Studies on the biology of the Indo-Pacific sandy shore crab, Matuta lunaris Forskål (Brachyura: Calappidae)

In this study, the relative growth, feeding, reproduction, absolute growth and population structure of the Indo-Pacific sandy shore crab, Matuta lunaris(Forskal)(Brachyura: Calappidae) were investigated, using samples collected in monthly intervals from Pallarenda beach, Townsville, Australia, between April, 1984 and May, 1985. The relative growth patterns of 15 morphological characters were determined using direct plots, log regressions and relative proportions. Three functional units were recognized, namely, the carapace, the chela and the abdomen and its associated structures. There were no marked changes in the relative growth patterns of the carapace dimensions with size, sex or sexual maturity. However, there were variations in the growth patterns of the chela characters and those of the abdomen and its associated structures, i.e. the thoracic plate and the pleopods. These variations appeared to be associated with the feeding and reproduction. Those of the chela were primarily related to size during ontogeny and were discussed in relation to changes in its mechanical capabilities. Those of the abdomen, the thoracic plate and the pleopods were related to sex and sexual maturity and were discussed in relation to the differences in the specific reproductive functions of these structures. Analysis of the stomach contents using the percent occurrence and percent point methods indicated that M. lunaris is a facultative scavenger and a predator of small crustaceans and molluscs. In addition, there were marked changes in the composition of its diet during ontogeny with small individuals primarily feeding on small crustaceans such as sergestids and copepods, and large individuals primarily feeding on hermit crabs, gastropods and bivalves. The reproductive biology was investigated using gonad indices, histological analysis of the gonads and field and laboratory observations of sexually mature individuals. Reproductive activity in terms of gamete production, mating behaviour and brood incubation was continuous throughout the year with marked asynchrony between individuals and no apparent seasonality. The mating behaviour involves a prolonged precopulatory grasping between a postpuberty male and a prepuberty female, after which the female undergoes a puberty moult and copulation occurs. Ovulation and oviposition were found to occur several weeks after copulation. Adult females were found to be capable of producing more than one egg batch from a single copulatory event with each batch containing approximately 65,000 eggs. The absolute growth pattern was determined based on the analysis of moult increment data. Both sexes were found to exhibit a determinate growth pattern with the puberty moult being the terminal moult. However, marked differences in the growth strategies of the two sexes were found. Male absolute growth is characterized by constant but relatively small (24.7%) moult increments and an unknown and possibly variable number of instars, each with a wide size range. Female absolute growth is characterized by relatively large (41-85%) but variable moult increments, and at least 5 distinct instars, each with restricted size ranges. The population biology of M. lunaris in Pallarenda beach was assessed in terms of relative abundance, sex ratio, population structure and growth. M. lunaris was found to be abundant throughout the year, and although the population was dominated by large individuals (30-50 m carapace width) most size classes were consistently present. The sex ratio remained constant at 1:l. The estimated time between settlement and maturity was approximately 119 days in males and 148 days in females