Do You Know Who You're Dealing
Get to Know the Real Ilyanassa obsoleta
If you're in the
market for a cleanup crew, you might search the Internet for
vendors of Nassarius snails. Many of the results will
be vendors of the carrion-feeding snail Nassarius
vibex, but you'll also find vendors selling a much
cheaper "Nassarius" snail called Nassarius,
Ilyanassa or Ilyanassarius obsoleta. Nearly
every vendor advertises these snails to be similar in behavior
to Nassarius vibex, and claims that they eat algae.
Wow; they're cheaper, and more helpful? What a deal! Surely
there's a catch, right? You bet - several.
"Who Are You, Really?"
So first of all, what is with all
the confusion about the species name? When it was originally
described in 1822, Thomas Say named the snail Nassa obsoleta
(Rosenberg 2005). Since that time, it has gone by many different
names, including Nassarius obsoletus. Though the name
Ilyanassa obsoleta (hereinafter Ilyanassa) had
been applied to this snail for decades, Nassarius obsoletus
seemed to be the favorite in the literature until the mid
1970's. At that time, the general opinion seemed to shift
towards putting this snail in the genus Ilyanassa to
reflect its differences from other species of Nassarius
(Zool. Rec. 1958-2006).
Figure 1. Ilyanassa obsoleta. Note the
round, relatively smooth shell with little sculpting,
often with the outer layer worn away near the tip.
Figure 2. Nassarius vibex. Note the heavy
sculpting, flaring lip near the opening of the shell,
and usually sharp, unworn tip.
The fact that they are still being sold as Nassarius obsoleta
so long after the change should immediately tell you one of
two things about the vendors (usually the collectors themselves)
labeling them as such, either: 1) they're intentionally misrepresenting
their product as something more desirable to consumers, or
2) their source of information about the animal isn't accurate
The second reason certainly seems harmless enough. Who cares
if they got the name wrong? They've seen first hand how the
animals behave; they shouldn't need sources to tell them about
their feeding habits and behavior.
It's not always that simple, though. Anyone who has been
in the hobby long enough can tell you that initial observations
can't always be trusted. For example, that fireworm eating
your clam didn't kill it, and your cleaner wrasse isn't picking
ich off your fish even though that's what it looks like. Similarly,
a vendor doesn't see the full picture of these snails' behavior
by just watching them for short periods of time.
As you may notice, all of the cited sources regarding this
snail's diet were published after Ilyanassa became
the preferred name. That means that the snail's diet probably
wasn't readily obvious by observation alone, and that a vendor
using a source from the time when it was still widely called
Nassarius obsoleta probably doesn't have very accurate
information about its diet. I've collected a small number
of these from the wild, and even after the few weeks that
I observed them, I certainly couldn't have given a very accurate
picture of what they were eating.
A Hot Topic
At the time of this writing, an eBay
search for Ilyanassa returned 25 hits for live snails;
all with the word "reef" in the description. Most
are offered in lots of 50-250 snails. But wait a minute -
every single vendor listing is from North Carolina. How has
North Carolina cornered the market on huge lots of super-cheap
reef snails? It hasn't. Ilyanassa is not a reef snail,
or even a tropical snail, at all. It is naturally found from
Newfoundland down to northern Florida and has been introduced
to the West Coast from British Columbia to Southern California,
where it is causing huge problems (more on this later).
As with most organisms, Ilyanassa is most abundant
near the center of its range and less common and slower growing
near the outer edges of its range, where the environment approaches
the animal's maximum tolerances. The average water temperature
in the area near one of the North Carolina eBay vendors is
about 20.2° C (68.4° F) (Fautin). Since North Carolina
is roughly in the middle of its range, it's probably a good
assumption that the temperature there is close to the ideal
for the species. While that doesn't seem much of a departure
from the average reef tank temperature, physiologically it's
a huge jump. As a general rule, it takes only a 10° C
change to double the rate of metabolic processes. Average
reef tank temperatures are about 5-8° C higher than the
average ocean temperature where this eBay vendor is located.
To put it into perspective, the species' southern limit is
only about 4° C warmer, on average, than the vendor's
The increased metabolic rate is a double-edged sword for
the snails. Not only are their bodies stressed by being forced
into overdrive, but the very enzymes they need to speed up
metabolic reactions start to fail. Enzymes are simply proteins
used to catalyze metabolic reactions. Proteins, structural
or enzymatic, are designed to work at a specific temperature
and pH. When the environment is outside those parameters,
the enzymes start to catalyze their reactions less efficiently.
Eventually, the proteins start to denature and become useless.
