Recognizability of algae ingested by abalone

Studies of the diet of abalone and other herbivorous gastropods, based on gut contents, may be biased against some species of algae, especially those that are most preferred. The blacklip abalone Haliotis rubra was fed for short periods on monospecific diets of eight algae, including red, brown and green species that span the range of preference. In addition, two preferred species were fed to abalone after one month's, one week's, or no starvation. The number of recognizable fragments of each alga per unit volume of crop contents was examined. Although key characters of some species remained recognizable even at an advanced stage of digestion, other algae were intrinsically less recognizable. Preferred red algae disappeared rapidly after one week's or no starvation but more slowly after one month's starvation. Less preferred algae were not eaten without a long starvation period and became unrecognizable relatively slowly, especially the least preferred brown algae Ecklonia radiata and Phyllospora comosa, which have high polyphenol contents. Thus, the gut contents of starved abalone in the field contain recognizable fragments of less preferred species for long periods, whereas well-fed abalone retain recognizable fragments of preferred species only for short periods.