Late 19th century; earliest use found in The Monist: a quarterly magazine devoted to the philosophy of science. From planktology + -ist; compare -ologist.
Definition of planktologist in US English:
planktologist
(also planctologist)
nounplaŋ(k)ˈtɒlədʒɪst
An expert in or student of planktology.
Origin
Late 19th century; earliest use found in The Monist: a quarterly magazine devoted to the philosophy of science. From planktology + -ist; compare -ologist.