Fosforlu = phosphorescent, glow in the dark
Martılar = seagulls (singular is martı = seagull)
Martıların = of the seagulls
göründüğü, comes from the verb görünmek which means: to seem, to appear, to look, to show up…
akşam saatleri = evening hours, when you add the akşam saatlerini it refers to the hours when the seagulls appear phosphorescent.
In Turkish you don’t have to start with “do you know…” the verse starts with the seagulls looking phosphorescent. But that is grammatically correct.
Both “ille” and “illa” mean: certainly, necessarily. Almost meaning that something has to be, that there’s no other choice.