Wow, it is great that you have such a great goal to aspire to already! I am sure that like with any job, salaries would depend on what company or capacity to work as in the Marine Biology field. Money is not always the most important thing if you do not like what you have to do every day anyways!
I think the idea for protein skimmers are based upon nitrates quite a bit. Keep in mind that it is possible for a saltwater tank to run with no filters at all...as far as the traditional meaning of 'filter' is concerned. For example, my saltwater tank does not use any filters, other than a skimmer, and relies completely on the bacteria and other microscopic life on the live rock and live sand to deal with the fishes' wastes.
In reef tanks, the corals, fish, and other inverts like anemones are very sensitive to water quality. Because as the Ph levels of water get higher and higher, the toxicity of ammonia, nitrites, and nitrates gets higher...and saltwater tanks have a Ph of around 8.4...it is more important to find methods to reduce nitrates. The ammonia and nitrites are pretty easy to control by not over feeding and stocking very slim but in general, removing nitrates is done by water changes in freshwater fish tanks. So, the use of filter like a cannister filter can actually trap debris and detrius within them and add to the nitrate problem. Since this is bad for a reef, 'reefers' as they are sometimes called, do not want to use them. A skimmer works differently and actually removes protein, which is dead or decaying waste or organic matter without using any of the sponges or media that a traditional filter would use.
I think that people, including myself, get a bit confused by the term 'surface skimmer' because it implies that it is skimming the surface of the water. This is not really how it works. In general, they all use a Venturi effect (might be good to google that and learn more to really impress your teacher) to create bubbles, which need protein to make the 'skin' of the bubble. Then all of that 'bubble skin' is collected in a cup and most of the water is placed back into the tank.
I hope that makes some sense. In a nutshell, everyone has been right so far...skimmers reduce the nitrates in a tank by taking out the organic matter before it decays into an ammonia source. If you read a bit about how a tank cycles here:
http://www.fishtankforums.com/5-fres...-aquarium.html, you would learn how benificial bacteria turns ammonia into nitrates. Skimmers are also used becase they do not trap detrius within a place where the tank water can move through and thus do not add nitrates back to the tank.
Anyways i need to know what surface skimming is? Like why is it important to a reef? If someone could please answer my question i would greatly appreciate it! 
