Brittle Stars and Fireworms
What Are They?
Fireworms
Of the class Polychaeta (phylum Annelida), including the species Hermodice
and Eurythoe. Fireworms sting if touched. The body of H. ca
runculata,, is covered
with fine,
white, bristles that break if touched; they become
imbedded in human skin and produce a substance that is
irritating. The
bearded fireworm is usually found on reefs, under stones in rocky areas
of the sea, and on some mud bottoms. It is encountered throughout
the tropical western Atlantic and pacific. It can be found near ocean
reefs and
at most 150m deep. The fireworm primarily eats detritus but also
can eat coral and anemones.
Brittle Stars
Two
thousand living species of
marine invertebrates comprise the class Ophiuroidea (phylum
Echinodermata). They have five thin and often forked and
spiny
arms and radiate
off the the small disk-shaped body. They can easily "drop" and
arm as a defense mechanism. Brittle stars are mainly scavengers and
plankton feeders, but sometimes trap sizable animals. Brittle
stars are common members of reef communities, where they hide under
rocks and even within other living organisms.
What were we testing?
The relationship between fireworms and
brittle stars was tested. Brittle stars and fireworms tend to be
found together more than apart, we wanted to answer whether this was
coincidental or not. We also wanted to look at substrate and rock
type so we could conjecture as to the reason they are found together.
Hypothesis
It is not by coincidence that brittle stars and
fireworm tend to occur together.
Null Hypothesis
Brittle stars and fireworms only occur together
randomly and by coincidence.
Methods
To
perform this study 51 rocks were turned over within a 5 meter lane
parallel to the ocean (every rock in the transect that could be flipped
over was flipped over). A straight line was walked in zone three of the
inter tidal zone. The zone was determined by finding the correct
indicator species. The rock type (basalt/coquina), number of
brittle stars, number of fireworms and substrate type
(rocky/sandy) were recorded. This was performed at Station Beach,
Puerto Penasco, Mexico on September 9th, 2007 from about 9 PM to 10
PM. The weather was about 75-85 degrees fahrenheit with
little or no wind. The only material used was a tape measure,
which indicated the 5 meter path used.
Results
Below
are the final chi squared values, these chi squared values show that
our results are significant and that the occurance of fireworms and
brittle stars together are not coincidental.
|
BS Present |
BS
not Present |
| FW
Present |
20 |
4 |
24 |
| FW Not
Present |
8 |
19 |
27 |
|
28 |
23 |
51 |
|
|
|
|
| Expected |
BS Expected |
BS no Expected |
| FW
Expected |
13.1764706 |
10.8235294 |
24 |
| FW Not
Expected |
14.8235294 |
12.1764706 |
27 |
|
28 |
23 |
51 |
|
|
|
|
| Chi
Squared |
|
|
|
|
3.53361345 |
4.30179028 |
7.83540373 |
|
3.14098973 |
3.82381358 |
6.96480331 |
|
|
x^2= |
14.800207 |
|
|
p= |
0.0019 |
|
|
df= |
3 |
| Rock Number |
B/C |
Fireworm |
Brittle Star |
Substrate |
| 1 |
b |
0 |
0 |
rocky |
| 2 |
b |
1 |
1 |
sandy |
| 3 |
b |
0 |
2 |
sandy |
| 4 |
b |
1 |
2 |
sandy |
| 5 |
b |
0 |
5 |
sandy |
| 6 |
b |
0 |
1 |
sandy |
| 7 |
b |
1 |
5 |
sandy |
| 8 |
b |
2 |
1 |
sandy |
| 9 |
b |
1 |
2 |
sandy |
| 10 |
b |
1 |
1 |
sandy |
| 11 |
b |
2 |
1 |
sandy |
| 12 |
b |
6 |
1 |
sandy |
| 13 |
b |
0 |
0 |
sandy |
| 14 |
b |
0 |
0 |
rocky |
| 15 |
b |
1 |
0 |
rocky |
| 16 |
b |
1 |
4 |
sandy |
| 17 |
b |
0 |
2 |
rocky |
| 18 |
b |
0 |
1 |
rocky |
| 19 |
b |
0 |
0 |
rocky |
| 20 |
