Recognizability of algae ingested by abalone

Abstract

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.

Gastric evacuation time and digestive enzyme activity in abaloneHaliotis midaefed a formulated diet

“…Foale and Day (1992) observed that the rate of seaweed digestion in H. rubra did not differ significantly between animals fed daily and those starved for seven days. It can therefore be assumed, with reasonable certainty, that the three-day starvation period prior to the present trial probably did not affect the rate of digestion.…”

“…However, no work has been published on the rates of digestion of formulated diets. Less digestible algal species may remain identifiable in abalone guts for more than 48 h, whereas preferred species are largely digested within 24 h (Foale andDay 1992, Day andCook 1995).…”

“…As feed is the single biggest operating cost in intensive aquaculture, extensive work on factors influencing gastric evacuation time has been done on economically important fish species (Smith 1989). Feeding frequency and diet quality have been shown to influence the rate at which abalone digest algae (Foale andDay 1992, Day andCook 1995). However, no work has been published on the rates of digestion of formulated diets.…”

Drift algal subsidies to sea urchins in low-productivity habitats

“…Gut contents provide information on an organism's diet in the relatively short term but can overestimate the contribution of the most recently consumed food items and those that are digested more slowly (Foale & Day 1992). Chemical tracers may provide longer-term and less biased dietary information (Iverson et al 2004), but their interpretation may be complicated if animals consume mixed diets or modify chemical signatures of their food (Peterson 1999, Kelly et al 2008.…”

Vibrio superstes sp. nov., isolated from the gut of Australian abalones Haliotis laevigata and Haliotis rubra

“…Compared to the abundant populations of V. halioticoli and its speculated symbiotic contribution to the conversion of alginate to acetic acid in the gut of Japanese and South African abalones (Sawabe et al, 2003), V. superstes may not be able to form such associations with Australian abalones because the major food of Australian abalones is red algae (Foale & Day, 1992). Differences in feeding behaviour of host abalones may affect the microflora of the gut microbial ecosystem and select for biochemical traits of these …”