[1]
INTRODUCTION
Spider Crabs, Libinia
emarginata, are from the species of crab, stenohaline. They live in the Atlantic Ocean on the coast of North America, but can be found
from Nova Scotia to the Florida Keys, and the Gulf of Mexico.
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They have long
legs, round spiny bodies, and 9 spines down their back. They live at depths up
to 150 feet Females can only reproduce after molting. The young hatch from eggs
as zoea larvae [5]. Since predation is a concern for these crustaceans, these
crabs will attach pieces of shell, seaweed, and algae to the sticky hairs on
their bodies for camouflage [1]. The crabs also use the greenish-brown algae on
their back to help hide it from predators [2].
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DESCRIPTION OF THE
RELSTIONSHIP
Spider crabs come from
the genus and species Libinia emarginata. These crabs can grow to be up to 12 inches from claw
to claw [5]. They have different claws than other crabs do in order for them to
scoop up algae [3]. Spider crabs and algae share a mutualistic relationship. “A mutualistic relationship is when two organisms of
different species ‘work together,’ each benefiting from the relationship” [2]. Even though this
is a mutualistic relationship, it is a facultative relationship
for both meaning it is not obligatory for either organism. Both organisms benefit from the relationship with the
other: the crab gets to blend in with its surroundings and the algae get a
place to live [2]. The relationship is established when L. emarginata scoops up the
algae. This relationship is not unique to spider crabs. Spider crabs are not
the only animals that use algae for camouflage. Devil scorpionfish are
camouflaged to their environment because they allow algae to grow on them.
Also, other types of crabs use this camouflage technique by allowing algae and
dirt to stick to hairs on their body [4].
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COST/BENEFIT ANALYSIS
Benefit for spider
crabs: As previously
stated, the spider crabs benefit from the relationship with algae by using it as
camouflage. Because of this, the crabs have a better chance of surviving
predators.
Benefit for algae: Since the crabs pick up the algae, they get a
permanent place to live. It is also protected from predators now because it has
a permanent home on the crab [2].
Cost for spider crab: The spider crab spends energy to find, collect, and
scoop algae onto its back.
Cost for algae: Even though the algae get a place to live, the
crabs possibly could take them into a new, unfamiliar environment. Therefore,
it might not be as successful there.
Since this is a
mutualistic relationship, there is not a great amount of cost for either the
spider crab or the algae. Any “cost” is outweighed by the benefits. Even though
the crab spends energy recruiting the algae, it pays off since it can hide from
predators.
Since this symbiotic
relationship shows strong, beneficial qualities for both organisms, it seems
like this relationship will proceed.
REFERENCES
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