This study investigated habitat selection in the burrowing brittlestar Ophiophragmus filograneus by examining preferences for grain size, vegetation, and structure. Experiments found the brittlestar significantly preferred very fine grain sand and habitats with the sea grass Halodule wrightii. The presence of physical structure, like sea grass, was an important factor in habitat selection. The study demonstrates grain size and structural habitat components like sea grass influence the patchy distribution of this brittlestar species.

1. Habitat Selection by the Burrowing Brittlestar Ophiophragmus filograneus:
Grain Size, Vegetation & Structure
Lee Ann J. Clements, Ph.D. & Indira Brown; Dept. Biology and Marine Science, Jacksonville University
Hypotheses Experimental Design 80.00%
70.00%
 O. filograneus prefers to burrow in fine grain sand with Four grain sizes 60.00%
the sea grass Halodule wrightii (Standard Sand Company, Jacksonville, FL)
Percentage
50.00%
 The attractiveness of sea grass micro-habitat is due to Very fine (50/140) 40.00% Natural sea grass rhizomes (Halodule
the presence of physical structure. wrightii).
Fine (45/60) 30.00%
Medium (30/65) 20.00% 70.00%
Ophiophragmus filograneus Coarse (20/30) 10.00%
60.00%
0.00%
VF FV 50.00%
 Family Amphiuridae: the Individual choice arenas
Percentage
burrowing brittlestars Figure 2. Results of grain size choice experiment to 40.00%
12 animals per experiment
 Burrows in sediment 5 - 7 cm determine differences in preference of finest grain sizes.
Repeated 4 times, N= 48 The very fine (VF) sediment was significantly preferred 30.00%
deep over the fine (F) sediment. (Freidman’s Rank Sums test,
 Patchy distribution = 0.05). 20.00%
 Seagrass communities 10.00%
 Collected from Banana River, Medium 70.00% 0.00%
FL (28o12’ N, 80o37’ W) A VF B
60.00%
 Central Disc diameter ~ 1 cm 50.00% Figure 4. Results of experiment to determine
Percentage
 Arm length ~ 10 cm preference for structure vs. bare sand. B indicates
40.00%
that animals chose to burrow at the border between
Fine 30.00% the two treatment. The artificial sea grass (A) was
Very 20.00% significantly preferred over the VF sediment.
(Freidman’s Rank Sums test, = 0.05).
Fine 10.00%
Coarse 0.00% Conclusions
SG VF B
Figure 3. Results of experiment to determine  Patchiness is the result of habitat
preference for sea grass vs. bare sand. B indicates
selection in a heterogeneous
50.00% that animals chose to burrow at the border between
45.00% the two treatment. The sea grass (SG) was environment
significantly preferred over the VF sediment.  Grain size is an important determinant
40.00%
(Freidman’s Rank Sums test, = 0.05).
Collection 35.00% of burrowing site for this brittlestar
Percentage
 Banana River, near 30.00%  Structure, represented by the sea-
Melbourne, FL (28o12’ N, 25.00%
grass Halodule wrightii is also
80o37’ W) 20.00%
important for this organism
 Salinity 24 ppt. 15.00%
 Natural Sediment 0.15 cm 10.00%
sieve 5.00%
0.00%
Lab holding conditions VF F
V M C
Other submerged vegetative structures
 Ten-gallon aquaria Artificial sea grass
 2- inch deep natural sediment Figure 1. Results of first grain size choice experiment. Lines rhizomes made from (the macro alga Caulerpa) may also be
connect treatments that were not significantly different ribbon and string. attractive as a structural component of the
 Seawater at 24 ppt (Freidman’s Rank Sums test, = 0.05).
 24 hours habitat.