Habitat Selection by the Burrowing Brittlestar Ophiophragmus filograneus in the Banana river Lagoon, Florida.

Indira Brown, Department of Biology and Marine Science, Jacksonville University.

Abstract

Brittlestars are motile Echinoderms inhabiting the oxidized subsurface layer of soft-bottom

substrates in every marine environment. Burrowing brittlestars typically have a patchy

distribution that may be influenced by sediment organic content or presence of sub-aquatic

vegetation. Few studies have been undertaken to determine specific substrate preferences.

Ophiuroids from the Banana River Lagoon near Merritt Island, FL were collected to determine

their substrate preferences based on four sediment grain sizes. In controlled laboratory tests of

grain size preference, brittlestars preferred to burrow in the very fine and fine grained

sediments (N=48). Subsequent experiments testing preference between these two grain sizes

revealed a preference for the very fine sediments. Further experiments of grain size with

vegetation and artificial vegetation were performed. Results indicated Ophiophragmus

filograneus’ patchy distribution in the natural environment may correlate with very fine

sediment, seagrass and structural distribution.

KEYWORDS: Ophiophragmus filograneus, brittlestars, sediment preference.

Introduction

Benthic invertebrates play a vital role in the physical, chemical and biological structure of their

sedimentary environment. They are known to recycle nutrients and detoxify pollutants through

burrowing, feeding, and respiring (Peterson and Quammen 1982; Fukuyama and Oliver 1985;

Kvitek et al. 1992; Micheli 1997). The mobility of sediment-associated cadmium (Cd), for

example, may be increased during resuspension of sediments by a shift from reducing to

oxidizing conditions and by altered pH (Khalid et al., 1981; Förstner, 1987; Peterson et al.,

1996). Ophiuroids are one of the numerous benthic invertebrates that contribute to the

oxidization state of the subsurface sediment layer in the marine environment. They are also an

important component of the marine trophic system in shallow waters (Turner and Meyer 1985).

Ophiophragmus filograneus belongs to the Family Amphiuridae, which is also known as

the burrowing brittlestars. O. filograneus burrow in the sediment 5-10 cm deep. They are one of

the smallest known brittlestars with disk diameters of approximately 1 cm, and arms up to 10

cm in length. O. filograneus are common in the marine littoral regions from the southern tip of

Florida to Pensacola Bay on the North West coast and to Cape Canaveral in the North East. They

have also been found in Cedar Key, Florida. O. filograneus are unique because they occur in

estuaries at reduced salinities and not in the open sea. In the past, distribution of

Ophiophragmus was assumed to be limited because it was known to adapt to environments

with reduced salinities. However, recent studies indicate O. filograneus functions better at

higher salinities and therefore its restriction to estuaries is probably due to other factors such

as food resources, sediment type, competition, or predation or some other factor (Talbot and

Lawrence 2006).

Within estuaries Ophiophragmus filograneus still shows patchy distribution. The factors

that define their irregular distribution are unclear. Some possible factors influencing their

distribution are sediment size and the presence of sea-grass, or other submerged aquatic

vegetation. The burrowing brittlestar Micropholis gracillima preferred to burrow in fine grained

sediment with some organic content (Zimmerman 1987). The goal of this study is to determine

the substrate preference of Ophiophragmus filograneus with regards to sediment grain size,

seagrass and artificial seagrass substrate. The proposed hypothesis is that Ophiophragmus

filograneus would prefer fine and very fine.

Methodology:

The collection site for this experiment was in the Banana River, near Melbourne, FL

(28o12’ N, 80o37’ W) (Figure 1). The salinity of the water was recorded at 24 ppt. Sediment was

collected by the shovelful in shallow water (no more than 3 feet in depth) and then sieved

through 0.15 cm sieve in order to obtained the specimens burrowed within the sediment. The

specimens were placed in a bucket with portable air pumps filled with natural seawater from

the site. The specimens were transported back to Jacksonville University’s wet lab. The

specimens were placed in two ten-gallon aquaria with a 2 inch deep layer of natural sediment

from the collection site and natural seawater at 24 ppt. The brittlestars remained in the holding

tanks for 24 hours to acclimate to their new environment before testing began. The salinity was

adjusted with distilled water as necessary to maintain a constant 24 ppt. Specimens were fed

every other day with finely powered fish food flakes.

