TIME FOR PROTECTION

By Ellen Vaughn

 

 

The Cushion or Reticulated Sea Star is a large, dynamic creature found on the floor of the ocean around South Florida, The Caribbean, and the West Indies. Having observed the spectacular cushion sea star, a question arouse as to how it protected itself from it’s enemies. It has a hard spiny aboral surface facing upward with an oral surface facing the bottom which contains the mouth and five radiating grooves, the ambulacra. When turned over on the oral side, the sea star is far more vulnerable and makes gallant efforts to return to the more protected aboral side. This observation created the question, how long does it take for a sea star to return to its upright position with the aboral surface facing up? Does the speed of turn over vary from sea star to sea star? Does the environment affect the speed of the turn over? Does size affect the turn over response time? Are there other factors which affect the turn over rate of this wonderful creature?

 

  • PROCEDURES:
    1.  
    2. Locate a sea star *1.

       

    3. Measure the length of the sea star from the end of one tip to the end of the opposite tip.

       

    4. Note the environment of the sea star - water conditions, depth, and type of ocean bottom. (Sea grass, sand, rock).

       

    5. Turn the sea star over on it’s aboral side and record the time necessary for the sea star to turn back over to its oral side.

     

     

     

     

     

     

    1 The sea stars included in this study were limited to those witnessed and timed by the author. Many other sea stars were timed by peers. The statistics of the others were shared; however, the conditions under which the sea stars were timed was unclear. Therefore, the data has not been included in this research.

     

    RESULTS:

    After looking at the skimpy data from the ocean floor it was decided to seek sea stars in a more controlled setting such as a touch tank. Data was compiled from both locations with the results being presented in Chart 1. The location, depth, size, type of bottom, and the time necessary for each sea star to turn over is included in this chart.

     

     

    Type

     

    Depth

     

    Length

     

    Conditions

     

    Type

     

     

     

    Cushion

    Cushion

     

    shallow/8 ft.

    shallow/8 ft.

     

    27 cm

    27 cm

     

    quiet bay

    quiet bay

     

    sand

    sand

     

    2.07

    1.27

     

    Cushion

    Cushion

    Cushion

     

    deep/15 ft.

    deep/15 ft.

    deep/15 ft.

     

    27 cm

    27 cm

    27 cm

     

    wavy water

    wavy water

    wavy water

     

    sea grass

    sea grass

    sea grass

     

    3.00

    2.50

    4.00

     

    Brown Spiny

    Brown Spiny

    Brown Spiny

     

    shallow/6 in.

    shallow/6 in.

    shallow/6 in.

     

    14 cm

    14 cm

    14 cm

     

    touch tank

    touch tank

    touch tank

     

    shell

    shell

    shell

     

    2.10

    2.15

    2.15

     

    Brown Spiny

    Brown Spiny

    Brown Spiny

     

    shallow/6 in.

    shallow/6 in.

    shallow/6 in.

     

    8 cm

    8 cm

    8 cm

     

    touch tank

    touch tank

    touch tank

     

    shell

    shell

    shell

     

    2.18

    2.43

    2.20

     

     

     

    Chart 1: Turn Over Data for Cushion Sea Stars

    and Brown Spiny Sea Stars

     

     

    Looking at the ocean sea stars (Cushion Sea Star) it seems the depth or water conditions affected the turn over rate. The sea star in the wavy, deep water took longer to turn over than the sea star found in the shallow quiet water. Graph 1 demonstrates the differences in turn over times. According to this graph there seems to be significant differences in turn over time, but before any conclusions could be drawn more experimentation needs to be done with several sea stars, not just one per location.

     

    (Jim, you need to scan in a chart here)

     

     

     

     

     

     

     

     

     

     

     

    Graph 1: Turn Over Time For Cushion Sea Stars

    In Relationship To Depth

     

    Several different experiments could be done with the different factors shown in Chart 1 - the depth of the water, the activity level of the water, and the type of bottom upon which the sea star is located (sand, sea grass, shell, and others). Each of these could prove to be significant factors in the turn over rate and could be a study in itself.

