The seagull symoblises her 'idle' destruction at the hands of Trigorin, as well as Konstantin's creative frustration/impotence in conveying his feelings
Nina
Trigorin
Konstantin
The Lake
Annotations:
Each character is 'drawn' back to the lake for tragic/poignant reasons; mostly for the gratification and sense of self worth that is achieved in the company of their admirers, you could argue that the magic of the lake is no more than the intoxicating 'magic' of flattery and nostalgia.
Trigorin
Dorn
Nina
Love/Destruction
Annotations:
These relationships (which are essentially all the romantic relationships in the play) demonstrate the destructive power of love, as they are all respectively stripped of self worth, creativity, and happiness. The central irony to this theme is the fact that no one character appears to be interest in love that is given freely, and continuously pine over inaccessible/disinterested parties
Nina and Konstantin
Trigorin and Arkadina
Konstantin and Masha
Nina and Trigorin
Dorn and Polina
Shamrayev
Thwarted Ambition
Sorin
Konstantin
Masha
Trigorin
Nina
Youth/Age
Annotations:
all characters battling with either the niavety of youth or the bitter loss of it.
Nina
Sorin
Masha
Medvedenko
Arkadina
Konstantin
Time/Memory
Annotations:
this is also linked to the lake, the house and lake act as a focal point for nostalgia and subsequently causes characters to question their decisions, like Sorin, or wallow in their previous achievements in attempts to escape on going impotence/fading