The first experiment was designed to determine brittlestar preference when presented

with four sediments. The sediment sizes were very fine (50/140), fine (45/60), medium (30/65),

and coarse (20/30). Sediment was purchased locally from (Standard Sand & Company Services,

Jacksonville, FL) and was clean of debris and organic material. Finger bowls (8 inches diameter)

were used as individual testing arenas. Natural sea water was placed into each of the bowls to a

depth of 2 inches. Each bowl was divided into four pie-shaped sections with plastic dividers to

prevent mixing of the different sand sizes. Sand was placed into each section so that all four

sizes of sand were represented in each bowl. The size of sand in each section was indicated

along the outer perimeter of the finger bowls (Figure 2). For example, the coarse treatment was

placed between the very fine and fine at the southern perimeter of the bowl, while the medium

treatment was placed between the very fine and fine at the northern perimeter of the bowl.

The sediments were allowed to settle for 24 hours before placing brittlestars in each bowl.

An individual O.filograneus was placed at the center of its assigned bowl at 3:00p.m.

After placing the brittlestars in each of the 12 bowls, the blows were covered with a box to

prevent light penetration that might influence the specimens’ substrate preference. After 24

hours the boxes were removed and the location of the burrowed brittlestar was recorded as its

sediment preference (Figure 3). The specimens were then removed and placed into a separate

holding tank from the brittlestars that had not yet been tested. The 12 finger bowls were

cleaned in order to remove all scent of previous specimens tested. The finger bowls were then

reset with new sediments and allowed to settle for 24 hours before testing resumed. Each set

of 12 finger bowls tested is referred to as a block. The experiment was repeated 4 times for a

total N of 48. The data were analyzed with a Freidman’s Rank Sum test (Table 1).

A second set of experiments was done to determine the preference of brittlestars

between the two sediment sizes most often chosen in the first experiment, which were the very

fine and the fine (Figure. 4). The same exact method from the previous study was used, except

in this case the arenas were divided into 2 sections instead of 4. The data was also analyzed

with a Freidman’s Rank Sum test (Table 2).

The third set of experiments was performed to determine brittlestars preference

between the very fine sediment and seagrass (Holodule wrightii). The same exact method from

the second set of experiment was used, except the brittlestars remained in the holding tanks

for 48 hours to acclimate to their new environment before testing (Figure 4). In addition, the

seagrass rhizomes were submerged within the very fine sediment as its’ blades were above the

sediment submerge in water. Due to the irregularity of placing the sediment at the edge of the

arenas, the experiment was performed again. During the second set of testing, the seagrass

were placed in the center on its side of the arenas. The data were analyzed with a Freidman’s

Rank Sum test (Table 3).

The fourth and final set of experiments was set up exactly as the pervious experiment in

order to determine the preference of brittlestars between the very fine sediment sizes and

artificial seagrass (Figure 5). The artificial seagrass was constructed using Diamond coffee

stirrers and Berwick curling ribbons. The ribbon, which was seven inches in length, was folded

in half then tied around a coffee stirrer in an overhand bend knot. The same exact method from

the previous study was used. The data was also analyzed with a Freidman’s Rank Sum test

(Table 4).

Results

In the first set of experiments, the brittlestars within each block appeared to have

selected the very fine and fine sediments most often, with very few brittlestars selecting the

medium or coarse sediment. Block 1 is significantly different from blocks 2, 3, and 4, (Figure 6).

However, despite this anomaly, the overall trend was that the majority of animals preferred the

very fine and fine sediment size, and rarely preferred the medium and coarse sediment size

(Figure 7). In this case, 44% of the brittlestars preferred the very fine sediment, 40% preferred

the fine sediment, 6% preferred the medium sediment and 10% preferred the coarse sediment

(Figure 8).

In the second set of experiments, the brittlestars’ preference between the fine and very

fine sediments was tested. Once again block 1 showed a different trend from blocks 2, 3 and 4.

For example, in block 1, seven brittlestars preferred the fine sediment and five brittlestars

preferred the very fine sediment. However, in all of the other blocks the very fine sediment was

most often selected (Figures 9 & 10). In total, 69% of the brittlestars preferred the very fine

sediment and 31% preferred the fine sediment (Figure 11).

In the third set of experiments, the brittlestars’ preference between the seagrass and

the very fine substrate was tested. The brittlestars within each block appeared to have

preferred the seagrass in the very fine sediments most often. Very few brittlestars selected the

boarder or the region between the seagrass and very fine sediment. For example in block 1, six

brittlestars preferred the seagrass bed, four preferred the very fine sediment and 2 preferred

the border. Block 3 was slightly different since no brittlestars preferred the boarder (Figures 12

& 13). In total, in all the blocks the seagrass substrate was often selected. Therefore, 60.42% of

the brittlestars preferred the seagrass substrate, 29.17% preferred the very fine sediment and

10.42% preferred the border (Figure 14).

