Introduced armored suckermouth catfishes (plecos to aquarists) are scrubbing Floridian manatees of their algae growing on their skin. What impact this may have on the manatees is unknown; it could be possible the loss of algae renders the manatees less capable of thermoregulating and it’s also possible the manatees needlessly expend energy avoiding the catfish.
Nico, L. et al (2009) Interactions between non-native armored suckermouth catfish (Loricariidae: Pterygoplichthys) and native Florida manatee (Trichechus manatus latirostris) in artesian springs. Aquatic Invasions 4(3), 511–519.
Nico, L. (2010) Nocturnal and diurnal activity of armored suckermouth catfish (Loricariidae: Pterygoplichthys) associated with wintering
Florida manatees (Trichechus manatus latirostris). Neotropical Ichthyology 8(4) 893–898.