This video covers the "Diving For Treasure" Survival Challenge in the Pirates of the Caribbean Premium Level Kit for LittleBIGPlanet. The only thing to do here is collect the optional The Bends Trophy, and I show you some strategies that can help you do so with only one player. (Multiple players make the job easier, but this video shows that it's not too difficult to do it with just one.)
The Trophy requires you to get 7,000 points, but you should know that that minimum is not sufficient. Dying (which is obviously required to legitimately get to the Scoreboard) deducts 5% from the total score. If you are playing alone, this means you should aim for a minimum of 7,370 points to safely land you at about 7,001 points when you die. That's barely squeaking by, so I recommend you get at least 7,500 or more, especially if multiple players are present. I accidentally died due to a lack of air around the 9,865 point mark in this recording, but I could have easily continued for a while longer using the displayed strategies.
As shown in the video, the key to a sufficiently high score is using Prize Bubble collection and score multipliers to your advantage. It's easiest to earn high multipliers early on when you don't have to worry so much about the deadly buoyant spiked objects, and I recommend you try to pull off at least one x10 or higher multiplier to give you a wealth of points. If you are having trouble pulling off double digit multipliers, at least try to rack up multiple x5 or higher multipliers. Getting anything less than x5 means that you're not properly taking advantage of the early low-hanging fruit. By the time the spiked object spawns start covering up most of the screen at once, you'd be lucky to pull off measly x2 or x3 multipliers at that point; That's why you're best off trying to rack up a hefty multiplier early on.