Possible factors affecting predation of Ophioderma appressum and Ophiocoma enchinata – Stephanie and Nicole

Abstract picture
A brittle star at the start of one of the time trials.

Two species of brittle stars that are abundant in the reef flat of Discovery Bay are Opidoderma appressum and Ophiocoma enchinata, commonly known as the Banded-Arm brittle star and the Blunt-Spined brittle star respectively. When threatened, these organisms use their long arms to quickly find cover. If they are caught they have the ability to detach their arms in order to escape. We hypothesized that Ophiocoma enchinata would have a faster escape rate because they tend to be larger than Opidoderma appressum. Our hypothesis was not correct. Our data showed that larger brittle stars were not necessarily faster than the smaller ones and there was no difference in velocity between the two species. However, we did find that there was a significant difference in velocity among the different color variants of Opidoderma appressum, which led us to believe that surface color may have an effect on the velocity. We hypothesized that the color variants would move faster on a lighter surface when compared to a darker surface. We found that the average velocity significantly increased when the brittle star was placed on a light surface compared to a dark surface. As a result, we hypothesized that Opidoderma appressum may have a color preference. We found no statistical significance that would support our hypothesis but our data for this experiment was skewed due to a lack of specimens. 

 

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