Are there inherent problems in simulating marine environments, as compared to terrestrial systems?
It probably depends on the type of marine organism you're referring to, some will be much more hardy than others and some will not be able to adapt to change at all. Due to the vast scale of the environment that marine fish come from it's likely that in their natural habitat the conditions they live in are not subject to drastic changes in water chemistry or temperature [1][2]. So recreating those exact conditions for them in man-made habitats, let alone maintaining them is going to be extrememly difficult.  Also, if you think about the conditions that most (there will be some exceptions) terrestrial animals and plants have to deal with on a day-to-day basis they have to be able to cope with some fluctuations in humidity, temperature, weather, light etc and therefore are highly adaptable by necessity.

Other issues can be supplying the correct feed. In artificial settings food may have to be a non-natural substitute and this will likely cause problems for species who require a highly specialised diet. The terrestrial animals we tend to cultivate extensively are omnivorous/herbivorous which are not difficult needs to meet. On the other hand a fish from the sea that requires a particular other kind of fish only found in a particular area and that needs very specific conditions to thrive is going to be problematic.

Check out this article http://www.vliz.be/imisdocs/publications/301.pdf , it might be for a specific fish but it highlights some of the general issues i think you are referring to.

[1] http://www.bestfish.com/saltg.html
[2] http://www.aquaticcommunity.com/marineaquarium/
(both general articles on keeping marine fish)

hope this helps!