One of the interesting things I saw in my columns within the first week were many polychaete worms:

http://upload.wikimedia.org/wikipedia/commons/4/46/Nerr0328.jpg

These are very common marine organisms so I wasn't shocked to see them, however, they only lasted a few days. I also had a large zooplankton, about 5-8mm long. I planned to save and attempt to ID it but it died before I could find the time to catch it.