Sediment bioturbation and impact of feeding activity of Holothuria (Halodeima) atra and Stichopus chloronotus, two sediment feeding holothurians, at Lizard Island, Great Barrier Reef
Abstract:In aquarium experiments and during field observations, Holothuria (Halodeima) atra (Jaeger, 1883) and Stichopus chloronotus (Brandt, 1835) consumed an average of 67 and 59 g dry wt of sediment individual−1 d−1, respectively. A model calculation showed that a mixed population of both species on a reef flat near Lizard Island, GBR has the potential to rework about 4600 kg dry wt yr−1 1000 m−2 which is approximately the weight of the upper 5 mm of sediment in this area. Gut content analyses showed no significant decrease in phycopigments (chlorophylls a and c and fucoxanthin) during gut passage. In both species the oesophagus pigment content was similar to the concentration in sediments directly in front of the individuals. However, pigment content in front of S. chloronotus and in all gut segments of this species were significantly higher than the corresponding values in H. atra suggesting patch selectivity in the former species. Extremely low meiofauna contents in holothurian guts indicated that meiofauna play a negligible part in the nutrition of H. atra and S. chloronotus. In contrast, the ratio of living to dead diatoms was significantly lower in the guts of both holothurian species compared to the adjacent sediment, indicating digestion of the ingested diatoms. In aquarium experiments, feeding and bioturbation activity of both species significantly reduced microalgal biomass (measured as chlorophyll a concentrations) in sediments inoculated with diatoms or cyanobacterial mats.
Document Type: Research Article
Publication date: 1999-01-01
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