As of December 20, 2012, Teuber has published three previews (#1, #2 and #3) in German about Catan: Explorers & Pirates on Catan.de, and I've combined the information in those previews with the details included in the Mayfair Games press release to bring you the following detailed description:
Second, instead of using cities, Catan: Explorers & Pirates allows players to build port settlements for two corn and two ore, with a port settlement supplying one resource when the adjacent number is rolled at the start of a turn. Like cities, port settlements are worth two victory points (VPs), and the number of VPs required to win depends on the scenario.
Third, if a player receives no resources during the production roll (other than on a roll of 7), she receives one gold in compensation. Two gold can be traded with the bank for a resource of the player's choice. Gold has other uses as well, such as helping you escape from pirates.
The five scenarios included in Catan: Explorers & Pirates are:
• Land Ho! Explore the seas of Catan and discover two new islands to expand your settlements. Once you've discovered an island, you must use ships to ferry settlers from one island to another and colonize distant lands. (Introductory scenario)
• Pirate Lairs! In this scenario, pirates prowl the seas along with your trading vessels. Pay tribute to the pirates or drive them off, then find and capture their lairs to earn gold and VPs! (One mission scenario)
• Fish for Catan! The people of Catan are short of food, so it's time to take to the ocean to fish for meals. These are deep water fish, though, so first you must find their shoals before you can catch them! The Council of Catan will reward players with VPs for returning fish to the island, as well as for capturing pirate lairs. Just watch out for roaming pirates, as not only will they demand gold for tribute, they might also get to the fish before you do! (Two mission scenario)
• Spices for Catan! In this scenario, the Council of Catan wants you to find fish and spices for the people of Catan! As before, they reward the most industrious merchant captains with VPs. Obtaining spice will require you to become friends with the mysterious inhabitants of the Spice Islands, but in return they will not only trade you spices but teach you their knowledge of sailing or even pirate fighting techniques! (Two mission scenario)
• Explorers and Pirates! This lengthy and challenging scenario brings everything from the previous scenarios together! Explore new lands, capture pirate lairs, find fish, and befriend the inhabitants of the spice isles! (Three mission scenario)