Ocean Chronicles
Sea Lemon exposed with the tide © Chelsea Mathieson
SPECIES IN THE SPOTLIGHT
THE SEA LEMON Anisodoris Nobilis Josh McInnes
The Northeastern Pacific is home to countless
beaches are likely to find them in tide pools or cling-
marine organisms that capture our imagination, while
ing to exposed rock faces covered in kelp. Sea lemons
leaving us hypnotized by their beauty. One such or-
can also be found in association with their main prey,
ganism is the brightly yellow coloured sea lemon (Ani-
which consists of several similarly coloured species of
sodoris nobilis), a species of nudibranch or “sea slug,”
encrusting sponges. Their preferred prey is the bread-
that earned its name from their bright yellow to or-
crumb sponge (Halichondria panacea). They use their
ange body colouration that is shaped and looks like a
radula, a conveyer of small tooth like structures, to
lemon peel. Generally sea lemons are 10 cm in length,
rasp off sections of sponge that encrust rock.
but some deep water specimens have been measured to 26 cm. Similar to most nudibranchs, sea lemons are
The sea lemon, like all species of nudibranchs, is her-
dorsally flat with short rounded projections that have
maphroditic-a specialized sexual characteristic en-
black blotches. In addition, sea lemons have forward
abling this ‘sea slug’ to be able to produce both eggs and
facing tentacles or rhinophores, which are believed to
sperm. When mating both sea lemons extend penises
be chemosensory devices aiding the “sea slug” in find-
to exchange sperm and fertilize each other’s eggs. Sea
ing prey and mates. The posterior end of the sea lem-
lemons produce large light yellow coloured ribbon
on is dominated by a gill plume 1.0 cm in length. The
like structures, which contain as many as 2,000,000
gill plume aids the sea lemon as a respiratory structure,
eggs. However, less than 1% of the larvae will survive
allowing for absorption of oxygen and secretion of car-
and reach adulthood.
bon dioxide. The sea lemon can easily be confused with the similarly coloured Monterey Dorid (Archidoris
Sea lemons have very few predators, and like most
montereyensis). However, in the sea lemon the blackish
nudibranchs display bright colours and distinctive
blotches do not extend or reach the tubercles.
odors to repel potential predators. The odor of sea lemons has been likened to that of fruit. Researchers
Sea lemons are distributed from the cold temperate
at California State University have demonstrated that
waters off Kodiak Island, Alaska south to the sub-trop-
sea lemons produce toxins by extracting mucus from
ical waters of Baja, California. They are commonly
outside glands of the animal, and testing it against po-
sighted in the low intertidal zone, but have also been
tential predators. Their findings showed that several
viewed at depths of 230 m. Keen naturalists searching
predators were successfully deterred.
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