Hi There:
That's a pretty open question. You mentioned flora and fauna, but those are both big categories. Are you simply shooting for inventory, in which case all you need are some reasonably sharp, focused pictures with even lighting, or are you making scenic images? By flora are you simply referring to flowers of herbaceous plants or are you shooting everything from mosses and lichens to trees? Fauna in an estuary can include everything from aquatic invertebrates to large mammals, songbirds, reptiles, amphibians...
Depending on what you're photographing you may need close-up equipment, a lighting tent or diffuser for the flower shots or a blind for shooting images of waterfowl.
Once you get started you'll likely develop more specific questions, and there are many here who will be able to give you more specific answers...
Mike.