Plant-like organisms

Photosynthesis and chemosynthesis

There's not as clear a distinction between plant and animal life on Nemoros as there is on Earth, with mobile organisms engaging in photosynthesis to an extent. With a dim sun and a thick hazy atmosphere little light reaches the surface, leaving very little energy for photosynthesis. Most photosynthesis is done in the infrared part of the spectrum, where more light passes through the moon's tholin lair. This is also supplemented with a great deal of chemosynthesis. In fact, on such a dim volcanically active planet there is often far more chemical energy available than solar energy.

In both photosynthesis and chemosynthesis, the energy obtained is used to create larger hydrocarbons from methane and ethane in the moon's oceans and lakes or in the atmosphere. Hydrogen is produced in this process, contributing to the 2% hydrogen present in dry air. Life on Nemoros also needs oxygen and nitrogen for their biochemistry, so plant-like organisms absorb water ice and ammonia ice from the ground to obtain oxygen and nitrogen, and many single celled organisms take nitrogen from the atmosphere. Below is a general equation for the production of carbohydrates on Nemoros.

CH₄ + H₂O > CH₂O + 2H₂

Chemosynthesisers depend on volcanic activity deep below the moon's surface for a constant source of energy. Of particular note are hydrogen sulphide, sulphur dioxide, and carbon dioxide, all used by chemosynthetic life on Nemoros. These substances exist in high quantity in the subsurface water-ammonia ocean, but are occasionally released from here onto the surface via cryovolcanoes. This way, chemicals produced from hydrothermal vents near the rocky core eventually make their way upwards. At the cold temperatures on the surface, these substances are solid, so they make up very little of the atmospheric content.

Hydrogen sulphide is of particular importance, as the elemental sulphur produced from it's reactions with sulphur dioxide or carbon dioxide is also important to many chemoautotrophs. These organisms engage in sulphur reduction, reacting sulphur with atmospheric hydrogen to produce hydrogen sulphide.

Ecology and biology

Since methane and ethane are their main sources of carbon, the methane/ethane oceans are so thickly filled with photosynthetic and chemoautrophic organisms that they're fairly opaque, appearing black. This doesn't allow much light to come through, so only organisms near the top engage in photosynthesis. The rest are pure chemosynthesisers, filling the oceans just as densely as organisms closer to the surface do. This makes the methane very thick and muddy in a lot of places, with the relatively slow moving mobile organisms unable to get around easily. 

On the surface there's much more breathing room, with well spaced out "plants" and plenty of space to move. Trees grow extremely large to compete for sunlight, and a hair-like chemoautrophic organism somewhat similar to fungus grows on the ground. Trees are able to grow so large in part because of the lower gravity, but also the presence of hydrogen sacs that provide them with buoyancy. The fact most trees obtain the majority of their methane directly from the dense atmosphere, instead of taking it from the soil and carrying it up stems, also contributes to a higher upper size limit. 

Most photosynthetic life on Nemoros is very dark or black in colour, allowing them to obtain as much light as possible from the dim, distant star. Plants are even darker in the infrared part of the spectrum, from which they obtain most of their energy (or at least the ones close to the surface do). The reason for this preference for infrared light is two-fold; firstly, Aulea orbits a red dwarf star that emits more light in the infrared part of the spectrum, and secondly infrared light is less hindered by the tholin lair than visible or ultraviolet light. This means infrared light is more plentiful on the surface than other parts of the spectrum.