Feeding ecology of the abalone Haliotis iris (blackfoot paua): feeding preference, foraging behaviour, and interactions with other benthic herbivores

Abstract

Abalone are herbivorous marine molluscs commonly found in rocky reef ecosystems around the world. In New Zealand, Haliotis iris is a common and often abundant species whose feeding ecology, and thus role in subtidal reef communities, is not well-understood. The purpose of this study to examine H. iris's feeding ecology in the laboratory, specifically examining feeding preference, foraging behaviour, and interactions with other benthic herbivores, especially sea urchins. Results of laboratory experiments on feeding preference of H. iris demonstrated that both adults (104-134mm) and juveniles (8-16mm) generally preferred to feed on brown algae over reds and greens. Additionally, while H. iris preferentially consumed drift algae over attached algae, it was also capable of grazing on attached algae and did so frequently. When water movement was increased, overall H iris feeding decreased due to a decrease in the grazing of attached algae. The role of algal accessibility (i.e. height above the substrate) was complex. Easily accessible algae were consumed more when water motion was low, compared to when water motion was high, and when water motion was high accessibility played no role in determining the consumption of algae. In another set of experiments where accessibility of algae and algal species were separately manipulated, a less preferred, but more accessible species of algae (the red algae (Gigartina circumcincta) was consumed at higher rates than a highly preferred, but less accessible species (the kelp Lessonia variegata). The role of algal age on feeding was also examined, and contrary to a priori hypotheses, did not influence H. iris consumption rates. Finally, laboratory experiments examined the competitive interactions of other co-occurring herbivores with H. iris. The sea urchin Evechinus chloroticus is the most likely naturally occurring competitor, and appeared to inhibit the consumption of drift algae by H iris. High densities of conspecifics resulted in lower growth rates, and less consumption of unattached algae for H. iris. The opposite effect was recorded E. chloroticus, which consumed more attached algae at higher densities than at lower densities for the first five weeks of an experiment. The results presented herein show that while it is important to understand an herbivores' preference for specific types of algae, preferences demonstrated by laboratory experiments can play a less important role than the accessibility and morphology of algae in determining the intensity of herbivory that a particular species of algae may experience in the field. This study also highlights how factors such as herbivore foraging behaviour, environmental conditions, herbivore density and the presence of competitors may play a role in determining the interactions between herbivores and the algal community.