SIO final study guide
Ocean acidification and corals
-Natural uptake of carbon is non-uniform (depends mostly on vertical mixing go nthe ocean). Therefore the timescale of influence will vary for diff specific regions -Actual mechanism by which ocean pH influences calcification is unknown -Relative vulnerability of various reef taxa is not well understood on a detailed lvl, and, for this and other reasons, community responses cannot be predicted with confidence -Corals that depend on higher concentrations of carbonate ion in seawater for calcification will grow more slowly. Thus, any recovery from disturbance will be much more difficult for coral sin an ocean that is lower in pH -CCA calcification slows greatly in low pH media
Ways Ca2+ can get into calcifying fluid
1. transport of specific ions through cell gaps 2. wholesale leak of seawater** 3. enzymatic pumping of calcium across membrane 4. combination of transport of specific ions through cell gaps AND enzymatic pumping of calcium across membrane.
Coral bleaching history
1998- huge underwater heatwave killed 16% of the coral on reefs around the world. Triggered by El Nino of that year Second global bleaching event that struck was triggered by the El Nino of 2010 NOAA announced the third global bleaching event in October 2015 and is still continuing in some locations today- largest scale mortality ever documented
Nutrient pollution
Addition of nitrogen or phosphorus to reef waters. Oligotrophic systems- Excess nutrients fertilize reef algae Algal blooms happen when algae outcompetes coral Case study: Kane'ohe Bay Oahu: dumped sewage in the 70s, and green algae overgrew corals and cased phase shift. First large-scale evidence of the effects of nutrient addition on coral reefs.
Sedimentation
Addition of terrestrial soil to reef systems -clearing of forests -dredging of channels -channelizing streams -building over estuaries Impacts: smothering coral, reduced light penetration, overall stress, may also bring pollutants Coral stress reduces competitive ability with algae
Calcitic vs aragonitic in the past
Aragonitic: high-Mg calcite: corals and CCA Calcitic: sponges and bivalves win
Adaptive bleaching hypothesis
Bleaching might be adaptive. Some evidence that corlas adjust the symbiont density to keep ROS (reactive oxygen species) below damaging levels. ROS are produced in excess when photosystem 2 is damaged "Shuffling" symbionts (to dominance of one vs another) has been observed in transplant experiments. Not known how common this is in reefs.
What macro- and micro-scale processes govern the availability of carbonate?
Balance between photosynthesis/respiration and calcification. -Photosynthesis drives pH of closed system towards being more basic by removing acid form of DIC. -Respiration of organic material returns acid CO2 to the system, driving the pH down. -Building of calcium carbonate skeleton removes carbonate ion from solution, driving ambient water (remaining water) towards lower pH.
Isotopic tracers in corals tell us about pH
Boron isotopic ratio in the skeletons is a measure of pH of the calcifying fluid. Fixed ratio of boron in seawater. Corals only incorporate charged boron into their skeletons. Measurement of boron isotopes in corals might give a record of changing pH of seawater.
Ocean acidification and corals
Burning of fossil fuels loads atmosphere and ocean with carbon Ocean ultimates takes up extra carbon load, through acid-base rxn Ocean uptake alters pH of the ocean, because the carbonate ion is reduced in the neutralization of acid fossil fuel CO2 Corals (calcifiers in general) that depend on higher concentrations of carbonate ion in seawater for calcification will grow more slowly Thus, any recovery from disturbance will be much more difficult for corals in an ocean w/ lower pH
Why are different minerals of CaCO3 precipitated by reef organisms? How does this affect vulnerability?
CCA uses more magnesium than corals do. They have different crystal structures that are more susceptible to dissolution in seawater. Why: The chemistry of seawater has changed and different organisms have evolved different capabilities to deal with the dissolved ion concentrations
Review of Benthic functional groups:
CCA: active reef builders, stabilize habitats. Some species facilitate coral settlement. Grow slowly, enhanced by grazing activity, release little DOC; limited microbial interactions. Turf Algae: Mixed cyanobacteria and filamentous algae. Prevent coral recruitment and grow rapidly. Trap sediments, increase in the absence of herbivory, release large amounts of DOC; enhance microbial activity. Allelopathy? Macroalgae: Highly diverse group of larger seaweeds, some calcified. Highly variable roles and effects on corals; shading, abrasion, overgrowth. Some release large amounts of DOC, some enhance microbial activity. Some allelopathic and some benign.
