulation. • The rate at which it is occurring is ~50 times greater than the rate of CO2 change associated with glaciation-deglaciation. • Natural buffering mechanisms that worked in the past don’t operate at those rates. CO2 (air) <=> CO2 (aq) atmosphere/ocean exchange Precipitation/Dissolution equation: CaCO3 + CO2 + H2O <=> Ca++ + 2HCO3- • Decreasing pH pushes reaction  (to the right) causing dissolution • Rising ocean pCO2 decreases ocean pH - “acidification” - causing carbonates to dissolve Two Key Questions for Coral Reefs in an Acidifying, Warming Ocean • What are the fluxes of Carbon across the benthos, within the reef system, and from land, atmosphere or the open ocean? • How will these Carbon fluxes, and consequently the reef respond to rising temperatures and ocean acidities?Koseff - 4 February 6, 2009 PLIF ImagingTest Section:3m by 0.6mLaserScanning MirrorImaging Window30 Hz Camera1024 x 1024 pixel Constant Head Tank9 mLight SheetWavemakerPumpFlowCoral Test SectionStudying Coral in the Laboratory Ocean creatures find the reef use sense of smell to find the reef. The dye enhanced image developed in a laboratory experiment to visualize odorant coming off the reef. Dye simulates movement of the “reef smell” that fish, fish larvaie and other sea organisms use to find the reef. Image Scale:17 cm tall by 22 cm wide1 pixel = 0.05