You're probably thinking of land-based sources of omega-3 fatty acids, such as linseed, which are indeed composed only of ALA. Algae oil, on the other hand, is rich in EPA and DHA. In fact, fish themselves don't synthesise their own EPA but obtain it from the algae they (or their prey) feed on.
“Conclusions: We conclude that vegans have low baseline omega-3 levels, but not lower than omnivores who also consume very little docosahexaenoic and eicosapentaenoic acids. The vegans responded robustly to a relatively low dose of a vegetarian omega-3 supplement.”
Specifically: "On the basis of the data available, the Panel concludes that a cause and effect relationship has been established between the dietary intake of ALA and the reduction of blood cholesterol concentrations."
linked to which is: "The Panel considers that the maintenance of normal blood cholesterol concentrations is beneficial to human health"