If the surface ocean is supersaturated with respect to aragonite and calcite, then why do the corals need to elevate the pH of their calcifying fluid and why do they need to pump protons at all?
Calcitic vs aragonitic seas: different relative availability of both Calcium and carbonate. Aragonite is open architecture crystal and it is made by certain classes of organisms in reef environment (like corlas). Once the structures are precipitated, the solubility of calcium carbonate is different depending on the mineralogy. Some forms of high Mg calcite (CCA precipitate) is really susceptible to dissolution in lower pH (lower carbonate ion) levels. Mg is a proxy for pH Humans driving chemistry towards calcitic organisms- though not high magnesium calcite like CCA
How is the intracellular pH elevated to sufficient extent to allow skeletal formation?
Calcium pump takes in calcium ions and puts it into the ECF, pumping hydrogen out in the process and lowering the pH of the ECF.
Phase shifts
Can be the result of coral death where algae simply settle on dead coral (removal of competition btwn coral and algae)- global or regional scales OR The algae may actually outcompete and kill coral as a result of overgrowth, shading and smothering, etc (factors that increase the competitive ability of algae)- local scales
Carbonate levels per depth
Carbonate is high at the surface, low at depth This is because respiration-derived CO2 increases with depth However, the surface of the ocean has less total carbon because photosynthesizers take it up
How does the ocean maintain charge balance?
Carbonic acid is the main weak acid in the ocean, and in general the dissolution and speciation of dissolved inorganic carbon in the ocean reacts in a way to maintain charge balance. Dissolved CO2 (carbonic acid) > Bicarbonate (high sevens, low 8s)> carbonate is higher pH -Photosynthesis drives pH of closed system towards being more basic by removing acid form of DIC. -Respiration of organic material returns acid CO2 to the system, driving the pH down. -Building of calcium carbonate skeleton removes carbonate ion from solution, driving ambient water (remaining water) towards lower pH.
Human impacts on coral reefs
Competition, facilitation, predation -Disease- not completely sure what link is, but increased frequency of disease over last decade -Storm damage- Increasing frequency of storms over time associated with warmer climate
Benthic community structure across central pacific
Coral and macro algae only account for 19-55% of benthos: what occupies the rest? Can other members of the benthos provide insight into the relative health or degradation of coral reefs? Reefs with people are dominated by fleshy algae, but uninhabited islands are dominated by reef builders
Production and burial of Calcium Carbonate in diff environments:
Coral reefs- lots of calcium carbonate goes through the system, and lots is produced and accumulated. Banks- A decent amount goes through the system, and some is produces with less accumulation Non carbonate shelves- Little goes through the system, little accumulates. Carbonate shelves/halimeda- Little goes through the system, but some is produced Deep sea- little goes through the system, but lot is accumulated. Takewaway: reef and open ocean CaCO3 burial are roughly comparable.
Overall balance of carbon in the world
Corals play an important role in determining the overall balance of carbon in the atmosphere. A more basic ocean draws carbonic acid from the atmosphere. **GRAPH: When there is more calcium carbonate input than burial, the ocean becomes more basic When there is more calcium carbonate burial than input, the ocean becomes more acidic. From the alkalinity and dissolved inorganic carbon, we can estimate the surface water pressure.
Other extreme climate events
Cyclone: forms where ocean water is warmest Hurricane: tied to the distribution of warm water and atmospheric convection (El Nino). When storm's latent heat is focused over a large area, like in El Nino, hurricanes can't intensify.
pH on reefs varies daily
Day time: pH increases Photosynthesis releases O2 and uses CO2 Decreases in night.
