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

Full description

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.

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Statement: Statement: Analysis of chlorophyll a and phaeophytin in sediments:Sediment samples were dried at 60°C for 48 hours and 1.5 g of the dry sediment was extracted in 3 ml ethanol following the method of Sartory and Grobbelaar (1984). The extract was measured in a spectrophotometer at 750 and 665 nm before and after acidification. Chlorophyll a and phaeophytin concentrations were calculated applying the formula of Nusch (1980). Nusch, EA (1980) Comparison of different methods for chlorophyll and phaeopigment determination. Arch. Hydrobiol. Beih. Ergeb. Limnol. 14, 14-30.Sartory, DP, Grobbelaar, JU (1984) Extraction of chlorophyll a from freshwater phytoplankton for spectrophotometric analysis. Hydrobiologia 114, 177-187.Nutrient analysis of water samples:Analysis of dissolved inorganic nitrogen and phosphate was carried out using the techniques described in:Ryle VD, Mueller, HR and Gentian P (1981) Automated analysis of nutrients in tropical seawater. AIMS Oceanography Series, AIMS-OS-82-2, 24pp.

Notes

Credit
Uthicke, Sven, Dr (Principal Investigator)