The sea cucumber Australostichopus mollis: Juvenile feeding ecology and habitat

Abstract

The aspidochirote sea cucumber Australostichopus mollis is a commercially valuable species of research interest as a candidate for aquaculture or polyculture. Understanding juvenile habitat and feeding biology is essential to furthering aquaculture efforts and expanding knowledge of the ecology of the species. Surveying within the Mahurangi Harbour, New Zealand, revealed highly patchy distribution of juvenile A. mollis at one site within an area of high adult density. High juvenile density correlated with sediment qualities favouring epibenthic detritivorous deposit-feeding. Juvenile A. mollis showed no distinct spatial separation from adults and no association with dense macroalgae or preference for shallower depths than adults, as may be expected from studies on other sea cucumber species. Wild caught juveniles displaced to non-juvenile habitats with novel surface sediments showed rapid growth. The results indicate that the highly patchy distribution of juveniles in the harbour is not due to differences in the food quality of sediments but rather other localised effects. Juvenile A. mollis show an ability to exploit a variety of benthic sediment food sources, with growth rates comparable to other cultured species. Juvenile A. mollis exhibited positive selectivity for organic particles both in situ and in the laboratory. Juveniles exhibited an ability to distinguish between different sediment TOM levels, an ability which became limited once TOM exceeded 3%. The results reiterate the specific nutrient recycling role of deposit-feeding sea cucumbers and may help explain the patchy distribution of juvenile sea cucumbers in heterogeneous habitats. In addition the research indicates that diet homogeneity and stability will be important in development of A. mollis artificial diets while a broad range of artificial diet grain sizes will be consumed. Juvenile A. mollis fed a high rate of mussel waste diet over three months exhibited significantly higher specific growth rate (SGR) than those fed natural sediment or algal diets. The results indicate the suitability of mussel waste as a juvenile diet and show that rapid growth can be expected among juvenile sea cucumbers cultured beneath mussel farms provided sea cucumber stocking rates are managed appropriately. Bioavailability of potential artificial diet ingredients was also systematically tested for juvenile A. mollis. Apparent digestibility was moderate for common carbohydrate sources and excellent for a range of artificial protein sources including low-cost protein sources. However, growth on artificial diets was poor and diet performance may need to be improved using fermentation steps or similar before they become viable. Rapid growth and flexible feeding preferences show A. mollis to be well suited to future aquaculture and polyculture.