Omega
Degree of supersaturation {Ca2+][CO3-2]in situ/[Ca2+][CO3-2]saturation Crossover point from supersaturation to undersaturation- omega goes to values <1
Destructive vs Standard fishing practices
Destructive: physically destroys habitat, kills coral, reduces three-dimensionality, impacts all organisms in system, leads to system collapse Standard: Removal of one or more key groups of fish, effects on coral reef ecosystem will depend on the trophic level and degree of fishing Direct: reduced abundance of fish Indirect: may lose entire trophic levels
How corals can survive bleaching
Diff clades of zooxanthellae Clade D Symbiodinium are more thermally tolerant and increase the resistance of corals that harbor them to elevated temps - not as efficient at translocating energy to corals -symbiont switching Corals can feed w/o zooxanthellae
Overfishing
Excessive removal of organisms from a reef for human consumption/use Can directly kill coral and destroy habitat- direct effects -dynamite fishing, cyanide, muro-ami -more yeild Can simply remove organisms from reef- indirect effects
How do ions make it to the calcifying fluid?
For Calcium: leak of seawater. This makes corals especially vulnerable to seawater chemistry changes. The calcium pump serves to modify what leaks in. For Carbon: This is more complicated because dissolved inorganic carbon (DIC) consists of several species, whose abundance is tied to pH. No carbonate cross-membrane transporter, so the carbonate comes from the seawater leak and carbonic acid that is then changed to bicarbonate in a chemical process using the enzymes -carbonic anhydrase (converts CO2 to HCO3) -and Ca ATPase (facilitates Calcium exchange and alters pH gradient)
MPA types (marine protected area)
Fully protected no take of any kind Partially protected= seasonal closures, gear restrictions, or species specific closures Goals are to protect what is there, and recover what is lost (depending on damage done)
Reef development in context of relative sea level rise or fall:
Give-up: stays where it is even when sea level rises Catch-up: sea level rises and reef slowly grows on itself Keep-up: sea level rises and reef rises with it Back-step: new reef grows closer to shore
Most significant threats on global scales?
Global warming Ocean acidification Storm damage Disease
Future warming and coral reefs
Greenhouse gas-related warming can be expected to raise the avg temperature of the tropical oceans. Extremes in temperature may increase with increasing average temperature. Therefore, corals that are less adaptable to temperature stress are severely jeopardized. Observed coral bleaching temperature thresholds vary from place to place, and seem to dep
Predicting ENSO (el nino/southern oscillation)
Hard because the interaction between the fluctuations in the ocean and atmosphere involves a lot of diff variables, and most climate models don't do a good job of simulating a full El Nino cycle. Coral records suggest that ENSO strength varied considerably over the last 7k years with no real systematic pattern (except the late 20th century is relatively strong).
Herbivores
Help corals because they keep down algal levels Types: Scrapers Browsers Grazers Territorial damselfish Significant effect of human activity on fish populations. Herbivores are being taken out of the water, except for damselfish, which increase in population because they compete with parrotfish and other herbivores that are more tasty. They also suck because they increase algal levels because of farming.
Schematic of calcification mechanism in corals
In calicoblastic cell, the cell membrane is impervious to passive ionic transport. Calcium cations are pumped into the ECF, and Hydrogen is pumped out, setting up a pH gradient between the calcifying region and the cell/surrounding seawater. The pH is higher in the ECF than the rest of the cell. Carbon enters the ECF via diffusion from the surrounding seawater. Carbonic anhydrase, if present in ECF, catalyzes the hydration of CO2. Sea water DIC leak is the main source of calcium in the ECF despite the calcium pump. The calcium pump acts to modify the pH of the seawater in the ECF. Temperature dependent: CaATPase pump, chemical formation of CaCO3 Carbonate turning in to calcium carbonate is pH dependent. Won't work if too acidic, because the carbonate turns into bicarbonate. Possible solution to ocean acidification: CaATPase pump must run faster than the seawater leak.
Why didn't diversity seem to matter so much for success of reef building in the face of substantial climate change?
