The spell of warm weather recalled walking on a west coast beach and the excitement I felt when I found nudibranches in tidal pools. Another less glamorous name for them is sea slugs – i.e. soft-bodied marine slugs or snails without a shell.
Globally, it is estimated there are close to 3,000 known species and many of them are spectacular in appearance – often brightly, even garishly (almost neon) coloured with many frilly or wavy appendages (the naked gills) in contrasting colours arranged in clusters or lines along their backs.
The bodies can be striped, spotted, almost rough or seemingly translucent. The fleshy gills are often pointed and tipped with white or other bright colours, but some are highly branched like little trees.
Some nudibranchs have colouration that matches their habitat and there is even a green species that has been described as a “plate-sized, solar-powered” marine slug that incorporates photosynthetic algae into its body and then “farms” the algae for nutrients.
A nudibranch’s soft body is mostly a large muscular foot, and they appear to have no protection. However, the flashy colouration serves as a warning to would-be predators that many species are covered in cells containing toxic compounds.
Others have stinging cells (nematocysts) deployed all over their bodies, acquired by eating fire corals, sea anemones and hydroids. The tightly coiled stingers can be shot out at potential predators at high speed.
Nudibranchs have only very small “eyes” that can detect light and dark. They mainly sense (smell, feel and taste) their world using rhinophores (sensory tentacles) mounted on their heads. They also use chemical signals to detect food.
Most sea slugs are hermaphrodites - each one having both male and female sex organs. They can lay eggs in ribbons, coils or tangled clumps containing as many as two million eggs each.
Some fish species, sea spiders, turtles, sea stars and a few crabs eat sea slugs. They are also eaten by people in Russia and Alaska who describe the experience as like “chewing an eraser.”
They survive in both warm and cold marine waters and some even live in deep-sea vents.
I have seen the orange/lemon peel sea slugs and white ones with frosted gill tips among others. I’m told there are good places to see them on the Rushbrook trail in Prince Rupert Harbour.
