Growth, stomach contents and parasites in a tidepool population of the hippolytid shrimp Heptacarpus futilirostris, with reference to reproduction

Abstract

The biology of the hippolytid shrimp Heptacarpus futilirostris (Bate) was studied in a tidepool at Kominato, central Japan from January 1983 to June 1984. In males, the relative growth ratio between the third maxilliped length and body length revealed a turning point at approximately 15 mm in body length. Population recruitment was presumed to continue from April to December. The range of body length did not increase from July to October, and thereafter increased rapidly in both sexes up to a maximum range, i.e. from 6 to 29 mm in January. The wide range was presumably due to the simultaneous occurrence of rapid growth with population recruitment. The growth rates of size groups above and below 15 mm were different in the males observed in January. Large males disappeared, probably due to death, and small males participated in reproduction after July. The growth rate increased from late autumn to spring and decreased from summer to early autumn, and was influenced by relative food abundance, especially seaweeds. Two parasitic isopods were identified: Bopyrinella antilensis nipponica in the branchial cavity, and Epiphryxus sp. on the abdomen. It is suggested that parasites have more influence on maturity than on growth. Ovigerous females were found from January to October, with the breeding season peak between April and June. The relationship between female body length (L) and clutch size (N) was expressed by the regression equation: N=5.11 L1.6347 (r=0.57). This species is identified as a multiple breeder. The relatively large number of larvae presumably compensates for the low larval survival rate.