It is one of the most abundant and widespread of all the British sea pen species, as it has a tolerance to a wide variety of sediments, salinities, and temperatures.

[10] In surveys completed off the coast of the western coast of Scotland, the slender sea pen has shown to prefer salinity from 27 to 35, muddy sediments with low percentage of gravel, and depths from 5 to 200 m.[11] Slender sea pens typically feed on zooplankton and other organic particles, however they also have been known to feed upon small animals that have been swept into their branches.

They possess nematocysts, so the species is capable of both passive predation of small animals and suspension feeding of particles.

Due to their ability to retract into the sediment, they are not very suitable for epizoic organisms to sit on[12] The sexes are separate, with each colony of polyps being either male or female.

[1] Little other information is known about the reproductive cycles of slender sea pen, though research inter similar species suggests that up to 200,000 eggs could be produced per female colony.