In the final experiment, brittlestars’ preference between the artificial seagrass and very

fine sediments was tested. Once again the brittlestars within each block appeared to have

selected the artificial seagrass and very fine sediments most often, with very few brittlestars

selecting the border or the region between the seagrass and very fine sediment. There was no

difference between the trends in each block. For example in block 1, seven brittlestars

preferred the fine sediment, four brittlestars preferred the very fine sediment and one

brittlestar preferred the border. In all of the blocks the artificial seagrass substrate was most

often selected (Figure 15 & 16). In total, 60.42% of the brittlestars preferred the artificial

seagrass substrate, 31.25% preferred the very fine sediment and 8.33% preferred the border

(Figure 17).

Figure 1. The collection site of O.filograneus in the Banana River is indicated by the red Oval.

Figure 2. Photograph of experimental set Figure 3. Brittlestar burrowed in one bowl Of testing arenas from the first set of experiments. Location

of the brittlestar is very obvious.

Figure 4. Photograph of experiments 2 through 4 testing arenas

Figure 5. Photograph of testing arina with artificial seagrass.

Table1. Statistical analysis of data from the first set of experiments. The numbers in the table reflect the rank of choice within each block. A choice of very fine sediment was assigned the value of 1, fine sediment was assigned the value of 2, medium sediment the value of 3, and coarse sediment the value of 4.

Bowl Number Block 1 Block 2 Block 3 Block 41 3.5 3.5 8.5 3.52 8.5 8.5 3.5 11.53 3.5 8.5 8.5 8.54 9 3.5 3.5 3.55 11.5 9 8.5 3.56 3.5 8.5 8.5 8.57 3.5 8.5 3.5 8.58 11.5 8.5 9 8.59 3.5 8.5 8.5 3.5

10 11.5 3.5 3.5 3.511 3.5 3.5 3.5 8.512 8.5 3.5 11.5 8.5

Rank 81.5 77.5 80.5 80Rank2 6642.25 6006.25 6480.25 6400

∑ Rank2 553.5208∑ Ranks2/12 46.12674

H -0.51466t 11 11 10 11T 1320 1320 990 1320

sum of T 4950

adjusted H -3.50669

Table 2. Statistical analysis of data from the second set of experiments. The numbers in the table reflect the rank of choice across the entire experiment. A choice of very fine sediment was assigned the value of 1, and the fine sediment was assigned the value of.

Bowl Number Rank 1 Rank 2 Rank 3 Rank 4

1 41 17 41 17

2 41 17 17 17

3 17 17 17 17

4 41 17 41 17

5 17 17 17 41

6 41 17 17 17

7 17 17 17 41

8 41 17 17 41

9 17 17 17 41

10 41 17 17 17

11 17 17 41 17

12 41 41 17 17

∑ Ranks 372 228 276 300

∑Ranks^2 138384 51984 76176 90000

∑ Ranks^2/12 11532 4332 6348 7500

H 150.8418

t 33 15

T 35904 3360

sum of T 39264

adjusted H 233.9318

Table 3. Statistical analysis of data from the third set of experiments. The numbers in the table reflect the rank of choice across the entire experiment. A choice of very fine sediment was assigned the value of 1, seagrass was assigned the value of 2, and the broader between very fine and seagrass was assigned the value 3.

Bowl Number Rank 1 Rank 2 Rank 3 Rank 4

1 7.5 29 29 7.5

2 7.5 29 7.5 7.5

3 29 7.5 29 7.5

4 29 29 7.5 46

5 46 46 7.5 29

6 29 29 29 29

7 7.5 29 29 7.5

8 29 7.5 29 29

9 46 29 29 46

10 29 29 7.5 29

11 29 29 29 29

12 7.5 29 29 29

∑ Ranks 296 322 262 296

∑Ranks^2 87616 103684 68644 87616

∑ Ranks^2/12 7301.333 8640.333 5720.333 7301.333

H 147.0221

t 14 29 5

T 2730 24360 120

sum of T 27210

adjusted H 195.0274

Table4 . Statistical analysis of data from the third set of experiments. The numbers in the table reflect the rank of choice across the entire experiment. A choice of very fine sediment was assigned the value of 1, artificial seagrass was assigned the value of 2, and the broader between very fine and artificial seagrass was assigned the value 3.

