There is one meaning in OED's entry for the noun hydro-biology. See 'Meaning & use' for definition, usage, and quotation evidence.

4 дня назад · indicating or denoting water, liquid, or fluid. hydrodynamics. hydrolysis · indicating the presence of hydrogen in a chemical compound.

7 дней назад · The meaning of HYDRO is an establishment offering hydropathic treatment (as for weight loss) : health spa.

6 дней назад · a combining form representing hydrogen in compound words, denoting esp. a combination of hydrogen with some negative element or radical.

8 дней назад · short for hydroelectricity: electricity produced by the force of fast moving water such as rivers or waterfalls.

Prefixed to the name of a compound substance, hydro- usually means the addition or substitution of hydrogen in its constitution, e.g. benzoinC 14H 12O 2.

Hydrobiology is the science of life and life processes in water. Much of modern hydrobiology can be viewed as a sub-discipline of ecology. Training and studies · Organizations

The meaning of HYDROBIOLOGY is the biology of bodies or units of water; especially : limnology.

Hydro, a term for a hydropathic establishment, often preserved in the names of hotels that no longer offer the water cure · Hydro Majestic Hotel, New South Wales ...