An observation of brittle stars Ophiothrix suensonii, Ophinoreis reticulata, and Ophiocoma enchinata, and their preference in sponge selection among Alypsina fistularis and Niphates digitalis.

Brittle stars are naturally a negatively phototaxic species; therefore the species we tested were placed in a closed tank covered from light. This enabled them to attach to a particular sponge species for reasons other than avoiding light. By positioning a selected species of Brittle stars in an assigned pre-measured area, we were able to observe their final location after three hours in the dark tank. After conducting 4 trials for each star species it was observed that the majority of Brittle stars were found not attached. Sponge Brittle Stars were the first to be selected for testing and were found to have low attachment to any of the sponges in the controlled environment. This was peculiar since all of the Sponge Brittle stars collected in the wild were found attached to Niphates digitalis. They were mostly found in the middle showing the least activity, low tolerance for stress, and very susceptible to de-attaching their podia. Reticulated Stars were more active than the Sponge stars, and were never found at their initial position (the center), but mass numbers were found compressed in corners where the net divider and tank wall met. Those found on sponges were mostly found on Niphates digitalis and Aplysina fistularis. Blunt Spined Brittle Stars have shown to be the most active when seeking out sponges in the tank. The majority of these stars were found on the cover of the tank, and on the other side of the net divider. This species seemed to be attracted to Aplysina fistularis the most compared to the other species.

– Kasey and Brooks