Here are the Details of Truk,Yap and Palau.

When to go
Good All year round. Exceptional Oct - May.
Marine Life
Palau is rich in marine life, boasting more than 1500 species of fish, over 70 species of coral and anemones, plus manta rays, turtles, mautilus, sharks and rare species such as giat tridacna clam and dugongs. Truk or Chuuk as it is now known, has outstanding soft and hard corals and abundant marine life besides its more famous WWII wreck attractions. Yap is fames for its large concentration of manta rays.
For the Intermediate to advanced diver. Palau is regarded as one of the world's top diving areas for its pristine reefs, coral gardens, caverns, drop-offs, drift and wall-dive sites as well as wrecks. Truk's fame is the sunken armada of more than 60 ships and planes of the Japanese navy's fourth fleet, which have become artificial reefs. But it also has a barrier reef and drop-offs. Yap is relatively undived and offers a variety of diving experiences for all levels.
Palau's top dive sites include blue holes, the 1000 foo Ngmelis drop-off, Blue Hole and Shark City. Among Truk's dive sites are the aircraft carrier Fujikawa, with four Zero fighters in its hold, and Sankisan Maru - containing a cargo of trucks and machines guns. Yap's Mill Channel has a resident manta population offering guaranteed sightings, while concentrations of sharks can be seen at Shark City and Gilman Tip
In Water
Water temperatures of 28 degrees centigrade mean only lightweight one-piece suits are needed as protection against coral and wrecks
On Land
Light tropical clothing is the norma year-round in Micronesia. Attire is very casual.
Saltwater crocodiles and venomous sea snakes apart from the normal reef hazards. Biggest danger - the volatile cargoes on wartime wrecks.
US Dollar-locals use Giant Stone still