The term watercraft encompasses everything we do as an angler to catch carp, it's not just about one thing. To catch a single carp might be down to luck but to be consistent wherever you go, you need good watercraft.
So learning about what is going on below the water as well as above is important because this is where some of the most fundamental things to understand are happening. You don't need to know the name of all the species of crustacean or plant, although of course it's desirable, all you need to know is what effect it has on the fish.
At this time of year below the water is much the same as above in that the first green shoots of life are appearing. The carp will be waking up from semi-hibernation due to the low temperatures but as the sun shines ever more the water warms and so the activity below increases.
Coots are a very good indicator of where this fresh new green weed is as they like to eat it, but also they like to eat the crustaceans. The crustaceans like to eat microscopic organisms like algae which grows on the plants . Algae needs photosynthesis and this comes from the ever increasing sun.
Carp like to eat the same things as coots so it should be obvious, scare the coot away and fish it's spot :-)