Bowl Number Rank 1 Rank 2 Rank 3 Rank 41 46.5 7 7 72 7 30 30 303 7 30 30 304 30 30 30 305 30 7 30 76 7 30 46.5 307 30 7 7 46.58 30 46.5 30 309 30 7 30 30

10 7 7 30 711 30 30 7 3012 30 30 30 30

∑ Ranks 284.5 261.5 307.5 307.5 ∑Ranks^2 80940.25 68382.25 94556.25 94556.25

∑ Ranks^2/12 6745.021 5698.521 7879.688 7879.688H 143.1424t 15 29 4T 3360 24360 60

Sum of T 27780adjusted H 191.1886

Block1 Block2 Block3 Block 40

1

2

3

4

5

6

7

VFFMC

Num

ber o

f Bri

ttle

star

s

Figure 6. Results of sediment preference among four sediment grain sizes with each block shown separately. VF = very fine, F=fine, M= medium, C= coarse.

VF F M C0

1

2

3

4

5

6

7

Block1Block2Block3Block 4

Num

ber o

f Bri

ttle

star

s

Figure 7. Results of sediment preference among four sediment grain sizes grouped by grain sizes. VF = very fine, F=fine, M= medium, C= coarse.

VF V M C0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

30.00%

35.00%

40.00%

45.00%

50.00%

Perc

enta

ge

Figure 8. Results of sediment preference among four sediment grain sizes with all blocks combined. VF= very fine, F= fine, M= medium, C= coarse.

Block1 Block2 Block3 Block 40

2

4

6

8

10

12

VFF

Num

ber o

f Bri

ttle

star

s

Figure 9. Brittlestar sediment preference between very fine (VF) and fine (F) sediment size

VF F0

2

4

6

8

10

12

Block 1Block 2Block 3Block 4

Num

ber o

f Bri

ittle

sars

Figure 10. Brittlestar sediment preference by sediment grain size—second set of experiments. Blocks are indicated by the different colors.

VF V0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%Pe

rcen

tage

Figure 11. Brittlestar sediment preference by sediment grain size with blocks combined. VF= very fine, F= fine.

Block 1 Block 2 Block 3 Block 40

2

4

6

8

10

12

VFSGB

Num

ber o

f Bri

ttle

star

s

Figure 12. Brittlestar preference between seagrass (SG) and very fine (VF) sediment size.

VF SG B0

2

4

6

8

10

12

Block 1Block 2Block 3Block 4

Num

ber o

f Bri

ttle

star

s

Figure 13. Brittlestar preference between seagrass (SG) and very fine (VF)-third set of experiments. Blocks are indicated by the different colors.

SG VF B0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

Perc

enta

ge

Figure 14. Brittlestar substrate preference between seagrass and very fine grain size with blocks combined. VF= very fine, F= fine.

Block 1 Block 2 Block 3 Block 40

2

4

6

8

10

12

VFAB

Num

ber o

f Bri

ttle

star

Figure 15. Brittlestar preference between artificial seagrass (AG) and very fine (VF) sediment size.

VF A B0

2

4

6

8

10

12

Block 1Block 2Block 3Block 4

Num

ber

of B

ritt

lest

ars

Figure16. Brittlestar preference between artificial seagrass (SG) and very fine (VF)-third set of experiments. Blocks are indicated by the different colors.

A VF B0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

Perc

enta

ge

Figure 17. Brittlestar substrate preference between artificial seagrass and very fine grain size with blocks combined. AF= very fine, VF= very fine.

Discussion

Although block 1 was statistically different from the other blocks in both experiments, the

results from the experiment indicated that Ophiophragmus filograneus preferred smaller grain

sizes, and specifically the very fine grain size in the absence of aquatic vegetation. The reason

for the difference in brittlestar behavior between block 1 and the subsequent blocks may have

been a result of handling time during experimental set-up. The process of transferring the

brittlestars from the holding tank to the bowls took longer for block 1 than for any of the

subsequent blocks. This trend was also true for the second set of experiments.

In addition, it was taken under consideration that brittlestars tend to be associated with

seagrass, (Halodule wrightii). This raises the questions “Do they prefer soft sediment or

seagrass substrate? Or do seagrass prefer the soft sediment? Due to the above mention quires,

further research in the laboratory and in the field was undertaken. The results from

experiments three and four indicated that Ophiophragmus filograneus preferred structure

substrate, especially in the presence of aquatic vegetation. The reason the third experiment

was performed a second time was due to the position of the seagrass within the bowl and the

difference in brittlestar behavior in block 1. In addition, the variation in block 1 may have been a

result of not having sufficient acclimation time. The process of transferring the brittlestars from

the holding tank to the bowls took longer for block 1 than the other blocks during experimental

set-up. The brittlestars were given an additional 24 hours to acclimate in subsequent

experiments. As a result there were no statistical differences between the blocks in the third

and fourth experiment.

