A Successful Partnership
are many wondrous adaptations that have evolved in the coral reef ecosystem.
One in particular is the symbiotic relationship between the Banded or
Yellow Watchman Goby (Cryptocentrus cinctus) and the Tiger Pistol
Shrimp (Alpheus spp.). There are three type of symbiosis: commensalism,
parasitism, and mutualism. Commensalism is an association between two
species where one organism benefits without harming the other. Parasitism
involves an association where one organism benefits to the detriment
(harm) of the other. The symbiotic relationship demonstrated by the
shrimp goby and pistol shrimp is classified as mutualism. Mutualism
is a type of symbiosis where two (or more) organisms from different
species live in close proximity to one another. They rely on one another
for food, protection, or other life functions. Both members of this
partnership derive some benefit from this relationship. In the case
of the shrimp goby and pistol shrimp, the shrimp goby provides security
while the pistol shrimp maintains their shared burrow home.
The shrimp goby and pistol shrimp live in the sandy sediments
that surround reefs, where there is lots of food, but little protection
from predators. Because the pistol shrimp is virtually blind, it is
especially vulnerable to predation above the surface and finds it necessary
to live underground to provide it some protection. The pistol shrimp
excavate burrows and tunnels in its shallow muddy or sandy bottom habitat.
The shrimp goby, characteristically being small, also finds life precarious
(dangerous) aboveground. They can perceive predators but may not always
have a place to conceal themselves from them. Undoubtedly, at some point
in their evolution, the goby and pistol shrimp lived separate lives.
Then by chance, a goby and a pistol shrimp discovered that living together
gave them a better chance of survival. Natural selection reinforced
this partnership and today the lives of shrimp and goby are absolutely
intertwined. This mutualistic relationship provides the pistol shrimp
with early warning of predators and the shrimp goby with a place to
The burrows and tunnels constructed by the pistol shrimp
require continuous maintenance. The entrance to the burrow home is typically
1 inch in diameter and the tunnel length is usually several feet long.
The pistol shrimp can be observed removing sand and debris out of the
tunnel. Furthermore, the shrimp can lift twice its weight with its enlarged
snapping claw. While the shrimp maintains the burrow and tunnels, the
goby is diligently providing security. Occasionally, the goby will dart
out to get food or filter the sand through its gills. The pistol shrimp
when out will always maintain contact with the goby by placing an antenna
on the tail of the goby. The goby and shrimp will develop signals over
time from a caution twitch to a panic thrash. When this happens the
shrimp will always enter the tunnel first. The time recorded for both
to hide is about 1/10th of a second.
Gobies belong to the Gobiidae family, and make up the largest
family of marine fishes and consist of over 200 genera and 500 Indo-Pacific
species. While gobies are relatively small fish, usually reaching a
size of only three inches in an aquarium, some can reach a length of
over 20 inches in the wild. These fish have long, tubular bodies, blunt
heads, most have two dorsal fins and all but a few species lack gas
bladders. Gobies are found throughout the world in tropical and temperate
waters. They inhabit coral reefs, rocky areas, and lagoons. Also, they
reside in brackish and freshwater habitats. Most Gobies are found in
pairs or small groups, and are often associated with crustaceas or sessile
invertebrates. Some Gobies spend their lives with pistol shrimp, sharing
a burrow; other species of gobies live on the branches of sea fans,
sponges, or live corals. A small number of Gobies also act as cleaners,
picking parasites and dead skin from larger fish.
Aquarium currently exhibits the Yellow Watchman Goby with its pistol
shrimp symbiont or partner in the Symbiotic Relationships Exhibit. Also
featured in this exhibit are the Anemonefishes and Yellow Coral Gobies.
Banded or Yellow Watchman
Goby (Cryptocentrus cinctus)
Herre, A. W. C. T. 1936. Eleven new
fishes from the Malay Peninsula. Bull. Raffles Mus. 5-16
Myers, R. F.
1999. Micronesian Reef Fishes:
A Comprehensive Guide to the Coral Reef Fishes of Micronesia,
pp 239, Coral Graphics, Guam
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