1) Caves and coral reefs 2) Coral reefs 3) Environmental units 
The interacting system of all the biotic community and its abiotic environment.(Living things in their environment) communities of animals, plants and micro-organisms, together with the habitats where they live
are systems in which organisms interact with each other and with their environment. According to the originator o the term, there are two parts; the entire complex of organisms (biome) living in harmony and the habitat in which the biome exists
habitats
A collection of living organisms and their environment
a geographical region defined by all the living organisms (biotic) as well as the nonliving (abiotic) components such as climate, topography and geology.