Yes the species of diatoms differ from salt to fresh water. Mainly in fresh water pennate forms like Nitzschia sp. , Gomphonema sp. and Navicula sp. dominate along with some centric forms like cyclotella sp. In sea water centric diatoms like skeletonema sp., Thalassiosira sp., coscinodiscus sp., chetoceros sp. will dominate along with pennates like Nitzschia sp., Achnanthes sp., Navicula sp.. In sea water we find more planktonic forms were as in fresh water there are more benthic forms.