Appunti di Marine Ecology

NITROGEN

Required for the synthesis of aa• Occur in 3 inorganic dissolved forms: ammonium (NH₄), nitrate (NO₃), nitrite (NO₂)• 4 3 2Occur also in dissolved organic forms: urea, amino acids, peptides• Ammonium is the preferred form of N from a nutritional perspective•The highest concentration of dissolved N in the ocean is NO₃, NO₂ is the less abundant.3 2New production: the amount of primary production attributable to nutrient supply from deeper water (ex: upwelling).Regeneration (or recycled) production: the amount of primary production attributable to excretion of zooplankton andbacteria, decomposition and respiration in surface water (recycling processes).F-ratio: ratio of new production to total (new + regeneration).F-ratio, average global value: 0.3 0.5–F-ratio, oligotrophic open ocean: 0.1F-ratio, coastal regions or site of coastal upwelling: 0.8Cycle in the Sea:1. Nitrogen fixation: Nitrogen-fixing bacteria convert nitrogengas to ammonia by means of the

1. enzyme nitrogenase
2. Anaerobic process
3. Nitrification: nitrifying bacteria (Nitrosomonas) convert ammonia to nitrite and other bacteria (Nitrobacter) oxidize nitrite to nitrate O required
4. Denitrification: denitrifying bacteria like Pseudomonas, Bacillus, Clostridium, reduce nitrate to ammonium ion and can return nitrogen to atmosphere in the form of gas Only in anaerobic condition
5. Nitrogen is mainly incorporated into marine food web through the process of nitrogen fixation especially accomplished by cyanobacteria. Some cyanobacteria nitrogen fixers are found in anaerobic sediments of coastal regions, saltmarsh, estuaries, roots of seagrasses. Other cyanobacteria (Trichodesmius) in tropical oligothropic water where can bloom.
6. PHOSPHORUS
7. Used primarly in the energy cycle of the cell (ATP)
8. Inorganic forms: PO₄^3-, HPO₄^2-, H₂PO₄^-
9. Organic compounds classified together as DOP
10. Phosphate (PO₄^3-) is the form preferred by phytoplankton and exchanges rapidly between phytoplankton and

its• concentration increase with the depth.

Sediment: 10 million Gigatonnes (10⁹)

Inorganic carbon: 39000 Gigatonnes

Dissolved organic carbon (DOC): 700 Gigatonnes

Particulate organic carbon (POC): 30 Gigatonnes

The supply of inorganic carbon for photosynthesis and algal growth is rarely a limited resource in marine systems.

Inorganic Carbon: Chemically reactive forms in water tends to equilibrium–CO₂ + H₂O <—> H₂CO₃ <—> H⁺ + HCO₃^- <—> H⁺ + CO₃^2-

Buffering capacity keeping seawater at pH ~ 7.8 - 8.4

HCO₃^- is taken up by algae and converted to CO₂ (the substrate for Rubisco) within the cell or in the outer cell surface by the enzyme carbonic anhydrase.

Although seawater pH is relatively stable it changes with depth due to the amount of carbon dioxide.

Upper Depths (generally 8.5 pH): warm water and photosynthetic organisms (less CO₂)

Middle Depths: more CO₂ present from respiration of organisms, decrease of pH

Lower Depths: 1,000

meters = more acidic again because the decay of sinking organic materials produces CO₂

There are many algae and phytoplankton groups that deposit calcium carbonate (CaCO₃) in their cell walls (calcification).

Calcification is related to photosynthetic activity and the effects of pH on the dynamics of calcium-carbonate-bicarbonate in seawater.

SULPHUR

High presence of sulphate (SO₄) in seawater (rarely is a limiting nutrient)

• Vital nutrient for amino acids and protein synthesis
• Phytoplankton and algae produce dimethylsulphonioproprionate (DMSP) used as osmolyte, antifreeze and anti-grazing
• Phytoplankton help to make clouds and have an important effect on regional and global climate!!

DMS reaches the atmosphere, where it is rapidly oxidized to sulphate haze, forming an aerosol able to thicken the air humidity forming clouds. The aerosol clouds generated are also particularly reflective, preventing the solar rays from reaching the ocean surface. Thus the phytoplankton species

thatproduce DMS have an important function of cooling the planet.

The most prolific producer of DMSP are:

• (planktonic colonial alga) in coastal waters
• Phaeocystis (coccolitophore) in oceanic waters
• Emiliana huxleyi
• Ulva (green algae) intertidal region

They contribute to 10% of the global marine primaryPhaeocystisproduction and it is one of the most efficient producers of DMSto the atmosphere.