Denaturing is just a fancy term for when chemical bonds within
the proteins start to break and their molecular three-dimensional
shape changes. Because a protein's function relies on its
structure, as the structure changes, the protein will stop
functioning normally. This is exactly what you do to the protein
in an egg when you fry it. This denaturing happens to a small
degree under normal situations, but increases exponentially
even at slightly elevated temperatures and can overwhelm the
animal's mechanisms for refolding the proteins.When enzymes
are denatured in large amounts, the metabolic reactions they
catalyze start to bog down. Obviously, this is physiologically
Ilyanassa, and many other intertidal and upper-subtidal
snails that are exposed to periods of elevated water temperature,
aren't defenseless against heat stress, though. They have
special proteins called "heat shock proteins" (HSPs)
that go around refolding denatured proteins back into their
working shape (Downs et al., 2001). Making and using
HSPs, however, is very energetically expensive and is only
a short-term solution. The long-term solution is to use different
forms of enzymes optimized for different temperatures - something
Ilyanassa can't do to the degree it needs to in order
to successfully adapt.
Because these snails are adapted to deal with elevated temperatures
for daily, and even seasonal, periods the heat damage generally
goes unnoticed by hobbyists. It can take a year or two for
the damage to build to lethal levels, and at that point the
aquarist often assumes that the snail's death was just due
to old age. Considering that these snails can live for up
to 40 years, that explanation is unlikely (Curtis et al.,
How "Reef Safe" Are They?
So, if they aren't really reef snails,
what about the claims that they are "totally reef safe,"
"eat detritus and most forms of algae" and "will
not attack any of your population" (as seen on eBay listings)?
Well, as you may have guessed, they aren't entirely accurate,
either. Ilyanassa is an omnivore. A large part of Ilyanassa's
diet is indeed made up of algae and algal detritus. However,
it is selective, preferring certain types of diatoms rather
than indiscriminately gobbling up any algae (Connor and Edgar,
1982; Connor et al., 1982). They also require meat
in their diet to survive and reproduce (Curtis and Hurd, 1979;
Hurd, 1985). This meat comes primarily from carrion and predation
on sandbed fauna, including other snails (Race, 1982). Besides
direct predation on sandbed life, Ilyanassa's foraging
is so disruptive that in areas where they are found, amphipods,
copepods and worms that would normally be present are absent
(Dewitt and Levinton, 1985; Hunt et al., 1987; Kelaher
et al., 2003). To me, this hardly sounds "totally
reef safe," and is especially troubling if you utilize
a sand bed as a filter or food source for mandarin dragonets
(Synchiropus spp.) or similar fish.
Ilyanassa is such an effective competitor that in
areas where it has been introduced, such as San Francisco
Bay, it has forced out native species and completely disrupted
ecosystems. Tidal flats that once housed diverse assemblages
of snails, worms and crustaceans are now monocultures of literally
billions of Ilyanassa (Race, 1982). Outside of
its natural range, this snail is considered an extremely damaging
pest. Virtually nothing eats them in large enough numbers
to reduce their population, and at this stage in the game,
humans can do little to control them. The threat of their
accidental introduction into new areas makes the trend of
shipping large numbers of these snails throughout the country
even more troubling.
Are You Safe?
While the other problems with keeping
these snails in a reef tank concern the well-being of the
snails themselves and the tank's other inhabitants, one threat
could hit a little closer to home. Ilyanassa is an
intermediate host for at least nine species of trematode fluke.
In most populations, over 50% of the adult snails have at
least one species of this parasite, and in some populations
the rate of infection is as high as 94% (Curtis and Hubbard,
1990; Curtis, 1997)! While none of these flukes actually targets
humans as hosts, they do sometimes mistakenly burrow into
human skin and cause what is known as "swimmers' itch,"
or more properly, cercarial dermatitis (Sindermann, 1960).
This condition creates an extremely itchy rash similar to
poison ivy that can last for up to a week. Affected snails
will continue to release the infective stage of these flukes
into a tank for up to a decade (assuming the snails live that
long), and any exposure to the tank's water puts the aquarist
at risk of infection (Curtis et al., 2000).
Interestingly enough, the flukes that infect Ilyanassa
harm them not only by stealing nutrition and castrating the
animals, they can also actually control the snails' behavior.
Infected snails make more frequent trips to, and go higher
into, the intertidal zone where they are more likely to encounter
birds and crustaceans, which are the flukes' primary hosts
(Curtis, 1993). Coincidentally, that's also where they are
more likely to encounter livestock collectors. As a result
of this behavioral modification, it's highly likely that collectors
of these snails have an unintentional bias toward infected
As with any claims that sound too
good to be true, consumers should be skeptical of the claims
being made about Ilyanassa as an ideal reef snail.
Ilyanassa is not a reef snail at all. As a snail from
cold and temperate water, keeping them at reef temperatures
is sentencing them to a premature death. In addition, they
aren't entirely reef safe, especially in tanks with sand beds.
We're all aware that our hobby has a reputation for being
wasteful of and destructive to marine life. It's time for
hobbyists to start making informed and responsible decisions
about the animals we keep. With several truly reef safe snails
available in the hobby, it is in the hobbyists' and snails'
best interest to spend a little extra for more appropriate
species, such as this snail's cousin, Nassarius vibex.
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of feeding by mud snails, Ilyanassa obsoleta (Say),
on the structure and metabolism of a laboratory benthic algal
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by the mud snail Ilyanassa obsoleta. Oecologia.
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zone: Vertical migrations, infective stages and snail trails.
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on Reef Central.