Light Preference (Experiment):
Introduction:

Eurythoe laevisetis is very brightly coloured and is somewhat lacking in camouflage. In fact, when the animal is disturbed and cannot hide it flares out its bristles and has been known to change from a dull gray to a much more vibrant red colour making it more visible. This lack of suitable camouflage means that the polychaete probably relies on its bristles and hiding to deter any potential enemies.

Studies have been undertaken on Hermodice carunculata and other members of the genus Eurythoe on light preference and it was found that Hermodice carunculata is diurnal but Eurythoe specimens are nocturnal. This is supported by the fact that Eurythoe specimens lack suitable daylight camouflage have been known to hide in crevasses and under rocks during the day but come out at night to look for food (Edmonds et al. 2000). However no studies have been done to determine whether or not the presence of light affects the hiding preference of Eurythoe laevisetis.


Methods:
Specimens were collected off the Heron Island Reef and brought back to the aquarium. All of the specimens were housed together in a clear plastic container that had a mesh lid. The container contained pieces of the rock, which the fireworms were originally extracted from, to provide housing. Other organisms, both dead and alive, such as crabs, shrimp, peanut worms and brittle stars were collected off the same rocks and placed into the container with the fireworms to act as a food source.

Three specimens were used for experimentation. Six pipettes had two centimetres of each of their ends cut off and then three of these six pipettes were wrapped in aluminium foil. Three arenas (width nine centimetres, length thirteen centimetres, height six centimetres) were set up with each arena containing a clear pipette and a foil covered pipette. One hundred millilitres of water was poured into each arena. Two experiments were completed with each experiment having nine replications. Specimens were randomly allocated into arenas.

Experiment 1: Experimentation was conducted in the full light of the lab. Each specimen was placed into the centre of its arena. The two different pipettes were randomly placed on either side of each arena. The specimens were then left alone for fifteen minutes. At the end of the fifteen minutes the specimens choice of pipette to hide in was recorded. Specimens were given a five minute rest period together in between experiments in their regular container.

Experiment 2: Experimentation was conducted under a large aluminium foil covered plastic container to create a dark environment. Each specimen was placed into the centre of its arena. The two different pipettes were randomly placed on either side of each arena. All of the arenas were then covered with the large plastic container. The specimens were then left alone for fifteen minutes. At the end of the fifteen minutes the foil covered plastic container was removed and the specimens choice of pipette to hide in was recorded. Specimens were given a five minute rest period together in between experiments in their regular container in the full light of the lab.


Figure 5: Experimental set up of the Experiment 1 phase.
Catherine Russo, University of Queensland St. Lucia, 2014


Results:
A t-test determined that there was a significant difference between light preference (P = 0.024142785). Eurythoe laevisetis did have a light preference with the darker environment being the preferred one. This can be seen in Figure 6. 


Figure 6: A graph showing the number of times a certain pipette was chosen under the conditions of experiment 1 and 2. Red columns represent clear pipettes. Blue columns represent aluminium foil pipettes. Experiment 1 is light and experiment 2 is dark. A sample size of nine was used for each experiment. 


Discussion:
The results of this experiment determined that Eurythoe laevisetis did exhibit a light preference. Even though both pipettes were the same, in conditions where light is present they preferred to hide in the darker pipette where as in the dark experiment either pipette was deemed to be a suitable hiding place.

Studies done on the genus Eurythoe found that each eye consists of two confluent depressions - a deep ventral cup and a shallow dorsal cup. The lenses have a large surface area and curve from the lateral to the dorsal surface of the prostomium. All of the eyes are also heavily pigmented (Marsden & Galloway 1967). The results of this experiment and the large amount of pigment present in each eye indicates that Eurythoe laevisetis is able to easily sense changes in the amount of light present.

Reasons for its aversion to light could be because it does not feel safe from predators during the day due to its lack of camouflage. Even though the clear pipette provided the same amount of protection it still felt vulnerable because if light can get through no doubt it is still visible to potential predators who may try to force it out of its hiding place.

Further research should be done to determine whether or not Eurythoe laevisetis would attempt to hide in the clear pipettes if they are the only ones present and a predator is introduced into the arena. An experiment with a predator and both a foil and clear pipette should also be completed. A larger sample size would also be beneficial for this research.