thanks for the query posted .
This can definitely be due to the coral causing an acute allergic dermatitis
and infection in the area. Corals are not poisonous or else you would have easily got other symptoms like fever
, breathlessness in the area .
You should definitely book an appointment with the physician . the physician would clean the wound with an antiseptic .
and may also put you on oral medications like an antibiotic and anti inflammatory .
Thanks and take care