Organism and ecosystem responses to high pCO2 and low pH Flashcards
(27 cards)
What is an example of a location with long-term oceanic data?
Tatoosh Island (off Washington data) - long-term submersible data logger
How was pH found to vary in the different environments of Tatoosh?
- Open ocean = consistent
- Coral reef = small-scale variability annually and daily
- Estuarine systems = high-scale variability
Why might variations be identified in pH levels in estuarine and coral systems of Tatoosh and not the open ocean?
Because of intense biological activity — daily cycles of photosynthesis (removing CO₂) and respiration (adding CO₂), especially in algae-rich areas. This causes greater short-term pH swings than in deeper, more stable ocean waters.
What does short-term variability in pH in natural marine environments suggest for the organisms that live there? Why might this be good?
They are already experiencing significant pH changes and therefore might be more resilient to short-term fluctuations.
Note: the overall trend of pH despite small variations is still declining - so this resilience may not be sufficient.
Describe sediment pH structure through the profile. What drives this vertical pattern?
- Water column above sediment is homogenous (due to mixing)
- Below the sediment-surface interface there is a significant drop in pH to ~7 (intense breakdown of organic mixing)
- By 3-4 cm = oxygen minimum zone associated with even lower pHs (down to 6.6 - due to anaerobic processes such as sulfate reduction)
- A slight increase below this point back around pH 7 is observed, remaining consistent below this (due to accumulation of alkaline products below the minimum)
This is driven by oxygen concentrations.
What causes this reduction in pH with depth in marine sediments?
oxygen is rapidly depleted, leading to anaerobic respiration, which produces acidic byproducts and lowers pH. At greater depths, buffering compounds accumulate, slightly increasing pH again.
How do organisms drive changes in marine sediment pH?
Organism activity can mix these vertical stratified layers, introducing more heterogeneity into the system.
E.g., burrowing and bio irrigation -> Oxygen gets drawn into the burrow, increasing pH with this inside the burrow. The lowest pH is now associated with the burrow exit and surrounding sediments, and not depth.
How can coral organisms influence surrounding pH?
- Net community C production and calcification processes
- Photosynthesis and respiration
How do kelp influence surrounding pH? What was observed about short-term fluctuations?
- Photosynthesis and respiration
This showed that kelp could survive short-term exposure to high CO2 levels.
What was included in long-term measurements (18 months) of Amphuira filiformis to ensure a holistic experiment?
- Combined effects of pH and temperature (using corresponding values)
- Seasonality (ensuring natural cycles in the long-term)
What changed in terms of the brittle star metabolism after long-term exposure to low pH?
Were able of upregulating in the short-term, but after 18 months, the metabolism did not return to initial levels (did not bounce back in the second summer as expected).
After 18 months of exposure to low pH levels, what was the brittle star skeleton like under CT imaging?
- Greater pits identified in the skeletal plates
- Easy disintegration
What behavioural changes were identified in brittle stars after long term exposure to temperature and pH stressors? How does this link to wider impacts?
- No longer buried into sediments (if they were hypoxic and low pH)
Therefore they no longer contribute to sediment nutrient cycling -> wider impacts.
What do 380 µatm and 750 µatm represent in terms of OA experiments?
Refer to the partial pressure of CO2 in seawater.
380 µatm = Pre-industrial / near-present day CO₂ levels (i.e. control or ambient condition)
750 µatm = Future elevated CO₂ level scenario (i.e. ocean acidification treatment condition)
Describe the experiment to test the effects of pre-exposure of adult oysters to OA conditions on oyster offspring. Incorporate wild vs selectively bred oysters into this plan.
Step 1: Get two populations -> one for wild and one for selectively bred (typically associated with faster growth rates and disease resistance).
Step 2: Divide each population into two for pre-exposure treatments: ambient (no exposure) and elevated conditions [4 different groupings]
Step 3: Divide each of these groups in two, so one is tested under near-present day CO2 levels (380 µatm) and the other is tested under an elevated pH scenario (750 µatm) [8 different treatments]
What was the overall impact of elevated Pco2 (ocean acidification) on the early life stages of Sydney rock oysters (Saccostrea glomerata)?
Negative impact on larvae with:
- Reduced growth
- Slower development rate
- Reduced survival
How did pre-exposing adult oysters to elevated Pco2 influence their offspring’s response to ocean acidification?
Generated positive carry-over effects:
- Larger size
- Faster growth
Demonstrates ability to adapt and acclimate.
Note: However, larval survival largely remained the same regardless of pre-exposure.
What difference was observed between the response of selectively bred vs wild oyster larvae to elevated Pco2?
Selective breeding had positive carry-over effects on larvae:
- Greater survival and growth
- Faster development
Also exhibited greater resilience to elevated pCO2
Why is it useful to study natural CO2 vents when studying varying pH effects on communities?
pH dramatically decreases towards vents, meaning community changes can be used to predict future community changes.
What was identified in communities with increasing proximity to CO2 vents?
- Reduction in calcified epiphytes
- Seagrass beds = dense and high biomass near vents
- Decrease in sea urchins, barnacles, limpets and gastropods (shells dissolved)
Overall: less diversity/complexity and more homogeneity, with absence of calcareous organisms (including calcareous algae).
Why may some species with calcareous shells be able to better survive at lower pHs than others?
- Aragonite vs calcite (aragonite dissolves more readily)
- Some have a protective layer over skeleton (this requires energy to maintain, so most susceptible organisms would not be able to sustain this metabolically)
Why may sea anemones demonstrate increases in abundance and survival nearer CO2 vents despite the lower pH?
Can contain symbiotic algae:
- Enables them to maintain their metabolism and therefore better withstand lower pH conditions
- Symbiotic algae thrive with more CO2 = more photosynthesis = more energy
What was expected about seagrasses at low pH conditions near CO2 vents?
They use CO2 for photosynthesis, and therefore it was expected that they would be less effected due to CO2 take up and increased energy.
What was actually observed for seagrasses at low pH conditions near CO2 vents?
- Increased sucrose concentration in leaves increased with higher CO2, meaning they were also preferred by herbivores = more vulnerable to predation
- Structural integrity started to break down under these higher CO2 conditions -> this means that despite increased shoots, they are of lower quality
Therefore, did less well near vents than expected
