Nutrient excretion by the coral reef holothurians, Stichopus chloronotus and Holothuria atra, on the Great Barrier Reef

Excretion experiments were conducted at the Lizard Island Research Station on the Great Barrier Reef with the common holothurians Stichopus chloronotus and Holothuria atra, during January 1996 (summer) and June 1997 (winter). Specimens were collected from depths between 1 and 9 m.Experiments were performed in acid-washed jars containing filtered seawater, which were closed with plastic lids fitted with a tube for aeration and a tube for water sampling. Animals were deprived of sediment for a least 48 hours before being transferred to incubation jars and left to adapt for 10 minutes before initial water samples were taken. After 180-240 minutes (depending on the size of the animal) final water samples were taken and the wet weight of each individual measured. For each parameter measured, duplicate 10 ml samples were filtered, immediately frozen (-20°C) and later transported to AIMS for analyses. Samples from minimum of 24 individuals of each species were analysed per season. In June 1997, excretion rates of 9 anterior and 9 posterior sections of both species, resulting from asexual reproduction by fission, were measured. Also, two time-series experiments, each with 3 individuals and a control were performed to validate the assumption of constant excretion rates. Water samples were taken at 0 (before) and 5, 15, 30, 60, 90, 120 and 180 min after addition of animals. All summer water samples were analysed for ammonium and phosphate. DOP and DON, nitrate and nitrite were only analysed for a subset of samples. All winter samples were analysed for ammonium and phosphate. DOP and DON, nitrate and nitrite were only analysed for the time-series samples.Ammonium concentrations in water expelled during respiration in 20 individuals of each species were measured by quickly removing the animals from the holding tank and ejecting water (5 ml) from the anus. Concentrations were compared with ambient water in the holding tank. On the reef flat at Great Palm Island, water directly (~2 cm) behind 15 individuals of each species and 15 controls were sampled.The linear distance travelled by single animals was used to estimate the sediment area in direct contact with holothurians. In each of four experiments, 20-23 individuals were tagged and the start marked. After 60-120 minutes, the distance travelled was measured and converted to hourly rates, which were multiplied by the average breadth of the ventral surface of the holothurian. To estimate the area of sediment microflora which might be directly affected by excretion, a tank was set up with fine sediment (

本研究于大堡礁蜥蜴岛研究站开展海参排泄实验，实验对象为两种常见海参：绿刺参（Stichopus chloronotus）与黑海参（Holothuria atra），实验时间为1996年1月（夏季）与1997年6月（冬季）。
实验样本采集自1至9米水深区域。
实验在经酸洗处理的盛有过滤海水的广口瓶中开展，瓶口以塑料盖密封，盖体配备通气导管与水样采集导管。
实验动物需先在无沉积物环境中禁食至少48小时，随后转移至培养广口瓶，静置适应10分钟后采集初始水样。
经过180至240分钟（依动物个体大小调整）后采集终末水样，并测量每只个体的湿重。
针对每项测定参数，均取平行的10 mL水样进行过滤，随后立即置于-20℃条件下冷冻，后续运送至澳大利亚海洋科学研究所（AIMS）开展分析。
每个季节均对至少24只该物种的个体样本进行分析。
1997年6月，研究还测定了两种海参经无性分裂繁殖产生的9个前部切段与9个后部切段的排泄率。
此外，开展两组时间序列实验，每组包含3只实验个体与1组对照组，用于验证"排泄率恒定"的假设。
分别在投放动物前（0分钟）以及投放后5、15、30、60、90、120、180分钟采集水样。
所有夏季水样均检测铵盐与磷酸盐浓度；溶解态有机磷（Dissolved Organic Phosphorus, DOP）、溶解态有机氮（Dissolved Organic Nitrogen, DON）、硝酸盐与亚硝酸盐仅在部分子样本中开展检测。
所有冬季水样均检测铵盐与磷酸盐浓度；DOP、DON、硝酸盐与亚硝酸盐仅在时间序列实验的水样中开展检测。
针对两种海参各20只个体，通过快速将其从饲养槽中取出并从肛门排出5 mL呼吸排泄水的方式，测定其呼吸排泄水中的铵盐浓度，并与饲养槽中的环境水体浓度进行对比。
在大棕榈岛的礁坪区域，分别采集两种海参各15只个体后方约2 cm处的水体，以及15组对照组水体样本。
通过测定单只海参移动的直线距离，估算其与沉积物直接接触的区域面积。
在4组实验中，每组均对20至23只个体进行标记并划定起始位置。经过60至120分钟后，测定其移动距离并换算为小时移动速率，再乘以海参腹面的平均宽度。
为估算可能受排泄作用直接影响的沉积物微群落面积，研究人员搭建了盛有细沉积物的水槽（