Whilst diving at Port Noarlunga jetty over the recent King’s Birthday holiday long weekend, I saw a Crested Pipefish (Histiogamphelus briggsii) surprisingly close to a Southern Keeled Octopus (Octopus berrima). This particular Crested Pipefish(Histiogamphelus briggsii) was only one of several seen on the dive, and we also found several Rhino Pipefish (Histiogamphelus cristatus). All of them were full adults. All were in typical feeding mode, moving slowly with the surge on relatively bare sandy bottom, and were ignored by various smallish demersal fish species including Bluespotted Goatfish and female Brownspotted Wrasse, and were also seemingly ignored by the many crabs, including Rough Rock Crabs (N.integrifrons) and Bristled Sponge Crabs.
There were occasional clumps of mostly red seaweeds but the Pipefish generally didn’t seem to seek algal cover, and the ones we saw near the clumps were only there because mysids tend to concentrate around algae. But, as I have stated on iNaturalist, this particular Crested Pipefish swam very close to the octopus, and I am sure the octopus could easily recognise the Pipefish for what it was, and wasn’t fooled by the cryptic “drifting dead posidonia blade” trick that both Histiogamphelus species rely on heavily for survival.
As I reported on iNaturalist, it was an “Interesting encounter in interactive terms.” The Crested Pipefish seemed unfazed by the proximity of the octopus.
I went on to say that this discovery doesn’t prove that Southern Keeled Octopus never eat Crested Pipefish, “but maybe they usually don’t, and pipefish generally wouldn’t rate highly in nutritional value* with regards to many other readily available prey(s) in the habitat they often coexist in”.
* (Pipefish are very low value nutritionally for many predators because they have low tissue density, and their hard outer casing and long thin bodies must make the job of eating the best bits rather tiresome!)
Unlike the majority of local octopus species, Southern Keeled Octopuses are often diurnally active, hence they must frequently share their immediate surroundings with many different Pipefish, all of which, as far as I know, are essentially daytime feeders which hide overnight.
While it is a given that all Pipefish have predators, I suspect they don’t have to worry about octopuses, although juvenile octopuses may eat juvenile Pipefish.
Another surprise regarding the above-mentioned encounter was that an Ikeda genus worm was out in the open nearby. It seemed reluctant to retract, even when I got much closer. There were a few such worms seen feeding during this dive, and I suppose they were doing so at a time of low predation risk; tide almost fully out and relatively little fish activity, also middle of the day with improving water clarity inside the platform reef.