SILICON

Delivered to the ocean by wind and river transport

• Silicic acid is a constituent of seawater and is an essential nutrient for the secretion of skeletons of diatoms and radiolars
• Depletion of silicon inhibits cell division and suppress the metabolic activity of the cell

Nutrients status of the water

• Oligotrophic: waters with low concentrations of essential nutrients for growth. Low primary productivity
• Eutrophic: waters with high concentrations of essential nutrients for growth. High primary productivity
• Mesotrophic: waters between the two states.

Intermediate level of primary productivity

• On the basis of the annual primary production:
• Oligotrophic: 100-300 g carbon /m2/ year
• Mesotrophic: 300-500 g carbon /m2/ year
• Eutrophic: 500 g carbon/m2/ year
• Hypertrophic: >500 g carbon/m2/ year

Eutrophication: increase in the rate of supply of organic matter to an ecosystem.

Increase in inorganic nutrients such as N and P + run-off of artificial fertilizers from agricultural land determine the increase in algal growth, both phytoplankton and/or macroalgae (Algal Overgrowth)

Eutrophication is a process by which the productivity of an aquatic system is increased and therefore can be caused by factors other than nutrient input: reducing the suspended material in a water body increasing the light level or changing the residence time of water within a particular system. Eutrophication can be also a natural phenomenon not always associated with human activities. Eutrophication is a reversible process.

The nutrient uptake varies with:

1. Cell size
and surface area: almost all the phytoplankton sp. have more or less spherical cells. In spherical cell as cell size decrease, the surface area/volume ratio increases as well as the cell division rate. Smaller cells can be able to take up nutrients proportionally at a higher rate than larger cells (advantage where nutrients have low concentration). Larger cells can store more nutrients (advantage where nutrients have high concentration). 2. Turbulence: on the large spatial scale moves large parcels of water moving nutrients (es: upwelling). Moves cells through the water exposing the cells to new micropatches where nutrients may be higher. 3. Taxonomic group: different group of phytoplankton have different ability to take up nutrients. Different efficiency of cell membrane transport photosynthesis metabolic processes type of nutrient storage within the cells. Nutrient uptake rate may be measured: directly: in terms of nutrient taken up/cell/unit time indirectly: in terms of celldoubling rate. The cell doubling rate (D) increases with increasing nutrient , but reaching a• [ ]plateau at a value D max. K: the nutrient at which half the maximum D occurs (D max/2). K is the half-saturation[ ]constant and is a useful measure of nutrient uptake rate. Ocean phytoplankton nutrient uptake:
1. Inshore (more nutrients than open ocean): phytoplankton should be inefficient at low nutrients ut able to take up nutrients at far[ ] Bhigher than the open-ocean phytoplankton. Saturation reached with[ ]an higher nutrients[ ]
2. Open ocean (less nutrients): phytoplankton should be able to take up nutrients efficiently from low . Low maximum uptake rate (Dmax)[ ]because they never encounter high nutrients Saturation with lower[ ].nutrients.[ ]
K should be greater for inner-shelf phytoplankton. Clones of the same diatom species show high and low K depending if the clones are isolated from nearshore or oceanic waters. Oceanic phytoplankton is more efficient at taking up nutrients atlow, competitively superior to coastal form in low nutrients of the open sea but unable to take up high nutrients. Phytoplankton Succession Different phytoplankton species dominate at different times of the year (seasonal dominance) and this succession is controlled by a complex mosaic of factors: - Seasonal nutrient availability: different species require different types and amounts of nutrients - Cell size: earlier species have a large size to store nutrients. Later species are smaller to uptake low nutrients - Allelopathy: the production of toxic compounds by one organism to inhibit another - Irradiance and Temperature - Grazing activity by protozoan and zooplankton During succession, changes in relative phytoplankton species occur, but it is important to remember that all species are present at all times of the year. The diversity of phytoplankton tends to increase as succession progresses. Later phytoplankton successional dominants are often ornate with spines.es to environmental conditions, such as light and temperature, may also play a role in allowing different species to coexist. Additionally, some species may have specialized niches or adaptations that allow them to thrive in specific conditions or utilize different resources. Overall, the coexistence of multiple phytoplankton species in a nutrient-limited and unstructured environment is likely a result of a combination of factors including resource partitioning, physiological differences, and the dynamic nature of the environment.