in a nutshell-not easy...i have a marine science degree and graduated with high honors six years ago...needless to say i am currently teaching biology for an area night school and waiting tables to pay the bills.
it is a very competitive field with very low funding so jobs are very scarce! it is quite and interesting field to study, but honestly, employment will probably not be exactly what you are looking for. seems to me that friends of mine who graduated with me took any job even CLOSELY related to marine science, and some have abandoned the field altogether due to lack of oportunity.
not to doscourage you, but it is important to know the reality.
cheers