1.  Nitrogen Cycling

• N is an essential element in
• Protein: each amino acid has at least 1 N
• Nucleic acids:  nitrogenous bases
• N2 makes up about 79% of the atmosphere
• N2 is only usable by prokaryotes with the enzyme nitrogenase
• Cyanobacteria like Anabaena carry their nitrogenase in a low oxygen package, the heterocyst.

3.  Fixation

• Converts N2 to
• ammonia (bacterial)- NH₄ : 100 - 200 kg N/ha=90%
N₂ --> 2N
2N + 3H₂ --> 2NH₃
• Rhizosphere bacteria: mutualistic, some nodule formers
• Free-living bacteria (+cyanobacteria) ~ 12,000 species
• Nitrate (high energy discharge, like lightning) - NO₃
• NO₃ in atmosphere + water vapor = H₂NO₃
• Atmospheric fixation low: 8.9 kg N/ha/yr

• Major step in N cycle
• Biomolecules (proteins,nucleic acids) from dead organisms broken down by bacteria and fungi to amino acids then to CO₂ + H₂O + NH₄ + energy

• Fate: dissolved in H2O, trapped in soil, fixed in clay

• Nitrosomonas bacteria use ammonia in soil as sole E source

• Nitrobacter bacteria use the remaining E in nitrite ion and oxidize it to nitrate

• Pollution can result if nitrates build up in aquatic ecosystems

• Nitrates reduced biologically to N2
• Denitrifiers are facultative anaerobes
• Bacteria: Pseudomonas
• Fungi
• Formula
• C₆H₁₂O₆ + 4NO₃ -> 6CO₂ + H₂O + 2N₂

8.  Graphic:  Phosphorus Cycle
9.  Graphic:  Silicon Cycle
10.  Marine Ecology: levels of organization

• 1.  species:  unique, genetically similar, capable of interbreeding with the production of viable offspring
• 2.  population: group of individuals of a species that occupies a specific area
• 3.  communities: populations of a species that coexist and interact with one another and live in a particular area.
• 4.  ecosystem:  all communities in a region along with associated abiotic characteristics
• 5.  What is your "scale" ?  Micro -> landscape
• 6.  Niche?  N-dimensional hypervolume, job
• a.  fundamental (no competition)
• b.  realized (with competition, actual utilization)
• 7.  Habitat?  Where do you live?

• 1.  chain = linear

Producer ->
    1^o consumer (herbivore) ->
         2^o consumer (carnivore) ->
               3^o consumer (top predator)

• 2. Webs: complex, many branches and connections

12.  Biomass & Productivity

• 1.  biomass = standing stock, mass of a species per unit area
• 2.  productivity = rate, mg O2 liberated or CO2 fixed per unit biomass, per unit time
• i.e.  g C m-2 y-1
• tropical rain forest = 500 - 1800 g C m-2 y-1
• Sargassum= 2500 gC m-2 y-1
• Thalassia testudinum = 330 gC m-2 y-1

14.  Ecological Strategies:  dynamic

• Succession:  pioneer -> intermediate -> mature
• a.  1o:  bare substrate, no propagules (spores, seeds, larvae) to start
• b.  2o: after disturbance, some propagules, some sediments/soil
• models
• a.  facilitation:  modification by pioneers to ease transition to next successional stage
• b.  tolerance:  later stages overgrow pioneers
• c.  inhibition:  earlier stages prevent/interfere later
• pioneers vs. climax: Table 3-2
• annuals vs. perennials
• disturbance:  disasters vs. catastrophes

• saltmarshes
• mangroves
• coral reefs
• seagrass beds

• r & K strategies, typical growth curve

17.  r Strategist?  K Strategist?

• How fast do you reproduce and how many?
• Parental care?
• Perennial or annual?
• Disturbed or undisturbed habitat?
• High nutrients or low nutrients?
• Pollution tolerant?
• Invasive?

19.  Biological Interactions

• symbiosis (symbiont always wins)
• parasitism:  host (-), common within reds
• mutualism:  host (+), corals
• commensalism: host (0), epiphytes (?)
• competition:  both (-)
• predation:  prey (-), grazing, allelopathy
• biofouling:  epiphytes on man-made structures