Meet the Nudies!
With the beginning of Directed Studies week underway we set about collecting our study organism the nudibranch Hermissenda crassicornis!
H.crassicornis, the ‘Opalescent nudibranch’ has a slender, mainly transparent body with numerous cerata (finger-like projections of the digestive tract) with orange bands and white tips. This nudibranch also has a distinctive orange patch on its back lined by blue stripes. We had to have sharp eyes to find these guys because they range in size, growing to a maximum of approximately 8cm in length.
This species is a generalist feeder, known to eat a wide range of food, from cnidarians, tunicates, bryozoans, sponges, annelids, other gastropods, even other H.crassicornis. It feeds on cnidarians (organisms with stinging cells; anemones, corals, hydroids and more) in order to sequester cnidae (armed stinging cells) which it is able to transport via digestive sacs to cnidosacs in the distal ends of the cerata. Here the cnidae are still functional (remaining unfired) and act as a defense for the nudibranch.
H.crassicornis is found in a wide variety of habitats along the Pacific North coast of North America, from Alaska to Mexico. This species is abundant and common on rocks, eel grass beds, floats, docks and various other habitats, ranging from the inter-tidal zone to a depth of 35 meters.
Armed only with this background information, willing helpers, diving approval, buckets and plastic containers (…and a handy tip-off as to where they had been collected before) we headed down to the South Dock of the Bamfield Marine Science Centre, in Bamfield Inlet, Barkley Sound to go Hermissenda crassicornis hunting!
We were nervous about being able to find enough of our species among the wide array of species that call the South Dock home, however as soon as we entered the water someone yelled that they had found the first Nudie! The nudibranchs were carefully removed from their food, transported to sea tables and placed in individual flow-through containers with lids. To help our little guys settle in, all nudibranchs were given excess amount of hydroid and tunicate to feed on, given their own name, and left to acclimate to their new home!
Throughout the day and subsequent dives, the location of each nudibranch collected was recorded. Observation showed that most nudibranchs were found located on top of their common food sources,Obelia sp. hydroids and tunicates. The collection procedure was helpful in allowing us to recognize likely ‘nudi-territory’ for future collections and suggests the importance of Obelia sp. hydroids and tunicates as food sources for this generalist feeder.
An interesting pattern was also observed regarding the size of the nudibranch and their location. Smaller (presumably younger) nudibranchs were mainly found feeding amongst hydroids, while larger nudibranchs were generally found in more exposed locations feeding on tunicate. This raises another interesting research question regarding changes in food preference in relation to size and development of nudibranchs… so many questions! So little time!
So welcome to the family little guys! We look forwards to getting to know you better throughout the project!
Greenwood, P., 2009, Aquisition and use of nematocysts by cnidarian predators, Toxicon, 54, 1065-1070
Harbo, R., 2011, Whelks to Whales,Harbour Publishing Co., Madeira Park BC, p160
Hoover, R., Armour, R., Dow, I., & Purcell, J., 2012, Nudibranch predation and dietary preference for the polyps of Aurelia labiata (Cnidaria: Scyphozoa), Hydrobiologica, 690, 199-213