Size distribution of individuals in the population of Asterias amurensis (Echinodermata: Asteroidea) and its reproductive cycle in China

Abstract

To obtain baseline information on the size distribution of individuals in the population and reproductive features of sea star Asterias amurensis, monthly surveys of the population were carried out from May to December 2010 and March to May 2015 in coastal waters off Yantai, China. Spawning period was predicted by gonad and pyloric caeca indices as well as anatomical and histological methods. In the A. amurensis population, both large individuals (>143 mm) and small ones (<42 mm) were present in all sampling months. The population size structure was driven by the appearance of big cohorts of individuals less than 55 mm from May to August. The appearance of small individuals in all months suggested a prolonged spawning period at other sites in this bay or sea stars growing slowly because of food shortage. An arm length is a good predictor to wet body weight for A. amurensis. The development of gonad was relative slow from May to September but rapidly reached a peak of 20.95 in October 2010, and then dropped remarkably, indicating its spawning lasted from October to November. The same phenomenon was found from March to May 2015, suggesting another spawning during March to May, which was also verified by the results of histologic analysis on ovary. The gonad index (GI) and pyloric caeca index (PCI) tended to show a negative relationship. Due to the poor food availability, the reproductive characteristics of sea star were most likely affected by the shellfish mariculturein Yantai coastal waters.