FEEDING Stichopus horrens is a detritovore, feeding by processing sediment. S. horrens does not need to move quickly for this process, and feeds during the night. The feeding tentacles are extruded and used for feeding, when not being used they are pulled back into the mouth and held by a ring of muscle (Ruppert et al., 2004) RESPIRATION Sea cucumbers have respiratory trees which are attached to their cloaca, as such the anus needs to be exposed for respiration to occur by this method (Ruppert et al., 2004). I observed that S. horrens would only uncover the oral (front) half of the body when covered in sediment, which was in direct contrast of that observed in Holothuria atra, which immediately uncovered the oral and aboral openings. I would like to know what causes this difference, but it seems that S. horrens doesn't rely on the respiratory trees to the same extent as other species of Holothurians. REPRODUCTION S. horrens is gonochoristic, meaning that individuals are either male or female. They are broadcast spawners and reproduce during the summer with a peak in production of gametes in December (Conand, 1993b). S. horrens can also undergo fission, which is when the body splits into multiple pieces and these pieces all become functional animals (Kohtsuka et al.,2005). The size of first maturity in S. horrens is 270mm (Conand, 1993a). LOCOMOTION Investigation into flipping ability of Stichopus horrens Stichopus horrens is a highly valued species around the world. It is commonly collected as part of a fishery and farmed in many countries (Uthicke et al., 2010). Kropp et al. (1982) recorded movement of S. horrens in response to attack from a predator. This movement was described as ‘contraction of the body into a U-shape’ followed by ‘bounding’ away from the predator. They recorded that some individuals were able to escape while others were caught. What is the cause of difference between individuals? I found that S. horrens made the same shape recorded by Kropp et al. when trying to right themselves after being placed on their back (dorsal side). It is possible that individual variation in righting themselves/flipping speed can relate back to the escape ability observed in Kropp's study. The main aim of this study was to understand the cause for variation in flipping speed in Stichopus horrens. More specifically: - Does weight/size influence flipping ability? - Does ossicle density influence flipping ability? METHODS Study Site The fieldwork and behaviour studies were completed at Heron Island, Queensland, Australia. All laboratory studies were completed at the University of Queensland, St Lucia, Queensland. Study Organisms Eight Stichopus horrens individuals were collected from a near shore environment in the lagoon of Shark Bay, Heron Island (23°26'34.06"S 151°55'10.63"E). All individuals collected were found by flipping coral boulders and were then transported to an outdoor flow-through tank system. Experiments were conducted during a three-day period and all individuals were subsequently returned to the same environment they were collected from. Skin biopsies were completed prior to release. Animals were anaesthetised by cooling to 4°C and then a small piece of tissue (0.5cm X 0.5cm) was removed from both the dorsal and ventral side for ossicle analysis. Flipping experiment A tank was established with flow-through water system and all individuals were 'weighed' by using the displacement method. This is a more accurate measure of size when an animal is mostly water and weight is dramatically different in and out of water. Individuals were introduced to the tank one at a time and placed on their dorsal side. A stop-watch was started from the time the individual was released and stopped as soon as it was completely righted. Each individual was tested ten times with a break of 20 minutes between each trial to control for exhaustion. Individuals 1-8 were tested in the same order in each trial. Ossicle density and distribution A small piece of tissue was removed from the skin biopsy using a scalpel, and placed onto a microscope slide. This tissue needed to be thin enough that light could be seen through, to ensure accurate counting of ossicles. Ossicle density was counted as present or absent at 10X magnification on a compounding microscope using the reticule for calculating density. The reticule has a range of 0-100 and a count was taken every 5 increments, resulting in a maximum of 22 counts. Density was calculated by dividing the number counts by 22 and multiplying by 100 e.g. 16 counts of ossicles = 16/22 X 100 = 72.72% cover/density. Further analysis of ossicles was undertaken using standard methods to isolate the ossicles from the tissue. A small portion of tissue was placed into a small tube and inverted until the tissue was gone. Again, the tube was inverted, and a sample removed using a pipette and placed onto a microscope slide. The slide was analysed under a compound microscope. Figure 1: Tissue as seen when ossicles were counted (10X magnification under light microscope). Figure 2: Ventral ossicles as seen under the light microscope after bleaching. RESULTS There was no difference recorded between flipping time and ossicle density or weight. However, there was an individual difference in flipping time, ossicle density and weight. a) b) Figure 3: a) Trends of weight (measured by displacement (ml)) in relation to flip speed (min), R2= 0.5071. b) Trends of ossicle density (log) in relation to flip time (min), R2=0.04519 a)b) Figure 4: a)Individual variation in flip speed, 10 replicates per individual. b) Individual variation in ossicle density, 3 replicates per individual. Error bars indicate standard error. OBSERVATIONS This study found that each individual has variation which can be seen in all experiments completed. It seems that none of the factors studied were responsible for this individual variation. Future research could look further into anatomical differences that predict individual variation in this U-shaped response. It is possible that this research could be used to further understand the escape ability of individuals. The main constraint of this study was that dorsal ossicles were counted, however S. horrens has different ossicles on the dorsal and ventral side. Future studies may benefit from looking into the differences in ventral ossicles, and the proportion of each ossicle type present in the individual. Images obtained during the ossicle analysis have been placed in "Anatomy and Physiology" of this website.