Could you post a list (with a brief description) of the Prestige Classes in the book?
Ten-level unless otherwise noted:
Knight of the Pearl: 5-level PrC for a paladin order of one of the new races, the aventi (people of an Atlantis-esque society after it sank); gain abilities related to fighting underwater & opposing undead/evil.
Legendary Captain: Gain abilities related to being captain of a vessel of the high seas.
Leviathan Hunter: 5-level; gain abilities related to fighting Huge monsters (not only in the seas).
Scarlet Corsair: Gain abilities related to being a piratey sort, such as fighting on ships & a bit of sneak attack progression.
Sea Witch: 8/10 spell progression; gain curse abilities & summon maelstroms (whirlpool environmental hazards).
Stormcaster: 9/10 spell progression; gain storm-related energy resistances, spell CL bonuses, & powers. Interestingly enough, you do NOT 'cast better in storms' (despite the flavor text which claims otherwise), but can ignore certain normal storm-related penalties. Another one that could be useful in non-watery settings.
Wavekeeper: 9/10 spell progression; gain a domain, control waves & currents, breathe air or water, wild shape-like ability to become a water elemental, a few other watery odds & ends.