Ocean VL 6 Flashcards
How does oxygen concentration impact marine organisms?
1) Hypoxia (≤ 62 µmol/kg): Reduced fitness, aberrant behavior, increased mortality.
2) Suboxia (~5-10 µmol/kg): Disappearance of most multicellular life.
3) Anoxia (<1 µmol/kg): Only anaerobic microbes survive.
What types of bacterial symbioses are involved in nitrogen cycling in the ocean?
- Diatom-diazotroph symbioses (DDA) for nitrogen fixation.
- Diatom symbiosis with cyanobacteria transformed into an organelle.
- Rhodobacteraceae symbiosis with diatoms for ammonification.
What is the anammox reaction and its significance in the nitrogen cycle?
The anammox reaction (anaerobic ammonium oxidation) involves converting NH4+ and NO2- into N2 and water.
This reaction is significant for nitrogen removal in marine sediments, accounting for over 80% of N2 release.
What role do Thioploca bacteria play in marine nitrogen cycling?
Thioploca are giant bacteria which reduce nitrate with sulfide (sulfur globulus) in fluctuating environments, storing nitrate for reduction and maintaining low sulfide concentrations in surrounding sediments.
Filaments can migrate up and down. (Sulfite in lower sediment layer than Nitrate)
What are manganese nodules and how do they form?
Manganese nodules form slowly (5 mm per million years) under low sedimentation and oxygen-rich conditions in deep-sea environments. They contain valuable metals like Mn, Fe, Cu, Ni, and Co, and are of economic interest for deep-sea mining
What are the effects of deep-sea mining on marine life, especially microbial and metazoan communities
Mining disturbs benthic habitats by
* removing hard substrates,
* resuspending sediments, and
* reducing microbial activity.
This damages both microbial and metazoan communities, and recovery may take decades due to the slow growth of organisms in oligotrophic environments.
What are the causes and consequences of ocean deoxygenation?
Climate change increases water temperatures and freshwater input, reducing oxygen solubility and expanding oxygen-deficient zones (ODZs). This affects primary production and respiration rates, impacting marine species and ecosystems..
How does denitrification contribute to nitrogen cycling in marine environments?
Denitrification is the microbial reduction of nitrate (NO3-) to nitrogen gas (N2), typically in anoxic conditions.
It helps remove nitrogen from ecosystems and can prevent eutrophication. It can occur in sediment surfaces and anoxygen zones.
What is the role of foraminifera in marine nitrogen cycling?
Foraminifera store and respire nitrate within their own organelles, not needing associated bacteria, contributing to nitrogen removal in anoxic conditions.
They play a crucial role in reducing nitrate to N2 in anoxic sediments.
What are microbial ecosystem services in deep-sea environments, and why are they important?
Microbial ecosystems provide essential services, such as nutrient cycling, organic matter degradation, and novel biochemical compounds (e.g., antibiotics, enzymes).
Deep-sea mining threatens these services by disturbing microbial habitats and biomass.
What is the role of manganese in redox cycling in marine sediments?
Manganese undergoes redox reactions, cycling between Mn(II), Mn(III), and Mn(IV) states.
Manganese oxides act as terminal electron acceptors for bacteria, contributing to energy production and the degradation of organic matter in marine sediments.
What is DNRA, and where does it occur in marine environments?
DNRA is the process where nitrate (NO3-) is reduced to ammonium (NH4+) rather than nitrogen gas.
It occurs in carbon-rich, nitrogen-limited habitats, often through the activity of sulfur-oxidizing bacteria like Thiobacillus and Thioploca.
What are the key processes that reduce manganese in marine sediments?
Manganese can be reduced chemically by iron or sulfide, by organic compounds, or enzymatically by anaerobic bacteria such as Shewanella and Geobacter.
These processes play a significant role in sedimentary geochemistry and nutrient cycling.
Why is benthic fauna in deep-sea environments dependent on hard substrates, and what impact does mining have?
Benthic fauna like corals, sponges, and other epifauna need hard substrates for attachment and survival. D
eep-sea mining removes these substrates, causing long-term damage to the ecosystem, as recovery is slow or impossible. The minig also leads sedimentation which causes harm e.g for filterer.