b |
0 |
1 |
rocky |
| 21 |
b |
0 |
0 |
rocky |
| 22 |
b |
3 |
3 |
rocky |
| 23 |
b |
2 |
1 |
rocky |
| 24 |
b |
3 |
0 |
rocky |
| 25 |
b |
1 |
2 |
rocky |
| 26 |
b |
0 |
0 |
rocky |
| 27 |
b |
1 |
4 |
sandy |
| 28 |
b |
3 |
2 |
sandy |
| 29 |
b |
0 |
0 |
rocky |
| 30 |
b |
2 |
1 |
rocky |
| 31 |
b |
0 |
0 |
sandy |
| 32 |
b |
0 |
0 |
rocky |
| 33 |
b |
2 |
0 |
rocky |
| 34 |
b |
2 |
2 |
sandy |
| 35 |
b |
1 |
2 |
sandy |
| 36 |
b |
2 |
2 |
sandy |
| 37 |
b |
0 |
1 |
sandy |
| 38 |
b |
0 |
0 |
rocky |
| 39 |
b |
0 |
0 |
rocky |
| 40 |
b |
1 |
1 |
sandy |
| 41 |
b |
2 |
6 |
rocky |
| 42 |
b |
0 |
0 |
sandy |
| 43 |
b |
0 |
0 |
rocky |
| 44 |
b |
0 |
0 |
rocky |
| 45 |
b |
0 |
0 |
rocky |
| 46 |
b |
0 |
0 |
sandy |
| 47 |
b |
1 |
0 |
rocky |
| 48 |
b |
0 |
3 |
sandy |
| 49 |
b |
0 |
0 |
rocky |
| 50 |
b |
0 |
0 |
rocky |
| 51 |
b |
0 |
0 |
sandy |
Above is the raw data of the 51 rocks
turned over for the experiment, this data includes number of fireworms
and brittle stars, rock type and substrate type.
Discussion
The
focus of this experiment was to see if brittle stars and fire worms
would be found under the same rocks in Rocky Point Mexico. During the
course of this experiment 50 basalt rocks were overturned in order to
examine the marine life underneath. This data is recorded in the table
above, showing if brittle stars and/or fire worms were found and the
number of each. Also, the substrate conditions (sandy or rocky) and
rock type (basalt or coquina) were observed and recorded, regardless if
brittle stars or fire worms were found. A series of chi squared tests
were done in order to determine the significance of the findings. The
first test that was done was to establish the significance of the
association between brittle stars and fire worms. The numbers of
brittle stars present and fire worms present together with when they
were not present gave a p value of 0.0019. The data suggests that
there is a significant association between the fire worm and brittle
star species in Rocky Point Mexico.
Many ophiuroids are scavengers or detritivores that
may also prey on small crustaceans or worms, and may be capable of
suspension feeding, using the mucus coating on their arms to trap
plankton and bacteria. Fire worms are omnivorous and will scavenge both
dead plants and animals. They use their mouth parts to scrape and
squeeze bits of food into their mouths. The association could be that
their food sources are similar and can be found in similar places. The
fire worms and brittle stars are found significantly more in the sandy
substrate. Which could indicate they both prefer the same
substrate.
This topic needs more study, an extensive search of
academic journals revealed no studies on brittle stars and fireworms
together. A study on the possible mutalisitic relationship could
shed light on why these two animals are found together. Perhaps it would reveal a true mutualism or even just a
habitat/substrate preference of both animals.
*Caption for graph: This pie graph represents the occurances of brittle
stars, fireworms or both found under the 51 rocks turned over.
This shows that a majority of rocks turned over had both fireworms and
brittle stars.
Sources
"fireworm."
Encyclopædia Britannica
. 2007.
Encyclopædia Britannica Online. 2 Dec. 2007 <http://www.britannica.com/eb/article-9034346>.
"brittle star."
Encyclopædia Britannica
. 2007.
Encyclopædia Britannica Online. 2 Dec. 2007 <http://www.britannica.com/eb/article-9016542>.
Web Page Created by Alex Tuttle, aeturtle@gmail.com, for Ecology 450:
Marine Discovery.