In the past, natural disturbances were different than human caused ones today. These didn't affect them as much as human disturbances, and now we need more diversity
Last 65 years of El Nino/ Southern Oscillation:
Intensity has waxed and waned over the last few decades. Don't know why. Not quite increasing...
Invasive species
Introduced intentionally: aquaculture, research, etc Accidental introduction: aquarium, hull fouling, spills, etc. Why problematic: Alter tropic dynamics and habitat What can we do about them? -Eradication, control, management, nothing -cost of keeping vs cost of eradication EX: Lionfish in caribbean -liberated into Biscayne Bay when a beach-side aquarium broke during Hurricane Andrew in August 1992 -voracious predators -eat juvenile fish and lobster Solution: develop market? Ex: Algae Can alter habitat, are ecosystem engineers
What are the basic energetics of the process of calcification?
Ion pumping process requires ATP supplied by zooxanthellae
Temperature and reef building
Little evidence to suggest temperature is a primary control on reef-building. Reefs have survived extremes of higher and lower tropical temperatures in the past. This means that: temperature changes were not significant enough temperature changes were mostly in the cold direction reef communities were not permanently sensitive to ice age climate variability or the disturbances were gradual enough to allow adaptation
Tourism and trampling
Many people don't realize corals are alive and trample them, which causes mortality Preventable with education
What can reefs tell us about the environment?
Mass- carbon cycle Changes in zonation- sea level Skeletal chemistry- temperature, salinity, nutrients, pH Chronological info- rates of change
Ice caps
Melt catastrophically, not in a smooth trend.
Normal state of the pacific vs el nino
More frequent or intense el ninos increase the thermal stress for reefs across the tropics, but especially in the central Pacific. Greater than normal temps for 4-5 months.
El Nino and bleaching on Fanning Island
No evidence for widespread bleaching associated with the big El Nino warm events in late 19th and early 20th century, but widespread bleaching during the warm years after 1975
Why is reef migration not an option?
No significant shallow water space available in higher latitudes Strong seasonal cycle of light availability in higher latitudes Cooler waters are almost invariably lower in pH
GBR bleaching
Northern sector of Great Barrier reef did worst: <1% not bleached, 81% severely bleached - was less impacted by other human impacts previously, which is scary because it negates the theory that places less impacted by humans should do better in the face of global warming
Degree days
Number of days that temperature is above average x the temperature anomaly for each day Ex: if the temp is 1 degree C above avg for 30 days, then the Degree Days are 30 x 1 = 30
Pollution
Nutrient pollution: sewage, fertilizer, and landscaping Sedimentation: runoff from land. Greater impacts with deforestation, stream channelization, removal of estuaries
Ocean acidification
Occurs when CO2 in atmosphere is absorbed into and reacts with era water to create carbonic acid Ocean acidity has already increased by 30% What is the natural variability of ocean pH? Need to monitor this continuously. pH more constant in deep reef because of currents, but shallow reef terraces show more variability and are more in danger Corals (aragonite) vs CCA (high magnesium calcite- more susceptible to OA) Adding CO2 reduces growth of calcified species, but can help fleshy species.
trade-off btwn reef Calcium Carbonate deposition and open ocean calcium carbonate deposition is an important aspect of the global carbon cycle and influences the level of CO2 in the atmosphere at any given time
Ocean can pull down more CO2 from the air because it is basic. When more carbonate is in the open ocean, it means more CO2 can be pulled from the air (?)
Coccolithophorid
Organism that removes most of the calcium carbonate from the ocean that is not deposited by reef organisms.
Most significant threats on local scales?
Overfishing Pollution Coastal development Invasive species
What factors affect coral reefs?
Physical: wave energy, physical disturbance, temp, salinity, etc Biological factors: competition, predation, facilitation, etc
What makes a heat tolerant symbiont?
