Everything that I have read says that biodegradable and reef-safe are the same thing. Reef-friendly is different though and not necessarily biodegradable. I like the Thinksport Mineral SPF 50+.
EDIT: You need mineral based, ie zinc or titanium oxide. It can’t contain chemicals or PABA. It also should not say “clear”, “nano”, or “micronized”. These have smaller mineral particles that can get into the reefs.