1. Basics of aquatic ecology

Ecology is the scientific study of the interactions that determine the distribution and abundance of organisms.

Organisms interact with their environment and are the product of adaptation trough evolution (natural selection).

Fitness is the measure of a genotypes long-term success.

Fitness is always relative to the other species in the system (no maximum -> optimization) and the species which can sustain the largest growth is the fittest.

The two main components are reproductive potential and survival.

The range of temperature changes is smaller in water than on land, therefore temperature is less lethal to aquatic organisms. The temperature is very important for the speed of physiological and biochemical processes.

The solubility of O2 is limited and depends on temperature, salinity and pressure.

To handle limited and fluctuating O2 concentration, organisms developed different coping mechanisms (O2 take-in over whole body, using atmospheric O2, hemoglobin with high O2,…)

Changes can directly lead to damages and disfunctions due to the role of pH in the ion transfer through cell membranes.

Indirectly it can change the solubility of metals, the dissociating of ammonium ions and the equilibrium of calcium-carbonic acid.

(Salinity) Species in freshwater must maintain their ions and are surrounded by more diluted water and must constantly remove water to retain their salts.

Because this does not happen in saltwater there are very few species which can live in the in between of both (river deltas).

Water flow in streams are responsible for the continuous change in resources.

They can be disastrous if they are fluctuating.

Morphological and behavioural adaptations to cope with these challenges.

Most organisms are denser than water and must swim (high energy cost) or reduce their sinking speeds through adaptation to stay afloat.