no, it is very good, may be you mixed up with the one in sapporo.
the one in sapporo is small but convenience.take bus only.
旭山動物園 not in sapporo, you need to take train(special decorated train, very cute) , about 1 hour to 旭川. I went there twice,once in summer and once in winter, my kids enjoy very much.
for marine park, is it the one in 登別?, also you need to train ~1 hour, it is not worth to go to marine park only, usually, people will stay for one night,enjoy the温泉, and visit the 熊牧場, marine park and 忍者村. besides train, some hotel offer shuttle bus, it takes ~2 hours, it can save money but waste time, and the time is not fexible to meet your scheudle