Seasonal changes in fecundity and fertility of the crown-of-thorns starfish, Acanthaster planci, from Davies Reef, Great Barrier Reef

Adult crown-of-thorns starfish (Acanthaster planci) were collected from Davies Reef between August 1990 and January 1992. Sampling was infrequent during the winter non-spawning period, but was as frequent as once per week during the spawning season. At each sampling, the gonad index of 10 male and 10 female starfish was calculated (gonad wet weight/total wet weight). During the winter, the total gonad weight was determined from the average weight of the gonads in three individual arms of a starfish, multiplied by the total number of arms. During the peak of spawning season (November to December), all gonads were dissected from starfish, since ripe gonads could not be assigned to a particular arm with a high degree of confidence.On seven occasions, between October and the end of January of the 1991-92 spawning season, experiments were carried out to examine fertilization rates and development success, using starfish collected from Davies Reef. All experiments were conducted under laboratory conditions either on land or on board a research vessel. Five male and five female starfish, identified by syringe biopsy were used in each experiment. Gonad tissue (1-3 g) was dissected from each animal and placed in 50 ml of .0001M 1-methyladenine in seawater for 30 minutes. The gonads were then removed from the solution and the concentration of gametes remaining (eggs and sperm) was determined in each of the containers. Counts of sperm were obtained using haemocytometers, while small plankton sorting trays were used to count eggs in aliquots from the original suspension. Suspensions of eggs or sperm from each starfish were then adjusted to concentrations of 3x10³/ml for sperm and 3x10²/ml for eggs. Sperm from each male was crossed with eggs from each female. Controls for sperm contamination were prepared using eggs alone with no additional sperm added. For each cross eggs, or eggs and sperm, were placed into three replicate 20 ml glass scintillation vials. The proportion of fertilised eggs was scored 2 hours after the addition of sperm. All eggs with fertilization membranes were scored as 'fertilized'. Approximately 100-150 eggs were counted. The vials containing the eggs were then resealed and re-counted 24 hours later. Eggs or embryos (100-150) were scored as either 'gastrula', if they had developed a definite archenteron, or 'non-gastrula', where this invagination was lacking or where fertilization had not occurred.
Experiments were conducted to determine whether there was a systematic decrease in fecundity (measured as gonad index) and fertility (measured as fertilization rate) of Acanthaster planci through the spawning season.

1990年8月至1992年1月间，从戴维斯礁（Davies Reef）采集了成年棘冠海星（Acanthaster planci）。冬季非产卵期采样频率较低，而产卵季采样频率可达每周一次。每次采样时，均计算10只雄性与10只雌性海星的性腺指数（gonad index），即性腺湿重/总体湿重。冬季时，通过称量海星3个腕足的性腺平均重量，再乘以总腕足数，得到其总性腺重量。在产卵盛期（11月至12月），需将海星的全部性腺解剖取出，因为此时无法高置信度地将成熟性腺归属于某一特定腕足。

1991-1992年产卵季的10月至1月底期间，共开展7次实验，以探究采集自戴维斯礁的棘冠海星的受精率与发育成功率。所有实验均在陆地或研究船的实验室条件下进行。每次实验使用经注射器活检鉴定性别的5只雄性与5只雌性海星。从每只个体中解剖取出1~3克性腺组织，置于50毫升浓度为0.0001 M的1-甲基腺嘌呤（1-methyladenine）海水溶液中静置30分钟。随后将性腺从溶液中取出，并测定各容器中残留配子（卵子与精子）的浓度。精子计数使用血细胞计数板（haemocytometers），卵子计数则采用小型浮游生物分选托盘对原悬浮液的等分试样进行计数。随后将每只海星的卵子或精子悬浮液调整至指定浓度：精子为3×10³个/毫升，卵子为3×10²个/毫升。将每只雄性的精子与每只雌性的卵子进行交叉受精。设置精子污染对照实验：仅使用卵子，不添加额外精子。将每个交叉组合的卵子或卵子与精子分装至3个重复的20毫升玻璃闪烁瓶中。在添加精子2小时后，统计受精卵比例：带有受精膜的卵子均记为"已受精"。每次统计约计数100~150枚卵子。随后密封闪烁瓶，24小时后再次计数。将100~150枚卵子或胚胎分为两类：若已发育出明确的原肠，则记为"原肠胚"；若缺乏该内陷结构或未发生受精，则记为"非原肠胚"。

本实验旨在探究棘冠海星在整个产卵季中，繁殖力（以性腺指数衡量）与受精能力（以受精率衡量）是否存在系统性下降。