Keel Kelp CR 5
Keel kelp is semi-sentient plant that lives within 2 to 4 miles of certain tropical islands. From the bow of a ship, keel kelp appears to be nothing more than a large floating mass of tangled seaweed and kelp, between 20 and 50 feet in diameter; if found near coral or rocky areas, it is likely to be interwoven with kelp of the standard variety. As a ship sails into the mass of keel kelp, the substance suddenly becomes very rigid, with sharp-edged fronds. When congealed into such a intractable state, the keel kelp has a hardness of 5 and 10 hit points per 10 ft. of diameter (break DC 20).
Any ship sailing through a hardened mass of keel kelp takes damage equal to the ship’s current speed divided by 5 (i.e., a ship moving at a speed of 30 takes 6 points of damage to its hull). This damage occurs every round the ship moves through the keel kelp, until it finally breaks out on the other side. The ship’s speed is reduced by half.
Slashing weapons inflict normal damage to the kelp, while piercing and bludgeoning weapons do half their listed damage. Magical effects harm the kelp, but fire-based spells cause only half damage. Keel kelp is immune to water-based spells.
It is speculated by many esteemed sages that keel kelp was created by a rogue hydromancer (water elementalist) as a means of defending his island home from his considerable enemies. The theory is sound, except for the fact that keel kelp can be found in almost any part of the ocean. Many sailors believe the kelp was created by a volatile god of the sea as a tool of vengeance against those who failed demonstrates the proper reverence. The only thing that everyone agrees upon it that keel kelp is a deadly delicacy. Fresh keel kelp can sell for many pieces of gold at any large port town. The acquisition of this food of kings has left many a ship in a watery grave.