I actually wrote a paper for my Seminar on Marine Mammals class last year about the healing factors of bottlenose dolphins. I have the paper on my other laptop, but I'll try to remember what I can. (As far as dolphins are concerned) Surprisingly, when they get a laceration, their dive response actually kicks in. When this happens blood flow is diverted away from non-essential physiological parts of the body for oxygen and heat conservation. But in this case, blood flow is just diverted away from the lacerated area (or more than the whole area beacuse they can't just block blood flow to one specific part of the body). As this occurs, blubber from around the wound covers the lacerated area while new pink, or "granulation", tissue forms from the bottom of the wound to the surface of the body. The blubber that covers the wound acts a barrier to the environment and contains anti-bacterial properties that speed up the healing process. Then as the wound heals, the non-essential blubber is pseudo-surgically removed (the removal of the blubber is debrided) so that new tissue growth can occur. Granted, this is for dolphins (and not much is known about this subject), but it is similar for other marine mammals and different for others, like seals and sea lions, beacuse they don't spend their entire life in the water. And it's hard to study these kind of things beacuse the animals are good at masking their pain and discomfort, so it's hard to tell if they are injured.

Source: Senior Marine Biology major; wrote a >5 page research paper on dolphin healing factors; also, this article sheds a little light on the subject.