Buenavista biosphere reserve

As far as I know, this "biosphere reserve" is broken up in a lot of different parts. I don't know which, if any, of them might be reached entirely by public transport. My suggestion would be that, assuming you are flying into Havana or Varadero, you take a Viazul bus to Santa Clara (about 4 hours), and there rent a car (available at the airport). In your rental car, travel north for about 45 minutes to the town of Remedios, and from there on out the looooong causeway to Cayo Las Brujas and Cayo Santa Maria. (good highway all the way, and not much traffic).

I believe Cayo Santa Maria is one of the centres for this biosphere reserve, but I have not visited the centre, so can't tell you what you'd find there. Most of these biosphere centres, or "estaciones ecologicas" as they're called in Cuba, are tiny places, usually with a few researchers (Cuban and foreign) on hand, and a couple of guides, often ones which do not speak any language other than Spanish. Although sometimes you get lucky and find one who speaks your langage as well--or maybe one of the researchers stationed there will. I repeat, I have not visited the station in Santa Maria, so it may be different. But this has been my experience at other biosphere reserves.

There are good places to stay in this area--although not any great number of them. First, you could stay in a licenced casa in Remedios, and drive across the causeway (3-CUC fee) whenever you want to visit the islands. Or (my recommendation) you could cross the causeway and stay at Villa Las Brujas on Cayo Las Brujas, which is about 5 km before you reach Cayo Santa Maria. Or you could continue on to Cayo Santa Maria and stay there in a big all-inclusive resort complex. I can say unequivocally that Villa Las Brujas, which consists of individual apartments on a bluff overlooking an exquisite beach would be preferred by nature lovers. When I was last there, the apartments rented for around 80 CUC/night. There was an open-air restaurant overlooking this same beach.

Both Las Brujas island and Santa Maria island are mostly wild, with no human habitation beyond what is centered on their respective resorts--and, I suppose, the "estacion ecologica" which I did not notice when I was there. If there are any tours avaiable, you could probably find out about them at either Villa Las Brujas or the big resort complex on Cayo Santa Maria. Or at least find out where the estacion ecologica is located, and find out what they can offer by way of a tour.

P.S. In the winter there are charter flights that fly directly from Canada (and maybe from Europe as well--I don't know) into Santa Clara. If that fit your plans, then having a rental car waiting for you at the Santa Clara airport would be the way to go. It's a small airport, and easy driving distances to the various parts of the Buena Vista Biosphere Reserve, as well as the cloud forest around Topes de Collantes (2 hours south of Santa Clara), and only about 3 hours to the Zapata Swamp (if birdwatching is your motivation for visiting this area).