Algae

Algae are the primary producers -- they use light to convert CO2 and dissolved nutrients into living biomass and oxygen. All algae in the model share the same core photosynthesis mechanics (light limitation, nitrogen and phosphorus limitation via Liebig's law of the minimum, CO2 limitation, carbon storage, and photorespiration) but differ in growth rate, surface attachment, grazer vulnerability, and environmental tolerances. Every algae species can exist in both a free-floating (planktonic) form and attached to surfaces. They settle onto surfaces at species-specific rates weighted by surface area and roughness, and detach back into the water column. When nitrogen is scarce, algae reduce their photosynthesis rate but can still fix carbon into storage compounds (like starch or lipids), which increases their carbon-to-nitrogen ratio up to a species-specific maximum. All algae species can use dissolved CO2 for photosynthesis, and most can also use bicarbonate to varying degrees through carbon concentrating mechanisms. At high oxygen-to-CO2 ratios, photorespiration kicks in -- the photosynthetic enzyme RuBisCO mistakenly grabs oxygen instead of CO2, reducing net carbon fixation and oxygen production.

Diatoms have an additional requirement: dissolved silica (DSi). Their cell walls (frustules) are made of amorphous opal (SiO2*nH2O), and they cannot divide without a supply of silicic acid from the water. This makes silica availability an independent co-limiting factor on diatom growth, beyond the standard light/N/P/CO2 suite that applies to all other algae.

The diatom and cyanobacteria functional types are each split into two subcommunities that share their flux() machinery but diverge in growth strategy, habitat, and life history. Centric and pennate diatoms represent the planktonic "spring bloom" specialists and the benthic "brown algae" biofilm dwellers respectively, while planktonic and benthic cyanobacteria represent the bloom-forming toxic-water-column community and the mat-forming "BGA" pest community of planted aquaria.

Species

• Centric Diatom Community -- fast-growing planktonic spring bloomers (Cyclotella, Asterionella)
• Pennate Diatom Community -- slow-growing benthic biofilm "brown algae" (Navicula, Gomphonema)
• Planktonic Green Algae Community
• Benthic Green Algae Community
• Planktonic Cyanobacteria Community -- bloom-forming toxin producers (Microcystis, Dolichospermum)
• Benthic Cyanobacteria Community -- mat-forming "BGA" pests (Phormidium, Oscillatoria)