    As mentioned before, due to the low sampling of the cushion sea star, sea stars in another setting were included in this study. Two Brown Spiny Sea Stars living in a touch tank were included. Chart II demonstrates there is not much difference in the turn over rates of these two sea stars with only 35 seconds difference from the slowest to the fastest.

     

    (Jim, you need to scan in another chart)

     

     

     

     

     

    Graph II: Turn Over Time For Brown Spiny Sea Stars

    In Relationship To Size

     

    In graph form; however, it becomes apparent, the larger sea star (D) took a little longer to turn over than the smaller sea star (C). Once again there is room for more experimentation in this area. Would the trend for larger sea stars continue with more tires/

    Another very important factor to consider is the number of times the same sea star was targeted. Is there a fatigue factor to consider in the timing of the turn over? Looking at all the sea stars in this study (see Chart I), excluding Sea Star A, there are indications this could be such a factor. All samples took longer the second time they were targeted. The results of sea star B strongly suggests it was tired the third time it had to turn over. This same result was not seen in sea star A; however, Trial 3 showed a decline from Trial 2 but still an increase from Trial 1. This indicates the fatigue factor could be in play.

    With this in mind, further testing was done in the touch tank setting. The data included in Graph III was gathered at one time with the primary purpose of investigating the fatigue factor in the turn over time of sea stars. This time three different sea stars were used - two Brown Spiny sea stars and one Netted Sea Star. The different sea stars were used to show a pattern across species. It must also be noted there were not three sea stars inhabiting the touch tank, therefore they all became subjects for this part of the study.

     

    (Jim, scan in another chart in this area)

     

     

     

     

     

     

     

     

     

    Graph III: Turn Over Time Of Sea Stars

    In Relationship To The Fatigue Factor

     

    As seen by the information on Graph III, there is a strong tendency for each of the three sea stars to slow down in their ability to turn over. It also becomes evident the smaller sea stars tend to tire more quickly than the larger ones. It would have been interesting to make more trials but time limited the possible number of trials. Would the larger sea star demonstrate the dramatic time difference shown by the smaller sea stars or would it have continued on the same gently incline seen on Graph III?

     

    CONCLUSION:

    Several trends come to light through this research, yet these trends cannot be cited as fact. Much more testing would be necessary for significant results in any of the areas mentioned.

    1.  
    2. In the ocean setting, depths of or the types of water conditions seem to play an important role in the turn over reaction of Cushion sea Stars. As previously stated, more experimentation with tighter controls for the above factors would be necessary to claim significant results.

       

    3. In the touch tank situation, size and type of sea star play important factors in the turn over time. The results of this section of the study cannot be compared to the results dealing with Cushion Sea Stars since they are two different species of sea stars in two different environments and the "turn over" conditions were a little different (the natural ocean verses an artificial, extremely shallow touch tank).

    The only true result of this experiment is "sea stars don’t stay on their oral side and they turn over as quickly as they can when placed on their aboral side - usually within a 2 minute period. There also tends to be an increase in the time to turn over after several tries. This fatigue factor seems to be greater for the smaller sea stars than the larger ones. It was expected the larger sea star would have tired faster than the smaller ones since they probably used more energy to make these turn overs. An explanation for this result might be the smaller sea stars have a higher metabolism than the larger sea stars, therefore, use up their stored up faster than the larger ones. Researching this hypothesis would be a very interesting extension to research done here.

    All in all, the Cushion Sea Star, the Brown Spiny Sea Star, and the Better Sea Star are "neat" creatures which could be the targets for more controlled experimentation. Next time, it would be beneficial to pick one factor, size, water depth, or water conditions, with which to work. All of these factors then rely on the plentifulness of these wonderful creatures. Furthermore, much to the dismay of sea star lovers, the Cushion Sea Star has become quite rare in some areas due to avid souvenir hunters. This restricts the ability of researchers such as us to carry out plentiful experiments.

     

    (Jim, you need to scan in 7 different pictures)

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