user: ### NOW ANSWER:
Question: Which species on Réunion island is part of the procellariiformes order and is part of the hydrobatidae family and has less than 21 species worldwide?
Columns: ['Species', 'Order', 'Family', 'Species worldwide', 'Species on Réunion']
Types: ['text', 'text', 'text', 'real', 'real']
Sample row: ['Albatrosses', 'Procellariiformes', 'Diomedeidae', 21.0, 6.0]
SQL:

assistant: SELECT SUM("Species on Réunion") FROM "Table" WHERE "Order" = 'procellariiformes' AND "Family" = 'hydrobatidae' AND "Species worldwide" < 21.0;