Feeding Preference Experiment
Introduction
Of the three species of tropical abalone, Haliotis asinina the Ass's Ear Abalone seems to have been the most widely studied. It has been considered by a number of authors as a candidate for commercial harvesting or aquaculture (Angell et al., 2012). Tropical abalone are reported to prefer red macroalgae over the coexisting green and brown varieties (Tahil and Juinio-Menez, 1999; Cornwall et al., 2009; Angell et al., 2012).
A number of studies have been published on the diet of H. asinina, but little appears to be known of the dietary preferences of H. ovina. The aim of this study was to examine the feeding preferences of H. ovina, and to determine if this species has a similar preference for red macroalgae such as Hypnea spp. and Laurencia spp. like the coexisting H. asinina (Tahil and Juinio-Menez, 1999).
Dorsal (left) and ventral (right) view of H. ovina.
Materials and Methods
The specimens used in the study associated with this web page were taken from the reef crest of Heron Island Reef within the permitted area north-east of Shark Bay, pursuant to Great Barrier Reef Marine Park Authority permit (QC11/022). All specimens were returned to a similar habitat at the conclusion of the experiment. They were kept without food for 24 hours prior to this experiment to standardise hunger levels as described in Tahil and Juinio-Menez (1999).
Three H. ovina of similar size and weight were placed in separate 30 x 40 x 20 cm plastic tanks with a flowing source of seawater. The tanks were placed outdoors and shade cloth was used to cover the tanks during daylight.
Five gram samples of each of the three macroalgal genera Laurencia, Padina and Chlorodesmis were attached by zip ties to a weighted plastic grid and placed at one end of each tank. The macroalgae were not able to be identified to species level. The abalone were placed at the opposite end of the tank at the beginning of the experiment. Observations of the position of each H. ovina specimen were made at one hour intervals over a 35 hour period.
One of the tanks with the three macroalgae genera Chlorodesmis spp, Laurencia spp. and Padina spp. (from left to right). Abalone were placed at the end of the tank furthest from the algae (bottom of picture) at the start of the experiment.
Results
Within one minute of being placed into their respective tanks at the beginning of the experiment, all three abalone made their way rapidly from the far end of the tank to the area where the macroalgae samples were placed, but they did not make contact with the plants. At no time in the next 35 hours was any animal observed on the macroalgae. So little movement was observed (despite being monitored every hour) over the experimental period, that no statistical analysis of the data was able to be undertaken.
Discussion
It was not unexpected that no feeding behaviour was observed during the day, but as H. ovina is a nocturnal feeder, some feeding was expected to be seen during the night. This study did not elucidate any feeding preferences of H. ovina, but this result has been observed by others (Viana et al., 2000) where they found that this species would not feed under captive conditions. This was observed for both natural and artificial diets.
There are a number of possible reasons or even combinations of reasons for this outcome under the experimental conditions of this trial. The species of macroalgae which were used in this experiment may not have been the preferred food source of H. ovina and the artificial way that the algae was presented may also have contributed to the abalones' reluctance to feed. The animals may have been under some transfer shock after being taken from their natural habitat and may not have had sufficient time to acclimate to their new surroundings as this experiment was conducted over a three day period. They were deliberately not provided with substrate under which they could hide during daylight, thus altering the lighting regime that they are habituated to. A larger sample size would have been desirable for this study, but time constraints prevented more specimens being obtained.
They were housed in small tanks of about 40 L in volume which allowed the water temperature to increase to 25ºC over the course of the daytime. This is much higher than the water temperature they would experience in the natural environment. The abalone is a thermoconformer and as such its body temperature varies with environmental temperature (Garcia-Esquivel et al., 2006) and combined with the altered light regime mentioned earlier this may have caused stress to the animals resulting in cessation of their feeding behaviour.
Although this study did not produce the expected results, it has posed questions about the biology of H. ovina such as its response to being removed from its natural environment and disruption to the natural diurnal rhythms and how these impact on the behaviour of this organism, compared to H. asinina which has shown feeding behaviour under similar conditions (Hoskin, 2011).
Acknowledgements
I thank Professor Bernie Degnan and Andrew Calcina, Jabin Watson, Federico Gaita and Ben Yuen for their advice and assistance in this project.
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