Sexual and asexual reproduction in geographically separated populations of the fissiparous asteroid Coscinasterias calamaria (Gray)

Abstract

Sexual reproduction and asexual reproduction by fission were studied in four populations of Coscinasterias calamaria (Gray), two in Otago Harbour in the South Island of New Zealand and two in the North Island near Auckland. The annual reproductive cycle in both islands of New Zealand is clearly defined with a spawning season between November and January. In both sites the pyloric caeca index was approximately inverse to the gonad index cycle as found in other forcipulate asteroids. There are substantial differences in the sex ratios of mature starfish at each site studied, with 1:1 ratios in two populations, one population heavily biased towards females and the fourth consisting almost entirely of males. Morphometric variation in arm number due to splitting was studied and the frequency of splitting varied considerably between the four populations. Generally speaking sublittoral C. calamaria divide less frequently than intertidal starfish and populations in which food is less abundant or of poorer quality are more fissiparous and put less energy into sexual reproduction, than populations with plentiful readily available food in the form of mussels. The significance of the different reproductive patterns in C. calamaria is discussed.