Despite the anomaly of block 1, the overall trend was for brittlestars to prefer the

smaller grain sizes. In addition, the overall trend suggests that brittlestars prefer seagrass

substrate in the presence of aquatic vegetation. Just as important, brittlestars prefer structural

substrate in the absence of aquatic vegetation. This suggests that the hypothesis about

brittlestars sediment preference, seagrass and structural substrate were correct.

Ophiophragmus filograneus’ patchy distribution in the natural environment may correlate with

sediment distribution, seagrass distribution and structural distribution. This remains to be

verified in the field. However, It must be taken into consideration that the different sediments

were clean and major organic compounds were absent. Zimmerman et al 1987 showed that

organic content of the sediment is an important factor for other burrowing brittlestars.

References Cited

Bryant, Benjamin. (1999). Effects of hydrodynamic stress on the skeletal regeneration rate of the infaunal brittlestar Ophiophragmus filograneus (Echinodermata: Ophiuridea) Undergraduate research, Jacksonville University. Jacksonville, Fl, USA.

Clements, L.A., S. Bell, and J.P. Kurdziel. (1994). Abundance and arm loss of the infaunal brittlestar Ophiophragmus filograneus (Echinodermata: ophiuridea), with an experimental determination of regeneration rates in natural and planted seagrass beds. Mar. Biol. 121:97-104.

Dobson, W. E. (1988). Early post-autonomy tissue regeneration and nutrient translocation in the brittlestar Microphiopholis gracillima (Stimpson) (Echinodermata: Ophiuroidea). Ph.D. Dissertation, University of South Carolina, Columbia, SC, USA.

Dobson, William E., Stephen E. Stancyk, Lee Ann Clements, and Richard M. Showman. (1991). Nutrient Translocation during Early Disc Regeneration in the Brittlestar Microphiopholis gracillima (Stimpson) (Echinodermata: Ophiuroidea). Bio. Bull. 180: 167-184.

Dulzaides, Carla. (2006). Do Sediment Characteristics Affect Brittlestar Distribution. Undergraduate research, Jacksonville University, Jacksonville, Fl, USA.

Fancony, Evelyn Preciosa (2006). Infauna Association of Brittlestars in the Seagrass bed of the Indian River Lagoon. Undergraduate research, Jacksonville University, Jacksonville,Fl, USA.

Keegan, Brendan F., and Connor,Brendan D.S. (1984). Echinodermata. Unversity College, Galway, Ireland.

Lawrence, John. (1987). A Functional Biology of Echinoderms. Salinity Tolerance of the Brackish-Water Echinoderm Ophiophragmus filograneus (Ophiuroidea). Melbourne, Fl, USA.

Levinton, Jeffrey S. (2001). Marine biology: function, biodiversity, ecology. Second ed. New York: Oxford University Press.

McAlister, Justin Scott. (1998). Effects of variable water motion on regeneration of the infaunal brittlestar, Hemipholis elongata (Say, 1825) (Echinodermata: Ophiuroidea). M.S. Dissertation. University of South Carolina, Colombia, SC, USA.

Stancyk, S.E., H.M. Golde, P.A. Pape-Lindstrom, W.E. Dobson. (1994). Born to lose I. Measures of tissue loss and regeneration by the brittlestar Microphiophlis gracillma (Echinodermata: ophiuridea). Mar. Biol. 118: 451-262

Stancyk, Stephen E. (1970). Study on the biology and ecology of ophiuoids at Cedar Key, Florida. MS thesis. University of Florida. Gainesville, Fl, USA. pp. 11-66.

Talbot, Tiffany D. (2002). The effects of salinity on production in the brittlestar Ophiophragmus filograneus (Echinodermata: Ophiuroidea) University of South Florida, Fl, USA.

Turner, Richard L., and Meyer, Cathy E. (1987) Salinity Tolerance of the Brackish-Water Echinoderm Ophiophragmus filograneus (Ophiuroidea). Melbourne, Fl, USA

Woodley, J.D. (1975). The Behavior of some Amphiurid Brittlestars. J. of Exp. Mar. Biol. Ecol. 18:29-46.

Zimmerman, Kerry M., Stancyk, Stephen E. and Clements , Lee Ann. (1987). Substrate Selection by the Burrowing Brittlestar Microphiopholis gracillima (Stimpson) (Echinodermata: Ophiuroidea). Unversity of South Carolina, Columbia, USA.