Sediment patch selectivity in tropical sea cucumbers on the Great Barrier Reef

Five species of aspidochirotide holothurians, (Holothuria atra, Holothuria edulis, Holothuria nobilis [now whitmaei], Stichopus chloronotus and Stichopus variegatus) were subjected to multiple choice feeding preference experiments in aquaria, to investigate selectivity of sediment patches. Experiments on Holothuria atra, Holothuria edulis and Stichopus chloronotus were conducted at AIMS using specimens collected from Great Palm Island. Experiments on Holothuria nobilis and Stichopus variegatus were carried out at Lizard Island on specimens collected from the local reefs. Sediment was collected from the natural habitat of each species, for the culture of sediment microalgae. Samples of sediments were subjected to one of four treatments (which were designed to create sediments with differing amounts of microalgal biomass) for a period of 8-12 days: TR1=dark, TR2=nutrient reduced, TR3= normal, TR4= nutrient enhanced. Only TR1 and TR3 were prepared at Lizard Island.Five replicate sediment samples per treatment and experiment were analysed for chlorophyll a and phaeophytin prior to commencement of each experiment. Duplicate water samples from all treatments used in 2 experiments with Holothuria atra, 1 experiment with Holothuria edulis and 3 experiments with Stichopus chloronotus were analysed for dissolved inorganic nitrogen (ammonium, nitrate, nitrite) and phosphate.Experiments were conducted with Holothuria atra, Holothuria edulis and Stichopus chloronotus by placing individuals in aquaria with one pre-weighed sediment dish from each of the four treatments placed randomly in the corners of the aquaria. After 48 hours, the sediment dishes were removed and re-weighed. Experiments with Holothuria nobilis and Stichopus variegatus were conducted in a similar manner except that two dishes of each of the two treatments prepared for these species were placed randomly at each corner of the container.Field sediment samples for analysis of chlorophyll a and phaeophytin were collected from underneath the feeding tentacles of holothurians (15 samples for each species) and also haphazardly collected from the surrounding sediment (15 samples). Sediment was collected at Great Palm Island from a shallow area where Holothuria atra and Stichopus chloronotus occur and from a deeper area where Holothuria edulis occurs. Samples were collected from the reef flat at John Brewer Reef for Holothuria nobilis and from the reef slope at Britomart Reef for Stichopus variegatus. To investigate whether holothurian species are patch selective in their feeding behaviour.