At first, I was a bit disappointed in this result, but then I realized it’s actually rather interesting in a negative sense. Investigators tested the effects of squid ink on other squid; the entirely reasonable idea being that it could contain an alarm pheromone that would have the function of alerting neighboring squid in the school of trouble. It works — adding ink to a tank of Caribbean reef squid sends them scurrying away.

However, when they removed the pigments from the ink and added that, the squid couldn’t care less. That says there is no chemical signal, only a visual signal.

That makes sense, I suppose — oceans are big and would dilute any chemical signal fairly rapidly, so pheromones would only work well over a fairly short range (although some fish certainly do have extremely sensitive olfactory senses, so it could be done). Still, Aplysia eject some potent chemical signals with their secretions, which work when directly squirted into the face of a predator, so there was a chance the cephalopods might have evolved something similar.