Production of enzymes that quench the ROS (reactive oxygen species) Adjustment of pigments to highest thermal and light regimes to allow the absorption of light energy Manufacture of membrane lipids surrounding the chloroplast that are heat resistant Synthesis of heat shock proteins
Recovery after bleaching
Rapid propagation of heat-tolerant corals/symbionts? Repopulation from refugia? Phoenix effect of colonial regrowth from surviving tissue? Migration is not an option
Reef richness and diversity
Reef richness does not necessarily mean that it is diverse. In modern reefs, diversity and functional redundancy seem essential for maintaining reef health, suggesting that the human-induced stresses on the reef ecosystem are fundamentally different from the natural disturbance, probably because they are multi-faceted and simultaneous.
Oxygen isotopic composition
Relative ratio of O18/O16 Linearly related to salinity The oxygen isotopic composition of solid coral skeleton also depends on temperature O18 composition of Palmyra coral is statistically equivalent to instrumental records of El Nino.
Adaptability of corals to thermal stress
Restricted to certain clades of zooxanthellae, mostly clade D
Overfishing cascading effects
Sea urchin extremely abundant after overfishing of other herbivores Early 80s massive mortality due to disease Algal overgrowth of coral occurred across the Caribbean First large-false evidence of the importance of herbivores on coral reefs.
Bleaching
Species specific. Some have high tolerance, others bleach consistenty The holobiont dictates thermal tolerance, not the coral host On one colony itself, can have some sections bleach and other sections that don't.
Global warming
Sustained warming events coupled with ENSO causes corals to bleach
Future warming in climate models
Taking average assumptions of carbon emissions in several models predicts a global average surface temperate increase of 3-5 degrees C by the end of the 21st century Two positive feedbacks produce this result: 1. snow an dice reduction in high latitudes leads to an albedo feedback 2. warmer air holds more water vapor and increased water vapor leads to increased greenhouse effect.
How do you tell which way Ca2+ makes it into the calcifying fluid is the most important?
Test: calcein dye experiment Dyed calcium and based conclusion off of where calcein was found after incubation. Seems as though the leak of seawater is most important pathway for ions to make it into the calcifying fluid Test: mapping other cations in seawater that mimic calcium by labeling the medium with isotopes Also found that leak of seawater is most likely the dominant source of calcium.
Basis for Ocean Acidification
The chemistry of the ocean can be throughout of as a giant dissolved antacid tablet Ocean uptake of fossil fuel CO2 occurs as an acid/base rxn. As the CO2 pressure in the atmosphere rises and the concentration of dissolved CO2 in the ocean increases, the "base" in the ocean is consumed, driving the ocean to lower pH
Coral reef restoration types
Transplantation Artificial reefs Managing reef loss with herbivores Boos natural abundance of heat-tolerant algae inside reef corlas Used to increase abundance of corals in areas following mortality
Options for human mitigation of climate change effects on coral reef
Transplanting corals associated w/ clade D? (impractical) Genetic engineering? (too costly) Reducing the influence of other stressors (to encourage "normal" recovery from bleaching) Maximize protection for those corlas that are best able to cope with rising temperatures. (Last two options make most sense. Problem is that rising temperatures are not the only source of jeopardy for corals)
Will the variability of climate change with increasing global temp? (ex: will the intensity of El Nino events or the intensity of drought/flood cycles or hurricanes increase?)
Uncertain
El Nino Southern Oscillation phenomenon
Walker circulation: thermally direct cell of atmosphere in the tropics Heating of atmosphere from sea surface in contact with warm ocean water, rising of ocean in atmosphere, and eventually it descends and the loop is closed by the trade winds at the surface blowing east to west Upwelling in east, warm water in west from trade winds: reinforces the system. During el nino, the trade winds relax, disrupting system. Warm water not as pushed to west, and can migrate to east, which changes where atmosphere is being heated most strongly. Stresses corals out
Why do corals bleach when exposed to warm water events?
Zooxanthellae released Oxidative stress- If exposed to increased temperatures, the cells start malfunctioning and cell damage occurs Oxidative stress can cause damage to lipids, proteins, and DNA. Single greatest determining factor as to whether a coral survives a bleaching event is the amount of time that it is exposed to elevated temperatures under high light conditions
