Caramel Nudibranch (Glossodoris rufomarginata)

Caramel Nudibranch (Glossodoris rufomarginata) known to tropical fish keeping enthusiasts as the White Margin Sea Slug is found in tropical Indo Pacific waters from localities as far apart as Tanzania in Africa and Mayotte in the Indian Ocean.

From Sri Lanka to Polynesia, the Caramel Nudibranch is considered to be a relatively common species. They are abundant in Hawaii, but are less common and rarely observed in the Marshall Islands.

Glossodoris rufomarginata is mostly found on sheltered reefs, among rocky areas, and exposed shady environments.   They are active during daylight hours but avoid bright sunlight and have a decided preference for shaded areas.

Caramel Nudibranch (Glossodoris rufomarginata)

The Caramel Nudibranch (Glossodoris rufomarginata) has an off white body color with the surface of the dorsal and foot densely speckled with a coat of tiny red to orange brown dots that at first glance gives the nudibranch a light brown look.

The well developed wavy mantle edge has a broad white band with a red to orange brown outer border, and the foot has a white outer margin.   The retractable branchial plume and rhinophores are red to orange brown with a white median line on the rhinophores and a white highlight on the gill axis.

In the Marshall Islands, Caramel Nudibranch frequent caves and ledges of the windward seaward reef’s groove and spur system where they feed on dark gray clumping sponges of the family Thorectidae.

For the majority of the year, this zone (where the seaward slope meets the intertidal reef) is pounded non-stop by heavy waves and intense water surges making diving the area quite dangerous.   The heavy pounding often dislodges or tears off pieces of the sponge when it grows too large and washes it across the intertidal reef into the lagoon’s sandy slopes where Glossodoris rufomarginata are often still attached.   In the Marshall Islands, Glossodoris rufomarginata grow to almost 2 inches in length.

Unfortunately, sponges of the family Thorectidae which are the the sole prey of the Caramel Nudibranch, do not normally live in this area.   Once the sponge has been completely eaten and the Carmel Nudibranch cannot find another sponge colony washed up from the seaward side to feed on, the nudibranch may starve to death.

Fortunately, piles of rock that have washed all the way across the reef from the seaward groove and spur zone often have algae, sponges, and corals attached to them that are generally found only in that area.   Specimens are often collected on the back sides of gray sponges buried in the piles of rocks.

The Caramel Nudibranch is one of the most commonly observed species in Hawaii.   Specimens here grow to a max length of around .75 inch and inhabit relatively shallow reefs where their sole food source, a dark gray sponge named Cacospongia, thrives on the ledges and in the caves.

Because of their specialized feeding habits,  the Caramel Nudibranch has a relatively short life expectancy in an aquarium environment.    They are voracious eaters of sponges and are best housed in an established reef tank of at least 55 gallon capacity with plenty of mature live rock, a sandy substrate, and obviously plenty of sponge growth specific to the territory they were collected from.

Carmel Nudibranch require a good amount of water movement, so at least one or more powerheads are recommended in the reef system to keep them happy.  Like most invertebrates, Glossodoris rufomarginata is very sensitive to rapid changes in water quality and requires stable water conditions.

They are especially sensitive to higher levels of nitrates and cannot tolerate any amount of copper in the system.    When acquired, they should be slowly drip acclimated with the lights off or under dimly lit conditions when introduced into a new reef system.

In established reef aquariums, regular spawnings are common when Glossodoris rufomarginata are maintained together.

Glossodoris rufomarginata is a specialty feeder that requires plenty of live sponges of the family Thorectidae to thrive.   Lacking a steady supply of live sponges in their diet, they will usually not eat enough of anything else to thrive and will slowly starve.

Because of this and their short life span, only expert tropical fish keeping enthusiasts should attempt to maintain this species.

The Caramel Nudibranch (Glossodoris rufomarginata) is occasionally available to tropical fish keeping enthusiasts from specialty shops, Nudibranch forums,  and online from a variety of sources.

Caramel Nudibranch (Glossodoris rufomarginata)

Minimum Tank Size: 55 gallons
Aquarium Type: Established Reef
Care Level: Moderate
Temperament: Peaceful
Aquarium Hardiness: Relatively hardy
Water Conditions: 72-78°F, dKH 8 to 12, pH 8.1-8.4, sg 1.023-1.025
Max. Size:  2″
Color Form: Yellow, White, Brown, Red
Diet: Specialty Carnivore
Compatibility: Reef Compatible
Origin: Tropical Indo Pacific Oceans
Family: Chromodorididae
Lifespan: Unkonwn
Aquarist Experience Level: Expert Only