ecosystem worldbuilding

i think fundamentally daunts me from trying to talk about my worldbuilding project is that because of the scale there's so much that i havent even had the time (or education) to start thinking about. recently thanks to my beloved agus i've been thinking more about marine ecosystems in terms of 1) how massive and diverse they are 2) how they affect even life on land. which is also a ridiculously rich tapestry at every level of existence and the oceans are almost THREE TIMES AS BIG. and obviously this is a huge blind spot because this is a planet that is visibly non-earth even though most of the structrures (biological and otherwise) are somewhat analogous to earth because sadly im not that creative, so why would there be sardines swimming in this alien sea. which means i badly need to start learning more about biology i guess. oh god