Subject: A pair of Emperor shrimps (Periclimenes imperator) are hitchhiking a ride on a couple of Tryon’s Risbecia nudibranchs (Risbecia tryoni). These commensal shrimps feed on detritus that they pick off the bottom. Thanks to the nudibranchs they travel faster and cover more feeding grounds. Emperor shrimps are not cleaner shrimps and they don’t benefit their host in any way. This form of symbiosis, where one species benefits (the shrimps) and the other (the nudibranch) is not significantly harmed or helped is called commensalism. The sausage-like small purple objects on these nudibranch’s gills are the egg sacs of a female copepod (a small parasitic crustacean) and are left alone by the shrimps.
Technique: To get the best out of this scene I positioned myself as low as possible and pointed the camera upward in order to get the dark blue of the ocean as background. In post-production we boosted the red of the little shrimps and the purple edge of the nudibranchs’ mantle.